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

[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

[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]

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]

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]

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

[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

[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.

[Chuck H]

Ok... Vintage design amps were not intended as distortion generators. But they were used that way by players anyway. So the familiar distortion sounds you hear are the result of these vintage designs being driven and cranked up into generating distortion. This is a LOUD business! The clean signal on vintage design amps is intentionally designed to NOT clip before the power tubes do so that a full power clean tone can be delivered. Now...

Once the preamp does start clipping (after the power tubes are already clipping) you now have plenty of signal to drive the power tubes into clipping comig from the preamp. But now the power tubes are clipping an already clipped signal. This generates additional harmonics in cranked vintage amps. Still very loud. So...

When you add a master volume to these vintage designs ALL OF THAT is completely lost and gone BECAUSE THE POWER TUBES AREN'T CLIPPING!!! So all you have left is whatever the preamp was doing before the power tubes clipped that signal. In vintage amp designs this is NOT what you should expect from the amps tone strictly at reduced volume. I have outlined clearly that the master volume removes a critical tonal aspect. It's to be expected. So what's left???

Lower volume is the goal of a "master volume" circuit. But equivalent tonality IS NOT. So what you get with a master volume is strictly what the preamp sounds like. With the master volume turned down the power tubes are no longer part of the distortion generating process and all you get is whatever the preamp offers. for most vintage designs this is usually a disappointment because a critical tonal element has been removed.

Preamps designed for good clipped and overdrive tones are a more recent concept than anything existing when the Twin Reverb and A30 were designed and sold.

There's A LOT more to it than this. I only hope the help you understand why any "master volume" added to these vintage designs can never give you the magic of their tone at lower volumes,.

Sigh.

[Justin Thomas]

A long bit on why the need for all the different names for "gain" or "volume" controls... Not professing to be an expert, but just trying to put a complete "beginning-to-end" explanation in a single long post. I'm also open to corrections of gross errors, but I'm also trying to keep it simple without lots of math. Basically I'm trying to be Dave Hunter the author here...

Regardless of WHAT they call it, Gain, Volume, Pre, Post, Master, Loudness, they all do the exact same thing. They all adjust the amplitude of a wave.

A "gain stage" (usually a single triode or half of a 12AX7) will amplify a small signal up to a point cleanly; after that point the signal will distort & eventually clip if you keep giving the stage a bigger and bigger signal.

So, you have a guitar signal of say, 0.1V going into a triode gain stage. That stage will amplify that signal say, 20 times. So the Gain is 20. I'm just going to pick numbers based on very simple math here because I don't like math. So when that signal exits the triode, it's now 2V. Then it goes to a "gain" control. So let's say you wind that "gain" control to 10 & so you then pass that 2V signal to another triode gain stage that amplifies another 20 times. Now your signal is at 40V. Feel free to add gain stages like this as many asyou want; you can see that the "gain" quickly gets out of hand, because remember - each stage can only CLEANLY amplify a signal to a certain point. Probably after maybe 3 stages like this, without any tweaking of volume knobs or voltage dividers, you're probably making a square wave or something else just as audibly & visibly as ugly. So consider this an extreme example - this amp would probably be incapable of passing a clean signal of any usable "actual volume" or, loudness.

So, what a knob called "Gain" on a guitar amp is trying to do is, to amplify a signal right into distortion early on & easily. Since in Guitar-Land "Gain" = "Distortion," then the name "Gain" describes the "primary function" of the knob's use - adding distortion. Or you could set the knob low & not add lots of distortion...

After that gain stage distorts the signal good, there might be a voltage divider that will reduce the SIZE of the wave while keeping the SHAPE of the wave. This smaller signal then will feed a second gain stage which can also only amplify a signal to some point before it also starts to distort. After this particular stage, there might be another "gain" control to adjust the size of that wave after that stage but keeping the shape the same. Or you could just keep cranking the knobs until you get total sludge. Etc. Etc. One of my favorite activities on my amps is to just crank all the knobs on 10 except the Master Volume just to see what kind of horror show I can unleash; my Fender 75 is especially horrible!

So amplifier makers will put in various "gain" controls at various points in a circuit to keep the amp under control, and to allow a wide variety of sounds at a variety of loudnesses. Fenders use one of these controls simply labeled Volume, which is located fairly early in the circuit; Peavey & Mesa can have 3 or more. My last amp build has 4 "gain" knobs - I'll label them Gain 1, Gain 2, & Master Left/Master Right. The Master on my amp is a concentric one that allows me to send a different size signal to each side of the phase inverter; most amps will use a dual pot that turns both at the same time with a single knob.

