I Think My Interface is Shot

S

shoggoth80

Member
So. It's been a while since I dabbled with using my interface to do a vocal take. I've noticed some... issues.

The output into the computer isn't as hot as I recall. It's been several years since I did any diving in, but my interface is the same, as are 3 of the mics.

This weak signal is with gain and output cranked. If I put my Fethead Germanium into the chain, I get distortion on playback, almost regardless of what the levels are set to, and across the mics. It'll sound pretty nice through my headphones monitoring though.

Other issue: phantom power. I don't know how much the Fethead needs to run, but it does run. There does seem to be a weird cyclic effect happening on playback though, which again isn't heard in the cans. My condenser, when I have plugged it in has super low output, and even cuts out. That mic is 48v +/- 4v. I put my multimeter on the cable, and I'm getting 40-42v. It seems I'm under powered.

I even managed to get it to cut out on a dynamic with the Fethead in line. That was a couple days ago. The interface is an ART USB Dual Pre, made back in 2010.
It wasn't especially high end, but all I could afford at that time. Shoot, I can't afford a whole lot more now. Lol.

Most of the mics get rotated in household karaoke fun, and what few cables I have get used similarly with no noticeable fatal flaws. Haven't tried the Fethead in with the mixer, because the board doesn't have phantom. I have yet to try it powered with the interface phantom through the board.

The interface is the common denominator among other known good pieces. Think it's toast? I'm not looking for an excuse to upgrade/ update... but it's tempting. The skill set to isolate and repair isn't quite there, and the cost to replace isn't ridiculous.
 
You've got to do substitution tests. Take a known good mic straight in, then plug the interface into a DIFFERENT computer with the right driver and do your test. good mic, different computer and a problem means the mic. If it works fine then swap the computer, if that's fine, swap the good mic. you need to just have a baseline to start testing - you could have interface, mic, cable, computer or other problems - so you need to establish a working system first - then do the swaps.
 
The driver is generic. Pretty sure there's not any device specific drivers. It was originally natively supported with Win XP.

I know the dynanic mics and cables are ok, as they get used semi regularly on a small sound board.

Using a different computer is possible, but needs a little coordination. Worth trying just to see what happens.

I've tried it through Reaper, and Audacity, with similar result. So even using multiple types of DAWs the result is similar, which takes that software element out of the equation.
 
SILLY QUESTION - but what versions of Windows are you using USB v1.0 is a long time ago and it's possible it's just not supported by your computer? However - this is easy to test. Does it play back files from your computer to your audio system without distortion? If the issue is just with the preamp side - I guess it could simply be faulty?
 
Using Win10 currently. Using the interface as a playback for audio not recorded by it works. I don't think I have any USB 1.0 on my board, or my hooked on through the case's front panel. The box was built in 2014 or 15 or somewhere there about.

The interface wasn't new when I built the computer. It was on loan to a friend for a long time, and it spent a few years boxed away in my storage unit as well. It might not be compatible with the current rig, and I'm not certain if ART ever updated the model.

Some caps may have dried out in storage for all I know. I do know phantom power at the XLR is below spec, and to get what seems like reasonable output, I gotta crank it, and then it's distorted at playback regardless of which mic is on the input side of things.

It might be worth updating just because it's just realistically outdated, functionality issues aside. It wasn't a new model even 11 years ago if memory serves.
 
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I thought you said you had 40 something volts? That's pretty typical really - but one thought. Was that on both legs, or just each one - you'd need to add the two resistors to measure exactly, but the current available is always the killer feature. often struggling phantom power supplies do a big dive when one mic needs current they n' manage any more. You mentioned you have a dynamic mic? Does that work fine with no distortion?
 
It runs 40-42v with a little fluctuation. Checked with my multimeter at the cable. The condenser mic is an AKG that specs as 48v plus or minus 4v. It'll output really weak, then cut out and not respond to input. I'm tempted to get a little separate phantom power box.

The dynamics are a mix of various Electro-voice mics, an AKG D790, and a Beyerdynamic. They get used through a small PA and powered mixer pretty regularly. No issues with mic functionality there.

