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#11 |
diyAudio Member
Join Date: May 2012
Location: Near Huntingdon, Cambridgeshire, UK
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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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#12 |
diyAudio Member
Join Date: Jan 2008
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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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#13 |
diyAudio Member
Join Date: May 2012
Location: Near Huntingdon, Cambridgeshire, UK
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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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#14 |
diyAudio Member
Join Date: Jan 2008
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Some tweaks there and there...
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#15 |
diyAudio Member
Join Date: Feb 2009
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Very interesting amplifier, just need to find a way to get more power.
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#16 |
diyAudio Member
Join Date: Jan 2008
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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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#17 |
diyAudio Member
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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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#18 | |
diyAudio Member
Join Date: Jan 2008
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Quote:
LM3886 unity gain |
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#19 |
diyAudio Member
Join Date: Feb 2003
Location: ..
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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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#20 |
diyAudio Member
Join Date: Feb 2013
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I like your idea of making cooling holes using a shotgun.
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