Need Help Racking Up Some Altec 1588 Input Modules

[meblumen]

I apologize if anything like this has come up here before or if my questions appear quite dumb but I'm new to this forum and somewhat new to electronics as well. I also apologize for the length of my post but I tried to include as much information as possible to better facilitate any responses to my post.

Anyway, I have a couple of 1588 Altec input modules which I have been using as mic pres for sometime. For the time being I've been connecting them to a 12volt wall wart and then to a xlr input jack and 1/4 output jack all via hook-up wire and allegator clips. Having no enclosure I usually just put the thing on a non-conductive surface and goto work. However, while the altecs aren't my goto pres, I do like them and was thinking about racking them up so I don't have to rig them up everytime I use them. Also I wanted to add phantom power and phase reversal to the pres and if possible a way to attenuate their gain (fixed 33db). In addition I wanted to put them in a proper rack mount enclosure with xlr inputs and 1/4 outputs.

Now for my questions:
1)I want to use 2 modules in one rack mounted enclosure, I was told that they need 40mA of power each and that I should power them via a 12v powersupply. I also want to add phantom power and if possible a pot or something to change the gain, hence I know my power supply requirements are going to be a bit more. I also want it to have an on/off on the front along with a LED that lights up when the unit is functioning. I want this to be a professional looking and operating unit and thus wanted to build a powersupply to do all this but have no idea where to start or how to design one. I have pretty good soldering skills (I've made tons of cables), I have done some basic work on guitars and amps, replacing pick-ups, replacing caps and installing 3-prong cables in old amps so I have a basic knowledge of electricity but don't know where to start when tackling this type of project having never built or designed anything electronics-wise in my life.

2)I have done some research on this and have found a bunch of schematics for phantom power circuts, could I just pick any of them and stick it before the input of the pre-amp module, basically how would I go about designing and encorporating phantom power into the pre?

3)As for the phase reversal, all I need to do is use a DPDT switch hooked up to pins 2 and 3 on the module's input right?

4)I like the existing tone of the module and don't wish to alter it drastically so I wanted to know what would be the most effective way to change the gain without altering the tone of the pre? Someone suggested I use something like an OP07 opamp, with a potentiometer in the feedback loop or a multi-stage gain switch to reduce noise and set up as an inverting amplifier, so I could change the gain by maybe +/-20dB but I don't fully comprehend what all of that means or how to go about implimenting it. If it would be to difficult to provide a way to change the gain I would skip this step and just run the output signal through other gear if I needed to make adjustments but I thought building it into the unit would be a nice touch.

5)I want to put this all in a nice rack mounted enclosure. I've heard plenty of people recommend par-metal. Looking over their site the stuff looks nice, I didn't expect things to be so expensive. My main problem is while I have a soldering iron, solder sucker, soldering braid, screw drivers and a whole bunch of other tools, I don't have a drill, certainly don't have a drill press nor the speciality bits necessary to do all the metal work involved in altering the enclosure to fit my needs. Hence, could somebody recommend a place either online or somewhere in my yellow pages I should look for that might do this work for me. I suppose if worst comes to worst I could borrow a drill and if its not to expensive buy some of the bits but seeing as I don't do a ton of this diy work I would rather not have to purchase any new tools.

Well, I think thats it. My apologies for being so wordy. I've been recording music for a long time and recently got the urge to start delving into the more technical aspects of gear and electronics and figured this might be a good place to start. Once again I'm sorry if any of this has been discussed here before but I would greatly appreciate any suggestions, links to other useful sites or book recommendatoins that would get me going. Thanks in advance all for your time and help.

 

[lanxe]

could somebody recommend a place either online or somewhere in my yellow pages I should look for that might do this work for me. I suppose if worst comes to worst I could borrow a drill and if its not to expensive buy some of the bits but seeing as I don't do a ton of this diy work I would rather not have to purchase any new tools.

well, i dont know if you are in the US, but here is a good place to get some machining done...........just download their free design program (it tells you the cost and everything)
http://www.frontpanelexpress.com/

 

[meblumen]

Thanks lanxe I'll take a look at the site. Does anybody else have any suggestions. I know I'm asking a lot and I'm pretty inexperienced when it comes to this kinda stuff but I'm anxious to learn so any assistance would be greatly appreciated.

