Schottky diodes in diff pair in PWM amp?

[JohnRoberts]

http://etylab.ece.utexas.edu/pdfpubs/apl_jan04.pdf

Here is a paper on reverse leakage in GaN  type Schottky diodes.  (I don't know if this is typical process or representative).

The IR (reverse leakage) looks pretty high on diode data sheets and has a temperature sensitivity.

This "low leakage" Schottky specs 12uA at 15V
http://www.farnell.com/datasheets/1700331.pdf

Maybe I'm lucky, or just cheap,  (both?) but I've never used a Schottky clamp in an audio circuit.

JR

 

[ricardo]

The design is from the same company. I have not measured phantom power so far.

Shot noise is the basic mechanism which makes leakage current "itself noisy", as far as I understand; surely it is not the root cause here because the magnitude is not sufficient to explain the gross effects.

Can you measure the noise spectrum of the leakage current?

I don't have the offending diodes anymore.

You have to remember I'm a real beach bum.  Doing SMD work is a real PITA for me with Jurassic tools.  I lifted a pad during my surgery 

The noise was loud, pinkish and very variable.  Sounds like leaky P48V caps.  Loadsa 1/f.  Which is another reason why I don't think its shot noise.

I queried TI well after this, about using 1n4004 instead of Schottkys.  They tested 1n4004 with PGA2500 with a clean bill of health.  Not sure if these tests were as comprehensive as "The Phantom Menace" etc.

No idea if or when these recommendations will filter down to their datasheets.  eg the THAT demo kit datasheets still show Schottkys though their device datasheets have been updated.  (THAT did "The Phantom Menace" etc.)

http://etylab.ece.utexas.edu/pdfpubs/apl_jan04.pdf

Thanks for this JR. But  arhl hav 2 lern 2 reed en rite to unnerstan it 

 

[JohnRoberts]

Thanks for this JR. But  arhl hav 2 lern 2 reed en rite to unnerstan it 

No worries I didn't read it... I don't use Schottky diodes either...  ;D

JR

 

[k brown]

Resurrecting this thread to give my experience with an eBay MkI Traveler. All four pres very (and equally) noisy. Out of curiosity, I shut off phantom power and powered the mics with crummy little USB-powered phantom supplies, and the noise was completely gone.

Something not age well in the phantom supply circuitry?

 

[Khron]

Something not age well in the phantom supply circuitry?

May well be the case. Wouldn't be the first time ceramic caps s**t the bed. I've done teardowns of both the mk1 and mk3 Travelers over on my blog.

Tiny "OCD"-nitpick side-note: to my knowledge, there is no such thing as "Traveler mk2". Granted, the first one (as well as the "mk1" Ultralite) could be counted as being from the same generation as the 828 mk2, but nomenclature-wise they're not. Well, if we wanna get even more nitpicky, the Traveler & Ultralite may well be "mk2.5" generation, since the 828 mk2 still had analog preamps (with those god-awful long-shaft custom two-different-resistance pots), and all after that went with PGA2500's. Just saying...