"Two-Channel" Tubescreamer Complete

[sta63bmx]

I finally finished this pedal AND got it pop free.  It's really handy. 



This is a poor quality shot of the top with temporary dymo labels.  Two drive knobs, two level knobs, master tone control, and then a clipping diode switch and a "more treble" switch.  Second footswitch for the boost.



Here's the guts.  I used ribbon cable for almost all the hookups.  Here the boost footswitch is on the left, on/off is on the right.  I just put some tape over the bottom of the board to rpevent shorts, since I didn't want to drill or glue in standoffs.



More guts.  I had enough room with the ribbon cable.  It is a little more compact than single conductor wire for the pot wiring, especially.



More guts showing the pots.

The way I implemented this way to start with a regular old TS-808 clone, and then do a couple of mods.

1. Symmetrical/asymmetrical clipping, all silicons.  Symmetrical is a little smoother.  This is pretty subtle.

2. More/less treble.  This switches the 4.7k resistor to a 1k resistor on the opamp input.  You can definitely hear this one.  The Walsh setting is more treble with the 1k.  It has a ton of high end that way, not quite as smooth.

3. Volume boost.  I put a 1M pot in series with the regular 100k volume pot.  I figured I'd go up an order of magnitude for "twice" the possible volume.  I think I used log taper.  The pot is just wired as a variable resistance so I'm really only using two lugs.  THen there is a jumper in parallel with this pot.  The jumper is footswitchable.  When the jumper is switched out, the "volume" resistance is the 1M pot setting plus the 100k pot setting, which gives the boost volume.  When the jumper is switched into the circuit (back to the normal channel) it shorts around the 1M pot and goes back to normal volume.

4. Drive boost.  I put a 1M pot in series with the regular 500k drive pot.  I can't remember what taper.  THe pot is wired like the other one as a variable resistance, using two lugs.  That pot is in parallel with the regular 51k resistor in the original schematic.  When the boost channel is engaged, the 51k resistor is switched out, and the drive resistance is the 1M setting plus the 500k setting.  When the boost is turned off, the 51k resistor is switched in parallel with that pot, effectively making it a 51k resistor plus the regular 500k drive pot setting.

The boost footswitch (on the right on top view) just engages more volume and more drive and lights the boost LED.  These mods are really, really simple, but make for a nice lead boost.  The only thing I don't like is that the boost and normal channels aren't fully independent.  But if you're gonna switch on a boost, shouldn't it be "more" anyways?  If you turn the boost channel volume all the way down, then there is no change in the volume resistance when you switch channels.  If you turn the boost drive all the way down, you get a tiny bit less OD on both channels, since the 51k resistor is switched out and you have a zero resistance there.

The only part that's a bit tough to tame is that if you crank the boost drive, the volume shoots up by default, since you have a lot more gain in that stage.  And you can't have less volume with these mods than you have on the normal channel.  But it's not the end of the world. 

So the pedal essentially becomes a two-channel tubescreamer with a normal channel and a lead boost.  Lots of high end, and a pretty transparent pedal.  It still sounds "like a pedal" but it's useful.  Doesn't seem to be quite as smooth as the TS-808 reissues.  Normal channel has a little less drive than one of them, but more high end, I think.  I used all metal films and then all poly film and mica caps as called for, no tantalum anywhere.  I can't remember if this one has the reiusse JRC4558 or a TI4558.  It's a pretty useful pedal.  SOunds best into a good tube amp.

PROBLEMS: If you try to do that switching by having 51k OR the 1M pot (for drive) and having the jumper OR the 1M pot (for volume) you are asking for a nasty pop.  I had a horrible pop until I went to doing the jumper and 51k resistor in parallel.  I think trying that OR switching in the high gain part of the circuit is asking for pop issues.  This sounds the same and is pop free. 

[petemoore]

  That's a whole lotta TS for the box size. 
  Flexability...a bit more work up front...
  Moddability...more work down the road...less instantly flexible.
  Hopefully, That should satisfy your TS's needs. Looks like it was 'tightwork', getting it 'all in' and working right.

[sta63bmx]

I was lucky in that I built a less attractive version in a steel box first.  I used fixed values for the drive boost and volume boost and the OR switching that didn't work so well in the nice pedal.  This one didn't pop, for some reason.  Better switch?  Oh well.  Here's "that one".  This one is kind of like the less-attractive friend who doesn't get asked out.



Outside shot.  I had it built as a regular TS clone before I decided to add the boost.  The footswitch and second LED were just slapped in there without measuring or anything.  I mean, not that you can tell from the precision engineering...



And the guts.  I know it has a trimpot, but I just used it as a fixed resistor since I didn't have a 1M resistor when I got the idea for this mod.  Mostly solid-core wire except the black/green pair. 

These steel-stud enclosures are just the greatest thing ever for this sort of thing.  I was too lazy to make mine "nice" but they're surprisingly solid.  I built about ten this winter and have yet to use them all.  This pedal is pretty crude, but still very useful.  It'll be kind of hard to make changes to the finished Walshinator later on, but I left enough ribbon cable that I can pull the board out and get to it.  I am leery of jacking around with ribbon cable like that, but I tried to solder quick and keep it from wicking up the cable.  It was easier to make it fit if I left the board free to "float" on the wiring.  I usually just velcro the battery to the inside of the case.  I also had a lot more room in my steel enclosure.

And that switch will make sound EXACTLY like Billy Gibbons or Joe Walsh, because I used point-to-point wiring, all carbon film resistors, a vintage JRC4558 chip that I received from the emperor of Japan himself, and I used cloth-covered wire (the cloth is hidden under the rubber) and Class A circuitry to uh...change the flux capacitor in uh...nevermind.