On 7/17/06, Olin Lathrop wrote: > Mark Rages wrote: > > (Olin: the circuit was attached to the first message. Scroll back in > > your threaded MUA and you'll see it.) > > Yeah, right. I'm supposed to keep old PIClist messages on various machines > I'm on, and then dig them out and refer back to them to give free help? > Think again. > Want a gmail account? Solves both the "keep old messages" and "various machines" problem. > > What op-amp are you using? > > But that was listed on the circuit he posted. I guess you don't keep old > messages either. Actually, it doesn't list the amp. You assumed that in your first response. > If I remember right the opamp was a 741. It's not a great choice for noise > and supply headroom, but should work for the sound trigger the OP was trying > to make. I don't think the opamp is his problem assuming it has sufficient > supply voltage and headroom. 741 would work, but it's offset is too big for this DC-coupled circuit. 741 has a 1mV typical, 5mV max offset. The typical offset is the same order of magnitude as the signal. Even worse, the 1/2 Vcc reference is different for each stage. If it is built with 5% resistors, that's a bigger source of offset than the amplifier choice. Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist