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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Questions on a mixer module for my lunetta
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Draal



Joined: May 18, 2010
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PostPosted: Wed Jun 30, 2010 6:06 am    Post subject: Questions on a mixer module for my lunetta Reply with quote  Mark this post and the followings unread

Can't help but seem noobish on this one, but I'm having trouble visualizing my mixer module. Here's a snippet from Beavis' site. Would this be a good template to follow? I assume I keep the diodes there to keep signals from bleeding together?

If anyone has other layouts/advice for a simple mixer it would be appreciated.

Draal


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-minus-



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PostPosted: Wed Jun 30, 2010 4:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, yes. I built a passive mixer last year. Looks similar to the one you have posted. Here's a link to the DOD Resistance mixer I built:

http://web.archive.org/web/20060630001422/http://geocities.com/worthekik/mixer.html

It's been a very handy device and ultra simple to make. It is the only mixer I have! The only criticism of it is I have problems when plugging this 808 kick drum clone into it. It works, but when I adjust the volume on any of the mixer pots I get a static crackle when they are turned. It doesn't do it when i use anything else BUT the 808. I think it could be that the 808 it +/- 9V and it's having some sort of issue with the other devices... OR it's an inherent problem with the 808 itself.

I think if I used diodes as your schematic does, it may solve this problem. I just haven't got around to fiddling with it yet! The mixer I have linked to and built would be something I will be making for my Lunetta. Either this or one from Ray's Music from Outer Space:

http://www.musicfromouterspace.com/analogsynth/monomixerpage.html

http://www.musicfromouterspace.com/analogsynth/AAA_AudioMixerIndex.php?page=ANALOG

The panning mixer on the link above looks like fun!


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concretedog



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PostPosted: Thu Jul 01, 2010 1:29 am    Post subject: Reply with quote  Mark this post and the followings unread

I built a passive mixer a while ago thats exactly the same idea as the DOD layout link that minus posted. Really useful little mixer to have around for sure. I got my layout for it from Nic Collins book "Electronic Music, The Art of Hardware Hacking" which has many useful bits in it.
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Draal



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PostPosted: Thu Jul 01, 2010 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks guys! With a new baby coming in 11 days, Keeping it Simple is my new motto. I have to get this lunetta up and running pronto! Laughing
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-minus-



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PostPosted: Thu Jul 01, 2010 4:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Build like mad Draal!!! You know how babies can turn your life upside down! Anyway, I won't hold you up.... you have soldering to do! Good luck with the birth too. Thought of any names yet? How about Lunetta for a girl... or CMOS for a boy. Just a thought.... Smile
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Draal



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PostPosted: Thu Jul 01, 2010 4:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Laughing It's going to be a boy...maybe Stan? Now to only convince the wife Wink !
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concretedog



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PostPosted: Thu Jul 01, 2010 5:30 am    Post subject: Reply with quote  Mark this post and the followings unread

With a 12 week old and a 3 year old...fast lunetta hacking is a must for me also...
I reckon XOR or NAND are good names too!
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RF



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PostPosted: Thu Jul 01, 2010 5:45 am    Post subject: Reply with quote  Mark this post and the followings unread

concretedog wrote:
I reckon XOR or NAND are good names too!

Naming kids would be SO easy if it was up to guys. I'd take either of those in a heartbeat.

bruce

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Stream Operator


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PostPosted: Thu Jul 01, 2010 9:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I had a cat named CMOS once. She was black and white in color and very intelligent.

Les

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-minus-



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PostPosted: Thu Jul 01, 2010 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

I can see you with a cat named Cmos, Les!

... Did she have 14 or 16 legs? Smile
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Draal



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PostPosted: Thu Jul 01, 2010 5:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

This thread has giving me a a good laugh Laughing . Thanks fellas!
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PostPosted: Thu Jul 01, 2010 7:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

-minus- wrote:
I can see you with a cat named Cmos, Les!

... Did she have 14 or 16 legs? Smile


She was a 4 pin DIP package!

