Well, the red x input is labeled “Mic/guitar”, and it has a gain stage with gain 11 (it says 10x in the description but it’s 11x right? 1+10k/1k?) so I’d say that’s right. Synth level is higher so that input bypasses that gain stage.
The AC input has a decoupling capacitor to remove DC offset from the input signal, the DC input doesn’t. There’s also a third input with an “unbalance” pot to add DC offset “thus changing its characteristics. The unbalance function is not unlike a wet/dry mixer.”
I’m curious about the mix of NE5532 and TL07x op amps here. As I understand the NE5532 has lower impedance but lower noise, but it’s not at all clear to me how that influences the choice of which to use where in this circuit.
But here the 5532 is used for the carrier input and for the second stage of the signal input, TL07x for the first stage and for both stages of the output. Strikes me as haphazard but I don’t know much about this stuff.
I guess another way to put it is the 5532 is used for the synth level inputs and the TL07x for the mic/inst input and the outputs. From that point of view it’s less arbitrary.
I think the confusion here is that the term “AC” is usually associated with “wall current”, the 110 or 230V you have in every house.
But in this context it means the literal Alternating Current. Which is when the signal goes negative during its swing.
I get the impression by reading up on wikipedia about the workings of a ring modulator that the ‘unbalance’ input will influence 2 of the diodes in the ‘ring’ by giving them a small constant current which probably makes the center point of the modulation move off center and create an unbalanced output signal. I’m not sure about this though, nor about how that will affect the sound.
This is what ring modulation does to a sine and a square wave:
@Dud Have you been able to find/buy the transformers as described in the schematic or are you improvising with some transformers you already have?
The modulator is made with 2 transformers 42TM018 and 1N60 germanium diodes.
To sum up, it was an old passive modulator project that I had done in a box, then wanted to turn it into a module, but it had a very low signal, I tried to add an opamp on the output, but I ended up not putting this module in my 3rd case.
I hope i’m going to end up putting it in my next one when I do it with this full active schematic.