Altec Mic Pres

newguy12 · Post by **newguy12** » Sun Nov 16, 2003 6:06 pm

I just saw some Altec mic pre input transformers on ebay which I'm thinking about picking up. My question is, how do you go about hooking them up. They have an 8 pin configuration on them and I know they need obviously need to be hooked up to a power supply, a 1/4 or xlr output and a xlr input but how do I know which pins to connect each one to. Also, do I build the powersupply and if so how do I go about building one or can I purchase a pre-made one from mouser or some place? I was also wondering, I was thinking about rigging it up with phantom power and a phase reversal switch on it, but like everything else I don't have a clue how to go about building one to work in conjunction with the pre, so could someone point me in the right direction. I have some soldering experience, making cables and a few other oddities but I've never racked up any mic pres before. One last question, I wanted to put them in a rack mounted case, any recommendations on decent yet moderatly priced rack cases and where to get them.

meblumen · Post by **meblumen** » Sun Nov 16, 2003 6:20 pm

Which mic pres? I just got a pair from toothpastefordinner so hopefully he will see this and post a response, hes really knowledgeable about this kinda stuff. To wire them up connect the ground pin on a 1/4 jack to pin 1 of the xlr jack and then connect the pins 7 & 8 on the input transformer to pins 2 & 3 on the XLR jack. From there you want to connect pins 5 & 6 on the input transformer to the power supply and connect pin 1 on the input transformer to the tip on the 1/4 jack and wire the grounds to the '-' on the power supply and the input transformer. I'm pretty sure you can buy power supplys from mouser or digikey but I haven't done so, so I'm not sure. To do a phase reversal you can install a dpdt switch to that is connected to pins 2 & 3 on the XLR plug like what you would do to invert the phase on an XLR cable. As far as phantom power goes there are a bunch of schematics all over the net for building stand alone unit but I have no idea where a built in one would reside in the preamp or what effects it would have on it. My question is, if your input modules are like mine they have a fixed db level, how does one go about building a circut to adjust the gain on the mic pres, I know I could just run it through a comp or something after to jack up the volume or put a pad in front of the pre to lower the gain but there has got to be something I can do/build to adjust the gain at the pre. Hope this helps a little, hopefuly someone more knowledgable will come along and better answer your question.

Wire ground to the ground pin on the 1/4" jack and to pin 1 of the xlr. Wire module pins 7/8 (inputs) to pins 2/3 of the XLR jack. Wire module pin 1 to the tip pin on the 1/4" jack. Wire module pins 5 and 6 to your +12v power supply... and that's it! (Wire your grounds to the "-" power terminal the module too.) This makes no provisions for gain adjustment (fixed at 33dB gain), phase (you can switch pins 2/3 of the XLR with a DPDT switch if you want phase control)

joeysimms · Post by **joeysimms** » Sun Nov 16, 2003 7:13 pm

They're octal plug mic pre transformers.

If you didn't want to do any work, you could look for an altec mixer to plug them into.

There's always a ton of them (mixers) on ebay, some already have the transformers, some don't. The one I have has 4 mic pres into one out, with an insert for eq or compression.

Tom

newguy12 · Post by **newguy12** » Mon Nov 17, 2003 7:49 am

meblumen, I know I'm probably being stupid but from the picture (and granted it was hard to tell) I couldn't see any of the pins being labeled so are they or how do I know which pin is which? Joey, are those mixers any good? They sound interesting but I think right now I would rather build something myself. So if anyone else knows anything I would greatly appreciate your help.

joeysimms · Post by **joeysimms** » Mon Nov 17, 2003 8:53 am

The opinions on the mixers range from great to run-of-the-mill. I haven't used mine enough to tell, though when I tried a 57 on a guitar amp through my soundcraft delta 200 channel vs. the altec, I preferred the altec.. I plan on using it for, say, three mics on a source, mixed and blended to one out. My comment was more based on the practicality of getting your own power source and wiring something up, or, just plugging them in a mixer they were designed for. Something like this:

http://cgi.ebay.com/ws/eBayISAPI.dllVie ... gory=23787

Right beneath the xlr ins on the back is where the transformers plug in.

Mine has 4 of the purple one's (# escapes me..). The 4722 peerless one's are supposed to be good.

Tom

toothpastefordinner · Post by **toothpastefordinner** » Mon Nov 17, 2003 8:54 am

I have wired up a few of these and they are fairly simple -BUT- I would not suggest getting them unless you have some experience soldering and reading schematics.

The instructions meblumen gave are pretty much dead on... here are the external parts you will need.

