bah...wrong diodes

[Toney]

Ordered some 1n34a's recieved ..... cdsh270's

They are shown as a valid replacement for 1n34's but... the central semi site shows them as schokky diodes?!

I wanted germs for the  Bosstone I'm making but schotties?? Not sure what to expect but  I'll give these a whirl.  Can anyone comment on the validity or otherwise of these in this application?

[Khas Evets]

While the thresholds may be similar, the knee is very different. Germs are much softer.

[Ge_Whiz]

The schottkys will sound much harsher - though not necessarily in a bad way... :wink:

It is very naughty of companies to advertise germanium diodes and then supply schottkys as 'valid replacements'. In all the applications I have for them (stompboxes and radio) they are most definitely not equivalent.

[Toney]

Thanks guys.

I have the Bosstone board finished now. Used 1n4148s for the first try which will be tomorrow.

Tired....... beer calling.

Will fire her up then give the 270s a try too. Harsh might be good .  
Am curious.

[Paul Perry (Frostwave)]

As Ge_whiz says, those companies are naughty.
I think the problem is that most people buying Ge diodes are using them in crystal radios, where the Schottky is OK.

I suppose to be one-up in the distortion game, one could use an old copper oxide rectifier from a 1940s meter! Or, better still, a gelena cats whisker diode.. http://www.acmi.net.au/AIC/CRYSTAL_SET_3.html

[Ge_Whiz]

Well actually, my OTHER application of Germanium diodes IS in crystal radios - and although Schottkys can be used, they rarely work well as direct replacements. I think that the main application is actually in low-loss rectifier arrangements (including such things as ring modulators), charge pump circuits, and high-speed logic switching where discrete diodes are still sometimes used. For crystal radios, I still prefer a good AAZ18 or OA47. However, for my 'Strawberry Ice' passive overdrive, Schottkys are just what the doctor ordered.

[Mark Hammer]

I may well be making too much of the number, and not enough of the letter prefix, but it is worth noting that 70's era MXR stuff used 1N270 germanium diodes.  Most people will use 1N34 or 1N60's instead these days because 1N270's are next to impossible to find.  Are these possibly a suitable replacement for 1N270's from another company?

[Fret Wire]

Most people will use 1N34 or 1N60's instead these days because 1N270's are next to impossible to find.

A dealer I'd previously bought 1N270's from, offered me 2000 of them for .12 cents apiece. I didn't see myself building 1000 Dist. +'s, so I passed.

[Paul Perry (Frostwave)]

Ge_Whiz, that is interesting that Ge is better in crystal sets. I think they would be better in ring modulators too, because the 'passive' ring mod, relies on the diode curve approximting a square law... what is wanted in 'smooth' distortions also.

[Fret Wire]

Makes sense now, alot of the 1N270 auctions on ebay list crystal radios as an app. for the diodes.

[Ge_Whiz]

The issue of using Schottkys in crystal sets is to do with impedance matching between the (passive) tuned circuit and the diode, and then to the headphones (a matching transformer is usually required). Get the impedance wrong, and the Q of the tuned circuit takes a dive (you lose both sensitivity and selectivity). When Schottkys are employed instead of germanium diodes, it is common to use several (up to eight, in fact) diodes in parallel. That also gives rise to issues, so for many enthusiasts, one germanium diode is preferable.

Another 'equivalence' issue relevant to stompbox builds is when you order low gain transistors - say BC108A / BC549A - from a supplier, only to be sent BC108C or BC549C because they are "superior in all applications".