yet another EH 12ay7 thread

[KennyLusk]

I don't remember seeing any internal pot on the PC board. I could be wrong but I think somebody's messing around.

[Recycled_Brains]

after my first one died, i got another last week and tried it on electric guitar. i, too, was getting that crackle on distorted, electric guitar. i thought i was blowing up my ribbon mic and freaked out. but when i changed pres, it was fine.

so are people saying to just switch to the 1/4" output or turn the trim down on the internal pot?

for you folks who turned the internal pot, is there a noticeable change on how it works with other sources? i used to really like this pre on top snare and vocals.

I think the "crackle" is happening because you're eating up the headroom of the preamp, and the tubes are breaking up/distorting. Happens from time to time with my tube pres. Usually backing the mic off, or changing the angle of the mic, or turning the guitar amp down takes care of it. Or try using a lower input gain setting (don't worry about recording dist. guitars "hot" in a DAW). I've found that the 12AY7 and other tube pres tend to break up faster when you have the input higher, because you're feeding the tube on the input stage more level, driving it to distort more quickly(often a cool sound, but not always). I find this to be a problem more often with loud guitar amps and vocals, than with other sources.

The preamp you changed to probably just has more headroom than the 12AY7.

That internal trim pot might be a bias of some sort, for the tube, but I don't know for sure. I think it's been addressed in another thread, so maybe do a search to see if you can come up with something.

Adjusting it might affect the headroom, and allow you to feed it a hotter signal before clipping. If you do adjust it, just make sure you mark the original position so you can put it back if you need to.

EDIT: I found this post from the dude that designed the thing:

the trim pot is the current source set. it does not effect the gain until it is almost off or insanely on. it is most definitely NOT user adjustable. you would need a scope and voltmeter to set it.

And this from a poster on the same thread:

Everyone! After some minor electric chocks, I found a trim pot inside the 12AY7 which seemed to help out alot. The level is now lower out from the preamp BUT I can have my guitar amp really loud going in to the 12AY7 and I can use full gain without nasty clipping.

[permanent hearing damage]

hmmm... i know a headroom issue would be the easiest explanation but just a few details have me second guessing that. i had the gain at maybe 9 or 10 o'clock. the peak light didn't even start to flicker until at least 1 o'clock. some other details: i was using an orange ad-30 reissue (it only puts out 30 watts, and def was not cranked). it was mic'd about a foot away with an oktavamod apex 205 ribbon - a relatively low output mic. oh and the pre i switched to was a sytek, which obviously has more headroom.

i just thought it was weird because it was a different type of crackle. it didn't sound like an overload, ya know? and it seemed other folks were having this same problem, no? or did they just determine it to be headroom. i kinda lost track when people started talking about the hum and 234897 other things about it.

thanks for clearing up the stuff about the adjustable pot. over my head entirely. ha

[punkrockdude]

I was the one who got some minor electrical chocks opening this thing up. When I lowered that small pot from full, like 5 o'clock, to 3-4 o'clock, all the crackling dissappeared. The volume change was not major so that it was a problem at all. I also got crackle micing really quiet stuff but this really solved my problem with it and I almost love this preamp now. Regards

[KennyLusk]

Sometimes you have to do some real deep investigations on your own cause no one else seem to be able to give the right answer. It was a while ago, but I think i remember the solution. Open up the pre and inside on one of the pc boards there is a trim knob that is flat and small. Just lower it from 5 o'clock to 3 or 4 o'clock. Woila!

I hope this helps you out and please write back and tell me/us how it went. Regards

I finally got the time to open the box back up and check out this fix and I can hardly believe my ears!

It actually worked! The crackling and squealing stopped completely. Now I can buy another to make a pair and rackmount them with confidence.

Punkrockdude, you're the man! I owe you dinner and a couple of beers next time I'm in Sweden. Thank you.