!N34A Ge diode

[1wahfreak]

So I'm moving on to build an Octavia which require a couple of Ge diodes. Are all 1N34A diodes created equal or are there "vintage" ones that are better. Am I in for the same life long mission as old Ge transistors? Any info would be great.

[brett]

Hi.  Although each type (1n34/oa47/1N60...) is fairly consistent, there's some significant differences in the forward voltages between types.  Generally, you'll want the lowest forward voltage.  There's an article on the web somewhere suggesting that oa47s have significantly lower forward voltages than other Ge diodes.  Having said that, I use 1N60s coz they're cheap and readily available where I live.  You might also like to try Schottky Si diodes (they have 1/2 the usual voltage drop of Si diodes).

Have fun!

[Andy]

If you want, I have some 1n34a's for sale.  Anyone email me if interested.

ThePhantom@Catt.Com

[Mark Hammer]

My experience is that there is a little more variation than what Brett suggested.  I get Ge diodes with anywhere from a 180mv to 320mv forward voltage spec, and Si diodes with anywhere from 400mv to 700mv specs.  In the grand scheme of things that may not seem like much of a range but in the small-signal world of guitar pedals you can hear that sort of difference.  So, while there is no overlap between types, you can get some that pose higher and lower clipping thresholds for each category.  I seriously doubt whether ANY of that has to do with "vintage" properties; it is simply a function of batch and MAYBE manufacturer.

That being said, I find it is always wise to measure your diodes and select them by properties, rather than simply by number.  I don't think the properties are nearly as critical as they might be for Ge transistors, but for some applications matching can be important.   In the case of the Octavia, my hunch is that some matching of diodes may be an important part of achieving a nice octave-to-fundamental balance.  You certainly won't have to buy a ton of them and precision match the way some folks do with phaser FETs, but it may take ten or so to get you a pair that are within 20-30mv of each other.  Fortunately, they often get sold in bubble packs of about that many anyways, so you should get what you need easily.

I'd be curious to know if those who have made Octavias have any comments about using diodes with higher or better/worse matched forward voltages.

[Doug H]

I'd be curious to know if those who have made Octavias have any comments about using diodes with higher or better/worse matched forward voltages.

Matching does seem to be important but I'm not sure if the difference in fwd voltage drop between 2 1n34a's out of the same bag is going to be that significant. When I built the bobtavia, I wired in an extra pair of si diodes to raise the output voltage and give me more drive into an amp. But when I tried yet another pair, I started to lose the octave effect. I suspect after stringing so many together in series, minute differences added up. That's my theory anyway, I didn't measure the voltages at the time.

If I remember correctly, Si's didn't sound too good in the tycho circuit. But I didn't match the Ge's either, just grabbed 2 out of the same lot and they worked fine.

Speaking of diodes: oddly enough I found this diode called a "1n46" surplus. It -sounds- just like a 1n34a with the soft clipping. It -looks- just like a 1n34a, glass case, etc. But the fwd voltage measures around .6-.7 V like an Si diode....? I'm not sure if it's Ge or Si, but I used it in a circuit I was experimenting with because it sounded like Ge, but gave me a hotter voltage swing, like an Si. Weird...

Doug

[Paul Perry (Frostwave)]

The 1N46 is Ge, and here's the data link:
http://www.americanmicrosemi.com/products/specs/Diodes-03-1100.phtml

[1wahfreak]

So if I get a batch of 25 or so and find two with the lowest foward voltage (between 20 and 30 mv of each other), that would be adaquate? I am also assuming that a higher forward volatge would not actually be bad, it's just better to have lower. I found a few places on the web that sell them in qty. so it won't be hard to find them as long as I'm not trying to find any thing old. I saw one for sale on ebay from 1953 for amost $10.00 which is why I asked about the "vintage" aspect.
Can I test them with my DMM or am I going to hit the wife up for a new $300.00 diode tester?? :lol:

[george]

You've probably got the stuff you need to test already ...

I'd just wire them up on a breadboard in series with a current-limiting resistor (the datasheet should tell you the max current the diode can take), hook up a 9V battery and measure the voltage drop across the diode.

You can work out the resistor you need from good ole R=V/I.  probably 10K will do the trick.

[Doug H]

The 1N46 is Ge, and here's the data link:
http://www.americanmicrosemi.com/products/specs/Diodes-03-1100.phtml

Thanks Paul. I was curious about those. For circuits with shunt clipping diodes, I prefer these over the 1n34a because of the higher fwd voltage.

Doug

[tungngruv]

DOUG H wrote:

When I built the bobtavia, I wired in an extra pair of si diodes to raise the output voltage and give me more drive into an amp

Could you explain that a little more? I built one and put it first in line (after my guitar and before a "Boutique Blender"). I think it sounds really good like that but there is a slight volume drop. Did your adding the diodes fix that in your Bobtavia?

[Ge_Whiz]

Crystal radio nuts will tell you that, although the 1N34A has a specification attached to it, over the years all kinds of generic point-contact germanium diodes have come to be labelled with this part number so nowadays there is enormous variation in performance, appearance and packaging of "1N34A"s.

Germanium diodes come in two basic flavours - 'point-contact', with higher forward voltage values (~0.3 - 0.45 V, e.g. 1N34A, OA90, OA91, OA95) and 'gold-bonded', with lower Vf values, down to ~0.18 V (e.g. OA47, AAZ18). Otherwise, their clipping characterisitics are similar (unless the circuit they are in is particularly sensitive to diode impedance).

Schottky silicon diodes, although having typical Vf values of ~0.4V, have different I-V characteristics and the clipping they produce sounds rather 'harder'. Not unpleasant, though. In fact, one strat copy I have with two anti-parallel Schottkys across the output gives one of the best overdrive sounds that I can produce.

[Fret Wire]

Funny about diode specs. It brings to mind the popular TS mod where you sub in one 1N4001 to give some asymetrical type clipping. A lot of the 4148's and 4001's I measured are in the same range. If you didn't measure them first, it would be easy to waste your time.

Awhile ago, I took 4148's, 4001's, 1N60's, 1N34a's, and 1N270's and measured 25 of each. If anyone's interested, I'll dig up the notes and post them.

I treat them like resistors, and check them before I solder them in. I've found a few dead ones before.