The reason they all have different names is because various amps are different circuit structures & ALSO, because in Guitar-Land, the term "gain" has come to mean "DiStOrTiOn!" But "gain" technically is about voltage gain, or, how much bigger a signal is coming out than going in. On MOST (MANY?) amps, the idea of a "Gain" control is to indeed amplify a signal to absolutely ridiculous proportions in order to intentionally distort the wave shape. So to keep that distorted wave shape the same SHAPE to pass on to a following stage, there will be a "Volume" control to adjust the signal size. Now, the amp maker might call that knob "Volume." But Peavey used to call their "gain" (distortion) knobs "Pre" & then a later "volume" control "Post" followed by a final "Master."

Finally, you will have a "Master Volume" which will be last in the signal chain and which will set the loudness of the signal. You can either have "quiet but distorted" or "loud & distorted" or maybe you can set your Gain & Volume knobs to not drive any stages into distortion & you can then have "clean & quiet" or "clean & loud" depending on where you set the Master Volume.

The thing is, every amp design is going to be different & every manufacturer will call their various "gain knobs" different things. Each knob SHOULD be called something different, because if you have 3 or 4 "gain" controls & you want to change the sound or loudness, you have to know which knob to turn. If they were all labeled "Gain," you wouldn't know which one did what & it would just be more confusing than it already is. It's kind of like when I'm at work & some customer says "can you pass me a jug of milk?" & I hafta say "can you be a little more specific, please?" because I'm looking at half gallon, gallon, skim, low fat, whole, chocolate, & about 6 different brands. So yes, even though all of the various knobs are all "gain" knobs, they get different names depending on the usual purpose in the circuit. Some mad scientist could theoretically string up 20 gain stages with a "gain control" before & after each stage, having 40 different knobs labeled Gain 1 through Gain 39 with a final Master Volume. It'd be massive overkill & likely practically useless, but it could be done...

The only real "constant" in the Knob Naming Game seems to be "Master Volume," since they're pretty much always the last control in the signal chain & they all basically set the "Loudness" of the amp. A Master Volume should affect the tonality of an amp little to none at all, depending on the design & where the Master Volume is in the circuit. That said, "should" is the operative word. Nothing is perfect, and some designs work better than others at certain goals. I myself don't like a "Crossline Master Volume" because at extreme settings (meaning, trying to play very quietly) it sounds crackly, thin, & just bad. A Crossline is good to "take a little off the top" but for playing sludge metal in my apartment I much prefer the post-phase-inverter Master Volume.

Hopefully this can help a little bit; I know it can all get kinda crazy...

Jusrin

[Justin Thomas]

Lower volume is the goal of a "master volume" circuit. But equivalent tonality IS NOT. So what you get with a master volume is strictly what the preamp sounds like. With the master volume turned down the power tubes are no longer part of the distortion generating process and all you get is whatever the preamp offers. for most vintage designs this is usually a disappointment because a critical tonal element has been removed...

But the goal of an attenuator <IS> to keep the critical tone elements of power tube clipping in the equation, which is why I and others so heavily advocate for them.

But! Like all things in life, trying to tame a genuine experience is going to water down SOMEthing. No attenuator is perfect but some will definitely perform better than others at preserving the full "cranked amo experience." And in <my> opinion, any attenuator is preferable to adding a Master Volume to an amp design that was never intended to have a Master in the first place.

Jusrin

[Sea Chief]

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.

Because Vol 2 -seems- to me in your diagram to imply it's the power stage.

If the input is next to the first stage bit, & that has Vol 1 written next to it... & I KNOW that the input is the guitar input.. then your Vol 1 in the diagram, is the preamp section: & I consistently read that introducing an MV is to to do with -preamp- stage. MV is often referred to as PREAMP distortion, no??

This is one reason why I'm confused g1.

If the very pg 1 basics seem back to front, then I have no way of understanding form here on it seems. Reminds me of pg1 economics: supply & demand, which also seems counterintuitive to me (& I'm as hopeless understanding it).

SC

[Sea Chief]

Chuck H Thanks again for trying. Ok if I break down your recent post into 6 paragraphs. Some I understand, I've always understood too.

Paragraph 1: always knew this.
Paragraph 5: again I knew this, & so never expect either TR or AC30 in their raw state to OD at low volumes.
Paragraph 6: I've always known that MV additions only ever achieve compromised results.

Para 2: When you say "Once the preamp does start clipping (after the power tubes are already clipping) you now have plenty of signal to drive the power tubes into clipping comig from the preamp".. I seem to find a contradiction: the preamp tubes clipping -after- the power tubes are in the opening section of this sentence, & this seems counterintuitive as I thought the preamp xyz always preceded the power tubes xyz. And to back this up, then '..power tubes into clipping coming -from- the preamp' seems back to logic/ intuitive/ as I expect.

So again, like the Vol 1&2 reversed logic g1 gets me in a pickle over, the exact same reversed logic is here: & furthermore you seem to even be stating revered logic, within one sentence.

