ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Re: Anybody built this compressor?

:

5/5/2000 7:00 PM
Rebel420	Re: Anybody built this compressor? Ya know, someone should just build this puppy, it's not a coplex circuit. If I wasnt leaving town in 2 days, i'd do it just to end the confusion

5/7/2000 3:38 AM

Note that this will not work unless
you connect pins 1 & 2 together
on the first 12AX7 (which acts as a diode).

Also, this circuit only *cuts* signal,does not
boost it.In fact it will cut signal even
if no compression is taking place (there's
an effective voltage divider between the
470K resistor and the half of the
12AX7 that actually does the compression).

Lastly, the output impedance is very high.
There's only a .01 cap on the output, to
avoid any appreciable low frequency rolloff
(which may be what they had in mind), it'd
have to be coupled into something like
a 1 meg load.

You'd probably get better results trying
to interface this with SS gear if you
put a cathode follower on the output.

A very similar circuit was used in Seeburg
jukeboxes, and IMHO, it's better suited
as an AVC (automatic volume control)
unit than as a compressor.Basically, that's
how the output works, like an electronically
controlled volume control.

IMA, speaking of stuff gleaned from
jukeboxes, RockOla used to use a neat
and clever little gizmo as an AVC controller:
a light bulb between a tube cathode & ground.

5/7/2000 5:05 AM

Thanks for the input, Tio Nedo. That's two votes for tying the grid to the plate, which makes sense, but I wonder why the schem doesn't say that... Anyway, the one remaining question is what plate voltage to use. I figured I'd play it safe - start with 150 and go up from there until it sounds best or combusts, whichever comes first :-)

:-)

I've got all the pieces, and I'm going to try to get it built by Monday. I was indeed planning to put a CF on the output, and possible a recovery gain stage before that if the insertion loss is too great. We shall see...

Thanks for all the input.

Reid

5/8/2000 4:54 PM

I came *thisclose* to building it up for a restaurant in my area that has problems with keeping the volume level on their bg music constant. I was going to use a 115:115 power tranny rectified to supply 161V at the first filter cap : in other words, I was going to use ~150 B+ and see how it sounded, same as you.

After hearing Ned's juke-box comments, I think I WILL build it up for him, what's the worst that could happen? Swap junk-box parts for free dessert? I mean, the thing sure couldn't BE any simpler . . . .

-j

5/19/2000 6:12 PM
J Epstein	I've got all the parts now, I'll report back as soon as I get it built. -j

5/28/2000 9:19 PM

Tobias Karlsson

quote:
"I've got all the parts now, I'll report back as soon as I get it built."

How did it go?

I understand Reid was also going to build it.

Just curious about this one. I've been discussing it with friends here and they all say it looks weird.

Best Regards
Tobias Karlsson in Sweden

Page 3 of 3