Interesting Mod: a Boss SD-1 with a 12AX7 in it.

[paulyy]

I don't know, I am not a fan of hybrid circuits...I don't want opamps with tubes in the same box. But yeah that's me!

I see your point but I guess it depends on what you like.

[kissack101]

I know this thread is abit old but I just tryed this mod on a SD1 with a 12au7 tube and got great results. Its pretty easy to do and one tube can be used as 2 diodes or 1 diode. Im rehousing my SD1 so installing tube will be easy to do. Ill post a link when I get done with the pedal someday.

I tried this in a DS-1 a couple of years back (with a 12AX7 tube I think?). The tone was nice when you played through it but the background noise when you weren't playing was horrendous - was this something that you found? If so, any tips on how to combat it would be appreciated!

[paulyy]

I know this thread is abit old but I just tryed this mod on a SD1 with a 12au7 tube and got great results. Its pretty easy to do and one tube can be used as 2 diodes or 1 diode. I'm rehousing my SD1 so installing tube will be easy to do. Ill post a link when I get done with the pedal someday.

I tried this in a DS-1 a couple of years back (with a 12AX7 tube I think?). The tone was nice when you played through it but the background noise when you weren't playing was horrendous - was this something that you found? If so, any tips on how to combat it would be appreciated!

Sounds fine. no background noise that I can recall. Haven't tried a 12ax7 yet. maybe its the tube. Don't know. I'm still learning the pros and cons of this mod my self. I did notice that you don't need to hook the tube up to any power source for this to work. The tube part is just for looks. Ill be out of town for a week but when I get back Ill have more time to experiment with this mod. I hope the pros out way the cons on this mod.

[kissack101]

I did notice that you don't need to hook the tube up to any power source for this to work. The tube part is just for looks.

My (albeit limited) understanding of tubes was that you had to heat the plates otherwise it simply wouldn't function? Is it really possible to use a 12A?7 tube passively as clipping diodes?

[paulyy]

I did notice that you don't need to hook the tube up to any power source for this to work. The tube part is just for looks.

My (albeit limited) understanding of tubes was that you had to heat the plates otherwise it simply wouldn't function? Is it really possible to use a 12A?7 tube passively as clipping diodes?

Power or no power sounds the same to me. So far and I dont see why you couldnt use any 12A?7 with this mod. You Could get different sounds or just the same sound.

[MetalGod]

how did you hook this up? - I'd like to try this out.

[MetalGod]

ok, I hooked up a 12AX7 as a diode clipper according to the way I found demonstrated in another thread (the 9v valvecaster thread, page1).  what I noticed was that in this diagram, the anode of triode1 is connected to the cathode of triode2 in order to make the 'diode'.  this doesn't seem right to me as each triode is independent of the other, so it would make sense if the anode and cathode of the respective triode sections made the 'diode' (i.e. pins 1 and 3, then pins 6 and .

when I tried the valve diode clipping with the anode of triode1 connected to the cathode of triode2 in order to make the 'diode' (and vice versa for the other anode and cathode to make a back-to-back pair), I got the exact same tone whether the valve had voltage applied to the heaters or not and also whether the valve was in the socket or completely removed (i.e. there are no clipping diodes 'in circuit').  this would explain one of the previous poster's findings where he stated the same results were gained regardless of any voltage being applied to the heaters. 

I'm gonna try it the way I think this 'should' work, but I'm not hopeful of this working as it didn't when I tried it with a 5726/6AL5 (it's been suggested that this is because the valve diodes require a larger PP voltage to break over than a silicon diode; which would make sense).

[MetalGod]

ok, tried this again - no dice, I get less gain than in bypass.

pins 1 to 3 connected, then pins 3 and 6, then 6 to 8, then 8 to 1 - that should give the diagrammatic equivalent of a back to back diode pair (right?).

if anyone has successfully got a 12AX7 to clip in a SD-1, please help me out here.

Cheers!!!

[paulyy]

how did you hook this up? - I'd like to try this out.

I got the idea from the same thread. The 9V Valvecaster Thread. I like the way it sounds but I think it might be to much. I have to dial my settings way down to get it sound good.

[MetalGod]

how did you hook this up? - I'd like to try this out.

I got the idea from the same thread. The 9V Valvecaster Thread. I like the way it sounds but I think it might be to much. I have to dial my settings way down to get it sound good.

I've tried it like in that thread - the diodes don't clip.

Any chance you can post pictures so I can see exactly how you've wired this up.

[MetalGod]

I've played with this some more, and to get the valve diode arrangement in a 12AX7 to clip, you need to tie the grid to the plate.  After all this effort, I can report that its not really a very satisfying too - HARD clipping like Ge diodes when used in an SD-1.

[MikeH]

I've played with this some more, and to get the valve diode arrangement in a 12AX7 to clip, you need to tie the grid to the plate.  After all this effort, I can report that its not really a very satisfying too - HARD clipping like Ge diodes when used in an SD-1.

You could try it with some other diodes (like LEDs or 4148s) in series.  That would bring the clipping threshold up.  Not saying it will sound good though!  It seems to me that a tube is a pretty expensive set of clipping diodes...



It does look pretty sweet though. 

[Willypp]

I know this is a necro thread revival, but I recently replaced the clipping LEDs in a Crunchbox for poops and giggles with a 12ax7 I had lying around, using this layout here, and only 9v after seeing something about the Zendrive 2.


It worked, but it was massively bassy.  I messed around a bit with the input cap but I couldn't get what I wanted out of it.  It was a bit of fun but that's about it.

[vigilante397]

Yeah I've never been thrilled with tubes as clippers. I figure if you're going to put one in a circuit, it may as well be a gain stage or two