Vol/ Master Vol : Redux.

[Sea Chief]

Greetings strummers. Please dont exclaim profanities of my asking a further Q regarding this insatiably confounding subject, for me that is. I will try to be quick.

I have seen this execellent YT tutorial http://www.youtube.com/watch?v=b871FRjDWAs for numpties as you can call me no doubt, of s'one explaining the distortion 'chain' along a tube amp. Although as my previous thread suggests Im still finding the differences -between the various vol knobs that sit in the preamp stage- a struggle but I am not concerning myself with that here (my brain can't take any more thinking of the possible reasons/ differences: I cant be done with it).

This tutorial section, in the part to which my Q is related, shows a simple explanation of:

1) The input/gain vol set to 10, and the Master Vol set to 2: preamp distortion, not great.
2) The input/gain vol set to 2, and the Master Vol set to 10: much better pwr tube distortion, "perfect lead tone for a Bls Jr that is" he says. I agree. I can even clearly hear it via my PC spkrs. Actually it sounds damn good albeit a typical boxy Bls Jr sound.
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*All understood. This guys examples are terrific even the waves and clipping egs are spot-on too esp for "newbies".

So: both examples are of comparative volumes then, relatively low volume, its just opposing ways of setting the amp's two stages.

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Then he goes on to talk about attenuators, showing again in superb clarity a typical loud amp, and a typical attenuator etc etc. **The following is what I don't understand*** (this is after reading the previous thread three times, re-watched this tutorial twice in case I missed s'thing, & scratched my head almost 1273 times)...

So the guy then goes on to consider, 'now if we want power tube distortion at low volume, we must consider an "attenuator" etc etc etc.

EH?

B.. bu.. but you just showed us how power tube distortion WAS OBTAINED CLEARLY RIGHT THERE, AT LOW VOLUME, SIMPLY BY DIALING THE MASTER TO 10 & THE INPUT/GAIN VOL TO 1 ?! (and also showed by rolling off the GTR volume a clean sound can be got too/ a medium od sound midway= so all my 'three tones' at low volumes by proper power tube distortion for v good sound)................... so why didn't he say this?/ stick there? & I dont understand: therefore why the need for an attenuator at all?? (If the vol 1/ Master 10 sound was as poor as the vol 10 / Master 1 preamp buzzy od sound, I'd understand. But its not. Its good: he said so himself, and showed so himself).

SC.

[Steve Conner]

The power tube distortion probably was not obtained at low volume.

The thing you need to understand is that pretty much all cheap recorders and cameras have a compressor that evens out the volume of the recorded soundtrack.

I'm going to post something I did myself as an example. Here is a YouTube clip of me demonstrating an amp I built myself. It was filmed with a Panasonic camcorder that compresses heck out of the soundtrack. Note that the volume doesn't change that much as I work my way through the power settings. As the amp gets louder, the camera backs its recording level off to compensate. (For what it's worth, this amp has a built-in attenuator so it can get lots of power tube distortion at low volumes, but also go loud if needed.)
https://www.youtube.com/watch?v=DZigVupYve4

And here is a file from a pro-quality audio recorder that was running at the same time, with no dynamic range compression. It shows what the volume was really like in the room.
http://scopeboy.com/scopeblog/wp-con...te-demo-hq.mp3

[Sea Chief]

Hi Steve- ok that might explain my perception of the audio from that YT clip.

But its more the overrding Q I was pressing twds: why not just turn the Preamp vol to 0, turn the Master to 10 so no vol is heard and then just increase the vol fractionally to get a low overall vol.. & therefore there is no need for an attenuator?

I would undertand if the pwr tube distortion obtained -without the addeed preamp distortion- (ie as its on 0.5) is pretty shoddy, like the preamp distortion alone is.. but its not (not just useable either- its good).

[Sea Chief]

The power tube distortion probably was not obtained at low volume.

The thing you need to understand is that pretty much all cheap recorders and cameras have a compressor that evens out the volume of the recorded soundtrack.

I'm going to post something I did myself as an example. Here is a YouTube clip of me demonstrating an amp I built myself. It was filmed with a Panasonic camcorder that compresses heck out of the soundtrack. Note that the volume doesn't change that much as I work my way through the power settings. As the amp gets louder, the camera backs its recording level off to compensate. (For what it's worth, this amp has a built-in attenuator so it can get lots of power tube distortion at low volumes, but also go loud if needed.)
https://www.youtube.com/watch?v=DZigVupYve4

And here is a file from a pro-quality audio recorder that was running at the same time, with no dynamic range compression. It shows what the volume was really like in the room.
http://scopeboy.com/scopeblog/wp-con...te-demo-hq.mp3

Good clip. Lovely amp. One day I before I die I will be able to play an amp in such a break-up mode! I will- one day!