 

[NewYorkDave]

1588As, Bs or Cs?

They can run on up to 24VDC, I believe. Try it; you might like it.

I have a bunch of 1588Bs and Cs but never got a chance to mess with them. I do have a schematic for the "C" lying around somewhere.

 

[meblumen]

Thanks for the help Dave, I was wondering where you disappeared to, I used to see you post all the time on the tapeop board.

As for the altecs, they are actually 1588A's. I know what each pin corresponds to and how to hook them up to run as a straight pre with a fixed gain, powered off a 12volt wall wart, but I how would I go about building my own powersupply, keeping in mind I would like to add phantom power and if possible some way to alter the pre's gain.

As an aside, I used one of the 1588Bs in an altec 1591 pre/comp. Of course the electronics of the unit contributed to a difference in sound and the 1588A, B and C are all slightly different (I think mostly the B and C have some noise buffer or something added on) but the general sound of the pre was similar. They have a very 70's, can be thin at times but useful sound especially for snare and guitar. Hardly something I would use on every session but since the modules are so cheap I figure why not.

Anyway, thanks again for the help, keep the suggestions coming.

 

[soundguy]

par metal chasis are actually exceptionally stellar values for what you get. Everyone here would probably agree with that. Somehow some myth about DIY being cheap arose and its just that, a myth, you are gonna spend some money.

You can build your own supply, but you might be better off, just to keep things simple, to purchase an open fram supply, like a powerone from digikey. You could fit a small 24v and 48 volt power supply easily in a 2 space par metal box.

If you search the member list, Rlaury has made some really nice boards that mount right on an XLR connector, so you dont have to mount them directly to the chasis. It has a -20dB pad, which you need for the front end. Will also give you a phase flip and phantom power switching. Use 48v relays and power the relays from your phantom supply. Not the best idea, but not the worst either and saves you the trouble of adding a third supply just for relay switching.

Put a variable attenuator on the output of the amp, search here, there is lots of info and links on several options there. You can spend a little or a whole lot on building an attenuator.

If you are going to do this twice in your life, buy a drill press and a stepper bit.

good luck

dave

 

[meblumen]

thank you soundguy for the advice. How come you don't frequent the tapeop board anymore either? I know the whole DIY thing isn't cheap, I just didn't realize how expensive a stupid little enclosure could be. Its the usual disdain at having to shell out cash for mundane purchases rather than cool audio gear or other devices that actually do something rather than sit dormant, housing my electrical projects. Anyway, I appreciate all the help, Dave and Dave you have once again really helped me out. Thanks.

 

[NewYorkDave]

The "B" and "C" have input transformers; I believe the "A" does not.

Here's the only documentation I have, three pages about the "B." I apologize for the poor quality; this is a scan of a twice-faxed document!

Page 1
Page 2
Page 3/Schematic

 

[meblumen]

Thanks for the documentation, every bit helps. Well it looks like I have quite project ahead of me, wish me luck. Thanks again for everything.

Michael

 

[jho-audio]

For the power supply, pull out the iron and DIY! Very easy and rewarding.

I ordered a number of supplies from JLM (JLM AC/DC PCB):

http://www.jlmaudio.com/JLM%20Power%20Supply.htm

You can get all of the components from JLM to keep it simple or place an order with digikey. Digikey has a great selection of toroidial transformers that suit this supply for around $20. All told, maybe $50 for the full supply which gives you +- and 48v.

A Par-metal chassis comes to around $50, ~$30 for frontpanelexpress and maybe $20 in switches, wire and beer :guinness:

So, for around $150 you buy yourself a whole lot of fun and some beer :green:

 

[thomasdf]

Sorry for digging up that deep

I am in the process of wiring 4 Altec 1588Bs as mic pres.

I was just wondering if the high gain mod (that gives them 50dBs of gain) was compatible with this wiring :

Especially the pad switch? It is a bit of a mystery to me, is it a gain switch or output pad? Maybe I don't need if I use the output pot?

I was think for my pres : input pad (value to be determined) > altec preamp > 1K pot > output transformer.

 

[PRR]

> is it a gain switch or output pad?

It's the lower leg of a NFB gain-set network.

Why don't you just tack those resistors on and see what happens? The 11K(!) certainly can't hurt anything. I doubt the 2K can hurt it.