Tony, I have no training in electronics and am easily lost during some of your explanations, but I still find them fascinating. I am impressed with your thorough knowledge and willingness to share that knowledge, and I absolutely agree that you should include that content. You are my favorite person to listen to for this information and I think you would make an awesome instructor. My hope is that younger people are training under you so that this expertise is passed on and those young people who are interested in the field can have a good career. Keep up the wonderful work and vids!
Good presentation. I would give 10 out of 10 on this one. It gives us the full detail Tony. Don't listen to comments where some subscriber says ' don't tell us how it works..tell us how to fix it"... Understanding the basic principles of any piece of electronic equipment is the key to a better solution in replairing/ I liked your detailed description of SCR power control when you explained how the soft start works. I used to work on SCR invertors years ago, and it all came back to me when you explained it. I like your approach and taking] the time to do it right, which includes upgraded wiring over the original. Thank for your videos and your repair tutorials.
Keep going with your pace Tony , I really enjoy your normal presentation, we learn a lot along your description you are so generous to share you knowledge and expertise
There's over twenty five hundred subscribers and more than half is subscribing because they enjoy theory from you and insight to the workings of the "combustible engine". Please continue the good work and you'll be reaching three thousand very soon. Many many thanks and appreciation for the work and thought that goes into each one of videos.
I think your videos are entertaining regardless of the format you've picked. You clearly enjoy doing them and enjoy the work itself so it's all good. Ignore the vocal detractors.
I really enjoy your long videos. When you have schematics out and explain how the circuit works is a big plus. So please keep those long videos coming because my knowledge in electronics just keeps getting better after watching them.
Really enjoyed this video, Tony. because I have a NZ-made Craft CA1 power amp, made in 1983. It's not as compact as yours but many similarities in the circuit design, power MOSFETs, huge power supply caps, plenty of heat sinking but no fan. It is rated at 180 wpc, but I do not have the equipment to measure that. I like the hand-made aspect of these amps and your analysis of the schematics here was extremely interesting. It's like a 1 hour tutorial and there are plenty of us subscribers that appreciate the time and effort that you put into your videos. Keep it coming, you are truly an inspiration to us amateur audio techs !!
Very appreciative of the theory you include I your videos. I also have been doing this for a very long time and always glean something from your excellent videos.
I don't mind if you keep it short or rather go into details and schematics.It's always a good show that is much appreciated by me. One thing though: if it's possible (copyright etc.) could you maybe add a link to schematics when you go into details. On the video they are pretty blurry. That would be awesome to have and to follow you along. Thanks for sharing!
Wow! What a wonderful analysis and rebuild of this PCR-800 related Soundcraftsmen power amplifier. I currently own at least three PCR-800s, a PM-860, and a post-MTX purchase A400. These are wonderful power amplifiers but I am constantly challenged WRT replacing the always-wearing-out and noisy 120VAC fan motors with ultra-quiet 12VDC computer case fans. You can't buy OEM 120VAC replacements. It's a total PITA to grind off the fan mounting rivets and replace them with machine screws and nuts, and then make a compact 60 Hz transformer DC power supply to make a low-noise fan power supply rather than use a switching buck regulator off of the +70 VDC rail.
LOL - "Long speech is done, you can unclick your fast-forward-button".... NO! I've seen that video at least 2nd time but still enjoy all explaining and in-depth-explaination of what goes where and does what. I was trainee way back in the early ninetees at exactly such stuff but do love hearing of your thoughts about stuff like this and still do get new hints tips and tricks or new ideas from your video, so that's really great stuff you are delivering, Tony! THANKS A LOT for ALL OF YOUR GREAT VIDEOS! I enjoy every single one. I hope you'll have a lot of fun in doing these videos still another long time! 👋👍🍷
These look like Hitachi mosfets. Six of them in each output stage is a very conservative rating-just about bulletproof! I built some 100 Watt amps from the Hitachi design specs with just a pair of these and they are still working. I even bridged a pair and got 400 Watts output. Great vids, I've just come across your channel and I'm looking forward to watching all of them. Cheers from the UK.
I bought one in Boston in 1986 and used it on and off until 2019. It was used to drive a pair of Tannoy studio monitors. I remember I also had a Hafler and an Adcom power amps which were wired in my studio, the Soundcraftsman was a better sounding amp to my ears.
Subscribed because your explanation and was probabaly the most informative I've run across. Thinking of putting 20- 25kuF caps in mine. Loved the video, thanks!
Don't stop doing it your way because some ADHD infants want to skip the theory and engineering. I used to repair industrial servo drives and VFDs and many of the circuits are astonishingly similar to audio amps. So a lot of what you go through are applicable to different kinds of amps. Stepping through the operation of the protection circuits was very interesting to me, even the fan speed theory and design. I hadn't seen anything like that before, probably since industrial amps don't care about noisy fans! Thumbs up and 10/10 video. Keep 'em coming, I enjoy your videos and JohnAudioTech's as well. My wife hears me watching these and just rolls her eyes and calls me a geek. In the most loving way possible, I'm sure. ;-)
It is well know here on YT that Dave's waffle (his endless blabbering, Dave from EEVBlog) is what has made him famous. It might be annoying to some (the ADD folks out there), but I swear gold comes out of your mouth when you speak! I learn so much! Don't ever stop Tony! And awesome video. I've actually been waiting to see a vintage amp with a microwave-oven style fan in it as I'm considering doing that as a mod to an old amp of mine.. Cheers!
