Page 1 of 1

transformer preamp buffer

PostPosted: Sun Jul 07, 2013 5:23 pm
by jetpack
HI all.
Not quite a guitar amp question, but...
I've built an aikido linestage to use as a preamp for an acoustic violin with piezo pick-up. I've also made a small ss buffer to transfer the impedance from high (coming out of the piezo) to something more suitable as input for the preamp. However, I've found an old Triad microphone transformer (from 1948!) that I think might perform this function better. Here are the specs: Microphone or Line transformer (600/250/150/62.5 ohms) to Grid (86500 ohms), 20 – 20kHz; 10dBm maximum level. I also have the pin details. Any thoughts on how I might make this work (or even if it is a good idea)?
Thanks!

Re: transformer preamp buffer

PostPosted: Mon Jul 08, 2013 4:26 am
by Geek
Hi,

Don't use a transformer with a piezo.

The high input-Z of a tube pre (use a 220K to 1meg grid resistor) is ideal for the output-Z of a piezo.

Cheers!

Re: transformer preamp buffer

PostPosted: Mon Jul 08, 2013 12:20 pm
by jetpack
Thanks Gregg.
That helps.
I'll give it a go. Maybe I'll try to use a variable resistor to audibly test for input impedance .... unless somebody is willing to post an equation for calculating this.

Re: transformer preamp buffer

PostPosted: Mon Jul 08, 2013 1:54 pm
by jetpack
Sorry, but could you clarify, is it the grid leak resistor I should increase or the grid stopper?
Thanks again.

Re: transformer preamp buffer

PostPosted: Mon Jul 08, 2013 8:51 pm
by Geek
Grid leak.

The grid stopper is fine at a low value.

Cheers!