It’s great to see that you constructed a “dim bulb” current limiter. For 40+ years a similar device has been on my workbench. It is essential for “non destructively” powering up audio gear and many other mains-powered electronic devices. Most solid state amplifiers can be tested and listened to at low volumes with the “dim bulb” current limiting in place. I only apply full mains current after confirming that everything is functioning as it should.
Sometimes you learn more when you blow stuff up, because first you have to figure out how you blew it up and what happened when you did that, and then you have to fix it (and sometimes even that doesn't go perfectly). I'm glad to see the entire repair process, warts and all, so thank you for these videos.
13:03 If you're using a variac or similar, when you ramp up the voltage slightly you monitor the current draw. If the current draw continues to rise as you increase the voltage that is the indicator that there is a short or issue causing it to draw excessive current which would normally blow stuff up but as you can turn up the voltage slowly, you prevent damage due to being able to recognise there's a problem and turn it off again. I do a lot of electronics and electronics repair, high voltage stuff, vacuum tube electronics repair etc :)
Great save. I read that these amps were ground breaking when released in 1979 and incredibly popular, so well worth your efforts. Still looks modern today. 😊👍
Nice to see you repairing an amp rather than a computer, as it's been ages since you last repaired one though I like the computer repairs as well of course! Hoping you will do more amp or other audio repairs in future as well as continuing of course doing computer repairs especially the Commodores which are my favourites!
Hey Jan, When I was in the trade (audio engineer) I used to have capacitors in series with my speakers to prevent blowing them up if I was stress testing an amp.
You can make poor mans non polerized electrolytic capacitors by connecting 2 back to back in series. IE Amp+ ---)|--|(-- Speaker+ If you are feeling really fancy you can put some LED's with resistors series across the capacitors to indicate any voltage polarity. I used the red/green LEDS that show yellow with AC across them. In a working situation on a split rail amplifier there should not be any DC on the output. However on a single rail amp you will get DC whilst the output caps charge. (Not thst see many of those these days).
Great work, Jan. I agree that sometimes things go wrong during the repair process. It happens to us all. I am looking forward to your bias video for this 3020.
Yes we all have that sinking feeling when we make a mistake and it goes Bang!. Often it is such a silly mistake that you would not believe. We learn, hopefully lol :-D
your absolutely correct very few videos on youtube about repairing the nad 3020 .. i have a 3020i that blows internal fuses as soon as its turned on ... so i have a feeling i will be making a similar video ... thank you also for the dim bulb tip .. i had seen this before but had compleatly forgotten about it , look forward to more video on hifi repairs
If you find a NAD 3240PE, don't hesitate. Get it! It's even better because of a bit higher output and Soft Clipping. I had one with a NAD CD-player without a remote, that costed extra back then.
Maybe try putting banana plugs that also take bare wire on the back. I am replacing my Verit 1980s speaker terminals with bananas because they will last longer. The old one broke just like yours did. I love the old HiFi repairs. I learned a lot. Keep up both.
Great, I would like you to show how to set the low current on this amp. It would be nice to put 4 or 8 ohm 100 watt resistors instead of speakers and use a generator to display the distortion on the oscilloscope.
Awsome job Jan. Love the old amps. Well done. Those 'nemisis' fixes of things that have sentimental value are the best and the old Class A analogue amps are much better imho. Big up on the series lamp tip. I need to tidy mine up as it is just a bit of flex with a lamp connector lol
I've replaced the speaker connectors on this model before and it was hard to find the slot-in part. The standard chinese once did not fit. Found the correct on the 3rd try...
