EHX 12AY7 Mic Pre - Hum Problem Solved

SonicAlbert said:
I got yet another negative feedback from the person. But this time he left a message explaining why:

"You're part of a shill selling thread."
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I hate to fan any flames, but I'm hoping that raising a stink might help to resolve the problem. I got the same negative feedback treatment as SonicAlbert:

"These EH threads are clear shill selling, and you are participating."

Actually, I bought my EHX preamp as a result of reading threads on this board and on the TapeOp board. So, if anyone has been duped, it was ME. Furthermore, even if my intention was to participate in a shill operation, I don't really think that offering technical information for solving an electrical hum problem is going to serve to lure people into buying a $200 preamp. To this point, I haven't actually said anything positive about the preamp. So, if I'm a shill, I'm a pretty lousy one.

Now, let's get back on topic with this swindle...er...thread. :cool:

I had a chance to use this preamp on a Fender DeVille 4x10 amp this afternoon. It worked nicely with a Beyer Soundstar MKII mic flat up against the grille on crunchy and moderately overdriven sounds, but I didn't like it as much on a heavily distorted source. The heavy distortion patches worked better when I used a Sennheiser E609 Silver mic. The EHX wouldn't be my first preamp choice with this mic and this amp, but it was very usable. Finally, everything sounded surprisingly huge when I used an Audix i5 mic on the amp (again, with the EHX preamp), but it would need some heavy EQ to sit well in a mix. There was also a faint but noticable recurrance of the electrical hum when I used the i5 that I have yet to figure out. It was much more faint than the hum that I got when using unbalanced cabling, but it was still annoying. I'll post a solution here if and when I figure out what's causing it.

Now, if you'll excuse me, I need to get back to my job of selling tonic that makes an ordinary human as strong as an ox, enlarges your penis, and gives you an incredibly low mortgage rate.

- Jerfo
 
well,

shill thread or not, the moron is still a coward..he never signs...shouldnt be too hard to find though, just look for a guy walking around with a Gestapo flag pole up his ass. and red chiclet in his pocket ;)

now...i dont really give a damn about the reputation points...but mistaking enthusiasm with saying this is gold and everyone should get one is one stupid thing...even if ppl, me included, were saying that this pre is gold, what would anyone have to do with that?? mind your own fucking business, no one's making you buy the thing...besides, there's been some very good samples posted, made with regular and ordinary interfaces, and lots of talent...i think that speaks volumes about this pre. shill thread!? who the hell are you and who's concepts do you live by!? what about when the wharefdales came out, everyone jumped on the wagon.."well if more than 20 ppl go with that", all of the suden is not shill anymore!? or do u have to have like 4505493 positive rep points to be alowed to show enthusiasm for a piece of affordable but GREAT gear!? i bet if that thread was about the new neve pre everyone would have positive rep..

a great company that does nothing but great gear for 20 years, and somehow keeps it affordable, obviously deserves no credit or enthusiasm. lets all give it to neve and his 1400 dollar pre (he sure as hell needs the push), or that company that makes 3000 dollar rack stands, or whatever company that makes a pair of active monitors and puts a 10000 dollar tag in them..whatever.
 
SonicAlbert said:
Somebody gave me negative REP feedback just for participating in this thread. Weird.

Anyway, Ben, that PL-8 II is really not a power conditioner, it's a rack power strip with some filtering and a surge suppressor. True conditioners actually take the incoming power, clean up the signal, and then output the cleaned up power. The real deals have very heavy transformers in them, which the PL-8 II doesn't.

However, I have several Furman Pl-Plus rack power strip units and they are well built. If you can afford to keep the PL-8 II it's an improvement to have the power outlets in a nice solid rack unit in my opinion. I just don't know how much good it is going to do in solving your hum problem.

I really think the place to start searching for your problem is in the rack cables and how the cables are run. While I realize those hum eliminators can work, I think using them is like putting a bandaid on the problem. Better to really sort out what the root cause of the hum is and then fix it.

