Reading/understanding diode forward voltage

[Bret608]

Hi everyone,

I'm hoping for some insight on understanding, and making productive use of, diode forward voltage readings.

On the "Fuzzball" project (see irmcdermott's recent post in Member Projects), I'm hoping to experiment with diodes for the first time. Right now, I have a 1n270 and a 1n914 in there. I plan to keep the 1n914 as a constant and try out different ones for the germanium. The idea is to create a bit more contrast between the diode-in and diode-out modes on the circuit.

I was comparing my 1n270s with some 1n34s I also have. On my DMM, the 1n270s read around 200-ish, and the 1n34s something like 600. What does that tell me exactly? I usually see forward voltage numbers with a decimal in front.

Thanks in advance for any pointers! I know there are plenty of variables to take into consideration here, but I thought this was a productive way to start the conversation.

Cheers,

Bret

[midwayfair]

I was comparing my 1n270s with some 1n34s I also have. On my DMM, the 1n270s read around 200-ish, and the 1n34s something like 600. What does that tell me exactly? I usually see forward voltage numbers with a decimal in front.

Those are milliamps (1000 = 1V), assuming you're using the continuity/diode setting and not voltage or ohms, and are the forward voltage of the diode.

What multimeter are you using? 600 is very high for germanium.

Fv (forward voltage) is the total voltage "lost" (or more precisely blocked) across the diode. Diodes are semiconductors and therefore voltage only flows in one direction, from the anode to the cathode.

[Bret608]

Hi Jon,

It's a cheap Harbor Freight DMM, but I could totally be remembering that 600 wrong. For some reason the number 338 is sticking out in my head too. I noticed that numbers jumped around a bit due my sometimes less than steady hands. I did have it on the continuity/diode setting. Thanks for the clear explanation as always!

Can you suggest a forward voltage that might be a slightly assymetrical, darker sounding match to a typical 1n914? The Fuzzball circuit has this nice, trebly bite that I love, so I was thinking I could darken up the diode-on setting for some contrast. I have access to 1n60s also (I love working at a tech college with an electronics lab where most of the folks think of the parts we like as obsolete!), and I remember you describing those as darker.

[midwayfair]

Hi Jon,

It's a cheap Harbor Freight DMM, but I could totally be remembering that 600 wrong. For some reason the number 338 is sticking out in my head too. I noticed that numbers jumped around a bit due my sometimes less than steady hands. I did have it on the continuity/diode setting. Thanks for the clear explanation as always!

Can you suggest a forward voltage that might be a slightly assymetrical, darker sounding match to a typical 1n914? The Fuzzball circuit has this nice, trebly bite that I love, so I was thinking I could darken up the diode-on setting for some contrast. I have access to 1n60s also (I love working at a tech college with an electronics lab where most of the folks think of the parts we like as obsolete!), and I remember you describing those as darker.

.338v sounds more likely.

Lower forward voltages will sometimes sound darker than higher forward voltages. I can suggest .... some .... diodes ....

http://www.madbeanpedals.com/forum/index.php?topic=5399.0
(FYI: these are no longer for sale.)

The 1N60 germaniums were some of the darkest diodes I'd ever heard at the time I tested them. They also have a pretty low Fv (.25v). However, a single diode change alone is not going to revoice a circuit. It may provide a different character to the distortion, not to the total character of the pedal. There are also kind of weird mathematical situations where the wave forms are not clipped at a pleasant ratio, or at a ratio that results in cancellations. The most pleasing results are 2:1 ratios and ratios that conform to the golden ratio (1:1.618). 1N34A and 1N4001 are the most likely to fall into those ranges. You should also try the diodes in both arrangements (lower Fv going to ground and vice versa) -- this can change things pretty drastically.

[DutchMF]

....and ratios that conform to the golden ratio (1:1.618).

It finally made it on the forum!! Yeah! You another Leonardo fan, Jon?

Paul

Didn't mean to derail the thread, sorry! 

[midwayfair]

It finally made it on the forum!! Yeah! You another Leonardo fan, Jon?

If you mean the turtle, yes, yes I am. (heh.)

It's far older than Da Vinci.

My favorite usage of the golden mean was describing why certain human faces are considered prettier. John Cleese did a documentary talking about it.

This can't possibly be the first mention of Phi on the Phorum can it? We should start a thread about where it's useful if so ...

[Om_Audio]

It finally made it on the forum!! Yeah! You another Leonardo fan, Jon?

We should start a thread about where it's useful if so ...

+1

[Bret608]

Wait, Leonardo the turtle as in TMNT Leonardo? This is an excellent derail! And you mentioned John Cleese to boot.

[oldhousescott]

Remember, too, that the rated forward voltage drop is usually somewhere in the knee of the conduction curve. The actual amount of voltage drop depends on the current through the diode.

[Bret608]

Just resurrecting my thread here for a pretty specific question...

What effect does wiring diodes in series or parallel have on forward voltage drop? Does one or the other double the fv, average it, etc.?

[midwayfair]

Just resurrecting my thread here for a pretty specific question...

What effect does wiring diodes in series or parallel have on forward voltage drop? Does one or the other double the fv, average it, etc.?

In series = the sum of both diodes' Fv
In parallel = it's complicated.

In parallel, they don't exactly divide, but the Fv is lower. I'm not sure exactly how much lower, but I'm sure there's something google could turn up. I do know it changes current draw.

The common belief that one diode will "take over" when they are put in parallel is erroneous: Two diodes in parallel sounds different than the single diode with lower forward voltage. You can sometimes fake very odd forward voltages with this trick (e.g. 4.5v, which falls in the middle of a pretty big gap in diode forward voltages).

[Bret608]

Thanks for the clear explanation, Jon. This was more helpful than the Googling I did!

Here's why I was asking about this--I just finished boxing a Distortion + I did (using Culturejam's Plus-Dist board), and after watching one of Chromesphere's clips in which he tested a bunch of diodes in this circuit, I thought it would be fun to experiment myself.

So, I've started off with a 1n270 on one side and a 1n4148 on the other. It does sound quite good--more volume, straddles the line between crunchy and fuzzy drive, and sounds good on chords. But when I play certain combinations of notes (especially arpeggiating on the high strings high up the neck), I can hear this slight atonality, almost like it's edging towards some upper octave. I wonder if I've got a pair that are too asymmetrical to one another? I thought maybe putting a germanium in parallel with the 1n4148 would lower the fv a bit, allowing me to keep the benefits of a bit of assymerticality, but have them all be more in step with each other.

Let me know what  you think!

[Om_Audio]

This "Dead Easy Dirt" is an awesome circuit to test diodes, caps, and ic in- very fun and I know what you mean about overtones and harmonics- they change a lot w diff diodes, caps, input/output volumes, etc.

http://www.madbeanpedals.com/forum/index.php?topic=6915.msg59245#msg59245

Regards,

Clifford