Here's another (nearly) new one from me. It's a tricked out super mod of the old Electro Harmonix LPB-1 circuit that produces some lovely singing overdrive tones reminiscent of an old VOX from their 1960's heyday. I took the Lovepedal Englishman (A supposed Vox AC30 / AC15 emulator) as a base and went from there - Firstly I wanted a little more gain, hence the 4k7 collector resistor. Along with more gain I wanted more emphasis and clipping on the higher mids to replicate that treble laden Vox overdrive hence the 82nF bypass cap and the 47k/22nF mids filter at the end of the circuit. These changes make the circuit sound livelier and give it more character. The use of the *super* low forward voltage SB340 diode in combo with the BAT46 diode produces harmonically rick asymmetrical clipping, the levels of which can be controlled using the "Headroom" control. The headroom control also allows a nice rich low end to be retained while allowing the top end to be clipped, as you roll back the clipping a nice tube like "note attack sag" effect becomes prominent - it's quite pleasing and cool to play with. The use of the 2N3565 transistor is due to some tests carried out a while ago where it was found that the 2N3565 sounded best in these sort of applications, you can replace it with a 2N5088 or BC108 or, in fact, any decent gain NPN transistor.
Hi ! i Just built this pedal, but could'nt find sb340. I used sb360 instead. Everything works fine, but as i increase the headroom pot, i have more overdrive but the volume gets really really low.. Could it be the sb360, can i use BAT46 instead? Or is it something else? Thanks
ReplyDeleteThe Headroom pot essentially allows you to blend in the clipping diodes, so that will alter the volume of the pedal. You'll probably just have to crank up the Volume pot if you lower the Headroom pot.
DeleteHi, i have built and it works, but i dont understand what is the meaning of headroom, because i turn it up has no different. Thank you
ReplyDeleteI have done this circuit for some time, but I forgot to mention something that I found very special, the combination of these clipping diodes, give a very musical and dynamic touch, that I had never heard anything like it, the SB340 is exactly the same thing than the 1N5822, much more common and easy to arrange, but huge. I already got some smd to replace. The transistor at the time, I remember that it was not easy to find, I bought only ten because they were expensive, but in the end, I ended up with some other one because I did not notice much difference.
ReplyDeleteBut only by the combination of the diodes is it worth to test this circuit!
I build this pedal the other day and it's really good. It sounds like playing two different amplifiers at the same time because of the diodes sounding so different from one another. I would not say that it sounds like an old vox per se, but I sound very interesting on it's own. I would personnaly rename the headroom control ''blend'' as it blatantly blend one diode into the other. I would also rename the volume control ''gain'' and the master control ''volume''. The volume controls act much like a non-master volume amplifier (as you turn the volume up, it starts to break up into overdrive) hence the name ''gain''.
ReplyDeleteI finally ordered the SB340 diode and built this circuit, using my own veroboard layout. Agree with Croustanoune in that this doesn't sound like the typical Vox AC30 overdrive/distortion pedal - if you back-off the headroom control (which, to me, is wired backwards - full CW is max clipping and I would think that a "real" headroom control would act just the opposite), you still get a rich, sweet collection of harmonics that ring-out on certain notes and with an edgy pick attack. I recommend a 10KC (reverse log) for the headroom control as I found most of the useful settings are in that last 1k of resistance. Posted pics of my pedal at reddit: https://www.reddit.com/r/diypedals/comments/ha9x6w/vox_64_tone/
ReplyDeleteQue efecto hace este circuito ???? Gracias por si me ayudan 👍
ReplyDelete