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

[Sea Chief]

I've politely pm'd this guy if he could not post on my thread.

Maybe instead of his unkind request mods, you could kindly suggest he just doesn't post- it's easy for him do nothing at all.

Thanks, SC

[Greg Robinson]

Tbh I've never considered how turning the gtr vol down can actually make the amp vol diminish.

Now I am thinking how on god's earth this happens. So I've got another connundrum to consider.

I might hazzard a guess though, that it diminishes the signal going from the guitar into the preamp. IE if it's 0.5mV at gtr vol 10, then it's 0v at gtr vol 0. If it's a pot on the guitar, it can only affect whatever's emanating from it. I have no idea though.

SC

How does a shut off valve on your water main work? Why would you need one if you've already got a tap (faucet) to control the flow of water? Am I painting a mental picture for you?

[Sea Chief]

How does a shut off valve on your water main work? Why would you need one if you've already got a tap (faucet) to control the flow of water? Am I painting a mental picture for you?

No, your only making me go more mental, Greg. I can see the analogy of a tap/ water pipe is useful for explaining electricity (current etc), but as an analogy for a far more complicated guitar amp of two distinct sections you plug something into with a vol knob on, I'm not with you (why would you need this extra one? I've no idea why: sorry I'm really not on board with your point).

SC

[Chuck H]

FWIW in my diagram above each horizontal row represents the signal flow through the amplifier. In case that wasn't obvious.

[loudthud]

Why not? The volume control could be located at any point along the signal path.

Strictly speaking, this is not true. In a non-Master Volume amp, the Volume control is (almost always) located between the first and second preamp tubes. This is done so that if you are just plugging your guitar into the amp without any kind of distortion, clean boost or overdrive pedal, you can turn the Volume control down and always have a clean signal as long as the signal level at the power amp input is not overdriving the power amp. Remember that it has been said that in a non-MV amp, the power tubes are the first to clip or distort the signal.

[Chuck H]

Strictly speaking, this is not true. In a non-Master Volume amp, the Volume control is (almost always) located between the first and second preamp tubes. This is done so that if you are just plugging your guitar into the amp without any kind of distortion, clean boost or overdrive pedal, you can turn the Volume control down and always have a clean signal as long as the signal level at the power amp input is not overdriving the power amp. Remember that it has been said that in a non-MV amp, the power tubes are the first to clip or distort the signal.

Right. This^^^^^^^^^^^^^^^^^^^^^^^^^^

Guitar amps are no longer "reference" amps. Though the earliest designs and some much later continued to emulate this. What Mr. Thud points out makes perfect sense WRT guitar amps because you absolutely couldn't place a single volume control at the end of the signal chain on, say, a Peavey 5150 and hope for anything like a clean tone from a guitar plugged into it. This is an extreme example of course but what I hope to illustrate is that THEORETICAL operation and intuitive operation in practice can be very different. Yes you could send a small enough input signal to a wide open 5150 preamp that it would not clip. But for too many reasons that should not even need explaination for anyone that's ever played an electric guitar through an amplifier this is not practical.

[Justin Thomas]

What Mr. Thud points out makes perfect sense WRT guitar amps because you absolutely couldn't place a single volume control at the end of the signal chain on, say, a Peavey 5150 and hope for anything like a clean tone from a guitar plugged into it.

Who needs a 5150? Hell, a couple 5879s in series to an LTPI is more than adequate to destroy any semblance of clean tone if you don't put some Chaos Mitigation Strategeries in there! And this thing started as a projector! So that's why it has a TMB tone stack & a total of three Volumes - one for each amplifying stage (5879, 5879, & the LTPI amplifies a lil bit)[actually each side of the PI has an individually adjustable Volume control a la @g1 because FUN! & "why not?"] And it's still not particularly clean unless everything is at 50% or less.

I initially built it with NO controls whatsoever. That was fun! I'm sure the neighbors disagreed. I like to start out simple & complicate it as I go along.

Jusrin

[Chuck H]

Oh I know. I just picked an amp everyone on the forum could identify with for ridiculous gain.

