just built this really simple diode distortion with switchable flavours and want to build one for my kosmo
any ideas on how to convert the 9vdc to 12vdc
i would probably like to build in a second input too with a mixer just for creating more complex stuff
You need to calibrate the bias voltage again (i.e. tweak R3 or R4) if you change the supply voltage, in the same way as if you change the transistor (this circuit has no feedback, so you’re extremely dependent on the properties of the specific JFET you’re using), but that’s the only obvious voltage dependency. You could maybe replace R4 with a variable resistor to make that easier.
Is VR1 some kind of tone control? (I assume it’s meant to be wired as a variable resistor, same way as VR2)
nah the schematic is right on the wiring front
i dont quite know how it works but its acting as a jfet booster and giving me more signal to push through the diodes, its a gain pot
i think its something to do with the JFET operating backwards and the lower the current drawn over it the higher the output
so regarding the resistor value im about to display my meager knowledge of ohms law
at present in this setup there is a current of 6ma over the resistor
9/15k = 0.0006a
so with a 12v input the resistor should be 20k?
12/0.0006=20k
thats as far as i can get on my own, with 9v you just have power and earth cables, i understand the middle pins on a ribbon are ground but how would i deal with the +12 and -12, wouldnt that make it AC?
The schematic shows a potentiometer (VR1) with its wiper connected to nothing, and it has little arrowheads on both sides of R4 whose significance I don’t understand.
That would be correct (or rather 0.0006 A with a capital A would be correct) if the bottom of the resistor were at ground potential, but it isn’t. Voltage drop equals current times resistance — not voltage at one end regardless of voltage at the other end…
No, those are just two separate DC supplies, one for 12V above the ground rail (0V), one for 12V below. You can use the +12V and ignore the -12V if that’s what you need.
btw, here’s a Distortion Unit for Kosmo
ah ace, lemme check that out!
ah its a pretty simple read, i never even really though about soft clipping in there too.
hard clipping is easy enough to have a diode selection process just after the on/off switch
soft clipping im not really sure how i would seperate that circuit to allow for multiple different diodes
I could probably do away with the soft clipping entirely and just have the hard clipping for now, i would quite like to have a switch for each side of the diodes to allow for asymetrical clipping too.
nice one for this, i reckon i could make this work, is there an easy way to double the inputs and outputs, just chain jacks together?
You can add inputs by replicating what’s there, jack and capacitor and resistor, with the right sides of all the input resistors connected together and to the op amp inverting input. All inputs would be summed. Normal the jacks to ground.
You want more outputs that just duplicate the original output? You could just connect more in parallel, like a passive multiple; plugging in a second output module may affect the signal at the first output module though.
Alternatively you could duplicate everything right of the clipping switch and have a second output with its own separate drive pot.
For selection of different diodes use an on-off-on spdt switch or rotary switch (with one position connected to nothing) and replicate the stuff the switch connects to: pairs of diodes to ground in one case, diodes and resistors to the op amp input in the other. Or as you say just put a toggle switch in series with each diode and go crazy with mix and match.
ok awesome thanks for the tips, how does this look as an adaptation
excuse the sloppiness, still getting used to the software, should be obvious where the rotary switches go, also i couldnt find the right symbol for the electrolytic capacitors, so excuse the shortcut too.
so if i wanted volume for the inputs would i just add a pot to the right of the 10k resistors post input, pre op amp?
also i followed the schematic linked above but there were no showings of where the power inserts into this circuit, is it something to do with the TL082 arms going nowhere?
Yes, the tl082 receives power (-12V and +12V in a Eurorack or Kosmo system) but this isn’t normally shown in schematics.
Edit: I’m not sure why you replicate the input and output circuits. Are you trying to make a stereo unit? You will not get a true stereo output here because both signals follow exactly the same path.
The unconnected vertical lines are the power pins. A TL082 (you can use a TL072 which is more common) has two op amps on a single chip, so only one pair of power pins for the two. But you also can use a TL074 which has four op amps on a chip since your circuit has three op amps in it. (Connect the non inverting input of the fourth op amp to ground and the output to the inverting input.)
Sometimes you see something like this
where the four op amps on one chip are designated U1A, U1B, U1C, and U1D, and U1E is the power connections.
Other comments:
You should have a separate 100k input resistor for each of the two output stages.
You could reduce your six switches to four by getting rid of the two single throw switches and instead adding one more position on each of the rotary switches that connects to nothing.
I’m not sure why you replicate the input and output circuits. Are you trying to make a stereo unit? You will not get a true stereo output here because both signals follow exactly the same path.
so the double inputs are for mixing two signals together, considering its Kosmo and i have space to play with i figure i might aswell add in some other functionality
however the double outputs are maybe a tad pointless, could be handy having two copies of the same thing but maybe a bit redundant
is there anyway of reversing the polarity of the second output maybe? to give two subtle differences in output, probably would be too subtle
thanks for the tips, i might just reduce it down to one output and use a TL072
good idea on the switches too
i think this is closer to what im gonna build
i would like volume pots on both my inputs, is it as simple as wiring pots after the input resistors?
Before the resistors. After the resistors the voltage is essentially zero (a virtual ground) since the op amp tries to keep both inputs at the same voltage, so the place to attenuate the input voltage is before the resistors. Connect pin 1 to ground, pin 2 to the resistor, and pin 3 to the capacitor.
Also — with 10k input resistors you want the pot to be no more than about 10k. But that brings up another point, which is that a 10k input impedance is kind of low. 100k is more typical. You could try using 100k resistors and 47 pF capacitor in the first op amp stage, I don’t know if or how that would affect the performance. (I’m guessing you’d want to leave the 470k resistors alone.) Or you could buffer the inputs, using a TL074 instead of TL072 and adding a voltage follower between each pot and the 10k resistor. Then the pots could be 100k. Hmm, maybe in that case drop the input caps to 1 µF?
haha thanks
ill breadboard it and mess around with the values, how does one generate eurorack power for a breadboard
i have one of these, is it as simple as setting it to 12v and connecting it to VCC+ (ground to VCC-)?
i still dont quite understand the +/- aspect of euro power
what do you mean by first op amp stage?
man you are the best, thanks for all the effort you go through to be helpful on here
couldnt i just plonk some wires into a ribbon cable pin (hole 1) for -12v - pin 5 for ground - pin 9 for +12v
or even better wires from 1/2 for -12v 3/4/5/6/7/8 for ground and 9/10 for +12v
so i got the power in and built it up with only the hard clip section
one input works fine and one is really quiet, if i swap the input capacitors over then they switch over in volume, its quite peculiar, ive tried with a bunch of different components but its definatly something in the circuit, it seems so strange that switching the component over would make it work but it does. tried it with both ceramic and electrolytic and the same result. It doesnt even have to be the same ‘working’ component. when i switched from electro - ceramic then back to electro it was the ‘working’ one that all of a sudden wasnt working and the ‘not working’ one that worked perfectly
also the one thats full volume operates perfectly in the circuit, and the one that isnt gets clicks and pops whenever i flick a switch and the drive pot doesnt function properly
maybe the circuit isnt built for 2 inputs and i should just have one?
yes my friends!
so its all working in breadboard, just waiting on diodes to arrive for a vero build
would be really nice to control the drive input with cv, how easy is that functionality to build in?
