I recently got my hands on the one ampI wanted for quite while now a NAD 3140 silver and apart from one minor problem it was in nice cond ition. This one problem was that the right and left channel only played at the same volume when I turned balance to about 9 o clock. So I searched the web for this kind of problem and found out that its most likely a bad cap in the preamp section and I actually found a bulgin 10mfd 35v cap in the preamp regulator...wile I was at it I pulled all 5 caps of this value and replaced them with same value and voltage silmics along with the two 470/63 main regulator caps.
So Iset everything up for testing just to find out its all still the same with a weak left channel...so balance back to 9 and me sitting on the couch looking for another cure and all the sudden the left channel kicked in quite loudly as balance was set to left...now it works like a treat, no scratching or anything whatsoever...my question would be...why...is it possible that a left channel cap over time lost its oxide layer and that it got kinda reformed from getting its specified voltage again?
Thanks a lot
Arne
So Iset everything up for testing just to find out its all still the same with a weak left channel...so balance back to 9 and me sitting on the couch looking for another cure and all the sudden the left channel kicked in quite loudly as balance was set to left...now it works like a treat, no scratching or anything whatsoever...my question would be...why...is it possible that a left channel cap over time lost its oxide layer and that it got kinda reformed from getting its specified voltage again?
Thanks a lot
Arne
Hi Arne, what you describe doesn't immediately sound like a faulty cap to me. One quick thought is that it could be a speaker relay problem (oxidation on the contacts) and if so then the problem often goes away the louder you play the amp, at least until next time.
I don't know if the NAD uses relays like that but they are a common problem across all makes and models and the typical symptom is low and perhaps distorted sound at low volume. Turn the volume up and the current punches through the oxidation layer temporaily fixing things.
If its not that then the next steps would really be to check and compare levels on a scope within the amp and see where the lack of signal voltage is occuring.
I don't know if the NAD uses relays like that but they are a common problem across all makes and models and the typical symptom is low and perhaps distorted sound at low volume. Turn the volume up and the current punches through the oxidation layer temporaily fixing things.
If its not that then the next steps would really be to check and compare levels on a scope within the amp and see where the lack of signal voltage is occuring.
Tanks for the quick response Mooly. The 3140 doesnt have speaker relays and I did play around with a the pots already to make sure this is not the source. I will have to see if it acts up again but for now its all fine. What puzzles me is that it went from being low to being just fine within half a second, no pots scratching, all smooth and totally on its own and only a few mins after changing caps.
Thanks
Arne
Thanks
Arne
Faults that heal up on their own can be a bit frustrating. Does it have a headphone socket that switches the speakers on and off. Things like that could be suspect, as could any switches in the signal path.
Its also worth having a good prod and poke at the board while the amp is running to see if any physical problems show up.
You will have to see how it behaves from a cold start.
Its also worth having a good prod and poke at the board while the amp is running to see if any physical problems show up.
You will have to see how it behaves from a cold start.
Yes indeed...I'd rather like to know what it was but for now I will just enjoy the fact that its playing as intended and see if it still does tomorrow. The headpone socket is switched separately with the speaker selection knob set to off. As I had planned to do a full recap anyway I guess at some point I will meet the fault face to face if it still exists 🙂 Thanks a lot so far!
Arne
Arne
Just in case anybody else is just rebuilding or tweaking an early NAD like 3020, 7020 etc and is tempted to replace all the jumper wires for copper ones like I have read in some posts...dont! They ARE copper...tinned copper.
About relays in 3140 models.....
This model shares some of the old habits of the original 3020 series. It is modernised and improved but there are still the same old 1.5A circuit breakers used for protection of the amplifier's 3020 design output stage. They aren't exactly relays but they are very cheaply made parts that break the output circuit just the same - until any arcing burns the plain metal point contact at least. These are TB1 & TB2 on the schematic and are located just back from the output transistors (labelled "Breaker", I think).
I can never determine whether these are in acceptable condition on any early NAD amps so I have routinely replaced them as they are quite cheap and there are aren't any high grade versions available even if you would prefer them.
However, the circuit breakers aren't the only possibility and it's likely an intermittent type fault such as poor soldering which is like a needle in a haystack to find. Freeze spray is sometimes helpful in bringing on or clearing the fault and narrowing down the area, once you have determined in which circuit area the fault lies, by tracing the signal. Otherwise, you can waste a lot of freezer and money in spraying it everywhere in hope of a response.
This model shares some of the old habits of the original 3020 series. It is modernised and improved but there are still the same old 1.5A circuit breakers used for protection of the amplifier's 3020 design output stage. They aren't exactly relays but they are very cheaply made parts that break the output circuit just the same - until any arcing burns the plain metal point contact at least. These are TB1 & TB2 on the schematic and are located just back from the output transistors (labelled "Breaker", I think).