Tony, I have a pair of PCR 800's running a pair of Polk Audio SRS 1.2 TL's that have developed a hum at what sounds to be about 60hz, but as I have played musical cables and eliminated different equipment from the rack, I found that almost everything has this hum. Some more that others. I also have a Harmon/Cardon Citation Eleven and a Citation Sixteen, Rockford Fosgate DSLONE and 3 QSC USA 800's. I then started checking the ground at the service entrance and discovered noise there. I ran dual 8' grounding rods and have eliminated about half of the audible noise. The scope now shows (zero) noise to ground at the service, but still have a hum in the audio. My assumption is the filtering caps have dried out. Since most of my gear is of the same period and has about the same mileage, they are all starting to feel the effects of age. I have noticed in previous videos that you do work for hire. How can I reach you about this? Paulie
i dont mind the long talky bits it's great stuff and i learn learn learn, a concept that's been lost in todays generation. ignore the complainers you do a awesome job love the videos keep up the good work :-)
the zener diodes on the drivers are there for protection to limit the amount of voltage sent to the gates of the mosfets. Mosfets don't like more then 20ish volts gate to source, so that diode string is there to shunt away excess voltage in the case of a gross overdrive. BJT amplifiers will often have transistors that sense the current across the emitter resistors and then turn on once a certain point is reach doing the same shunting action
I have one of these Amps. I love mine. I bought it about 8 or 10 years ago from a Syracuse University college professor who was the original owner. The fan never worked but the Amp worked and i ran a small house fan on it when i used it. i unhooked it for a couple of years and hooked it back up recently. i noticed my lights no longer flash when i turn the Amp off, as they should in normal operation. So i figure now it's time to see about getting it serviced. It's a clean sounding power house of an Amp. not alot of low end, so best suited for certain types of speakers. Not Klipsch. great as a subwoofer amp or mono block if you can find two. bridgeable to something like 5 or 600 watts. it's rated 205/8 ohm and 300/4 ohm i Believe. And she gives you ALL of it.
Good job on the rebuild and I think that is one really interesting amp! From the clever little fan circuit alone you know some thought went into this design. From the 20-20 and clean sine waves I bet the distortion would be low as well.
The silver main caps in these amps have been really reliable (all things considered), the later units used black EPCOS units, much higher failure rate IMHO. That 10watt fan ballast resistor often times will get so hot that they desolder from the power supply board or even break a trace sometimes. The pot towards the top of the schematic will allow you to change the voltage rail somewhat (this has limits). Nice vid!
@xraytonyb I have a Soundcraftsman PE2217 pre-amp equalizer Akai GXC760D cassette deck, and Carver M-400 amp. When Julian Hirsch tested the Carver he said it was a humbling experience since it put out 200 watts per channel with 3db overhead on momentary peaks and it kept tripping the 15 amp breaker on his shop table. I believe it was the real canons used on the 1812 Overture. The Carver weighed a whopping 10 pounds and everybody at work said I was nuts. They said no one could make a 200 watt amp that weighed 10 lbs. I could have made a bunch of money. Instead I walked over to the grocery bag I had quietly brought into the maintenance shop while everybody was milling around waiting for assignments. I said I could even pick it up by the power cord. After the outburst died down I reached into the bag and very slowly pulled the amp out by the power cord and gently lowered it down on the bench. It was brand new and very much against all my training to ever pull on the cord. And it was the last time I ever had to do it. While they were all looking at it I also informed them of the 3db overhead. Then I told them the outputs could be bridged and that could give you 800 watts peak per one channel. Just a story. I live in Slidell and Katrina covered all my gear with 3 feet of salt water. .
before I button up I use electronics corrosion control spay on any rusty area, around chassis , inside covers, on transformer covers,hardware ect. protects all that work you did. See bullfrog emitter block, can be left inside units for protection. displace moisture.
People tend to enjoy Harmonic Distortion, like from tubes, more often than from solid state. It's pretty easy to see THD on a scope too. I believe we are much more sensitive to intermodulation than we think. Here's the anecdote: A Golden Eared reviewer claimed he heard ultrasonic ringing from an amp! The manufacturer took a look and sure enough, there was ringing at 50khz. I think the reviewer heard intermodulation between the constant Ultrasonic ringing and the lower frequencies we can hear, in other words, he heard the beat frequencies. It's rather like a superheterodyne circuit.
Hi, you were talking about increasing the capacitance of the power supply, the short circuit current may exceed the output transistors max current and cause them to fail. it seems the designers were very careful to limit the currents. I like your thoughts on the circuits, it is far easier to repair electronics if you have an understanding of what the electronics is doing and not just changing components that look bad. Rich
Thanks for a nice instructional video! I've got a PCR-800 that is ready for an overhaul and it would be nice to learn from your experience. Can you provide the specs/part numbers for the caps and parts you used? Those power caps that fit would be particularly useful so I don't have to spend a lot of time tracking them down. Thanks again!
Take your time and explain like you do, like you said, there's always the skip button. PS i have an SAE A502 and A202 amplifiers, do you know where i could find rail cap fro them? They are some odd shaped in those amps. I have a Heathkit AA-1640, changed the power supply caps to almost 3 times the uF of the originals and now than amp sounds better that it did 35 years ago when i built it.
Is there anyway you could do a video on wire wrapping? The tools techniques. Removal and replacement. I have an old pioneer to work on that I may need to unwrap some leads. I don't want yo make matters worse. Thanks. Great video!!
The diodes and zener diodes between the bases of the drivers is for drive limiting. See it all the time on Denon and Marantz units. Not especially effective in preventing failures though, in my experience.
I did that video 4 years ago, so I don't entirely remember. I believe that I used those taller capacitors, as they still fit in the amp. If I recall, the terminal spacing was the same but the cans were a bit taller. They raised the board up a bit, but they still fit in the cabinet. I'd have to watch it again to know for sure.
In the vid he does say upgraded 100 volt 15000 uf caps (same physical size) as originals. He also replaced the SCR's with upgraded units. I have a PM 860 used to drive a dual voice coil subwoofer at 4 ohms both channels driven, So pushing 600 watts. Also ordered another one because these are a really clean nice sounding amplifier. Thanks for the Video If mine ever give me any problems this will be a go to video. Very well explained theory of operation.
