Switchable clipping diodes?

[Jmsteele187]

I want to mod a sd-1 that I just picked up.  I know which mod I want to do, but I'd also like to add switchable clipping diodes.  The mod I'm looking to do, calls for d4 & d6 to be replaced with a 1n34a and 1n4001, and d5 to be replaced with a 1n4001.  I'd like to also switch to LED's as clipping diodes, but keep the asymmetrical clipping.  I've done a switchable clipping diode mod on a ds-1, but the asymmetrical clipping of the sd-1 has me a little confused.  Can anyone help me out with this?

[Jmsteele187]

Edit*. D4 and D6 call for a 1n34a and 1n4001 in series, and D5 a 1n4001.  I also have a spdp switch on hand that I can use, but if I have to pick up a DPDT switch to make it work, that's fine too.

[Mark Hammer]

A stock SD-1 uses a trio of 1N914 equivalents, with the clipping threshold for one half of the wave roughly double the clipping threshold for the other.  The diode trio you are attempting to switch to, also  provides for some asymmetry, but will place the clipping threshold for one half of the wave about 50-60% higher than the other, rather than double.  It will also result in a little more audible clipping and slightly less maximum output volume.  Is that what you are aiming for?

[Jmsteele187]

To answer your question, I'm really not sure.  I haven't actually heard the mod in person, just on YouTube.  Here's some more info on the mod I'm trying to do, though.  I know it as a fullclone mod.

Here's the exact mod in case any of you folks want to give it a
Location --------Mod value
C2 ---------------.022 uf
C3--------------- .1 uf
R6---------------- 2.2K resistor
C6 ----------------.022 uf
C10 --------------1 uf film

D4 ------------Germ. And 1n4001 series
D5 ------------1n4001
D6 ------------Germ. And 1n4001 series

Note: Germ implies 1n34a germanium diode.

I'd like to make the clipping diodes switchable between what's listed and LED's, for some variation in the character of the clipping.

[duck_arse]

here is something. ignore the various caps and resistors, the switches the thing.



if you wire the "ground" end (of the asst diodes) to pin 6, and the "X" end to pin 7, you should have symmetric led clipp, symmetric 1n914 clip, and an assymetric clip pos. or you choice of vaiations on that theme.

[Jmsteele187]

I'm not quite sure that's what I'm looking for, but I could be wrong.  I'm not that great at reading schematics.  I'd like to keep the asymmetrical clipping.  If I were to hook up a clipping diode switch, with LED's on one side, would I end up with symmetrical clipping?  Or is it all in how I wire everything up?

[Jmsteele187]

A good way to think of what I'm after with this mod is; the fullclone mod with a modified Ge. 5* mod all wrapped up together.

[Jmsteele187]

Ok, I've figured out the 5* mod.  In that mod, D5 is removed and a 1n34a and an LED is wired to a switch, then wired into the D5 slot.  Now my question is; with the fullclone mod having two diodes wired in series, in both D4 and D6, will an LED in D5 end up giving me symmetrical clipping?  Also, since the the fullclone mod has germanium diodes (that won't be wired to the switch), how do you think they will sound with the switchable LED?  Or will I just have to experiment with it and find out?

[duck_arse]

a general rule of thumb is that "the diode with the lowest Vf wins". look your datasheets for each type diode, they will have a forward Voltage listed. for all your diodes pointing in one direction, add the Vf of each. which is lowest will do the clipping.

so a led may have a Vf of 1V7. if you wire/swich a Ge across, for example, with a Vf of 0V3, the Ge wins. any string of diodes totalling less than the 1V7 of that led will do the clipp. the same goes for the opposite direction. and when the Vf of both directions is (near enough) equal, the clipping will be symmetric.

if you use my diagram, and nominate some Vf's for the diodes on the switches, you can work out which will be workable combos, and which won't.

[Jmsteele187]

From the info you've given me, Duck, I should have asymmetrical clipping no matter what position the switch is in.  Because I'll be using NTE110mp Ge diodes (I just have more of them in my stock pile) and 1n4001's my total combined Vf should be around 3v2 for D5&6, since they are in series and 2v1 for D4.  D6 will have a 110 and 4001 in series, D5 switchable between a 4001 and LED, and D4 a 110 and 4001 in series.  Unfortunately, I don't know the Vf for the LED's off hand.  From what you've told me, they may not even make a difference in sound.  I'll just have to experiment and find out.  Thanks for the help.  I'll post back when I've tried it out and let you know my findings.

[Jmsteele187]

Well I did the mods.  With the diodes switchable, there wasn't a significant difference. So I decided to go with just the original mod, and leave the switch out.  All in all it sounds pretty good.  Now, I may add a light plate, I just have to figure out what size resistor I need in R30.