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Old 26th January 2007, 08:13 PM   #1
LBuzzer is offline LBuzzer  Canada
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Join Date: Mar 2006
Location: Eastern Ontario
Question Need help re: input signal decoupling caps

The Velleman amp kits I've just built have a 10uF electolytic cap inline with the input signal. My questions are:

1. If I'm not worried about DC inputs, would taking the cap out and jumping it with a wire improve the sound?

2. How is the capacitance value arrived at? Can I tune the sound by changing the value of the cap? Is there a danger to the circuit when doing this?

3. Is there a particular type of cap that is regarded as the best for input signal decoupling?

4. Are the super-high voltage caps (hundreds of V) sold by Mundorf et al. OK for SS signal handling, or are they geared more towards tube equipment? Is using a high voltage cap detrimental to sound if the cap value is kept stock (10uF)?

If it helps any, the amp kit is TIP142/147 based (kit # K8060)

Thanks for any guidance and help, guys!
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Old 27th January 2007, 02:25 PM   #2
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Location: Cheltenham
Dont you mean coupling caps? . . I removed the coupling caps on the input of my power amp because i already had one on the output of my preamp. . . On the output of my CDP, i like polypropylene but in my pre amp i like BC128's, bypassed with 10nf polypropylene. . . Watch out for bass roll off if you go lower than 10uF, higher is fine and higher voltage is also fine.
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Old 27th January 2007, 08:11 PM   #3
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Default Re: Need help re: input signal decoupling caps

Quote:
Originally posted by LBuzzer
The Velleman amp kits I've just built have a 10uF electolytic cap inline with the input signal. My questions are:

1. If I'm not worried about DC inputs, would taking the cap out and jumping it with a wire improve the sound?

2. How is the capacitance value arrived at? Can I tune the sound by changing the value of the cap? Is there a danger to the circuit when doing this?

3. Is there a particular type of cap that is regarded as the best for input signal decoupling?

4. Are the super-high voltage caps (hundreds of V) sold by Mundorf et al. OK for SS signal handling, or are they geared more towards tube equipment? Is using a high voltage cap detrimental to sound if the cap value is kept stock (10uF)?

If it helps any, the amp kit is TIP142/147 based (kit # K8060)

Thanks for any guidance and help, guys!
1) Only you can tell what it does for you. Some folks think that all caps are "BAD" - especially electrolytics.

2) The cap is there for DC isolation. The value is chosen to be large enough so that its reactance at the lowest frequency of interest is equal to the total impedance (~resistance) of the input circuit. Your amp is specced at -3dB at 3Hz which is very low I doubt that your speakers will get anywhere near this value. And survive.

Your amp has roughly 3K3 input resistance. Search and do the maths.

All you could "tune" is put in a lower value to restrict the low end response. 1uf would raise it to 30Hz approx.

3) Not decoupling, that is PSUs etc. Plastic of some some sort is considered better.

4) The voltage rating of a cap is its maximum sustainable voltage before it blows up. There is no benefit in using an HV type, nor any problem.

You have obviously read/heard about the "sound" of caps. This is still very contraversial except in certain circumstances. Don't believe all you read!

Given the nature of your Velleman amp I really would not expect the input cap to be significant, but by all means experiment.
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