Great video! Love my 30+ year old PCR800. recently failed. need help where to start. when powered up, clip lights go full ON and really loud bad sound going out to speakers. any advice on where to start? Thanks and loved the video.
i have 8 mosfets in my pcr 800 and i noticed the 860 has 12 by the way i picked up mine at a pawn it seems to be pretty powerful and clean not so flat sounding i noticed that the fan rpm's goes up the more volume you apply thats it peace out .
Hello, thank you for your video. I recently bought this amp but I have a problem. The amp works for a few seconds then no sound comes out. The fan starts to run very quickly and the two front LEDs are red. If I turn it off and back on it works again for 10 seconds then the same problem. Do you have any idea, I was thinking of a power capacitor problem. Thank you in advance.
What's up with the phase difference between channels? There some stray capacitance somewhere or a dirty contact? Some inductance in the cabling? Seems like if they were in phase you wouldn't get as much output because of both channels peaking at the same time.im happy to be proven wrong btw as long as I learn something lol
I used a two channel signal generator and connected ch 1 to left and ch 2 to right. I forgot to align the phase between the two channels (there's a button to do that) when I turned the signal on.
@@xraytonyb ok cool. My sig gen doesn't have two channels so I wouldn't have known that, now I've learned something :-D thanks. So I'm left wondering what difference would it make having those two channels in phase since both channels would draw peak current at the same time and not one after another. Maybe nothing for high frequencies but might be a slight drop at low frequencies? I only ask because I'm eager to learn and your the guy to teach lol
Great vid, and discussion of how the amp works. You stated it had adjustable bias from looking at the schematic, but you never went over your bias readings, or if you had to adjust it to bring it into spec. Can you specify what your readings were after your rebuild, and if you had to change any parts to bring it into spec? What is acceptable bias in this amp design. What about DC offset, what offset readings did your amp have and what is acceptable on this design? I've read that this amp doesn't have an adjustment for setting offset. Did you have to change any transistors to bring your offset into an acceptable range? I like the clear schematics you have, can you point me in the right direction to obtain these schematics? Thanks, xraytonyb.
It takes double the power to increase just 3 decibels... a 10 decibel increase requires 10 times the power... power gets used up quick when playing music loudly. Logarithms.
Tony, where do you get large capacitors like that? I've got an Onkyo Integra A-8087 that has both the power supply caps shorted out. The originals are Nichicon 20000 uf @ 65wv, and I'm having a hard time finding replacements for less than $50 each. I've checked Mouser and Digikey, but don't really know where else to look. Any suggestions?
Funny, I look at how long the videos are to determine how good it's going to be. I like the longer videos. - Besides, the only things you have a right to complain about are the things you actually pay for.
Wonderful video! I have a PM840 that is in need of repair I am willing to ship it to get it fixed, are you interest in fixing it or clould you recomend someone? I am in Dallas Tx and would like very much to have my PM840 repaired. Thanks in advance,
Hello there, this is a great video, because it just so happen I have Two of these amps. I have the 90's verison when MTX bought out soundcraftmen and just some small cosmetic changes like labelling. I had watch your video over and over again and I do have some electronic experience. The two amps I have is the S-860 and the A400 home verison. The same but different chassis. Okay, so I have follow your leed. I have already bought the SCR's. I have them ready to go. I just need help with BIG capacitors the Nitchicon direct replacements. I believe (100v@15,000uf). If you can please help me with the part number or please point me in the direction for those replacement caps please? Also, 1 small ?. Did you recap the amp board as well as the power board? Thank you super much! Once again great vid....
Tony: Did you consider possibly using Supercapacitors (Supercaps) to replace your power supply filter caps? [From what I know, you can get a few FARADS in a small space. Albeit the voltage rating tends to run low. But even then, you can put a couple of 1F caps in series to double the voltage rating. A 1/2F cap is a whopping 500,000uF !!!]
Well this transistors are LEGENDARY and no matter how much i searched for them I couldnt find them anywhere (atleast original ones) Does anyone know what equivalents I might use instead?
In order to double the sound pressure level (SPL) you need 10 times more power; it is a logarithmic relation. So 225 watts or 200 watts makes almost no difference to your ears.
To run in bridged mode requires each channel to be run in opposite phase and the two positive speaker leads go to the speaker. You basically need a Soundcraftsmen preamp model such as a DX4000 or one of the others that has the bridge mode reverse phase outputs to accomplish this. Or you can build a preamp circuit that does this which is not particularly difficult using an op amp to provide the phase inverted signal for one of the channels. I have bridged a pair of PCR-800's (for all practical purposes are identical to a PM-840) using a Soundcraftsmen DX4000 preamp. Just two powerful to be practical for a home audio system. Also the DX4000 is rather noisy and its noise and hum was amplified in bridged mode making this combination unacceptable for low volume level listening. But still was a ton of fun playing around with it and will return to this setup at some point in the future after I rebuild the DX4000. I need to address some the shortcomings in its design and construction of the day (1980's). It is so satisfying playing around with old gear though and plan to setup my listening room to include these along with a Kenwood KR9600 (I bought new when I was only 21 and still looks practically new) and a Carver M-500t. Both need restoration before put back in service.
@@multicyclist So, I need a preamp (or pwr amp) that Has Bridge Mode Reverse Phase outputs to Authentically produce Mono Bridge power: 200 to 400-800w? I thought Simply connect both red positive post from pwr amp to 1 spkr +/- .
