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Old 1st November 2004, 05:09 PM   #1
sajti is offline sajti  Hungary
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Default What do you think about this hybrid amp?

The attached file contains my latest hybrid amplifier plan. The output power should be 60W/8ohms, and the gain is 20..

Any comments?

sajti
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Old 1st November 2004, 05:45 PM   #2
DougL is offline DougL  United States
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Just a quick first impression: R21 needs to be split into two resistors, on for each cathode to ground.
This will prevent current hogging.

Doug
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Old 1st November 2004, 06:46 PM   #3
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Not an issue for dual triodes, they are matched normally quite well inside the envelope.

What I don't get is why someone would go to the trouble of adding a tube and a whole power supply for it just to reduce performance of an SS amp. It doesn't even give any tube distortion, being wrapped in global NFB.

Tim
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Old 1st November 2004, 10:23 PM   #4
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Sch3mat1c

What I don't get is why someone would go to the trouble of adding a tube and a whole power supply for it just to reduce performance of an SS amp. It doesn't even give any tube distortion, being wrapped in global NFB.

Tim

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Old 1st November 2004, 11:36 PM   #5
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I think that if you want a tube amp, you go all tubes. Hybrids are for people that cannot make decisions. They give some sand owners the false sense of commaraderie with tube guys, but it doesn't work, no self respecting tube lover is gonna fall for that trick. Besides putting sand in a tube amp is like putting a gas engine in a transport truck, it just doesn't cut it.

Well I guess you can guess where I stand on the hybrid issue.
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Old 1st November 2004, 11:54 PM   #6
kevinkr is offline kevinkr  United States
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My experience indicates that DougL is right, the 6922/6DJ8 do not normally feature that close a section to section match transconductancewise and in fact providing independent bias resistors is a good idea as it allows the sections to find their bias points independently of each other. I am not a big fan of paralleled triodes in general these days and of any member of the 6922 family in particular.. I would recommend 6SN7 or 6CG7 as better choices, and why not run without global feedback? Possibly use SRPP driver circuit for low drive impedance. Use lots of local feedback in the output stage, run it at unity gain and see what you end up with. You might also want to use a 2nd order integrator in your offset servo, and make sure the -3dB integrator corner is down around 1Hz or lower.. Some of the later Counterpoint hybrid amps (mosfet outputs) sounded decent and somewhat mildly tubular.
IMHO even as an avid SET fan I think this is well worth experimenting with, it is how one LEARNS.
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Old 2nd November 2004, 06:07 AM   #7
sajti is offline sajti  Hungary
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Hi All,

thanks for the comments!

The input valve is E82CC, not E88CC, and I used some of them with paralell connected. I never had problem with the current sharing.
I already built valve amplifier and ss amplifier too. Now I want to try how does it work together.

Ti kevinkr:

I know that octal based valves would be better, but I have lot of E82CC, and I want to use them for testing. If it works, than I can modify the circuit as necessary.
The -3dB of the DC servo is far lower than 1Hz, see: 330kohms+1uF.
The overall feedback is necessary for the CFP output. But it is not too much, just 12dB.

sajti
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Old 2nd November 2004, 06:36 PM   #8
sajti is offline sajti  Hungary
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Here is another idea:
SE class A, bidged with about 15W for 8ohms. It's under construction, so one or two week, and I can report the sound quality...

sajti
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Old 5th November 2004, 12:38 PM   #9
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Quote:
Originally posted by sajti
Here is another idea:
SE class A, bidged with about 15W for 8ohms. It's under construction, so one or two week, and I can report the sound quality...

sajti

Satji

se is a nice design!

i like your projects.

Hybrids are specific: a good project coud show the benefits of both tubes and ss. Especialy direct coupled (what a pity).

In fact this is a se source follower loaded by ccses and bootstraped preamp.

After weekend please write if you had to regulate the offset and which was the sound?
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Old 5th November 2004, 04:50 PM   #10
sajti is offline sajti  Hungary
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Quote:
Originally posted by padamiecki



Satji

se is a nice design!

i like your projects.

Hybrids are specific: a good project coud show the benefits of both tubes and ss. Especialy direct coupled (what a pity).

In fact this is a se source follower loaded by ccses and bootstraped preamp.

After weekend please write if you had to regulate the offset and which was the sound?
Unfortunately I will not finish in the weekend, due my transformer is not finished. Currently, I try to avoid the DC servo from the circuit, and gives fixed gate voltage for the IRFs. If it will be succesful, than I can forget the PCB, and can use ptp wireing, due the simple topology.
Due the high dissipation, I think that fan cooling will be necessary for this project.

sajti
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