Vox AC30/ 6 (TBX). Add an MV ?

[g1]

I'm still trying to figure out that simple 2 volume box diagram earlier, & wondering which is Master Vol (as for some ungodly reason, neither was labelled as such) or if they are switched sometimes according to Mfrs (as you alluded to), or if neither are a Master Vol at all.

I asked you before if you had even read the description included with the diagram and you claimed you had done so. What part of "Vol2, aka MV" is it that is so far beyond your comprehension?
Read better, or if you can't be bothered, stop griping about people trying to help you.

[Sea Chief]

Let me give you guys one clear example of how this is confusing for me.

I have had a few amps recently, including a Randal RD5 & a Music Man 4-10. Both have two Volume-type knobs each.

On the MM 4-10, it had a channel Volume and over last RHS a Master Volume. I dialed the Volume to max, & crept up the Master Vol = some 'meh' distortion.

On the Randall, I had a Gain knob and last RHS was a Volume. Now, I can't recall if I put the two knobs in similar guise as above (IE the first Gain one to max, & crept up the RHS one) bit let's assume so (it's not working at the mo or I'd plug it in to confirm) = huge shredding distortion.

Now. Three things here are different between the amps.

Firstly: the RHS knob was labelled 'Master Volume' on the MMan, & 'Vol' on the Randall.
Secondly: the LHS knob was labelled 'Gain' on the Randall, & 'Volume' on the MMan.
Thirdly: one amp had an OD type distortion (at full 1st knob rotation), the Randall had a full-on shredding distortion (full rotation).

So it -seems- & I think this may have been confirmed in replies, that the term Master Volume can sometimes be called just Volume. I'm not 100% sure, but this uncertainty shows you just how unclear all of this is, for me. And/or the Master Volume knob can be placed at different positions, on the controls, implying it is either some other function to what it says it is, or..... I almost had it but slipped my mind. Sudden brain mash.

THAT ^^^^^^^ is how my brain is receiving the info, so far. I have got no further than this. A mess admittedly.

--

Small therapy horse clip.

SC

[Sea Chief]

Right! This^^^^^^^^^^^^^^^^^^^^^^^^^^^

This is "gain structure". If the amp you have gets much of it's distorted tone from clipping the power tubes, and the master volume is before the power tubes the power tubes will not be distorted when drive to them has been reduced (simple). That said, preamps can generate distortions of their own. Though typicially at higher drive levels than where the power tubes do (NOTE: Otherwise it would be impossible to get a full volume clean tone from the amp!). So when a master volume is included you should actually expect LESS distortion than what you get with no master volume, but playing at higher volume with the power tubes driven into distortion.

There is one exception... Modern high gain amps are typically designed to get distortion from the preamp and then the power amp is (by design) limited to amplifying ONLY what the preamp is doing in it's distortion generating. This is a good case for why such amps are often channel switching. Because it takes a different preamp topology to achieve max clean tone than it does to achieve max "preamp distortion" tone. So different "channels" are needed for intuitive performance.

I don't fault any guitar player, and that includes you SeaChief, for seeing the state of modern amps and distortions hard to grasp. This divide in understanding has been the bane of designers since square wave clipped signals became popular in the 60's!!! So no one is accusing anyone of "failing" to understand the circumstances. Learning gain structures as they apply to guitar amps can be hard for the lay players. I only ever pointed it out here because it would benefit you a lot on the path you're taking. Especially considering that you know tone and own a Twin Reverb and an AC30 for your own reasons. You know what these amps sound like. So how to make them sound like that without skinning the neighbors? I like attenuators because I feel these tones are best represented when the amps are at least humping the way they did on the recordings, right.?. But the simpler "master volume" solution is SOOOO attractive and circuits abound from people that claim to have managed what it will take to "unlock your amps tone" BULLSHIT. (<period) Master volumes suck the life out of vintage design amps like the TR and AC30. But that isn't to say that they don't have merit BECAUSE...