A frequent problem in the original 3020 was the pre-driver transistor shorting for no good reason, which drove the driver and output transistors to full output and then death. I'd check those too, just to be sure. Later versions of the 3020 and the 3020A had an under-rated capacitor controlling the mute circuit between the pre-amp and amp sections. It was 47uF at 63VDC, but over 80 volts were applied to it BY DESIGN! It's in the schematic! Fortunately, yours is not one of the later versions - I don't see that capacitor on your circuit board. Tschüss!
good to have new driver transistors with a higher voltage rating! maybe that NAD amp is rated for 220 Volts main. Now we have 240 Volts power supply. that means, that the voltage coming out of the transformer is higher. so please check also the capacitor ratings. exchanging the main capacitors after the rectifier. if you change them to double capacity and using low ESR caps, like panasonic fc or fm, you probably get better stability in the control loop. maybe also check the potentiometers for noise. on my rotel rc-995 the balance potentiometer is extreme shit! i guess, i bridge it completely. who needs balance anyway :-)
I used to work for a shop in 1982 where we sold those. Hopefully 4 decades on the weird smell has gone. You should get away with the lower voltage transistors, I believe they were fitted to the first versions, but due to UK line voltage being c240v they tended to explode leading to a very high workload for the repair department. They do sound nice but I prefer my Crown ;)
Some times when you use that type of tester you need to test it both ways ( test pins 1 2 3 then flip it over 3 2 1 ) I have tested transistors one way with bad or unknow part then flipped over and tested good with the right part name and type.
It seems that board also has pads for TO-3P case. So no need to hunt TO-3 case for 2N3055 MJ2955. Replacement in TO-3P case is TIP3055/2955. With that heatsink then 115W to 90W TPD in transistors isn't issue.
I'm risking commenting before watching the video here - there is a small catch with the 3020 if you fit newly made 2955/3055 transistors. The original types were of "hometaxial" construction, and that allowed NAD to get away without using the emitter resistors that you normally see on power amplifier output stages. New types will be "epitaxial" construction, and will go into thermal runaway without emitter transistors. The way I have dealt with this before is to solder some 0.22 ohm 3W metal oxide resistors to the bottom of the board, breaking the track where appropriate. This also makes setting the bias a bit easier, because you can now simply measure the voltage drop across the emitter resistors as you would do with any other amplifier :) For the driver transistors, as the 2N6551/4 are obsolete, I have used MJE243/253. You need to bend the leads around, because the 2N's are EBC and the MJE's are ECB, but it's doable.
and i should have watched all the way through, because you mention adding the extra resistors at the end :) They are nice little amplifiers indeed, especially as they were "budget" in the early 80s. Its a shame they took the gamble by leaving out the emitter resistors really, as that;s often the cause of failure with these amps
Hello and welcome . I'm struggling with the 3225 pe, which I have a problem with a short circuit in the left channel, everything seems to be OK and it plays, but after adding the volume, almost all the transistors and two resistors light up, what could be the reason? I've already checked almost all the condos and they are ok, so what could be the reason? cause this condition. Turned on by a 100 W bulb, it glows slightly. Thank you in advance for all your suggestions
@@JanBeta All good. You mentioned the difficulty in chasing down those drivers. Would the outputs also be as hard to source? I have a vintage Kenwood receiver showing all cans shorted and would like to refurbish.
I have a NAD stack with a 705 reciever with some issues, if I turn on the amp one or both channels is not giving sound, if I crank the volume way up the the channel is starts working. replaced the relais but that is not the solution. have someone a idea what the problem is.
@@MultiArrie The symptom you wrote about surely can be from worn or dirty pot, without scratching. Step one, regardless of cause whatever it may be, is DeOxit the pots well.
Nice to see a successful amp repair! Just did DC offset to +/- 1 mV on my Sony STR-7045. It has been with me since birth, used every day, and my familiy is original owner. It has an outrageously unbeatable sound at normal money prices. Main speakers = Marshall cab I rewired to stereo (sick!) and "B" speakers are Sony 3-way floor standers. Check here: ruclips.net/video/OwIojFGeAaY/видео.html
Build an amplifier with absolutely zero percent distortion and next to nobody will buy it. Add a tiny bit of distortion and people will think that model sounds good.
