MVee

altec 1588c standalone mic preamp
« on: January 27, 2016, 06:23:49 PM »
Hi all,

I have two Altec 1588C cans that I would like to use as standalone microphone preamps.

I can't seam to wrap my head around the simple device as I can not get them to pass any sound. 

I have simply connected power (20v from a lm317 regulator fed from a 24v dc supply) and XLR connectors to input (balanced pin 7+8 and GND at pin 6) and output unbalanced Pin 1 and GND at pin 6)

I would also like tu use the phantom capabilities of the 1588C and an input pad at some point.

would anyone have a full schematic to use the 1588c as a standalone preamp ?

your help is greatly appreciated.


Mike


MVee

Re: altec 1588c standalone mic preamp
« Reply #1 on: January 30, 2016, 07:22:18 AM »
bump, anyone ?

Sredna

Re: altec 1588c standalone mic preamp
« Reply #2 on: January 30, 2016, 12:30:51 PM »
Here's a spec sheet for the 1588C with a hookup example.

Dont forget to connect the gain and in your descriptionen you didn't mention the groud connection from the PSU ;)

You get phantom power to your microphone when you connect pin 3 (center tap on XFRM) to pin 4 (20V).
If you need higer phantom voltage, you'll have to use a dedicated phantom supply and connect that to pin 3.

The gain pin (2) could be connected to ground for aubout 34dB gain or insert a resistor/pot for varying the gain between 20-34dB.

« Last Edit: January 30, 2016, 12:46:55 PM by Sredna »
Hmm... in which direction do the electrons actually go?

MVee

Re: altec 1588c standalone mic preamp
« Reply #3 on: January 31, 2016, 04:31:18 PM »
Thanks Sedrna for the explanations.

Alas, I have tried the Pin 2 to ground but it still doesn't output audio.   The ground connection to the PSU is connected to Pin 6.

I have a feeling these old modules might need new capacitors at the least. 


Sredna

Re: altec 1588c standalone mic preamp
« Reply #4 on: February 01, 2016, 11:43:06 AM »
Try to rule out every other possible error before you open those things!

The 1588C is tightly packed and on one version (see pic, right side) you need to desolder the Xformer to have full access to the PCB, the Xformer has a plastic bobbin that'll melt if you're not extremely careful.
Hmm... in which direction do the electrons actually go?

Whoops

Re: altec 1588c standalone mic preamp
« Reply #5 on: February 02, 2016, 08:50:57 AM »
Hi all,

I have two Altec 1588C cans that I would like to use as standalone microphone preamps.

I can't seam to wrap my head around the simple device as I can not get them to pass any sound. 

I have simply connected power (20v from a lm317 regulator fed from a 24v dc supply) and XLR connectors to input (balanced pin 7+8 and GND at pin 6) and output unbalanced Pin 1 and GND at pin 6)

I would also like tu use the phantom capabilities of the 1588C and an input pad at some point.

would anyone have a full schematic to use the 1588c as a standalone preamp ?

your help is greatly appreciated.


Mike

Hello Mike the 1588c is not a standalone preamp, it's a plugin module that needs an output stage, you will need around 30db's more to use it as a mic preamp, also you will need some sort of balancing out circuit (transformer or opamp)

Imagine the 1588C as the first amplification stage of a Neve 1290, it's just the first stage is not the whole mic amplifier. In the case of the Neve 1290 there's 3 stages of amplification and then an output transformer.

Some ideas for you:

1) Do a breadboard of the output stage of a Neve 1290 circuit, use carnhill output transformer, connect the 1588C to the input of the neve output stage

2) Connect the 1588C to a 2520 Opamp, and use the servo out to have a balanced output, or use an Ed Anderson transformer Output (more expensive)

3) Or for a simple and nice solution ,set up an 5532 opamp makeup stage with a potentiometer to control volume, use the That 1646 chip to balance output after the 5532. Easy and Solid.


mjrippe

Re: altec 1588c standalone mic preamp
« Reply #6 on: February 02, 2016, 10:35:25 AM »
Or study the 1589 circuit - it mixes two 1588 into a single output but you could build it twice for two preamps.

Whoops

Re: altec 1588c standalone mic preamp
« Reply #7 on: February 02, 2016, 01:28:51 PM »
Or study the 1589 circuit - it mixes two 1588 into a single output but you could build it twice for two preamps.

Yes you can do that and it will work great, but also need an output transformer, as far as I remember those units use a Peerless output transformer. It will be hard to get. But you can use instead of it transformers from Cinemag, Sowter, or the for more affordable options Edcor or OEP.

Following mjrippe great idea of keeping it Altec, I remeber I once modified an Altec 1592B mixer. Modified sx 1588B plugin modules for higher gain and balanced direct out using That1646 chips, those outputs dont sound good at all.
But 2 channels were left stock were theu go through the last amplifier stages and have a simpre treble and Bass EQ, and in the end Output transformer. Let me saw that those 2 channels sound great, and the EQ is simple but really good sounding also, the bass EQ is really round and FAT, loved it.
You could try to ad to your 1588C cans the output circuitry of the 1592 with EQ, with this option or the 1589 I think you will like the sound.

Just note that the other 3 options I gave in my last post are easier to do since those boards and projects are readily available (2520 opamp, BA283 pcb), if you go by the altec output option you will need to do a board yourself.


Re: altec 1588c standalone mic preamp
« Reply #8 on: April 10, 2016, 01:57:48 AM »
Having built several multi-channel units with these, I can tell you that if you strap the output with a 1K pot and feed 1:1 iron, they DO have enough gain for standalone use without extra stages. This is assuming you don't need heaps of gain.

The last ones I did were built as a 4 channel, direct out only, desktop box with 4 vintage Jensen transformers.   That unit is doing duty in a studio up here in Woodstock, NY as utility mic pres mainly for drums and louder sources.

Ymmv.

-J

Whoops

Re: altec 1588c standalone mic preamp
« Reply #9 on: April 10, 2016, 07:14:02 PM »
Some implementations,
this one was a drawing I did straight from the implementation of these modules in the Altec 1592B mixer.



Whoops

Re: altec 1588c standalone mic preamp
« Reply #10 on: April 10, 2016, 07:17:45 PM »
You can use it unbalanced out like this schematic attached.

Although I really dont like the sound of the unit this way, I really advise you to had another stage of amplification after and an output transformer. You can use BA283, or 2520 opamp, etc

Anyway here it is:

Whoops

Re: altec 1588c standalone mic preamp
« Reply #11 on: April 10, 2016, 07:22:56 PM »
If you know Japanese check this build here:

http://green.ap.teacup.com/tubemansound/195.html

If you dont know Japanese you can check the attached image although Google translation doesnt help much.
LOLOLOLOLOL