I can never determine whether these are in acceptable condition on any early NAD amps so I have routinely replaced them as they are quite cheap and there are aren't any high grade versions available even if you would prefer them.
However, the circuit breakers aren't the only possibility and it's likely an intermittent type fault such as poor soldering which is like a needle in a haystack to find. Freeze spray is sometimes helpful in bringing on or clearing the fault and narrowing down the area, once you have determined in which circuit area the fault lies, by tracing the signal. Otherwise, you can waste a lot of freezer and money in spraying it everywhere in hope of a response.
Hi Mooly, I may be wrong about the breaker's current rating since this amplifier is a 40W model. PCB mounting breakers seem to be almost extinct now but there is also a Chinese 4A version which may be closer, if still not correct. The first pic is that of a type fitted to early NAD models.
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Interesting. They would be easy to prove/disprove by simply shorting them out and seeing if the problem clears.
This is the one in the 3020i (and 3225PE) that I have repaired.
The 3140 can apparently comfortably put out in the region of 75W (although officially rated at 40W) which is around 4A into 4 ohm? Not sure where they can be had from over there but in Oz we can find them on eBay and Jaycar (4A PCB Mount Thermal Circuit Breaker (SPST) | Jaycar Electronics) for not too much coin.
Anyway, as you say Mooly, an easy item to jump and test.
The 3140 can apparently comfortably put out in the region of 75W (although officially rated at 40W) which is around 4A into 4 ohm? Not sure where they can be had from over there but in Oz we can find them on eBay and Jaycar (4A PCB Mount Thermal Circuit Breaker (SPST) | Jaycar Electronics) for not too much coin.
Anyway, as you say Mooly, an easy item to jump and test.
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Hi Ian, until now the problem seems to be cured. I'm almost certain that this one bad cap in the regulator (it was a 10mfd 25v) indeed was the source of it as it was in a really really bad shape. The rubber seal had been pressed out almost entirely, all the others of this value were looking fine though. I let the amp rest over night and also when started cold it's playing quite nicely. I spent the last hours replacing two more caps and installing new speaker posts as it was a pain getting my cables in those clamps. I removeed the cables for the second speaker set and also the clamps and used the two slots for one channel each...and actually it didnt blow up as expected, still all fine 🙂
I'm still puzzled though why there was such a delay between cap replacement and the left channel kicking in.
As for the breakers, they are 4.0 ampere units except for a few early 3140 which accidently had the 2.0 A ones.But thanks for reminding me to remove them.
Can anyone tell me if the head phone jack implemented in the circuit like it isa on the 3020'`s or can I just remove it? From the schematic I would say I can remove it with no further changes but I'm not 100% certain as I never learned to read schematics untill I felt the urge to mod a 3020 about a year ago...
Thanks a lot so far, this really is a great community 🙂
Arne
I'm still puzzled though why there was such a delay between cap replacement and the left channel kicking in.
As for the breakers, they are 4.0 ampere units except for a few early 3140 which accidently had the 2.0 A ones.But thanks for reminding me to remove them.
Can anyone tell me if the head phone jack implemented in the circuit like it isa on the 3020'`s or can I just remove it? From the schematic I would say I can remove it with no further changes but I'm not 100% certain as I never learned to read schematics untill I felt the urge to mod a 3020 about a year ago...
Thanks a lot so far, this really is a great community 🙂
Arne
Hi Arne, I'm not entirely convinced that the slow start is a good sign either. It is still possible that another cap. could be faulty, slow to charge up etc or there is actually an intermittent solder connection. However, there is no point in disturbing the headphone connector as it has no switch, does nothing and connects to nothing until the phones are plugged in. In any case, the headphones are disconnected simply by removing them. See attached circuit of channel B o/p stage. Unless the speaker switch itself is damaged, there is nothing to remove there that could improve the speaker connections or eliminate some influence on audio quality.
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Hi Ian, well the slow start only happened once and since then it behaves just like it's supposed to. I'm going to replace all the caps anyway so if another cap is faulty I will find it but for now I'm glad that the problem seems to be eliminated. I was asking about the phone jack because I dont use it anyway and was thinking about placing a Ir receiver for a motorpot where the socket sits or just replace it with a gold one I found in my parts box and since it is a bit smaller I was afraid the internals might be different...so if it doesnt interfer with the speakers it doesnt matter. I had some 3020/2140 front panels made out of carbon fibre by a friend and I think a gold socket might just look very nice...thanks for your advise I will let you know if I stumple upon anything unusual during recapping.
Best regards
Arne
Best regards
Arne
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