Les

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Stream Operator


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PostPosted: Thu Jul 01, 2010 7:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Draal wrote:
This thread has giving me a a good laugh Laughing . Thanks fellas!


CMOS had two output states: sleep and feed_me_now!

Les

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adamon



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PostPosted: Thu Jul 01, 2010 9:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Draal, try using resistors instead of diodes for a different effect (all the same value). Diode summing tends to get crunch and produces a lot of nice stuff when you're mixing high frequencies. Resistor summing will produce smoother mixing; each voice will stand better on its own in the mix. I've made both versions for my system as I find both enjoyable/useful for different things (of course you can always just use switches to choose either diode or resistor summing).

If you opt for the resistor summing, you may have to play around with values of resistors and pots to keep channels from cutting other ones out when one is turned all the way down (this gave me trouble for a while; eventually I ended up using 10k resistors with 100k pots, and that works well enough). I also use 0.1uf caps for each channel (in line with the resistors) to keep the frequencies from getting shifted when the pot is turned all the way up (not sure exactly why this happens, but the caps seem to take care of it... I need to review my old circuits stuff...).

Good luck!

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Draal



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PostPosted: Fri Jul 02, 2010 4:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks adamon, I'll be using 100k pots so your tips on that and the resistor/cap values are very helpful.
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tjookum



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PostPosted: Fri Jul 02, 2010 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
She was a 4 pin DIP package!

Laughing

Great thread, humor and some very usefull information in between, loving it.

Quote:
http://www.musicfromouterspace.com/analogsynth/monomixerpage.html

I've breadboarded this some time ago, it worked but I got really confused with the op-amp section. The sound was very dull and didn't really work with my pc speakerset. What does the op-amp actually do? If it's just amplification, can I use a lm386 instead? I would like to keep my entire machine on single 5v supply and preferably without op-amp or transistor circuitry(Im just glad Im getting the hang of cmos, and not really willing to cram anymore info in my head at the moment).

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richardc64



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PostPosted: Fri Jul 02, 2010 7:32 am    Post subject: Re: Questions on a mixer module for my lunetta Reply with quote  Mark this post and the followings unread

Draal wrote:
Can't help but seem noobish on this one, but I'm having trouble visualizing my mixer module. Here's a snippet from Beavis' site. Would this be a good template to follow? I assume I keep the diodes there to keep signals from bleeding together?
Draal


Does no one else see that if one pot is turned to ground then they're all at ground? There should be a resistor from each wiper to where they come together.

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Stream Operator


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PostPosted: Fri Jul 02, 2010 7:52 am    Post subject: Re: Questions on a mixer module for my lunetta Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Draal wrote:
Can't help but seem noobish on this one, but I'm having trouble visualizing my mixer module. Here's a snippet from Beavis' site. Would this be a good template to follow? I assume I keep the diodes there to keep signals from bleeding together?
Draal


Does no one else see that if one pot is turned to ground then they're all at ground? There should be a resistor from each wiper to where they come together.


Yes, and also every time you change any of the pots, you change the equivalent shunt resistance of every other voltage divider in the network. So it's really an adjustment nightmare - but then again, for Lunettas maybe that's a good thing, haha!

Les

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PostPosted: Fri Jul 02, 2010 7:57 am    Post subject: Reply with quote  Mark this post and the followings unread

tjookum wrote:
Quote:
http://www.musicfromouterspace.com/analogsynth/monomixerpage.html

I've breadboarded this some time ago, it worked but I got really confused with the op-amp section. The sound was very dull and didn't really work with my pc speakerset. What does the op-amp actually do? If it's just amplification, can I use a lm386 instead? I would like to keep my entire machine on single 5v supply and preferably without op-amp or transistor circuitry(Im just glad Im getting the hang of cmos, and not really willing to cram anymore info in my head at the moment).


The opamp in the upper left is forming an inverting summing amplifier circuit. This solves the problem of interaction between pots since the summing node is held at virtual ground. If you were running that circuit from a single supply then you would have to set up a virtual ground for the opamp to work properly. An lm286 is a speaker driver and as such would not be appropriate for this circuit. The other opamps in the circuit are for buffering and gain.

