Schottky Diodes + Clipping

[Dylan]

Hi,

I came across this page: http://projectguitar.com/tut/blackice.htm

And tried it out yesterday. I got some Schottky diodes from Mouser, and set it up like the diagram said... but it does not work. I looked on Stewmac's site, at the actual Black Ice unit and read this:

"In order for this passive circuit to work, the pickups must have a DC resistance of at least 10K ohms. Guitars with pickups with a lower DC resistance will not “drive” the Black Ice to properly clip the signal."

I don't know what the DC resistance of my pickups is, but I think a possible problem may be that it is less than 10K ohms because they are not hot to my ears by any means.

My questions are,

1. How do I check DC resistance? (I have a multitester kickin' around here somewhere)

2. Are there any solutions if the DC resistance is indeed to low?

Thanks,

Dylan

[lovekraft]

Try a forum search for strawberry ice or black ice schottky - this is one of those gimmicks that works well only with fairly hot pickups, and you may or may not care for the results, but it 's been discussed to death around here, so you shouldn't have any trouble finding more info than you ever wanted!

[Robert_the_damned]

A quick and rough way of measuring pickup resistance I use is to turn all pots to full, sellect the pickup you want to test (and ONLY this pickup), plug in a guitar lead and measure the resistance between the tip and the sleeve on the lead. saves you taking the guitar appart to measure the resistance and its acurate enough in most cases. if you told us what guitar it is then I'm usre someone knows what DC resistance the pickups are!

Robert

[mammoth guitars]

The pickup impedance is not always an indication of the pickup's output. The magnet type and pole configuration have a lot to do with it as well. You must use germanium diodes which switch at .3 volts. 300mV is considered a high output pickup. It will probably work best with pickups that are 400mV+ output. This will give you better playing dynamics.

[lovekraft]

You must use germanium diodes which switch at .3 volts.

No, that's the whole point of using schottky diodes - at low currents, some schottkys have a Vf as low as 150mV. Seriously, unless you're using Invaders or something similar, this project is likely to disappoint. When you can pick up a DS-1 or a YJM-308 for less than fifty bucks (or a B€hring€r or Dan€l€ctro for half that), why even bother?

[mammoth guitars]

You must use germanium diodes which switch at .3 volts.

No, that's the whole point of using schottky diodes - at low currents, some schottkys have a Vf as low as 150mV. Seriously, unless you're using Invaders or something similar, this project is likely to disappoint. When you can pick up a DS-1 or a YJM-308 for less than fifty bucks (or a B€hring€r or Dan€l€ctro for half that), why even bother?

I agree and some shottkys can have a .5 vf. It will be a crackly sound at best.

[lovekraft]

...some shottkys can have a .5 vf...

That's quite true, if we're talking about power schottkys - however, any small signal schottky that's suitable as a RF detector diode (BAT41 springs to mind, but there are literally hundreds of others) will exhibit a Vf similar to or lower than that of a germanium device. The point is that regardless of which device you choose, your pickups will have to produce a voltage swing well in excess of the forward voltage of the chosen diode for clipping to occur, and whether that Vf is 300mV or as low as 100mV, there aren't many pickups that will produce enough voltage swing to clip hard enough to impact the sound much except on the initial attack. You can always get around the problem by using a preamp to boost the pickup's output, but then you've built 75% of a DS-1, and it's silly not to just complete it and have a distortion box. Like Bob always said, there ain't no such thing as a free lunch.

We go through this same question cycle every few months, and never seem to come to any conclusions, so here's my final word on this:

Lovekraft's Passive Clipper FAQ

• Q. Does the Black Ice/Strawberry Ice/passive diode clipper really work?
  
• A. Yes, to a limited degree.
  
• Q. Will it make my guitar sound like a tweed Fender?
  
• A. Probably not. It still might be a sound you like - the only way to find out is to try it.
  
• Q. Is it worth the trouble to try it?
  
• A. Well, since a pair of schottky or germanium diodes are fairly cheap, probably, especially if you keep your expectations low, and you have hot pickups. If you can't handle disappointment or view failure as an indication of lower self-worth, please avoid this project!
  
• Q. What's the easiest way for mw to find out if my setup will sound good with a Black Ice/Strawberry Ice/passive diode clipper installed?
  
• A. Try soldering a pair of anti-parallel diodes across your output jack temporarily - that will give you the sound of this unit wide open. If you like it, proceed to wire it in permanently with whatever pot and switching options you find useful.
  

As always, YMMV!