On box of rock, TMB tone stack and buffer...

[Renegadrian]

I write this while experimenting on the pedal, so I want to write the experiences till now and maybe have some suggestions.

Projcet: have a Box of Rock with a regular marshall TMB tone stack.
a schem for reference
http://files2.soniccdn.com/old/1140704a981b9c69e93.gif

I built the overdrive section up to the 3rd mosfet, then after the 1µ (NP for me) I have a modified Marshall tone stack, socketed the bass cap to experiment (22n-47n-100n) 56k slope resistor 50kb mid pot. volume control after it. connected the TS straight or with a bjt buffer.
now, I know the buffer shouldn't add gain, but I do have a good boost with it...
quite unusual...Also, do I have to have a cap between the buffer emitter and the TS input or going straight to it would do no harm? I see amps have no cap after the follower, so I went that way.

http://www.muzique.com/images/buff5.gif
this is the buffer I used, but without caps (As I wrote it is feeded by the 1µ after the 3rd mosfet, and it goes to the treble cap and the slope resistor)

it sounds quite good but not perfect - tone stack is a bit awkward to me, and some other, any suggestion to make it better?! THX

[Kipper4]

Heres a single knob useful little stack that might perform well between some of the BOR stages.
and you can use the unused op amp as a buffer.

http://www.diystompboxes.com/smfforum/index.php?topic=112900.0

[Renegadrian]

thx for replying rich but that is out of the project - i need to get a good regular TMB stack, not a different one knobber...otherwise I'd go two (which is always better than one! :-D ) and have a james!
I think I'll get rid of Marshall and go Fender, they may look similar but the result is so much better to my ears, better tones and ease of settings...

[J0K3RX]

I see you have settled on the Fender stack which is probably not a bad choice. Drew this up earlier figured I might as well post it..

[Quackzed]

you don't need a cap before the ts, if you puzzle it out theres no way through the t.s. to the output without going through a cap , so its dc blocked already.
22n 47n 100n 56k slope, isnt the  treble cap usually 220n? or 470n? fender/marshal rather than only 22n? may be a typo? but thats 10x smaller than i expect to see given the other 'amp' size values...
i'd guess the boost could be from the tone stack being a hefty load? and the buffer can drive it much easier? not sure how low the output imp of a mosfet is compared to a buffer...
i'm actually modding my amp to a plexi/jcm800 preamp, something you might try as an addition is to add a 'cap blend' to c2. if you make c2 .0022uf then parallel a .022 cap/100kpot to it you can dial in a 'plexi' lead channel voicing at one side and the original style voicing at the other, really just a treble input control but it'd let you tailor how fat/tight the distortion character is... you could just swap c2 for a .0022 and see if it would be worth it... with the blend you could dial it anywhere between the 2 sounds. less bass into a highish gain setup tends to tighten up the tone, rather than just making it brighter. might add some xtra versatility and because you have the full ts you can use the cab blend to tighten/fatten the character of the dist, and use the tone stack to adjust the treble/bass balance for each sound...

[robthequiet]

Yes, I see 270p, .02, .02 with 56K, even 500pf for treble depending on model, for Marshall JTM. Blend cap is a cool idea, going to try that.

[Renegadrian]

22n 47n 100n 56k slope, isnt the  treble cap usually 220n? or 470n? fender/marshal rather than only 22n? may be a typo? but thats 10x smaller than i expect to see given the other 'amp' size values...

As I wrote, the bass cap is socketed, so I can try those values listed. Marshall is 22n. treble cap is 250p on Fenders and 470p on Marshall.

i'd guess the boost could be from the tone stack being a hefty load? and the buffer can drive it much easier? not sure how low the output imp of a mosfet is compared to a buffer...

Yeah the buffer drives it so much better, it seems there's no volume loss...

i'm actually modding my amp to a plexi/jcm800 preamp, something you might try as an addition is to add a 'cap blend' to c2. if you make c2 .0022uf then parallel a .022 cap/100kpot to it you can dial in a 'plexi' lead channel voicing at one side and the original style voicing at the other, really just a treble input control but it'd let you tailor how fat/tight the distortion character is... you could just swap c2 for a .0022 and see if it would be worth it... with the blend you could dial it anywhere between the 2 sounds. less bass into a highish gain setup tends to tighten up the tone, rather than just making it brighter. might add some xtra versatility and because you have the full ts you can use the cab blend to tighten/fatten the character of the dist, and use the tone stack to adjust the treble/bass balance for each sound...

thx for this suggestion...

[Renegadrian]

I see you have settled on the Fender stack which is probably not a bad choice. Drew this up earlier figured I might as well post it..

J0K3RX thank you so much for posting your scheme - now that's a good variation on a theme!
how does that tone stack behave!? Why the base of the buffer doesn't get any resistor?! Also no cap from the last mosfet to the buffer. 1n5, very high value for a treble cap, usually I see 250p or 470p. The slope trimmer has a low value compared to the usual values you find (33k or 56k). Did you built it or is it just a preliminary drawing!? Yeah I think I'll stick to Fender ts but your schem is very interesting...Please tell me more about it!

[Kipper4]

I've built one of Jims stacks before with the slope trimmer and it's good.

[PRR]

> Why the base of the buffer doesn't get any resistor?! Also no cap from the last mosfet to the buffer.

The MOSFET Drain is about half-voltage, perfect for an emitter follower to be directly coupled (no cap). Basic circuit simplification.



> 1n5, very high value for a treble cap, usually I see 250p or 470p. The slope trimmer has a low value compared to the usual values you find (33k or 56k).

Capacitor values don't mean anything alone. They do something *in relation* to the Resistors they work with.

Treble is traditionally a 250K pot. Here it is 50K, 5X smaller. 1.5nFd (1,500pFd) is about 5X bigger than a traditional 330pFd top cap. They do the same thing, but at lower impedance.

Why lower impedance? Tubes don't like pulling loads smaller than a hundred-K. These transistors easily pull tens of K.

[Renegadrian]

PRR you wrote great info as always! thanks

[Renegadrian]

I did try J0K3RX tone stack - once you find the trimmer best spot, the controls are very useful, the way I like a TS to behave. Gonna use that for other ckts too, I guess!!! Thank you very much for your suggestion, Jim, it really satisfied my need!!! 

[alfafalfa]

Hi Paul ,

Could post the picture of the schematic again in a higher resolution, I can't read the values of the parts.

Tia, Alf


Sorry , dont bother , I noticed Jok3rx's schem which is very legible !!   

[PRR]

> I can't read the values

Refer to post #1.