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Advice about NPB buffer transistor please !

post #1 of 3
1/28/10 at 3:21am
Thread Starter 
Hi,

oops, typo, I mean NPN. Here's the circuit. I needed a 12-15v tone control so that's why I chose this.

What's the best npn buffer transistor ? Would I need to change the input bias resistor from 1k for the upgrade transistor ? Thanks !



I'm using MKP1837 Vishay caps in the baxandall-type tone control and Blackgate n caps for coupling. I've replaced the op amp with LME49720HA but maybe an AD8620 will work better.
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post #2 of 3
1/28/10 at 3:51am
You could use BC546B, or better yet, BC550C. Actually, almost any small signal low noise transistor should work.

If you're not opposed to a dual-rail supply (and get rid of the coupling caps), look at this circuit I posted a few years ago:

http://www.head-fi.org/forums/1236578-post6.html

I recommend using a FET-input opamp for low DC offset.
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post #3 of 3
1/28/10 at 4:11am
Thread Starter 
Thanks ! I know nothing about transistors - just the basic science really. All discrete circuits are a mystery to me. I really should read up on long-tailed pairs etc.

I'll go for the higher bandwidth bc550c. Thank you ! Again !

I'd much prefer to use a dual rail psu to get the best from the op amp but unfortunately it must share a psu that also drives a Charlize amp, and fit in a confined space. But the BG N coupling caps are pretty good and also fit in the space so it doesn't seem to bad a compromise.
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