Diodes in tube distortion box(es).

[Boy Howdy]

A recent discussion on the Black Ice passive distortion device at another forum has me thinking that maybe my Nady 80s tube distortion and overdrive pedals benefit little if any from having tubes in them, that the distortion really comes from the diodes. So, I'm of course wondering what they would sound like without the diodes. What would be the proper way to do this?

Memory DOES NOT serve in this case, but I vaguely recall someone removing (I think) diodes from some device (a tube preamp maybe?). Seems like they got less distortion or something. That would be fine in the case of my OD-1 (distortion) and possibly with the TD-1 (overdrive) as well.

Hip me to this, ya'll.

[Luijo]

Without a schem for those pedals it would be a guessing game to know which diodes to remove since they must have a few in there besides the clipping ones.
If you want to be a little adventurous just jump each diode with a little wire while you have someone else play, just stay away from any diodes that are close to the power supply section. Maybe they can be easy to spot, they are supposed to be very close to each other, wired in parallel but with opposing polarity.
You will definetively get less grit but most probably the pedal will become more dynamic. Just don't expect it to sound like a nice tube amp, just a different version of what you already have there.

[Boy Howdy]

Here's the schematic...

Thanks, Luigo.

This Westbury is the same as my TD-1.

http://www.freeinfosociety.com/elect...iew.php?id=985

I'll try your suggestion. Shouldn't be too hard to spot the correct ones.

[hasserl]

The clipping diodes are the 1N914x2 diodes between the output of the second stage and the cathode of the first stage. You could remove those diodes and replace with a 220k to 1m resistor to ground. The higher the value the more gain the circuit will make. If the value is too high you might see some blocking distortion. I would go with 220k for starters, if you've got a decade box it makes these experiments easier. I would also delete the 10uf cap and go with just a resistor to ground there.

BTW, that's not a true bypass circuit, the input is still connected to the first gain stage even when switched off, which will load it down a bit. You could add a 3PDT switch to isolate the input completely when switching it off, making it true bypass, FWIW.

[Boy Howdy]

Thanks, hasserl.

I'm going to crack this thing open and see what I can get going. Though, I think I'll hold off on the true bypass until I get it sounding like I want. It needs a tone control too. Any recommendations there? The TO-2 overdrive model has treble and bass controls that use a dual pot. I imagine it would be a matter of just copying what's already in the TO-2 into the OD-1. Make sense to ya'll?

I don't think there's a schematic for the TO-2 online, but I'll check.

[hasserl]

Why don't you give it a simple one knob tone control like the Fender tweed Princeton. It's basically a treble bleed off, but it would give you a basic tone control. Adding a tone stack with Bass and Treble controls will sap a lot of gain (which may be just fine, I don't know).

[JimiRayBoneKing]

This is kind of a side note, but I've been replacing the silicon diodes with LED's of various colors to produce assymetrical smooth clipping distortion in my TS pedals.
Someone did a study with an o'scope to determine the type of clipping that certain color LEDs will produce.
I couldn't find the URL but it still has to be around somewhere.
This site probably best explains the TS circuitry:
http://www.geofex.com/Article_Folder...ch/tsxtech.htm
But the diode clipping function is still the same.
I've used this with TS -5 -9 -10, Rat and Dean Markley (Blue Tube) pedals and it seems that many OpAmp OD pedals use the same clipping trick.
Hope that this info is useful.

[Ray Ivers]

Here's a chart that helps determine LED clipping thresholds, just in case it's of interest - I've used it for designing a bunch of different LED-related circuits:



Ray

[Matt T.]

FWIW, I think white LEDs are up there between yellow and blue on Ray's graph.

The only tube overdrive I currently own is a rackmount Chandler Tube Driver. I went through several different iterations of Tube Drivers to find one I liked. When I swap the tube out for a 12AU7, the gain and amount of distortion doesn't change that much...but the tone and the character of the distortion does change however it's not a huge difference either. I like it better with the 12AU7 but in any case...the much lower gain tube didn't seem to effect the gain or amount of distortion very much.

