What does the 'Master Volume' on the ac15cc really do?

[Phil]

Hello all!

Recently I found some free time, and I stumbled across this problem with regards to the 'Master Volume' knob on popular amplifiers.

The main subject amp here would be the Vox ac15cc.

Link to the ac15cc's product specifications,
http://www.voxamps.co.uk/products/ac15/ac15cc.htm

As seen, the ac15cc has a 'master volume' control as well as a 'volume' control.
So what I would generally associate with a 'master volume' control is that it would allow me to get the power amp distortion at low volume.
How true is that in the case of the Vox ac15cc?
Does it really lower the power output after the power-amp stage?

Okay, so assuming that it does not do the above.
Am I correct to say that the 'master volume' on the ac15cc,
1.) is cutting the power between the final preamp stage and power amp.
2.) and when I turn up the gain control or anything similar, I am actually overdriving the preamp stage instead of the desired power-amp stage?

So the 'volume' control = power-amp,
and the 'master volume' = preamp?
Vice-versa?
I'm quite confused as to which is controlling which, and how I am supposed to utilise the 'master' and 'volume'.

Do I up the 'volume' to push poweramp, and lower the 'master volume' to lower overall volume?
Do I use the "master volume" to push the preamp to full saturation at lower volume, of which allowing me to balance the preamp and power amp saturation?

Thank you very much for reading.
Please do entertain me. It has been quite awhile since I have found some time to worry about silly details, and to cook up ambiguous and obscure questions :lol: .

Here are the schematics for the Vox ac15cc, hopefully it helps. Apologies for the size.

 

[stars_jy]

hi..

yes.. i think wad u said is true..

master volume controls the amt of signal to the power amp..
when u turn the volume knob.. you are actually juz overdriving the preamp

to get power amp distortion at lower volume.. you will need a attenuator.. or mayb apply the london power scaling thingy into your amp.. so that u can scale it to lower wattaage to get power amp distortion at bedroom volumes..

i hope im right and this helps..

thanks.

 

[embryo]

Very Good topic!

Some mojo voodoo tips that I learnt along the way that will be very useful for all.

Here's my take if I may share my own tips. The Master volume knob controls the power amp section not by boosting the power tubes. No, what it does is actually controlling the output of the preamp section to be fed into the power amp section.

The way to get the juice from the output tubes is to lower the pre amp section (volume knob) and max out the power section (master volume). Depending on how hot the siganal is hitting the amps input jacks, how one dials in the tone knobs, tube type and gain type and propreity circuit designs with the choice and number of speakers and of course the cab material and design usually the sweetspot for the power amp side is between 60% to 80% of a typical master volume knob. Set it too low and you'll get no power tube juice which translates to a colder or thinner type of grunge. Higher and the amp gets really dynamic and becomes what I'd describe as a Boss BD2 trying hard to come across as dynamic. Set it too high however and you'll lose dynamics. The mojo or some people say "God" is in that elusive middle ground somewhere at the 3rd quarter of the master volume knob really. Heh

The Pre amp section should be very discreetly dialled in. Not too much and not too little.

The above is a general guide on how to get real lipsmacking juices out of your lovely tube amps whatever make it may be. God and the angels seem to always reside somewhere between the pre and power amp sections. Must be why the tubes have that warm orange glow then I guess! Mmmmmm!

Hope this helps ya.

 

[Phil]

Thanks for the replies.

So it's all about balancing and finding 'God' eh?
Thanks for the '3rd quarter master volume' trick, Randolf!

:lol:

 

[gsonique]

imagine the "volume" as a drive knob on od pedal...and the "master" as the volume of a OD pedal :wink:

 

[embryo]

Thanks for the replies.

So it's all about balancing and finding 'God' eh?
Thanks for the '3rd quarter master volume' trick, Randolf!

:lol:

Sure anytime mate!

I like to think the devil resides behind the preamp knob and god is in the master volume. Must be all tube though! Heh

 

[Phil]

imagine the "volume" as a drive knob on od pedal...and the "master" as the volume of a OD pedal :wink:

That helps, thanks!

 

[Phil]

Must be all tube though! Heh

You referring to the pre and power being both tubed? Yeah then no problem since the AC15cc is all tubed. I hope I'm not mistaken though. :lol:

 

[embryo]

Yup ur amp is full tubed so u can smile well assured you got urself a nice one there!