Doepfer A-138b


Mixer with Logarithmic Potentiometers

  • Primarily suitable for audio signals
  • Width: 8 HP
  • Depth: 35 mm
  • Power requirements: +10 mA (+12 V) / -10 mA (-12 V)
available since January 2004
Item number 166482
sales unit 1 piece(s)
Modul Type Mono
Width 8 TE / HP
55 €
Including VAT; Excluding 19,90 € shipping
In stock
In stock

This item is in stock and can be dispatched immediately.

Standard Delivery Times
Delivery approx. between Wednesday, 6.07. and Thursday, 7.07.
Doepfer A-138-B Mixer
Blair 18.11.2013
The A-138b is essentially a 4 into 1 mixer optimised for audio signals rather than control voltages. the 'b' in the name means the the mixer uses logarithmic rather than linear potentiometers.

For me the A-138b is an essential piece of equipment because it enables me to sum the outputs of up to 4 sound sources (for instance VCO's or noise sources) before sending the combined output to my A-108 Low pass filter module.

With one input employed, and with the channel and master levels set to 10, the volume of the output is the same level as the input signal. in other words, this module will not increase the gain of an input, it will only attenuate it.

When using multiple inputs I find I have to reduce the levels of the individual channels quite a lot, otherwise the output from the mixer becomes to much for next module in the chain. So if I am using 3 inputs, I will use a maximum of about 33% of each channel's volume.

The mixer appears to operate very quietly. It does not introduce much 'hiss' into the sound. Some reviewers have found otherwise , so it may be that my ears are not as sensitive as theirs.

I have rated the A-138b as 5 stars except for features, which I have given a 4 for. The reason for this is that the Doepfer website indicates that with no input into channel 1, the channel 1 level will act as a +5 volt DC offset. In other words, the unit *can* increase the level beyond that of an input signal. However, my unit doesn't work like this. As delivered, all 4 inputs on my A-138b work in the same way. The manual says there is a jumper I need to re-position on the rear of the circuit board to achieve the +5 volt DD offset with input level 1. I think this option should have been made available as a toggle switch on the front panel. It would be useful on occasions when I am only using 3 inputs, but I do not want to have to remove the unit from its case and re-position a jumper each time to achieve this!

Overall, another useful and great value unit from Doepfer, in my opinion.


MiguelDF 06.11.2017
I bought this item to use as a mixer for my Doepfer modules, I own 3 more modules and in order to be able to send only one output from my 3 modules I found out this mixer. I was not able to find any disadvantage for this item, the knobs have a good sensitivity, both inputs and outputs work just fine, and it is possible to connect this mixer to the main power suply.
For a low number of outputs, as the ones I have this is a great choice for these systems, for biger systems maybe other options should be considered.
So, all in all, I definitely recomend this item to incorporate in a Doepfer based system


Does its job!
Anonymous 19.01.2017
Very useful 4 into 1 mixer. I've used it to mix VCO waves into the Wasp filter and the A-116 wave processor.
Will be used a LOT.


Mixer for all seasons
LiamJ 10.02.2015
If your modular system is growing and you don't have a mixer, buy one. If you have more than 1 Oscillator in your setup, a white noise module or separate drum modules, you'll want this to to mix your sounds nicely, super simple but super effective and does the job it was set out to do.