Tube Amps / Music Electronics
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|previous: Ed Rembold Thanks Doug,||View Thread|
|11/7/2000 12:46 PM|
|Doug H||Re:Hey,Doug- noisey?|
[QUOTE]I remember when Jack did his write up on modding the Rat, he mentions that the LM308 was a "noisey"
opamp, and did his Fat Gnat with a TLOxx if I'm
Yeah, I know. If I remember right, the Fat Gnat is voiced more darkly than this circuit is. In this booster circuit, the LM308 has a lot of high content in the low-moderate gain level. When you max out the gain it gets darker. The 100pf feedback resistor doesn't seem to affect it that much one way or another, which surprised me. However the 33pf compensation cap makes a big difference. I tried using smaller values to open up the highs more in high gain and it really shrieked.
Back when I was proto-ing my Shaka 4, I was trying to get more gain out of it. But it oscillated too much, given the high freq content I was voicing it for. My experience has been the TL072 will work in a high gain circuit if you roll off the highs somewhat.
Any of these op amps are going to have limitations wrt freq & gain. In general, you can push one or the other, it's a tradeoff. If you push both, you may hit the limit sooner. In this particular circumstance, the LM308 goes into a slew distortion. Somewhere someone decided that sounded cool and the rest is rock&roll history, as they say. In the same set of circumstances, the TL072's I bought from Mouser squeal - not cool.
Of course, I could be completely wrong too. In that case, completely ignore what I said.
|Ed Rembold Doug, I'm sure your right-on.|