Diode Substitution?

[Canucker]

Wanted to build my first project in a couple months and decided ona Lofo Mofo since it looks like a quicky project...I don't have a 1N5817 Diode so I was wondering if anyone had advice for a reasonable substitute.

[armdnrdy]

Substitute with just about any schottky diode.

You might be able to use a 1N4148 or 1N914 but there will is a higher forward voltage with these diodes which might change the response of the control.

[Kesh]

you could try a germanium like 1n34 as they have similar fwd V to  schottky

[Canucker]

in an odd turn of events I was close enough to the not at all local electronics shop I go to sometimes and I managed to pick up a 1N5819 so hopefully its suitable as a substitute. Thanks for the input guys!

[bluebunny]

For your application, a 1N5819 is a 1N5817, but with a higher V_RRM (Repetitive Peak Reverse Voltage) - 40V vs. 20V - and a slightly higher V_F (Forward voltage drop) - 0.55V vs. 0.45V (@ I_F=1A).

[Canucker]

so for what I'm doing it doesn't matter? I was aware of the  40V vs. 20V but wasn't sure how it would effect the project. Its still on the "to do list" but its the first thing once I get some time to build.

[Jdansti]

The reverse voltage is the tells you how much voltage will kill the diode if the polarity is reversed. In your case, you're interested in the forward voltage, which is the voltage at which the diode begins to conduct, or turn on.

Edit-Please see my post below for a better explanation.

[Canucker]

so really 10 or up would be fine since the project runs off of a 9volt power source? As i've said many times I have no actual formal training in this stuff... I'm good at building things/working with my hands and the rest I'm learning all the time. This place is the best resource on the internet as far as I'm concerned.

[Jdansti]

I'm not an expert on circuit protection, but my guess is you wouldn't want to cut it so close by using a diode with 10Vrrm to protect against 9V reverse polarity. I'd use at least a 2x safety factor. There could be other considerations, such as the reverse current killing the diode. At issue would be the available current from your power supply.  A 9V battery has pretty limited current capacity, but a power supply rated at 1 or 2 amperes could do some serious frying when reversed.

The diode in the Lofomofo, is used to distort the signal, not for circuit protection. The location of the diode is between ground and a pot, which in turn is connected directly to the input. You need a diode with a low turn-on voltage because the circuit is relying on the voltage generated by your pickups to turn the diode on. Schottkys turn on around 0.2-0.3V, germaniums around 0.3V, silicons around 0.7V, and LEDs around 2V. Don't confuse the turn-on voltage with the forward voltage drop Vf, which varies with current.

[Kesh]

Don't confuse the turn-on voltage with the forward voltage drop Vf, which varies with current.

The turn on voltage is the forward voltage drop at an arbitrarily decided small current.

[Jdansti]

^Thanks. The problem is that most of the data sheets list the forward voltage at 1A or some other current that's higher than a guitar signal's current.  The curves provide a better idea of the lowest turn-on voltage.