transformer preamp buffer

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transformer preamp buffer

Postby jetpack » Sun Jul 07, 2013 5:23 pm

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!
jetpack
 
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Re: transformer preamp buffer

Postby Geek » Mon Jul 08, 2013 4:26 am

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!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Re: transformer preamp buffer

Postby jetpack » Mon Jul 08, 2013 12:20 pm

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.
jetpack
 
Posts: 49
Joined: Wed Jul 18, 2012 12:13 pm
Location: New Zealand

Re: transformer preamp buffer

Postby jetpack » Mon Jul 08, 2013 1:54 pm

Sorry, but could you clarify, is it the grid leak resistor I should increase or the grid stopper?
Thanks again.
jetpack
 
Posts: 49
Joined: Wed Jul 18, 2012 12:13 pm
Location: New Zealand

Re: transformer preamp buffer

Postby Geek » Mon Jul 08, 2013 8:51 pm

Grid leak.

The grid stopper is fine at a low value.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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KT88
 
Posts: 3585
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Location: Chilliwack, British Columbia


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