But although yes thru my spkrs its relatively similar I guess.. I can clearly hear a difference between your 0.3/3/and30. Now whether this is a perception thing or what (it must be to do with recognising how a loud GTR sounds even at low volume through my headphoes/ pc spkrs. I could -feel/ hear- 1st a quiet amp, then a loud amp then a damn loud one).. I dunno.

[g1]

Here is what I think you are missing. Power tube distortion is what happens when the amp hits full power. It can not happen at lower volumes, only at the full volume of the power amp. As Steve mentioned, it may appear to be happening at lower volumes due to recording levels. But if you were in the room hearing it live, it would be very loud.
So, power attenuators are what is used between the power amp and the speaker. The amp can be run at full power, with the attenuator "soaking up" part of that power, and the balance going to the speaker.

[Sea Chief]

Hi g-one.

Nope. Its not that. The example showed the guy turning his MV up to 10. The power tubes were therefore distorting. He turned his amp input vol to 1. It wasnt loud. It was comparable in fact to the eg hoe showed simultaneously of Vol10/MV1.

[Steve Conner]

But its more the overrding Q I was pressing twds: why not just turn the Preamp vol to 0, turn the Master to 10 so no vol is heard and then just increase the vol fractionally to get a low overall vol.. & therefore there is no need for an attenuator?

Power tube distortion always happens at loud volumes. A 50 watt amp has to reach 50 watts of output before it will even start to distort. Only a VVR type circuit or an attenuator can change this. (My amp has both built in.)

The tutorial you linked (which is very good BTW ) was recorded with two separate mics. He used a lapel mic for his voiceover and a close mic on the amp. That means he could adjust the relative volumes to make his voice seem louder and the amp seem quieter.

I've tried both the Blues Jr. and the 5E3 cranked wide open. The 5E3 is a bit louder, but I think they would both annoy your neighbours.

[Sea Chief]

Its not that I dont understand what an attenuator does, or where it sits in the 'chain'.

Its just that if pwr tube distortion can be achieved by turning an amp with a single vol knob to max, or an amp with an input vol and and MV vol turned to max.. then why, if I can attenuate this distorted huge volume with the input volume right down to minimum, why then is a separate attenuator in all its cost and bother (and relative unsafety) even made/ in need of consideration for a vol/MV amp?

And therefore why would anyone, as is mentioned some would choose, or 'ok for this n that maybe' why would anyone choose -in any capacity whatsoever- to use the preamp distortion if the far better sounding power-amp distortion is available right there by simply reversing the two vol knobs?? ie instead of vol 10 /MV 1 the far better vol 1/MV 10.

[eschertron]

But its more the overrding Q I was pressing twds: why not just turn the Preamp vol to 0, turn the Master to 10 so no vol is heard and then just increase the vol fractionally to get a low overall vol..

Aha! That's exactly the kind of amp we started with, whether it's a 5W champ or an early 100W marshall. Am amp with NO master volume control, is functionally the same as the amp above with the MV turned all the way up to 10. ...or maybe 11, if you want
At low volumes you get what you expect, the soft clean sounds. As the pre/gain/vol whatever control is turned up, it's gonna get louder until the power tubes arrive at their sweet spot. Probably louder than you want for home use, as you've already found out!

[g1]

The example showed the guy turning his MV up to 10. The power tubes were therefore distorting.

This is the part you are not understanding. Having the master at 10 has no bearing on whether the power tubes are distorting. It may happen if the signal level is hot enough, but is not necessarily the case.
But you can not have power amp distortion without the amp delivering its full power capability. That is what power amp distortion IS.

[Sea Chief]

Power tube distortion always happens at loud volumes. A 50 watt amp has to reach 50 watts of output before it will even start to distort. Only a VVR type circuit or an attenuator can change this. (My amp has both built in.)

The tutorial you linked (which is very good BTW ) was recorded with two separate mics. He used a lapel mic for his voiceover and a close mic on the amp. That means he could adjust the relative volumes to make his voice seem louder and the amp seem quieter.

I've tried both the Blues Jr. and the 5E3 cranked wide open. The 5E3 is a bit louder, but I think they would both annoy your neighbours.

