Altec 1599B caps?

Hey, I just got an Altec 1599B today and i plugged it in to test it out and i'm only getting up to about -40dbu of gain on all the inputs and they're all incredibly distorted. So i popped it open and took out the PCB and all the caps look very old. On the other side of the PCB a ground trace had been cut and there was a funny looking capacitor across two resistors that had started leaking. It's shaped like a carbon comp resistor but one side is white and the other red (+). C1 and C12 have a similar look and i was wondering how i could go about finding the values of these so i can recap the unit.

C1 reads:
10M
20V
(2) +
7713+

C12 reads:
H+
+ 20%

and the unmarked cap:
unintelligible
25V
+ 20%

If anyone has a schem for this that would be awesome, but i'd still need to find out what the unmarked cap is. Thanks so much!

I have a 1599A that I modded.... which capacitor are you talking about? Can you take a pic?

http://www.fivefish.net/diy/Altec1599A/default.htm

I can tell you though that even before I modded mine, it didnt sound distorted.

hey owel-

thats a great web page! everyone that has one of those altec mixers should take a look at what you've done.

now that youve had it for a while, what are your impressions, how does it sound?

dave

Here are some audio clips if you're interested hearing what it sounds like. The vintage transistor preamp cans cannot tolerate a large input level, it's going to clip. It's mostly designed for dynamic microphones, so if you're going to use it with line level output devices, make sure to lower the volume going in.... or use the -10db, -20db pad switches on the front of the unit.

About the clips, I'm not a keyboard player... these are just impromptu keyboard goofing around one afternoon to record the sound of the Altec.

African in Red

Euro Space Love Song

"Hero Had a Boo-Boo" Film Soundtrack

Irish Rock

Last Gasp of a A Dying CPU

Stuck In The 80s Mode

The Lonely Galaxy

Hey thanks for the replies guys, i uploaded some pics:

here's the cap that was leaking on the underside of the PCB


and here are a few more links of pics
http://members.cox.net/soma/101MSDCF/PCB.jpg
http://members.cox.net/soma/101MSDCF/PCB2.jpg
http://members.cox.net/soma/101MSDCF/C1.jpg
http://members.cox.net/soma/101MSDCF/C12.jpg
http://members.cox.net/soma/101MSDCF/underside.jpg
http://members.cox.net/soma/101MSDCF/underside2.jpg

on the C12 pic i've drawn in where the PCB cut is that connects the two resistors and i've also circled the cap that's similar to the broken one.

Last night i messed around a bit and placed a .1uF cap, a .068uF, and a .33uF cap just to see if i could get some sort of signal. The first time i put the .1uF in i got very very loud clipping but not overly distorted signal, i then tested the others because the heatsink on the reg was getting wayyy hot with the .1. When i reinserted the .1 finally i couldn't get any more signal but the reg was still getting pretty hot, very confusing, i'm guessing there's some more stuff going on here cause the outputs (there are two multi masters like the 1599A but also a strip with a 600ohm balanced out and the optional battery connection) are going in and out. That mod article is really great owel BTW i'm def gonna spif this guy up if i can! Thanks again.
Yale

That looks radically different from my PCB.

Here WAS mine.
http://www.fivefish.net/diy/Altec1599A/images/pcb.jpg

Notice mine uses discrete transistors instead of a socketed IC. And no transformers. Yours must be a higher model... thus, "B" version.

Can you sketch out the schematic? i.e. reverse engineer it? That way, it will be more obvious what the function of that capacitor is. What IC chip does it use?

Hmm i'll have a go at some RE but i'm kinda confused about a few things, in the C12 pic you can see there is a 555 timer there, what is that for? It times a 12v relay so i'm guessing it's for powering up something but the replay outputs are connected to the output transformer, i'll need a little time for that. The IC is a TI RC4136N quad opamp, i've never heard of this opamp but it looks like they're still in production? Aside from that there are only two other transistors. I've deduced that C1 is in fact a 10uF cap cause it is blocking DC from the 6 summed channels, that's one down, two to go. One last thing, the preamps that came with this mixer are the 1588C type which are equipped for phantom, but i've heard that they only put out around 22volts or something like that. Maybe the PCB mod is to allow for phantom? Wild guess, i should probably be checking voltages before i spout of like this so i'll post back in a bit. Thanks!

>t times a 12v relay so i'm guessing it's for powering up something but the replay outputs are connected to the output transformer, i'll need a little time for that.

Could be a delay timer so you don't hear the THUMP when you power on the unit.

Hey well i just wanted to post an update to the situation. I've scrapped the main PCB board and have started wiring up a pretty novel mod for my mixer. I have two of the bridging transformers 600:600(150) and i've changed around the connections so that a mic goes into one 1588C can into the bridging transformer set up 600:150 which steps down impedance and also balances the signal to go into another 1588C, so in the end i'll have a dual pre amp, each pre having two stages with transformer coupling. I've got one channel working and it actually sounds really pretty interesting and usable to my ears, and it's very cool having two volume knobs so i can drive the second stage if i ever wanted too (don't know if i would tho). I'm gonna make a better PSU and leave the outputs unbalanced and run each out a master multiple RCA jack.

Also one more question, I know for a fact that the input voltage on the 1588C cans is internally wired to pin 4 so it would seem that you can only get 18 phantom. But looking at the octal sockets it looks like pins 3 & 4 are soldered together with pin 3 being the center tap on the input tranny so... can i put 48v on the center tap connection, i think i've heard bad things about this, and if so could i just use something like SSL's power supply? Thanks so much guys.
Yale

> each pre having two stages with transformer coupling.

Won't that overload the 2nd stage? too much input? or is that the reason why you have 2 volume control for each channel?

Post some sound clips!

I finally made the PSU last night, and this thing is alive and kicking! I have a few pics and an mp3 which kinda sounds horrible (excuse some of the singing also) but i very much like the distortion that i can get from this pre. That having been said, i recorded the sample with both volume knobs at max and neither pad engaged, so it can be quite clean too.

http://members.cox.net/soma/newpreamp.mp3







As i stated above the mod is simply taking the output of the first 1588C and feeding it into a 15356A altec transformer wired for 600:150 and then taking that rebalanced signal and feeding it into a second 1588C and then out to one of the unbalanced RCA jacks on the back.

The power supply i've concocted is very simple and is also kinda noisy, i can hear it rippling if i turn up the guitar track, but i'm busy designing a better supply with phantom for later.
Going against everything George M. said in that audio interview i really like the way this pre can color my sound, it is a little muddy for complex sounds but for vocals it really pleases me. If i ever get an oscope i'll probably find something horrible, but that probably won't be for a long time.

Again, sorry for the clip, i just hammered it out in my excitement, i'll make some more flattering ones later to entice any modders out there.