stupid question regarding EH12AY7 or any other outboard pre

[analoghacker]

hey,
this is jc morrison i am the guy that designed the mic pre. while i am happy that many of you are enjoying yourselves with this gadget, i am suprised and sorry there has been so much difficulty understanding its operation. i tried to make it as simple to use as i could. nearly ALL of the difficulties reported to us have come from 2 situations. some converter boards are not really balanced in, or are but only with certain settings (delta 1010 comes to mind..., it must be on the +4dB and NOT the -10dB in). nearly all of these complaints come from converters using TRS and not XLR inputs (other converters). the other problem we hear about is that the line voltage in germany is actually 220v. france and spain are supposed to be but are really always much closer to 230v. this means that the line voltage is too low for the wall wart we supply to germany. we stopped shipping there until the new wall warts are ready. i think they are on the boat now. chances are, if you are in germany, you can't get a 12AY7 mic pre anyway. we shipped less than 50. by far those are the most common issues i hear about. we do not currently have much in the way of production problems and every unit shipped is plugged into a mackie mixer with a marshall condensor mic (cheap and likely to be commonly encountered) and tested AFTER the electrical tests. none leave without sounding good. we do not have a converter board selection here... although, i've learned more than i care to about other companies' digital products...

yes the blue LED goes dim or out with certain condensor mics (the marshall, for example...). this does not effect the operation of the pre. it does show you how much sag the wallwart has when you add the draw of the phantom supply. this is the one area where the economy of the unit is apparent. i accept the responsibilty completely. if you can replace the 12VAC 1A wall wart with a 12VAC 2AMP supply, this will "fix" the lamp and the bass will be punchier too.

the 12AY7 mic is a cheap BALANCED gadget. just because it is affordable, does not mean that it is poorly made or designed. its a real tube mic pre. it does not rely on opamps to function. if you pull out the tubes, it will not operate, unlike some other "tube" pres you can find. the boards we designed are double sided heavy copper and cleverly layered to fit all the crap into the box. it is not cheap crap. we fit many other distortion, modulation, EQ and compression effects into the same box and that helps keep costs down. we use the same wallwart for all of them. i cannot agree with the notion that the board is cheap or poorly made. my friends and co-workers, the venezuelan and dominican women who assemble the boards, have more patience and a better attention span than myself, or any man i have ever met. i doubt many among you could do the work they do.

the number one problem for us was how to make it tubed and transformerless. that was how we could make it affordable. as a note to ken, if you have a "hum eliminator" or a transformer coupled DI box, you can check to see if the problem really is the tube socket or your converter. if the transformer eliminates all hum, the problem is most likely your converter. you pushing and shoving the tube just changes the capacitive loading of the high gain part of the circuit (hi Z). that changes the balance temporarily. it means the converter is not really balanced. if the hum remains, its the mic pre and it is a power supply problem... it is NOT a ground loop because the power is from an isolated wall-wart. the only ground connection is the one at your board, unless you ground the mic someplace ahead of the pre? the pre is balanced and does not require a grounded in. in fact, grounding one of the inputs will probably make hum, if the ground is dirty (you are essentially "unbalancing" the unit when you do that and it does have 50dB of gain...). this is why it is important to connect the output to a balanced input. many "prosumer" products are not truly balanced in. they ground or leave floating one leg and go unbal in to a non-inverting opamp gainstage. many differentially connected opamps do not have great balance, or they do but only at one particular input impedance.

the circuit of the 12AY7 mic pre is a classic tube "instrumentation" amp, such as you might find on the input of an old tek or HP scope. the one modern innovation is that the differential input is balanced with a FET current source, that forces balance to the tune of 100dB of common mode rejection. this is the only way to get good balance using tubes without an input tranny. trannies do better than this but add $40-50 to OUR costs. we could have used an opamp that cost $0.17 and it would have been more flexible and quieter. but it would not be a tube pre and i don't think it would have sounded as good either. you can buy any one of the cheaper "tube" preamps if you want that anyway. this is not that. in any case, the best way to get good results is to use it BALANCED in and out.

one other thing you should all be aware of... you can also "tube roll" with this pre for an added dimension of sonic flavor. provided you have a high impedance input to plug into, you can replace the 12AU7 with any 12A_7 type tube for some interesting changes. you can also replace the 12AY7 with a 12AX7 for a little more gain, a 5751 for a darker color, a 12AT7 for a more "frontal" or direct sound... (punchier but less detailed). mix and match. if you need to drive 600 ohms, forget it... leave the 12AU7 right where it is. i personally like using 2 12AY7s... its more delicate and colorful for airy things. 12AZ7/5965 is also very nice. but don't take it from me... play around with it. you can even put 2 12AU7s in it and use it as a balanced line driver... (lo gain). just make sure the tube you plug in is a 12A_7 type or pin for pin compatible. if you are not sure, don't do it. you'll void your warranty.

the addition of a transformer coupled DI box does make this unit more flexible and you can easily understand why so many people go crazy about transformers. it makes connection issues go away at some small sonic penalty or shift. but you also understand the savings in cost by eliminating the trannys.

i hope this is helpful to someone?

i will try to answer questions as i can...

ps: i do not have any connection to the sales side of things here so please do not ask about that. call new sensor and talk to customer service... or go to your local music store and buy one!

[trodden]

Mr Morrison,

Thanks for your lengthy and informative reply. Its greatly appreciated that the people designing the gear are also available to communicate about the gear.

