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Old 26th September 2011, 02:24 PM   #21
Gudmund is offline Gudmund  Iceland
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Originally Posted by knutn View Post
So now Gudmund, you have something to do to next summer!
Yes Knutn......I do not dare ask for more.

rgds
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Old 31st December 2012, 11:45 AM   #22
Gudmund is offline Gudmund  Iceland
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Default "The End mkII" DC amp

"The End mkII" ready ...a superfine sounding amp with 3281/1302 and Tip 41/42C
Overall: L.H. Clausen was right..... http://www.tubeamp.hobbysider.dk/
Faster and bettter drivers tried....not worth it! The better specs do not deliver better sound! ....there's a lot of "torgue" in the Tip 41c and Tip 42 drivers. "crab"? hmm.....
Following OP's tried 3281/1302 , 5200/1943, 2922/1216....the last with only one pair. Conclusion: use 3281/1302 ...cheap and strong.

The irritating part is that The End mk3 version needs close matched input transistors....but great sound then!!...it was essential with close cobberlines on the mkII PCB to keep the recommended transistor mounting.(heat balance). DO NOT add DC to the RCA input terminals = burned four outputs and drivers!
Super sound amplifiers.

Last edited by Gudmund; 31st December 2012 at 11:48 AM.
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Old 31st December 2012, 03:29 PM   #23
Telstar is offline Telstar  Italy
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Originally Posted by Gudmund View Post
Following OP's tried 3281/1302 ,2922/1216....the last with only one pair. Conclusion: use 3281/1302 ...cheap and strong.
This is an interesting comparison. The 3281/1302 are my favourite output transistors... If you can get all pairs of the 2922/1216, it would be worth trying them again.

Cheers
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Old 31st December 2012, 05:48 PM   #24
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Originally Posted by jan.didden View Post
Well I'm sure it will sound good.
Technically, it isn't a no-feedback design - there's lots of local feedback / degeneration; has to be to get good sound.
But it certainly is a non-GLOBAL-feedback amp.

jan didden
Yes, the right topic in the headline should read: Power Amp with local serial feedback and without global NFB. Maybe the moderators is able to perform a correction in the headline.
Please let me know follow regarded the schematic in post #1:
1) How is to calculate the voltage gain factor?
2) which commercial power amp device uses this topology
3) which commercial power amp device is configurable between this topology (i. e. without global NFB) and with global NFB ?

Thank you for your advices.

check out in this case also this thread:
Better Audio with or without NFB (Negative Feedback) - for me the wrong Question

Last edited by tiefbassuebertr; 31st December 2012 at 05:51 PM.
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Old 31st December 2012, 06:19 PM   #25
Boscoe is offline Boscoe  United Kingdom
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It boggles my mind why people people think sans feedback is better.
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Old 31st December 2012, 06:29 PM   #26
Bigun is offline Bigun  Canada
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We don't want to see your mind all boggled and stuff do we now...

I suspect there are some reasons why people think sans fdbk is better. Apart from the usual witchcraft that pervades this hobby.

a) distortions are different (measurably higher) and some like this sound
b) for square law devices I believe it was derived mathematically that feedback makes distortion profile worse unless enough feedback is used. Perhaps tube amplifiers with 3/2 law devices fall into this category.
c) I have found that the compensation needed to make a feedback amplifier stable has a profound effect on the sound. I'm talking Cdom here.
d) Interaction between amplifier and load is different with fdbk
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Old 31st December 2012, 06:38 PM   #27
Telstar is offline Telstar  Italy
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For me only B is true. Ok also D, but mostly applies to woofer or complex passive speaker loads.

There is also the woodoo of the signal fed back to the input that sounds wrong from my logic POV, but I have amps with GNFB that sounds good too, so I'm not sure what I really prefer.
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Old 31st December 2012, 06:41 PM   #28
Telstar is offline Telstar  Italy
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Originally Posted by Bigun View Post
c) I have found that the compensation needed to make a feedback amplifier stable has a profound effect on the sound. I'm talking Cdom here.
This deserves a separate answer. Do you think is the presence of miller compensation by itself or the fact that it affect phase and HF distortion?

I suspect the latter, Leach docet.
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Old 1st January 2013, 01:38 AM   #29
Bigun is offline Bigun  Canada
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Originally Posted by Telstar View Post
This deserves a separate answer.
I don't really know enough to answer in much depth, but my observations tell me that the compensation has a clear affect on the sound.

Compensation is needed with -ve feedback. Compensation affects the sound. Therefore, -ve feedback affects the sound. It's one way of looking at it.
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Old 1st January 2013, 03:26 AM   #30
AKSA is offline AKSA  Australia
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Further, we need to examine why ngfb/compensation why affects the sonics.

If you believe that this is nonsense, then the clear conclusion is that ngfb is the best solution and there is no conundrum. Most feel this is the correct conclusion, often based on studies of THD.

If you think that ngfb does degrade the sound (or the lag compensation as Bigun posits) you come to magic $64k question. Why do changes of lag compensation affect this sound, and by any non-metric, such as subjective listening, are you correctly hearing your ears?

You choose one school or the other, and the choice is definitive, opening out one of the biggest issues in audio. And if you believe non-ngfb improves the sound, you are on a limb.......

Hugh
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Last edited by AKSA; 1st January 2013 at 03:28 AM.
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