ART MPA GOLD - Excessive Hum from output gain
#31
10th April 2009
Old 10th April 2009
  #31
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Quote:
Originally Posted by Cpartipilo View Post
I'm pissed!!! i sent the unit back to ART for repair due to the hum i have and was returned saying line and inst input tested and no hum was heard.

I cannot even use the +20db switch because the hum is extremely loud, is not a faint hum.

With the unit only plugged into the AC and the balanced out to my 003 and no line or mic connected gain and impedance all the way down, phantom and +20db switch out when i bring the analog output all the way up the meter in protools registers the hum at about 20% of the meter.

How can this crap be up to specs?!!! anyone knows who could help me?

I accept hiss as is part of the amplification process and better components and tubes might make it quieter/better but this is stupid!
Sometimes if you have your stuff plugged in the ac outlets in the wrong manner, hitting the ground lift won't do squat.

I'm guessing that this is a "home set up".

Your main recorder and mixer should be plugged directly into the wall and both should be grounded well, this means your daw too. Your amp or monitors should be on the next branch out, the rest of the stuff can be branched off on outlet strips or rack units as needed, making sure they all come off the same outlets to avoid reversed unmarked outlets.
Cpartipilo
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#32
10th April 2009
Old 10th April 2009
  #32
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Thanks memphisindie i understand grounding schemes but i isolated the unit completely. I don't have any other hums in my whole setup. (7 preamps)

My test Chain ART MPA > Presonus HP4 > mdr 7506.

both units plugged into the same AC outlet with NOTHING connected to the ART, no mics, no nothing.

Gain and impedance are all the way down. Balanced cable from ART to HP4 (mogami) and as soon as output gain is around 11 o'clock the hum starts, when it's all the way down is strong enough that i could not hear someone talking in the room and if i dare to press the +20db switch at that point is about the level i listen to music at. (remember input gain is at zero)
With the +20db switch out the input gain knob does not affect the hum but i can hear a sligh change in the hiss waaay in the back.

I did the same test in my home, neighbors and my office. Same result.
#33
10th April 2009
Old 10th April 2009
  #33
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Quote:
Originally Posted by Cpartipilo View Post
Thanks memphisindie i understand grounding schemes but i isolated the unit completely. I don't have any other hums in my whole setup. (7 preamps)

My test Chain ART MPA > Presonus HP4 > mdr 7506.

both units plugged into the same AC outlet with NOTHING connected to the ART, no mics, no nothing.

Gain and impedance are all the way down. Balanced cable from ART to HP4 (mogami) and as soon as output gain is around 11 o'clock the hum starts, when it's all the way down is strong enough that i could not hear someone talking in the room and if i dare to press the +20db switch at that point is about the level i listen to music at. (remember input gain is at zero)
With the +20db switch out the input gain knob does not affect the hum but i can hear a sligh change in the hiss waaay in the back.

I did the same test in my home, neighbors and my office. Same result.
I'm only guessing, not being able to put my hands on it, but, either way, you need to contact ART and see what they can do if it's in warranty.

OK, if it isn't an accidentally reverse wired cord between the units, which I'd check,
it might be that the ground wire that should be connected to the input is not making connection also it sounds like it may be further down the line to me, like where all signals need a ground before the output section.
Could be a fractured solder joint.
#34
12th May 2009
Old 12th May 2009
  #34
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I've also got the hum problem

I really like the tone of this preamp with my NOS Telefunken and GE 12AX7's in but the hum is unacceptable!

None of my other preamps have this issue. I even used the same mic and cable with my Tampa and there is no hum!

I only have one mains socket in my room which all my gear is plugged into.

Not sure what to do as I like this preamp but if I can't sort this hum issue out the MPA will have to go!
#35
12th May 2009
Old 12th May 2009
  #35
Wow that's really odd, I've been having the DIgital MPA for 4 months now, bought it used, no problems at all.
Cpartipilo
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#36
12th May 2009
Old 12th May 2009
  #36
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I sent my unit to ART for repair under warranty. They sent it back because supossedly is still under design specs.. i wonder which design specs, if the ones for this units or the oreck vaccum cleaners...

I bought it from ProAudioStar.com and they offered to help. we'll see what happens.
#37
12th May 2009
Old 12th May 2009
  #37
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Mind if I pop inhere? I had a hum issue with 2 of these. I was sure it was the units I received. I suppose in some way it was. But I discovered that there was something I could do about it before giving up on it and now it's all good...

I had my MPA gold plugged in to an interface going in to my laptop.

When my laptop was unplugged and running on batteries, no more hum.

SO I realized that the hum was because of the MPA and Laptop being part of the same circuit in my house. I got a long extension chord and found an outlet on the same floor that would allow AC power power to the laptop without any hum.

