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Old 17th August 2010, 07:23 PM   #1
TB is offline TB  United States
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Default YAHA with output buffer: need help

Hello,
I have searched the forum for the information, but with no avail.
I intend to build YAHA headamp as the safest aim at tube amplifier. I have all needed parts, but I would like to use slightly different output part than suggested on Headwize. Instead of operational amplifier I want to try to test Analog Devices BUF-03J buffer ( I still have two of them ) and discrete diamond buffer. And here I need your help...

In YAHA article it is being said than using buffer outside of negative feedback loop might cause oscillation (the reference is made to BUF 634). Can anyone point me to schematic or help me to alter the circuit to place the output buffers inside of the feedback loop?
The schematic would be the best way for me to understand the change.

I would like to mention that my version of YAHA will be stationary, not portable, powered from regulated PSU.



Thanks for the help !!!
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Old 24th August 2010, 01:17 AM   #2
TB is offline TB  United States
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Hello,
Anyone ?
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Old 25th August 2010, 04:45 AM   #3
passive is offline passive  United States
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I don't think that stability will be an issue. The Millett Hybrid uses a similar configuration without any problems. If anything, I would assume that the FET-input BUF03 would be an improvement because of it's higher input impedance.

I think the amp would work fine open-loop, but you could still add a feedback loop if desired. It's a good method of reducing excess gain and it lowers distortion. I recently built a low voltage 6GM8 based amp this way, except that I used a single ended MOSFET output stage instead of IC buffers. The feedback loop also helped reduce the audibility of the mismatch between the two internal triodes.
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Old 25th August 2010, 04:17 PM   #4
TB is offline TB  United States
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Join Date: Jun 2004
Location: Northern VA
Hello Passive,
Thanks for the response. This is what I am trying to find is how to add feedback loop. I do not want to get into situation where excessive testing would be required. I do not have tools or knowledge to pinpoint the problem.
How to alter the circuit to add feedback loop?
Thanks
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