stupid question regarding EH12AY7 or any other outboard pre

[analoghacker]

well, not so easy to clip the 12AY7... with ordinary mic levels. and, it will swing alot of volts before it does. depending upon your particular set of tubes, it will be somewhere between +18 to +28 dBu output. it has alot of headroom. it will clip the crap out of your destination... especially if its a bit o prosumer kit. its easy to adjust a board fader that you can send to first, but lots of simpler equipment has a buffer in front, which you will mosh. given its 40-something dBu of gain, an input level of -20 something will do it. so, if you can get 70.7mV RMS into the wide open input, that should get you into pre-clipping territory. 120mV should definitely clip it hard.

[standup]

I've looked at these EH 12ay7 threads and I'm not finding the answer -- does anyone know (JC does, but may not be around) which tube goes in which socket? Mine shipped with 2 x 12au7's, I've now got a 12ax7 on one side and 12ay7 on the other. Which socket is the "correct" one for the 12ay7? Left or right?

[Recycled_Brains]

I've looked at these EH 12ay7 threads and I'm not finding the answer -- does anyone know (JC does, but may not be around) which tube goes in which socket? Mine shipped with 2 x 12au7's, I've now got a 12ax7 on one side and 12ay7 on the other. Which socket is the "correct" one for the 12ay7? Left or right?

The answer is in this thread actually. haha. the AU goes in the left socket (same side as the input knob).

-ryan

[standup]

I got one Telefunken 12ax7 and I put it in the EH pre, but wasn't really blown away. Now I know which socket is the "right" one, I can either leave it there or put it back in a guitar amp where it's a little more fun.

[A-Barr]

I got one Telefunken 12ax7 and I put it in the EH pre, but wasn't really blown away. Now I know which socket is the "right" one, I can either leave it there or put it back in a guitar amp where it's a little more fun.

Probably biases pretty cold if it's in an AU or AY socket.

[analoghacker]

the circuit is a special case of cascode... thats why the gain doesn't change so dramatically when you switch from tube to tube. the 12AU7 is necessary to drive a low Z load... impossible with a 12AX7 or 12AY7. borderline with the 12AT7 too... the left side is the output side. right is the input. the current/bias is established with a current source so it doesn't matter which tube you stick in. as long as it has the right pin-out.

gfvbhnj

[JASIII]

Funny, mine shipped with 12ay7's in both sides. I got mine right after they came out.

[analoghacker]

well, in some ways that is typical for eh. i have worked here for 10 years tomorrow, pearl harbor day, and it is not a straightforward place to work or do business with. however, the one significant saving grace is that it remains devoted to making original interesting sounds. that, in this day and age, is saying something.

it doesn't matter if its 2 12AY7s or the 12AY/AU7 spec. for most of the situations where one would find themselves using a 12AY7 mic pre. very very few people are driving 600 ohm transformers these days. its all prosumer HI Z or 10K minimum everywhere. however, i wanted it to saturate and sound rich if someone with the taste and understanding to recreate the "old school" kind of kit to record with. a 600 ohm inline load (between pins 2 and 3 on the XLR) can be used to experiment with this. you WILL lose gain. but it will get "round and midrangey", a very 1960's kind of thing. make sure to use a 12AU7 in the right spot or you will have very little out. there isn't enough cajones in a 12AY7 or 12AX7 to drive 600 ohms at any level other than as a distortion box. thats another design you are welcome to screw around with on yr own.
jc

[jv]

it doesn't matter if its 2 12AY7s or the 12AY/AU7 spec. for most of the situations where one would find themselves using a 12AY7 mic pre. very very few people are driving 600 ohm transformers these days. its all prosumer HI Z or 10K minimum everywhere. however, i wanted it to saturate and sound rich if someone with the taste and understanding to recreate the "old school" kind of kit to record with. a 600 ohm inline load (between pins 2 and 3 on the XLR) can be used to experiment with this. you WILL lose gain. but it will get "round and midrangey", a very 1960's kind of thing. make sure to use a 12AU7 in the right spot or you will have very little out. there isn't enough cajones in a 12AY7 or 12AX7 to drive 600 ohms at any level other than as a distortion box. thats another design you are welcome to screw around with on yr own.
jc

JC,
This sounds interesting. Would the 600 ohm load need to be a transformer, or would a 600 ohm resistor have the same effect?

[Matti]

hey roddy,
you can generally load a dynamic mic or ribbon (not a condenser) with anything from 1:1 up to 1:10 source impedance to load impedance ratio without peaking... above 1:10 you can have a rise in the upper register, or even a peak due to inductive effects. loading a mic down (anything below 1:1 matching) will have a deleterious effect on output level, frequency response at the extremes and distortion. you can generally assume that the best bandwidth to output ratio will occur with a 1 to 10 loading (one order of magnitude) but this will not be true in all cases. it will depend on how the mic element is interfaced to the outside world. if the element is transformer coupled, and you add another tranny after it... you get a more complex situation due to the multiple poles and losses. condenser mics have active buffers or gain stages built in between the element and the rest of the planet. whatever the output impedance of the amp is, it will help to look "up" into its load. 4 to 10 times minimum is plenty. "infinite" is even better. in electrical terms, "infinite" is practically anything above one order of magnitude (X10). there is no ideal infinite in the adult world... only sort of infinite.
jc

Just to make sure ( my english sucks ) it would be OK to
put a 1:10 trafo to the input and use it with condenser mics also?
I?m thinking of putting a trafo on outside of the case in its mu-metal sreening, the round ones, you know.

Thank?s

Matti

[analoghacker]

hey matti,
your english is just fine.

but, it won't go so well to use the tranny the way you imagine because the condenser mic won't get the phantom supply voltage it needs. the tranny blocks DC, allowing only AC through, depending upon the bandwidth and power characteristics it has. it is a more invasive modification to move the phantom connections in the 12AY7 and to insert a step up tranny in between that and the rest of the preamp. however, that would be a great mod to make... and it would move the pre into a higher level of usefulness and performance. for the work you would be doing and the money spent, i would hope so! it is very do-able, but not for the electrically disinclined or the faint of heart. you will have to take the preamp apart, mod, and then put it back together.

jc

[Matti]

Thank?s for the answer! I know the phantom issue
but I think I could deal with it once I find the phantom 6k800 ohm
resistors?
I was thinking of using a Cinemag CMMI-10B or similiar.

Regards

Matti

[Matti]

That was: If i put the transformer in the point where
the phantom resistors are, or to be precice after them
like in>ph>trafo>rest
Am I lost or not

Matti

[analoghacker]

you have the flow of the circuit just right matti....
but it isn't only the resistors, but the phantom supply connections as well. there is a "soft start" circuit you will want to move too. you will need some shielded wire and a razor knife to cut and scrape some copper traces. a good soldering iron and simple tools. thats it. you can find the phantom stuff easy on the board, its the first stuff after the input xlr socket.
write when you get into it... i can help her online if you need it.
jc

[analoghacker]

hold it, i am an idiot! actually, its really easy! there are some 1u film capacitors that block the phantom from the preamp. just remove those and you can use the solder pads to attach the primary and secondary of your transformer. thats it. no cutting or chopping of any kind...
let me know how it goes.