Help with possible broken EHX 12AY7

[jckinnick]

Im running a 1/4 cable out of a Tascam DP01 into the 1/4 outputs on the EHX and then an XLR out of the EHX input into a mic. All I get is hiss i cant even hear the microphone. When I got the thing one of the tubes was loose and there was something rattling around inside I opened it up and it was some kind of clips I didnt see anywhere that the clips went so I left them out. I got it to work once but now its nothing but hiss.

[nlmd311]

Hey jckinnick,
You might want to see if any of these threads can help you out:

http://messageboard.tapeop.com/viewtopi ... 7+buffered

http://messageboard.tapeop.com/viewtopi ... 12ay7+hiss

http://messageboard.tapeop.com/viewtopi ... ight=12ay7

http://messageboard.tapeop.com/viewtopi ... y7+monitor

If I read your description correctly, it sounds like you are running out of the 1/4" monitor output of the 12AY7. If so, that could be your problem. The 1/4" output is a buffered out to be used for monitoring the signal, not as your source signal.
Have you been able to test it running XLR out of the 12AY7 to TRS into the DP01? Same issue? Try running balanced out of the 12AY7 into the DP01 and see if that doesn't eliminate the issue.

My apologies if you have already done this and I misunderstood somewhere.

-Darrill

[jckinnick]

Thanks for the help

Ive also tried XLR out and in and it does the same thing. Ill give those threads a look.

[jckinnick]

I know how to tell the difference between an balanced and unbalanced 1/4 cable but how do you tell on an XLR?

[nlmd311]

Assuming the XLR is wired properly, one pin will be your positive, one will be the negative and the other (traditionally pin 1) will be the ground. Your ground will be pin 1, while your pos. and neg. can be on either pins 2 or 3 (making sure they are the same on both ends so as not to introduce phase reversal...unless you are making a cable specifically for that). If it is an XLR to XLR cable wired "properly", it will be balanced. You can check to be sure the positive, negative, and ground wires are all in place by taking apart the connector.

Hope that helps

-Darrill

[jckinnick]

Assuming the XLR is wired properly, one pin will be your positive, one will be the negative and the other (traditionally pin 1) will be the ground. Your ground will be pin 1, while your pos. and neg. can be on either pins 2 or 3 (making sure they are the same on both ends so as not to introduce phase reversal...unless you are making a cable specifically for that). If it is an XLR to XLR cable wired "properly", it will be balanced. You can check to be sure the positive, negative, and ground wires are all in place by taking apart the connector.

Hope that helps

-Darrill

So I can assume an XLR-XLR factory cable is always a balanced cable?

[nlmd311]

It should be. Unless it was wired differently for some strange reason...But, yes, an XLR - XLR should be balanced.

Have you had any luck with any of the stuff that was discussed in the other threads?

Do you have an XLR - TRS cable? After looking at the specs. of the DP01, it appears that it is balanced. If you haven't already, try running XLR out of the 12AY7 to TRS into the DP01. This would be the recommended set up for connecting the two. This will keep everything balanced and will allow you to troubleshoot further. If the hiss is still around after this, then you can set the cabling aside and try a tube swap, or possibly a faulty power supply, maybe a bad solder joint on the board...etc.

If you happen to have any extra 12xx7 tubes around that you could swap with those that are in there currently, you could try to rule out it being a tube issue (since you mentioned that one of the tubes was loose when you got it), if you have ruled out the cable and way it is hooked up.

I'd start by hooking it all up balanced.

-Darrill

[jckinnick]

It should be. Unless it was wired differently for some strange reason...But, yes, an XLR - XLR should be balanced.

Have you had any luck with any of the stuff that was discussed in the other threads?

Do you have an XLR - TRS cable? After looking at the specs. of the DP01, it appears that it is balanced. If you haven't already, try running XLR out of the 12AY7 to TRS into the DP01. This would be the recommended set up for connecting the two. This will keep everything balanced and will allow you to troubleshoot further. If the hiss is still around after this, then you can set the cabling aside and try a tube swap, or possibly a faulty power supply, maybe a bad solder joint on the board...etc.

If you happen to have any extra 12xx7 tubes around that you could swap with those that are in there currently, you could try to rule out it being a tube issue (since you mentioned that one of the tubes was loose when you got it), if you have ruled out the cable and way it is hooked up.

I'd start by hooking it all up balanced.

-Darrill

All ive got like that is an XLR-TS and it didnt work Ive also tried a straight XLR-XLR cable. Ill try and change the tube and open it up and see if I see anything that isnt soldered good like I say when I opened it up out of the box one of the tubes wasnt in good and there were some clips rattling around in it. If that doesnt work I guess Ill have to buy a XLR-TRS and try that.

[nlmd311]

Yeah. The XLR - TS would be unbalanced so you wouldn't notice a difference in that. Does the DP01 you have have XLR inputs? From what I've seen on the Internet, the DP01 only has balanced 1/4" inputs, unless it is the DP-01FX...I only bring this up because you mentioned you tried XLR - XLR and I'm wondering if you introduced something else into the chain that may have caused a noise issue.

Funny you mention the tube thing again because it just made me remember an issue I had with my 12AY7 when I first got it. I noticed that whenever I flipped the Phantom Power on, the Power LED would dim and then go out. I checked the tubes and sure enough one of them was loose. I took out the tube and reseated it and haven't had a problem since. I am guessing that due to the way these are packaged, they probably get knocked around a bit in shipping and end up with a few loose tubes, and possibly some other parts. I know it is completely unrelated to the problem you are having now, just thought it was funny that mine also had a loose tube and that it ended up being the source of a problem.