You need to test all the cables, try swapping them out. Make sure that every cable in the whole audio chain is the proper cable for the gear on both ends of it. You'll probably have to read the manuals to sort all that out. What's balanced TRS what's unbalanced TS, etc.

Then (or maybe do this first) check to see how your cables are being run. You *must* avoid running audio cables near wall wart or lump in the line power supplies. Those kinds of power supplies are notorious for bleesing huge amounts of hum into audio cables. Keep your audio cables as far from those things as possible! I know this from experience.

Don't buy anything new until you completely troubleshoot your current setup.
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Thanks for the advice Albert. Maybe I should have conferred with you guys before ordering the Furman! If it doesn't help, I'm out 20 bucks worth of shipping. Oh well. :(

As far as cabling, I'm using brand new XLR to XLR for the input, and a new XLR to TRS on the output. My soundcard does have unbalanced inputs though. Diogo seems to think this may be the problem.

As far as room positioning goes, I've tried as many different room positions as my cabeling will allow - no difference in hum.

I wonder: at the music store, we plugged the EHX into a Behringer mixer to test it. I didn't hear any hum there, but it was a loud environment. This has got me wanting to plug the EHX into my FMR RNP, and then run out of the RNP into my soundcard. Will this hurt the RNP to have the EHX running into it? Fried circuits? I saw them do it at the music store with the Behringer...
 
It shouldn't be a problem, but the RNC is unbalanced as well. Seems like you need a properly wired XLR to TS cable.
 
That's something I haven't tried yet. Thanks for the tip Albert. I'll see if I can borrow one. It sounds like you're suggesting that running an XLR to TRS into an unbalanced input on my soundcard may be causing the problem (?)

What do you mean by "properly wired." Is there anything else to watch for when I go to pick up an XLR to TS cable?

Thanks again Albert. You really seem to have a handle on the electrical side of things. I'm strictly a newb when it comes to this side of the process.

One more thing: I've got an RNP, not an RNC. Is it okay to string two preamps together? I.E., run the EHX into the RNP preamp? At this point I don't believe it's going to cure the hum, but I might like to check out the sound.
 
It's okay to string two preamps together, as long as you realize that you will have a lot of gain going on. So you'll need to run either or both of them at lower levels. So if you need 50 db of gain for example, you'd have to divide that between the two preamps. As far as cabling, I think that would XLR from mic to the first preamp, XLR from the first preamp to the second, then XLR to TS from the second preamp to the soundcard input, if that is unbalanced.

Properly wired means to me that the cable matches the gear on each end and the wiring of the connectors on each end interfaces correctly. It's not that complicated really, but many people just throw whatever cables they have onto their gear. It often works fine, but some gear is more finnicky than others.

Since it seems others have commented on a hum from the EHX preamp, it might just be a problem with the unit. Make sure you keep the wall wart far away from the audio lines--very important!
 
Albert, you are indispensible. Thanks again. :)

I'm going over to a buddy's house right now to borrow a XLR to TS cable which I'll try running from the EHX pre into my soundcard with unbalanced inputs (btw - thanks to diogo for informing me that the M Audio 2496 inputs are indeed unbalanced - news to me). Next, I'll try the RNP / EHX scenario you outlined above. Thanks for breaking it down for me.

Who knows, after all this troubleshooting, we may just end up concluding that this pre is just a noisy piece of gear. Worst case scenario, I wont be able to use it on as many stacked tracks as I'd like. The sound of the pre itself is one I'm pretty stoked on.

Kudos to Walter Tore on his success with his so far.
 
Ben Logan said:
Albert, you are indispensible. Thanks again. :)



Who knows, after all this troubleshooting, we may just end up concluding that this pre is just a noisy piece of gear. Worst case scenario, I wont be able to use it on as many stacked tracks as I'd like. The sound of the pre itself is one I'm pretty stoked on.

