The thing I find amazing about your repair projects it that despite the fact that you have seen or spotted evidence of someone trying to repair a product, you are still able to repair or make some improvements to it.
I've never worked on a vintage Crown, though I hope to some day. QSC has pretty good support, even on the older amps like this. So far QSC and Crest are my favorite vintage pro amps. I'm actually working on a Crest right now, but it will be a week or two before I can make a video on it.
Great job. I just rehabbed an Altec-Lansing 9444a amp. Replaced all the electrolytic caps and replaced the NE5532 op amp in the input with an opa1642. Its now what I'd consider a hi-end stereo power amp. I also slowed down the fan by putting in a bigger fan resistor to quiet it down. My total investment for the amp and all the parts is about $200.
Hello Sir, Really love your vids, besides other restoration jobs on youtube, you explain the problem and the way out for the solution, it is really great. For hobbyist like me its great. Keep up your good work. Regards. Helder From Portugal.
Really enjoy your vids Maxx. Most bench tech's now change boards completely so it's refreshing to see (and it's bringing back my own hunger for component level troubleshooting) Thanks for the vids.
I've always liked the reliability and sound of QSC amplifiers. As in ex engineer for UCI cinemas UK we have used hundreds of QSC amplifiers over the years. The fans can be a little over kill at times. I mod we used to do was to fit a temperature cut out with a capacitor across it. With the cap in circuit the fan would run at about 25% full speed. Should the amp be driven hard into 4 ohms the cut out would click closed and return the fan to full speed. In the real world it was very rare for this to happen. Made the projection room much quieter with an average of 6 amplifiers per screen.
Broken connection to the speaker feedback circuit, where the filter cap was connected. This amp uses the main filter caps to also couple the signal to the speakers. It's a cool design, and also prevents DC from going to the speakers in the event of a malfunction.
1 thing I like about old amp's, it's more easier to repair than the one's now, too many surface mounted components. just repaired 1 qsc as well- rmx 2450, damn small parts, took a few hours to get it going.lol,
Yep, especially when the parts are only $10 or so total. I often have to wait until I am working on multiple projects before making a parts order, because the shipping cost is higher than the parts themselves.
@maxxarcade can you do a video and show us your benchwork , tools you use for your projects and and but not least make a tutorial video how to do solder , just find a board and use it as a sample to do your tutorial on.. I love stuff like this and would like to learn from the best.
I ran across your post on DIYAudio forums regarding the transistor replacement. How did you decide on your replacements? I could find absolutely no datasheet on the original transistors. What do you do in a case like that? I suppose if you have a working transistor, you could use proper measurement equipment to spec it out?
Hi Max,Im getting a cb radio for the car,but I will be running it in the house,its 40 chanel Usb/Lsb am is 4 watts and ssb is 12 watts.How many amps should the power supply be 3,6,or 9? Thanks.
I have a A 31 which is built identical to the A21. I'm a beginner and I'd like to see how you tore it down to get to the transistors and circuit board? Is it as hard as it looks? I really love this amp. I need whatever specs to adjust the trims. Can You help?
i just tested my at least 40 year old Vinyl player / amp , it is probably older then this but it uses same Transistorors . And i was checking with my finger if its wormed up , is it working cuz speaker was just humming and baam. It taped me real nice . Got my voltmeter , and its 50V. im like damn man aint that a lesson . So now im thinking . The body of transistor is base , the cooler should be neutral ,GND...there shouldnt be any voltage there . So i guess somwhere in it a cap is dry and it shorts DC to ground . so the bias voltage of first stage transistor 20v is shorted to the ground and second stage 40v is also. Is this correct . I checked the voltages on all transistors , 20/20V and 40/40V , on 4 transistors . I also noticed that the Vinyl motor is spinning always , i guess thats from reverse voltage it gets from ground . Does this make any sense ? should i trace that voltage ?
QSC are great amps. I have worked on a few, and are fairly easy to service and they seem to stand the test of time. I have heard, although I can't confirm this, that QSC decided to stop using tin plating on circuit traces in the late 80s/early 90s. Can anyone confirm this?
im a elec tech for over 21+yrs qsc amps are just mediocre. the WB calliper 500 is much better sound,build & performance. made in 1984!! when i see a qsc i cringe
Hi max, i recently i got HH Electronic MX1200 power amplifer.Before this it works great ,500watt per channel at 4 ohm,but the original owner has accidently shorted the speakers cable and caused it got no output sound.The power amplifier still can be power on, but did not get any output sound and seems the Signal LED's incator of both channel did not respond.What would caused this problem? Output transistor? or the preamp board?Thanks.
