SD-1 Blend Pot

[seanm]

I want to try adding a blend pot to my SD-1. Actually, I want to add a blend to a Fulltone, but it is not here yet and the SD-1 is

I think I can just add a pot before the level pot, but I wanted to check the collective wisdom of the forum before trying it. Does anybody see any problems with this idea?

I have shown the mod in light blue.

[G Kresge]

I can't view the pic, but I'd love to find out if it works, because I've been wanting to do that on an SD1 and a BD2 myself.

[airhole]

i think u need to add a buffer of sorts, else the signal get fed back into the loop. and it doens' t act as a blend.

cheers,
george

[Mark Hammer]

i think u need to add a buffer of sorts, else the signal get fed back into the loop. and it doens' t act as a blend.

cheers,
george

Ah, now that may end up being part of its charm!

[seanm]

I can't view the pic, but I'd love to find out if it works, because I've been wanting to do that on an SD1 and a BD2 myself.

Can you see the schematic now?

[seanm]

i think u need to add a buffer of sorts, else the signal get fed back into the loop. and it doens' t act as a blend.

cheers,
george

I never thought of that

[seanm]

Ok I updated the schematic to add a buffer to the dry loop. I think it will be easier to just bypass the current input buffer and add my own. This will give me a better input impedence and make the mod easier to add to the board.

I also am going to try putting the blend *outside* the level control. My thinking  is that you can use the volume control on the guitar for the dry signal level and the gain/level to control the wet gain or cut.

Comments appretiated!

[G Kresge]

I can't view the pic, but I'd love to find out if it works, because I've been wanting to do that on an SD1 and a BD2 myself.

Can you see the schematic now?

Yes, but I can't help with any suggestions. I can sort of figure out schematics, but I don't know how it all works very well.

[seanm]

I have tried it. First I should mention I had previously performed a "fat mod". I replaced the .047u cap (circled in red on the schematic) with a straight wire. I am also using a passive P bass.

The effect is much like the drive knob. The more wet signal, the more distortion. I so far haven't noticed the fattening of the distortion that I hoped for. Remember, this is at low volume levels.

The input buffer change seems to have really made a difference. Even with the effect bypassed I used to get slight distortion on the E string. This seems to be gone. I also think the sound is less "compressed", but again I would like to A/B it.

By turning down the drive and picking a mainly dry blend, you can get a very subtle overdrive. However, at really low settings you get the weird effect that distortion goes down as playing intensity goes up.

If I where to attempt this full time, I might try removing the drive pot and leaving it wide open. Then replace the drive with the blend.

[airhole]

sounds good!

can't wait to get my hands on a SD1 to try it! =)

[MR COFFEE]

Try hanging a load resistor from the wiper of the Blend pot to 4.5 volts so the blend control willl have a load and can do it's job better. Make it between twice the pot value and half the pot value. set it by which sounds best at both extremes AND in the middle. DO disconnect the output level control. You may, but probably don't, need to put some gain in the clean signal. OR you may need to attenuate it with a resistive divider before the Blend pot.

Enjoy

[seanm]

Try hanging a load resistor from the wiper of the Blend pot to 4.5 volts so the blend control willl have a load and can do it's job better. Make it between twice the pot value and half the pot value. set it by which sounds best at both extremes AND in the middle. DO disconnect the output level control. You may, but probably don't, need to put some gain in the clean signal. OR you may need to attenuate it with a resistive divider before the Blend pot.

Enjoy

I tried the load resister, but it didn't seem to help much. Removing the level control is a problem because the blend and  gain interact to change the volume. My blend pot is currently 50K if that matters.

So where to physically put the blend pot? There dosen't seem to be room for another pot. I thought out the side, but there is no room. Maybe stacked pots ala ODB3? Where do you get stacked, non-stereo, pots?

My other idea is to change the tone control to a "bright" switch and replace the tone with the blend. I think there is room for a small toggle.

Anybody have some other ideas?

[yano]

What if you buffer the output of the circuit before it goes into the blend control?

[MR COFFEE]

HI Sean,

Yeah, 50K matters. You probably don't get a lot of useful variation like that either, right?

If you don't mind losing an output volume that is externally available (usually a set and forget in most of my experience), you can lose your new pot and simply use the 10K volume pot as your Blend control to add in some more straight signal by tying the end that is now connected to 4.5 volts to the output of your clean signal buffer (though the cap you are already using, of course). I suspect you will want that load resistor hanging off the wiper, though. You can make it your set-and-forget volume control by using a small 10K trimpot with 4.5volts for the bottom end, and take the output to the Jfet switching circuitry from the wiper.

You do realize that your circuit already adds in some of the straight signal already by virtue of the fact it is a non-inverting clipper stage, right?

The improvement you get will be fairly subtle, not drastic, and will not be evident at all drive settings. With low amounts of overdrive, you should be able to get some sounds in the tweedy ballpark, with the blend set right. You can also improve the sound of the circuit (to my ears anyway) if you add some EQ in the clean signal path. I've built a few like that that sounded good to me. Gets a range of pretty natural overdrive sounds.

If you want even more straight signal for a very mildly overdriven sound, you could put some gain in your buffer circuit output - maybe x2, while you're playing around with the EQ. There's a lot that can be done with this general circuit IMHO.

[seanm]

Finally got back to this. And my conclusions? I think I will try making an external blender with proper levels for both sides. Just too many knobs for the SD-1.

However, I still think the opamp is a great replacement for the stock transister in the input buffer.

[G Kresge]

What about losing the "Tone" control knob, replacing it with a fixed value resistor, and using the vacant pot location as the blend knob?

[seanm]

What about losing the "Tone" control knob, replacing it with a fixed value resistor, and using the vacant pot location as the blend knob?

I actually tried that. Worked well. I thought of adding a switch so I could have a "treble boost". The problem is, I use the SD-1. So I had to keep putting it back togeather for practice.

I am now looking at making a Bass Blender pedal. I think this is a more gerneric solution. I am still in the prototyping stage.

[G Kresge]

Hmm... too bad you don't have an extra one on deck to experiment on. Maybe you could get a cheap one on eBay? If I knew more about this stuff, I'd try it and let you know how it works out, but I don't have the confidence to try it and risk irreversible damage to one of my boxes.

[Claus H]

Delete

[seanm]

If you are interested in this, you might be interested in the "B. Blender" thread I just started.

One outcome of the B. Blender is that, after testing, I like the blend at 50% with the SD-1. This gives me the overdrive, but keeps a lot of bottom. So I may still try modding the pedal, but with fixed resistors rather than a blend pot. Or maybe a switch that turns the blend on or off.