Strange diode configuration

[dano12]

I cannot figure out what is happening with those diodes. Any ideas?

[frequencycentral]

What's happening is that someone's blowing $15.83 per diode. 

[davidallancole]

The positive and negative wave will be clipped to the zener voltage plus 1 diode drop.  It works similar to the standard tube screamer, but instead of clipping at +-0.7 volts it will be more like +-5V.

[MattXIV]

NTE6074 is a high current rectifier diode (Data Sheet: http://www.nteinc.com/specs/6000to6099/pdf/nte6070_79.pdf).  It definitely won't conduct in reverse bias in that circuit, so I'd guess the schematic has the wrong part number.  It's probably one of the lower reverse voltage Zener diodes so it's Vr+Vf is less than the +/-4.5 V swing the power supply gives the op amp.

[MikeH]

What's happening is that someone's blowing $15.83 per diode. 

Wowzers.  And for NTE parts none the less!

[CynicalMan]

NTE6074 is a high current rectifier diode (Data Sheet: http://www.nteinc.com/specs/6000to6099/pdf/nte6070_79.pdf).  It definitely won't conduct in reverse bias in that circuit, so I'd guess the schematic has the wrong part number.  It's probably one of the lower reverse voltage Zener diodes so it's Vr+Vf is less than the +/-4.5 V swing the power supply gives the op amp.

Hmmm... NTE's zener diodes are all 5xxx numbers. 5074A is an 11V zener so that's unlikely too.
But looking at the schematic blown up, the diodes look more like schottky diode symbols that zener symbols. NTE has some schottky diodes with 60xx numbers, but 6074A isn't one of them. The list of them is here: http://www.nteinc.com/Web_pgs/schottky_barrier.html





Edit: Is it just me, or is that first opamp not biased to half supply voltage? Maybe someone just traced the whole schematic badly?

[davidallancole]

They do look like Schottky diodes.  If they really are then they won't do anything in this circuit because one of them will always be reverse biased.  They can't be NTE6074A either.  Google shows no response for that number.  NTE6074 does exist and like MattXIV all ready pointed out its a high current diode.  The only useful diode would be a zener in this type of configuration.

Where did you get the picture from Dano?

[stm]

Don't dismiss the schottky diodes so fast!

Looking at Digikey catalog I found schottky's with breakdown voltage as low as 1V !
See here:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=863-1126-2-ND

There are others with a breakdown of 3V, which would probably be just OK for this application.
See here too:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BAT%2063-02V%20E6327-ND

Unfortunately they are not in stock and have a tiny surface mount package, should anyone want to experiment with them.

[davidallancole]

I see what your saying stm. 

A diode that is appropriate for this circuit would have a Vz of ~2-3.  This way whe added with the other diodes Vf you would come out with a signal clipped around 2.7-3.7 volts.  Its more or less the same thing as just replacing a tube screamers diodes with LEDs.