On my Sony-7045, I am able to perceive the upgrade in sound from how it has been for decades at 30-40 mV D.C. offset to when I put it to less than 1 mV (both channels) a few weeks ago, and now. It was sounding fantastic before, but it is slightly clearer even more now, especially at higher volumes just as electronic knowledge dictates. Less harmonic distortion enables a more powerful sound, where the volume dial is in the exact same place, if that helps any readers know something. Another angle to ponder it is the engineering-base-goal of efficiency (as well as just plain correct in the first place.) All that being said, if anyone has an amp with 20, 30 mV, I would not say it is imperatve to get it down. It is not THAT super critical. But if you like things working and being the best they can for what they are, then yes, get it to 0 or as close as possible. If you are the type that is a close listener, music enjoyer, take it to any level more than an iPod baby, yes you will like the results. Higher numbers should definitely be brought down, without second guess.
I mean, why do things in this way and more think about shooting the video, how will it look etc. instaed of learning more about the circuit and electrical engineering as well. I will just make one point. You have mentioned not using thermal paste since you have placed insulator (mica, wafer, however you want to call those). Paste is a MUST becuase it fills in micro pores in the material. It would be better to put more knowledge than put out video showing shorted out components or destroyed piece of hi-fi equipemt. Some of those components are unobtanium and newly made components people most often than not put inside and cause even more problems than what they had in the begining. Oh well, what to say, your item, your prerogative to do what you want. And one more thing, conclusions like you say "...and hopefully it will work" is not the way to do things. I am always sad when I stumble upon such video and in most cases I am very disappointed. Moving on! :-(
The washers are silicone and you definitely don’t need thermal paste with them. They are slightly elastic, that’s how they fill the gaps. My videos are not tutorials, I’m always just letting people watch me doing things. And I don’t claim in any way to be a professional. You have to look elsewhere for that. And by the way, even professionals have the "moment of truth" after repairs when they are turning something on for the first time after working on that. There’s no shame in that. Learning from mistakes is still one of the best ways to learn. I’d rather talk openly about it than to pretend things are working first try (like many other RUclipsrs). That said, I’ve been repairing vintage audio equipment and studio gear as a hobby for a long time now (10+ years) and I definitely learned a lot along the way and fixed way more than I destroyed, with the occasional backlash.
It’s great to see that you constructed a “dim bulb” current limiter. For 40+ years a similar device has been on my workbench. It is essential for “non destructively” powering up audio gear and many other mains-powered electronic devices. Most solid state amplifiers can be tested and listened to at low volumes with the “dim bulb” current limiting in place. I only apply full mains current after confirming that everything is functioning as it should.
Nice to see a new record for lost time accidents.
Cool, i work in 2005/2008 at the german Authorized workshop from NAD 👍
My uncle still runs a full old NAD stack. It's so nice :)
Sometimes you learn more when you blow stuff up, because first you have to figure out how you blew it up and what happened when you did that, and then you have to fix it (and sometimes even that doesn't go perfectly). I'm glad to see the entire repair process, warts and all, so thank you for these videos.
Analog electronics are an art more than exact science it's amazing to me some people can work on these old receivers and get them working again.
its far easier to repair these class AB amplifiers than it is to repair anything class D based !
13:03 If you're using a variac or similar, when you ramp up the voltage slightly you monitor the current draw. If the current draw continues to rise as you increase the voltage that is the indicator that there is a short or issue causing it to draw excessive current which would normally blow stuff up but as you can turn up the voltage slowly, you prevent damage due to being able to recognise there's a problem and turn it off again.
I do a lot of electronics and electronics repair, high voltage stuff, vacuum tube electronics repair etc :)
A mix of videos is good & interesting. +1 vote for more non-retro computer videos.
Great save. I read that these amps were ground breaking when released in 1979 and incredibly popular, so well worth your efforts. Still looks modern today. 😊👍
Nice to see you repairing an amp rather than a computer, as it's been ages since you last repaired one though I like the computer repairs as well of course! Hoping you will do more amp or other audio repairs in future as well as continuing of course doing computer repairs especially the Commodores which are my favourites!
Jan Beta, The German Bob Ross.
Let's get a happy little smoke plume out of these trasistors...
"Danke für Ihren Kauf herzlich." Der französische Händler war ja sehr nett ;)
Nice to see you dusting of the old stereo gear repair skills! I enjoy these episodes just as much as the computer ones.