Going to do anything about the loud fan? i imagine it wasn't a consideration originally if it was going to be used for big PA stuff, but since you're just going to be using it in a small room, I imagine it'll be far more annoying.
What's the biggest flip you've ever done? Like bought something dirt cheap or got it for free because it was "broken" and then fixed it, like whats the most you've ever gotten back?
I love things like this, repairs that most people (including me!) wouldn't or couldn't do, but are only small things, and bang, you have a very high-quality product.
i am watching this listening to the vid thure via qsc 1400 nice job get rid of the crown crap go qsc oldschool detroit techno thats waht made the rave seen
I'm curious what criteria you use to replace transistors. If you can't find an exact match for all specs, what do you concentrate on for matching, other than package type, etc?
great vid. fyi bg micro deals in alot of absolete parts they have saved me a bunch of work before..and if you cant find it on the web site. call them somtimes they still have it. peace
There is really no way to predict fan failure. I've seen them run noisy for years, and I've seen quiet ones seize up. You just need to check it once in a while. But I guess the good thing about it being noisy, is that you know when it stops.
I just went with the complimentary to the original MJ15015 that were already in the amp. Also checked with QSC. When matching transistors, I use my meter to match Hfe. Finding substitutes is a matter of several things- Understanding the circuit, comparing to other amps by the same company, comparing datasheets etc. And a lot of the time, there are already other people in the same situation that post on forums with their findings.
Ya, I like shopping there too. They seem to find the most obscure parts sometimes. But the best thing about these older amps, is that they are almost always easily modified to accept modern parts.
Next time someone asks me to build one, I will be able to do a video. None of my own need any work done to them at the moment. Though I might be mentioning some workshop computer stuff soon.
(Ooops!! Continued from previous entry): i Had been watching tube amp repairs all weekend.. Cool to watch a solid state repair!! I want to learn rhos kinda stuff!! (Subscribed!!)
I have a QSC 1400. One channel was popping and eventually one of the filter caps blew. Do you think that it's likely that one of the rectifiers is bad?
The thing I find amazing about your repair projects it that despite the fact that you have seen or spotted evidence of someone trying to repair a product, you are still able to repair or make some improvements to it.
I've never worked on a vintage Crown, though I hope to some day. QSC has pretty good support, even on the older amps like this. So far QSC and Crest are my favorite vintage pro amps. I'm actually working on a Crest right now, but it will be a week or two before I can make a video on it.
The NE5532 is a nice little low-noise op-amp which doesn't cost too much. Dolby used them in the CP700 sound processor.
Great job. I just rehabbed an Altec-Lansing 9444a amp. Replaced all the electrolytic caps and replaced the NE5532 op amp in the input with an opa1642. Its now what I'd consider a hi-end stereo power amp. I also slowed down the fan by putting in a bigger fan resistor to quiet it down. My total investment for the amp and all the parts is about $200.
Hello Sir,
Really love your vids, besides other restoration jobs on youtube, you explain the problem and the way out for the solution, it is really great. For hobbyist like me its great.
Keep up your good work.
Regards.
Helder From Portugal.
Really enjoy your vids Maxx. Most bench tech's now change boards completely so it's refreshing to see (and it's bringing back my own hunger for component level troubleshooting) Thanks for the vids.
I've always liked the reliability and sound of QSC amplifiers. As in ex engineer for UCI cinemas UK we have used hundreds of QSC amplifiers over the years. The fans can be a little over kill at times. I mod we used to do was to fit a temperature cut out with a capacitor across it. With the cap in circuit the fan would run at about 25% full speed. Should the amp be driven hard into 4 ohms the cut out would click closed and return the fan to full speed. In the real world it was very rare for this to happen.
Made the projection room much quieter with an average of 6 amplifiers per screen.
Broken connection to the speaker feedback circuit, where the filter cap was connected. This amp uses the main filter caps to also couple the signal to the speakers. It's a cool design, and also prevents DC from going to the speakers in the event of a malfunction.
old amps are great .. i had a panasonic from the 70s and that thing had some sound :)
1 thing I like about old amp's, it's more easier to repair than the one's now, too many surface mounted components. just repaired 1 qsc as well- rmx 2450, damn small parts, took a few hours to get it going.lol,
It might have been on there for a while. I guess most sane people wouldn't buy something this messed up, but I like the challenge.
