Got a Nakamichi TA-2A reciever off eBay recently. Everything seems to be working fine. The treble control knob when turned makes a noticeable difference to the treble level. But the bass knob when turned doesn't seem to be making a big difference as I can notice with the treble control. I know these two controls are part of the Tone Control PCB assembly - any components in this PCB assembly that I should be first checking to see if it failed? Thank you.
Nakamichi TA-2A receiver - Bass control barely working
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northpaw
Super Member
This Nak is odd in that max loudness compensation is full-CCW (10 on dial). As long as you have the control full-CW ("normal" on dial), there will be no loudness compensation and we can proceed.
In what follows, I assume you are getting normal bass response, but that you are not able to adjust it with the tone controls. If you have any doubt, play something that you know has strong bass content to verify the unit is producing bass.
The Tone PCB has not only the tone controls, but much of the circuitry for the line amp. If you are getting bass, almost everything is working. The potential culprits are things with sliding contacts: the tone pots and the tone defeat switch, with the latter being the pesky one. It is a multi-pole switch (4P; it has to handle bass and treble for L and R channels) and seems to commonly develop issue, probably because it gets limited exercising in normal use. Often it makes static or even a thump when activated, which can be cured with cleaning the switch.
In your case I am guessing it isn't making contact with the bass control (pot) part of the circuit, so you are just getting normal bass. I won't rule out the bass pot being dirty/not working properly, but feel that is less likely. It is also possible there is a broken solder joint or lead somewhere on that board, but I also consider that much less likely; the Tone PCB is so small, does not hold heavy components, and is well supported, so in my estimation it is unlikely to get subjected to damaging flexing, etc.
The Tone PCB is hard to access in the TA-2A. It is deep in the unit, mounted with the component-side facing down. Removal of the bottom cover provides partial access to it; see here. There are enough holes/seams in the metal housing of the switch to apply a contact cleaner such as deoxit and/or CRC QD spray (my thoughts on this here:
https://audiokarma.org/forums/index.php?threads/nakamichi-stasis-ta-2a.810681/post-12184575).
It would be best to remove the switch to thoroughly clean it, but that would be a lot of work on this unit; I've never attempted it. I recommend first trying to generously flush the switch with a non-residue cleaner such as QD, as follows (after unplugging the unit):
1) Apply the spray using the siphon tube to direct it into the holes/seams in the switch;
2) Exercise the switch 20-30 times;
3) Repeat the above 2 or 3 times
4) You could also treat the pots now, if you want
After 10 minutes or so for the solvent to evaporate off, reconnect the unit and see if you have any improvement in bass control. If activating the tone defeat switch still produces some static or thumps, more cleaning is needed. I would repeat with QD for another cycle or two of the above, but you can eventually switch to deoxit, as it is a little more aggressive, but I would try to avoid using too much of it because the residual lubricant in it leaves a mess. I try to use it as a final step only, once the switch is operating as best as it can with QD.
Thank you for your detailed response. I am getting normal bass which I have noticed with some songs that I played and confirmed that. Just not enough change with the bass control knob. I will try to extensively clean the pot with Deoxit by following your steps above and see if that makes a difference.
Removed the front and back panels was able to easily access the bass control pot. Then cleaned the bass control pot with Deoxit a few times and I noticed much improved and immediately noticeable bass change now. I have it connected to a pair of JBL-26 and it sounds amazing. Thank you for your suggestions.