Thanks for your time.

[darjama]

Thanks for elucidating some of the design points. but you've piqued my interest. Can you describe further what would change by using a 2A power supply? Is there any reason not to try this with the current production units?

Also, as long as we've got you here, any word on the 4-channel rackmount unit that's been rumoured?

Thanks! I really like the pre.

[analoghacker]

the sag of the wallwart can be prevented by increasing the current available... however, that will only get you so far because there is another transformer inside to step up the voltage to over 200 volts... it isn't going to get any bigger. so there is only so much current available. because the phantom supply is derived from the high voltage supply in this design, the demands of the particular mic will determine how much current is drawn from the wall. older condensor mics draw very little. modern FET/transistor models draw more because of the preamp circuitry. in this mic pre, the phantom supply can draw more current than the amp does... because one supply is used to generate many voltages (for the different functions of the preamp), what affects the one, affects the many. this is why using a wallwart with more available AC current can help... but only so much. and it will NOT radically alter the sound. thats the point! but you might get a little more. it depends on how much effort you want to put into a $200 pre. the tube rolling will probably be more immediate and you can voice the thing for your own taste.
jc

[;ivlunsdystf]

Analoghacker - Thank you very much for your attention and detailed info!

[joel hamilton]

Thanks JC. I am sure your input will help a bunch of us along in enjoying such a cool, affordable "gadget" as you described it.

[nlmd311]

Yes. Thanks!
I feel like we just had a show and tell and we should be applauding your participation.
The "tube rolling" idea is great. Thanks for the tips on that. I had wondered if this would work out... can't wait to try it.
It's always nice to have a better understanding of something that finds itself at home in your studio.
Thanks again for going into such detail.

-Darrill

[luckybastard]

i think the tube rolling just convinced me to get one. i wonder is there a tube combination to give it a low-fi "squishy" sound...

[KennyLusk]

Hi JC,

As the others have said, thanks for taking the time to fill us in on some details about this new box.

I want to provide you with a few points of interest for your info:

***For an audio card I actually use the 1010(LT) which has XLR In's instead of TRS so I'm under the impression I'm getting true balanced conversion. If you're aware of that not being the case I'd like to know so I can rectify it. However, tonight when I get home I'll insert one of my passive DI's into the signal chain between the pre and my card as a test.

***I didn't actually "push and shove" the tubes around when troubleshooting. I gently manipulated the socket because I could clearly tell there was a "shorting" problem and thought I'd isolated the problem at the tube sockets. By gently tapping my finger on the tops of the tubes I could hear shorting from the tubes. The tubes all checked out on my trusty B&K 667 so I figured the sockets must be the issue. Eventually, after carefully manipulating the sockets I was able to make the hum go away. Again, I'll insert a passive DI between the pre and the audio card to test the theory that it could be my card's converters.

***All power to the pre is conditioned so the hum is not coming from my power supply. I don't have much faith that the Hum X Eliminator will remedy the situation but I'm dedicated to finding out on my "user-level" what the heck is going on with this box.

It's a great box with an incredible sound. Like the other's I appreciate you taking the time to address some of our questions about the build.

[creature.of.habit]

fellas that have this already...

has anyone tried it with ribbons?

im wondering wether or not it has enough gain for that...

maybe with the tubes that JC described that would give the pre a little more gain...

anyway i really hope it can handle ribbons...

anyone?

[;ivlunsdystf]

It lacks the gain necessary for my ribbon (Shinybox 23c) the way it is shipped. I suppose tube swapping would help. EH dude, are you still there?

[analoghacker]

hey diogo,
the usefulness of the pre with ribbon mics will depend entirely upon which ribbon and for what... i will say right off the bat that it is not enough gain for a beyer m130 in a blumlein or other spaced mic setup. it is more than enough gain for an oktava ML-52 on a nasty guitar cabinet. if you are using the oktava or older RCA up close for a "cantelopes for balls" gene vincent style proximity effect on a male vocal, it'll work fine too. for other stuff, you'll have to try it and let us know... i don't know what the hell people end up using the stuff for! i spent a few days at studio G and saw all sorts of un-natural things... i even participated in some of it. ah well. thats your job.
jc

[jv]

Hey JC,
Thanks for all the info on this box. I just got one, and I've been digging it and so far, I haven't noticed any of the problems described by others. I do have a question, I was thinking of adding an input transformer, what do you think about that? I have a 10:1 transformer with 600ohm/60kohm impedance, and I thought that might give me enough extra gain to use it with my tape op ribbon mic. I didn't see any spec for input impedance on the 12ay7, it seems that could be a problem if it's too low.

[creature.of.habit]

i spent a few days at studio G and saw all sorts of un-natural things... i even participated in some of it. ah well. thats your job.
jc

lol

JC,

thanks for the reply (both of 'em). It will be used on a guitar cabinet (fender hotrod deluxe 40watts and epiphone valve junior 5watts), acoustic guitar (near the soundhole probably or around the 12th fret) and for a baritone like voice that can go pretty high as well (proxy effect and big vocal sound on some songs, yep). I'll be using this piece of chinese crapola..and be proud of it but i really hope it can deliver...i was really hoping to make the EH pre my only pre.

http://www.thomann.de/thoiw10_artikel-180190.html

thanks again for the support JC.

[KennyLusk]

diogo,

How do you like your epi valve junior?