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Old 1st April 2012, 02:57 PM   #1
diyAudio Member
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Location: Bloemfontein
Default Bypass caps, worth it ?

Gooday all,
What is the last word in bypass caps on the main caps in the power supply. Is it worth the effort ? If so, what would the value be on two paralleled 6800uf caps per rail and what make and value ? New to the diy setup The cover is off the amp to replace output relay so I can add bypass caps at the same time.I have read the threads on the topic and still do not know if left from right, such a lot of different opinions.

Thanks for your input.


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Old 1st April 2012, 03:11 PM   #2
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

A simple premise is to bypass them on the PS board with similar values to
the rail decoupling capacitors that should be on the power amplifier board.

rgds, sreten.
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Old 1st April 2012, 03:15 PM   #3
DF96 is offline DF96  England
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Join Date: May 2007
What is the last word in bypass caps
It depends on who has the last word. But you seem to already be aware of this, so why ask?
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Old 1st April 2012, 03:22 PM   #4
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
I tried that more than 35years ago when I thought I knew what I was doing.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 1st April 2012, 03:29 PM   #5
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Location: Virginia
You probably have already something on the amp PCB and before rectifiers.
Most manufacturers add a 0.1uF on each rail (to ground) on the amplifier board. It prevents the HF noise from the rectifiers to propagate in the rest of the system (using the wires inductance).
Some manufacturers (Accuphase) add also 0.1uF on the main capacitors.

Last edited by SoNic_real_one; 1st April 2012 at 03:32 PM.
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Old 1st April 2012, 03:55 PM   #6
diyAudio Member
Join Date: Jan 2012
Location: Bloemfontein
Default bypass caps

Thanks for the reply's you guy's, I am learning from you people, I want to get it right the first time. I like it a lot more to relax and listen to to music that to struggle to get it right .I am reading a lot and are amazed by the wealth of knowledge that you have. You are more clever than a tree full of owls ! DF 96, just trying to piece everything together.

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Old 1st April 2012, 04:08 PM   #7
diyAudio Member
Join Date: Mar 2012
Hey Jan

I have replaced bypass caps and as a rule keep the values the same but simply use better quality caps. I have also added a small film cap inparrallef which also seemed to improve things.

And remember " Hou die blikcant bo". (Hope that's right)

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Old 1st April 2012, 04:55 PM   #8
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Join Date: Jan 2012
Location: Bloemfontein
Upuesto Paul,
Thanks for the tips,I will incorporate it. One learns from listening, everybody learns everyday something new .Hehe, you're doing just fine, so weird to hear that phrase ! My dad used to use it to say goodbye to friends after a visit. Never heard it again in 22 years.Are you originally from South Africa ? or does it come from the dutch ? (Als van die beste vir jou en jou familie )

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Old 2nd April 2012, 04:58 AM   #9
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Join Date: Aug 2008
I had 0.1uF on my main caps, then 1R + 0.1uF also in the PSU, and an umbilical to the amp. When connected to my PC, there was crazy hum, which entirely went away when I removed everything but the bulk capacitors. This is with a centre-tap transformer setup.

On the amp boards there is 1,000uF || 10uF || 0.1uF.
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Old 7th April 2012, 11:42 AM   #10
Gopher is offline Gopher  United Kingdom
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Join Date: Nov 2005
Location: UK
This is a complicated matter.

Some people report good results when using smaller value bypass caps, others not so good or bad results. IMHO the reason is all to do with LC resonances between the inductance of the wires or tracks connecting the caps and the caps themselves and any resistance in the circuit which could act to damp those resonances. Since all these factors will be dependent on the particular amp layout, there's no definitive answer as to which is better I'm afraid.

My experience is that if you use good quality electrolytics close to the active devices with a bit of damping resistance you don't really need smaller value bypasses. In fact they can make things worse by exciting new resonances.

Last edited by Gopher; 7th April 2012 at 11:46 AM.
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