CBS Volumax 400 AM classification?

[sliebers]

The CBS volumax uses a diode bridge for the gain reduction element. It can loosely be categorized with the Neve 33609 or 2254 compressors as they both use diode bridges. The volumax sounds nothing like the Neve's. They have fixed attack and release and are very heavy handed. I had a pair of 400's and didn't find much use for them. If you need an aggressive comp on a room mic or something drastic, they can work well.

[uncle muscles]

Originally Posted by sliebers

The CBS volumax uses a diode bridge for the gain reduction element. It can loosely be categorized with the Neve 33609 or 2254 compressors as they both use diode bridges. The volumax sounds nothing like the Neve's. They have fixed attack and release and are very heavy handed. I had a pair of 400's and didn't find much use for them. If you need an aggressive comp on a room mic or something drastic, they can work well.

Interesting.. You wouldnt happen to have any info about the ratio attack and release would you? Thanks sliebers!

[uncle muscles]

I think I read somewhere that theres some sort of FET element involved somewhere in the design too?

[sliebers]

Originally Posted by uncle muscles

Interesting.. You wouldnt happen to have any info about the ratio attack and release would you? Thanks sliebers!

I don't. There was a discussion some time ago over at group diy about adding variable attack and release. The schematic is on the web as well. The Volumax 400 models I had did not have any FET's in them.

[tpad]

The Volumax is a LIMITER. Attack time was in the order of milliseconds and release time was in the hundreds of milliseconds. You thinking of buying one?

[radiovoiceone]

Yes, designed to be used in conjunction with the Audimax which was a level controller.
The Volumax was a peak controller.
The Audimax was usually installed at the studio, driving the STL or landline to the transmitter site where the Volumax was installed.

[uncle muscles]

Originally Posted by tpad

The Volumax is a LIMITER. Attack time was in the order of milliseconds and release time was in the hundreds of milliseconds. You thinking of buying one?

I did tpad. And im lookin forward to foolin around with it!

[uncle muscles]

Originally Posted by sliebers

I don't. There was a discussion some time ago over at group diy about adding variable attack and release. The schematic is on the web as well. The Volumax 400 models I had did not have any FET's in them.

Interesting. I'm looking forward to hear what kind of color it brings

[12ax7]

Originally Posted by uncle muscles

Interesting.

I'm looking forward to hear what kind of color it brings

Here's one on a vocal.

...Although it's the FM version, the 411 (but it gives you the idea):

Volumax Vocal (mp3)

(The mic is an EV 666.)

.

[tpad]

For many years, WGBH-FM (local NPR station here in Cambridge) used to run a Volumax 4111. That was the only processor in the xmit chain and they had it set so that if the board operator was paying attention to levels, they would just barely touch the broadband limiter. Sounded pretty good.

[Bassmankr]

The CBS Volumax and Audiomax are strange ducks in some ways. It's probably best to classify them as Diode due to their circuits. Many of the transistors are used for push pull class A amp stages before and after the diodes.

First the Volumax, a limiter (high ratio) that has the diode section kick in a few milliseconds (quick grab that gives it a FET type sound) and ALSO a relatively slow AGC action to both positive and negative excursions. You can set input and ouput levels via set screw from the front. I've got the newer single rack space (but ungodly deep) 4100 Volumax. It's a one trick pony that you set how hard you want to drive it and forget it. The gain reduction meter however ONLY reads the AGC action so it's something you set by ear. Just a very good sounding unit that will work the best for some things. Even with mods I suspect there would be little variation in it's sound signature so something best to stick in a rack hooked to a patchbay for a quick audition with a source to see if it works for that application.

Now the Audimax, a diode AGC compressor that does two things differently than other comps. First it uses "Gain Platform" which gain remains on a stable plateau over a wide range of input levels (no thumping / pumping). Next it uses "Gated Gain Stabilization" (no swish up of background noise) for what it does between events. Again not much to adjust and a one trick pony. My Audimax is out of the compressor rack as I have other units covering it's ground so I have not used it in a bit to get into more detail.

Given these were designed for and used heavily in TV and radio at the transmitter for unattended use to boost content while minimizing the negatives they hold up very well for studio use. They can be found for not much money but are something you would add to your rack AFTER you have many other comp/limiter bases covered first.

