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leach super amp question
leach super amp question
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Old 1st May 2008, 12:00 PM   #1
rtate is offline rtate  Canada
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Default leach super amp question

I have a few leach superamps ver.4 and I was wondering about by-passing the power supply caps.
I am using 6, 10,000 uf caps rated at 100v per mono block.

Would by-passing improve the sound quality?
If so what value/voltage would be best to use?
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Old 1st May 2008, 12:28 PM   #2
Andy L. Francis is offline Andy L. Francis
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Hi,

I'd suggest 47uF/100V (22...100uF/100V) electrolytics, soldered directly on the "reservoir" capacitors.
These will improve sound quality.

(On the margin there is a permanent thread about Leach amplifier in our Solide State forum. Have you searched?)
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Old 1st May 2008, 12:36 PM   #3
rtate is offline rtate  Canada
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I thought that "by-pass" caps should be film type and of a smaller value to get the best results.

What are the effects of lower versus higher values as by pass caps?
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Old 1st May 2008, 01:29 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
if you want decoupling caps to work then they must be fitted where the devices consume the currents, i.e. across the output devices and possibly across the drivers.

Bypass caps across the main smoothing will need careful selection to avoid ringing. A series resistor is usually enough to do this, but that only compensates at the PSU. The bigger problem is to prevent glitches from the amp output affecting the supply rails and then leaking through the other stages back into the output.

BTW,
this info was garnered by reading this Forum.
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Old 1st May 2008, 04:04 PM   #5
rtate is offline rtate  Canada
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after doing more reading it appears that "bypassing" the power supply caps can do more harm than good!!
Yet I wonder why I alot of high power solid state amps have it??
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Old 1st May 2008, 05:32 PM   #6
djk is offline djk
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"after doing more reading it appears that "bypassing" the power supply caps can do more harm than good!!
Yet I wonder why I alot of high power solid state amps have it??"

Because it sounds better.

Leach uses a 22F electrolytic plus a 0.1F film cap on each rail.

"The bigger problem is to prevent glitches from the amp output affecting the supply rails and then leaking through the other stages back into the output."

That's why Leach uses a 100R resistor to feed the front end voltage followed by a 100F electrolytic and a 0.1F film cap.

The diff pair tail is returned to a zener regulated supply fed from the front end stabilized voltage. The zener is filtered and bypassed by a 100F electrolytic and 0.1F film pair.

This note should be read:

http://users.ece.gatech.edu/~mleach/lowtim/pwrsply.html

The bypass caps should be grounded to where the current is consumed (speaker return). Adding values less than 1F (film types) right at the outputs generally require a small resistor of less than 10R to stop ringing, so I generally don't do this.

In modifying existing amps I find adding 22~100F across the main filter caps to be best.
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