API 3124 problem?

[Grasshopper]

I picked up my 3124 in June of '05 and couldn't have been happier. The thing sounds great. A little over a month ago I noticed that the #1 pre had a buzz. I assumed it was my soldering job on my newly installed wall fixture. Nope. I unplugged everything from the thing and the buzz was the same. I plugged it into a differnt converter channel, same buzz. All three of the other pres are fine and sound identical. I called Mercenary, they were great. Got me an RA number and I mailed it off to API. Ray, over at API, said he wasn't hearing it. I'm inclined to believe him. He tried to get it to buzz over a couple of days and nothing. So when I got it back I tested it and I didn't hear it either. Ok, great, right? A couple of days ago, guess what? Its back! Is there anything I might be missing here? Could it be something on my end or is it probably just some come and go problem with the pre?

[Doublehelix]

I had a problem with one channel of a 3124 as well, so I sent it back to Mercenary and got a lunchbox with 4 512Cs...that way if one channel goes down, I only have to send back the bad module and I don't lose the rest of my APIs...

Just so you know, Jay at Mercenary couldn't hear the problem with mine when he got it back either...so go figure.

I love th 512Cs, and am glad that I coughed up the extra cash...its nice to have the flexibility to add some other flavors of pres if I want to later (A-Designs, Shadow Hills, Buzz Audio, etc.).

Good luck, but be persistent and swap the cables with one of the other 3 channels and see if the sound goes away.

[Grasshopper]

yeah, I did everything I could think of and the noise is only on CH1.

what do you feel are the differences in sounds when comparing the 312 and your 512?

[Doublehelix]

Originally Posted by Grasshopper

yeah, I did everything I could think of and the noise is only on CH1.

what do you feel are the differences in sounds when comparing the 312 and your 512?

I really didn't have the 3124 for very long (a week or so) as it was broken out of the box, I made the decision pretty quickly. I'd have to say they are pretty similar, but I honestly can't remember. I'd really have to A/B them directly to compare. I don't even remember if I have any old recordings left over from that week...

[waffle waitress]

we have had the same trouble...one of our 3124's had a noisy channel...it would only make the noise every now and then...sounded like static...

I love api as well though...who doesn't?

[max cooper]

How about switching out the opamps in channels 1 and 2 and see if the noise moves or stays?

[ulysses]

Off the top of my head, an intermittent buzz could be caused by a power transformer in another piece of gear mounted above or below the API in your rack. It could also be caused by a ground loop, but that gets a little trickier to understand how it affects just one channel of a transformer-balanced preamp. It's possible, but not probable. Preamps are very high-gain devices, so it's actually rather difficult to keep all the noise sources out. But that's why you paid all that money, so you should get 4 identically noise-free channels. Just make sure it's not caused by your studio before you try returning it again.

[Grasshopper]

So I should take it out of the rack and see if it makes the same noise? I also forgot to mention that when the direct input is active there is no noise.

[bradavenson]

You might see if the DI jack switches are a bit flakey. Often preamps use the DI jack to switch parts of the circuit, so that may be the culprit if it never happens with a DI input.

[ulysses]

Originally Posted by Grasshopper

So I should take it out of the rack and see if it makes the same noise? I also forgot to mention that when the direct input is active there is no noise.

You could just turn off the other devices in your rack to check for possible induced noise.

The fact that the noise goes away when the DI is active is a huge clue. It means the problem is not in the amplifier itself. When you plug a cable into the DI on this type of preamp, it disconnects the input transformer. If there was hum being induced into the input transformer, disconnecting it would make the noise go away. There are other possible scenarios, but right now I think the best bets are either induced hum in the input transformer caused by a nearby field, or else a bad connection (either internally or externally) on one of the signal input legs or ground points. I assume you've already tried swapping out cables and/or snake channels?

[mindbend]

I got a brand new API 3124 yesterday and noticed a hum problem right off the bat. It is quite strange, and it drove me nuts for a few hours last night. It causes a low level hum with only the outputs connected. It is not even plugged in to the wall, and nothing is plugged in to the inputs. I disconnected the outputs, inputs, and power cables from everything else in my rack and it still hums. Here is what is weird, when I turn the 3124 on, the hum goes away! It's like the API does not ground itself until it is powered on. I even tried the exact same inputs and outputs on my shadowhills gama 8 and it causes no hum whatsoever, leading me to believe there is something wrong with my API. Any thoughts?

Thanks

[Jack P]

I've had the same problem with my API 2500 compressor - very bad interference type noises on one channel, but sometimes if i leave it on for a couple of hours the noise goes... The problem doesn't happen when the unit is on bypass, tried switching op amps to no avail..

anybody have a clue ??