Players who understand the gain process through an amplifier can make concessions or corrections for what's NOT happening and find themselves on the happy side of what they get for a tone. These players are in the minority. Much to the shagrin of designers. That said...

A guy who has a GREAT understanding of gain structure without being an official electronics nerd would be Pete Thorn. His *outube videos are a great source for players to glean some understanding of what gear implementation and manner of use mean to "tone".

Not sure if this helps. I'm trying a different idea.

Hi Chuck, very kind post. Appreciated. You won't be surprised to know most of it is very difficult for me to understand: your early 'Simple' bit... I've read 6x but it still doesn't click, my head literally hurts trying to understand just this. Drive you see, is a word not yet used. I have to strain my head trying to decipher what this could mean. So I kinda got 3/4 of the way understanding your 'simple' bit. Then the 'Drive to the power tubes' has me up against a (new) brick wall.

This word Drive then crops up in the next section, & tbh I can't understand any of this section. I'm more lost with this than anything I've come across yet: it's FAR in advance of me. Tbh I'm still trying to figure out that simple 2 volume box diagram earlier, & wondering which is Master Vol (as for some ungodly reason, neither was labelled as such) or if they are switched sometimes according to Mfrs (as you alluded to), or if neither are a Master Vol at all.

There are vague parts of the rest though, that form some comprehension. Modern High Gain amps: now this term I can ascociate with shredding sillyness, huge kinda pedal-like distortion. That seems to chime with what you write. And this word Gain I also see on my Randall RD5, which too has a form of silly pedal-like ultra distortion using this knob. So can I therfore ascociate the word Gain...... with pedal-like ultra distortion? How can I not do so? Yes. But some folks have said my Gain knob, is a Master Volume knob. So the mystery of all this, instead of getting clearer, just expands.

--

Fluffy dog therapy time.

SC

[Helmholtz]

Sorry, I can't comprehend this answer. Change the function? I'm lost. Available loudness?

In simpler terms:
After adding a MV the channel volume will work just as before, only the MV will limit maximum loudness (depending on setting).

Is MV sometimes called Volume, & Volume sometimes called MV... from mfr to mfr?? .

No.
Channel volume is never called MV. Might be called "gain", though.

[Sea Chief]

Better ask Vox.
Would you prefer the term "Master Treble Reducer"?

Not important HH. I seem to recall just now, that the treble & bass are for the Top Boost channel -only- & so perhaps CUT is a tone control (of sorts) for the other two channels. Which would answer my own question. I think that's basically correct.

Actually re-reading your "Master Treble Reducer" has just made my head explode. I assume a joke- good for you if so!!

Adding a MV doesn't change the function of the channel vol - except that the MV limits available loudness.

Sorry, I can't comprehend this answer. Change the function? I'm lost. Available loudness? Lost. Apologies HH.

Ok a question. Is MV sometimes called Volume, & Volume sometimes called MV... from mfr to mfr?? (IE if so, then my trying to establish if the MV is specifically dedicated to the preamp, or to the power amp [I'm still confused as to whether it even is implicitly connected to either] is complete moot/ pointless).

Maybe that question, is too complicated in wording, for a yourself with English as a 2nd language (if so I could be shooting myself in the foot trying to understand your reply!!)

---

Fluffy animal.

SC

[Helmholtz]

So why the **** isn't it called treble then?? And why are there TWO 'treble' knobs?? Anyway a red herring.

Better ask Vox.
Would you prefer the term "Master Treble Reducer"?

I never had any use for the cut effect.

Now you say MV -can- be considered the power amp volume, does this confirm my "theory" then: if you add a MV, then the Vol knob ---- becomes---- the MV, & the additional pot you've installed, is now the Volume.

Adding a MV doesn't change the function of the channel vol - except that the MV limits available loudness.

[Sea Chief]

The cut control cuts (or lowers) treble. More cut = less treble. Zero cut = full treble.
Should be easy to hear.