They are rated at 300 WPC RMS @ 4 ohms. They do meet the Soundcraftsmen published rating. I have used a pair of these with a Soundcraftsmen preamp in bridged mode for 600 WPC RMS @ 8 ohms. You may ask why? Well because an amp in bridge mode doubles the slew rate and to me sounded better than in 200 watt mode. Just was way too powerful for a home audio system and could have easily ruined my high quality audio system speakers so I switch to a different amp system. I still have 3 of these amps that I plan to use in the future though.
Please continue to utter any taught that you have about anything related to electronics and electricity. Even that comment about line voltage creep and this being a analog amplifier makes me think about the whole system,
my home build power amp has 120 000uf pr 2 channel .Each channel in 120w 8ohm.the circuit for the amp i build has no gloab or local feeback loop.it is very linear.no hiss when the amp is connected to a amt type tweeter with 94db 1w 1meter senistivity,cant hear hiss at all.my old nad poweramp give hiss around 4 times more.rotel power amp even worce.that hissis no proble if i have used speakers with passive crossove inside.but i use a dsp type active crossover from ground sound.so i have one amp for each driver the hole system is with active crossover around 50% more effective.
if there is a resistance in series with the emitter of a transistor crossed by the audio signal, then there is a counter-reaction. if there are very large capacitors but few transistor pairs, the large capacitors are not useful.
They have now become unobtainium. There are a few NTE2993's out there for sale, but very expensive. Other than that, you have to get them from eBay used or NOS.
You can still get NOS 2SK133/4/5 and 2SJ48/49/50's on eBay, not very cheap, some chinese fakes of course, but the modern equivalents are made by UK company Exicon: www.exicon.info/products.php There main advantage over bipolar seems to be lack of secondary breakdown and immunity to thermal runaway - MOSFET amps don't tend to die. Made an amp back in the early 80's and still going strong (though I did find one channel was running hot, needed rebiasing a bit).
Could you help please? I have a soundcraftsmen power four-17 something burnt on power supply board. Was wondering if you had a way I could send you a pic and let me know what you think it could be?
Actually...the PCR or Phase Control Regulation system works a lot like alight dimmer. at idle, no load, the scr's fire part way through the wave form, much like how a light dimmer works in your house. as the load increases, the Phase control circuitry fires the SCR's sooner much like turning up a light dimmer. its the same principal, the load is monitored and by controlling the firing angle of the SCR's, you can increase the current/Voltage of the power supply to maintain the voltage. This SAME circuit is used in the A2502 with a standard non regulated power supply and only develops 140 watts per channel due to power supply sag.
If that is true wouldn't the +70 and -70 volt supplies have been regulated the DC rail voltages down when there was no load or low audio input signal? If they were it wasn't shown. If it changes rail Voltages it would act like some Carver amps.
@@danlewis243 This regulator keeps the rails at +/-70volts, as you draw current...IE over 10 amps at max power into a 4 ohm load, the power supply voltage would sag and you would get a form of compression. the Bulk DC supply would be something like +/-84 in this amp if it wasn't regulated DOWN to 70, and as the load draws more power from the supply, the regulator works to keep the rails as close to the rated voltages as it can.
Carver supplys work in a different way. the actually fire the transformer much in the same way an ignition coil works on your car. plus they have a class-H rail switching scheme that switches on and off multiple power supply rails. which is not as good sonically.
@@overkillaudioinc Right I had a Carver TFM -22 and It does and did not sound as clean as the PM 860, poorly damped bass as well. I like the sound of the H class Soundcraftsmans I just bought another today
![Felix "Unfair" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/Oswujxm2Ag0/mqdefault.jpg)
I used your video for a rebuild of a PCR 800, worked a treat! Thanks so much!
Definitely keep doing the theory it's so important. RUclips is full of little short videos. I'm here for the juice! I'm here for the details!
I enjoy long repair videos. Keep em coming!
Thanks, I love seeing old amps get restored, good job.
Tony, I have no training in electronics and am easily lost during some of your explanations, but I still find them fascinating. I am impressed with your thorough knowledge and willingness to share that knowledge, and I absolutely agree that you should include that content. You are my favorite person to listen to for this information and I think you would make an awesome instructor. My hope is that younger people are training under you so that this expertise is passed on and those young people who are interested in the field can have a good career. Keep up the wonderful work and vids!
Please keep talking, I want to learn more.
Your are very entertaining and your analysis are very clear.
Tanks Ton
I don’t believe you could make a long enough video once you get on a role explaining what’s going on in these circuits, thanks again Tony👍
Good presentation. I would give 10 out of 10 on this one.
It gives us the full detail Tony. Don't listen to comments where some subscriber says ' don't tell us how it works..tell us how to fix it"...
Understanding the basic principles of any piece of electronic equipment is the key to
a better solution in replairing/ I liked your detailed description of SCR power control
when you explained how the soft start works. I used to work on SCR invertors years
ago, and it all came back to me when you explained it. I like your approach and taking]
the time to do it right, which includes upgraded wiring over the original.
Thank for your videos and your repair tutorials.
Keep going with your pace Tony , I really enjoy your normal presentation, we learn a lot along your description you are so generous to share you knowledge and expertise
There's over twenty five hundred subscribers and more than half is subscribing because they enjoy theory from you and insight to the workings of the "combustible engine". Please continue the good work and you'll be reaching three thousand very soon. Many many thanks and appreciation for the work and thought that goes into each one of videos.
I think your videos are entertaining regardless of the format you've picked. You clearly enjoy doing them and enjoy the work itself so it's all good. Ignore the vocal detractors.
Love the theory, keep giving us the theory, I find it very informative. Thanks.
You completely demystified that PSU for me , it made sense, fantastic amp, great vid...cheers.
I really enjoy your long videos. When you have schematics out and explain how the circuit works is a big plus. So please keep those long videos coming because my knowledge in electronics just keeps getting better after watching them.
I am a electronics and computer technicien and I find your videos very informative and interesting so please keep making your long vidéos.
