5-channel Attenuverting Mixer 2nd run

rjd2 · Joined: Sep 02, 2007 Posts: 236 Location: philly

thanks for the help, fonik. i now have all 4 pots wired per your instructions.

i have the jacks just wired to "tp" to tip and the blank pad/ground to sleeve. from the pdf, i thought that just omitting the switching pin meant that you lost the individual output cutting off the "sum out". i have my sum out jack wired to "sum tp". the "sum" ground pad is where all my jack ground ties come in.

i ran a stereo signal thru channel 1, and the pot seems to work properly in relation to L to R, but i am only getting ground hum with very faint signal. and again, measuring DCV at the output 1 jack, i still get 0V, and no play from trimmer.

just to clarify, you said the ac/dc/ switch can be wired across pins 1 and 2, but im not sure which pins those are; the ones above the label "SW1", or the opposite first 2 pads? the ones all the way to the RIGHT of the "SW1(closed DC)" labelling?

thanks for the help.

fonik · Posted: Tue Jan 27, 2009 9:49 am Post subject:

rjd2 · Joined: Sep 02, 2007 Posts: 236 Location: philly

ok-so if if just bridged each of the jack output pads' "SW" to "TP", then each attenuverter would be permanently running to "sum out"? maybe i'll just do that.

sorry, when i said "stereo signal", i meant a signal from my stereo! i should have said LINE LEVEL. i can plug this in my modular, and see what happens with a CV at input.

back soon with more info. thanks for the help!

EDIT: i got the trimming sussed. very obvious in hindsight; i SHOULDNT have seen a voltage at the output pins with no voltage at input. duh.

one last thing; i tried bridging the "SW" and "TP" pads for each channels output jack. it provides no attenuation at the "sum" output now; each side of the pot is 100% from 1 oclock to 5 oclock, so to speak. how can i maintain the attenuverter aspect of each channel at the "sum out"?

fonik · Posted: Wed Jan 28, 2009 12:57 am Post subject:

you solved a lot of issues now. great.

rjd2 · Joined: Sep 02, 2007 Posts: 236 Location: philly

thanks senor fonik; let me explain further.

"
fully clockwise and fully counterclockwise there will be no attenuation. full attenuation (no signal) will get achieved with potentiometer in 12 o'clock position. "

with signal at input 1, the output 1 gives me the above properties. it works right-sweeping thru the range of the pot gives a steady increase in volume. the problem is that when i monitor at SUM OUT, the pot doesnt function as a pot. if the pot is set to 1'o clock, or 3 oclock, or 9 oclock, i still get full level signal. its at 100%volume all the time. since im mainly gonna be using these as VCO mixers, i want to have the pot functioning at the sum out.

you said to bridge the blank pad of the output jack with "SW". the blank pad being ground, is that what i want to do here? or is the mixer designed in a manner where attenuvertion should not be happening at the "sum out" stage?

fonik · Posted: Wed Jan 28, 2009 9:49 am Post subject:

numbertalk · Posted: Mon Feb 09, 2009 8:45 am Post subject:

Regarding the alpha pots with center detent, I find there is more play in the detent position than I anticipated. I built my mixer a few weeks ago and found trimming it a little tricky because of this and also find that it's very difficult to fully attenuate a signal on any of the channels- it's unfortunately not simply a matter of dialing the pot to the detent position.

Matthias, do you think regular pots would work better or is setting channels fully attenuated/silent a very slim threshold and tricky dial in, right between attenuated and inverted, for this mixer even with regular pots?

Great module, by the way, thanks for this project! I'll post a photo tonight of it paneled up in my synth.

neandrewthal · Joined: May 11, 2007 Posts: 672 Location: Canada

Has anyone used center tapped pots, with no detent? Are they any good in this context? Any tips on where to get them?

fonik · Posted: Mon Feb 09, 2009 11:52 pm Post subject:

numbertalk · Posted: Fri Feb 13, 2009 7:53 am Post subject:

Oh well. You live you learn. Guess I'll be swapping these out. Anyone who hasn't gotten their pots yet or built their board I would highly suggest you stay away from the center detent pots, unless you don't mind it being a bit of a hassle to fully attenuate any of the signals in the mix.

Thanks Matthias.

EdisonRex · Posted: Fri Feb 13, 2009 8:15 am Post subject:

fonik · Posted: Fri Feb 13, 2009 9:09 am Post subject:

IIRC there has been a discussion on the synth-DIY list of using pots with center detent. i cant recall the whole thing, but for me at least the bottom line was to stay away from it.
so what i have done is carefully calibrating each channel for itself, that is sufficient, i think: when no offset is wanted, you would choose AC mode anyways to remove any offset.

BananaPlug · Posted: Sat Mar 14, 2009 7:46 pm Post subject:

I finally got one of my attenuverters built. It's a frac format. Both the AC and DC coupled Mix outputs are brought out to the panel. A sixth "Aux" input is tacked onto the mix summing point through another 47k resistor. Inputs 2-5 have toggle switches to selectively add them to the mix. The LED's a bipolar red/green. The panel started out as one of Blacet's blank panels and a local shop lasered the graphics for me.

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fonik · Posted: Sun Mar 15, 2009 4:28 am Post subject:

man, what a nice build. great module.

i't liked to ask you if i could post this picture on my site?

BananaPlug · Posted: Sun Mar 15, 2009 7:26 am Post subject:

Funky40 · Posted: Sun Mar 15, 2009 11:37 am Post subject:

Funky40 · Posted: Sun Mar 15, 2009 11:43 am Post subject:

I would like to have more of this utility mixers,
but with a precision voltage referenze for the CV offset.
Seems to be a need when offsetting VCOs

fonik · Posted: Sun Mar 15, 2009 12:52 pm Post subject:

the offset function was originally meant as a goody, not a major feature of this module. the offset voltage changes whenever you turn one of the processing potentiometers.
nevertheless one could improve the perfomance of the offset function or stabaliue it by replacing the two resistors of the voltage divider creating the 7.5V by a 1k resistor and a Zener Diode. this has been entioned by serenadi (member here), i implemented it and will post the details soon.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

This new "Lunar Experience" module looks suspiciously similar...

http://www.lunar-experience.com/525.html

fonik · Posted: Fri Apr 17, 2009 1:48 am Post subject:

i met gerd at the musikmesse and we have had a short talk. he does this stuff for decades as a hobby and has recently been talked into selling modules, IIRC. his website does not reflect his modest and humble character, i believe.

i would say, his attenuverter does not mix signals, has no optical indication and no DC-mode. his mixers inputs are not normalled to a reference voltage.

i still believe the fonitronik attenuverting mixer is a very versatile module - if it ever would come to a 3rd run, i would improve and add some features (real stable reference voltage, on/off switches for each channel).

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

His first input (and by way of chaining, all the others) is connected to a +10V reference.