Paras 3 & 4: are therefore incomprehensible to me, because I have this 'counterintuitive imbalance' has been in place by the previous paragraph.. so I can't possibly understand both paragraphs.

Apologies, this must be frustrating for you I realise. Infuriating I'm sure. SC

[Sea Chief]

But the goal of an attenuator <IS> to keep the critical tone elements of power tube clipping in the equation, which is why I and others so heavily advocate for them.

But! Like all things in life, trying to tame a genuine experience is going to water down SOMEthing. No attenuator is perfect but some will definitely perform better than others at preserving the full "cranked amo experience." And in <my> opinion, any attenuator is preferable to adding a Master Volume to an amp design that was never intended to have a Master in the first place.

Jusrin

Hi Justin,

I have always known this: an attenuator is far easier to comprehend as it's a physical box -after- the whole amp. I've even built one, but it seemed lacking/ I may resort to rebuilding it entirely, just to satisfy myself that any mistake can be corrected like so. This attenuator idea is my 4th choice, well, becuase it strains the tubes: I do not want (or can afford) to fork out £80 on 4x el84's every 2 years. So I may make one for occasional use, only. Which kinda defeats the point a bit.

Thanks alot, SC

[Sea Chief]

Justin Thomas I'm going through your previous comprehensive post, hugely appreciated.

I am though, stuck fairly early on, even with this: you see sinewaves & squared off bits of it (I vaguely know this = clipping) to consider ontop, is too much for me when I haven't got the basics beforehand. I'm also confused as to why I'm told my AC30 isn't very good for an MV addition, when I know it has additional preamp tubes to other amps (I do know that the Top Boost, for eg, adds one 12ax7 itself, & the very idea of this WAS to provide an additional gain stage).. so another black & white counterintuitive situation, yet another, it seems to me lands on my plate.

Tbh I honestly just don't think I'm ever going to understand it.

I'm just going to have to make something, my Pro even kindly said he'd make me a VVR thingy for me to put in (this idea is my 3rd choice), without understanding the basics of Gain/ MV etc. Heck, I've built a Twin Reverb without knowing what a tube actually does! (again: tried & tried but nothing clicks really- they just seem like little magical mystery bottles!!).

Very kind, SC

[Chuck H]

Chuck HPara 2: When you say "Once the preamp does start clipping (after the power tubes are already clipping) you now have plenty of signal to drive the power tubes into clipping comig from the preamp".. I seem to find a contradiction: the preamp tubes clipping -after- the power tubes are in the opening section of this sentence, & this seems counterintuitive as I thought the preamp xyz always preceded the power tubes xyz. And to back this up, then '..power tubes into clipping coming -from- the preamp' seems back to logic/ intuitive/ as I expect.

So again, like the Vol 1&2 reversed logic g1 gets me in a pickle over, the exact same reversed logic is here: & furthermore you seem to even be stating revered logic, within one sentence.

I may have a bead on where some of the confusion is. Your perception seems to be that the preamp should set the tone characteristics (distortion level and equalization) and then the master volume should set the volume. To your credit this is exactly the case with modern high gain amplifier channels.

But even these amps usually include a "clean" channel which would be designed to send a big enough clean signal to the power tubes so that the power tubes distort before the preamp. This is also how all vintage designs were made. Without this arrangement you could not get a clean tone at the amplifiers full volume. Now...

If you add a master volume to a "clean channel" on a modern amp (as some do) or if you add a master volume to a vintage amp THEN what the master volume does (when turned down) is to defeat the circuits ability to send enough clean signal to the power tubes to drive them into distortion. So now, since the power tubes will not be distorting, what you have left is what the preamp actually sounds like. Even to the point where the preamp distorts. This would never be heard if the master volume were not turned down. And strictly preamp distortion for "clean channel" modern amps and vintage design amps does not generally sound as musical as power tube clipping. That said...

Already stated above, a modern amp distortion channel (or "drive" channel or "gain" channel, etc.) is designed to create clipped and/or otherwise distorted tone that is then amplified by the power tubes. In this case a master volume only controls loudness. With the design goal being that a distorded tone must now be amplified to full volume. So this is indeed inverse of how clean channels and vintage designs are set up. And this is why master volumes used on clean channels and vintage designs often negatively affect the sound from the amp.

Even though master volumes used on high gain designes generally do not negatively affect the sound. only the volume. This is because moder high gain preamps are designed to generate "desireable" sounding distortions before being amplified by the power tubes. Where most clean channels and vintage design preamplifiers are NOT designed for desireable sounding distortions. Rather, they are designed to drive the power tubes into desireable sounding distortions. This is a hugely different job and adding a master volume to this type of amp actually defeats it's ability to sound as good as intended in it's design.