Your videos are amazing as they are. I do like when you get into theory! Keep it up! Great work!
Keep on talking! I really enjoy your video. I learn from you and this is rare nowdays. Best from Athens, Greece.
Really enjoyed this video, Tony. because I have a NZ-made Craft CA1 power amp, made in 1983. It's not as compact as yours but many similarities in the circuit design, power MOSFETs, huge power supply caps, plenty of heat sinking but no fan. It is rated at 180 wpc, but I do not have the equipment to measure that. I like the hand-made aspect of these amps and your analysis of the schematics here was extremely interesting. It's like a 1 hour tutorial and there are plenty of us subscribers that appreciate the time and effort that you put into your videos. Keep it coming, you are truly an inspiration to us amateur audio techs !!
I love the theory and the many insight's you provide with it! It makes you different from the others. Keep up the great work.
I got a pair of these... as of 4/28/2024. Both work.. im a journey electrician. I wanna learn to work on more audio electronics.....love your vids
Without theory and lots of details , not worth watching. Love you videos😀
Very appreciative of the theory you include I your videos. I also have been doing this for a very long time and always glean something from your excellent videos.
Really enjoyed this episode! Thanks
Tony, just keep on making videos like you used to do, you're doing just fine. Anybody have complaints, make your own videos.
I don't mind if you keep it short or rather go into details and schematics.It's always a good show that is much appreciated by me. One thing though: if it's possible (copyright etc.) could you maybe add a link to schematics when you go into details. On the video they are pretty blurry. That would be awesome to have and to follow you along. Thanks for sharing!
I enjoy the explanations and theory!
Wow! What a wonderful analysis and rebuild of this PCR-800 related Soundcraftsmen power amplifier. I currently own at least three PCR-800s, a PM-860, and a post-MTX purchase A400. These are wonderful power amplifiers but I am constantly challenged WRT replacing the always-wearing-out and noisy 120VAC fan motors with ultra-quiet 12VDC computer case fans. You can't buy OEM 120VAC replacements. It's a total PITA to grind off the fan mounting rivets and replace them with machine screws and nuts, and then make a compact 60 Hz transformer DC power supply to make a low-noise fan power supply rather than use a switching buck regulator off of the +70 VDC rail.
LOL - "Long speech is done, you can unclick your fast-forward-button".... NO! I've seen that video at least 2nd time but still enjoy all explaining and in-depth-explaination of what goes where and does what. I was trainee way back in the early ninetees at exactly such stuff but do love hearing of your thoughts about stuff like this and still do get new hints tips and tricks or new ideas from your video, so that's really great stuff you are delivering, Tony! THANKS A LOT for ALL OF YOUR GREAT VIDEOS! I enjoy every single one. I hope you'll have a lot of fun in doing these videos still another long time! 👋👍🍷
These look like Hitachi mosfets. Six of them in each output stage is a very conservative rating-just about bulletproof! I built some 100 Watt amps from the Hitachi design specs with just a pair of these and they are still working. I even bridged a pair and got 400 Watts output. Great vids, I've just come across your channel and I'm looking forward to watching all of them. Cheers from the UK.
You'll never please everyone. Just do what you want and ignore complainers:)
I bought one in Boston in 1986 and used it on and off until 2019. It was used to drive a pair of Tannoy studio monitors. I remember I also had a Hafler and an Adcom power amps which were wired in my studio, the Soundcraftsman was a better sounding amp to my ears.
Agreed I dumped a Carver TFM -22 for one of these, cleaner and when used as a subwoofer amp much better dampening.
I appreciate your time and effort with the theory and practical.
Subscribed because your explanation and was probabaly the most informative I've run across. Thinking of putting 20- 25kuF caps in mine. Loved the video, thanks!
Did you really just write "kuF"? Are people allergic to properly using metric units for capacitance values? 25mF.
I have always loved Soundcraftsmen Amps and other audio equipment. Really good stuff, but kinda obscure.
Don't stop doing it your way because some ADHD infants want to skip the theory and engineering. I used to repair industrial servo drives and VFDs and many of the circuits are astonishingly similar to audio amps. So a lot of what you go through are applicable to different kinds of amps. Stepping through the operation of the protection circuits was very interesting to me, even the fan speed theory and design. I hadn't seen anything like that before, probably since industrial amps don't care about noisy fans! Thumbs up and 10/10 video. Keep 'em coming, I enjoy your videos and JohnAudioTech's as well. My wife hears me watching these and just rolls her eyes and calls me a geek. In the most loving way possible, I'm sure. ;-)
"ADHD infants", It's not smart to stereotype.
Enjoy both repair and theory keep up the good job
Agreed. I vote for more of both. Love the theory! I wanna know how this stuff works.
It is well know here on YT that Dave's waffle (his endless blabbering, Dave from EEVBlog) is what has made him famous. It might be annoying to some (the ADD folks out there), but I swear gold comes out of your mouth when you speak! I learn so much! Don't ever stop Tony! And awesome video. I've actually been waiting to see a vintage amp with a microwave-oven style fan in it as I'm considering doing that as a mod to an old amp of mine.. Cheers!
Tony,
I have a pair of PCR 800's running a pair of Polk Audio SRS 1.2 TL's that have developed a hum at what sounds to be about 60hz, but as I have played musical cables and eliminated different equipment from the rack, I found that almost everything has this hum. Some more that others. I also have a Harmon/Cardon Citation Eleven and a Citation Sixteen, Rockford Fosgate DSLONE and 3 QSC USA 800's. I then started checking the ground at the service entrance and discovered noise there. I ran dual 8' grounding rods and have eliminated about half of the audible noise. The scope now shows (zero) noise to ground at the service, but still have a hum in the audio. My assumption is the filtering caps have dried out. Since most of my gear is of the same period and has about the same mileage, they are all starting to feel the effects of age. I have noticed in previous videos that you do work for hire. How can I reach you about this?
