DC Mojo Bender MKII Question

[Colonel Angus]

Circuit works great and is super raunchy with OC75s in there, especially with the bias really cut back.

My question is: Is it supposed to be so quiet? Even at full volume and with the bias cranked the effect volume is much lower than bypass volume. Can someone confirm that this is just the nature of this effect of did I screw something up?

My friend in the Long Gones wants to play it on a radio program in NY next week. I just want to make sure everything is top notch

[kodiakklub]

link to a schem? por favor....and why not 81's or the like? a bender is on my (super)shortlist. do you know if theres a huge diff between the npn and pnp vers of the bender? i sadly bought 3 OC81's (new production) from mammoth for almost 20 bucks before i learned that the pnp's gotta run off a battery. i dont really do batteries so im prob gonna end up with an NPN version. sorry if im hijacking your thread in advance

[Colonel Angus]

Sorry Barry and Dcountry13, GuitarPCB requires a login, so direct link was not possible.

I choose the 75's because it hit the right mojo/price ratio. Apparently you can use a wallwart to power these as per this layout, but I'm not that brave, especially after frying a maxx chip with a shitty wallwart just yesterday. Battery seems pretty safe.

Hijack away good friend !!! At least someone is talking to me 

[Solidhex]

  If you're having a problem with the output try bumping the 470 ohm to 820 ohm. You can increase the output cap to .02 or larger. Doing this can get you more output but will also give you more low end and midrange. It tends to overshadow the cool fuzzy texture in the treble which gives the MkII a lot of its character. Its up to you how much the extra output is worth to you.
  This is a positive ground layout for a positive ground circuit. Any 9v fuzz circuit can be powered with a wall wart as long as the tip and sleeve are connected to the circuit in the right orientation. What you CAN'T do is power multiple pedals that share different ground references. If you use a wall wart, dedicate that one to that pedal unless you have some other old school positive ground circuits you'd like to power along with it.

[kodiakklub]

what about isolated 1/4" jacks from the box and putting blocking caps on the ground lugs? could i then use the pedal with other negative ground pedals?

[smallbearelec]

what about isolated 1/4" jacks from the box and putting blocking caps on the ground lugs? could i then use the pedal with other negative ground pedals?

I had to draw this out to understand why it won't work. Even if isolated from the enclosure, the "ground" side of the jacks in this pedal would have to go to power supply positive. Anything plugged into those jacks therefore has its ground connection at the same potential. The other jacks/plugs in the system are at zero volts, so you get a short circuit. The power path Must be DC for current to flow, which is why the blocking cap idea does not help.

Also note: An unmodified wall-wart will be disastrously hum-inducing in a high-gain pedal like this. Either search past threads for ways to add filtering and regulation to a wall-wart, or build a Small Wart:

https://www.smallbearelec.com/Projects/SmWart/SmWart.htm

and have something really useful to add to your gig-bag.

[kodiakklub]

yeah i figured it was a shot in the dark. oh well. thanks steve. yeah i have a very beefy PSU centered around a bulletproof meanwell LED power supply:
https://www.mouser.com/Search/ProductDetail.aspx?R=PLC-30-9virtualkey63430000virtualkey709-PLC30-9
ultra clean. but thanks for the link!

[smallbearelec]

yeah i figured it was a shot in the dark. oh well. thanks steve. yeah i have a very beefy PSU centered around a bulletproof meanwell LED power supply:
https://www.mouser.com/Search/ProductDetail.aspx?R=PLC-30-9virtualkey63430000virtualkey709-PLC30-9
ultra clean. but thanks for the link!

I see. So you are spoken for for +9 but need -9 at very small current? A way to get this with very few components would be a charge pump circuit using a MAX1044 or similar chip. Again, search past threads for How-Tos.

SD

[Colonel Angus]

.02 cap brought things up to a reasonable level. Thanks!

[newfish]

...and a pair of back-to-back diodes in parallel with the 100K (Q3 emitter to Q2 base) tightens things up like you wouldn't believe!