A few years ago I started noticing that my C370 is sounding very dark (lacking in high frequency compared to all other amps and compared to memory of it).
Being a mostly clueless dolt, I replaced every single electrolytic cap. It made a big difference and the sound I remembered came back.
What I did was highly unscientific but in my case it worked.
The two "towers" can live without the plastic caps on top.
Just be careful with anything on the amp boards because they're subjected to a lot of heat so areas can be brittle and the traces can be pulled up rather easily.
Being a mostly clueless dolt, I replaced every single electrolytic cap. It made a big difference and the sound I remembered came back.
What I did was highly unscientific but in my case it worked.
The two "towers" can live without the plastic caps on top.
Just be careful with anything on the amp boards because they're subjected to a lot of heat so areas can be brittle and the traces can be pulled up rather easily.
Hi A Jedi.
Thank you for the reply 🙂
Yes, today I noticed the top was made of plastic and could not provide any shielding. I have put them on any way using some construction adhesive - that way it looks as before, but there is a opening all the way around for better cooling - maybe?
I am putting the amp back together, when that is done I will make the adjustments descriped in the service manual, listen again and - maybe - do some measurements.
On one hand I want to get the best from the C 370, on the other hand I would like a new amp. You know that feeling.... it's time to try something different, without really knowing why 😉
Of course. I have multiple amps but had no reason to get rid of the 370 so I just refreshed it.
Hi My C372 gradually looses volume in the right channel after some playing. So the effect is that the whole image moves to the left. After power rebooting it plays normal again. Where should I look ?
I would start with searching for bad physical contacts - the first suspect would be the tone defeat switch.
Next step would be to determine whether the problem is in the preamplifier or power amplifier (the amp has pre-out and main in sockets so this should be fairly easy).
"power rebooting" means power OFF/ON cycle?
These intermittent audio problems are relatively difficult to fix. Try using the unit with the cover off and/or a fan blowing air across the mainboard. Diagnostic freeze spray might help at a cost of $25 to $100.
yes, after on/off plays eually, switching tone defeat has no effect. today after 4 days being off , the right chanel was almost gone (not totally) in a minute or so
Looks the preamplifier is good. I managed to catch the unsymmetry effect , so connected a signal generator to both channels and the preamps outputs gave the same amplitude e.g. 50mV and 52mV (at constant and varaible outputs)
Measure DC at the output leads. Power on, volume down, no speaker connected. This is the first thing to check.
The output relais may be burned, do they operate by changing speaker out? If the "click" the burned contact may work again, for a short time. That is all you do when you cycle power.
If the fault is there, carefully tap the relais. Does the sound come back for a few moments?
It is better to check the easy things first instead of renewing a lot of stuff, just to find out it was a basic part or adjustment.
The output relais may be burned, do they operate by changing speaker out? If the "click" the burned contact may work again, for a short time. That is all you do when you cycle power.
If the fault is there, carefully tap the relais. Does the sound come back for a few moments?
It is better to check the easy things first instead of renewing a lot of stuff, just to find out it was a basic part or adjustment.
R channel fading is at speakers A or speakers B - does not matter. Some days ago I was testing by connecting 8ohm 50W resistors and running few watts into both channels and no fading for few hours on my desktop with cover open
Did you change speakers for a test? Defective capacitors in a speaker crossover or loose contacts / solder points can have similar effects.
I am just starting a rebuild and repair of one of these myself… was thinking of starting a thread on my journey and then found this one… I’m basically doing a complete tear down and rebuild, replacing all electrolytic caps and refinishing the case etc. today I started working on the speaker terminals, which were a bit damaged, so I drew up a replacement and printed a quick test print to check the dimensions… now that they fit, I’ll send it out for SLS printing of the replacement part and move onto the next job… 🙂 Not sure how this forum works yet, so if you want me to move this to a separate thread, just let me know. 🙂
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Interesting. I will follow your progress 🙂
I have just made the adjustments from the manual and am considering to change the caps in the signal path.
Maybe you can get something out of this: https://quirkaudio.com/?p=1123
Thanks @Nik_DK_NADC370 for the link, that’s really interesting!! I’ll post some more here once I make some progress. 🙂
@madis64 I’m trying to keep the amplifier as original as possible with respect to the case etc. all the ones from eBay that I found have different centre distances or would require some other modification. This drawing took me about 45 minutes and then the test print another 45 minutes and now I’ll get it SLS printed for probably about $20, so it’s just more economical and interesting to me to do it this way… SLS gives you an almost perfect finish and I’ll cerakote them afterwards if the finish isn’t exactly what I want… just my thoughts for now… 🙂
@madis64 I’m trying to keep the amplifier as original as possible with respect to the case etc. all the ones from eBay that I found have different centre distances or would require some other modification. This drawing took me about 45 minutes and then the test print another 45 minutes and now I’ll get it SLS printed for probably about $20, so it’s just more economical and interesting to me to do it this way… SLS gives you an almost perfect finish and I’ll cerakote them afterwards if the finish isn’t exactly what I want… just my thoughts for now… 🙂
Ok, if this is the goal then I understand.
I was meaning more like those:
https://speaker-terminal.com/en/produkt-kategorie/nad/
- should provide the ability to use speaker cables with banana connectors.
(some years ago these were also sold on eBay, do not kow the current state).
What is the base material that is used during SLS printing?
And how do you "cerakote" them?
@madis64 those terminals you linked to look great! I’ll definitely keep them in mind for future projects, I hadn’t seen them before…
The SLS printer I’m working with uses Nylon12 powder which is one of the more rigid types… the surface finish is really nice, and you can barely tell the difference between sintered or injection moulded, except the SLS parts have a more textured finish. Cerakote is great for next level finish, because you can directly apply it to the SLS parts without much prep and then it bakes on and gives you a hard ceramic finish. They use it on firearms and race car parts. With plastic you generally coat it and then bake it at around 60c for two hours, depending on the exact version of coating you’re using…
The SLS printer I’m working with uses Nylon12 powder which is one of the more rigid types… the surface finish is really nice, and you can barely tell the difference between sintered or injection moulded, except the SLS parts have a more textured finish. Cerakote is great for next level finish, because you can directly apply it to the SLS parts without much prep and then it bakes on and gives you a hard ceramic finish. They use it on firearms and race car parts. With plastic you generally coat it and then bake it at around 60c for two hours, depending on the exact version of coating you’re using…
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If you are able to print the base plates per amplfier seating area yourself then speaker terminal sets do not cost much on eBay
www.ebay.de/itm/204852813296
www.ebay.de/itm/204852813296