Kudos to Walter Tore on his success with his so far.
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Hi Ben: I hope it goes well. If it still hums, bring it, your mic, and all your stuff to the local music store. There is something going wrong in your chain of lines, gear. I just posted another song, Going Back to 1963. It is a solo harp song, with 2, C414 mics, placed the same distance apart, and deep from me. one mic was throught the EH, and the other through the ART TPS. The EH is panned full left and the ART full right, in the mp3. I used guitar cables from the preamps to the soundcard. I hear no hum. Walter

http://www.soundclick.com/bands/7/waltertoresspontobeat.htm
 
As promised, I made a couple sound clips of the EHX preamp in a couple of different scenarios:

1. Electric / Distorted guitars:


This track uses a variation of the mic technique documented in another recent thread on this board. Instead of using an AKG 414 and an SM57, I used a Studio Projects B1 and a Beyer Soundstar MKII. The mics are positioned roughly 4-6 inches from the grille, pointed towards the left corner of the top right speaker of a Fender Deville 4x10. I also added my homemade omni mic about 10 feet away from the amp. The B1 is going through the EHX mic pre, the Beyer is going through an Art Pro Channel, and the omni is going through an M-Audio Tampa. The distortion is provided by a Roland VG88. The guitar is a Godin LGXT.

The clip starts with just the B1, panned <100. The second strum is of the Beyer, panned dead center. The third strum is the omni mic, panned <50. The fourth strum is all three mics. Then, the rest of the clip is those three mics combined with an overdubbed second take. I used a slightly different guitar sound on this take and panned everything as a mirror image of the first take.

The EHX preamp was a real pain in the butt during this recording. The input gain knob is ridiculously sensitive (and noisy) around 8:00. If you move it clockwise just a hair, the gain is way too much. If you move it the other way just a hair, it's too little. I spent about ten minutes just tapping the thing in the hopes of it settling on an appropriate middle ground. The good news is that there was no hum.

2. Acoustic Guitar -


I was recording an acoustic guitar track with an odd tuning - DADABD - and started noodling between takes. This is a recording of that noodling. I used Studio Projects B1 and C3 mics in a mid-side formation. The B1 went through the EHX preamp, while the C3 went through the Tampa. I also used the direct sound from the guitar, which went into the Pro Channel. The guitar is an Adamas carbon fiber top guitar; I don't know the specific model number off hand. The noise floor in the recording is partially from the EHX preamp, but mostly from the Tampa/C3. I like how mid-side sounds on acoustic guitar, but you really need to crank up the "side" mic when you do it. That typically leads to a bit more hiss than I'd like. There was no hum coming from the EHX preamp.

I hope that these clips give you an example of what the preamp sounds like on a couple of different sources and mixed with other preamps.

- Jerfo
 
Hum

Hi. If you're like me, you bought a 12ay7 pre and got some nasty low frequency hum from it even out of the XLR balanced outputs into balanced gear. Here's a tip to try that fixed the issue for me if you are one of these folks.

Disconnect the shield (pin 1 wire) on the mic cable going out of your EH pre. Lifting the shield can sometimes cure these type of problems with certain gear. Some consoles (like our DDA-DMR12) like to have the shield lifted at the destination end anyway. I keep some short mic cables lying around with the shield (pin 1) lifted anyway just in case I need this type of interface. This cured my hum issue and the pre is very quiet now with plenty of gain for many things :-) Now, if only mine didn't pass phantom power ALL THE TIME even with the switch off!

Hope this proves useful to some folks.
 
Lifting a shield never truly cures grounding problems. It only masks them. The hum is still there. It simply has no place to go. Whether this is a significant problem or not depends on how the device is wired, but either way, I tend not to like to lift grounds if I can help it.

By denying the hum a path out of the gear, you are preventing it from passing through the output cable's shield (where it would induce hum in the signal lines on its way). The problem is that this means you still have a significant voltage potential between the signal ground and true ground. If that signal ground is also the chassis ground, this could result in a nasty shock if you touch that piece of gear. The AC potential has to go somewhere, and it is better if it doesn't go through you. :D

The best fix, IMHO, is ground bussing. Properly ground the signal and chassis grounds using a large gauge wire (10AWG is usually sufficient) to an earth ground. This will basically act as a "hum sink". Thus is relatively easy to do.