"severely happy"
That's a term I haven't heard before, I like it
Yes always do a check with your multi meter that the Power Transistors are not shorting to earth Good old Mica Insulators
Hey Jan, When I was in the trade (audio engineer) I used to have capacitors in series with my speakers to prevent blowing them up if I was stress testing an amp.
You can make poor mans non polerized electrolytic capacitors by connecting 2 back to back in series. IE Amp+ ---)|--|(-- Speaker+ If you are feeling really fancy you can put some LED's with resistors series across the capacitors to indicate any voltage polarity. I used the red/green LEDS that show yellow with AC across them. In a working situation on a split rail amplifier there should not be any DC on the output. However on a single rail amp you will get DC whilst the output caps charge. (Not thst see many of those these days).
So many enthusiasts started with NAD, it usually served us well but like all older electronics they do require a li'l TLC to keep up 😃
Great work, Jan. I agree that sometimes things go wrong during the repair process. It happens to us all. I am looking forward to your bias video for this 3020.
La NAD piace anche a me,ho un'amico che ha un amplificatore NAD e ha un suono perfetto.jan,ottimo lavoro.
Love the audio repair stuff!
I bought my 3020 in 1976 and it still delivers the best sound into my EV 150 speakers.
Oh, so so nice, I just asked for this in the old vid commentary. Here We Go.
Yes we all have that sinking feeling when we make a mistake and it goes Bang!.
Often it is such a silly mistake that you would not believe.
We learn, hopefully lol :-D
Great video. So satisfying to get the amp up and running again.
👍 I really admire your love for repairing retro equipment!
Congratulations Jan, I know the joy of repairing a thing after such a long time :)
Great video! I started with the updated version of this classic amplifier, the NAD3020i emptying my piggy bank 😄
your absolutely correct very few videos on youtube about repairing the nad 3020 .. i have a 3020i that blows internal fuses as soon as its turned on ... so i have a feeling i will be making a similar video ... thank you also for the dim bulb tip .. i had seen this before but had compleatly forgotten about it , look forward to more video on hifi repairs
I find this kind of video and the retro computer videos equally interesting.
those focus 10 tunes remind so much of 80's film soundtracks for some reason
If you find a NAD 3240PE, don't hesitate. Get it! It's even better because of a bit higher output and Soft Clipping.
I had one with a NAD CD-player without a remote, that costed extra back then.
Excellent repair and some bad luck earlier, but that's name of the bisnes. Thanks 👍
Maybe try putting banana plugs that also take bare wire on the back. I am replacing my Verit 1980s speaker terminals with bananas because they will last longer. The old one broke just like yours did.
I love the old HiFi repairs. I learned a lot. Keep up both.
Great, I would like you to show how to set the low current on this amp. It would be nice to put 4 or 8 ohm 100 watt resistors instead of speakers and use a generator to display the distortion on the oscilloscope.
Dood you gotta do some Carvers like the M-400 cube. That thing was awesome.
Awsome job Jan. Love the old amps. Well done. Those 'nemisis' fixes of things that have sentimental value are the best and the old Class A analogue amps are much better imho. Big up on the series lamp tip. I need to tidy mine up as it is just a bit of flex with a lamp connector lol
I've replaced the speaker connectors on this model before and it was hard to find the slot-in part. The standard chinese once did not fit. Found the correct on the 3rd try...
A great AMP I use mine everyday for my PC
Great video!
I too repair old audio equipment. I just love 1970s Japanese audio gear.
A frequent problem in the original 3020 was the pre-driver transistor shorting for no good reason, which drove the driver and output transistors to full output and then death. I'd check those too, just to be sure. Later versions of the 3020 and the 3020A had an under-rated capacitor controlling the mute circuit between the pre-amp and amp sections. It was 47uF at 63VDC, but over 80 volts were applied to it BY DESIGN! It's in the schematic! Fortunately, yours is not one of the later versions - I don't see that capacitor on your circuit board. Tschüss!
Interesting. Time for a quality Japanese cap replacement, I think!
