Bass Balance on STA-2100D

[TheDHndrsn]

Have been running a Realistic STA-2100D for a few months now. Love the receiver. About a week ago I noticed significant loss of bass on my left channel - some output still there. At first I believed it was crossover related so switched speakers. Same issue.

Had to get a few things off of the bench so listened to the STA tuner off and on over the next few days (not a good idea but have been too busy to swap something). I noticed the bass response on the left channel go from almost nothing to complete nothing. At the same time I noticed bass response swamping the right channel.

Pulled the receiver and checked transistors and outputs. The only thing I found was a short on B outputs (I never run anything on B side). I have yet to trace that short back to the source. Otherwise, not finding a smoking gun among the usual suspects.

The whole thing is a bit confusing (to me at least) from a troubleshooting standpoint. Thought I would float this out there before I began tracing the short and walking through the entire service routine. Has anyone seen something like this and ideas on where I should focus?
Dave

 

[NAD80]

Hello TheDHndrsn. If you need the Service Manual. It can be found here. http://www.vintageshifi.com/repertoire-pdf/Realistic.php . The 2100d is a good receiver.

 

[TheDHndrsn]

Hello TheDHndrsn. If you need the Service Manual. It can be found here. http://www.vintageshifi.com/repertoire-pdf/Realistic.php . The 2100d is a good receiver.

Thanks! Have a d/l copy which I have gone through a few times. Just not seeing anything to wrap my brain around. Midrange and treble A-OK but bass loss on left whilst saturated on right. Hmm ...
Yes. I love this receiver. It has become my go to. Have also a 2000D and a 2080. All three are great performers.
Once I track this down will post a reply in the event someone else bumps into this scenario. For now, call me confused.
Dave

 

[Jamaica1985]

I have the EXACT same issue on my device. Left channel very weak, almost only highs and mids and it looks like all the lows missing from the left channel is now sitting at the right channel and sounds as if the loudness was on. My STA 2100D is in a "mint" condition other than this issue, super clean insite, nothing burned and all other functions just working great.

I really don´t want to perform any repairs as with me this is a 50/50 chance of screwing things up even worse. In my case I believe the issue lies in the balance knob behind the volume knob. I noticed when checking all switches that the balance knob caused some crackling but didn´t made change to the issue you described at first. Then I thought, ok, maybe the contacts inside the potentiometer are just dirty so I moved the knob a bunch of times from left to right and suddenly all sounds good again. The annoying thing though is, that I have to do this like every week as it seems that if you do not use it for a while it happens again. I really doubt that there are replacements for these and opening up the case I am not seeing a way to throw deoxit into the potentiometer...

 

[llwhtt]

Swap the pre out/ main in connections, left pre to right power and vice versa, to see if the problem changes channels. If it changes the problem is in the preamp, if it doesn't change it's in the power amp. Depending on that we can troubleshoot further.

 

[woodj]

"mint" condition

Not hardly "mint".

 

[Jamaica1985]

Not hardly "mint".

A receiver which aesthetically is perfect, no scratch to be seen, operates 100% but has a ONE dirty pot which I could clean properly with deoxit I would say is mint. no matter, just hope the topic starter has the same issue which would be easy to fix and hope my comments would help.

Thanks

 

[TheDHndrsn]

I have the EXACT same issue on my device. Left channel very weak, almost only highs and mids ...

Busy with other repairs and only now getting back to this one, Jamaica1965. I am going to take a look at the pots again. I agree it sounds like the same issue. When I first purchased this receiver I had problems with the pots. Not as bad as a 2000D I have, but bad enough. Kept working them until things cleared up. I agree there is no easy way of getting to them with Deoxit. I am hoping I find a way once I remove the front panel. The service manual for this receiver is excellent, BTW (copy out on HiFi). Running I think the STA-2100 is possibly the best sounding receiver I own. I absolutely love it. I have it matched with a pair of Mach One's. Whether impedance or other there is something magical about these two together. Of course, I haven't heard it through that set of Kenwood's. May be close.

Swap the pre out/ main in connections, left pre to right power and vice versa, to see if the problem changes channels. If it changes the problem is in the preamp, if it doesn't change it's in the power amp. Depending on that we can troubleshoot further.

This is possibly one of the best receiver tips I have come across, llwhtt. Obvious if you think about it. Going to put this one in my top 5. Will run a test as proposed and respond with results.

Thanks folks!
Dave

 

[Jamaica1985]

Busy with other repairs and only now getting back to this one, Jamaica1965.....

This is possibly one of the best receiver tips I have come across, llwhtt.....

Thanks folks!
Dave

Was indeed a great tip from llwhtt and make indeed a lot of sense when troubleshooting, I also used it to be sure it was not my outputs... In the weeks that passed I actually grew the balls to open my amp enough to be able to clean the balance pot and while I was at it I did all other pots and knobs too. Everything literally sounds much more crisp now. The bass issue has gone and the mids and highs even sound better. I also absolutely love this amp, with many amps I always want to upgrade to better ones but I think with the STA 2100 Im at a point I don´t need and want another amp