Principles of Tone: beyond the output

[Reeltarded]

These are the things I have found to be worthwhile areas to focus beyond the obvious choices when building any given circuit.

1. Controls for each gain stage

2. Independant control for each stage's treble bypass in as many values as you can fit

If I can run gain 2 hard but barely crack gain 1 I have very fine tone control of an amp with virtually one less stage. Gain one can be unbypassed or peaked at 5 different values to supply what the next stage needs to make a joyful noise.

If I run gain 1 wide open the bypass is defeated anyhow and now gain 2 can be moderated with gain 1 acting as a virtual tube distortion while gain 2's peaking/bypass controls the signal and peaked bands

I can moderate both in a continuously variable manner and use the treble bypass settings for both stages to very finely shape anything from very clean to extreme drive

These two sets of controls with variable SLOPE, selectable PEAK over stage mixing, and variable NFB can make useful amplifiers out of just about any cathode and plate combinations in any basic topology.

[pompeiisneaks]

Very good info! I do have a dumb question. I keep hearing people use the term slope resistor, and you're using "SLOPE" there as well, but I'm still unclear exactly what that is.

There's my dumb question for the day.

~Phil

[Rockwell666]

I have recently been adding a 5 way rotary switch to amps I build/modify with diff coupling cap values. I enjoy being able to cut bass esp if using pedals. I never thought of doing that from the treble side of things...could be a lot of fun. (def for hi gain preamps to help with attack). as for the dual gain controls Ive never been a huge fan but if the stages are biased up differently it could create a lot of tone variability. the few amps I did with dual gains had similar biased stages and I found one of the two control to be redundant.

[Rockwell666]

Very good info! I do have a dumb question. I keep hearing people use the term slope resistor, and you're using "SLOPE" there as well, but I'm still unclear exactly what that is.

There's my dumb question for the day.

~Phil

im sure he is talking about changing the tone stack to shift freqs to cover more ground tone wise.

[pompeiisneaks]

I'm just wondering what the term 'slope resistor' means? Where is it in the circuit? That's something I've read about but don't remember ever of 'why' or 'how'

~Phil

[sluckey]

R6 is the slope resistor in this schematic...

http://sluckeyamps.com/tdr/tdr.pdf

[Reeltarded]

Yep, in the tone stack, the slope resistor sets the range and actual slope of the curves the controls do.

If you take a common M 1959 model circuit the 33k/470p, a Fender common value is 100k/250p.. I bottom limit a pot and make that variable from 33k with 68k of travel. In lots of my amps a common settling falls between 50-80k.

I could live with fixed tone and a variable slope.

Using bypass is more powerful than swapping couplers, fer sherr!

My bypasses aren't identical on both stages. The top might be as high as 2200p.. I even have a less used 5kp bypass on the first stage on one. Normally on a 6 position rotary values might be (always start with 100p) null, 100p, 250p, 500p, 1000p, 2kp.

These ideas make amps that speak with many voices.

[thejaf]

Haha - I read this post title and thought it'd be a discussion of room acoustics

[Reeltarded]

Maybe I should change the title to "before beyond the output"?

[pompeiisneaks]

Gah that makes sense. Don't know why I never retained that. Thanks

Phil

[Leo_Gnardo]

I'm just wondering what the term 'slope resistor' means? Where is it in the circuit? That's something I've read about but don't remember ever of 'why' or 'how'

~Phil

As sluckey and reeltarded said. Early Sunn amps had this control, they called it "contour." At the time - VietNam era - "slope" was a disparaging term for Asians, wise of Sunn to choose an alternate term & avoid possible hassle from being misinterpreted as being politically incorrect.

[TUBEDUDE]

Slope resistor accurately defines the resistor function. Cowering to the PC world of progressives is a wasted effort. Speech control is the first wave of generally accepted thought control.
Rant aside, I think the idea of a variable slope control is genius.

[brewdude]

I don’t think that “pc” was a thing in the Vietnam era.

[M Fowler]

It wasn't on my mind.

[sluckey]

...Early Sunn amps had this control, they called it "contour."

The Contour control on the old Sunn amps was just a fancy name for a mid control. Mid and Contour were exactly the same.