Replacing main filter caps, need to re-bias? - diyAudio
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Old 5th May 2007, 05:23 AM   #1
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Default Replacing main filter caps, need to re-bias?

I replaced/upgraded all the 'lytics in my BK ST140.
But for the big filter caps, I used 22,000uf per rail, replacing the old 17,000uf ones.

Would this call for re-biasing the amp ?
It sounds excellent now, btw. But it did before as well !!

after pics..:
Click the image to open in full size.

http://i5.photobucket.com/albums/y17...t/DSCN2065.jpg

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Old 5th May 2007, 05:31 AM   #2
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Normally your upgrade wouldn't require re-biasing, however it's always a good idea to check the bias, while the amp is on the workbench
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Old 6th May 2007, 01:34 AM   #3
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Thank you ACD.

Off topic....I've acquired most of the Lynx parts. Should I wait for you to finish V3 ? ...or should I do an earlier version?
(I will be soldering point-to-point.)


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Old 6th May 2007, 04:35 AM   #4
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You can make the v3.
It's only the PCB layout that hasn't been verified
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Old 12th May 2007, 02:09 AM   #5
K-amps is offline K-amps  United States
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Jan's right... Always good to check bias.

22mF is a big cap... needs a bypass. Did you bypass it with smaller caps? Usually a good idea.
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Old 12th May 2007, 07:05 AM   #6
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Quote:
Originally posted by K-amps
Jan's right... Always good to check bias.

22mF is a big cap... needs a bypass. Did you bypass it with smaller caps? Usually a good idea.
No bypass caps yet.
1 uf maybe?
I have many values sitting around. (films)

I'm new at Power Amps.....I will search on how-to check an amp's bias.
If you have a favorite link...? (ths amp has easy-to-reach trim caps, so I assume this is not too hard.)

Thanks,

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Old 12th May 2007, 03:11 PM   #7
K-amps is offline K-amps  United States
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Depends how extreme you want to go.

Minimum 0.1uF

More extreme... : 2200uF, 220uF, 22uF, 1uF, 0.1uF



Up to you If you go extreme then keep the leads as small as possible. I would move the 220uF & 22uF towards the OP boards.
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Old 12th May 2007, 03:19 PM   #8
sam9 is offline sam9  United States
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Merely changing PS filter caps isn't going to affect the bias one way or the other. The two are independent.

Nothing wrong with checking the bias provided you know how it is supposed to be done for your particular amp. If you are not sure about how to perform this I suggest you abide by the rule "do no harm". and leave it alone.

Please don't be offended by the above if you really DO KNOW how to set the bias. It's just that there seem to be so many folks who are driven to compulsive madness by the sight of an untouched trim pot.
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Old 13th May 2007, 08:05 AM   #9
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Agreed. Maybe at some point I'll check it when I'm more confident.
Building some amps soon, and bias adjustment topic is necessary in those, and well documented too.
I don't use pre-made boards, only p2p....helps me really think about the circuit.

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Old 13th May 2007, 11:17 AM   #10
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Quote:
Merely changing PS filter caps isn't going to affect the bias one way or the other. The two are independent.
Quote:
Nothing wrong with checking the bias provided you know how it is supposed to be done for your particular amp. If you are not sure about how to perform this I suggest you abide by the rule "do no harm". and leave it alone.
Quote:
Please don't be offended by the above if you really DO KNOW how to set the bias. It's just that there seem to be so many folks who are driven to compulsive madness by the sight of an untouched trim pot.
All very good points here....

Sometimes a bias pot that hasn't been touched in years will go full tilt when you try to adjust it. Many years ago I learned after rebuilding an amplifier to replace the bias pot because it isn't expensive and by replacing it you can safeguard the work that you have done. I learned the hard way when the bias went full on and my handywork was destroyed in heartbeat. This also brings into play the importance of a variac and a lightbulb in the AC feed.

Simple rule to follow in electronics...If you don't know how to do something seek the help of a knowledgeable person to guide and help you learn.
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