I'm still sticking with the cable as being the culprit though, until that is completely ruled out.

Any chance you have any TRS connectors around? Any TRS cables sitting around that aren't getting used all the time? If so, you could take one off of one of those cables, and swap it onto one end of one of your XLR - XLR cables.

-Darrill

[jckinnick]

Yeah. The XLR - TS would be unbalanced so you wouldn't notice a difference in that. Does the DP01 you have have XLR inputs? From what I've seen on the Internet, the DP01 only has balanced 1/4" inputs, unless it is the DP-01FX...I only bring this up because you mentioned you tried XLR - XLR and I'm wondering if you introduced something else into the chain that may have caused a noise issue.

Funny you mention the tube thing again because it just made me remember an issue I had with my 12AY7 when I first got it. I noticed that whenever I flipped the Phantom Power on, the Power LED would dim and then go out. I checked the tubes and sure enough one of them was loose. I took out the tube and reseated it and haven't had a problem since. I am guessing that due to the way these are packaged, they probably get knocked around a bit in shipping and end up with a few loose tubes, and possibly some other parts. I know it is completely unrelated to the problem you are having now, just thought it was funny that mine also had a loose tube and that it ended up being the source of a problem.

I'm still sticking with the cable as being the culprit though, until that is completely ruled out.

Any chance you have any TRS connectors around? Any TRS cables sitting around that aren't getting used all the time? If so, you could take one off of one of those cables, and swap it onto one end of one of your XLR - XLR cables.

-Darrill

Yeah its actually a DP01 FX which has the XLR and 1/4 inputs thats how I was able to go XLR-XLR out of the Tascam and into the 12AY7 which didnt work. I need to get some TRS cables anyway and get everything balanced. All ive been using on everything is TS cables. I read that TRS cables are less susceptible to hum and hiss anyway correct?

[nlmd311]

Well, the problem with running XLR out of the 12AY7 and XLR into the DP-01 is that you are basically amplifying the already amplified signal. You'll want to bypass the internal preamplification of the DP-01 by inserting the 12AY7 after the DP-01's pre's. That would be where the balanced 1/4" TRS inputs would allow you to bypass this. When plugging in an external preamp you want the DP-01 to see a Line level signal, not an Mic level signal.

Balanced cables in general are less susceptible to hum. In a balanced cable, the two signal carrying wires are 180 degrees out of phase from one another. Think of it the same way that a humbucking pickup works on a guitar. The signal passes through, but hum is reduced, or hopefully eliminated.

-Darrill

[jckinnick]

Ok I found a TRS - XLR cable lying around with a gold pin on the 1/4 side, plus I changed the 12AX7 tube out and opened it up and looked around to see if anything was loose. Nothing seemed loose and the boards looked good no burn marks. I can now at least hear the mic I have plugged in and theres no hiss but there is a terribly loud hum. I dont think the hum issue was ever resolved in the other thread besides giving it a good whack. You had an issue with yours having a very loud hum at first to didnt you what did you do to yours to get rid of the hum?

[creature.of.habit]

Ok I found a TRS - XLR cable lying around with a gold pin on the 1/4 side, plus I changed the 12AX7 tube out and opened it up and looked around to see if anything was loose. Nothing seemed loose and the boards looked good no burn marks. I can now at least hear the mic I have plugged in and theres no hiss but there is a terribly loud hum. I dont think the hum issue was ever resolved in the other thread besides giving it a good whack. You had an issue with yours having a very loud hum at first to didnt you what did you do to yours to get rid of the hum?

i had 2 of these, kept 1 (selling it). the first 1 i bought works flawlessly, i understand it's one of the first units..no hums no nothing. second unit was very recent (in relation to the other) and it hummed no matter what - different valves, different cabling, different PSU (EH one), different room, etc.

nothing worked. i kept the good one but i'm also selling that one as well. sorry bout the shameless plug. if anyone's interested, let me know.

[E.Bennett]

send it to electroharmonix. if it's out of warranty, include $15 and a note describing the issue. they have a pretty quick turnaround.

[nlmd311]

Ok I found a TRS - XLR cable lying around with a gold pin on the 1/4 side, plus I changed the 12AX7 tube out and opened it up and looked around to see if anything was loose. Nothing seemed loose and the boards looked good no burn marks. I can now at least hear the mic I have plugged in and theres no hiss but there is a terribly loud hum. I dont think the hum issue was ever resolved in the other thread besides giving it a good whack. You had an issue with yours having a very loud hum at first to didnt you what did you do to yours to get rid of the hum?

Cool. I'm glad you were able to at least week out the hiss. As a last ditch effort, have you tried plugging the AC adapter into a different outlet? Or even flipping it the other way around in the same outlet? I have read that sometimes flipping the polarity of AC power cables and at times eliminate or reduce hum. I'll see if I can find the pages I read that on and post them up.

I don't recall mine ever having a hum issue. The main problems mine had from the start were the Power LED situation mentioned above, and very low gain. All of this ended up being related to the tube being loose and not properly seated. The tube was loose and once I seated it properly, the Power LED would stay on when Phantom was applied, the gain improved improved, and the pre opened up noticeably.

-Darrill