Help w/Bass Fuzz

[Ben Lyman]

I have been working on a new fuzz pedal for a bass player and it sounds great on the breadboard but I want to know if you guys are seeing any red flags in my plan before I continue with it.
It is an Ursa Minor distortion from Small Bear plus a diode distortion blend circuit from somewhere else, maybe Jack Orman or Muzique.com, I can't remember. I want to bee able to throw a single toggle switch that does 2 things at once, highlighted in yellow:
Position 1: clipping diodes/cap are connected AND input resistor is bypassed (Jumpered?)
Position 2: the opposite of position 1
I need the input resistor when in clean boost mode so the bass won't overload and cause a clipped/delayed signal. In this mode there is the ability to blend clean signal w/diode OD signal.
I need the input resistor to be bypassed when the diode/cap are engaged because it just makes an awesome sounding super fuzz bass pedal that way 
Thanks!

[peterg]

Can you post a schematic of what you have in mind?

[Ben Lyman]

Sorry, my pic service must have been down, hopefully it is showing up now.

[PRR]

Since this is for someone else, add these frills.



The cap in the diode line, stock, will charge to different DC voltages on or off. POP! The 10Meg bleed will keep the DC voltage the same on or off. 10Meg will not leak enough diode action to affect the clean tone. (If you have over-supply of 4.7Meg, that's fine also.)

The 100uFd power cap is good, but works much better if there is some series impedance. This can make a real difference if the user plugs a crappy power supply to it. (And his crappy supply will be your problem.) Since the total current demand is super low (0.2mA), a 1K resistor can be used.

[Ben Lyman]

Very cool, will do, thanks!
Is the 1k resistor something I can use in series with a polarity protection diode?
Or is it something to use instead of a diode?

[antonis]

If it's 1/8 W you can use it as a fuse..

You can always use it in series with a reverse polarity diode protection but, perhaps, you'll have to take in mind the total voltage drop (Diode forward voltage drop + Resistor voltage drop) which will be about 850 - 900 mV..

[anotherjim]

With 1k in the feed, I think the reverse diode can be parallel "backwards" across C1. I don't usually think much of that arrangement, but in this case the 1k resistor will limit current enough when a reverse polarity supply is connected to reduce the risk of a burn-out anywhere. Often we see a parallel protection diode with much less than 1k in the feed -  often no resistor at all -  and that's just asking for trouble.

All that said, I don't think a diode junction voltage drop in the feed will harm the the circuit, so the protection diode can be "forward" in series with the 1k. Use a Schottky diode if you want to reduce the diode drop.

[PRR]

Reverse polarity probably won't do any harm. I would not bother with a diode.

[Ben Lyman]

Thanks guys, very helpful information, much appreciated. I'm still not sure what best reverse polarity protection would be. I have plenty of resistors but my only diodes are 1n4001, 4002, 4004, 4007, and 1n914. Are any of those suitable?

Reverse polarity probably won't do any harm. I would not bother with a diode.

Oh, OK, thanks. I am going to put a DC jack as well as battery clip but I doubt the guy will ever plug a DC power source into it.

[antonis]

(For future use..)

Any of 1N400X series is suitable (they are rated at 1A at X Volts, where 1=50, 2=100, 3=200, 4=400, 5=600 e.t.c) as a series diode..
(you can even use 1N914 or 1N4148 with a current limiting resistor in reverse parallel connection but it's not recomended for power supplies with current capability of more than 200mA..)

[anotherjim]

FWIW, I would use the protection. Paul's right, the circuit won't mind - except C1. Prolonged application of reverse charge will damage the electrolytic cap (although it won't blow up).
Also, the circuit might appear to work somewhat and pass some signal. In that case, will the owner think their power supply is wrong or that your pedal is faulty or just sounds that way on purpose? With protection -  it no worky and nothing harmed.

As long as the suggested 1k resistor is placed in series with the +ve power feed, a diode can be fitted across C1 with cathode to +ve of C1. With correct polarity the diode will do nothing.
For a practical worst case supply say 20volt (people will sometimes try any supply with a plug that looks like it will fit!), then if it's also reverse polarity (most common out there is centre pin +ve so it probably will be reverse!), the diode will conduct and prevent anything more than a diode voltage drop being applied to the circuit. With a 1k series resistor the diode current will be limited in this worst case to around 20mA - so almost any diode will do, but the robust 1N4001 is the usual choice.

[Ben Lyman]

Cool, thanks.
It was suggested I might try an amp recovery stage to raise the volume a bit. I couldn't find any info on that so I just put together an EHX LPB-1 circuit (minus input cap) in the middle and it seems to work. Any reason I shouldn't do that?

[antonis]

I just put together an EHX LPB-1 circuit (minus input cap) in the middle and it seems to work. Any reason I shouldn't do that?

No reason, as long as you didn't notice any tone altering...

You even could "incorporate" the LPB-1 transistor circuit as an amplifier in your pedal..

[Ben Lyman]

...You even could "incorporate" the LPB-1 transistor circuit as an amplifier in your pedal..

cool, thanks. Do you mean something like the LPB-1 as the last stage right before the level pot and output jack? Also, do you mean it could serve as a way to use the pedal to actually amplify a speaker or headphones? That would be really cool, I have a very old drive-in movie speaker box that I'm dying to turn into a practice amp

[antonis]

Do you mean something like the LPB-1 as the last stage right before the level pot and output jack?

Yeapp...

Also, do you mean it could serve as a way to use the pedal to actually amplify a speaker or headphones?

Only if your earphones wattage is suitable..
For your movie speaker I presume that it will be more than enough but you can allways try to tweak gain with Rc/Re ratio..

In both cases you can calculate your amplification stage output power to see if it matches with your speaker or headphones..

[Ben Lyman]

Thanks for all the help everyone, it works great! Love the blend feature.
I'm leaving off the DC jack and LED until after the buyer tests it and decides
if he wants those features.

[anotherjim]

That looks really neat. Nice to see some good old pot case ground bonding too.

[Ben Lyman]

Thanks Jim, it just seemed a lot easier to put the cap, diodes, and resistors directly on the gain and blend pots before I put them in. Then I just linked all the pots to ground.
I had a hard time getting the Alpha pot to take the solder and decided to take it out and start over with a clean one. I guess the shaft was thicker than my other pots because the knob was stuck so tight that I destroyed the pot trying to get it off. I got the new one in now and used my gigantic solder gun to pool the solder to the pot, it looks way better now.

[anotherjim]

It does take a lot of heat to solder the can, a normal iron will have heated up everything by the time the can is hot enough and damage any plastic part, so 100W plus is needed! I find I have to file off a bit of plating on most types. On some of the larger cans, you can sometimes bend out the anti-rotate tab (it isn't cast on the front) and that gives a smaller area to solder the wire on. To be honest, I only bond pot cans if I'm getting noise/feedback problems when testing outside of the case - but know I should anyway just in case. Most of my builds are experiments just for me and it's a PITA to unsolder if the pot needs changing.