1N34A FTM question...

[jpiddy118]

Hey all... building a few of my own hybrid/modified Foxx Tone Machines for friends, and found something interesting... i'm getting a nicer, tighter bite to the overall sound when using solid black 1N34A diodes, as opposed to the more typical glass style. I usually check voltage for pairing, but couldn't tell you the exact differences from one unit to the next... can't recall them being far off from one type to the other, nothing that caught my attention. Anyone else notice this? I've ruled out just about every other possible variable.

[GibsonGM]

Something to do with the diodes' capacitance, maybe?  Worth looking into (data sheets?)

[amptramp]

Are you testing this outside of the box or inside?  If you have glass diodes exposed to light, it will give you some reduction in back resistance compared to what they do in the dark.  They will give you a photodiode effect and germanium is leaky enough without it.

Run a test with them in ambient light then in darkness and listen for the difference.  In artificial light, it could even add 120 Hz hum.

[duck_arse]

amptramp, do you know if anyone has tried led/glass diodes on purpose? I know I've read people wanting sag or compression change with envelope, do ya rekon this would be a method?

[amptramp]

amptramp, do you know if anyone has tried led/glass diodes on purpose? I know I've read people wanting sag or compression change with envelope, do ya rekon this would be a method?

I used to work in avionics, specifically cockpit displays and we were looking at various types of touch screen - resistive, capacitive, surface wave (sonar) and photoelectric.  There are some specialty companies that produce these things, but we determined that photoelectric was most suitable for our purposes.  All the designs we had (or could buy) were infrared and there was always the problem of what to do with ambient light - a photocell system under a bubble canopy is asking for trouble, even with pulsed drive and synchronous detection.  Some enterprising soul in the company suggested that to reduce the interference, we should try green LED's as photodiodes using green LED emitters because there would be less ambient light in the green part of the spectrum than the infrared.  We built it and it worked - sort of.  The LED photodiodes had substantial leakage current, enough that temperature changes could wipe out the bias point and latch up low.

Just out of interest, we also built touch panels using infrared silicon photodiodes and infrared LED's as emitters.  We used the most sensitive photodiodes and most powerful emitters we could get and it was the only racially biased piece of equipment I have seen - the one black guy in our group could operate it but the light went through all the Caucasian fingers.  No problem with flight gloves though, so we did actually get it into operable condition.

I have mentioned this before to people who wanted the clipping diodes of a fuzz to be visible from the outside so that the light would show the clipping level.  But it would also react to ambient light including the 120 Hz modulation from fluorescent lighting.  It is a bad idea to expose diode junctions to light if you don't want light-induced effects..

[duck_arse]

It is a bad idea to expose diode junctions to light if you don't want light-induced effects..

exactly this. not a light-induced effect, but a diode-induced one, controlled by the internal, shielded, envelope driven leds. is there enoughlight-to-junction effect to make diode clipping, for instance, noticably different? enough to shift a bias point to sound like sag? subtly different?

[amptramp]

It is a bad idea to expose diode junctions to light if you don't want light-induced effects..

exactly this. not a light-induced effect, but a diode-induced one, controlled by the internal, shielded, envelope driven leds. is there enoughlight-to-junction effect to make diode clipping, for instance, noticably different? enough to shift a bias point to sound like sag? subtly different?

Get some black paint and find out.  Anything opaque will do and you don't need much but don't get caught stealing your wife's nail polish if you don't like being interrogated.