Volumax

[Phazinhead]

Hi Craptical !


thanks for your reply. Do you use the CBS 410 manual ? the only one I found on the web has a very poor quality schematic and it is very hard to read the components name. Where do you see C202 ? ( is it the symetric of C203 such as C10 is symtric to C11 ?)

As for time tweaking, I still bet on altering C202 and C203. Lowering value of R216(?, resistor following conn. F on control board) *might* speed up charging of cap..? Huh

In the manual it is explained that there are 2 separate time constants, depending of the frequency band, so it would mean that the two boards are such as 2 separate compressors. So, we could two separate attack-release time (and this would be very nice to have that kind of control !!),so what value to change on the first board (the one with C1 and C11) for changing attack-release time ?

thank you very much for your help guys !

 

[craptical]

Yes, I also have the somewhat hard-to-read manual schemo. C202 is the "symmetric" counterpart to C203 on the Control Board. These two caps (and resistors around them) forms the time constants. The caps on the two AGC boards only do decoupling and such, if I got things right. The AGC boards amplifies and rectifies the control signals and then sends it the Control Board where the time magic happens... Left side (C202) controls full range and right side (C203) controls the treble (EQ block on schematic). To summarize: put in switches to alternate the values of C202 and C203, maybe alter the before mentioned resistor (and treble counterpart) to fiddle with att. time; raising value might give slower response... (I read the manual which states as fast as 1uS attack, you don´t need faster than that, a Fairchild has 50uS IIRC :)

And again; don´t kill me if I´m wrong on some point!

Good luck!

/Dave

 

[Phazinhead]

Hi Craptical !

thanks for your advice ! and don't worry, i'll never reproach anything if what you tell me is wrong, it very nice to help me 
Okay I understand better now how the Volumax works  but I can't work on my volumax for a long time (manny months). Does somebody have any advice to give about recaping the Volumax ? It looks like very old caps and I'm a bit afraid of breaking old cables and connexions when moving them out of the rack ...  :-\

 

[guitarrock04]

Craptical's got it. I would be curious as to what a variable resistor on R216 would do... I might give it a whirl in mine.

As far as recapping electrolytics, it's pretty straightforward. I just went through the mouser catalog and picked out cheap electro caps of the same or closest value with a same or higher voltage rating. You probably want radial mounted, but either way is doable.

If the internal wiring looks that bad, then it might be worth replacing. Mine weren't too bad, but I still pulled out all of the boards at the same time just to be safe.

The only other recommendation I would make is to replace your power cord. Mine came with an ungrounded, so I did a simple swap to ground while I was in there.

Best of luck.

 

[bootyfox]

Back from the dead: The volumax thread....

I just felt like sharing this:

I have modified my Volumax 400 and despite what some say, this can indeed be a very usable unit, even a tinsy tiny bit flexible  ;D

Anyway, I did the mods suggested in this thread, added a four pos rotary with different cap-values for fast-slow time constants. I also added a seperate switch for choosing clean, symmetric & assymetric limiting.

My problem with my particular unit was that I couldn't get much gain reduction without having to raise the input gain quite much - which in turn resultet in heavy distortion (even with diode-clipping defeated).
The thing I was still missing was some type of threshold or gain-reduction control that would let me adjust the gain reduction independently of the input gain.

Now I have replaced R44 & R45 with a 50k dual pot in the detector amp - giving me the option to either raise or attenuate level of the sidechain signal before it hits the amp.

I have also taken out R63 right before the cap-to-ground on the meter board in order feed the timing circuit with a bit more level. I tried a pot first, but the difference was too subliminal to waste that pot.

After adjusting all trimmers according to manual and my ears I must say that the Volumax could be branded the new poor-man's 175b.  8)
Ok, maybe it's just the looks...

Anyway, if anyone has better suggestions for controlling the gain-reduction or even threshold, pleeeze let me know! This is a great unit to study and learn about how compression works!

 

[MagnetoSound]

I'm more familiar with the Audimaxes (II and III) than the Volumax, but a few things look likely at first glance ...


R44 and R45 are part of the bias circuit for Q10 and Q11, I would leave these unchanged.

