Building my own PSU for Audio Technica AT 4060 tube mic!HELP

[squizo]

My car was broken into a few years ago, as these things usually go, the thieves stole a bunch of random crap and missed most of the valuable stuff. In their stupidity, they stole the PSU and the 6-pin tube mic cable for one of my AT 4060 tube mics, but they totally missed the mic in its square black case (maybe it was dark), so ive had a tube mic with no PSU or cable, reducing my awesome stereo pair of 4060's to mono boredom.

So when i had some extra cash recently i called up Audio Technica in Ohio, they politely informed me that they could sell me a replacement PSU for $480 plus $40 shipping (i live in kansas) and that a replacement cable would be $130 plus $25 shipping. For some reason shipping cant be 'combined' which is really nice of them. I was biting my tongue, but i kept my cool and asked them nicely if i could buy some 'parts' for the PSU, maybe the transformer or something and i got an even more polite 'NO'.

SO, im on a mission to build my own PSU for my 4060, does anyone here have any knowledge of suggestions as i move forward?

I recently took the other PSU i have to a tech friend to pull apart and give me the skinny on it. The tech, knowing about my delightful call to AT, was kind of dying to know what was inside this box that made it $500 to replace. To his and my dismay, it was kind of a joke really, according to him i need to find a transformer with 115v-120v Primary (duh) and two secondaries, one at 120v and one at 20v. Ive tried to search around the internets but have had no luck so i thought id share my story here.

Any help would be appreciated, as i plan to post my results of this journey as i plod along. I have actually acquired from MARKERTEK the weird 6-pin XLR cable mounts as well as the 6-pin XLR panel mount, Im assuming that a normal 7-pin tube cable like what REDCO carries will suffice as the 6-pin cable replacement.

Here we go.......

[The Scum]

Hammond probably make the transformer you need. Tubesandmore.com had a couple of house-brand transformers that might fit, as well.

Alternatively, there's the old trick of using a pair of regular transformers - 120V:20V, and then the other one connected backwards to that 20V to step back up to 120V.

Any idea how much current you need at each voltage?

What sort of regulation takes place in the supply? A couple pictures would be helpful.

[Nate Dort]

based on the schematic of the mic:

http://img314.imageshack.us/img314/5781 ... 0010fz.jpg

You need 120VDC on pin 5 and 6.3VDC on pin 4. Pretty simple. I don't think 20V on the secondary is necessary. That's a lot of wasted voltage. The 6922 tube runs on a 6.3VDC heater.

This Antek transformer will get you there. It's probably overkill for the current you'll need, but it's cheap enough.

http://www.antekinc.com/details.php?p=637

A few diodes and caps (maybe an RCRCRC network to smooth everything out), and you're set.

Also, pin 6 is floating, so theoretically you could get away with 4 conductors and a shield. That's what the Royer tube mod mics used. Star-quad cable works fine for this, and it's cheaper than dedicated tube-mic cable. I'd just keep the length fairly short to reduce possible interference between the voltages and the signal. Maybe 10 ft or so. If you filter the heater and B+ voltages enough, you won't have any issues with interference anyway.

[squizo]

Many Thanks NATE DORT!

Transformer and the other parts and pieces have been ordered. Stay tuned

[themagicmanmdt]

nate and squizo:

the 20v secondary winding is used because you're taking 20v AC and needing to filter it to 6.3v DC. usually you don't want to run AC winding through 20+ feet of sensitive cabling because, even though they're tightly wound, you have a likely chance of getting hum in your sensitive mic signal.

so, in short, you don't need a 20v secondary per se; but you do need one under about 30-40 volts in order to do recification and filtering to DC. the filtering will most likely involve a large choke/inductor, since filament draw pulls higher current, which means that using just an RC filter will either cause too much voltage drop, or, when using the right values for voltage, won't be filtering enough.

so, my thoughts are that your 6.3vAC winding used directly to provide filament power to the mic will yield most definitely a noisier mic of your stereo pair. it may be definitely sounding good, but also tube mic 'gurus' say they hear a difference in AC and DC filament powered versions of the same mics.... although I would say the difference would be slight in the tonality they're mentioning.

if you do build the mic using AC filaments, please post back and let us/me know if it's as quiet as the other one; and if you hear any difference between the mics that you didn't hear before. curious!