And yes, you could call a MV the power amp volume.

So why the **** isn't it called treble then?? And why are there TWO 'treble' knobs?? Anyway a red herring.

Now you say MV -can- be considered the power amp volume, does this confirm my "theory" then: if you add a MV, then the Vol knob ---- becomes---- the MV, & the additional pot you've installed, is now the Volume.

Is this right??

Fluffy dog clip. Right now.

SC

[Sea Chief]

I have to visit happy dog clips, immediately after dipping into this, to get my stress levels down again!

SC

[Helmholtz]

The cut control cuts (or lowers) treble. More cut = less treble. Zero cut = full treble.
Should be easy to hear.

And yes, you could call a MV the power amp volume.

[Sea Chief]

That "backwards wiring" of the cut pot makes sense as it makes the treble cut increase when turning cw.
Of course it's easy to reverse for normal MV operation.

I actually haven't a clue what the cut knob actually does! I mean just playing the amp (not trying to understand the physics of what it is- that's impossible for me).

Some channels it seems to do something, others not. But what it does, well I have no idea. The word CUT is completely arbitrary vocabulary, & not featured on any Fender I've ever known. Nor Marshall perhaps too. Some kind of treble thing.. who knows. And yes it does seem 'backwards' too which adds to the mystery.

Anyway it's not important.

SC

[Sea Chief]

You see Volume, & Master Volume over the course of a thread.. has seemed to me to have stealthily expanded to include two other Volumes: Preamp volume, & Gain; terms used willy-nilly by those of you who understand it all, but suddenly making it all yet more unfathomable, to me.

Thanks enormously for trying to help me though, I do appreciate it chaps.

SC

[Helmholtz]

For some unknown reason Vox wired the cut pot “backwards” making it zero ohms when fully cw and 250k fully ccw.

That "backwards wiring" of the cut pot makes sense as it makes the treble cut increase when turning cw.
Of course it's easy to reverse for normal MV operation.

[Sea Chief]

That's exactly what a MV is supposed to do: Varying loudness without changing the tone.
Don't expect a MV to add distortion.

So hang on then.. maybe this is correct: if you add a MV, then the Vol -----becomes----- the MV?? Is this right??

I forget where I am though, as my head aches dipping in & reading/ replying, that I need 2 days break to consider things (& typically give up because I can't understand it),

I do know one thing now. The fact that MV occurs at the far RHS of the knobs (typically, as I have noticed a pattern like this amp to amp) has had me assuming this is the power amp volume control, because it has the word Master in (which implies ultimate authority.. which a bigger power amp section DOES HAVE over the smaller & prior preamp section).. & perhaps.. this is incorrect. But now I haven't a clue where I am, & need another break.

Thanks, SC

[Justin Thomas]

I think your cross line mod could have been working. It had zero output with both vol pots fully cw which it would do with the “cut” cap shorted. For some unknown reason Vox wired the cut pot “backwards” making it zero ohms when fully cw and 250k fully ccw.

Sea Chief VERY interesting point Dave makes here. It MIGHT be worth checking this again, except leave what was the Cut comtrol full CCW & then start adjusting various Volume & Gain controls to see if you can get any decent output.

Jusrin

[Dave H]

Referring to the diagram in post #44

It doesn't matter what the manufactures call Vol1 and Vol2 (gain, drive, vol, master vol etc.) they are both just volume controls but at different points in the circuit.

If you want clean turn Vol2 fully cw and use Vol1 to control loudness.

If you want dirty set Vol2 to a low value (not zero) and adjust Vol1 for the required amount of dirt then set the loudness with Vol2.

You could call Vol1 “Gain” and Vol2 “Master Vol”

I think your cross line mod could have been working. It had zero output with both vol pots fully cw which it would do with the “cut” cap shorted. For some unknown reason Vox wired the cut pot “backwards” making it zero ohms when fully cw and 250k fully ccw.