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previous: GFR I guess you mean a single transisto... -- 10/6/1999 2:47 PM

Re: DIY Parametric EQ at GEO

10/6/1999 3:50 PM
R.G.	Re: DIY Parametric EQ at GEO Yes. The single transistor usually has too low an input impedance - in this instance it shouldn't noticeably load a 1M resistor - and as you mention, that pesky tendency to oscillate. A two-transistor rig can fix the input impedance as well as being much more linear than a single transistor, and may even have some advantages over an opamp in terms of gain-bandwidth for gyrators above a few kHz. However, unless you're already running into these problems, a two transistor rig will use more components and board space than an opamp, so it's something that should only be used where it's really needed. The drawbacks to a single transistor do show up even at low signal levels. It's worth while to note that nonlinearities and quirks are sometimes very useful musically, so it's worth messing with them to see how they sound. I suspect that a musically useful quirk from a transistor would depend on transistor properties, like the sound of a Fuzz Face does. In any case, the right thing to do is to experiment!!

10/6/1999 3:50 PM

R.G.

Re: DIY Parametric EQ at GEO

Yes. The single transistor usually has too low an input impedance - in this instance it shouldn't noticeably load a 1M resistor - and as you mention, that pesky tendency to oscillate. A two-transistor rig can fix the input impedance as well as being much more linear than a single transistor, and may even have some advantages over an opamp in terms of gain-bandwidth for gyrators above a few kHz. However, unless you're already running into these problems, a two transistor rig will use more components and board space than an opamp, so it's something that should only be used where it's really needed.

The drawbacks to a single transistor do show up even at low signal levels. It's worth while to note that nonlinearities and quirks are sometimes very useful musically, so it's worth messing with them to see how they sound. I suspect that a musically useful quirk from a transistor would depend on transistor properties, like the sound of a Fuzz Face does.

In any case, the right thing to do is to experiment!!

Replies:

GFR Thanks!... -- 10/6/1999 3:56 PM