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Doepfer a-110 modification thread
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Author Doepfer a-110 modification thread
wetterberg
Ross G and I have been going back and forth a bit about how to approach a mod session with the a-110. it has lovely stuff going on under the hood, like linear fm, soft sync, an lfo mode and some improvements to be made to the sine output as well.

this thread is an attempt to collect some of the data we're digging out.
Muff Wiggler
awesome! thanks for doing this guys.... really appreciate you putting it in a thread, was hoping to see lots of modification threads eventually when I made the blacet ones. Anything you can add, photos whatever, will be super appreciated by anyone who is interested in the same modifications. thanks!
wetterberg
alright , so the first place to dig is, obviously, the yahoo group.

There I've dug up the page for the sinewave mod - which basically makes the wave a sine wave and not a lame clipped tri wink
http://mysite.wanadoo-members.co.uk/tstinchcombe/synth/110_mod/110_mod .html
wetterberg
Linear FM / Soft sync:

ingo wrote:
my a110's have these patch points on a separate front panel.
if i recall right you just have to solder a jack
to these points and you're done. but to be sure you should
verify this and ask the technical staff at doepfer.

soundwise i'd say that linear fm on an a111 sounds better,
but anyway it is always nice to have linear fm capability
available on a vco. the soft sync feature is also a bit
different compared to the a111 soft sync.
wetterberg
Fine tune range can also be modified:

Quote:
Quote:

Wider
> tunings have to be done with the octave switches. If you don't like
> this, then the tuning range can be extended very easy (adding a single
> resistor).
>
> Florian
Florian, looking at the schematic, it appears that R5 would be the Resistor to
change. Drop it down to 470K or so... I'll try this tonight.
Chuck E. Jesus
sorry, i've had to do domestic crap...i'm not going to be able to go full out until next week or two (i believe i already mentioned this to mr. wetterberg), but we will be on it soon, i got a new pair of specs coming and some new solder gear just arrived SlayerBadger!
wetterberg
awesome, Ross - having the kit ready to go is essential for getting things done for me, so I'm going to set up a permanent station in my little studio-nook here.

God I wish this diy crap didnt take up as much space!
Tim Stinchcombe
Wandered into this thread whilst browsing:
wetterberg wrote:
There I've dug up the page for the sinewave mod - which basically makes the wave a sine wave and not a lame clipped tri wink
http://mysite.wanadoo-members.co.uk/tstinchcombe/synth/110_mod/110_mod .html
and thought I'd post a working link:

www.timstinchcombe.co.uk/synth/110_mod/110_mod.html

Tim
wetterberg
Thanks for the update, Tim - much appreciated!

Andreas - who can't believe he hasn't gotten around to this update yet d'oh!
cerebrosis
updates? im all ears.
wetterberg
been way too busy with other things...
cerebrosis
what exactly would it take to add a lin/exp switch for the cv2 input? there is a lin fm area on the circuit board but no wires are coming off of it. anybody?
Tim Stinchcombe
cerebrosis wrote:
there is a lin fm area on the circuit board but no wires are coming off of it. anybody?
Yes that can be used for linear FM, and in the past has been mentioned and tried by several at the Doepfer Yahoo group (including myself, a long time ago). It is shown on the A-110 schematic:

http://www.doepfer.de/a110_tec.htm

at C11+R14, and from a quick look at one of mine, those components are on the board. Thus if you feed an (AC) voltage to the point marked 'LINEAR FM' on the PCB, you should hear the effect - from some really old notes it looks as though I calculated that the voltage swing could be about +/- 2.5V before the oscillator actually 'stops' on the negative swing. In fact if you stick a jumper on the nearby 'AC/DC' point, and carefully apply a small DC voltage (of about the same size, i.e. -2 to -3V), you should be able to determine where this point actually is. Of course if the applied AC voltage is in the audio range, you simply won't notice that the oscillator stops for small periods of time, other than the fact that this will introduce all sorts of weird harmonics into the output sound...