-mt

[squizo]

the 20v secondary winding is used because you're taking 20v AC and needing to filter it to 6.3v DC. usually you don't want to run AC winding through 20+ feet of sensitive cabling because, even though they're tightly wound, you have a likely chance of getting hum in your sensitive mic signal.

so, in short, you don't need a 20v secondary per se; but you do need one under about 30-40 volts in order to do recification and filtering to DC. the filtering will most likely involve a large choke/inductor, since filament draw pulls higher current, which means that using just an RC filter will either cause too much voltage drop, or, when using the right values for voltage, won't be filtering enough.

so, my thoughts are that your 6.3vAC winding used directly to provide filament power to the mic will yield most definitely a noisier mic of your stereo pair. it may be definitely sounding good, but also tube mic 'gurus' say they hear a difference in AC and DC filament powered versions of the same mics.... although I would say the difference would be slight in the tonality they're mentioning.

if you do build the mic using AC filaments, please post back and let us/me know if it's as quiet as the other one; and if you hear any difference between the mics that you didn't hear before. curious!

Im going to try and pretend i fully understand what you are talking about but it seems to make sense, as soon as i finish this session on wednesday, i'll post some pictures of the insides of the original PSU i have and see what you all think. SO NOW

Did i order the wrong transformer then???

thanks for your input magicman!

[Nate Dort]

nate and squizo:

the 20v secondary winding is used because you're taking 20v AC and needing to filter it to 6.3v DC.

You're right. I totally blanked there for a second.

However, you'll have no problem with the Antek transformer. It has dual 6.3VAC @ 2A windings. Just wire them in series to get 12.6VAC and use that as your input to the 6.3VDC regulator circuit. You could get away with a LM317 regulator as the 6922 only draws about 300mA on it's heater.

[themagicmanmdt]

good thinkin', nate!

squizo - yep, totally possible still - series heaters! nate's got the idea. regulator is fine, but since filament is about steady, an active voltage regulator might not be necessary - depending if you're building from schematic, though - then never mind!

squizo - hook those heaters in series. to do that (with the right AC polarity, mind you, to work!), take one lead from each of the 6.3v windings, solder them together, and tape them off. you should have two bare/unused ends (one from each 6.3v winding) along with the 'combined' end that's taped off. measure the voltage, AC, from the two unused ends. if it measures 12.6v or above, then they're in the right polarity on the first guess. if it measures much less, then we've got the polarities opposite on our 'combined' end (sometimes it's a guessing game, depending on the transformer)... unsolder that combined end and switch *one* of the 6.3v winding wires out with it's other 'unused' one.

so, in short, there's two windings. winding 1, winding 2. they have two leads, A and B. so, we have:

winding 1a; winding 1b, winding 2a, winding 2b.

first, solder together winding 1b and 2a. measure voltage in AC between 1a and 2b. if it's NOT 12.6v (or close to it), then unsolder 1b/2a, and instead solder together 1b and 2b. measure voltage between 1a and 2a, that should then be the 12.6vAC you're looking for. work with the schematic from there.

ta-da!

[squizo]

Sorry to delay the proceedings for so long, all my parts came in.....well all the important ones anyway.

Heres a few pictures of the guts of my other PSU, and my 6-pin parts which i will list if someone else needs to do the same thing i am.

One quick question for nate and magic or anyone, How difficult would it be to make one PSU power both mics that i have?


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[drago]

Hi !!

Does anyone have or know where to get the schematics for the psu?

Best!!!