If you want to add a master volume control to it, remove the 47k resistor and use a 50k pot. Lug 3 to the Out pad, lug 2 becomes effect out, and lug 1 goes to ground.
Friday, January 16, 2015
Zvex SHO - Crackle Okay
The Zvex Super Hard On has become one of the sought after boost pedals today. Derived from the preamp section of a 60s recording console, the SHO uses negative feedback to control the gain (which is what gives it the crackle when adjusting the knob). It's capable of being a clean boost and adding some sparkle to your tone, or pushing your tube amp to break up and creating a great overdriven sound.
If you want to add a master volume control to it, remove the 47k resistor and use a 50k pot. Lug 3 to the Out pad, lug 2 becomes effect out, and lug 1 goes to ground.
If you want to add a master volume control to it, remove the 47k resistor and use a 50k pot. Lug 3 to the Out pad, lug 2 becomes effect out, and lug 1 goes to ground.
Thanks for the great layout. Works great, built a few, interested in trying the Master Volume mod. What curve would you recommend for the replacement 50k pot?
ReplyDeleteProbably audio/log taper, though linear will work as well.
DeleteHi! i think there is one mistake in reversed layout - insted of connection with D1 3 leg of the pot is connected to empty space just under second leg of the pot.
ReplyDeleteThis schematic is a bit different of others schematics on internet.
ReplyDeleteThe schematic that I've seen on internet has 2 diodes 1n4148 (d1, d2) and hasn't zener.
Do you know what is the effect of these diodes?
http://www.luciferstrip.com/fuzz/sho-schematic.jpg
The diodes in both versions are to protect the MOSFET transistor. They both do the same thing, though I believe the zener does a better job of it. Zvex initially used 2, 4148s then switch to the single zener.
DeleteHi friends. I have a trouble, when I move the pot I listen a noise. This is usual?
ReplyDeleteYes that's normal for the SHO.
Deletethat's why it says "crackle okay"
DeleteGreat classic!
ReplyDeleteFor more volume range, I recomend to use 100k resistor intead the 47k one.
just for curiosity, made what you suggested for high volume and it is better now. Thanks :)
DeleteDo you have a schematic for this?
ReplyDeletehttp://www.matsumin.net/diy/bunkai/Z_vex_SHO/Z.Vex_SHO_sch.BMP
DeleteBasic schem there, though it shows the wrong diode.
On most layouts of sho, there are 10M resistors instead of 1M. What is the difference?
ReplyDeleteIf you look at the schematic linked above, you'll see the use of 1M resistors. Both work as they're essentially creating a voltage divider at the gate of the MOSFET. If it bothers you, just use 10M.
DeleteI notice that, compared to that schematic, have an extra 1M resistor (the one all the way on the right) as well as the 4001 diode, the 47uf cap, and the 82 ohm resistor.
DeleteI'm guessing the 3 on the left are for power conditioning/protection, but what about that extra 1M resistor?
It's a pull-down resistor, it reduces a 'pop' when you engage the booster. Such mod is widely used in high-gain and volume boosting schemes
DeleteHello, my SHO just has low volume, even with the pot at max, the volume is lower than when it's bypassed.
ReplyDeleteHas same problem((
DeleteBS170 and other MOSFETs (2N7000 also can be used in this pedal, but mirrored) are very sensitive to static. Be very careful while soldering them.
DeleteLooks like your transistor is dead, consider installing a new one
Is the pot meant to be mounted on the component side?
ReplyDeleteNo, from the solder-side.
DeleteBuilt a modified version of this design (100Ω instead of 82Ω and no 4001). Sounds absolutely killer! Thanks very much.
ReplyDeleteI'm trying to get a better understanding of layouts could you tell me what the 82Ω resistor and 4001 is for?
ReplyDeleteThe 82Ω resistor is there to help regulate/filter/smooth the incoming voltage. The 4001 diode is to protect the circuit if a reversed polarity power supply is plugged into the pedal.
Delete