Need help with fixing bass response of my nad c372 integrated amp. Recently while playing music volume increased for a couple of second and came back to normal level by itself. This volume fluctuation happened twice. Post that tone defeat button stopped working. Bass response got drastically reduced, mainly the lower end of the bass became too silent. Only the lower end of bass got disappeared and other frequencies are playing fine. while playing bass heavy tracks, bass feels incomplete. It has lost its punch. Also, pressing the tone defeat button is not increasing the volume Like it used to. There is no audible difference between tone defeat on/off but can hear some crackle sound when button is pressed. Please help me on what to do for this problem.
Mine has a v5 board if it helps.
Thankyou for your time.
Mine has a v5 board if it helps.
Thankyou for your time.
First try cleaning the tone switch with a good contact cleaner. If that does not help,
it could be some of the electrolytic capacitors in the tone circuit.
it could be some of the electrolytic capacitors in the tone circuit.
Amps get polite when the rail caps dry up. Peaks of music arent there. Bass response is especially reduced because it takes a lot of coulombs to get through 1/60 of a second until the next time the transformer gives another hit of current. Also ESR is up and dried up rail cap is just like putting a 5 ohm resistor in series with your speaker.
Turn your amp up until just below clipping (bit of a siren sound) and measure AC voltage on the speaker with a scope or analog VOM. On scope average voltage is .7 that of peak to peak. Amps are often down to a tenth or twentieth of their power rating with bad rail caps. P=(v^2)/Z where Z is speaker impedance. If you don't know your speaker impedance, measure speaker resistance and multiply by ~1.3.
Could also be a crossover problem in the speaker, or bad connection in the wire to the speaker.
Per Rayma, at >15 years all the electrolytic caps in the amp are suspect.
When one goes bad, I change them all for new ones having >3000 hours service life rating. 2 at a time between auditions, so I know if I made it better or worse. Worse, I know exactly where the the problem is, whatever I just did. Use trash speaker for auditions or put a 4700 uF capacitor minus to minus in series with the speaker. Bad solder joints can cause DC voltage on speaker, which can damage them.
Turn your amp up until just below clipping (bit of a siren sound) and measure AC voltage on the speaker with a scope or analog VOM. On scope average voltage is .7 that of peak to peak. Amps are often down to a tenth or twentieth of their power rating with bad rail caps. P=(v^2)/Z where Z is speaker impedance. If you don't know your speaker impedance, measure speaker resistance and multiply by ~1.3.
Could also be a crossover problem in the speaker, or bad connection in the wire to the speaker.
Per Rayma, at >15 years all the electrolytic caps in the amp are suspect.
When one goes bad, I change them all for new ones having >3000 hours service life rating. 2 at a time between auditions, so I know if I made it better or worse. Worse, I know exactly where the the problem is, whatever I just did. Use trash speaker for auditions or put a 4700 uF capacitor minus to minus in series with the speaker. Bad solder joints can cause DC voltage on speaker, which can damage them.
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Lack of filtercaps should cause heavy distortion on bass, due to clipping, not simply reduce its level I think. It can also cause oscillations that add distortion and noise and all manner of unpleasantness (including volume change, thinking about it)
The temporary increase in volume also suggests something in the switching, or perhaps a component in a feedback loop starting to go intermittent.
Or it might have gone already, briefly recovered (higher volume) and failed again. That could be anything in the signal path - the loss of low freqencies suggesting capacitance bridging the gap (can be the case with a hairline crack).
A cool spray or insulated poking stick might be good ways to try and identify the component or area of pcb involved, and have a good play with all the switches. Check the switch solder joints and bodies for signs of dry joints, cracking or damage too, then get a lot of mechanical stress over time.
The temporary increase in volume also suggests something in the switching, or perhaps a component in a feedback loop starting to go intermittent.
Or it might have gone already, briefly recovered (higher volume) and failed again. That could be anything in the signal path - the loss of low freqencies suggesting capacitance bridging the gap (can be the case with a hairline crack).
A cool spray or insulated poking stick might be good ways to try and identify the component or area of pcb involved, and have a good play with all the switches. Check the switch solder joints and bodies for signs of dry joints, cracking or damage too, then get a lot of mechanical stress over time.
The caps quality is not so good for this model, suggest you replace all the caps first.
Maybe just recap is ok.
Maybe just recap is ok.
The symptoms in #1 don't seem like power supply caps failing at all. The volume just increases for no apparent reason then the tone defeat circuit doesn't do anything any more. It seems like a preamp/tone control circuit problem to me so I would loop the controls and bypass switch out of circuit with jumper leads and see what's going on there.
If that now proves to work correctly, then I would look at signal coupling capacitors and the condition of the signal routing switches before spending up on the big caps. It may well need recapping but just replacing those big caps may not solve the problem at all.
If that now proves to work correctly, then I would look at signal coupling capacitors and the condition of the signal routing switches before spending up on the big caps. It may well need recapping but just replacing those big caps may not solve the problem at all.
Measure the power out, not the caps. Or if you want to take the cover off, measure the rail voltage at maximum volume. yeah, you can overdrive into clipping, but you are not forced to.
I disaggree with Mark Tillotson, a lot of amps have nice polite unimpressive bass without distortion at 1/20 the rated power right before they go silent. Had 2 Allen S100's do that in 2017, 2 watts into 4 ohms the Monday after a silent Sunday service. Bar bands may overdrive into heavy clipping at the end, but church organists don't.
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