Clipping Diodes - LED vs Silicon vs ...nothing? Help me out.

[Outlaws]

I am re-modding my MXR Distortion+.  A long time ago I added a DPDT switch on the side what I thought were germanium diodes (look like the factory glass, but without the green stripe).  There wasn't a huge difference in sound, definitely no drop in volume, as germanium is supposed to have.  So I went about my life because I don't think the output of the pedal could stand to be lower anyways.

Not I am back and I have ripped into my D+ once again.  I removed my DPDT (with factory and whatever I bought still attached) and plugged it into a bread board.  I put new wires to the D+ pcb and put those to the bread board.  Then I tossed on some LED's...3mm/3v/15ma red ones in parallel, and two 5mm/1.8v/20ma red ones in series with a parallel 5mm/3v/20ma yellow one to try out asymmetrical clipping.

Now for the good and bad news.

With the LEDs, my output went way up.  My bass got thicker.  And the LEDs lit up as I would play.

But...for fun I decided to play it without any diodes.  Hmmm.....  Sounds the same as with the LEDs.  I cannot tell the difference.

The only thing I can think of is later I might try the two red 1.8v ones to see if there is any difference, as I didn't really pay attention to the specs when I did it.  Would that be my problem?  Even 1.8v seems like it might be too much.


CLIFF NOTE VERSION
I cannot hear a difference between LEDs and having no clipping diodes.

[burnt fingers]

The LED's aren't going to provide as much clipping due to the high (1.8v as opposed to .7v for silicon) forward voltage required to get them to clip.

You may try one LED and one 1n4148 and see what that get's you.

Scott

[km-r]

dont overdo the clipping section... try placing just two LED's first. then swap it for two Si diodes...
having a simple clipping section might give you the ability to differentiate clipping behaviors...

i personally like red LED's signal to ground clipping...

[Outlaws]

dont overdo the clipping section... try placing just two LED's first. then swap it for two Si diodes...
having a simple clipping section might give you the ability to differentiate clipping behaviors...

i personally like red LED's signal to ground clipping...

The problem is there is no difference at all between the two LEDs and when there are no diodes in the circuit at all.  I am not running Si and LED at the same time.

EDIT:
I just tried the two 1.8v LEDs and there is a minor difference between them and just leaving the diodes out of the circuit.  I guess the LEDs will give me a booster distortion mode.  I might not even use them.

[Outlaws]

I have done some further experimenting.

But first, here is a picture of the factory glass diodes with the green stripe.  Does anyone know what they are?  The DMM says .26v, which seems low for silicon, but would be good if I were to get some germaniums as I would be less likely to loose volume.
The second pic with the black ends are what I had bought.  I have long forgotten what they are.


Now for my breadboarding...

I got some diodes from Radioshack.  Mix assortment.  Mostly 1N4001's with some 1N4002, 1N4004, and 1N4007's.  The DMM shows them all right at .54v +/-.  Thought they all sounded about the the same.  So, I stuck with using mostly the 1N4001's since those are the ones I see in a lot of schematics.  They actually made a sound I happened to like, although I had to compensate with the level control since they were noticeably louder than the factory diodes, that could be my imagination as sometimes louder sounds better even if its not.

I don't think I like LEDs.  They might have their place, but I don't think it is in a D+ circuit.  They are just too boomy.  It might work for a while, but I swear that you can get almost the exact sound by just leaving them out all together, especially if they are over 1.8v.  However, they do matter if you are using the gain control all the way down, at which point LEDs do offer a hint of gain, instead of a simple clean boost.

I put 1N4002 diodes in series one way with 1N4007's in series the other, and it increased the volume a bit, but I don't think the decrease in clipping was worth it.

At this point, I am torn between ordering some germanium diodes (is cold outside though, so I am hesitant to order atm), and using the 4001's with the factory for a little bit of a boost.  I got a 3 position switch also in case I want the ability to remove the diodes, but I really am leaning against it because the output is so much greater going into my UniValve, that I can't image what it would do to a solid state.  This really puzzles me because my Fulltone FatBoost doesn't even increase the volume that much, it just saturates the input.  This thing is physically boosting the volume a great deal.

That was probably way too much information, but if you have anything to add, I would appreciate it.

Also, doesn't the Diode function on the DMM show the forward voltage?  All my 3v and 2.1v LEDs are right at 1.74v, where my 1.8v LEDs are actually at 1.8v.  My silicons I bought are .6v and register at .54v, so they are fine too.  Its the 3v and 2.1v LEDs that are confusing me.

[Mark Hammer]

1) Although I have never seen a clunky black-with-white-stripe diode that looked like a 1N400x but wasn't (I'm ignoring all those zeners and Schottkys for the moment), I have seen plenty of big glass diodes that looked for all the world like they were Ge (but weren't) and small orange glass diodes that looked for all the world like they were 1N914s or zeners (but were Ge).  Go figure.  Best strategy is still to either have a very good magnifying glass (to read the numbers) and/or measure them.

2) The Distortion+ is known to simply not get clean at all, no matter where you set the gain or whether you use diodes.  My feeling is that it has something to do with the "starved bias current" used for the Vref.

3) There is enough gain and headroom in the D+ to get some crunch out of LEDs, but not really enough to be really distorted.  My own favourite is simply plain old 1N914/4148 type.  If you wanted to experiment, I suppose you could use an 18V supply and bump the maximum gain up by switching the 4k7 resistor to ground for 2k2.

[WGTP]

IIRC there is a 10k resistor and an Electro cap between the op amp and the diodes.  Try placing a 1k resistor there instead of the 10k and dropping the cap across the diodes from 1n to 22n.   That should get those LEDs lighting up a lot more.   

[Outlaws]

Now this is interesting!
http://www.pedalpartsplus.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PPP&Product_Code=4000&Category_Code=DIO

Looks like the factory diode in my D+ was germanium?!?!?!?!  So I guess I did get a germanium diode when I ordered one.  The reason the sound between them was so small was because I wasn't going from a silicon.

Can anyone confirm that the D+ (circa about 5 years ago) shipped with germanium?  I was under the impression that they hadn't been used since around the script logo era.