Federal AM-864 Compressor w/Output Control

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schmidlin

Well-known member
Joined
Jul 7, 2008
Messages
165
Location
Ohio
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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  • AM-864.jpg
    AM-864.jpg
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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.
 
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
 
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.
 
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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