What do you think about this hybrid amp?

[sajti]

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

Any comments?

sajti

 

[DougL]

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

 

[Sch3mat1c]

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

 

[Zen Mod]

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

ya nutz!?

 

[rcavictim]

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.

 

[kevinkr]

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.

 

[sajti]

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

 

[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

 

[padamiecki]

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?

 

[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?

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

 

[altor]

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

Sajti, this is balanced one channel ot 2 stereo channals ?

I think 1st, otherwise - I can't understand how you reach 15W @8R with +-10v rails?

Yea, of course, 15W @ 8R = 11v RMS, that means 15.5v amplutude, so you'll need at least +-17-18 v rails.

 

[sajti]

Sajti, this is balanced one channel ot 2 stereo channals ?

I think 1st, otherwise - I can't understand how you reach 15W @8R with +-10v rails?

Yea, of course, 15W @ 8R = 11v RMS, that means 15.5v amplutude, so you'll need at least +-17-18 v rails.

This is balanced (bridged???) mono channel. So one stage provide 7.5W/4ohms, which is about 5.5Vrms...
When I tested this application of IRF mosfets, I found that they sound better, if the bias is higher. So bridged solution is ideal for it.

sajti