How to refine the Son of Screamer ?

[HOTTUBES]

So ... if your pretty much a noob like me , how do i figure out what components are the same on both of these layouts ?




Thanks for any help !!

[rockhorst]

By looking at two pictures that tell the same story: one is a schematic, the other is a layout. Good exercise is to make a schematic from the renegadrian layout. It should roughly amount to cutting off the in- and output buffer and the bypass switching and maybe some component changes (for unbuffered biassing of the signal). So see if you can verify for yourself that this is about it:

(very rough cutting, not 100% accurate and some traces missing...that's the exercise. Just start at the input and follow along, see what you get).

[HOTTUBES]

i have gone through these both a few times , but i'm still having some stress understanding what components are common to both layouts etc ...

As you see both have a C1 cap of .047uf .... but the C2 cap in the Vero is not the same function as the C2 cap in the SD1

[earthtonesaudio]

on a slightly different tack. one thing i don't understand about the ts is why the emitter followers have their bases biased from the 4.5V line.
i guess it doesn't matter on the original circuit much, but with diode mods it means less headroom and the output buffer may also clip when diodes' clipping thresholds and gain are up. and ugly clipping that will be.

It's because the original TS was not designed to be modded. It was designed to be as inexpensive as possible to build while meeting its performance objectives with the stock/no mods circuit. I suspect the original designers had no clue that cloning would happen or that it could possibly be as pervasive as it is today. If they did, I want to hire them as prophets. 

You could bias the emitter followers at 4.5V plus V_BE and get that headroom back.  But if you A/B compared the two you might decide it's not worth the effort.

[rockhorst]

@Hottubes: oh wait, it's a SD1 schematic you posted. Get a TS808 schematic (it's not called son of screamer for nothing). In the SoS layout you referenced the first 47n is the input cap, the second one is in the feedback loop of the first opamp stage. Together with R4 it sets the 'mid hump' frequency of the TS. On the SD1 diagram it's C3 and R6. Those two components are worth messing with (lower R4 for more gain for instance (but also a higher frequency), higher capacitance lower frequency (so you can compensate the lower resistor)).

[HOTTUBES]

@Hottubes: oh wait, it's a SD1 schematic you posted. Get a TS808 schematic (it's not called son of screamer for nothing). In the SoS layout you referenced the first 47n is the input cap, the second one is in the feedback loop of the first opamp stage. Together with R4 it sets the 'mid hump' frequency of the TS. On the SD1 diagram it's C3 and R6. Those two components are worth messing with (lower R4 for more gain for instance (but also a higher frequency), higher capacitance lower frequency (so you can compensate the lower resistor)).

Ok !   i see it now ....

I like the idea of lower the R4 resistor cause to my ears this SOS layout is all Bottom end heavy !
I understand it will increase the gain , but for the sound i'm looking for i think it's needed  !


Thanks for the Help !!

[rockhorst]

Check the drive pedals I mentioned earlier to get some interesting ideas for that part of the feedback loop! Really worth messing with.

[HOTTUBES]

The one i have built before that i really liked was the Lovepedal Eternity , the highs were just a touch crazy , but tamable ( if that's a word ha !)

Klons are nice as well !

[rockhorst]

The Eternity really is a SoS, with 1k and 220nF for the resistor and capacitor to soup up the gain. Check out the ZenDrive Voice control if you want more flexibility.

[HOTTUBES]

But it seems to have a very bright top end to it .....and that's what i liked about it !
How would i go about getting that bright top in the SOS .... ? copy the cap / resistor combo from the Eternity ?

[ubersam]

http://i1085.photobucket.com/albums/j431/onflooraudio/boss-sd1-super-overdrive.gif



So ... if your pretty much a noob like me , how do i figure out what components are the same on both of these layouts ?

I was bored at work so I took a crack at it. Here's what I came up with, the SoSD1:

[HOTTUBES]

http://i1085.photobucket.com/albums/j431/onflooraudio/boss-sd1-super-overdrive.gif



So ... if your pretty much a noob like me , how do i figure out what components are the same on both of these layouts ?

I was bored at work so I took a crack at it. Here's what I came up with, the SoSD1:

Dude !!

You Rock !!

Thanks for taking the time !!