EDIT: In fact I'm working on a design right now that uses only 2x12ax7's and 2xel84's (four small bottles) and achieves modern tone and gain levels but morphes into a classic vintage amp tone when turned below 5. Well past what the Orange Tiny Terror did. It behaves more like a vintage amp below 5 on the volume control but ramps into metal territory as you get to 10. This required using multi gang pots to change other circuit parameters as the volume is adjusted. So far so good but it's only in a CAD right now. No idea when I'll get to a prototype but it looks REAL promising.

[Greg Robinson]

No, your only making me go more mental, Greg. I can see the analogy of a tap/ water pipe is useful for explaining electricity (current etc), but as an analogy for a far more complicated guitar amp of two distinct sections you plug something into with a vol knob on, I'm not with you (why would you need this extra one? I've no idea why: sorry I'm really not on board with your point).

SC

My point was that in the same way that you can control the flow of water at your tap, or at the main shutoff valve, but if the main valve is closed, the tap no longer has control, the same applies to, in order: your guitar volume control, the volume/gain control in the amp, and finally any "master volume" - if present. If you turn the guitar volume all the way down, it doesn't matter what you set the other controls too - there's no signal to amplify, it's cut off at the guitar. Similarly, if you turn down the volume/gain control (which is traditionally immediately after the input stage of the preamp, and then is followed by the rest of the preamp), there's no signal for the power amp to amplify. And again, if you turn down the master volume, which is between the pre amp and power amp, the power amp can't amplify that now cut off signal.

[Sea Chief]

My point was that in the same way that you can control the flow of water at your tap, or at the main shutoff valve, but if the main valve is closed, the tap no longer has control, the same applies to, in order: your guitar volume control, the volume/gain control in the amp, and finally any "master volume" - if present. If you turn the guitar volume all the way down, it doesn't matter what you set the other controls too - there's no signal to amplify, it's cut off at the guitar. Similarly, if you turn down the volume/gain control (which is traditionally immediately after the input stage of the preamp, and then is followed by the rest of the preamp), there's no signal for the power amp to amplify. And again, if you turn down the master volume, which is between the pre amp and power amp, the power amp can't amplify that now cut off signal.

Hi Greg, ok thanks. This is forming a vague, fuzzy semblence of sense to me. I do need to read it about 20x until my heads hurts though.

I'm still having trouble with this signal chain thing, presuming the signal goes from the preamp into the power amp, then out to the speakers: I still can't see any logic to not having a single volume control at the end of this chain, before the speakers. Which is, until the recent bombshell hit me 2 days ago, what I have always thought (so shifting this idea, after 40 years, is not gonna happen fast).

Again I am asking this question. My hifi has two boxes, a Preamp box & a Poweramp box. The input goes into the preamp (Turntable) & -something/ signal?- goes out to the speakers. I have one Volume control on the preamp box. I do not have a Volume control on my Poweramp box.

Putting aside the aspect of distortion (which is now sidelined as a subject, until I understand the Volume thing): is this two-box hifi a good example to use, for me to try & understand this preamp volume thing? If it is, I can ask on my hifi forum (where my modded preamp has many likes indeed, even my capacitor choices are followed by folks FAR more knowledgeable than me) about this preamp volume aspect. THEN I can come back & possibly understand distortion: 'power amp clipping before preamp' is so illogical in principle to me & impossible to understand at this point. I have no clue on earth why this should be so, or what significance it has to anything.

Thanks, SC

[Helmholtz]

Summary for guitar amps:

Every guitar amp has a preamp volume in the front part of the preamp.
This volume adjusts the signal level fed to all following stages.
As distortion depends on signal level, it makes sense that the (first or only) volume pot sits before all amp stages that contribute to distortion.
This wiring gives the preamp volume the best control of clean or distorted sounds.

Hifi is different.
The volume typically is at the output of the preamp.
So it's more like the master volume of a guitar amp.

[loudthud]

Hifi is different.
The volume typically is at the output of the preamp.
So it's more like the master volume of a guitar amp.

The Hifi I'm familiar with has a Volume control right after the selector switch where line level signals are selected. This allows any signals that are too loud to be attenuated. If so equipped with a phono preamp, the output of that would also be selected at the switch. Next inline would be a buffer stage and tone controls. Lastly, a stage capable of driving a cable of moderate length and a power amp with an input impedance as low as 10K Ohms.

