1628 Automatic Mixer

[RodC]

Thanks CONVERGENCE, I downloaded those before, they are totaly different.

Yep Todd W. White its old, but this old green face stuff is really loved by a lot of us in the recording end. Those old 1588b modules really color the sound in some desirable ways. I really want to understand the other portion of the circuit in the preamp board of this unit and I would like to find one of the green face series that provided Phantom power. The 1588b modules have a pin marked Phantom, is this where the phantom power is applied? If so, how much can be appplied +12 +48??

I'll try to email IraTec.

Thanks for the replies!

[RodC]

No luck guys, the phantom power is only 15V on this unit. I'm just going to stick with my external or maybe wire some to the XLRs on the back.

I would still like to get a schematic, so if you run across one keep me in mind.

Thanks for all your help.

[RodC]

Measured at the jumper 15V, and at the XLR.

I hoped there was a voltage doubler in there as well so I hooked the phantom power up to a 1588C module, only got 15V at the XLR jack as well.

I thought 48V was a standard for a long time as well.

[bfish]

Oh well, at least now we know. I dug a 1607 out of the pending-projects pile today, to check out my 1588C for you, only to find the 1607 has PS problems. That's the way the whole day went, one forward, three back.......and I don't even know how to two-step.......probably would have been funny to watch!
Take care, man!

[bfish]

Rod,

Did you get 15VDC at the input barrier with a 1588C(not B) installed, or was that just the voltage at the phantom jumper in the mixer? Since the 1588C is an active device, it may boost the 15VDC provided it by the mixer to the 48VDC I presume you're looking for at the input barrier. I would suspect this to be the case, as 48V has long been the standard, and if anyone was a stickler for adhering to standards, it was Altec.

[RodC]

I guess Iratec dont have any service info, I received no reply.

[RodC]

BUMP

I would still love to get my hands on a schematic for this unit. Any info would be greatly appreciated.

Thanks!

[Russ Farrell]

Hi Rod:
Altec paid Dan Dugan for the right to use his patent in making the 1628. Since there was then nothing on the market that operated the same way, Altec was very protective of the circuitry details. They wanted to get as much return on the investment as possible, before someone found a way around the patents. I was a D.M. then, and had contractors and consultants asking for schematics. I was flatly told no. Defective units were to be returned to Anaheim for repair. I can't say for sure, but I'd guess that only Altec repair and engineering departments had schematics.

One of the main reasons the 1588C was designed was for phantom power. The Altec (AKG) C70C and C71 microphones required +12 to +50 volts. The 1588B could not be adapted for it. Operating voltage range for the 1588B and C is +12 to +20 volts. This same level voltage is sent to pin 4 of the octal plug. Pin 3 is the center tap of the input transformer. Pins 3 and 4 of the octal socket on the mixer or preamplifier are normally jumpered. So phantom power would normally be sent to the microphone. For use with an unbalanced source, the 1588C operating instructions recommended cutting the jumper, or putting 2 capacitors in series with the mic cable. AFAIK Altec never did put this info into the O.I.'s for mixers, preamps, etc.

The 1588B noise floor wasn't a problem to the best of my knowledge, but I do remember being told the 1588C is much better (although my spec sheets say both are -124 dBm or better), and the distortion was a bit lower also. That may or may not be a good thing as far as coloration. You might want to check the technical info on the condenser mics you have. They might work OK at lower voltages. I took a quick look at some old catalogs and saw condensers that worked from 11 to 52 volts; 12, 24 or 48 volts; 12 to 48; and many that were 48 only. Make sure the output level at the lower operating voltage meets your needs. Good luck.

Russ

[RodC]

Thanks Russ for the info, that prob explains why there isnt a lot of info about these units.

A lot of the condensors I have require the full +48V. Im really past the Phantom power and was diving into what else is on each board.

The pres sound pretty good for what I'm doing but I was trying to get a bit more gain out of each stage. After tracing/scratching my head it turns out there is no more gain to be had on each board. All the Op amps on each board are used for the gating logic. Right now Im looking at pulling a lot of the parts and adding my own op amp circuit, OR just live with it the way it is.

I have modded it for 8 outputs and added a pot to the front for each stage so I can adjust both Gain and output level so I can push each stage however much I want. I think now a schematic wont do me much good.

I have a thread detailing it on the TapeOp Message board.