Build a short "pigtail" cable (XLRM to XLRF in this case, but you can do the same trick with 1/4" cables). Build it like you would a normal audio cable, but on the end of the cable that plugs into the misdesigned unit, add a 10 AWG (or larger) green wire (safety first: always use green for a ground) connected to the ground pin. For XLR, ideally, you should also jumper that ground pin to the shield contact on the plug to zero out the chassis ground.

Next, you should connect the other end of the green ground wire to the ground pin on a power plug. Plug the plug into the wall outlet. This should stop hum dead unless you have a bad building ground. :D

Once you have a ground bus established for one device, you can take advantage of the same technique to make the noise floor for your studio absolutely plummet. Add a ground bus adapter to every piece of your gear in your studio, then tie them all together at a single common point, and finally, tie that common point to the electrical outlet's ground, as mentioned. You would be amazed at the difference this can make.
 
Nice info, dgatwood. Basically you're suggesting a studiowide "star grounding" scheme, no? Out of the vast array of gear at the studio, the EH pre is the only piece I've ever had that has this ground hum (if that's what it is) in the last 9 years at this location. Everything else in the control room is connected and grounded through the same power source (same in the main live room-different source) and is dead quiet into Pro Tools (except for some older pre's and devices we have that were inherently a bit noisy- but no 60 cycle, just less than modern signal to noise specs). I have had literally tons of very new, very used, and very old gear come through here with no issues (thankfully). Something was just fruity with this unit or build. The EH pre has a 2 prong wall wart power supply so maybe you know how this type unit would be grounded? It is on a PCB and the power output has a two cable lead to it (I'd assume hot and ground).
Good info on the pigtail ground rig!
 
thats why i would never buy into the the real tube pre for cheap. most eh stuff looks pretty crappy to me. i would rather save. i remeber that big muff though. you would step on it and that thin cheesey metal would buckle not to mention the way it would eat batteries. i mean they look so kool and retro but to me its like buying a set of headaches. good luck with it. if it were me i would sell it though.
 
bounce said:
Nice info, dgatwood. Basically you're suggesting a studiowide "star grounding" scheme, no?
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Yup. Rigged my home TV studio that way back home in Tennessee, and ended up doing the same trick for my home recording studio here in Cali. Works quite well.

bounce said:
The EH pre has a 2 prong wall wart power supply so maybe you know how this type unit would be grounded?
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It isn't grounded. Two pin power plugs are hot and neutral. Therein is the problem. The whole preamp has a floating ground. While that isn't always a problem, it can be, depending on how well they filtered the power supply before it enters the case and whether they mistakenly treat one side of that power rail as a signal ground. When the power supply ground is completely floating, that's one of the rare cases where you -do- want a separate signal ground, since you don't have a true ground anyway.

Anyway, yeah, this sounds like a prime candidate for a grounding pigtail....
 
This is all quite informative but I'm thinking it is all speculation unless we're specifically referencing the design of the EH pre; the preamp in question here. Since the adapter is not grounded, one would think it is a "floating gorund" or some similar setup (I'm no electronics expert for sure- someone who has one of these preamps feel free to chime in here). Therefore, one would think the design surely would not use the shield on the XLR out as the main power grounding artery. I don't think EH would be able to get these on the market in the US with such possibly dangerous design. Can anyone with an EH pre and a good electronics background clear up the issue with the hum and lifting the shield as a solution? :-)
 
Thanks, Lucio :-) I had read that thread before and went through it again. Excellent. Trick is with mine that I'm going straight out of the balanced outs to my (not prosumer) Digidesign 192 I/O converters and was still getting the hum until I disconnected the shield (some fruity gorund loop that only that pre gives me).
I posted on the tape op thread to see if JC might know why phantom is always on on my unit :-)

Thanks again.
 
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