[sleepyhollos]

I have a Volumax 4300 decent enough unit but I rarely ever find that I use it on it's own. It's always in seriec with another compressor doing the majority of the work and then hitting the Volumax quite hard for it's 'effect' type sound. Not sure I'd shell out for one again if this one gave up but it's quite handy for something different. The meter is very interesting too.

[Joe Haze]

I have two Audimax III, one is stock and the other modified to have a release. They are cool, I know of several producers and top mixers who have them. ;lol

[tpad]

Volumax is a limiter, whereas Audimax is a automatic level control, employing CBS Labs "GGS" gated-gain stabilization technique. Totally different beasts.

[uncle muscles]

Originally Posted by tpad

Volumax is a limiter, whereas Audimax is a automatic level control, employing CBS Labs "GGS" gated-gain stabilization technique. Totally different beasts.

I actually read on a DIY board somewhere the other day that the volumax can shift between 5:1 to 100:1. Can anyone confirm this?

[uncle muscles]

And anyone have any idea how to calibrate the meters on this thing?!

[tpad]

No way does the volumax exhibit a limiting slope of 100:1. I remember it at being somewhere around 10:1. As with many feedback limiters, the actual slope will vary somewhat depending how far above threshold you are. As to meter calibration, I do have a manual for a newer model, but it is up in a very hot attic, so you'll have to wait till things cool down. I'm surprised that there isn't a service manual up on the web somewhere.

[12ax7]

Originally Posted by tpad

I'm surprised that there isn't a service manual up on the web somewhere.

There is now:

cbs-AM-volumax-400.pdf

[tpad]

Ah! I knew someone had a manual. So, with this particular model, the linear compression ratio is around 6:1. With respect to the 100:1 compression ratio, I think that they were probably referring to output clipping on overshoot.

[uncle muscles]

Originally Posted by tpad

No way does the volumax exhibit a limiting slope of 100:1. I remember it at being somewhere around 10:1. As with many feedback limiters, the actual slope will vary somewhat depending how far above threshold you are. As to meter calibration, I do have a manual for a newer model, but it is up in a very hot attic, so you'll have to wait till things cool down. I'm surprised that there isn't a service manual up on the web somewhere.

I actually found it somewhere then quickly proceeded to lose it as fast as I found it

Originally Posted by tpad

Ah! I knew someone had a manual. So, with this particular model, the linear compression ratio is around 6:1. With respect to the 100:1 compression ratio, I think that they were probably referring to output clipping on overshoot.

AH-HA! Interesting...

[uncle muscles]

Originally Posted by 12ax7

There is now:

Attachment 304395

12,

You know anything about introducing a 10k pot on R61 for threshold control? Looks like a guy over at DIY did it and was successful

"Thanks a lot for your advice!! I replaced R61 with a 10k pot and that actually did it!

Now I can turn down R65 so that there's very little to no distortion, while still keeping the compression action going. Very nice!

So many combinations possible now: clean + pumping, distortion + gentle limting etc."

[uncle muscles]

Originally Posted by uncle muscles

12,

You know anything about introducing a 10k pot on R61 for threshold control? Or maybe a different type of resistor? Looks like a guy over at DIY did it and was successful

"Thanks a lot for your advice!! I replaced R61 with a 10k pot and that actually did it!

Now I can turn down R65 so that there's very little to no distortion, while still keeping the compression action going. Very nice!

So many combinations possible now: clean + pumping, distortion + gentle limting etc."

EDIT; I'm an idiot.. Only I could mix up input and output. What I meant was the output level pot is missing on the pcb and it's clipping my 96 when I adjust the input gain from the screw on the front panel and I have no idea what to do about it.

[uncle muscles]

Well.. I totally figured out what was going on. And with a little country boy elbow grease I found a rigged-fix for my little quandary.. Turns out the tech that had used to work on this particular unit had completely ripped out the output level pot for some godforsaken reason ill never know. And I had read on a DIY board somewhere that R62 was thought to be the threshold control. So I mustered up a pair of balls, popped her open and shure enough that little 10k pot on R62 was the threshold control. So I basically just turned R62 all the way up for no GR, and I turned the input down about 4 db to match the level I was sending through it and adjusted the thresh to meet up at the red/green junction and it completely solved my case of the missing output level pot/output level clipping my converters. And it couldn't preform any more beautifully on some funk bass guitar I recorded.