Thank you for the video. I have to such amplifiers on the workbench for repair. Greetings from Poland.
good to have new driver transistors with a higher voltage rating!
maybe that NAD amp is rated for 220 Volts main. Now we have 240 Volts power supply. that means, that the voltage coming out of the transformer is higher. so please check also the capacitor ratings. exchanging the main capacitors after the rectifier. if you change them to double capacity and using low ESR caps, like panasonic fc or fm, you probably get better stability in the control loop.
maybe also check the potentiometers for noise. on my rotel rc-995 the balance potentiometer is extreme shit! i guess, i bridge it completely. who needs balance anyway :-)
I used to work for a shop in 1982 where we sold those. Hopefully 4 decades on the weird smell has gone. You should get away with the lower voltage transistors, I believe they were fitted to the first versions, but due to UK line voltage being c240v they tended to explode leading to a very high workload for the repair department. They do sound nice but I prefer my Crown ;)
Awesome... I have a similar one from 1984. Probably due for a recap.
Some times when you use that type of tester you need to test it both ways ( test pins 1 2 3 then flip it over 3 2 1 ) I have tested transistors one way with bad or unknow part then flipped over and tested good with the right part name and type.
Glad i never booked my amp repair in with you with that turnaround time hahaha
Great work jan love your channel.
It seems that board also has pads for TO-3P case. So no need to hunt TO-3 case for 2N3055 MJ2955. Replacement in TO-3P case is TIP3055/2955. With that heatsink then 115W to 90W TPD in transistors isn't issue.
I'm risking commenting before watching the video here - there is a small catch with the 3020 if you fit newly made 2955/3055 transistors. The original types were of "hometaxial" construction, and that allowed NAD to get away without using the emitter resistors that you normally see on power amplifier output stages. New types will be "epitaxial" construction, and will go into thermal runaway without emitter transistors.
The way I have dealt with this before is to solder some 0.22 ohm 3W metal oxide resistors to the bottom of the board, breaking the track where appropriate. This also makes setting the bias a bit easier, because you can now simply measure the voltage drop across the emitter resistors as you would do with any other amplifier :)
For the driver transistors, as the 2N6551/4 are obsolete, I have used MJE243/253. You need to bend the leads around, because the 2N's are EBC and the MJE's are ECB, but it's doable.
Also glad to know you know of the Dim Bulb tester :)
and i should have watched all the way through, because you mention adding the extra resistors at the end :)
They are nice little amplifiers indeed, especially as they were "budget" in the early 80s. Its a shame they took the gamble by leaving out the emitter resistors really, as that;s often the cause of failure with these amps
Quality choice of band t-shirt!
Um Jottes Willen!! :O DIE FORTSETZUNG! Nach all der Zeit!
Also a Les Savy Fav fan.
Nice Amp, I have a NAD 2400 myself
It's all good! Keep them coming!
Hello and welcome . I'm struggling with the 3225 pe, which I have a problem with a short circuit in the left channel, everything seems to be OK and it plays, but after adding the volume, almost all the transistors and two resistors light up, what could be the reason? I've already checked almost all the condos and they are ok, so what could be the reason? cause this condition. Turned on by a 100 W bulb, it glows slightly. Thank you in advance for all your suggestions
Hi Jan; where can i found the Focus 10 music? Thank's...
It was necessary to look for the reason why the transistors burned out.
Lovely Video Jan Had a Couple Of These Amps Gave One Away To a Friend And I Have Another One Somewhere he he Regards mike.
No emitter followers is a bad design . Thermal runaway isn't your friend. Bad NAD design.
may I know how to change the voltage input from 220V to 120V for 3020I? thanks.
cool I have a matching tape deck.
I checked online and confused. You stated the 2N6554 (and 6556) was NPN and 6553 as PNP whereas my source says they are opposite. Can you clarify.
Oh, I might just have misspoken there. You’re source seems to be correct. Sorry for the confusion!
@@JanBeta All good. You mentioned the difficulty in chasing down those drivers. Would the outputs also be as hard to source? I have a vintage Kenwood receiver showing all cans shorted and would like to refurbish.
