Switchable TS to SD-1 Mod?

Paul Marossy · November 11, 2007, 02:11:09 PM

Since the Boss SD-1 and Tube Screamer are nearly identical circuits, I had an idea to take my TS-808 clone and add a switch to it to make the output level pot a 10K vs. the std. 100K output level pot. I suppose while I was at it, I would have to add a diode in the feedback loop as well. That would effectively make it an SD-1, right?

Anyone ever try this? If so, is it worthwhile?

JHS · November 11, 2007, 02:27:36 PM

Got to your local music store and check out a TS and a SD, they sound way different.

Adding a diode and doing the output mod will not turn a TS into a SD, all you'll get is something like a asym. clipping TS9.

JHS

Paul Marossy · November 11, 2007, 02:58:22 PM

Huh, I guess you can't take everything you read at face value. According to this page, they are very close to the same circuit: http://users.sa.chariot.net.au/~gmarts/ampovdrv.htm

Mark Hammer · November 12, 2007, 11:22:08 AM

One of the principal differences is certainly the 3 vs 2 diode clipping network, and another is the maximum gain of the clipping stage. However, there are also some differences - quite a few in fact - in the filtering provided by the one vs the other. The gain stage in the SD-1 has no feedback cap to reduce the highs at higher gain settings. The tone stage does have a feedback cap, unlike the TS-9. The lowpass filter after the gain stage and before the tone stage has a different corner frequency. Consequently, switching the one over to the other would appear to be more than simply what you could accomplish with a single change here or there built into one toggle.

On the other hand the difference between having more vs less gain is easily compensate by using a 1M gain pot and not turning it up so high, and the 2 vs 3 diode thing is a no brainer. These will undoubtedly produce discernible changes, though whether they capture the total mojo of the SD-1 is another matter.

Paul Marossy · November 12, 2007, 11:39:20 AM

I took a few minutes to compare schematics, there are a lot of differences that I didn't notice before. I just did a real quick glance at the the two the other day. The schematics look a lot the same, but that is where the simillarity ends.

In any case, it gives me some ideas to play around with...

yeeshkul · November 12, 2007, 12:23:31 PM

Guys does the sym/asym clipping sound really different? I made this mod on my TS clone and can't hear much difference. Just really slight one.
Same for the TS8080/TS9 mod - very very slight difference in the sound.

StickMan · November 12, 2007, 12:30:32 PM

The two circuits are similar, but technically not "identical". That being said, the they both use a 4558 op amp with clipping diodes in the feedback circuit which is going to give a sound which is in the same ballpark.

The SD-1, however, is a $50 pedal with a number of issues "out of the box", that make it pretty much only a $50 pedal unless you do some mods. These are widely documented and extremely easy. Once done, the SD-1 is actually a pretty awesome pedal.

If you go a step further, you can add some switches to the SD-1 and make it an extremely versatile pedal, including a pretty good sound-alike for a TS. Currently, I've got mine set up to allow you to switch between germanium and silicone diodes which adds a huge amount of versatility to the unit. At low drive levels, the germanium diode is softer, warmer and buzzier than the silicone (and sounds better in my opinion). At higher drive levels, the silicone diode adds a lot of bite, high end and better definition to the notes.

As to comparisons with the TS. I've got a stock TS-10 which sees very little action since I modified my SD-1. I've played them side by side, and they are pretty comparable sounds.

From what I remember, the two diode circuit of the asymmetrical clipping on the SD-1 is rigged with the diodes in a parallel. This makes it super easy to cut out one of the diodes and turn it back into symmetrical clipping. I'd also be tempted to drop the whole parallel thing entirely (by simply removing one of the diodes) and then rig up two mini switches with one, two or no diodes of the same type and then run them in series. That would let you have the option of running symmetrical or asymmetrical, with a huge variety of diode combinations.

I spent hours farting around with the diodes on mine. I tried a bunch of different types in different combinations, and also tried MOSFET's and LEDs too. Eventually I stopped out of exhaustion. That was a while back, I'll probably try again soon.

Paul Marossy · November 12, 2007, 12:46:42 PM

The sound clips of the DS-1 at Musician's Friend don't sound that bad to me. For that price, I may just buy one.

StickMan · November 12, 2007, 01:56:45 PM

DS-1 or SD-1?

I can't imagine why anyone would want to emulate an SD-1. On the other hand, the SD-1 is basically good circuit, very close to a TS-9, easily modifiable to sound great and comes in a very solid Boss enclosure with a good switch, pots and jacks. All for $50.00!!!!!

So if you've already got a TS type distortion, and you want to make if more versatile or sound better; then fiddle with it. If you want to leave it virgin and are looking for a cheapo starting point to see how much the sound changes when you fiddle with the circuit, then buy an SD-1.

Paul Marossy · November 12, 2007, 01:59:07 PM

QuoteI can't imagine why anyone would want to emulate an SD-1. On the other hand, the SD-1 is basically good circuit, very close to a TS-9, easily modifiable to sound great and comes in a very solid Boss enclosure with a good switch, pots and jacks. All for $50.00!!!!!

