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Old 19th January 2013, 10:57 AM   #11
12E1 is offline 12E1  United Kingdom
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Nice concept IMO, using a power op-amp in this way for the buffer function. If I had the time (I don't) I'd be tempted to build one myself just for fun. What's the purpose of the LM317 configured as a current sink on the output? I note that you added it in the second version, but I could not find a reason for it when I scanned the OPA458 data sheet.
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Old 19th January 2013, 11:07 AM   #12
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LM317 constant current source makes OPA548 to stay in sinlge ended class A for first cca 0.5W. Simply it sounds better. It moves crossover to higher power levels.

Look at the bottom of the page at last schematics:
"http://www.tubecad.com/2004/blog0013.htm"
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Old 19th January 2013, 11:17 AM   #13
12E1 is offline 12E1  United Kingdom
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Cool. Thanks for that. It makes sense. I see that JB's schematic shows the old LM12 - I remember those from many years back - not the first high power op-amp, but one of the first that was really usable for audio.
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Old 20th March 2013, 08:48 AM   #14
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Default Latest schematics

Some tweaks there and there...
Attached Images
File Type: png Aikido Preamp noval.png (12.5 KB, 445 views)
File Type: png Aikido PSU noval.png (20.6 KB, 435 views)
File Type: png Hybrid 35W OPAMP PSU.png (8.9 KB, 436 views)
File Type: png Hybrid 35W OPAMP.png (9.5 KB, 440 views)
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Old 20th March 2013, 01:12 PM   #15
FOXYE is online now FOXYE  Israel
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Very interesting amplifier, just need to find a way to get more power.
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Old 20th March 2013, 01:39 PM   #16
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Default More power

I am thinking two options:

1) make LM3886 or TDA7294 unity-gain stable
2) OPA549 unity-gain in bridge mode configuration

Second should be doable, hopefully I can use CCS on output too woth bridge mode. BUT OPA549 is quite expensive, cca 25$. It is a lot money just for output stage. It should do about 150W into 8 Ohms. Nice thing about OPA549 is that you can current limit them with resistor, which should be usefull with bridge mode especially.
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Old 21st March 2013, 02:07 AM   #17
Junm is offline Junm  Philippines
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I wish you can do Lm3886 since I also have 6 pcs of it to use..also LM3875 and Lm1876. If these chips can be stable as unity gain buffers..My plan before is to have a gain of 5 and the rest is from the tube pre...but not done yet hope you will...
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Old 21st March 2013, 07:36 AM   #18
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Quote:
Originally Posted by Junm View Post
I wish you can do Lm3886 since I also have 6 pcs of it to use..also LM3875 and Lm1876. If these chips can be stable as unity gain buffers..My plan before is to have a gain of 5 and the rest is from the tube pre...but not done yet hope you will...
I am trying LM3886 non-inverting mode at unity at this thread, but I need help with it:

LM3886 unity gain
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Old 27th March 2013, 07:56 PM   #19
jcx is online now jcx  United States
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I suspect that with the shown Hybrid Amp schematic's series isolating 1 k and 220 pf to gnd the source impdance may be controlled enough to try the noise gain hack

the "sportiest" I would want to try with LM3886 would be to aim for noise gain of ~20 with asymptote/pole at 200kHz, which puts the low frequency zero at 10 kHz, I'd try noise gain R ~ 1kOhm

Last edited by jcx; 27th March 2013 at 08:00 PM.
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Old 6th April 2013, 12:03 AM   #20
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I like your idea of making cooling holes using a shotgun.
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