kriskalish
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- Joined
- Nov 25, 2011
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I've embarked on an amplifier design journey that is probably going to take me to something very similar to the pimeta. I'm currently thinking I want a 3 channel (active ground) design. One of the issues you seem to have to wrestle with is how to get your ground channel to sink the current sourcing of the other two channels combined.
Buffering immediately comes to mind. The pimeta uses an IC buffer like the BUF634 or LMH6321, but the 634s are expensive and the LMH6321 is somewhat expensive and not available in DIP. Given that, it seems like building a buffer out of discrete components is a reasonable alternative. I've also decided that discrete components are kind of sexy.
So this leads me to my question: What are some good discrete buffer amplifier designs?
The Jung diamond buffer looks nice but has a lot of parts. Will I be able to get decent audio quality with fewer parts? I've stumbled across a few class A designs, but that's probably not doable even though I'm using 8xAAA batteries.
I also found something called the Monofied Sijosae Buffer here on the forums.
Is this a class AB push-pull buffer? It looks like the JFETs are set up to pull current through the first stage of BJT's, but not really enough to make the whole thing class A. Also, should the capacitor be ceramic?
I tried to simulate a circuit using this as the output buffer and my amplifier breaks every time I put the buffer inside my op amp's feedback loop like so:
I also tried putting a 100pF cap in the feedback loop across the opamps output and inverting pin like Jung's article on op amps suggests, but this only makes a minor improvement. If I bump it up to 1uF I get a sine wave out of my oscilloscope, but the gain is only two. Between the ridiculous cap value and wrong gain I think I'm doing something wrong.
Any advice for buffering my amp would be appreciated,
-Kris
Buffering immediately comes to mind. The pimeta uses an IC buffer like the BUF634 or LMH6321, but the 634s are expensive and the LMH6321 is somewhat expensive and not available in DIP. Given that, it seems like building a buffer out of discrete components is a reasonable alternative. I've also decided that discrete components are kind of sexy.
So this leads me to my question: What are some good discrete buffer amplifier designs?
The Jung diamond buffer looks nice but has a lot of parts. Will I be able to get decent audio quality with fewer parts? I've stumbled across a few class A designs, but that's probably not doable even though I'm using 8xAAA batteries.
I also found something called the Monofied Sijosae Buffer here on the forums.
Is this a class AB push-pull buffer? It looks like the JFETs are set up to pull current through the first stage of BJT's, but not really enough to make the whole thing class A. Also, should the capacitor be ceramic?
I tried to simulate a circuit using this as the output buffer and my amplifier breaks every time I put the buffer inside my op amp's feedback loop like so:
I also tried putting a 100pF cap in the feedback loop across the opamps output and inverting pin like Jung's article on op amps suggests, but this only makes a minor improvement. If I bump it up to 1uF I get a sine wave out of my oscilloscope, but the gain is only two. Between the ridiculous cap value and wrong gain I think I'm doing something wrong.
Any advice for buffering my amp would be appreciated,
-Kris