What makes an Amp clean up on the Guitar Volume?

[leadfootdriver]

I love an Amp that cleans up. I usually practice with the Volume rolled back to cut down on the racket..

From my experience it's fewer Gain Stages with Power Tube Distortion..

Does lack of Stability help? The Trainwreck Express doesn't use any Grid Leak Resistors, making the Amp seem like it's microphonic..

What say you?

[Chuck H]

This is a much bigger question than you may realize. But you do seem to have a bead on it because, yes, amps that are cranked up to get power tube distortion generally do this better than preamp distortion based amps. But the reason is not what you seem to think. Basically, when you overdrive the power tubes the WHOLE amp is narrowed to the frequency response of the power amp, speakers and cabinets at full tilt. The later stages of the amp clipping obliterates the frequency altering affect of the tone controls. This generally moots any effect from tone controls and any greater range the speakers (or your ears) may have at lower volumes. So the tone get's squeezed up into more mid frequencies. That means the cranked up lead tone is nicely in the mids, where you want it, but the dialed down tone has more HF and LF dynamics. There's some degree of compression effect that happens as well with most amps that is greater when the power tubes are being overdriven because of voltage demands in circuit and offers more dynamics when less drive is applied at the input. These things don't happen in preamp distortion based amps. It has nothing to do with stability margins and there's no magic to it. Consider that Eddie Van Halen did this with a single bridge humbucking pickup guitar and a stock Marshall amp on nearly every recording. Other players find their own methods and there is often some sort of guitar volume control devices or circuits involved. Glen Kuykendall of recorded Trainwreck fame uses a Les Paul with "59" wiring AND low value bright caps on the volume controls AND incorporates both the guitar volume and tone controls when dialing in his "rolled off" clean tone. Joe Satriani has a guitar that uses a "treble bleed" cap for moderate volume reductions and an on the guitar switch to remove that cap from the circuit when he rolls way down for a cleaner sound. This is because the guitars volume control quickly reduces the circuits resonant peak when rolled down a little. But when it's rolled down a lot the pickups own resonant frequency becomes apparent again (typically at a higher frequency) so Joe no longer needs the "treble bleed" and in fact it would make the guitar too bright at these lower settings. Soooo...

It's not just the right amps that enable this. It's also a good artist finding useful tones wherever they can and using whatever amp or guitar circuits work for them to achieve useful tones. A lot of the rolled off tone thing is in the hands, gear that ISN'T the amp and just good musicians finding the musical qualities of tones that might not be that great in the hands of other players. In other words, there are no magic amps with a great dirty tone with any guitar cranked into it and a great clean tone with any guitar turned down. It's very muddled in the guitarist, technique and some un amp related gear specifics.

[Zozobra]

Fewer gain stages helps. Ultimately it's about managing the signal levels so that the latter stages aren't clipping hard. Easy with a JMP/800, but good luck with it on the red channel of a 5150iii.

An interesting outlier design that is good for high gain and cleans up well is the VHT/Fryette Deliverance series. VHT stuff has local NFB around the last stage+CF, which hugely increases the signal swing required to drive those last stages to clip, which in a round about way removes their distortion, BUT once it does clip the feedback loop collapses and the stages then clip full bore. I simmed it in LTSpice and I think the local NFB stage is good for something like 30Vpp before it falls apart from memory.

[leadfootdriver]

All my Passive guitars are wired 50's. I love it.
I own a D120. It's my favorite Amp. Anyone have a Schematic for a Deliverance??

[leadfootdriver]

I think about how much gain for each stage..
I don't have a scope. How much signal can I apply to a common 100k/1.5K stage before it starts to clip?
Could I clip a gator on the Grid Pin and set Meter for Min/Max AC millivolts? I'm brain storming..

[Helmholtz]

I don't have a scope. How much signal can I apply to a common 100k/1.5K stage before it starts to clip?

If your cathode voltage is 1.5V, positive input signal half-cycle will be clipped above 1.5V, corresponding to 3Vpp or 1.1Vrms.

[leadfootdriver]

Thanks.
Is there a good program that shows Load Lines and Bias Points so I don't need to print 100 pages of Anode Curves??

[The Dude]

I find this down to knobs. In other words, if you run the gain knob maxed out on a high gain amp, turning down the guitar volume isn't going to make much difference and isn't going to clean things up much. Whereas, if you run gain at a more reasonable level, things clean up more easily. It's my opinion, and just that- my opinion, that a lot of players use much more gain than necessary. If you listen closely to even (say) Angus Young, there isn't a ton of gain in that sound and yet it is certainly hard rock, and probably considered metal by some. I'd suggest if you can't get the guitar to clean up a bit with the guitar's volume control, simply try running a bit less preamp gain. This is actually how I play most of the time- a single channel amp using guitar volume for semi-clean. I've almost always been able to get there just doing a little amp dialing.

[WiderGates]

Thanks.
Is there a good program that shows Load Lines and Bias Points so I don't need to print 100 pages of Anode Curves??

https://www.vtadiy.com

[Chuck H]

FWIW I play with enough gain to mimic a lot of the flashy 90's rock tones. Bordering on metal distortion levels. I can't use a typical resistor/capacitor parallel "treble bleed" because it spoils the guitars volume pot taper and doesn't give me the control I need at the lowest adjustment for a clean tone. So I use a Kinman type, which is a resistor and capacitor in series, with odd values for the right level of brightness at the lowest volume pot settings. It's basically useless if you just want to dial down a little and specialized to dial down a lot. This works for me because...

I think tube amps really come into their own and shine best over other amp options in the range of mild to moderate distortion levels. Also, I think guitars (their electronics that is) really only shine with all the knobs up full. So for those less distorted but still crunchy tones I have to dial the amp down and keep the guitar up full. If I need more distortion in this configuration I have to use a pedal. I've just never been satisfied with the mild to moderate distorted tones just dialing back the guitar volume. Except for 'volume swells' my guitars volume knob may as well be a switch that goes from full up for heavy distortion to way down for clean with only less toneful options (for me) in between. But that's just MY rig. The Dude outlined his method too. Everyone will do it differently as I mentioned above.

[Helmholtz]

Thanks.
Is there a good program that shows Load Lines and Bias Points so I don't need to print 100 pages of Anode Curves??

No plate curves or calculators needed to answer your question.
As soon as the grid-to-cathode voltage approaches 0V grid conduction starts and positive grid signal peaks get clipped.
Grid-to-cathode voltage gets zero when the instantaneous grid/signal voltage equals the cathode voltage.
Grid conduction causes a soft, single sided clipping.

Otherwise I recommend Richard Kuehnel's book "Basic Theory" along with his online calculators on ampbooks.com :
https://www.ampbooks.com/mobile/vacuum-tubes/12AX7/
or Merlin's book for the basics.

Edit: My answer refers to a gain stage with a bypassed cathode resistor.

[g1]

Is there a good program that shows Load Lines and Bias Points so I don't need to print 100 pages of Anode Curves??

Another one is nickb 's Interactive Valve Data Sheet here: http://bmamps.com/ivds.html

From the looks of the BMamps website, Nick is now retired. Happy Retirement Nick !

[Helmholtz]

Check out this: https://www.valvewizard.co.uk/Common_Gain_Stage.pdf