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jetbat 10th June 2009 01:11 AM

Step down grid choke vs. interstage transformer
Hi, I am designing the high gain stage in a guitar amp and I don't like what the voltage divider between stages does to the sound. I know I can bypass one resistor with a capacitor but I am trying to keep the amount of caps down. I was wondering if anyone has any experience with step down grid chokes and step down interstage transformers?

Does the step down grid choke such as this,
have any effect on the sound?

For the grid choke I get a 2:1 attenuation and it protects against grid current. (thats something I found out I can do when I overdrive the tubes too hard) Maybe the current protection will allow me to drive the tubes harder and get a more unique distortion. Hmmm.

The interstage trans,
can be wired to get 4.5:1 attenuation and it will replace a capacitor in the circuit.

I think both would be the best way to go, but limited funds means I have to get one type at a time. The price higher for the interstage then the choke, $115 vs. $80.

Any thoughts would be appreciated.

Tom Bavis 10th June 2009 05:47 PM

How about a small toroidal power transformer? Amveco 70005 (from DigiKey - $15) is around 300 Henries, use the two primaries in series to get 2:1 step down. Wire the 22V secondaries in as well and get about 2.4: 1 and 1.7:1. Should work as 1:1 parafeed interstage as well (no DC...). Frequency response should be very good, loss will be considerable (but that's what it's for, isn't it?).

jetbat 11th June 2009 01:44 AM

Yes it is.

Those look interesting. And for $15, I'm going to have to try them out. I understand the wiring the primaries in series and the secondaries in parallel to get 2:1. But for the 2.4:1, would the two primaries be wired in series with one of the secondaries and the other would signal out?


Tom Bavis 11th June 2009 02:35 AM

I was thinking of connecting all the windings in series, like this:
120-22-22-120. Then you'd use it as an autotransformer, with center being 2:1 step down, and the other taps would be 284:120 (about 2.4:1) and 284:164 (about 1.7:1).

You could also use the two primaries as primary and secondary (1:1), and of course use it as designed for 3:1 step down. The autotransformer connections will have MUCH more inductance though...

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