Tim
cerebrosis
Guinness ftw!

this is what i was looking for, i think Mr. Green i got to wait til i get more oscillators though. i would hate to mess it up and then be short on VCOs.
worker8
Did the lin fm mod some weeks ago and I'm not fully satisfied with it. The sound isn't as metallic as expected.

Do you think there is a way to improve it ?
cerebrosis
worker8 wrote:
Did the lin fm mod some weeks ago and I'm not fully satisfied with it. The sound isn't as metallic as expected.

Do you think there is a way to improve it ?


the mod Tim explained? could you perhaps make some audio samples?

thanks
other Dave
I've been looking for these mods for ages, thanks for sharing applause
studiokpg
I did the tuning range mod, using a 100K instead of 470K as suggested. The 470K didn't seem to be much of an improvement but the 100K gives almost an octave up and down. So, I'm happy with that one.
But - I'm also trying to do the LFO mod, and not as successful. I'm testing it by touching the leads of a capacitor to the each end of C1 from the back of the board, and there doesn't seem to be much effect. I'm trying a range of values, including 470pF and 22nF (Dieter suggested 1nF and maybe 10nF and 100nF if I understand his post on Yahoo correctly.) I only have ceramic caps on hand, but the service manual says film only for C1. Could that be why I'm not seeing any effect? Has anyone else successfully done the LFO mod? hmmm.....
Tim Stinchcombe
studiokpg wrote:
I'm also trying to do the LFO mod... Dieter suggested 1nF and maybe 10nF and 100nF if I understand his post on Yahoo correctly.
If you can post the link, I'll take a quick look at it (couldn't find it after trying several different search terms - the Yahoo seach really isn't up to much...).

Tim
studiokpg
Here's the link to the post:
http://launch.groups.yahoo.com/group/Doepfer_a100/message/15416
I'll go ahead and quote it too...
Quote:
> On the idea for modifying the A-110 for a super low freq mode, I
> would need to spend more time to figure something like that...
> any ideas? I think this would be a GREAT mod as the 110 has
> everything you could want in an LFO.
>
> Tony

Simply add a capacitor in parallel to C1 (1nF). If you use a three-position
switch that adds two different capacitos (e.g. 10n and 100n) you obtain 3
ranges: ./.10 - normal - ./.100

Best wishes
Dieter Doepfer


Thanks for the help!
Tim Stinchcombe
OK, that puts your comments more in context, thanks. The standard value of C1 is 1nF, so placing a 10nF in parallel will give a total of 11nF, so effectively a divide-by-10 effect on the frequency (and similarly divide-by-100 for a 100nF). I suspect the 'touching' the cap across the pins of C1 just isn't making a good enough contact, if at all, which is why you are apparently not seeing any effect - better would be to carefully 'tack' it on with some solder, then I would expect you will see a difference, even if you use a ceramic cap. But a film or foil one would be better, i.e. more closely resembling the standard one fitted, as it will have much better stability with respect to temperature, and leakage etc.

Tim

[Edit: the timing cap is not C1, but C3. Hence touching a cap across C1 will not have the desired effect! The above applies to C3. See post below]
studiokpg
Thanks Tim - I'll try it again tomorrow and post my results.
Johnisfaster
Im thinking doepfer should just add switches for these mods stock and put this vco back on the map.
studiokpg
Well, very strange. I don't think the LFO mod is possible, at least not by adding capacitance to C1. I tacked on capacitors of a few different values parallel to C1, and none had any effect. To see if I could figure out what was going on, I removed C1 which is 100pF, and tried substituting different values. With and without C1, the lowest frequency of the oscillator (range and tune knobs at lowest setting) was 14hz. Small capacitors gave a much higher frequency. Larger and larger capacitors in place of C1 got closer to 14hz, but never reached it. The largest value I tried was 820 uF by stacking several caps in parallel, and that got me down to 16 hz.

I am definitely not an electronics expert, so maybe I am missing something obvious here, but I just don't get it. It doesn't seem that the mod as described by Dieter works. seriously, i just don't get it
felixer
studiokpg wrote:
I removed C1 which is 100pF

Tim Stinchcombe wrote:
The standard value of C1 is 1nF

hmmm..... you sure you got the right C1?
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