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ac to dc module?
MUFF WIGGLER Forum Index -> Eurorack Modules  
Author ac to dc module?
astroschnautzer
Is there any euro module that can convert bipolar signals into positive signals? a bias shifter that would be then I guess.
I know cwejman att-4 has this function but to pay over 200 euro for an attenuator and this function would be abit much for my current budjet. Any other options?

- Wille
BugBrand
I don't really know much detail of what doepfer offer, but you just need some sort of offset.

It appears that the A-138B mixer does that simply -- its a four channel DC mixer, but when nothing is plugged into input1 then this control acts as an offset:::::

New: From April 2004 an improved version of the module A-138b is manufactured. For the revised versions control In1 works as a DC offset generator (about 0...+5V) provided that no patch cord is plugged into socket In1. If this feature is not required it can be deactivated by removing a jumper on the pc board. Probably from summer 2004 even the A-138a will be manufactured with this improvement.
(from the Doepfer web)
astroschnautzer
Thaks for the info, didn`t know that. I wouldn`t have sold my a-138 mixers if I knew they`d function as dc offsetters too.
astroschnautzer
would this btw be easy to diy?
BugBrand
I don't know the particulars of this module, but it should be possible to DIY such pretty easy.

Check the doepfer diy tech page - they've got the simple schematic

http://www.doepfer.de/DIY/a100_diy.htm
astroschnautzer
I was thinking about diying a dc offsetter not the doepfer mixer, with a quick look I didn`t find anything about dc offsetting on the doepfer page, have to check it better with time.
flts
astroschnautzer wrote:
I was thinking about diying a dc offsetter not the doepfer mixer, with a quick look I didn`t find anything about dc offsetting on the doepfer page, have to check it better with time.


It's a part of the offsetting CV mixer circuit on that page, check out J4 and R8 and their descriptions there. So as I understand it, it's as simple as this:

1) You wire the positive power supply rail (+12) via a resistor to a jack and get a +n volt offset voltage from the jack, where n depends on the protection resistor value.

2) If you want to control the amount of DC in range 0...n volts (and you probably do), you add a pot that has ground and the +n volt offset on the sides and the output in the middle, so you can attenuate the amount of DC going to the output.

3) When you sum this DC (using some kind of mixer circuit) to the signal, you get an offset version of the signal. So if you just want a simple DC offset module without a multi-input mixer, you'd wire a 2 in 1 out basic opamp summing circuit so that one of the inputs is the +12 line through a resistor & pot, the other one is the signal you want to offset, and the output is the offset version of the signal.

Hope someone corrects me if I got anything wrong.
wetterberg
Quote:
From April 2004 an improved version of the module A-138b is manufactured. For the revised versions control In1 works as a DC offset generator (about 0...+5V) provided that no patch cord is plugged into socket In1. If this feature is not required it can be deactivated by removing a jumper on the pc board. Probably from summer 2004 even the A-138a will be manufactured with this improvement.
Plan B
The Plan B Module 14 has been doing this for four years!
chinard
yeah thats what i have been using my model 14 for.
Alternately you could also use the doepfer A-129-3 offset/attenuator but it doesnt have those handy status lights that the model 14 has that tells you visually which direction the offset is working.

Either way its a very handy way of converting a lfo for gate use.
REwire
The A-129/3 only has positive offset. The A-133 is a simple dual polarizer but the A-138c and Plan-B Model 14 are the only ones that can mix and offeset CV's.
dkcg
REwire wrote:
The A-129/3 only has positive offset. The A-133 is a simple dual polarizer but the A-138c and Plan-B Model 14 are the only ones that can mix and offeset CV's.


The A-129-3 doesn't mix, but it has 5 attens, 5 offsets, and some slew input which is part of the vocoder setup which i don't use. Works nicely with the PlanB M9 mixer.

I wish Peter could be cloned, even a mini-Peter to design some more elves, like a bi-polar offset elf to complement the leveler. grin
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