KA-8100 post recap Bass loss

darqnez

New Member
Hi all, first post/long time reader. With the help of the site and all you fine fellows I just recapped my KA-701 and it is outstanding. I used an assortment of Nichicon and some Elna sprinkled in. Went wonderfully, so with that and fixing several monitors and TV's (power supply caps die on these after a year sometimes these days) I recapped the KA-8100.

This was actually a much easier recap for me than the 701, fewer caps it seemed like, easier to get to, fewer solder joints dangerously close to another etc. However to my dismay once complete and connected up to my speakers my bass is all but gone, well into the mid-bass range. I'm guessing 400 to 600hz and down is diminished.


Trouble shooting thus far:

1) Changed the phase around for an hour on dif speakers no luck...my wires are clearly labeled for this amp so that was a prayer anyway. Played with ever setting little change. The mono setting is great for this as well, there is really no way to set the phase wrong and not know it with these.

2) Played bass test CD's that I use for my Cars. YEP! this aint right at all, the amp is just not putting out low frequencies even with bass all the way up and loudness set to 3, before the recap these CDs would rattle the mancave windows at 1/4 volume - not anymore. Around 800hz the tones start to feel more normal. BTW the tone controls - and i mean most all of them - bass, filter turnover, loudness, etc all have very little effect - They do have an effect but its is minimal difference and almost hard to detect...maybe this points to the control board being the issue?

3) Played the same CD on the 701 with like settings (similar between the 2 amps) and said window rattling instantly occurred at 1/4 volume and this amp has less power.

Plan for further troubleshooting

1) Go through each and every cap to make sure I didnt swap something stupid like a 10uf 50v for a 50uf 10v.

2) check solder joints to make sure I have no bleeding...there was one that I couldn't make out in the pictures I took for reference on the power amp that was of concern but appeared to be correct. I would expect a pop or something other than Bass loss if that joint was not suppose to be connected on the Power amp.

3) Test the pre-out to another amp to verify if that is OK or not - then reverse a source into the amp in.

4) I could try tapping into the pre to control to see if the bass is present there?

Basically asking for any experience with this kind of issue, or steps to determine if the issue is on the Pre, the Control, or Power boards.

Any advice here is appreciated.

Thanks
D
 
Another thing to check might be an electrolytic cap in the signal path the wrong way around. I don't know if this would cause the symptoms you describe, but I once did a Kenwood KA-7100 and installed one the wrong way around. It would go into protection whenever you engaged the tone controls. Like I said, not the same symptoms as you describe, but it might be something to check.

Lee.
 
Thanks Lee, I will look for that while double checking the values, good call.

Btw the Treble and highs seem to be good, the treble knob has a much greater effect than the Bass which is almost nothing so I am pretty sure its the control board at this point and will start there. :thmbsp:
 
well, its fixed...so I did find 2 things on the control board - one solder joint that looked suspect - my fault & these 2 10uf 25v caps at I think were C47 and C48 that had resistors soldered inline on the positive side, that seemed odd so i took them out and tested and its back to all its bass glory. Curious if that was factory or a repair?
 
Glad to see you fixed it and it wasn't too hard.
I'm not quite clear though on what happened with the resistors - they were present before, but now are removed?
 
Yes that is correct Lee. Now removed and all is well. Im not advanced enough to know why you would solder a resistor inline with a cap (unless your using a board that lacked the mapping for it) but that doesnt make sense for a mass produced amp like the 8100....
 
Im not advanced enough to know why you would solder a resistor inline with a cap (unless your using a board that lacked the mapping for it) but that doesnt make sense for a mass produced amp like the 8100....
Actually you see that pretty often.
Maybe you had a bad solder joint and re-soldering fixed it. If you're up to going back in, you might want to try re-soldering the resistors back in and see if it works OK. If there was no evidence that anyone had ever done work on the amp before, chances are they were put on at the factory.
 
Actually you see that pretty often.
Maybe you had a bad solder joint and re-soldering fixed it. If you're up to going back in, you might want to try re-soldering the resistors back in and see if it works OK. If there was no evidence that anyone had ever done work on the amp before, chances are they were put on at the factory.

Im sorry I wasnt clear, I tested first with reflowed joint and then removed them Cross, tested again and sounded better to me. Also its been a few days and the sound now seems to be getting moreeee...lush? Depth is expanding. I think I may put them back over the weekend after listening for several hours so my ears have a chance to get more accustom so the any changes will be more apparent just to see what happens as you suggest though. :thmbsp:
 
I'm glad I found this post. I am just in disassembly mode for a recap and found resistors on C47 and C48 as well. I also found it odd and just stopped to come here to see if they were normal. Looks like they are, so I think I'll leave them.
 
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