Step down grid choke vs. interstage transformer

jetbat · 10th June 2009, 01:11 AM

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,
http://www.jacmusic.com/lundahl/appl...id-Choke-1.jpg
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,
http://www.jacmusic.com/lundahl/datasheets/1660.pdf
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.
Scott

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?

Thanks

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...

10th June 2009, 01:11 AM	#1
jetbat diyAudio Member Join Date: Nov 2008 Location: Maryland	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, http://www.jacmusic.com/lundahl/appl...id-Choke-1.jpg 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, http://www.jacmusic.com/lundahl/datasheets/1660.pdf 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. Scott

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10th June 2009, 05:47 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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?).

11th June 2009, 01:44 AM	#3
jetbat diyAudio Member Join Date: Nov 2008 Location: Maryland	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? Thanks

11th June 2009, 02:35 AM	#4
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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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