Adding a clean blend to an SD-1

[kissack101]

Hey,

A friend of mine wants me to add a clean-blend to his SD-1 for him (I was going to use one of these: http://www.aronnelson.com/gallery/main.php/v/BarcodeVeroLayouts/Vero/BlendimumVero.gif.html)

My question is, is it possible to 'splice' the blender into the boss by-pass circuit so that when the pedal is bypassed, the blend circuit is too?

Any help would be appreciated!

Adam

[kissack101]

I'm using this schem as a guide by the way, I'm assuming it's accurate as the schems from this site tend to be pretty good.

http://www.freeinfosociety.com/electronics/schemview.php?id=169

[fuzzo]

yes, just put the clean signal just after the input buffer (by the way, like that, no need to add another one!) and connect the wipper of the blend pot into the enter of the ouput buffer.

That's simple but the bigger trouble is to find some space to put the pot in the boss box . 

[kissack101]

yes, just put the clean signal just after the input buffer (by the way, like that, no need to add another one!) and connect the wipper of the blend pot into the enter of the ouput buffer.

That's simple but the bigger trouble is to find some space to put the pot in the boss box . 

I'm going to drill a hole in the side of the pedal I think - it will require a small pot but I've done it before.

I've been staring at the schem for the best part of 20 minutes trying to figure out where the 'buffer' ends and the 'pedal' begins, any pointers on that front would be much appreciated...

[geertjacobs]

My attempt:

Start at the input on the top left.
Your input signal passes through one transistor: that's your input buffer
Then your signal can go two ways; through the opamps (that's your overdrive) or down (clean path) straight towards the switching section that is controlled by the flipflop on the bottom.
The switching section is left and right of the two 22k resistors in the middle of the schem.
From the middle out the two 22k's you go to the output buffer

[kissack101]

My attempt:

Start at the input on the top left.
Your input signal passes through one transistor: that's your input buffer
Then your signal can go two ways; through the opamps (that's your overdrive) or down (clean path) straight towards the switching section that is controlled by the flipflop on the bottom.
The switching section is left and right of the two 22k resistors in the middle of the schem.
From the middle out the two 22k's you go to the output buffer

So it pretty much looks like this?:



With the inputs and the outputs of the blender at the red dots?

[let me know if the image is blowing out people's browsers and I'll try to shrink it]

[geertjacobs]

That looks ok, with just one important remark: you need to decouple the guitar signal with capacitors before going to your blender pot.
Otherwise you'll probably have a "crackle okay" effect :-)

How I think it might work if you want to keep the switching:
Put the first dot (outer lug of your blend pot) after the 0.047u cap (towards the clean path)
Desolder the level pot wire from the pcb.
Connect that wire to the other outer lug of you blend pot.
The middle lug of your blend pot then goes to the pcb wire you desoldered the wire.

No idea with the optimum value for your blend pot would be though.

[moosapotamus]

If I could chime in...

I think kissack101 is planning to use the FET version of SeanM's minimal blender, yes? That's the stripboard layout that he linked in the OP.

If you try to use just a pot for a clean blend in this circuit, I'm guessing that you'd get some feedback through the pot and, while it might make some wild, cool noises, it may not end up sounding like the clean blend that you are looking for.

The minimal blender already has an input cap, so attaching the minimal blender's IN to the first big red dot might work just fine.

But if you attach the minimal blender's OUT to the second big red dot (as you've shown it), you will not be switching out the clean blend signal when you go to bypass. The clean output of the minimal blender will still be going to the main output because that point is after the two switching FETs. I think you need to insert the clean signal (minimal blender output) before the switching FET on the right.

So, to be able to bypass the distortion and clean blend together, I think you need to cut the trace between the distortion level pot and the second switching FET. Then you may also need to add a pair of mixing resistors, maybe 10k each, one at the output of the distortion level pot, the other at the output of the minimal blender's level pot. Then tie the other ends of the two 10k mixing resistors together and attach them to that second switching FET (the one on the right).

Doing it that way, the clean signal may still not be absolutely clean (or with any luck, it might be). But it should still allow you to tame the distortion signal with some clean blend no matter how much the drive pot is turned up.

If you want an absolutely clean blend, you might need to replace those two 10k mixing resistors with a buffer, maybe duplicating the main output buffer would work. Or, for example... something like SeanM's B. Blender.