I am looking to buy a 3124 but this makes me nervous as i don't live in the States so a repair isn't very easy..

[trodsky]

The exact same issue showed up on channel one of my 3124 last week! Ray Blevins got back to me and suggested first switching out the op amps and see if the buzz/hum follows the op amp. I'll be trying this tonight.

[Kiwiburger]

I'm trying to get my pair of API A2D's useable. I don't like the background hum/buzz. Using either an SM57 connected to the input, or a standalone battery amp with a single coil pup, I detect a lot of EMI coming from the API power transformer.

The top cover on the A2D's is aluminium. Is the 3124 the same? It seems to me that this is basically a large unshield torroid generating a huge EMI field. Would replacing the covers with steel help?

I get an audible buzz with nothing connected - just monitoring the digital output with a Benchmark DAC-1. I'm trying to hear the noisefloor of the converter, with the preamp on minimum gain. It gets worse with a mic connected - and the unit itself seems to be a main source of EMI in the room.

[yesac81]

just a thought on this one...

if it's in channel 1, have a look at the back of whatever piece of kit is directly above and below it. does the power input (the iec plug or whatever... where the power goes into the unit) line up with channel 1? i.e. is it on the right side as you look at the back of the unit?

same prinicpal for channel 4... it seems you guys keep talking about channels that aren't in the middle, most gear has it's power input off to one side, and the power transformer i 9/10 times right next to the power entry point.

maybe be worth a look into...

and if it is the problem... a sheet of mu metal either side grounded to the rack maybe??

just a thought, i don't own one of these but a i read this thread and had a slightly inspired moment

[trodsky]

Originally Posted by yesac81

just a thought on this one...

if it's in channel 1, have a look at the back of whatever piece of kit is directly above and below it. does the power input (the iec plug or whatever... where the power goes into the unit) line up with channel 1? i.e. is it on the right side as you look at the back of the unit?

same prinicpal for channel 4... it seems you guys keep talking about channels that aren't in the middle, most gear has it's power input off to one side, and the power transformer i 9/10 times right next to the power entry point.

maybe be worth a look into...

and if it is the problem... a sheet of mu metal either side grounded to the rack maybe??

just a thought, i don't own one of these but a i read this thread and had a slightly inspired moment

ok, so my dumbass pulls the 3124 out of the rack, opens it up and starts pulling out op amps and reseating them BEFORE I recreate the problem with the unit NOT in the rack.. of course, fire it up, no hum! get it back in its spot and there is HUM.. .simply power down the VLA right below it... AND THE HUM GOES AWAY!!... yep, and the hum was on channel 1 only, well a little on channel 2. ok, so i switch the api and the sx202, and now the 202 has hum, on channel one, which sits exactly where channel 1 of the api was.. not as much, but some.. maybe because since its a halfrack jobber, its sitting on a rack tray and has additional layer of metal between it and the VLA, but still there is hum.

What i don't get is that everyone was getting along fine for a couple of weeks before the VLA started interfering, started mid-session even. why is that?

[yesac81]

Originally Posted by trodsky

ok, so my dumbass pulls the 3124 out of the rack, opens it up and starts pulling out op amps and reseating them BEFORE I recreate the problem with the unit NOT in the rack.. of course, fire it up, no hum! get it back in its spot and there is HUM.. .simply power down the VLA right below it... AND THE HUM GOES AWAY!!... yep, and the hum was on channel 1 only, well a little on channel 2. ok, so i switch the api and the sx202, and now the 202 has hum, on channel one, which sits exactly where channel 1 of the api was.. not as much, but some.. maybe because since its a halfrack jobber, its sitting on a rack tray and has additional layer of metal between it and the VLA, but still there is hum.

What i don't get is that everyone was getting along fine for a couple of weeks before the VLA started interfering, started mid-session even. why is that?

dunno... changes internally as a valve burns in maybe? i am not sure. maybe you just started to notice it mid session, and once you notice something that in your gear, it's hard not to listen for it from then on. i don't mean any disrespect here of course :-)

maybe you could take the vla to a sparky friend, or if you are handy with a soldering iron and 110v... and swap out the power transformer for a toroid (less induced emi)

anyone want to weigh in here? is the vla one of those crazy psu designes where they back a step down and a step up transformer together to get the plate feed for the valves?

[danbronson]

So is this the problem everyone's having with their 3124s? Proximity to other units?

[trodsky]

Originally Posted by danbronson

So is this the problem everyone's having with their 3124s? Proximity to other units?

well after moving it away from the VLA, hum went away.

And no, the hum was not there before, it honestly started mid-session, loud enough for "everybody" to hear. Weird that it could start causing troubles like that.. its definitely something to do with the power supply.