The inline preamp is a Fethead Germanium. Part of what makes me think it is the interface is I managed to get a dynamic to cut out with the Fethead in the chain (runs on phantom power).

Using an inline preamp, along with the interface, I get a distorted playback on the computer. I don't get a distorted monitor signal to my headphones. The playback distortion is there even with the interface gain set low.

Without the Fethead, I get weak ish output even with the interface gain cranked way up (and still distorted playback). The levels on the DAW appear to be alright, and I can turn down everything, yet the playback is distorted.
It's odd.
 
I never bought the wall wart for it. The 9v for my turntable might power it. It can use a PSU, a 9v battery, or run off USB power. There's no difference between the 9v battery, or the USB results. I hadn't thought of trying an external PSU, just because I never had one for it.
 
shoggoth80 said:
I never bought the wall wart for it. The 9v for my turntable might power it. It can use a PSU, a 9v battery, or run off USB power. There's no difference between the 9v battery, or the USB results. I hadn't thought of trying an external PSU, just because I never had one for it.
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It might not matter, but if the polarity and plug size of the adapter are a match, it probably wouldn't hurt to try. It sounds like the interface just doesn't supply quite what is necessary for the devices you're plugging in. Whether that's by design or indicates failure, I don't know.
 
Are you sure you are measuring the total voltage on the centre of two 6K8 resistors in series across pins 2 and 3 to pin 1. If you are measuring the voltage on 1 to 2 or 1 to 3, it won't be 48V. Also - my AKG451 and 414 mics don;t cut out, they just get gently noisier as the phantom voltage goes down and a little - as in hardly any - less level.
 
When I checked voltage, it only registers any across the top 2 pins. So, I'm assuming that's correct, since that's the only probing that gets a result. I could be doing it wrong. Should I be bridging, and then checking?
 
The 48V is across the pin 2 and 3 connections - with a bridging resistance, so the 48V exists in a kind of limbo 'between' pins 2 and 3 - which is where the term phantom comes from - so measuring just one won't give an accurate result. you might find 40V on pin 2 and the 40V on pin 3 is different!
 
I ordered a basic little 48v phantom power box. This should let me check independently of the interface. It'll also let me run my Fethead into my little PA for grins (has Bluetooth, but no phantom). So we'll see.
 
Well, tested the mic with the external power box. Mic still cuts out. Bummer, as I really liked the mic. That doesn't help solve any of the other issues like low or distorted output, but at least I know there's an issue with the mic, and not the phantom part of the interface.
 
There seems to be some confusion here about phantom power and its measurement? The voltages must be measured WRT pin 1 and it is perfectly fine to measure one pin then tother. The voltages should be IDENTICAL. If they are not it means the internal 6k8 resistors are badly matched and that means even a tiny amount of noise, hum. on the 48V supply will get into the mic signal. However, checking off load with a DVM will not show the problem nor will it indicate the current capability.
Best answer. make up a test plug* with a 6k8 from pins 2&3 to pin 1. The resistors should be matched to the best you can manage so buy 10 1% metal film Rs and select on the DMM for best match. Now you will get about half the no load voltage at the plug pins and if it is much lower than half, the internal supply is poorly or of poor design. N.B. Phantom spec' is + or - 4V so OP's is just out of spec but I would expect most mics to run without issue at 40V (but it won't be 40V with the mic connected! Check on a connected, 'naked' XLR)

Spook supplies should also deliver 10mA but I doubt many budget AI do. Not that many mics need anything close to that.

I have bought a couple of cheap phantom PSUs over the years. One, a "sKy" brand was useless, another was USB powered and whilst not bang up to 48V powered a FetHead perfectly well.
Finally if OP is going for a budget AI the Behringer UMC 204HD takes some beating. If the plastic can stand it however he will be over our natural satellite with a MOTU M2 or M4!

*Most of us have a tin of XLR bits?! Bit more clarification perhaps? Say the no load voltage was 46V then you should get exactly 23V at each pin. You would not, but a tiny difference won't matter. Much more than 0.1V diff however is a bit ****. There are of course 4 tolerances to contend with. Your Rs and the two in the AI.

Dave.
 
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