Federal AM-864 Compressor w/Output Control

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schmidlin

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As usual, when I wrap up a new build, somebody asks for another option for it.
I'm looking to vary the output on the Federal, and think I am on the right track.  With all this hemming and hawing over triple stacked variable T pads, Daven attenuator$ and sourcing issues, do any you see why this would not work properly?  (I hope this 'attach' thing works ok)
Thanks in advance.
 

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schmidlin

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Ohio
Sorry for the image snafu, gang.  Here is the link:

http://i247.photobucket.com/albums/gg122/darthneighbor/AM-864.jpg?t=1226980172

I guess another Q would be how to embed images into these posts.  I tried my usual html, but no go.
 

edanderson

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atlanta
i've been able to see the attached image in the post since you posted originally earlier today.  some other posts apparently have images that i can't see, however.

what you're proposing seems like it will work in theory.  i'd be inclined to use a two deck rotary switch, but we know a pot "works" up front in the same way, so i bet a pot will work here also, at least as a proof of concept.

because there is generally way too much gain in these units, i'd say go ahead and use a higher ratio stepdown output transformer also, if you have that option.

ed
 

NewYorkDave

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It will work. I used a similar arrangement in the tube comp I designed--a dual-ganged level control between vari-mu stage and output amp. It should be mentioned that this is not a mod you can slap into any ol' tube compressor. It won't work in most "typical" vari-mu designs due to the take-off point for the sidechain. In those cases, the traditional 600-ohm attenuator after the output transformer is the way to go.

I agree with Ed... a stepped output control is best, but a regular dual audio-taper pot will probably work well enough unless the two sides track really badly.
 

schmidlin

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Ohio
Thanks for the input.  I assumed since the compression action took place prior to the mod, it seemed on track.

Do you all recommend the stepped control b/c dual pots are usually not matched quite right?
 

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