Yep, especially when the parts are only $10 or so total. I often have to wait until I am working on multiple projects before making a parts order, because the shipping cost is higher than the parts themselves.
Maxx, I don't really want to be bothersome, but when are your new vids coming out? Can't wait for more - really love your vids.
Great job Max! Like your tutorial. I learned alot from this video of yours. Thanks for uploading. Have great day!
You touch it, and it starts working.And it is beautiful.
I've been wondering how long it'd be until you would switch those speaker connections over to banana jacks/plugs.
Nice old amp though!
if you can get QSC with the balanced inputs but still made in America you got her made .
super video AGAIN love watching your channel.
@maxxarcade can you do a video and show us your benchwork , tools you use for your projects and and but not least make a tutorial video how to do solder , just find a board and use it as a sample to do your tutorial on.. I love stuff like this and would like to learn from the best.
wow, its been a long time since I seen a qsc
Hey Max, i like the new speaker terminal on your workbench speakers. When did you do that. And what kind of connection is that?
I ran across your post on DIYAudio forums regarding the transistor replacement. How did you decide on your replacements? I could find absolutely no datasheet on the original transistors. What do you do in a case like that? I suppose if you have a working transistor, you could use proper measurement equipment to spec it out?
alway's fun to see your vids dude
Do you know how to program ? If yes, which languages do you know and which one do you prefer and why ?
Great video like always, keep them coming.
good job, very neat little Amp :-)
nice find and it sounds great
I'll be talking all about these speakers soon actually. I still have more work to do. The connections are just banana jacks at the moment.
This was cool to watch!! Had been watching and learning tube amp
NIce video man i hope to see more!
Nice work , can you do more main amplifier repairs ?
damnit your lucky to find this shit id love to have something like this!
It is a BJT amp.
Put a simple temp-based speed control circuit on the fan. Speed proportional to heatsink temp. Quiet when the music is, loud when the music is.
Hi Max,Im getting a cb radio for the car,but I will be running it in the house,its 40 chanel Usb/Lsb am is 4 watts and ssb is 12 watts.How many amps should the power supply be 3,6,or 9?
Thanks.
Whats the first song (the piano one)?
Anyway nice video!
Is there a way you can replace the fan in this server mount one? ^_^ (Or rack mount)
i have an old cybernet spa - 80 and spr - 80, do you know anything about these units?
Hey max - What is that first test song? Thanks ^^
I haven't heard of those before.
I have a A 31 which is built identical to the A21. I'm a beginner and I'd like to see how you tore it down to get to the transistors and circuit board? Is it as hard as it looks? I really love this amp. I need whatever specs to adjust the trims. Can You help?
the best old school electronics,wath is the name of the song?
Where are you located I need a receiver fixed
Great video have you consider a quiet PC fan?
I fix arcade games, pinball machines, jukeboxes, computers, and other stuff.
Where do you work?
i just tested my at least 40 year old Vinyl player / amp , it is probably older then this but it uses same Transistorors . And i was checking with my finger if its wormed up , is it working cuz speaker was just humming and baam. It taped me real nice . Got my voltmeter , and its 50V. im like damn man aint that a lesson . So now im thinking . The body of transistor is base , the cooler should be neutral ,GND...there shouldnt be any voltage there . So i guess somwhere in it a cap is dry and it shorts DC to ground . so the bias voltage of first stage transistor 20v is shorted to the ground and second stage 40v is also. Is this correct . I checked the voltages on all transistors , 20/20V and 40/40V , on 4 transistors . I also noticed that the Vinyl motor is spinning always , i guess thats from reverse voltage it gets from ground . Does this make any sense ? should i trace that voltage ?
That's the song you were playing??
cool, thanks man, great video
What kind of speakers do you have playing?
eminence beta 8a i think i seen it it a comment he repllyed to hople this hellped :)
Same design as the Peavey CS 1000 with the back porch .
wha power supply are you useing?
Not much really. I usually make less than $100 profit on anything I do. That's why it's just a hobby, I could never live off it.
QSC are great amps. I have worked on a few, and are fairly easy to service and they seem to stand the test of time. I have heard, although I can't confirm this, that QSC decided to stop using tin plating on circuit traces in the late 80s/early 90s. Can anyone confirm this?