[HOTTUBES]

1.  If you play with the values of C5 and R7 , what would the net results be to the tone ?

2.  If you lower the R4 resistor to 1K , is there a different clipping diode that would work better in that case ?
     or does it not really matter ??

3.  How do you make the Volume pot more accurate etc ... i find the gain of the pedal does not get going until 75% .



Thanks for any help !

[Kesh]

1. It will turn into a Boss SD-1. Almost.

2. If you change R4, you will change the tone of the circuit, as well as the gain of the clipping section. If you want to just change gain, then do the opposite to C2 that you do to R4.

With regards to diodes. If you increase the gain (without clipping) by dropping R4, then the sound will be clipped by the diodes at quieter input levels. You could then up the clipping threshold by using something like LEDs, resulting in a similar input level threshold before clipping as before, but with the (supposedly) different sound of LED clipping. You have less headroom to play with though before the op-amp gets overdriven, and the output will be louder.

3. I'm confused whether you mean gain or volume pot. But swapping Log for Lin may be an option.

If it hasn't been recommended already I suggest you read RG's excellent article http://www.geofex.com/article_folders/tstech/tsxtech.htm

[Kesh]

Hey I just noticed. The schematic first on this page IS an SD-1, not a Tube Screamer.

[ubersam]

Dude !!

You Rock !!

Thanks for taking the time !!

You're welcome

[ubersam]

Hey I just noticed. The schematic first on this page IS an SD-1, not a Tube Screamer.

Correct. The two circuits are (almost) the exact copy of each other (but with different values and one additional clipper for the SD1). You can build one with the other's layout, like this, for example.

[HOTTUBES]

1. It will turn into a Boss SD-1. Almost.

2. If you change R4, you will change the tone of the circuit, as well as the gain of the clipping section. If you want to just change gain, then do the opposite to C2 that you do to R4.

With regards to diodes. If you increase the gain (without clipping) by dropping R4, then the sound will be clipped by the diodes at quieter input levels. You could then up the clipping threshold by using something like LEDs, resulting in a similar input level threshold before clipping as before, but with the (supposedly) different sound of LED clipping. You have less headroom to play with though before the op-amp gets overdriven, and the output will be louder.

3. I'm confused whether you mean gain or volume pot. But swapping Log for Lin may be an option.

If it hasn't been recommended already I suggest you read RG's excellent article http://www.geofex.com/article_folders/tstech/tsxtech.htm

So if you lower R4 to 1 k , and increase  C4 to .1uf or .15 uf , the gain will increase , but the tone will stay pretty close to the same as it was ?

C5 and R7 , do they play any role in this affair at all ?


Kesh !! Thanks for the tips !!!

[HOTTUBES]

Hey I just noticed. The schematic first on this page IS an SD-1, not a Tube Screamer.

yes , sorry about that , i kinda was misleading everyone !

I was making the comparison that i like the Boss Sd1 sound , and i was interested in trying to get this SOS vero to sound more like the SD1 ....

[Kesh]

So if you lower R4 to 1 k , and increase  C4 to .1uf or .15 uf , the gain will increase , but the tone will stay pretty close to the same as it was ?

You mean C2, yeah?

Changing C2 to 220n, if you drop R4 to 1k, will give pretty much exact same frequency as before. (resistor and cap values follow the same ratios where ever they are on the series - roughly - so 4k7 -> 1k is four steps on the E6 series, so go up four steps on the E6 series for the cap)

C5 and R7 , do they play any role in this affair at all ?

Yes. Like I said, Boss used this circuit but changed a few things, maybe the most significant was the tone control component values. It's somewhat involved so I seriously suggest you read RG's article. Ignore the parts about buffers and switching and just read the clipping and tone/volume sections, and the mod and clone sections, where you will find a schematic of the son of screamer.

If you want SD-1 tone control, change C5 to 27n if you can find it, and R7 to 470R. probably easier to use 22n and 560R. C4 to 18n (again if you can get it) and R6 to 10k. or you could try 8K2 and 22n for easier values to find. Also, for SD-1 sound, leave C2 and R4 alone, but change the gain pot to 1M. Remove C3. Change R8 to 10k and try to fit a 10n in parallel with it. Try and fit two diodes in series for one of the diodes. Or use an LED which has about twice the forward voltage of a silicon signal diode, like IR or maybe red.