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Altec 1592B repair, 1588B module, XLR pinout output etc

Recently i got a nice Altec 1592B mixer.

Each input requires a dedicated preamp/transformer module, for microphones there’s preamp, 1588B or preamp+12v phantom power, model 1588C.

I had to do a massive recapping job on the 1592B- the original caps values were all over the place-and i mean not only electrolytics-the only ones that were still measuring ok were the tropical fish and some of the lower values disc caps- though most of the electrolytics were good quality, Mallory or West Germany made, ROE (Roederstein). I replaced them all with Elnas (they seem to be the standard nowadays).

Also, the resistor after power transformer 7818 (that feeds part of the tone section, so if you have an unit that powers up but does not produce a sound, check for +18v at pin 6 of the tone board, that is linked to the power board after (out) the aforementioned 7818) was burned-clear sign that some damage had taken place. The schematic calls for a 10 Ohms resistor-i decided to put a 100 ohms substitute, much better.

Sounding good, i decided to recap also the 1588B module i have here (more are on the way, and when factory new, they were fitted with 3 modules).

After using a small screwdriver to pry the enclosure open, i took a look at this interesting blog (check it) for the schematic-i also took the time to sub the carbon comp resistors with metal film and yes-noise went down.

For your reference, here’s the resistors network:

Q1 and Q2 pinout:

Troubleshooting:

If the preamp is not working, check carefully the resistors-they break easily. One immaculate looking (inside and out, the spongy filler still in good soft condition, no leakages on the plastic screen etc) 1588B i have had a resistor broken at its base, and since the components are so squeezed together it was impossible to see it-i decided to test the transistors (thats why i took the q1 and q2 pics above) since everything was looking proper-and there-i spotted the broken resistor! The preamp would still burst in noise if i knocked the mic gently on the capsule, yet it wont amplify it properly. Thats the resistor connected to ground on the white wire-a pain to desolder too.

If you must desolder stuff, be patient-these boards wont take a 300 degrees hot iron-the circuit tracks will lift if you heat them up too much-use care.

Since someone over at the Tape Operator forum has raised the warning that the power supply may have been ill designed, i am powering it using an external psu (using the battery option), 24v dc.

Terminal: from left, my battery (external psu) connections (- and +) and pinout to wire an XLR balanced jack to the output: hot, cold and ground… in the mess between high and low impedance i went with, 600 ohms, good for any mixer or recorder input. PLEASE note 2 and 3 terminals are bridged (connected) at the terminal post. The signal is nice and strong.

I will not mod this unit, i like it as it is. Nice and retro sounding.

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x0xb0xes: made in China, Germany and USA

Ages ago i bought my first Mode Machines x0xb0x from Touched by Sound in Germany. They were the first fully assembled x0xb0xes on sale here in Europe and hence they have been reviewed a few months later on Sound on Sound. They came with those horrible looking MC303 knobs, but the idea of having a fully operational, Bassline clone with onboard sequencer was embarassingly exciting. In 2017 all this has changed, since the advent of the RE303!

From the description given to me by TBS and the sticker on mine, they indicated that they were Made in Germany.

One year later Mode Machines came up with the x0xb0x mk2, this time “guaranteed” to have been made in Germany. 

Would this second statement imply, mine was actually made somewhere else other than Germany, EU?!

Today i decided to pop my Mode Machines x0xb0x open and have a look inside.

The machine itself, sounds good but it loses more of the lower frequencies than it should as you turn the cutoff and resonance up, but it sits nicely in a mix because of this and it is quite squelchy.

Now on with the gutshots:

Dirt on the pcb, almost like corrosive traces of handling, etc

Components scattered on the board and soldered, clearly assembled as quickly as possible.

Grey looking solder joints. I dont know if rohs approved solder is supposed to look like this but it’s not shiny, they look almost like cold solder joints.

Rubycon electrolytic caps.. part of the standard kit i suppose..

More traces of handling.. dirt..
All in all, the only other example i can think of of a pcb that bears the same, corroding handling marks, grey solder joints and cowboy assembling like this, is my chinese made, battered components sporting, bog standard, cheap as hell, barely working, terrible looking digital oscilloscope. They even smell bad, the same way.


My personal feeling: my Mode Machines x0xb0x was really either made in China or made in Germany by hurried chinese workers in a very dark and unpleasant cabin.

BUT: it sports original 536 transistors, that give it a very impressive TB303 character! 

Sometime later, i got my hands on a NY made, x0xb0x from x0xs0urce: a whole different story.

Rounder sound, red leds instead of purple ones, and check these gutshots..careful assembling and soldering, etc. a work of love-mind you it costed twice the price of the mode machines..

Welcoming greenie caps as per the original tb303..

But ouch! This has 945 transistors (Roland mass production’s transistor of choice in those days)- it doesnt sound as wild as the Mode Machines!!