Sorry, I meant SD-1. And I think you meant DS-1 in your first sentence.

I'm sick today, my brain is only firing on half the cylinders that it normally is...

StickMan · November 12, 2007, 02:25:24 PM

No, I really meant SD-1.

Out of the box, they really do sound like a $50 pedal. Spend an 1/2 hour with a soldering iron on the insides, remove one capacitor, replace a couple others, swap out the op amp and I think two resistors and it sounds pretty damned good. But then it's not an SD-1 anymore, is it?

Paul Marossy · November 12, 2007, 02:35:59 PM

OK, I follow you now.

MetalGod · November 12, 2007, 02:40:03 PM

There are cap value differences that make them sound quite different imo - then theres the tone network cap and resistor.

Paul Marossy · November 12, 2007, 02:42:38 PM

Yeah, and the gain control network is also different. I can see why they would sound different from eachother.

StickMan · November 12, 2007, 03:10:25 PM

Yeah, but they don't sound that different.

Mark Hammer · November 12, 2007, 03:13:04 PM

Quote from: yeeshkul on November 12, 2007, 12:23:31 PM
Guys does the sym/asym clipping sound really different? I made this mod on my TS clone and can't hear much difference. Just really slight one.
Same for the TS8080/TS9 mod - very very slight difference in the sound.

The TS-9 -> TS-808 mod (at least the output part) is one that results in a different output load so how it sounds will depend on what you're feeding it to, and the cable that takes it there. The extra diode is a mod whose audibility will depend on how you play. One half-cycle will sound absolutely identical, whether it's a TS9 or SD1. The other half-cycle will clip only when the signal for that part of the half-cycle is somewhat higher amplitude. You may only notice that at the initial attack of the note.

StickMan · November 12, 2007, 04:05:39 PM

Quote from: Mark Hammer on November 12, 2007, 03:13:04 PM
Quote from: yeeshkul on November 12, 2007, 12:23:31 PM
Guys does the sym/asym clipping sound really different? I made this mod on my TS clone and can't hear much difference. Just really slight one.
Same for the TS8080/TS9 mod - very very slight difference in the sound.
The TS-9 -> TS-808 mod (at least the output part) is one that results in a different output load so how it sounds will depend on what you're feeding it to, and the cable that takes it there. The extra diode is a mod whose audibility will depend on how you play. One half-cycle will sound absolutely identical, whether it's a TS9 or SD1. The other half-cycle will clip only when the signal for that part of the half-cycle is somewhat higher amplitude. You may only notice that at the initial attack of the note.

The asymmetrical clipping is supposed to sound more "tube like", because that's what tubes do. Personally, I'm not sold that "tube like" distortion is a worthwhile goal for an SS stompbox. I think you're better off looking for a sound that you like, whether or not it resembles some other device.

My general observation from flipping around diodes in the SD-1 for hour on end was that the types of diodes that you use make a big difference, but the number of them placed in series or parallel, and whether or not the clipping was symmetrical or not were relatively subtle tonal changes. In the end, I left the stock silicone diode in one side and put a single switchable silicone and germanium diode on the other side. The choices from the switch were then: a) symmetrical silicone or b) asymmetrical with a silicone in one direction and germanium in the other.

I put a second switch in to control resistor values in another part of the circuit, but that's turned out to be a bust. Since I've already got the hole drilled and a switch in it, I'm probably going to go back and add some more diode choices with the second switch. That will mean another afternoon frittered away trying to see if I can hear any difference in between soldering practice.

yeeshkul · November 12, 2007, 05:50:40 PM

thank you for explaining my slightely out of the topic question

solarplexus · November 13, 2007, 12:25:30 AM

I used to mod the SD-1 like crazy. One mod I did to all the ones I had modded (I use to buy them, get tired of it, realise how dumb I was to get rid of it, get another one, you know the drill), I ALWAYS replaced D6 (if I remember right) with a germ diode to give a that kind of compressed tightness before the two other silicon diode, which I modded almost all the time to 1N4001 diodes instead of 1N4548. I always felt it gave way better overdrive. As for the cap values, I didn't tinker that much with them, except the tone pot cap and the input cap to have a little more bass. I love the SD-1 but right now I use my peppermill with to parallel diode wired to a ON/OFF switch and a TS808. If you do a search I did do one comparison of mods to a OD-3 and a SD-1:

http://www.diystompboxes.com/smfforum/index.php?topic=43460.msg315217#msg315217

They are not similiar circuits, but they both have some overall qualities that I liked. Check it out.

vanhansen · November 13, 2007, 05:20:22 PM

The SD-1 and TS-9 (and 808) are the same circuit with the main difference (design wise) being the asymmetrical versus symmetrical clipping. There's almost 20 part differences (value wise) between the two. I went through and changed my SD-1 to TS-808 specs and it sounds WAY different now.

Just changing the output stage and removing D6 doesn't do it (or with the TS-9, adding a diode and changing the output stage). There's a lot more involved. You'll get some flavor in there so you may be able to make it where only a few parts are changed with a switch on a daughter board or something.

News:

Switchable TS to SD-1 Mod?