Paulie
I be digging the teachin’,yo. Seriously,thanx!
i dont mind the long talky bits it's great stuff and i learn learn learn, a concept that's been lost in todays generation.
ignore the complainers you do a awesome job love the videos keep up the good work :-)
the zener diodes on the drivers are there for protection to limit the amount of voltage sent to the gates of the mosfets. Mosfets don't like more then 20ish volts gate to source, so that diode string is there to shunt away excess voltage in the case of a gross overdrive. BJT amplifiers will often have transistors that sense the current across the emitter resistors and then turn on once a certain point is reach doing the same shunting action
I enjoy your commentary. Keep it up.
I have one of these Amps. I love mine. I bought it about 8 or 10 years ago from a Syracuse University college professor who was the original owner. The fan never worked but the Amp worked and i ran a small house fan on it when i used it. i unhooked it for a couple of years and hooked it back up recently. i noticed my lights no longer flash when i turn the Amp off, as they should in normal operation. So i figure now it's time to see about getting it serviced. It's a clean sounding power house of an Amp. not alot of low end, so best suited for certain types of speakers. Not Klipsch. great as a subwoofer amp or mono block if you can find two. bridgeable to something like 5 or 600 watts. it's rated 205/8 ohm and 300/4 ohm i Believe. And she gives you ALL of it.
Don't stop talking! Every word form you is awesome information!
Good job on the rebuild and I think that is one really interesting amp! From the clever little fan circuit alone you know some thought went into this design. From the 20-20 and clean sine waves I bet the distortion would be low as well.
A real legendary class H Mosfet amplifier
The silver main caps in these amps have been really reliable (all things considered), the later units used black EPCOS units, much higher failure rate IMHO. That 10watt fan ballast resistor often times will get so hot that they desolder from the power supply board or even break a trace sometimes. The pot towards the top of the schematic will allow you to change the voltage rail somewhat (this has limits). Nice vid!
Keep talking it’s valuable. Thanks.
YOUR A WONDERFULL TEACHER SIR, STAY AWESOME MATE...BLESSINGS TO YA !!
I enjoy the theory and CAN FF! I would feel like I was missing something without the choice. The theory, BTW, is where we actually learn.
Love what you said about the skip button!!
@xraytonyb I have a Soundcraftsman PE2217 pre-amp equalizer Akai GXC760D cassette deck, and Carver M-400 amp. When Julian Hirsch tested the Carver he said it was a humbling experience since it put out 200 watts per channel with 3db overhead on momentary peaks and it kept tripping the 15 amp breaker on his shop table. I believe it was the real canons used on the 1812 Overture. The Carver weighed a whopping 10 pounds and everybody at work said I was nuts. They said no one could make a 200 watt amp that weighed 10 lbs. I could have made a bunch of money. Instead I walked over to the grocery bag I had quietly brought into the maintenance shop while everybody was milling around waiting for assignments. I said I could even pick it up by the power cord. After the outburst died down I reached into the bag and very slowly pulled the amp out by the power cord and gently lowered it down on the bench. It was brand new and very much against all my training to ever pull on the cord. And it was the last time I ever had to do it. While they were all looking at it I also informed them of the 3db overhead. Then I told them the outputs could be bridged and that could give you 800 watts peak per one channel.
Just a story. I live in Slidell and Katrina covered all my gear with 3 feet of salt water.
.
Awsome the explanation and the perfomance of the amp, Thanks for posted
before I button up I use electronics corrosion control spay on any rusty area, around chassis , inside covers, on transformer covers,hardware ect. protects all that work you did. See bullfrog emitter block, can be left inside units for protection. displace moisture.
People tend to enjoy Harmonic Distortion, like from tubes, more often than from solid state. It's pretty easy to see THD on a scope too.
I believe we are much more sensitive to intermodulation than we think. Here's the anecdote: A Golden Eared reviewer claimed he heard ultrasonic ringing from an amp! The manufacturer took a look and sure enough, there was ringing at 50khz. I think the reviewer heard intermodulation between the constant Ultrasonic ringing and the lower frequencies we can hear, in other words, he heard the beat frequencies. It's rather like a superheterodyne circuit.
I am surprised you did not put snubber caps on the bridge rectifiers to eliminate diode switching noise.
awesome video, yes i did enjoy your video keep it up
Hi, you were talking about increasing the capacitance of the power supply, the short circuit current may exceed the output transistors max current and cause them to fail. it seems the designers were very careful to limit the currents.
I like your thoughts on the circuits, it is far easier to repair electronics if you have an understanding of what the electronics is doing and not just changing components that look bad.
Rich
The diodes across the gates are a protection aspect
Thanks for a nice instructional video! I've got a PCR-800 that is ready for an overhaul and it would be nice to learn from your experience. Can you provide the specs/part numbers for the caps and parts you used? Those power caps that fit would be particularly useful so I don't have to spend a lot of time tracking them down. Thanks again!
Did you get a response? I’m in the same boat.
@@tryion99 No reply at this time.
What about replacing the big power fan resistor with a capacitor? No heat!!
Be strong and be yourself :)
Keep doing the details the others are modifying their microwaves into spot welders LoL :)
Take your time and explain like you do, like you said, there's always the skip button. PS i have an SAE A502 and A202 amplifiers, do you know where i could find rail cap fro them? They are some odd shaped in those amps. I have a Heathkit AA-1640, changed the power supply caps to almost 3 times the uF of the originals and now than amp sounds better that it did 35 years ago when i built it.
Is there anyway you could do a video on wire wrapping? The tools techniques. Removal and replacement.
