Making a tonepad tubescreamer a boss sd-1?

[JohnForeman]

Hi all,
In the build sheet of the tonepad tube screamer, it states you can use the pcb t make a ts808, ts9 and also a boss sd-1.  The instructions show the difference between the ts808 and the ts9, but how would one make a boss sd-1 from this pcb?  I'm not seeing it in the instructions.
Thanks

[Mark Hammer]

Here's the SD-1 schematic.  Spot the differences, and change them.  The most significant changeswill involve a 2+1 diode complement (which the Tonepad layout anticipates), a higher value gain pot, and some small changes to the tone circuit.

[Electron Tornado]

** Mark beat me to it, but here's my 2 cents,

If I recall, the difference between the Boss SD-1 and a Tubescreamer is a few component values and an extra clipping diode in the SD-1 for asymmetric clipping.

SD-1 schematic.....
http://cdn.tonegeek.com/wp-content/uploads/51.jpeg
http://www.hobby-hour.com/electronics/s/schematics/boss-sd1-super-overdrive.gif

Referencing those schematics - if you build the SD-1, leave out C6 for a better, clearer tone. Get yourself a toggle switch and you can select between symmetric and asymmetric clipping.

[JohnForeman]

thanks guys.  So tonepad is making the statement about the SD-1 based on the clipping?  That's the assumption that i was making, but figured i better check.

[Mark Hammer]

The Tube Screamer includes a 51pf feedback cap in the clipping stage that trims top end as the gain is increased, reaching a  (5.6khz rolloff at max gain).  That keeps the fizzies out of the output.

The SD-1 uses a fixed filtering effect, via C6, rather than a sliding rolloff, the way the TS does.  That may well be a smarter approach since the degree of treble-trimming you'd want when the Gain pot is up halfway would result in too dull a sound at higher gain.  (A 51pf feedback cap in the clipping stage would roll off around 3khz at max gain).

Note as well that the SD-1 uses R7/C4 to roll off mids and treble slightly higher up than the TS9 does (it uses a 1k/.22uf pair to roduce a 720hz rolloff, rather than the 880hz rolloff the D-1 produces).

[HOTTUBES]

I don't know all the technical numbers like you Mark , but i always found the SD1 to have more " Hair " than a TS9 etc ...

[Electron Tornado]

The Tube Screamer includes a 51pf feedback cap in the clipping stage that trims top end as the gain is increased, reaching a  (5.6khz rolloff at max gain).  That keeps the fizzies out of the output.

The SD-1 uses a fixed filtering effect, via C6, rather than a sliding rolloff, the way the TS does.  That may well be a smarter approach since the degree of treble-trimming you'd want when the Gain pot is up halfway would result in too dull a sound at higher gain.  (A 51pf feedback cap in the clipping stage would roll off around 3khz at max gain).

Note as well that the SD-1 uses R7/C4 to roll off mids and treble slightly higher up than the TS9 does (it uses a 1k/.22uf pair to roduce a 720hz rolloff, rather than the 880hz rolloff the D-1 produces).

It would be simple to add a cap in parallel with the clipping diodes similar to the TS, and see how it sounds. I found that removing C6 from the SD-1 was a significant improvement. Removing C6 got rid of some dullness. When modding the SD-1, be careful of how much you try to boost the gain as well, or it will start to sound brittle (IMO).

[Mark Hammer]

I don't doubt that it will remove some "dullness", but whether that's a good thing will be determined by context. 

A guy came over to the house last night to try out and buy a couple of pedals.  I had put them through their paces and tweaked them using my standard 2W battery-powered amp with 6" speaker. He tried them out using a single 12" cab I had made with an old Jensen being driven by my 5W tweed Princeton with the tone set to full treble.  The speaker removed  every smidgen of harshness (and even some sizzle), making everythng sound warm, chewey, and throaty, with none of the potential for harshness I would get on the smaller amp/speaker.

I mention this because C6 might be exactly what a person wants/needs if the unit is set for max gain and played through a system capable of extreme brightness.  Played through something that warms stuff up, though, removing C6 may be critical to getting the right amount of definition.

[HOTTUBES]

I don't doubt that it will remove some "dullness", but whether that's a good thing will be determined by context. 

A guy came over to the house last night to try out and buy a couple of pedals.  I had put them through their paces and tweaked them using my standard 2W battery-powered amp with 6" speaker. He tried them out using a single 12" cab I had made with an old Jensen being driven by my 5W tweed Princeton with the tone set to full treble.  The speaker removed  every smidgen of harshness (and even some sizzle), making everythng sound warm, chewey, and throaty, with none of the potential for harshness I would get on the smaller amp/speaker.

I mention this because C6 might be exactly what a person wants/needs if the unit is set for max gain and played through a system capable of extreme brightness.  Played through something that warms stuff up, though, removing C6 may be critical to getting the right amount of definition.

Interesting point !!

i guess one could put another switch inside the SD1 to have 2 different cap values in the C6 location ...
I myself like the C6 cap removed , but i have always liked a brighter tone ... but some players my not .