So I suppose it's a flaw (this doesn't happen with any other preamps I own) but my workaround works for me
#38
13th May 2009
Old 13th May 2009
  #38
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Quote:
Originally Posted by soul&folk View Post
Mind if I pop inhere? I had a hum issue with 2 of these. I was sure it was the units I received. I suppose in some way it was. But I discovered that there was something I could do about it before giving up on it and now it's all good...

I had my MPA gold plugged in to an interface going in to my laptop.

When my laptop was unplugged and running on batteries, no more hum.

SO I realized that the hum was because of the MPA and Laptop being part of the same circuit in my house. I got a long extension chord and found an outlet on the same floor that would allow AC power power to the laptop without any hum.

So I suppose it's a flaw (this doesn't happen with any other preamps I own) but my workaround works for me
That kinda makes sense. I have no hum problems, but I wired the plugs in the machine room and tracking room to seperate breakers. How is your setup powered, Chris?

Last edited by Old Goat; 13th May 2009 at 01:32 AM.. Reason: add
#39
13th May 2009
Old 13th May 2009
  #39
Quote:
Originally Posted by Old Goat View Post
That kinda makes sense. I have no hum problems, but I wired the plugs in the machine room and tracking room to seperate breakers. How is your setup powered, Chris?
To be honest, the preamp is right next to my flat screen monitor and it's very close to my computer as well. It's even in the same power outlet. No hum, no problem at all.
#40
13th May 2009
Old 13th May 2009
  #40
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I guess it's luck of the draw with these MPA Golds. Or maybe it's unique to how it interacts with certain computers or maybe it's with all laptops. Who knows?
#41
13th May 2009
Old 13th May 2009
  #41
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Maybe the input jack is grounding to the chassis when it shouldn't be or isn't when it should be and maybe the grounding scheme has a loose or fractured solder joint or connector problem.
#42
13th May 2009
Old 13th May 2009
  #42
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who knows? I ordered one, ended up having the hum problem in channel two, got a replacement, similar problem in channel two, got another replacement, this time the problem was in channel one. Dealt with the problem as described above.
#43
13th May 2009
Old 13th May 2009
  #43
When this preamp doesn't have problems, it's definitely the best in its price range (with NOS Tubes).
#44
13th May 2009
Old 13th May 2009
  #44
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I am indeed happy with my purchase, after all's said and done.

Another pair of preamps I now own is a pair of Electro Harmonix 12ay7. Highly, highly recommend it. It sounds more airy than the art mpa gold (even with a pair of telefunkens from Bowie). Each will have their own uses and are both keepers.

I've also got a pair of Studio Projects VTB1 preamps.

I'm done buying preamps for the foreseeable future.
Cpartipilo
Thread Starter
#45
13th May 2009
Old 13th May 2009
  #45
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i'm going to try swapping my unit but if i'm not sucessfull i'll go thru the boards.. i'm pretty sure i'm hearing 60hz hum so it might be something broken in the power supply area. The caps are all crooked anyway.

i have tried different outlets and just pluggin headphones to the output of the pre and get the hum so it's not a ground loop between equipments.
#46
13th May 2009
Old 13th May 2009
  #46
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To the OPer....any chance it's your tubes?

...I wanna tack on a question...can anyone help out?

What problems would you expect if you recorded acoustic guitar with the 20db engaged, the input gain to 5 o'clock and the analogue to about 12 o'clockish?

Am I using too much tube gain for an acoustic instrument like the acoustic guitar?

I recorded a simple GCD song strumming open chords last night and I am getting a perfectly clean and nice sound (NOS Mullard and Tele)....however there is a noticable and slightly more than obtrusive harmonic drone occuring and changing with the strummed chord.

I used a CADm177 1' from 12th...and an sm57 1' from body.

Have I used too much tube gain and in doing so produced too much sensitivity in the harmonics picked up?

thanks
#47
13th May 2009
Old 13th May 2009
  #47
When you record, keep your daw at -8db at least.
#48
13th May 2009
Old 13th May 2009
  #48
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#49
13th May 2009
Old 13th May 2009
  #49
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Quote:
Originally Posted by chrislago View Post
When you record, keep your daw at -8db at least.
Is that in reply to my post chris? Coz each guitar track I recorded peaked at somewhere around -10 and -11db
#50
13th May 2009
Old 13th May 2009
  #50
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That was my first thought, gain staging, but, I thought, no one on GS would have a problem there.
Has anyone tried re-seating the tubes or making sure the tube socket's pins are making contact?
Cpartipilo
Thread Starter
#51
13th May 2009
Old 13th May 2009
  #51
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i tried 3 sets of tubes (stock, nos mullards, new JJ's) all with the exact same hum. i doubt it would be the pins but it might be a cracked solder joint somewhere.

Still pisses me off that i bought the unit new and sent it to repair (i paid shipping) and was sent back 2 days later saying "up to specs" without them even giving me a call to find out what problem i was experiencing, etc.

