Doepfer

> Hi M.
> 
>> I've been trying to use my A-114 to double the frequency of a
>> waveform (as
>> suggested by some articles about modular synthesis), but
>> couldn't get it to
>> work.
>> (After all, a ring modulator gives the sum and the difference
>> of its inputs,
>> so having the same signal at both inputs would give only the
>> sum, the same
>> waveform one octave higher, yes?)
>> It seems that the sound doesn't change much at all if I send
>> the same sine
>> wave trough both its inputs.
> 
> From a quick look-see I did last night I'd say your 114 is probably working
> fine - I think the reason you are apparently not *hearing* a doubling of
> frequency is due to the rather approximate sine shape output from the 110. The
> 110 sine output is actually a kind of logarithmic approx to a sine wave, and
> it gets less accurate as the frequency is increased. On one of my 110's, if I
> feed the sine into both 114 inputs, at lower frequencies it clearly is being
> doubled, and switching between the two is easy to tell the difference by
> listening. However as the frequency is increased, because the 110 output gets
> more distorted, the doubled output from the 114 actually looks more like a
> full-wave rectified version of a sine wave (all the positive humps appear
> flipped to negative): whilst measuring it on the scope it does have half the
> period (i.e. double the frequency), listening to it I can hear very little
> difference between the doubled 114 output and the original from the 110 - this
> doesn't seem too unreasonable since all the frequencies arising from the sharp
> changes in direction of this 'rectified' wave are probably beyond hearing
> range. (In the 110's defence, this is working at about twice the 'as
> advertised' range of the module.) The output from a 122 or 123 filter in
> self-oscillation is a pretty good sine wave, and feeding this into the 114
> does give a fairly nice sine wave at double the frequency out, and switching
> between the two, the difference in sound is much more noticeable. (This may
> not help you if you don't have either of these though - I didn't try the 121
> multimode because the sine wave from this can be quite distorted.) I also
> tried the triangle wave from the 110 into the 114 - even though this also
> loses it shape at high frequencies, the output from the 114 is actually quite
> rounded, and to my ears sounded like there is a greater difference between the
> input and the doubled output, when compared to the sine wave.
> 
> Tim

Thanks Tim.
Well, I tried every signal source I have, A-110, various LFO's, A-121 and
A-123, and ran them through an oscilloscope and a frequency counter but the
frequencies stay roughly the same.
I don't get it. My A-114 seems to work fine when used "as a ring modulator",
but seemingly it won't do anything to the signal if I feed it the same
inputs. I've tried the trick on a Putney and that worked.
Maybe there's two different versions with different electrical behavior?

Hi M.

> Well, I tried every signal source I have, A-110, various LFO's, A-
121 and
> A-123, and ran them through an oscilloscope and a frequency counter 
but the
> frequencies stay roughly the same.
> I don't get it. My A-114 seems to work fine when used "as a ring 
modulator",
> but seemingly it won't do anything to the signal if I feed it the 
same
> inputs. I've tried the trick on a Putney and that worked.
> Maybe there's two different versions with different electrical 
behavior?

I'm baffled too. I think we must be overlooking something or 
misinterpreting readings. The circuit is relatively simple due to the 
fact that the 1496 chip takes care of the hard part - multiplying the 
2 signals together - so there are few external components. If it 
works for different signals, I see little reason why it shouldn't 
work for the same signal on both inputs (it would have to be a very 
subtle failure mode for it not to do so!). (Clutching at straws a 
bit...) are your 180 multiples wired as an '8-way' (all sockets 
connected together), or 2 '4-ways'? (there is a solder bridge in the 
middle of the 2 sets of sockets on the pcb, which can be removed - 
all mine are) - I'm wondering whether the signal isn't actually 
reaching one of the inputs. However, if it didn't you shouldn't get 
much out of the 114 at all (anything times zero is zero!), rather 
than, say, just the single input passing through. Very rough 
measurements from one section of my 114: with X in from 110 sine out, 
so +/- 5V approx, nothing connected to Y, sine o/p is approx +/- 
25mV, same frequency; with nothing on X, but signal to Y, o/p is a 
little bigger, +/- 0.25V and double frequency, but grounding the X 
input reduces this to approx +/- 50mV and restores it to same freq as 
input (there is always likely to be coupling between the 2 inputs of 
such a circuit). You could perhaps try this yourself for comparison, 
because another possibility is that your 114 isn't adjusted properly: 
without further tests I'm not sure what impact this would have on 
normal 'ring mod' operation, but I suspect such a check could 
highlight if the circuit is adjusted properly or not. I have 
a 'pseudo' 1496 lashed up on some breadboard at the moment - if I get 
the chance I'll take it out of adjustmeent and see what happens...

Tim

P.S. I've temporarily lost daily use of email/the internet (changing 
jobs!), so until I buy a PC of my own, I will be relying on visits to 
my local 'internet cafe', which will generally only happen at 
weekends, therefore there may be big gaps between my responses!