[sdiy] Multiplier vs VCA

[Tim Daugard]

From: "Derek Holzer" <derek at umatic.nl>

>>> 1) Ability to use LFO as modulator for slow AM.
>>
>> This module was created after reading my latest ARRL manual discussion on 
>> AM and ring modulators. The waveforms out of it resemble that of a ring 
>> modulator. This module avoids the cost of transformers. It also has a 
>> wider bandwith than a transformer coupled ring modulator. It works at DC 
>> (checked) to the end of the audio range and should work to the bandwidth 
>> limit of the opamp!

> So this multiplier could do a veeery slow "tremolo" amplitude modulation 
> as well as space/radio noises? How slow an LFO have you gotten results out 
> of this with, if you recall? Will breadboard soon and check for myself of 
> course!

Ring Modulation is more a vibrato then a tremolo am. I'll have to think 
about this. I think if you coupled an audio signal to one capacitor input, 
an inverted copy of the signal to the other capacitor input and then 
balanced the controls for no output, you could then feed a DC signal to one 
of the the resistor inputs. This DC signal should unbalance the input and 
provide a VCA.

A better module for tremolo is either of the two other modulators on my 
page. This module was built to be a ring mod after I had built my other two 
modulators. That is why there is no recording of it yet. I stopped recording 
the individual modules in test patches when it became apparent that there 
was not enough demand to make the book a comercial venture.

Tim Daugard
AG4GZ 30.4078N 86.6227W Alt: 12 feet above MSL
http://members.cox.net/synthfred/h_toctop.htm (Fred's online edition)