Adding a Slope Control

[roberto]

Hi all,
I've seen several versions of it but no-one has a slope control.
I think this amp could gain alot of versatility just adding a push-pull slope control:
- the push-pull adds a 240pf paralleled to standard 240pf in the tonestack
- the linear 100k pot is added in series to a 22k instead of the classical 33k/100k slope eq resistor.

What do you think about it?

[mhuss]

Sure, why not. Give it a try, and let us know how it sounds.

--mark

[roberto]

Now I'm working on a 100w 4ch head and some similar tricks on it, so until February I can't star a new project. I would like to know just some experiencies about it. ..have I to patent this idea?

[gcenker]

...have I to patent this idea?

Patent a potentiometer in series with a fixed resistor to vary the slope value? This trick is used extensively throughout the test & measurement world. When a part (usually a resistor) changes too far from its nominal value, a potentiometer is in series to bring that portion of the circuit back into specification. It’s a good idea, but you'll never get a patent for something so old - it would be like trying to get a patent on biasing a 12AX7 with an RC circuit.

I use this method all the time in the custom builds I make for clients. I have several strategically placed fixed series/ variable pots placed in my work mule chassis (that and switchable caps to see which voicing they prefer). Once I find a certain value which sounds good to them, I simply measure it and replace it with a fixed value.

FWIW ...

-Greg

[roberto]

Greg,
Obviously I was jocking! I put a big " ".
My reply means: why in a Trainwreck forum nobody thought about add versatility to the amp in such a simple way?

[gcenker]

Roberto,
I guess that's what I get for reading this stuff and responding so early in the morning

Doing what you suggested & what I presently do is the only way to really zero in on voicing the amp quickly without soldering/desoldering. I have a varible configuration in the PI (tail resistor), NFB loop and slope resistor along with switchable caps in the tone stack (go from 0.022 to 0.01uf). Makes life easy!

[roberto]

no problem at all!
Thanks for your help, hope to see other people on this thread.
I think this could be a great pot between gain and eq.
I think to open a thread in a couple of month about a trainwreck based amp with some tricks.
Keep in touch, I'll need some help!

[gcenker]

I take a lot of information from this forum so I like to give back when ever I can.

-Greg

[jerrydyer]

I do
www.surrealamplification.com
10k 33k and 56k

its a rotary switch like $6

[rhinson]

this (resistor with series pot) was used on a marshall model in the 80's i believe----the schematic for the model is in the doyle book. i've done this a couple times myself over the yrs. ----in the right amp it's pretty cool. rh

[gcenker]

I made several "tweaks" using my test mule. This is one I just shipped.
Now it's in MP3 format ... give it another try ..

[roberto]

jerrydyer,
does this mod is on pre-gain-eq amps? Or you do it in marshall-like amps?

rhinson,
I think you talk about valve-state's contour. Isn't it?

gcenker,
I can't play that file. Renamed with mp3 extension, doesn't work.

[gcenker]

Roberto, try it now ...

-Greg

[El_Martin]

I'm in a VALVE-STATE of mind

scnr

Ciao
Martin

[jerrydyer]

Mine are like marshall clones i guess tone stack is like 2204 type thang.. there is no reason why it wouldnt work in a tone stack that is somewhere in between v1a and v1b etc. Baxandal would be a different story as to I cant even identify the slope resistor in a baxandall. I could guess but???