~ Charlie

[kissack101]

So, to be able to bypass the distortion and clean blend together, I think you need to cut the trace between the distortion level pot and the second switching FET. Then you may also need to add a pair of mixing resistors, maybe 10k each, one at the output of the distortion level pot, the other at the output of the minimal blender's level pot. Then tie the other ends of the two 10k mixing resistors together and attach them to that second switching FET (the one on the right).

Doing it that way, the clean signal may still not be absolutely clean (or with any luck, it might be). But it should still allow you to tame the distortion signal with some clean blend no matter how much the drive pot is turned up.

Hey,

Many thanks for the chime, from your description the following seems to be the way to do it? I'll leave it up here for others to use and post once I've done to confirm it.

[geertjacobs]

If you try to use just a pot for a clean blend in this circuit, I'm guessing that you'd get some feedback through the pot and, while it might make some wild, cool noises, it may not end up sounding like the clean blend that you are looking for.

Hadn't thought of that.

Question: shouldn't the clean path have another stage to invert the signal in order to stay in phase with the two-stage distortion path?

[WGTP]

Check out the Sparkle Drive.   

[moosapotamus]

Hey,

Many thanks for the chime, from your description the following seems to be the way to do it? I'll leave it up here for others to use and post once I've done to confirm it.

Well, I think I need to amend my previous advice slightly (sorry)...

That does look pretty much like what I was trying to describe, but there is no way to control the clean level. The input to the blend board looks good, but I think the output (blend) still needs some tweaks. You need to add either a clean level pot or blend pot.

1) Blend pot option
The way the minimal blender scheme is drawn, it would be a wet/dry blend pot... the output from the distortion level pot would go directly to lug 1 of the 50K (linear) blend pot, the line coming out of the blend board that's labeled "BLEND LUG 3" would go to lug 3 of the blend pot, and lug 2 of the blend pot would attach directly to that second switching FET. Leave out the 10K resistors.

I have not built the minimal blender myself, but I'm guessing that it is designed to output unity gain. IOW, with the blend pot turned fully CW you get the dry signal with no increase/decrease in volume compared to the level of your bypass signal. The distortion level pot would, however, still allow you to increase the distortion level above unity. So, if you are looking for a boost when you step on this pedal, you will have to go with more than a 50% blend of the distortion signal for the boost, as the clean level may not go above unity. If you go with less than 50% distortion, you may not be able to get a boost.

2) Clean level pot option
Another way to wire this would be, instead of the blend pot, add a clean level pot in addition to the existing distortion level pot. To do this, keep the 10K coming off of the distortion level pot. Attach the BLEND LUG 3 line coming out of the blend board to lug 3 on an audio taper pot (value not really critical, anything from 100K to 1M should work), attach lug 1 to ground, and attach lug 2 to the second 10K resistor as it is shown. The junction of those two 10K resistors still connects to that second switching FET.

In this case, with the minimal blender, you may still not be able to get more than a unity level clean signal to blend the distortion with. In addition, the clean signal may not be 100% clean either. You may get some mild distortion even with the distortion level pot turned fully CCW. As I wrote above, if that's a problem, you might be able to get an absolutely clean signal by replacing the pair of 10K resistors with another buffer.

Something else to think about... If the minimal blender is not giving you enough output level (boost), you can also try replacing it with the booster of your choice, minibooster, stratoblaster, utility booster, SHO, whatever you like or happen to have the parts on hand for.

Question: shouldn't the clean path have another stage to invert the signal in order to stay in phase with the two-stage distortion path?

I may be wrong, but it looks to me like the signal path through the distortion section is net non-inverting... input to the first gain stage is on the non-inverting input of that opamp, input to the tone section is on the non-inverting input of the second opamp. Yes?

Check out the Sparkle Drive.   

Definately. Good example. If you can't find the Sparkle Drive scheme, try searching "Sprinkle Drive" for the clone version. Replace the tubescreamer section with the SD-1 and there you go...

~ Charlie

[kissack101]

Something else to think about... If the minimal blender is not giving you enough output level (boost), you can also try replacing it with the booster of your choice, minibooster, stratoblaster, utility booster, SHO, whatever you like or happen to have the parts on hand for.

Do you mean a booster in addition to the blend circuit, or will it work by simply splicing the booster circuit 'in parallel' to the distortion circuit, and then using the level control of the booster and the level control of the SD-1 to 'balance' the signal?

[moosapotamus]

Yeah, I mean instead of the minimal blender circuit, try using a similar but different circuit that can deliver more output volume.

[chimpzilla]

Any update of how thsi went ? I'm aboutto add a clean blend to a dirt pedal and was interested in your results.