Full wave rectifier for waveform converter?

StaticBuildup · Joined: Nov 19, 2018 Posts: 8 Location: London

I want to convert a sawtooth wave into a triangle wave by putting it through a full wave rectifier. I guess the voltage would have to be negative for half of the sawtooth, otherwise it would go through the rectifier unchanged. Is there a way of biasing the rectifier so that the voltage goes negative? If the input signal is 0-10v and the input is kept at +5v, would that work?

MapacheRaper · Joined: Feb 15, 2018 Posts: 166 Location: Spain

I guess you should feed the circuit with +-6.5 volts or more (+-9 or 12v) to achieve a rectification that goes +-5v

I have one module in my eurorack that does precisely it. Here you have the schematic:

http://www.bartonmusicalcircuits.com/fwd/documentation.pdf

Anyway, wait for some more expert one to ask the question. Maybe there´s a simpler way to get it

gabbagabi · Posted: Tue Dec 11, 2018 8:35 am Post subject:

hi,

ur right for the "classic" saw2tri waveshaper the saw has to be well centered around the 0V line.

as u mentioned in the other thread u like to produce sine waves? for that it would be more eficient if u use a triangle core oscillator.
Do u want it voltage controlable?

what kind of powersupply do u use? bipolar or unipolar?

ur going to use opamps or cmos-logic?

JovianPyx · Posted: Tue Dec 11, 2018 10:02 am Post subject:

As g.gabba said, it's really better to start with triangle and convert that to saw. The reason is that a saw core cannot instantaneously reset. The reset is actually a fast ramp, but a ramp all the same. If you try to convert saw to tri with the full wave rectifier, there will be a glitch at the peak of the output tri wave which is very audible. You can try to filter it, but it never goes away and the filtering will do other things you won't like such as reduced amplitude as frequency increases and the glitch will impart harmonics that don't belong in a tri. Low pass filtering will also cause the tri to have curved ramps

There are also imperfections going from tri to saw, but these are much less audible because a saw is harmonic rich anyway.

StaticBuildup · Joined: Nov 19, 2018 Posts: 8 Location: London

Thank you for the replies. Smile

gabbagabi · Posted: Sat Dec 15, 2018 5:09 am Post subject:

hm,
i know almost nothing about ribbon`s, but i guess you can produce a CV with it.
for that i did a simulation for a VCO unipolar 15V power supply (and you could use more than one osc in the future)

the vco is from the LM324 Datasheet, the LM324 is the only single supply quad-opamp i know of, it is probably not the best choice for a vco but it should work anyway.
i have changed on resistor for a trimmer to be able to trim for best symetry, if this is not of great interest one could just use a resistor instead.
i changed the 51k resistors to 50k.

one opamp is used to produce a 7,5V potential which is needed on the VCO and the sine waveshaper as a kind of fake-ground.

R4 and R5 needs to have a relationship of factor 3,4, it is factor 6,8 in the original one e.g yusynth vco, but our vco produce only 5Vpp signal instead of 10Vpp, of course you could replace one of them with a trimmer

the sine waveshaper is a standart one but it is provided also with the fake-ground potential

the vco works fine in the simulator as well as the waveshaper.
i had to simulate them seperatly, together they produced an simulation error, only god knows why Smile

happy breadboarding Smile

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