I can probably open the thing up and mod it to hell and fix "their" hum but i should not have to do that. is one thing to work on a unit to change/improve it and other to make it usable.
#52
13th May 2009
Old 13th May 2009
  #52
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I searched the forum and one thread stated unequivocally that the pins on the tube not making contact caused the hum and that bending them back into position fixed it,, on his MPA Gold.
What would a tube with pins not making contact sound like, part of normal maintenance on tube devices is cleaning and repositioning the pins in the tube sockets.
I think it's more likely than not, especially since it's the simplest solution.
#53
13th May 2009
Old 13th May 2009
  #53
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I had this hum with the stock tubes and now the NOS Telefunken and GE tubes.

I'm gonna try a few things tonight and see how I get on!
#54
14th May 2009
Old 14th May 2009
  #54
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Ok I tried using different tubes, leads, different mains sources etc and still have the hum.

It appears that I have the same problem as Cpartipilo.

I get the same problem without any thing plugged into the inputs and when I increase the Output to 12 o'clock upwards.

This is a real shame as I really like the tone of this preamp. Unfortunately this hum is un-acceptable and when I stacked vocal tracks the hum was a nightmare!

I may end up replacing this with a Chameleon Labs 7602 or PRE-73.
RTR
#55
14th May 2009
Old 14th May 2009
  #55
RTR
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Well this SUCKS, My mpa from PRoaudiostar will be here tomarrow..Sure wish I would have found this thread first!!
#56
14th May 2009
Old 14th May 2009
  #56
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As I understand it, these devices have two gain knobs, input gain and output gain, if the input gain is insufficient and you compensate by cranking the output gain, you will get hum in most cheap devices.

With nothing attached, recreate the hum, try ground lifting the device, with a three to two prong adapter, if that works, the device has a lame ground scheme, if it doesn't it still sucks, but, points toward an internal problem. Make sure you are wearing headphones and not monitoring with ANY other device connected.

You can also try with the ground flip or ground lift on the unit.
write down your results.
Cpartipilo
Thread Starter
#57
14th May 2009
Old 14th May 2009
  #57
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RTR, I would not worry about it. It's not like there are tons of threads with this problem. There might have been a bad run of units or there would be problem threads all over the place. Besides, the guys at proaudiostar have always been willing to help deal with ART in order to make it right. Test your unit and please let us know that yours is fine.

memphisindie I tried lifting the ground from IEC connector inside, no change. tried tying the chassis ground to the XLR's in/out, no change.

I understand what you are saying about compensating with the output gain. With any preamp design the higher the total gain from input to output the more floor noise you get. This is not the problem here.
There is a very clear difference between hiss and hum.

My unit hums terribly when getting into usable gain settings (+25 - +35db total) they might have had a bad run or something like that because most reviews in this unit are positive.

It's been a while since i experimented with the unit but when i did i could not get rid of the hum. i want to hook the scope to the output of the DC converter, i'd bet there is AC leaking there and finding it's way into the audio path. But we should not have to be electronic techs to use this stuff, it should be usable from the factory.

I have other preamps, from symetrix to universal audio and nothing else exhibits this hum.

hopefully i'll have time soon to star playing with it again soon and find a solution.
RTR
#58
14th May 2009
Old 14th May 2009
  #58
RTR
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Quote:
Originally Posted by Cpartipilo View Post
RTR, I would not worry about it. It's not like there are tons of threads with this problem. There might have been a bad run of units or there would be problem threads all over the place. Besides, the guys at proaudiostar have always been willing to help deal with ART in order to make it right. Test your unit and please let us know that yours is fine.

memphisindie I tried lifting the ground from IEC connector inside, no change. tried tying the chassis ground to the XLR's in/out, no change.

I understand what you are saying about compensating with the output gain. With any preamp design the higher the total gain from input to output the more floor noise you get. This is not the problem here.
There is a very clear difference between hiss and hum.

My unit hums terribly when getting into usable gain settings (+25 - +35db total) they might have had a bad run or something like that because most reviews in this unit are positive.

It's been a while since i experimented with the unit but when i did i could not get rid of the hum. i want to hook the scope to the output of the DC converter, i'd bet there is AC leaking there and finding it's way into the audio path. But we should not have to be electronic techs to use this stuff, it should be usable from the factory.

I have other preamps, from symetrix to universal audio and nothing else exhibits this hum.

hopefully i'll have time soon to star playing with it again soon and find a solution.
Thanks..I feel better now!!! I will let you all know how it works tomarrow...Dont know when it will arrive but I will test it and post FOR SURE!!!
#59
14th May 2009
Old 14th May 2009
  #59
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looking forward to reading your results.
RTR
#60
17th May 2009
Old 17th May 2009
  #60
RTR
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OK..I got my mpa 2 day's ago and, I think this thing sounds fukin great, I have grace m101 and a few other nice pre's but I am in love with this unit for the moment..I did some scratch acoustic guitar tracks with 2 different mic's for stereo and It sounded good for a fast test..I can post it if any one wants to here it!!
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