I have an old pioneer to work on that I may need to unwrap some leads. I don't want yo make matters worse. Thanks. Great video!!
you still do amp repair work i have the same amp trip lights come on fan goes into hi speed and it shuts down need some help please.. Ty
The diodes and zener diodes between the bases of the drivers is for drive limiting. See it all the time on Denon and Marantz units. Not especially effective in preventing failures though, in my experience.
What upgraded capacitors went into the soundcraftsmen pm860 become the first one he showed was to tall.
I did that video 4 years ago, so I don't entirely remember. I believe that I used those taller capacitors, as they still fit in the amp. If I recall, the terminal spacing was the same but the cans were a bit taller. They raised the board up a bit, but they still fit in the cabinet. I'd have to watch it again to know for sure.
Thank you for the info🙂
In the vid he does say upgraded 100 volt 15000 uf caps (same physical size) as originals. He also replaced the SCR's with upgraded units. I have a PM 860 used to drive a dual voice coil subwoofer at 4 ohms both channels driven, So pushing 600 watts. Also ordered another one because these are a really clean nice sounding amplifier. Thanks for the Video If mine ever give me any problems this will be a go to video. Very well explained theory of operation.
Great video! Love my 30+ year old PCR800. recently failed. need help where to start. when powered up, clip lights go full ON and really loud bad sound going out to speakers. any advice on where to start? Thanks and loved the video.
i have 8 mosfets in my pcr 800 and i noticed the 860 has 12 by the way i picked up mine at a pawn it seems to be pretty powerful and clean not so flat sounding i noticed that the fan rpm's goes up the more volume you apply thats it peace out .
Hello, thank you for your video.
I recently bought this amp but I have a problem. The amp works for a few seconds then no sound comes out. The fan starts to run very quickly and the two front LEDs are red. If I turn it off and back on it works again for 10 seconds then the same problem. Do you have any idea, I was thinking of a power capacitor problem.
Thank you in advance.
Model number for the SCR heat sink ? thanks
What's up with the phase difference between channels? There some stray capacitance somewhere or a dirty contact? Some inductance in the cabling? Seems like if they were in phase you wouldn't get as much output because of both channels peaking at the same time.im happy to be proven wrong btw as long as I learn something lol
I used a two channel signal generator and connected ch 1 to left and ch 2 to right. I forgot to align the phase between the two channels (there's a button to do that) when I turned the signal on.
@@xraytonyb ok cool. My sig gen doesn't have two channels so I wouldn't have known that, now I've learned something :-D thanks. So I'm left wondering what difference would it make having those two channels in phase since both channels would draw peak current at the same time and not one after another. Maybe nothing for high frequencies but might be a slight drop at low frequencies? I only ask because I'm eager to learn and your the guy to teach lol
Great vid, and discussion of how the amp works. You stated it had adjustable bias from looking at the schematic, but you never went over your bias readings, or if you had to adjust it to bring it into spec. Can you specify what your readings were after your rebuild, and if you had to change any parts to bring it into spec? What is acceptable bias in this amp design. What about DC offset, what offset readings did your amp have and what is acceptable on this design? I've read that this amp doesn't have an adjustment for setting offset. Did you have to change any transistors to bring your offset into an acceptable range? I like the clear schematics you have, can you point me in the right direction to obtain these schematics? Thanks, xraytonyb.
you were speaking of back-EMF
it would be interesting to research a Crown BCA design that actually stores back emf and the uses the energy
It takes double the power to increase just 3 decibels... a 10 decibel increase requires 10 times the power... power gets used up quick when playing music loudly. Logarithms.
Tony, where do you get large capacitors like that? I've got an Onkyo Integra A-8087 that has both the power supply caps shorted out. The originals are Nichicon 20000 uf @ 65wv, and I'm having a hard time finding replacements for less than $50 each. I've checked Mouser and Digikey, but don't really know where else to look. Any suggestions?
Love your video as a technician I love the theory too keep them coming
Kirk Jones put lower capacity caps its not that critical
how do u calculate the size of the capacitors(microfarads/volts) compared to the RMS power u want to be delivered?
HI I see a phase shift between the channels, are both channels driven with an in phase signal?
Rich
Love the video at to watch it twice bless london
Funny, I look at how long the videos are to determine how good it's going to be.
I like the longer videos. - Besides, the only things you have a right to complain about are the things you actually pay for.
Wonderful video! I have a PM840 that is in need of repair I am willing to ship it to get it fixed, are you interest in fixing it or clould you recomend someone? I am in Dallas Tx and would like very much to have my PM840 repaired.
Thanks in advance,
Hello there, this is a great video, because it just so happen I have Two of these amps. I have the 90's verison when MTX bought out soundcraftmen and just some small cosmetic changes like labelling. I had watch your video over and over again and I do have some electronic experience. The two amps I have is the S-860 and the A400 home verison. The same but different chassis. Okay, so I have follow your leed. I have already bought the SCR's. I have them ready to go. I just need help with BIG capacitors the Nitchicon direct replacements. I believe (100v@15,000uf). If you can please help me with the part number or please point me in the direction for those replacement caps please? Also, 1 small ?. Did you recap the amp board as well as the power board? Thank you super much! Once again great vid....
Tony: Did you consider possibly using Supercapacitors (Supercaps) to replace your power supply filter caps? [From what I know, you can get a few FARADS in a small space. Albeit the voltage rating tends to run low. But even then, you can put a couple of 1F caps in series to double the voltage rating. A 1/2F cap is a whopping 500,000uF !!!]
Well this transistors are LEGENDARY and no matter how much i searched for them I couldnt find them anywhere (atleast original ones) Does anyone know what equivalents I might use instead?
In order to double the sound pressure level (SPL) you need 10 times more power; it is a logarithmic relation. So 225 watts or 200 watts makes almost no difference to your ears.
How do you run this amp in mono mode (bridged) combine two red speaker leads? Which is plus which is minus ? Thank you in advance.
