Altec 1588

[floid]

i've got a few of these i've acquired here and there over the years, both B and C models, and am finally going to try to do something with them. i've got some questions about power, though:
seems like i remember finding a post somewhere describing what you could do to make these guys run on 24v, but can't find that anywhere now - true? just a matter of increasing some capacitor values?
could i apply phantom to the B's by means of a couple coupling capacitors and thus avoid frying the tranny?
if so, what's the most efficient (cheapest) way to get two voltages - say, 48v for phantom and 24v for the cans? Is it as simple as using a 48v source and then using a small resistor and correctly valued zener to clamp it to the lower voltage?

[anticpunk]

Floid,

I've built a bunch of boxes with these modules. IIRC the max voltage was 18VDC. I ran them at 12VDC, but if you could regulate your 48V down to that neighborhood, I dont see why you couldn't put phantom in there as well. Definitely use some coupling caps between the phantom feed resistors and the teeny-tiny input iron.

The "C" modules actually have a center tap for phantom powering, but the original units only sent 12V thru that tap and I wouldn't try anything higher.

I coupled my outputs thru some 470uf caps and into vintage Jensen 1:1 600ohm transformers. Make sure you strap the transformer with a 610ohm resistor to keep the impedance and subsequent reflected impedance correct for these little buggers. The cans are easy to open and service, and I'd suggest a recap if you haven't already...

Don't expect big gain factors. They are not really hot on the output, but do have enough headroom to handle loud sources and enough gain to do scratch vocals etc. They really do have a flavor of their own and are worth toying with.

Also, there were the 1588A which sound OK and the 1578A (i think that was the model #) which was similar to the 1588 but had an unbalanced input.
The studio I built had a 1592B in it that had a 1588B and C loaded into CH 2 and 3 so you could A/B them and still use the test oscillator on CH 1.

Hope maybe this helps.

-Jay

[wkrbee]

Do a search.There was also a few posts about modding the 1588 for lower noise and better bass response.

[Jitters]

Look for this guy...

[RodC]

I would introduce the phantom after the cans, just like any other preamp, especially if you need the full 48V. The best intro to this is here:

http://www.tangible-technology.com/powe ... nnect.html

I have so many different preamps I gave up a on adding phantom to them all. I have a separate phantom supply, 6 channels.

For the C models, if you have the Long ver, you will deff want to see if the caps are looking bad. If its the short ver, there are no electrolytics in there, see this:
http://www.beyondsanityproductions.com/ ... &Itemid=28

Both of these are rated for 12 to 20 volts. (I have the signal processing manual if you want a copy, it appears that Altec has changed their site drastically and I don't see their vintage stuff up there anymore)

The best thing to do with them is to add a gain control, search this forum for my 1628 mods.

For the B models, others have boosted the gain, but I'm sure the noise is worse.

They sound sweet on Snares and Bass guitar. And are nice for drums if you don't mind the "compression" provided by the limited head room.

[floid]

thanks for the replies folks. I actually picked this project up over the holiday, came up with a rather offbeat solution: I currently have 2 1588b's, 2 1588c's, and 2 PM1000 master channel boards all racked in a 2 space chassis, with each can driving an individual gain stage of PM1K, balanced through the 600:600 octals (i forget model #) Altec made. I'm using a linear 48v supply, and stepping the can voltage down with a power resistor. I haven't yet wired up phantom to the 1588c's...
1) should i derived phantom from after the same power resistor? turning on phantom would then result in a voltage drop to the cans, correct? how significant would this be?
2) there should be a resistor in the phantom circuit, right? Right now i have in place two 6.81k resistors that can be sent to pins 7 and 8... or should they perhaps be parallel to pin 4?
3) the power resistor is currently something in the 400 ohm range, stepping the rail down to 18 volts. But i know enough to realize if i pull one of the cans out, voltage will go up - so i need a better means of regulation. could i use, say, a 150 ohm resistor, followed by an 18v zener to ground, and have my two rail voltages that simply? Or do i need to use a more complex circuit?
4) i've read that a 1uF cap translates to a hpf @ 200Hz when place on the output of these cans. So, a 2.2uF should put me somewhere in the 80Hz region, right? I was thinking of using two 2.2uF caps in series on a 3 position switch, allowing a hi-pass of off/80hz/160hz

i've been having quite a bit of fun with these guys. I did the gain mod on one of my B's, and, damn, just a bit too ridiculous - the extra gain stage of the PM1K is already more than enough even for my Shinybox, so i settled for simply recapping and upgrading the resistors to metal film. I've gotta do an order to Mouser before i can get any further on this project, but i'm liking what i hear so far.