ac to dc module?

Cwejman, Livewire, TipTop Audio, Doepfer etc... Get your euro on!

Moderators: Kent, Joe., analogdigital, infradead, lisa, parasitk, plord

Post Reply
User avatar
astroschnautzer
Super Deluxe Wiggler
Posts: 1613
Joined: Wed Nov 19, 2008 5:58 am
Location: Finland

ac to dc module?

Post by astroschnautzer » Tue Dec 02, 2008 2:20 am

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

User avatar
BugBrand
Knowledge of Bugs
Posts: 7084
Joined: Tue Jul 15, 2008 11:59 am

Post by BugBrand » Tue Dec 02, 2008 3:34 am

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)

User avatar
astroschnautzer
Super Deluxe Wiggler
Posts: 1613
Joined: Wed Nov 19, 2008 5:58 am
Location: Finland

Post by astroschnautzer » Tue Dec 02, 2008 3:40 am

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.

User avatar
astroschnautzer
Super Deluxe Wiggler
Posts: 1613
Joined: Wed Nov 19, 2008 5:58 am
Location: Finland

Post by astroschnautzer » Tue Dec 02, 2008 4:22 am

would this btw be easy to diy?

User avatar
BugBrand
Knowledge of Bugs
Posts: 7084
Joined: Tue Jul 15, 2008 11:59 am

Post by BugBrand » Tue Dec 02, 2008 4:33 am

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

User avatar
astroschnautzer
Super Deluxe Wiggler
Posts: 1613
Joined: Wed Nov 19, 2008 5:58 am
Location: Finland

Post by astroschnautzer » Tue Dec 02, 2008 5:45 am

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
Super Deluxe Wiggler
Posts: 2984
Joined: Tue Mar 04, 2008 7:01 am

Post by flts » Tue Dec 02, 2008 6:06 am

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.

User avatar
wetterberg
Super Deluxe Wiggler
Posts: 7673
Joined: Thu Jul 24, 2008 5:31 pm
Location: Copenhagen, Denmark.

Post by wetterberg » Tue Dec 02, 2008 11:46 am

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
banned 4 repeated baseless legal threats
Posts: 284
Joined: Tue Dec 02, 2008 11:44 am

Post by Plan B » Tue Dec 02, 2008 12:24 pm

The Plan B Module 14 has been doing this for four years!

User avatar
chinard
Super Deluxe Wiggler
Posts: 2416
Joined: Tue Aug 12, 2008 12:57 pm
Location: Toronto

Post by chinard » Tue Dec 02, 2008 1:51 pm

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.

User avatar
REwire
Super Deluxe Wiggler
Posts: 1959
Joined: Fri Apr 04, 2008 5:30 pm
Location: Los Angeles

Post by REwire » Tue Dec 02, 2008 2:07 pm

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.

User avatar
dkcg
I pity the fool w/o enough VCAs
Posts: 9138
Joined: Mon Jul 14, 2008 12:35 pm
Location: LA

Post by dkcg » Tue Dec 02, 2008 2:30 pm

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. :D

Post Reply

Return to “Eurorack Modules”