1- XLR-F (female) jack

1- XLR-M (male) jack -OR- 1/4" mono jack (the altec mic pres are unbalanced-out, which you can either balance (hard if you're inexperienced, requires extra parts/knowledge) or send to an unbalanced output.)

1- 12V power supply. If you are new, again, I would buy one rather than make it. Jameco.com has very inexpensive wall warts which you can use to supply DC power, just make sure you put in filter caps since wall warts are testy sometimes and can hum if they're not made well. Or you can get a fully built regulated 12V power supply for anywhere from around $20 to $50+, these preamps use hardly any current (15mA apiece I think) so you should be safe with a small one.

1- enclosure. Either a metal box, a rack enclosure, or something else suitable. The preamp is in a metal can so it's shielded but you don't want to shove it all in a plastic box or something since those are flimsy. It is easy to forget that you need something to put it all in, that's why I am mentioning it

drew
toothpastefordinner.com

joeysimms · Post by **joeysimms** » Mon Nov 17, 2003 8:55 am

Which one's do you have, Drew? How do you like them?

toothpastefordinner · Post by **toothpastefordinner** » Mon Nov 17, 2003 11:14 am

I have four 1588A altec preamps wired up. They work okay, sound okay, like 'em best on drums (snare.) and guitar. I don't have any meters on them so I don't know how hard I'm actually hitting them w/r/t their headroom, but they sound good on loud stuff, much different than both my mackie preamps and my syteks.

drew
toothpastefordinner.com

aurelialuz · Post by **aurelialuz** » Mon Nov 17, 2003 12:15 pm

hey drew, how would compare the altecs to the opamp labs pre cans?

alex

meblumen · Post by **meblumen** » Mon Nov 17, 2003 3:33 pm

Any recommendations on rack enclosures that are reasonably priced and well made, not to mention easy to work with? Also does anyone know how to add phantom power to the mic pre input transformers or if its possible and how to provide a variable gain device into the circut? OBTW, newguy12, I'm currently working on building a pedalboard with a built in powersupply. Its quite different I imagen from a powersupply for the mic pres but when I get a moment I'm gonna see if I can go about making one for the pres and if I get something working I'll email the schematics. If your interested send me an email at meblumen@indiana.edu

toothpastefordinner · Post by **toothpastefordinner** » Mon Nov 17, 2003 3:41 pm

Rack cases-

Reasonably priced: Bud rack cases (get them from Mouser)- about $25 for a quantity of one 1U rack case. I have a few, used them, they're not monsters like some, but they get the job done for minor things. My 4 altecs are in one of these.

Reasonably priced and more sturdy: Everyone tells me, "Par Metal!" www.par-metal.com

Vs. the opamp labs-

Less of a "pinched" sound (not that the opamp labs are pinched, but just comparatively speaking) and about the same amount of color. I hate describing the sound of stuff, it's really hard unless one thing is blatantly much better or worse than another! If you like the opamp labs, get a couple of these, and try them out. (Alex, if you want a couple to try, I have a pair of spare 1588A's left, send me email.)

drew
toothpastefordinner.com

lichthaus-media · Post by **lichthaus-media** » Mon Nov 17, 2003 4:13 pm

joeysimms wrote:There's always a ton of them (mixers) on ebay, some already have the transformers, some don't. The one I have has 4 mic pres into one out, with an insert for eq or compression.

Which mixer do you have? I believe I have the compressor module for that mixer. I need the pin out. Can you open the mixer and take a picture? Do you have a schematic? I'll give you a few bucks for your trouble (paypal)!

Thanks!

james

rhythm ranch · Post by **rhythm ranch** » Mon Nov 17, 2003 6:28 pm

lichtme wrote:I need the pin out. Can you open the mixer and take a picture? Do you have a schematic?

Thanks!

james

Not sure which schematic you're interested in, but there are a few free resources out there:

Lots of stuff here.

And here.

And, what the hell, here's more.

And last, but not least, The Unofficial Altec Site.

Enjoy,
Mark

lichthaus-media · Post by **lichthaus-media** » Mon Nov 17, 2003 11:35 pm

Thanks. I'm actualy looking for the compressor option pinout on the 361b mixer/amp. I have not been able to find the schematics anywhere online except for musicparts.com (no response to the request). I have a 14678a compressor (the option) and I would like to know more about it.

Thanks for the effort.

-james

rhythm ranch · Post by **rhythm ranch** » Tue Nov 18, 2003 6:06 am

lichtme wrote:Thanks. I'm actualy looking for the compressor option pinout on the 361b mixer/amp. I have not been able to find the schematics anywhere online except for musicparts.com (no response to the request). I have a 14678a compressor (the option) and I would like to know more about it.

Try http://www.agtannenbaum.com/

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