R63 is part of the timing circuit and should also probably be left as is, or calculated with C14 for desired attack time.

R62 looks like threshold control, setting reverse bias on the rectifier diodes. If you want much lower threshold, try increasing R61.

That 5k trimmer on the meter board (R65?) probably sets the 'resting' gain, and might have an effect on threshold/ratio too. This may interact with the meter trimmer R68, in which case some to-and-fro adjustment will need to be done with that.

The manual should provide clues as to how far to go with this, if your ears are not sufficient.

 

[bootyfox]

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.

Nice!

 

[MagnetoSound]

Great! Now we know ...  ;D

http://www.youtube.com/watch?v=w4CQin03MDQ

 

[lassoharp]

I've got the 1st gen SS pair - Volumax and Audimax.  I briefly tried out several mods and concluded it performed best for itself in stock configuration.

Both were always "Set it & Forget it" devices to me. Sound was either edgy and forward or SS rich and thick depending on how well the transistors were seated. I left top panels off for easy poking.

Forewent the front panel mods for a trusty screwdriver kept permanently in the panel door.  ;D

 

[emrr]

Lose all the phase flip stuff in the SS volumax is pretty easy, and cuts the path way down.  % limit setting variance is useful. 

 

[bootyfox]

I left top panels off for easy poking.
Forewent the front panel mods for a trusty screwdriver kept permanently in the panel door.   ;D

I know a good screwdriver mod that enables you to adjust your Volumax from 20ft away  8)

 

[bootyfox]

Lose all the phase flip stuff in the SS volumax is pretty easy, and cuts the path way down.  % limit setting variance is useful. 

Sorry, I'm still kind of new to this, so some lingo is still beyond comprehension for me... Care to elaborate?

 

[opacheco]

Hi,

I am in the Repair and Mod process for my CBS 411 too!, but I would like to know if the C202 and C203 are necesarily to be TANTALEX(TANTALUM) CAPACITORS??...Why these capacitors can't be normal Electrolitic Capacitors??.....Have these TATALUM CAPACITORS a special time response performer??

I would like to mod these units for attack and release control but I am unsecure to use TANTALUM CAPACITORS there or ELECTROLITICS.

Opacheco.

 

[MagnetoSound]

Better matching, I should think. The tolerance achieved with tants was tighter than electro's could manage.

 

[emrr]

The tants have a sound too, think early Neve, which most people insist on being tantalum. 

 

[MagnetoSound]

They do, but C202 and C203 are not in the signal path.

 

[opacheco]

MagnetoSound, emmr:
Thanks for your comments!....If I want to modify the Attack/Release Time C202 and C203 in Volumax 411 I will need to buy some for try the performer.....this is the cost that we have to paid in order to mod these units because the Tantalun Caps aren't inexpensive like the Electrolitics Caps.

Opacheco.

 

[emrr]

Ah, so they aren't.  Even today, tants get used in timing circuits because of the tighter values.  Up to you.

 

[opacheco]

I'm more familiar with the Audimaxes (II and III) than the Volumax, but a few things look likely at first glance ...


R44 and R45 are part of the bias circuit for Q10 and Q11, I would leave these unchanged.

R63 is part of the timing circuit and should also probably be left as is, or calculated with C14 for desired attack time.

R62 looks like threshold control, setting reverse bias on the rectifier diodes. If you want much lower threshold, try increasing R61.

That 5k trimmer on the meter board (R65?) probably sets the 'resting' gain, and might have an effect on threshold/ratio too. This may interact with the meter trimmer R68, in which case some to-and-fro adjustment will need to be done with that.

The manual should provide clues as to how far to go with this, if your ears are not sufficient.

Dear MagnetoSound
What could you advise us for threshold control for the Audimax III? Follow your right similar ideas for the Volumax 410; will be possible a threshold control by add a pot(linear or log?) in series or parallel with R63 according the AUDIMAX III schematic, what you could to think about?.....how about the R84 and R85 in the same issue but for the memory threshold control?....and the ATTACK and RELEASE do you have any comments for these too?

I will appreciate any comment from you experience!!

Thanks a lot anticipated
Opacheco.