More like 10 years or so. But the board has been exchanged by MOTU, a
few years ago.

Am 06.10.24 um 22:40 schrieb thet via groups.io:

the MOTU may be different however, and it may depend on the manufacturer
drivers and how they work.

As far as I am aware, this is with Apple and everything audio per
firewire. I have the same trouble with my Beyerdynamic Headzone HRTF
processor.

Ralf

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well my circuit has P48 at the other end (output) but not at the input I'm trying to protect.

I'm concerned about stray ESD rather than P48 imbalances or plugging pins making contact in the wrong order.

BAV199 has the lowest leakage I've seen, but I'm not sure if its max current and voltage are sufficient.

I'd also welcome any thoughts anyone has on the gate series resistor and how much protection that offers. It should limit the current though not the voltage I would think.?

Would it be better to put that resistor before the BAV199 and the cap, to help protect the BAV199 from over-current?

I am in the same boat regarding my RME fireface interfaces.

however I have read in some forums from multiple sources that in reality the fireface interfaces still work right up to sonoma, even though all the official docs say they don't.

so I'm thinking of updating the mac on which I least need the fireface to work as a test. right now I have no incentive to update though, there's nothing I want in the newer versions.

the MOTU may be different however, and it may depend on the manufacturer drivers and how they work.

Am 06.10.24 um 21:43 schrieb Richard Lee via groups.io:

I would be grateful if you can open up your Traveler Mk3 and have a look.
MOTU, Oz, tell me nearly every Mk2 had to have its PCB swapped.
You can easily see evidence if this has been done to your unit as the
diodes are large.

Things are a bit hectic here, at the moment, but I will have a look in
the next few days and take some photos so you can see for yourself.

Shame as the Traveler(s) had SOTA portable preamp performance ... if it
wasn't for this problem and the shonky software/drivers.? New MOTUs
don't have quite the same level of LN performance.

My main grief with the MOTU traveler is that I'm stuck with Mac OS
Monterey because those *beeep* at Apple killed the firewire audio
support in all subsequent versions.

Ralf

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More like 10 years or so. But the board has been exchanged by MOTU, a
few years ago.

thet:

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yes they are expensive for a donor body - but they look much more solid than a BM800.

The ease of disassembly and the layout of the interior is exactly what I was hoping someone here might know.

BM800s are a pain to get large capsule assemblies inside because of the narrow opening to the basket - I wonder what these are like.

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BAV199 are suitable for mike preamps like THAT 1512 but are too noisy for condensor mike stuff.? You want something like Ir 0.2pA.? There's nothing spec'd to that level as its very temp. dependent.? You just have to guess that the paper spec. is pessimistic and by experience.

OK, so I accept it is impracticable on a condenser mic - the broader question for me is? - What is the upper limit of input impedance where a diode ESD protection scheme can work effectively with low noise? And which diode is best suited to that?

?

BTW, the THAT datasheets recommend 1n4004GP.? There's some AES papers on The Phantom Menace by THAT & Wayne Kirkwood that explains the choice.

do you mean this one?

From a brief look it seems it explains the protection circuit, but I couldn't see anything about why they chose 1N4004GP specifically. Unless it is implicit in some way I didn't understand.

They also seem to be mostly concerned about the sorts of faults caused by plugging in live phantom powered cables to a low Z mic input, which is quite a different situation from ESD on an exposed HiZ input.

A mic preamp input is concerned with noise because it has high gain following it, wheras my buffer circuit is unity gain or less and concerned with noise in quite a different way.?

I'm at least as concerned about diode leakage throwing off the fet bias as I am about noise. Though the solution may be the same.

?

I don't think diodes with leakage low enough not to introduce noise to a 1G input will protect anything.? They? will be too fragile and too low Vr Reverse Voltage.? They are suitable to run FETs at Idss for something like simpleP48.

?

That's not to say they don't exist cos some must be integrated in OPAs

yes, as above, I'm wondering where the practical upper impedance limit is.

_._,_._,_

Am 06.10.24 um 02:35 schrieb Richard Lee via groups.io:

How many months have you had your Traveler Mk3?

More like 10 years or so. But the board has been exchanged by MOTU, a
few years ago.

Ralf

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How would you know when it's done its job? just the noise levels?

If I have a build where the protection diodes are not replaceable separately from the fet they are protecting, what specifications of the diodes should I consider for robustness?

Thanks Richard this is setting me on the right track, but I have more questions...

On 05/10/2024 22:04, Richard Lee via groups.io wrote:

Dunno about piezo amps @ about 10M but for a LN condensor mike over 1G, the diodes must have VERY low leakage.
1n4148 far too leaky and noisy.

yes, I think it is degrading my noise levels even at the <5M input impedance of the circuit I linked to.

Guru Scott Wurcer liked a smoke alarm FET used as a diode. Another 'diode' for this is the BE junction of an old fashioned LN BJT like BC214 or 2n5087.

no space for this in my piezo circuit but I'll keep it in mind for future higher impedance pluggable setups.

Schottkys have very poor leakage which gets worse with time. The latest THAT 1510/12 datasheets for microphone preamps recommend cheapo 1n4003GP (Glass Passivated).

Why 4003 rather than say 4007?

and what is the advantage of the glass passivated? does it reduce the leakage?

I've seen BAV199 (dual low leakage surface mount) mentioned in some searching for fet input protection. The small size, though hard to solder, would actually suit me for my current application.

any comments on BAV199?

is overall beefiness a consideration? ie max forward current, max reverse voltage? BAV199 are small diodes with low voltage and current specs.

All P-N junctions become noisy under circumstances, particularly when they're driven in their Zener region.

I would say that a diode that has done its job of protecting a low-noise circuit should be replaced one day or another.

Hi
use xlrs
pin 1 shield longer than 2 and 3 pins
earth contacts first....

Never noticed anything like that with my traveler MK3

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I’m using the diodes ?am as this is text book protection for opamps ? Can’t speak to FET’s or a >10M input impedance?

Am 05.10.24 um 23:04 schrieb Richard Lee via groups.io:

I've personal experience of Schottky protection
diodes going noisy in several MOTU Travelers withing 12 mths and indeed
all da MOTU designs cured by replacing with 1n4003

Never noticed anything like that with my traveler MK3. Then again, I use
it mostly for recording... errr... noise, i.e. street scenes and
industrial ambiences.

Are these diodes in the mic amps?

Ralf

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