I only buy NAD amps for the last 20 years or so
I sold my 3020i about a year ago.
The color coding is normally the Beta range, no pun intended...
Jawol mein freund.
Love it
I have a NAD stack with a 705 reciever with some issues, if I turn on the amp one or both channels is not giving sound, if I crank the volume way up the the channel is starts working. replaced the relais but that is not the solution. have someone a idea what the problem is.
Worn potentiometer ?
DeOxit time on the pots and switches, as Tom F alludes to. If that is not the cure of the culprit, perhaps some transistor in the pre-amp.
@@MrChrisRP Its not a worn or dirty pot, ther is no constant crackling.
@@MultiArrie The symptom you wrote about surely can be from worn or dirty pot, without scratching. Step one, regardless of cause whatever it may be, is DeOxit the pots well.
The like number 777 here. 😎
Nice to see a successful amp repair! Just did DC offset to +/- 1 mV on my Sony STR-7045. It has been with me since birth, used every day, and my familiy is original owner. It has an outrageously unbeatable sound at normal money prices. Main speakers = Marshall cab I rewired to stereo (sick!) and "B" speakers are Sony 3-way floor standers. Check here: ruclips.net/video/OwIojFGeAaY/видео.html
They us to say 1 NAD watt is two any other watts.
The worst thing about the dim bulb tester these days is finding the bulbs
the blind leading the blind... kind of a thing...
we all make mistraces.😛😂
Opps
⭐⭐⭐⭐⭐
Build an amplifier with absolutely zero percent distortion and next to nobody will buy it. Add a tiny bit of distortion and people will think that model sounds good.
Design it with toroid transfos and audiophiles will love it.
On my Sony-7045, I am able to perceive the upgrade in sound from how it has been for decades at 30-40 mV D.C. offset to when I put it to less than 1 mV (both channels) a few weeks ago, and now. It was sounding fantastic before, but it is slightly clearer even more now, especially at higher volumes just as electronic knowledge dictates. Less harmonic distortion enables a more powerful sound, where the volume dial is in the exact same place, if that helps any readers know something. Another angle to ponder it is the engineering-base-goal of efficiency (as well as just plain correct in the first place.) All that being said, if anyone has an amp with 20, 30 mV, I would not say it is imperatve to get it down. It is not THAT super critical. But if you like things working and being the best they can for what they are, then yes, get it to 0 or as close as possible. If you are the type that is a close listener, music enjoyer, take it to any level more than an iPod baby, yes you will like the results. Higher numbers should definitely be brought down, without second guess.
Throw it up … ITS good for nothing
you have no idea how to properly restore an audio amplifier
I‘m just a hobbyist. I think I made that pretty clear. What would you have done differently?
I mean, why do things in this way and more think about shooting the video, how will it look etc. instaed of learning more about the circuit and electrical engineering as well. I will just make one point. You have mentioned not using thermal paste since you have placed insulator (mica, wafer, however you want to call those). Paste is a MUST becuase it fills in micro pores in the material. It would be better to put more knowledge than put out video showing shorted out components or destroyed piece of hi-fi equipemt. Some of those components are unobtanium and newly made components people most often than not put inside and cause even more problems than what they had in the begining. Oh well, what to say, your item, your prerogative to do what you want. And one more thing, conclusions like you say "...and hopefully it will work" is not the way to do things. I am always sad when I stumble upon such video and in most cases I am very disappointed. Moving on! :-(
The washers are silicone and you definitely don’t need thermal paste with them. They are slightly elastic, that’s how they fill the gaps. My videos are not tutorials, I’m always just letting people watch me doing things. And I don’t claim in any way to be a professional. You have to look elsewhere for that. And by the way, even professionals have the "moment of truth" after repairs when they are turning something on for the first time after working on that. There’s no shame in that. Learning from mistakes is still one of the best ways to learn. I’d rather talk openly about it than to pretend things are working first try (like many other RUclipsrs). That said, I’ve been repairing vintage audio equipment and studio gear as a hobby for a long time now (10+ years) and I definitely learned a lot along the way and fixed way more than I destroyed, with the occasional backlash.