The master volume knob - what is really going on

[powdermnky007]

Been wondering this for ages, I've researched a lot.

I have an Egnater Tweaker 15w head, and everyone says it "sounds the best with the master volume past 1:00" My question is this: what exactly is the defining factor in getting 'that sound'? Is it the position of the volume knob, or the volume of the sound coming out of the speakers?

Scenario 1: volume knob 1:00 with only a guitar plugged in. 110 db (the experiment control)
Scenario 2: volume knob 1:00 with a volume pedal turned down 95db
Scenario 3: volume knob 9:00 with a cranked ep booster 120 db

Will scenario 2 sound have "that sound", because the volume knob is at 1:00 even though the volume is quiet? Would it make the 'magic sound' even at a low volume for bedroom playing? (My guess is no, or else why would people need attenuators?)

Will scenario 3 have "that sound", because the volume knob is below the optimal position even though the output is louder?

I guess it boils down to this: How can you really tell how hard your power tubes are working? Is the speakers volume, or is the knob position the most critical factor?
If you read all of this, Thank you.... really!

 

[Lake Placid Blues]

Re: The master volume knob - what is really going on

"That sound" is the Power Amp (phase inverter, power tubes and output transformer) cranked up loud, and pushing a speaker loudly. Anytime there is less volume you don't get "that sound." It might be a good sound or a bad sound, but it is not "that sound".

 

[powdermnky007]

Re: The master volume knob - what is really going on

Cool. I'm glad you picked up on my "that sound" analogy. I rephrased my question a few times, replacing good sound. Because 'good sound' was too generic, and is different things to different people.

So you are saying that the overall volume is the main indicator, of how hard an amp is working, not so much the master volume knob position. When people say "have the master volume around 1:00", that is a generalization. If they were being scientific about it they would say have the speaker outputting > 110 db. Correct?

Thanks for the response!

 

[devastone]

Re: The master volume knob - what is really going on

I also depends on where the MV is in the circuit, so, it's not necessarily that there is more sound coming out of the speaker, although that helps, but also how hard the circuit is being driven in different sections.

A PPIMV (post phase inverter master volume) is a MV added between the phase inverter (last preamp tube) and the power tubes but are usually added as mods. Most MVs are somewhere in the preamp, usually before the fx loop. That's why a lot of people have added PPIVs to Master Volume amps like Marshall JMPs and JCM800s, so they could crank the original MV and drive more of the circuit harder, then cut the amount of signal right before the power tubes.

HTH.

*EDIT* But yeah, the best stuff is when when you are pushing more signal through the transfomer and speakers so the whole system is working.

 

[MakerDP]

Re: The master volume knob - what is really going on

It has nothing to do with volume per se.... It's how the waveform is being "distorted" by the tubes, the amount of voltage "sag" that is going on at higher levels, how much the output transformer is being saturated and how much the speaker is breaking up.

The MV control is lowering the voltage entering your phase inverter tube. If the knob is wide open, full voltage is getting through so more of all stuff above is happening. As you turn the knob down, less and less of a peak voltage is reaching your PI tube so less and less of all that stuff is going on. At some point in that range is the amp's "sweet spot" where all of that comes together to make tube amp magic.

The purpose of a PPIMV is to allow you to preserve the overdrive the phase inverter is contributing to the magic.

 

[powdermnky007]

Re: The master volume knob - what is really going on

Thanks for the responses, learned a lot!

 

[Mincer]

Re: The master volume knob - what is really going on

Yeah, my understanding (and what I define as 'that sound' ) is the volume high enough so the power tubes distort and are not being hampered by the master volume. It used to be that ANY amp with a master volume wasn't particularly good, but these days, amp design has come a long way, and master volumes are not what they once were. Main thing is, you have to decide what 'your sound' is, but experimenting.

 

[devastone]

Re: The master volume knob - what is really going on

Yeah, my understanding (and what I define as 'that sound' ) is the volume high enough so the power tubes distort and are not being hampered by the master volume. It used to be that ANY amp with a master volume wasn't particularly good, but these days, amp design has come a long way, and master volumes are not what they once were. Main thing is, you have to decide what 'your sound' is, but experimenting.

Most of the new high gain amps are generating their tone in the preamp, that's why a lot of them have 4 or 5 12AX7s instead of 3, although there are ways to get more distortion from 3 preamp tubes with a few component changes. I doubt many of the new amps are getting pushed to volume levels that allow the power tubes to add much to the distortion. Unlike the old days, where the tone was from an old non-MV Marshall or _____ getting pushed to its limits.

 

[powdermnky007]

Re: The master volume knob - what is really going on

Agreed. I have trouble pushing my 15w tweaker hard enough. I ALMOST got the bigger 40w tweaker. SO GLAD I DIDN'T!!!!

 

[Myaccount876]

Re: The master volume knob - what is really going on

What the volume knob scientifically/mathematically does is make your balls bigger the more you turn it up.

In all seriousness, any master volume control (regardless of the types of master volume circuits) is most basically a voltage divider. Power (in Watts) = Current * Voltage, Current = Voltage/Resistance. The volume control is a potentiometer (variable resistor), so as you increase the resistance the current will decrease. Assume the voltage to be constant between both equations. Power becomes = (V^2)/R. So as you increase the resistance, power output is decreased. When your volume knob is on "0", it has the potentiometer's max resistance applied as the voltage divider. When your volume knob is on "10" (or 11), the potentiometer's resistance becomes the lowest resistance across the potentiometer's resistive strip (usually a few ohms which will read as electrical continuity - the resistance can't approach zero otherwise the current will approach infinity).

 

[Matt42]

Re: The master volume knob - what is really going on

I also depends on where the MV is in the circuit, so, it's not necessarily that there is more sound coming out of the speaker, although that helps, but also how hard the circuit is being driven in different sections.

A PPIMV (post phase inverter master volume) is a MV added between the phase inverter (last preamp tube) and the power tubes but are usually added as mods. Most MVs are somewhere in the preamp, usually before the fx loop. That's why a lot of people have added PPIVs to Master Volume amps like Marshall JMPs and JCM800s, so they could crank the original MV and drive more of the circuit harder, then cut the amount of signal right before the power tubes.

HTH.

*EDIT* But yeah, the best stuff is when when you are pushing more signal through the transfomer and speakers so the whole system is working.

I really like the PPIMV. My main guitar amp has a PPIMV and I can get really really good sounds out of it even with the master around 9:00 or 10:00. It still sounds best with the master at like 3:00 or so, which is where I put it for 95% of my gigs, but when I need to dial it back it doesn't loose very much.

 

[Lake Placid Blues]

Re: The master volume knob - what is really going on

Many modern amps are designed to get most of the tone from the pre-amp, and then the-clean- power amp is just supposed to cleanly amplify that. In theory it shouldn't matter how loud it is in that case. The Soldano SLO 100 is an example of such design. But many will tell you that as good as the SLO sounds at low volume, it sounds much better with the master volume at 6 or higher. 6 on a SLO is really, really, loud! The power amp is starting to flex its muscles and the speakers are now being pushed. It is really hard to get to around this need to be loud for the best tone. Some people use attenuators, but attentuators still alter the sound some or a lot. Maybe we guitar players just like it loud?

 

[devastone]

Re: The master volume knob - what is really going on

Yes, they definitely sound better at high volumes, and yes, when pushed the power tubes definitely add to the sound. And the SLO is a great amp! I had a HR50+ that is one of the best amps I've owned.

But, still most of the gain, drive, and tone is coming from the preamp section until you get to wall shaking levels.