Also, FWIW, I have a Blue Balls OD that had 2 silicon switching diodes and as the note decayed the distortion didn't go away gracefully, it sounded kind of like static. But I replaced the diodes with white LEDs and it sounded much better. Then I added 3 silicon switching diodes to the white LEDs (arranged like the lead channel in a Marshall Jubilee) and I like it even more.

[Boy Howdy]

Yeah, that's what I was thinking. The bass control on the TO-2 doesn't do much of anything. I just run it all the way up anyway.

[Boy Howdy]

I used to have a Danelectro overdrive (Daddy something? the yellow one, whatever). I didn't much care for it, so I changed the LEDs to germanium, 2 on one side and 3 on the other. I liked it much better. It could get some really raucous sounds with the tone set brighter and some really nice sustainy stuff with the tone at the other end of the dial.

But yeah, I know LEDs are supposed to be more tube-like. I just don't get on well with most distortion pedals regardless of the diode type. But tube ones sound a bit better to me. No holy grail now, but better.

I hate tube screamers. It's a little known fact, but I have read SRV quoted to say that he really only used the TS as a booster, set with as little distortion as he could get away with.

[Matt T.]

I hate tube screamers. It's a little known fact, but I have read SRV quoted to say that he really only used the TS as a booster, set with as little distortion as he could get away with.

That's the way a lot of folks use it (me included). I mod mine to have even less 'grit' at the minimum Drive setting by replacing that 51K resistor in series with the Drive pot to 10K.

Lots of folks rave about the Landgraff Dynamic Overdrive and it uses an almost exact TS-808 schematic except there is a 3-way switch for selecting different diode combinations...2 LEDs/no diodes/2+1 regular diodes. You'll notice that all 3 switch settings have a higher threshold (less distortion but more output) than the stock 2 diodes.

Just last night I added a Ge diode to the 2 existing diodes in a Visual Sound Jekyll & Hyde green side (TS-808) and it reduced the distortion even more. Now with the Drive control at minimum it sounds as much like a compressor as it does an 'overdrive'. Haven't played it long enough yet...jury is still out whether I like it more or not.

[Boy Howdy]

You know, I've never used a TS as a booster. Which is surprising. I've used clean boost pedals, starting with boosters made for acoustic guitar transducers (because that was all that was available) since at least the mid 70s. I used Electro-Harmonix LPBs, two Barcus Berry's (one transistor, the other IC), an Intersound 'The Notch', an MXR Microamp, a DOD Bi-fet (whatever it's called). I even used an Orange Sqeezer like that at one point (it sort of worked). I had a Seamoon Fresh Fuzz that worked great as a booster.

But all this was back when I had amps that needed and or responded well to that sort of thing. Many modern amps have enough gain without all that business.

[Boy Howdy]

Holy crap, I guess it's been awhile.

Well, I finally got around to trying what Hasserl recommended for my Nady TO-2.

I bypassed the diodes and the cap before the diodes with a 220 resistor. What resulted was a little weak both in the amount of distortion and actual level of the pedal. So then I put in a 1 meg. That worked pretty well.

What resulted was a better, more dynamic (less compressed) and less fuzzy tone (not that the TO-2 sounds fuzzy, it's actually very natural sounding - my favorite distortion box ever).

But after all was said and done I ended up putting it back the way it was originally because, while the tone was better, I lost a lot of sustain. The distortion level was lower - like the difference between say Pete Townsend and Eddie Van Halen (actually, the TO-2 doesn't distort quite as much as EVH, but I can't think of another name that others would recognize - maybe Rithcie Blackmore on the live version of Smoke on the Water would be closer to accurate).

In its modded state it sounded great for rhythm, but not so good for lead. I considered that if I went to 2 meg I might get there. I had my doubts though, so I put a booster preamp in front of the TO-2, which improved neither the tone nor the sustain. From this, I decided that I wasn't going to get there - I needed those diodes.

The modded TO-2 would probably have worked great in front of an already distorted amp, but I'm rarely able to get loud enough for that these days.

Seems you either have to have multiple preamp tubes, power tubes or diodes if you want some sustain.

One other thing: I also tried just bypassing the diodes and cap with a wire. The volume and distortion levels were just way too low with this option.