Most companies have not been doing the tin plating these days. It's just solder mask over bare copper now. This is a good example why.
Maxxarcade have you ever worked on any Crown amplifire
qsc r mediocre amps
Never LOL.
im a elec tech for over 21+yrs qsc amps are just mediocre. the WB calliper 500 is much better sound,build & performance. made in 1984!! when i see a qsc i cringe
I've got some issues with my workshop that need to be fixed. Hopefully I'll have some updates this weekend.
I just look around for broken stuff that I can get free or cheap. I guess I like fixing it more than using it most of the time LOL.
Hi max, i recently i got HH Electronic MX1200 power amplifer.Before this it works great ,500watt per channel at 4 ohm,but the original owner has accidently shorted the speakers cable and caused it got no output sound.The power amplifier still can be power on, but did not get any output sound and seems the Signal LED's incator of both channel did not respond.What would caused this problem? Output transistor? or the preamp board?Thanks.
Looks like a triple-darlington design, possibly in a cascode configuration, which would explain the six transistors in each channel.
Going to do anything about the loud fan? i imagine it wasn't a consideration originally if it was going to be used for big PA stuff, but since you're just going to be using it in a small room, I imagine it'll be far more annoying.
What's the biggest flip you've ever done? Like bought something dirt cheap or got it for free because it was "broken" and then fixed it, like whats the most you've ever gotten back?
I love things like this, repairs that most people (including me!) wouldn't or couldn't do, but are only small things, and bang, you have a very high-quality product.
i am watching this listening to the vid thure via qsc 1400 nice job get rid of the crown crap go qsc oldschool detroit techno thats waht made the rave seen
Hi Max, what brand of amp would you recommend for pa/disco use, and is it cheaper to make speaker cabinets than to buy the complete speaker?
Regards
is this amp uses MOSFET BUZ 901 and BUZ 906 as output transistor?
I'm curious what criteria you use to replace transistors. If you can't find an exact match for all specs, what do you concentrate on for matching, other than package type, etc?
great vid. fyi bg micro deals in alot of absolete parts they have saved me a bunch of work before..and if you cant find it on the web site. call them somtimes they still have it. peace
There is really no way to predict fan failure. I've seen them run noisy for years, and I've seen quiet ones seize up. You just need to check it once in a while. But I guess the good thing about it being noisy, is that you know when it stops.
I just went with the complimentary to the original MJ15015 that were already in the amp. Also checked with QSC.
When matching transistors, I use my meter to match Hfe. Finding substitutes is a matter of several things- Understanding the circuit, comparing to other amps by the same company, comparing datasheets etc. And a lot of the time, there are already other people in the same situation that post on forums with their findings.
Can I just reflow the solder joints, or scrape down to the copper and resolder? Where are you located?
Ya, I like shopping there too. They seem to find the most obscure parts sometimes.
But the best thing about these older amps, is that they are almost always easily modified to accept modern parts.
Next time someone asks me to build one, I will be able to do a video. None of my own need any work done to them at the moment. Though I might be mentioning some workshop computer stuff soon.
Great video as always an that thing has a smooth sound thanks.
If you don't mind me asking,what do you do for a living?
10 minutes later and there are already five comments.
look up qsc 1700
I probably could, but I don't know how much airflow I could sacrifice yet.
In amps like these, it's usually from the inputs getting overloaded or zapped.
first
whats your recommendation for vintage pro amps? I was looking at some old Crown d150 series ii amps and then i watched this video... thanks
(Ooops!! Continued from previous entry): i Had been watching tube amp repairs all weekend.. Cool to watch a solid state repair!! I want to learn rhos kinda stuff!! (Subscribed!!)
I have a QSC 1400. One channel was popping and eventually one of the filter caps blew. Do you think that it's likely that one of the rectifiers is bad?
Love these vids
Cool :D!!!
I just used to watch your pc builds but I'm starting to get into these as well! What is your favourite restoration project so far
thats awesome man! ive always loved older stereos as well.... the bass always seemed more "fuller" i guess you can say
Probably my Marantz 1060.
yes but ive got a amp that has a transformer putting off a 60 hertz hum that sounds like a wahl trimer
What song was that?
ruclips.net/video/T0ZXeRQ4PeA/видео.html
How you check the channels
how did you find out that transistor was shorted? 0ohms between the pins?
yep