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Old 7th June 2009, 11:11 PM   #1
MJL21193 is offline MJL21193  Canada
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Default Looking for Feedback on this No Feedback Amp.

I have been playing with this, off and on, for a year. I posted the schematic in another thread but it didn't get much attention there. SO, I post it again here, to see if I can wrangle some comments out of the learned members.

I made it more accessible by changing the parts but it still operates the same way. Class A, currently at ~10 watts/8 ohms but I'd like to work this to be around 25-30 watts.
Thoughts? Comments?
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Old 7th June 2009, 11:25 PM   #2
Nelson Pass is offline Nelson Pass  United States
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Actually, it does have some loop feedback via R13 and R21.

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Old 7th June 2009, 11:31 PM   #3
MJL21193 is offline MJL21193  Canada
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From the master himself! I feel honoured.

Yes, you are right of course. I'm blind to some things...
No global feedback then. How does it look?
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Old 7th June 2009, 11:38 PM   #4
Nelson Pass is offline Nelson Pass  United States
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Looking for Feedback on this No Feedback Amp.
How does it sound?

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Old 7th June 2009, 11:56 PM   #5
Steve Dunlap is offline Steve Dunlap  United States
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Quote:
Originally posted by Nelson Pass
How does it sound?


I thought the sound didn't matter as long as it simms well.
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Old 8th June 2009, 12:00 AM   #6
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by Nelson Pass
How does it sound?

I have a prototype up and running but haven't actually listened yet. Next step, I guess.

Quote:
Originally posted by Steve Dunlap
I thought the sound didn't matter as long as it simms well.

Ah Steve, sim first, build second and listen last, right? Adjust if needed.

OR...

just throw a bunch of parts down and wire them up!
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Old 8th June 2009, 02:49 AM   #7
Nelson Pass is offline Nelson Pass  United States
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Before you rush off and do that, consider that you can probably do
that front end with +/- supply rails and get rid of the output cap.

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Old 8th June 2009, 02:57 AM   #8
Wavebourn is offline Wavebourn  United States
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Quote:
Originally posted by Nelson Pass
Before you rush off and do that, consider that you can probably do
that front end with +/- supply rails and get rid of the output cap.

-2mV/C

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Old 8th June 2009, 03:00 AM   #9
Bigun is offline Bigun  Canada
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Looking for Feedback on this No Feedback Amp.
I like this MJL, nice design indeed.

The schematic for my friends Chinese hybrid shows global feedback, since removed. What's interesting is that in it's modified form it's close (but not the same) to what you have - SS EF output stage and non-diff front end without feedback. And it sounds much nicer that it started so that should be a good omen.

It does use +/- rails but of course there's a cap between the tubes and the VBE.

A big difference is that the tube hybrid is ClassAB

I would love to see the spice FFT.
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Old 8th June 2009, 03:04 AM   #10
Nelson Pass is offline Nelson Pass  United States
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Quote:
Originally posted by Wavebourn
-2mV/C
Who's afraid of that?

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