Les

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adamon



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PostPosted: Fri Jul 02, 2010 9:14 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64, thats why I suggested using a 10k resistor in line with the input. There is still a slight drop in output when one is all the way down, but its minimal enough for me. Any bigger and the overall output starts to get too low (thats with a 100k pot of course).

tjookum, I too started out with the goal of keeping everything simple and powered off a single supply. I would suggest you try out the basic version I've described above; it's worked quite well for my system. One thing to note, if you're using diodes (say 1N914), you won't run into the same problem of cutting channels out when one pot is turned all the way down. Try the following:

input jack -> 100k pot -> diode -> sum all channels -> 100k pot -> output

(the diodes prevent any lower ground from being reached on the first 100k pots)

My wiring for the resistor summing mixer is as follows:

input jack -> 0.1uf cap -> 100k pot -> 10k resistor -> sum all channels -> 100k pot -> output

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Ajax



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PostPosted: Fri Jul 02, 2010 11:45 am    Post subject: Reply with quote  Mark this post and the followings unread

adamon wrote:

input jack -> 100k pot -> diode -> sum all channels -> 100k pot -> output

(the diodes prevent any lower ground from being reached on the first 100k pots)


This is what I've been thinking. Volume control without interference between the individual signals. When I did resistive mixing, the mixed sounds ended up interacting quite a bit... The first signal gated the second when I turned on the second, and those both FMed the third signal when I turned it on. How should I set up my mixer so that these interactions don't persist? I'm thinking the diodes should do it...
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tjookum



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PostPosted: Fri Jul 02, 2010 12:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
The opamp in the upper left is forming an inverting summing amplifier circuit. This solves the problem of interaction between pots since the summing node is held at virtual ground. If you were running that circuit from a single supply then you would have to set up a virtual ground for the opamp to work properly. An lm286 is a speaker driver and as such would not be appropriate for this circuit. The other opamps in the circuit are for buffering and gain.


Thanks Les, all clear now Very Happy . I have several op-amps laying around, I think I'll do a simple test with and without the inverting summing amplifier.

Quote:
tjookum, I too started out with the goal of keeping everything simple and powered off a single supply. I would suggest you try out the basic version I've described above; it's worked quite well for my system. One thing to note, if you're using diodes (say 1N914), you won't run into the same problem of cutting channels out when one pot is turned all the way down. Try the following:

input jack -> 100k pot -> diode -> sum all channels -> 100k pot -> output


Thanks a lot Adamon, I have some 1N4148 diodes so I'll try it somewhere next week. Maybe the best of both worlds and do a diode and resistince summing stage with a switch.

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adamon



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PostPosted: Sat Jul 03, 2010 9:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Just remember to put the resistor and/or diode after the first pot (not before, or you won't be blocking the ground created by the pot turned all the way down).

Ajax, I'm not sure what exactly would be going on with your setup to cause that sort of interaction. Diode summing will definitely make the voices cut into eachother quite a bit (intead of "beating" they just kind of cut eachother in and out). You should get more clean mixing with the resistor summing route. Make sure you've got your pots wired up right, and that the resistors are after the pots.

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Mikmo



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PostPosted: Sun Jul 04, 2010 12:09 am    Post subject: Reply with quote  Mark this post and the followings unread

I build a number of these:

http://www.generalguitargadgets.com/content/view/68/26/

very simle build, runs fine from 9V (even 9V battery).

The design can easily be expanded to more channels, i build both a 6 and a 8 channel version.

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-minus-



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PostPosted: Sun Jul 04, 2010 1:17 am    Post subject: Reply with quote  Mark this post and the followings unread

That looks like a great little mixer! I shall be breadboarding one up tonight if I get the time. Thanks for posting that. I think if this works (which I believe it will), I shall be using this in my Lunetta. Unless of course anyone else has some other suggestion...
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