Keeley may be on to something...

[jimijames]

Ok, so I modified a SD-1 I got off the bay to lovepedal eternity specs (well, close enough anyway), and it does sound very good, but I did have a few problems with it - to start off it doesn't have the body that my other sd-1 has, and it isn't as smooth.

Enter an OC44 transistor I took out of my BYOC tri-boost (I thought I had fried it b/c of the way the treble booster sounded). The Keeley 5 star Ge mod has a germanium PNP tranny installed in place of D6 (collector taped off, base as cathode, emitter as anode), so I figured I'd try it in the lovepedal sound-alike.

Man, what a difference one part can make. The tranny filled out the sound, brought the distortion closer to the way a treble booster sounds, (but without changing the eq so radically) and made the upper register sing much better than it used to.

Because of how drastic the improvement was, I installed an OC75 in my other SD-1 to see if the result would be similar. The pedal is a lot more compressed, but the improvement was along the same lines - the distortion sounded more natural and closer to what a treble booster produces, the pedal kept it's clarity, and overall, just sounded better.

Now I just have one last question: Would changing the pots reduce the compression I'm experiencing in the second pedal? I really really like the Lovepedal version, and I think it's because it is so much less compressed. It uses 100k pots for the level and gain, I was curious if making the same switch will help the other SD-1?

But yeah, if you don't like the way your SD-1 sounds, try installing a PNP germanium transistor in place of D6. I must say though, that I didn't do this in an otherwise stock SD-1 - both of the pedals I performed this mod on were already extensively modified.

 

[ratherdashing]

Re: Keeley may be on to something...

The compression you're hearing is coming from your clipping section. It's quite likely that the Ge transistor you stuck in there is choking on the hot signal being fed to it through the SD-1's feedback loop. This is quite common with Ge diodes in a clip section too. Usually I balance a Ge diode with a pair of beefy silicon diodes (1N4001 is perfect for this) so that it isn't too squashed.

Reducing the value of the drive pot and increasing the value of the level pot would reduce compression, but it will also reduce distortion. The schematic I have for the SD-1 shows the drive pot being 1 meg and the level pot being 10k. If you don't want a really drastic change, you could try replacing these with TS-808 pot values, which are 500k for drive and 100k for level. For a very subtle change, replace the 33k resistor connected to the clip section (don't know the ref ID, sorry) with a smaller value, like 10k or 4.7k. Personally I think 100k for a drive pot would be too low, but there's no harm in experimenting.

Good luck, and let us know how it goes.

 

[jimijames]

Re: Keeley may be on to something...

Ah, I see. The diodes I have in there right now are actually LED's, so they actually are already pretty beefy (I think...) I don't think I'd mind if the distortion is reduced as long as the compression is reduced as well. I finally learned how to use a breadboard to prototype different clipping circuits, so I think I'll probably use one to test out different pots to see which one sounds the best. I'll try the ts-808 values first, and if it's still too compressed, then I'll move on to dual 100k pots.

The reason I have 100k's in the other SD-1 is because that's what the modification instructions called for, so that's what I went with and they do make a big difference. I heard the pedal both before and after installing them, so I do realize that there will be quite a drastic reduction in the amount of distortion, but that's something I can live with as long as the pedal sounds great otherwise.

I'll also try changing the resistor connected to the clipping section - although I think the modification I've done on the pedal already calls for it to be changed, so I'll look into that. I do have a bunch of carbon comp 10k resistors - unfortunately, I've recently learned that the only audible difference between a carbon comp and a regular resistor occurs when enough current is moving through that resistor to cause the resistor itself to distort - this is why they sound great in amps, but don't really make a big difference in pedals. Or at least that's what I've heard after reading around about carbon comp resistors and why they're regarded as magic.

What's kinda funny is I've recently come to the realization that while I really enjoy messing around with the tubescreamer circuit, it probably would have saved me a lot of time to just get the FTL drive. The reason is that I primarily fiddle with the clipping section and the op-amps (beginner stuff, I know), and the FTL drive allows you to change the clipping with the twist of a knob - which is a whole lot easier than busting open a perfectly good SD-1.

Although, even if I had got an FTL drive, I'd probably still have messed with it just as much, so it's just as well that I can do it on cheapo SD-1s than on a nice boutique-quality overdrive.

Anyway, I'll post about how it goes once I get everything swapped out, and hopefully this will get the pedal to sound nice enough for me to part with the SD-1E. The only reason I got the second SD-1 was because I was itching to try out the Eternity mod that Rich_S liked so much, and now it sounds so good I can't really bear to part with it. The first SD-1 that I modified has so much patchwork holding it together that I can't really sell it with a clear conscience, so right now I'm trying to get it into the same ballpark as the SD-1E.

 

[Chaos]

Re: Keeley may be on to something...

Note:
"Tranny" is slang for a transformer not a transistor
That said, I don't know anyone who would abbreviate transformer "tranny", instead they would use "xfrmr"

 

[ratherdashing]

Re: Keeley may be on to something...

LED's have a ton of headroom, so that makes sense that the Ge transistor would sound super compressed compared to those.

White LED's have even more headroom than red. When I was prototyping the FTL, I tried a pair of white LED's as a clipping section. They give HUGE distortion, and could almost be used in metal I think. It reminded me of a Dual Rectifier.

As for the carbon comp resistor, it probably won't make too much difference in that position.

 

[jimijames]

Re: Keeley may be on to something...

Note:
"Tranny" is slang for a transformer not a transistor
That said, I don't know anyone who would abbreviate transformer "tranny", instead they would use "xfrmr"

My mistake, I had heard transistor referred to informally as tranny here, and so I thought it was a common abbreviation. I will make sure to spell it out from here on out to avoid confusion.

edit: RD, the LED's that I'm using in this are clear 5mm ones that give off a red light. A nice thing about them is that they retain most of the detail when they're distorting. I also installed a 47pf cap in parallel with the second one in the circuit (D5) to help smooth out the top end, but to my ears it doesn't make a huge difference. I may actually change them to plain old tube screamer diodes or germanium diodes once I have the 100k volume and 500k gain pots installed.

Actually, something that's weird about germanium diodes - I tried them out while I was trying different clipping circuits, and they have almost no distortion in the SD-1, even with the stock 1 meg gain pot. However, they don't have the huge amount of volume of an LED either, so I would like to get them in a higher-powered circuit to see how they sound distorted. Even with the third diode replaced with a transistor, the pedal was still barely distorted - In fact I'd say it was closer to a booster than an overdrive with that setup.