But Steve Im not talking about the amp at full volume. Conversely, Im talking about the amp a t low volume. The eg right there above shows two egs. He 1st uses amp vol 10/ MV 1 (rubbish preamp buzzy). He then reversed the process in order to show an eg of power tube distortion. This he did --as is clear he says/ its clear he does/ the diagram even shows diagramaticcaly the simple process of it: the power tubes are clipping, the signal fed prior to this was small because the input amp vol knob was low-- by simply reversing the two knobs: so now its vol1/ MV 10.

[I also dont undertsand now how my Q is being so misunderstood. I even add a clip. I cant make it any clearer. I think s'one's playing silly buggers on me.. thats how this feels!

[eschertron]

Its not that I dont understand what an attenuator does, or where it sits in the 'chain'.

Its just that if pwr tube distortion can be achieved by turning an amp with a single vol knob to max, or an amp with an input vol and and MV vol turned to max.. then why, if I can attenuate this distorted huge volume with the input volume right down to minimum, why then is a separate attenuator in all its cost and bother (and relative unsafety) even made/ in need of consideration for a vol/MV amp?

And therefore why would anyone, as is mentioned some would choose, or 'ok for this n that maybe' why would anyone choose -in any capacity whatsoever- to use the preamp distortion if the far better sounding power-amp distortion is available right there by simply reversing the two vol knobs?? ie instead of vol 10 /MV 1 the far better vol 1/MV 10.

Right. That's a mighty big 'if'.

If YOUR amp produces the distortion you want at the loudness level you need with the master at 10 and the gain at 1, then play and be happy.

edit: I'm not trying to be antagonistic, really I'm not.

If, on the other hand, you don't get the pleasing 'sweet spot distortion' without turning BOTH gain and master up to around the full volume positions, then you do understand the need for a power attenuator in that style amp.

Other amps, the ones that get their distortion from the preamp, have no problem delivering crunch and sustain with the master turned down. That's what it was designed to do.

[Steve Conner]

And therefore why would anyone, as is mentioned some would choose, or 'ok for this n that maybe' why would anyone choose -in any capacity whatsoever- to use the preamp distortion if the far better sounding power-amp distortion is available right there by simply reversing the two vol knobs?? ie instead of vol 10 /MV 1 the far better vol 1/MV 10.

Because the power tube distortion is fixed in terms of the volume it comes on at. If you have a 100 watt amp and a 100dB efficient speaker, you need to crank it to a sound level of 120dB to get your power tube distortion. (somewhere between a road drill 3 feet away, and a jet plane )

Practical example: Let's say you rock up to the gig with your amp set at preamp vol 1 and MV 10. It sounds great, but the sound guy starts to moan that it's too loud and is drowning out the drummer. OK, so let's turn the volume down...

But the distortion is coming from the power tubes, which are situated after both volume controls. Therefore, turning either volume control down will mainly just make the amp cleaner. You will lose your lovely power tube distortion before you get the volume down to a point that makes the sound guy happy.

So, let's do it again but with preamp vol on 10 and MV on 1. Now the distortion is coming from the preamp tube which is positioned before the MV. You can just turn the MV down, and the amp will get quieter, pleasing the sound guy, but it will stay distorted, so you get to keep your tone.

This is in fact the reason why master volume amps were invented. The preamp distortion doesn't sound quite as good as power tube distortion, but it's controllable.

Recently a belief has come around that power tube distortion sounds better, so various gadgets like attenuators, VVRs and simply lower powered amps have come on the market. They all function more or less like a master volume situated after the power tubes.

[Sea Chief]

This is the part you are not understanding. Having the master at 10 has no bearing on whether the power tubes are distorting. It may happen if the signal level is hot enough, but is not necessarily the case.
But you can not have power amp distortion without the amp delivering its full power capability. That is what power amp distortion IS.

But the eg shows it. Both his description, his sound, & his diagram: MV is at 10, & prior to this the input from the GTR was -decreaced- by the Vol (input) knob at 1 > then to preamp tube which then amplified this minimalised signal into a medium but not excessive/ no tube clipping' signal > which then fed the power tubes which were at max.

He said this eg is power tube distortion. So are you saying he is wrong?

[J M Fahey]

The example showed the guy turning his MV up to 10. The power tubes were therefore distorting.

Well .... no.
Power tubes *may* reach distortion with MV in 10 ..... if they are driven enough.
With preamp volume on 1 they definitely won't.

He turned his amp input vol to 1. It wasnt loud.

It wasn't loud? ..... then it wasn't distorting.