[Sea Chief]

Summary for guitar amps:

Every guitar amp has a preamp volume in the front part of the preamp.
This volume adjusts the signal level fed to all following stages.
As distortion depends on signal level, it makes sense that the (first or only) volume pot sits before all amp stages that contribute to distortion.
This wiring gives the preamp volume the best control of clean or distorted sounds.

Hifi is different.
The volume typically is at the output of the preamp.
So it's more like the master volume of a guitar amp.

Hi HH.

Ok thanks for this: this is kinda what I've needed to know since your bombshell that the Vol only sits in the preamp.

I've still got to get to grips with " As distortion depends on signal level, it makes sense that the (first or only) volume pot sits before all amp stages that contribute to distortion. " But at least I can consider the other sentences before & after this one, & these might click with me.

At the moment you see, I'm immediately asking why (if distortion is totally dependent on signal level) all distortion 'dials' aren't at the guitar start of proceedings. I know of booster pedals, which do this exact idea, but they're like not so frequently used. So, if a booster more commonly isn't used to affect signal, how can a guitar signal go over what the guitar vol pot stipulates without a booster?

Capt

[Greg Robinson]

I've still got to get to grips with " As distortion depends on signal level, it makes sense that the (first or only) volume pot sits before all amp stages that contribute to distortion. " But at least I can consider the other sentences before & after this one, & these might click with me.

Different guitars have wildly different output levels - a guitar with "hot" humbuckers will need less gain/lower volume control setting to achieve the same level of distortion/volume than a guitar with weak single coils. So, the amp has the volume/gain control immediately after the first stage *note 1 where it has the most control over what signal level the rest of the preamp/poweramp "sees" *note 2.

Note 1: Which typically stays clean unless overdriven with a booster pedal or similar.
Note 2: There are amps where the volume control is before the first gain stage, right at the input, but they are an exception, and this has further consequences re loading on passive guitars and source impedance/miller capacitance effects that result in loss of highs, but that's a different discussion.

At the moment you see, I'm immediately asking why (if distortion is totally dependent on signal level) all distortion 'dials' aren't at the guitar start of proceedings. I know of booster pedals, which do this exact idea, but they're like not so frequently used. So, if a booster more commonly isn't used to affect signal, how can a guitar signal go over what the guitar vol pot stipulates without a booster?

Overdriving the first stage with a booster will have different tonal effects than the first stage overdriving the second/subsequent preamp stages. Much in the same way that overdriving the poweramp by turning up the volume control on a traditional amp design vs turning up the gain/volume control and master volume down in a master volume amp will sound different.

Chuck alluded to this earlier by mentioning "gain staging". Gain staging is the art of carefully arranging where and how distortion is achieved for the most pleasing outcome. For instance, if you have two different distortion/overdrive pedals, which order you run them in will have different results. This is like order of operations in mathematics. If we simply went left-to-right for the equation 1+2x3= the answer would 9, however if we observe the correct order of operations with multiplication taking precedence over addition, the answer is 7. The SEQUENCE in which we do things matters.

[Sea Chief]

Greg Robinson Thanks, again parts of this I understand.

But thing is with guitars, I don't see wildly varying inputs. I see the opposite, single coils & humbuckers, p90's in the middle lets say. 3 positions as it were, rather like the ( limited) settings on a tele pickup selector. Limited, vs, wildly different: so it seems I'm still kinda on the opposite side of the fence in terms of understanding the very basics here, too. I also don't find huge difference between a tele & humbuckers- only a slight difference, from experience.

The distortion pedal thing/ aspect.. is far in the future of comprehension for me. I didn't really want to consider this aspect (as the whole idea, of the core of the thread, was my striving to -eliminate- distortion pedals: I find the ones I can afford lifeless, tone-draining & without any natural feel).

Anyway if I can go back to considering my hifi preamp/ poweramp, which seems to share the fundamental principle as guitar amps, that being a volume control not on the poweramp.. but located on the preamp: I need to get to grips with this idea, which still remains kinda alien to me.

Thanks alot, SC