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

[g1]

I just don't understand why, if I'm desperately trying to understand what Master Volume is, a diagram is provided.. without the inclusion of the term Master Volume. As much as it's kind of you to try & help, I find this omission fundamentally unfathomable, & quite bizarre.

Did you read the description?
If you did, you would see that vol1 is equivalent of gain, and vol2 is equivalent of master. As I also mentioned, you are getting hung up on the names and blocking yourself from understanding the concepts.

[Sea Chief]

I think I'm going to have to start afresh. I'll ask on another website, & try a completely different way of asking what A MV is.

I've obviously worded my questions totally wrongly, to get in such a muddle. I must reconsider how to ask this question.

--

On a different tangent though: I remember going in a shop, & playing a Music Man 2-10. It had a Volume & a Master Volume (as my 4-10 did). I was 18 years old. I didn't know what the difference was between these two knobs, but after a while of trying them interacting with each other, I found that turning one to 0 and the other to 10.. produced no audible noise. When I then increaced the 0 knob UP.. I got noise, & it was distorted. Turning it up further increaced the volume, but not the ammount of distortion. So at this point I could eatablish that the knob that was set to 10... was the one providing the distortion.

I switched this exact 'experiment' round, so the other knob was on 10, & the first one was on 0. I got the same results: firstly no noise, then by increacing the first knob up from 0, a distorted noise increacing in volume ( but not level of distortion).

The only discernable difference between these two identical 'experiments'.. was one produced a better quality of tone, than the other. Regardless of whether it was the one with more distortion.

So here, I was able to use a Volume knob AND a Master Volume knob, perfectly able................... even though................ I had absolutely no clue as to why I got the results I did. I just got them. I played the guitar. I didn't need to know the physics of why the first way the two knobs were set, seemed definitely better than the reversed way round, of the second way the two knobs were set.

What I'm trying to do, is add this second knob. What I realise is, that with all the will in the world to try & explain the physics of these two knobs interactions to me, I may not get there. BUT that doesn't mean I am prevented from adding it, if it's proven that I can solder something in perfectly well.

So all I can do, is ask how something is soldered in. Where to put X. Once this is done, & the second knob is added & functions... I'm effectively back as my 18 yr old self was, playing my guitar. With these two knobs interacting together. Without knowing why they are doing so, or needing to know.

Thanks, SC

[Sea Chief]

Did you read the description?
If you did, you would see that vol1 is equivalent of gain, and vol2 is equivalent of master. As I also mentioned, you are getting hung up on the names and blocking yourself from understanding the concepts.

Hi g1, of course yes I did, until my head hurt. About 6 times.

I was immediately flummoxed because I had thought the MV was Vol1. Because I assumed adding this MV knob, was something to do with overdriving the preamp. I asked if this MV was something to do with the preamp section (but no reply). So logic dictated that it could only be so.

But here, your now suggesting it's Vol2. Not Vol1. Vol2 in your diagram... is relevant to the POWER amp section.

So I am even MORE lost after reading your post here, than I was beforehand. I'm getting more & more lost. I thought I had the basis of understanding, that being you introduce an MV at the preamp area. Because ther's already a flaming great big VOLUME knob on the amp, which can only be changing the level of the whole bloomin thing, meaning it has to be changing the level of the POWER amp section.

If I add another Volume knob, & the general idea as I thought it was, is to introduce this at the preamp (somewhere: after tube 1,2,or 3? I asked this but no reply) area let's say... then in your diagram Vol1 should be MV. And Vol2 should be Vol. But you say it's the opposite. So I've never in my life been so bewildered, & tbh I just can't cope anymore trying to understand it. I don't think I'll be able to now, so much my head aches with this, & I just get more & more confused.

All I can do is ask how to affect the changes. I'll try the link C1 again, but if I turn either knob to 10, & the sound reduces to zero.. I have to conclude it is NOT working. For whatever reason. I cannot cope with someone saying that is to be expected. That is not logical.

What I can do, is affect the change someone else did -with the very amp I have- (not a similar one from 1970), as Pedro's is. I just need to ask him whether the addition he did, the mod he added, was effective. Properly decent. If it's only "hmm.. it was okay but a bit 'meh' " then I have to skip this 2nd idea, & consider a VVR. My lovely amp Pro even said he'd make me one to put in. But I do need to consider whether I have to have reasonable Volume to make it effective (rather like an attenuator does), because if so.. then it might be a pointless exercise. But if it can be reversed without bodging a hole in the amp or anything then nevertheless probably worthwhile for a last-last-gasp try.

Thanks, SC

[g1]

Your initial experience with the Music Man was incorrect. It was either broken or badly set up.
If you use this experience as a basis for understanding the MV concept you will never get it,.
When the master was set full and you slowly brought up the channel volume, it should have been clean and stayed clean until you hit the full power output of the amplifier.
A master set full up should give you the same response as not having a master at all. If you played around with the Crate amp you mentioned, that's how it would function (see post #36).

This is all I can do here. Good luck.

[Sea Chief]

Your initial experience with the Music Man was incorrect. It was either broken or badly set up.
If you use this experience as a basis for understanding the MV concept you will never get it,.
When the master was set full and you slowly brought up the channel volume, it should have been clean and stayed clean until you hit the full power output of the amplifier.
A master set full up should give you the same response as not having a master at all. If you played around with the Crate amp you mentioned, that's how it would function (see post #36).

This is all I can do here. Good luck.

So I was instead then having the Vol set to 10, & gradually brought up the MV (I can't recall) which meant the same ammount of distortion was heard.. just at various volume levels (but no doubt you'll cast doubt on this too).

You assume my amp was broken, but it was perfectly fine/ never put a foot wrong, same when bought as it was when I sold it on. And exactly the same as a 2-10 I played in a shop I mentioned, which wouldn't have been FS, if it was faulty.

This doesn't mean I understand MV any more though, just by switching these two knobs' settings around. Not one iota.

Capt

[Helmholtz]

So I was instead then having the Vol set to 10, & gradually brought up the MV (I can't recall) which meant the same ammount of distortion was heard.. just at various volume levels

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

[Chuck H]

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

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.

[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.

[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

[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

[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]

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

[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

[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]

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

SC