Looking for Feedback on this No Feedback Amp.

MJL21193 · 7th June 2009, 10:11 PM

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?

Nelson Pass · 7th June 2009, 10:25 PM

Actually, it does have some loop feedback via R13 and R21.

MJL21193 · 7th June 2009, 10:31 PM

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?

Nelson Pass · 7th June 2009, 10:38 PM

How does it sound?

Steve Dunlap · 7th June 2009, 10:56 PM

Quote:

Originally posted by Nelson Pass
How does it sound?

I thought the sound didn't matter as long as it simms well.

MJL21193 · 7th June 2009, 11:00 PM

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!

Nelson Pass · 8th June 2009, 01:49 AM

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.

Wavebourn · 8th June 2009, 01:57 AM

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

Bigun · 8th June 2009, 02:00 AM

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.

Nelson Pass · 8th June 2009, 02:04 AM

Quote:

Originally posted by Wavebourn
-2mV/°C

Who's afraid of that?

8th June 2009, 02:00 AM	#9
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	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. __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

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7th June 2009, 10:25 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	Actually, it does have some loop feedback via R13 and R21.

7th June 2009, 10:31 PM	#3
MJL21193 Account disabled at member's request Join Date: Mar 2007	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?

7th June 2009, 10:38 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	How does it sound?

8th June 2009, 01:49 AM	#7
Nelson Pass The one and only Join Date: Mar 2001	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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