To run in bridged mode requires each channel to be run in opposite phase and the two positive speaker leads go to the speaker. You basically need a Soundcraftsmen preamp model such as a DX4000 or one of the others that has the bridge mode reverse phase outputs to accomplish this. Or you can build a preamp circuit that does this which is not particularly difficult using an op amp to provide the phase inverted signal for one of the channels.
I have bridged a pair of PCR-800's (for all practical purposes are identical to a PM-840) using a Soundcraftsmen DX4000 preamp. Just two powerful to be practical for a home audio system. Also the DX4000 is rather noisy and its noise and hum was amplified in bridged mode making this combination unacceptable for low volume level listening. But still was a ton of fun playing around with it and will return to this setup at some point in the future after I rebuild the DX4000. I need to address some the shortcomings in its design and construction of the day (1980's). It is so satisfying playing around with old gear though and plan to setup my listening room to include these along with a Kenwood KR9600 (I bought new when I was only 21 and still looks practically new) and a Carver M-500t. Both need restoration before put back in service.
@@multicyclist So, I need a preamp (or pwr amp) that Has Bridge Mode Reverse Phase outputs to Authentically produce Mono Bridge power: 200 to 400-800w? I thought Simply connect both red positive post from pwr amp to 1 spkr +/- .
How much power would that amplifier do at four ohms did you test that
They are rated at 300 WPC RMS @ 4 ohms. They do meet the Soundcraftsmen published rating. I have used a pair of these with a Soundcraftsmen preamp in bridged mode for 600 WPC RMS @ 8 ohms. You may ask why? Well because an amp in bridge mode doubles the slew rate and to me sounded better than in 200 watt mode. Just was way too powerful for a home audio system and could have easily ruined my high quality audio system speakers so I switch to a different amp system. I still have 3 of these amps that I plan to use in the future though.
Please continue to utter any taught that you have about anything related to electronics and electricity. Even that comment about line voltage creep and this being a analog amplifier makes me think about the whole system,
my home build power amp has 120 000uf pr 2 channel .Each channel in 120w 8ohm.the circuit for the amp i build has no gloab or local feeback loop.it is very linear.no hiss when the amp is connected to a amt type tweeter with 94db 1w 1meter senistivity,cant hear hiss at all.my old nad poweramp give hiss around 4 times more.rotel power amp even worce.that hissis no proble if i have used speakers with passive crossove inside.but i use a dsp type active crossover from ground sound.so i have one amp for each driver the hole system is with active crossover around 50% more effective.
if there is a resistance in series with the emitter of a transistor crossed by the audio signal, then there is a counter-reaction.
if there are very large capacitors but few transistor pairs, the large capacitors are not useful.
2SK135 seems to be obsolete. Any modern audio grade replacements?
They have now become unobtainium. There are a few NTE2993's out there for sale, but very expensive. Other than that, you have to get them from eBay used or NOS.
You can still get NOS 2SK133/4/5 and 2SJ48/49/50's on eBay, not very cheap, some chinese fakes of course, but the modern equivalents are made by UK company Exicon: www.exicon.info/products.php
There main advantage over bipolar seems to be lack of secondary breakdown and immunity to thermal runaway - MOSFET amps don't tend to die. Made an amp back in the early 80's and still going strong (though I did find one channel was running hot, needed rebiasing a bit).
Modify the case,modify the case,put those huge Nichicon cans in :-)
(Soundcfrt860) (at about 5mns of play) (mono-bridge mode)Yellow lamp flashes extreme and fan runs extrmly fast, what's cause?? Amp doesn't feel warm
Thanks for the video. I was looking at these amps on eBay. Any idea how they sound compared to an Adcom GFA-555?
Could you help please? I have a soundcraftsmen power four-17 something burnt on power supply board. Was wondering if you had a way I could send you a pic and let me know what you think it could be?
Actually...the PCR or Phase Control Regulation system works a lot like alight dimmer. at idle, no load, the scr's fire part way through the wave form, much like how a light dimmer works in your house. as the load increases, the Phase control circuitry fires the SCR's sooner much like turning up a light dimmer. its the same principal, the load is monitored and by controlling the firing angle of the SCR's, you can increase the current/Voltage of the power supply to maintain the voltage.
This SAME circuit is used in the A2502 with a standard non regulated power supply and only develops 140 watts per channel due to power supply sag.
If that is true wouldn't the +70 and -70 volt supplies have been regulated the DC rail voltages down when there was no load or low audio input signal? If they were it wasn't shown. If it changes rail Voltages it would act like some Carver amps.
@@danlewis243 This regulator keeps the rails at +/-70volts, as you draw current...IE over 10 amps at max power into a 4 ohm load, the power supply voltage would sag and you would get a form of compression. the Bulk DC supply would be something like +/-84 in this amp if it wasn't regulated DOWN to 70, and as the load draws more power from the supply, the regulator works to keep the rails as close to the rated voltages as it can.
Carver supplys work in a different way. the actually fire the transformer much in the same way an ignition coil works on your car. plus they have a class-H rail switching scheme that switches on and off multiple power supply rails. which is not as good sonically.
@@overkillaudioinc Right I had a Carver TFM -22 and It does and did not sound as clean as the PM 860, poorly damped bass as well. I like the sound of the H class Soundcraftsmans I just bought another today
@@overkillaudioinc think i Got it now So it increases the conduction angle of the SCRs to maintain the ~70 volts when load increases.
I bet those caps were the most expensive parts that you put into that amplifier
Wasn’t Soundcraftsman owned by BSR?
Induction motor.
I bought a Soundcraftsman 5002 (?) In about '89 and returned it the next day. I thought the board quality and wiring were poor.
Me regalas el diagrama amigo por que no lo consigo te agradecería
👍