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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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DGTom



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PostPosted: Sun Jul 04, 2010 5:45 am    Post subject: Reply with quote  Mark this post and the followings unread

The only suggestion I'd make is to increase the value of the input AC coupling caps... 100nF seems pretty comman in these guitar orientated ccts. but, as we all know, the range of CMOS is ALOT wider than an ole 6 string.

I'd use 220nF or 470nF, on the inputs (C1 - C4 in the mini mixer) & something more like 4u7 all the up to 47uF on the output (C5) - 10uF is good as well.

One thing I found out after building my first lunetta modules was its a good idea not to tap the 40106s straight off - at first I was just running abit of wire from the pot to the output jack = lots of interactions.

Use a simple voltage divider to "seperate" the gate from whatever else it gets connected to, or, you can use an LED as a "buffer" by connecting the anode to the 40106 out & then to ground via a limiting resistor, the output is the the junction between cathode & resistor (think I got my anode & cathode round the right way then... you know what I mean) you can even use another resistor, from that junction to the output, that way you have a little headroom as well, start mixing all these rail to rail signals together & it can get kinda messy.
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PostPosted: Tue Jul 06, 2010 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Mikmo wrote:
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.


I've built a few of these for different purposes as well. Works great for mixing line signals.
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-minus-



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PostPosted: Wed Jul 07, 2010 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm... I've just breadboarded this mixer and I'm finding that with one input it works ok... volume pot adjusts volume, got output. As soon as I put another signal into a second input and adjust the volume pot, it seems to effect the other signal. Each of the pots are effecting each other. Something must be wrong here somewhere. It doesn't seem to 'mix' the signals well at all.

I might try the DGTom suggestion and swap the cap values to see if that helps.
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Draal



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PostPosted: Wed Jul 07, 2010 5:50 am    Post subject: Reply with quote  Mark this post and the followings unread

If I can get a bit of free time today (fingers crossed), I'll test mine out. Loosely based on that mini mixer schematic and another one.
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RF



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PostPosted: Wed Jul 07, 2010 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

I think the caps would be fine...you could even leave them out and it should work...
Check your pot wiring... perhaps change the pots to 100k..you are dealing with much higher signal levels here than with guitar...

bruce

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-minus-



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PostPosted: Wed Jul 07, 2010 6:33 am    Post subject: Reply with quote  Mark this post and the followings unread

...now it appears to be working. Changed to 100K pots as you suggested Bruce. I had the pots connected in reverse (as always happens), so a clockwise turn REDUCES volume. I was wondering about these Audio Taper pots. I know they differ from linear ones. With the pots wired back to front I was getting a quick ramp of volume at the start of a pot turn, then stable volume level for the rest. Only about 20 degrees of the turn seemed to increase sound. I wonder what's in these pots anyway??? Might smash one open and have a look right now! Twisted Evil Then I'll open a linear one and compare...

Don't worry folks... just thinking out aloud here.... Carry on with your soldering...


PS. Im not completely convinced about all this. Never worked out what all those TL072 TL074 things actually do... Seems to be a waste of time really. I guess they do SOMETHING. Op- amps... hmmm. But what does that mean? Maybe they make them for people with a soldering fetish. Perhaps there is nothing inside them after all! blah blah blah....
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RF



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PostPosted: Wed Jul 07, 2010 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

-minus- wrote:

PS. Im not completely convinced about all this. Never worked out what all those TL072 TL074 things actually do...


Designers just put them there to keep the riff-raff away from DIY.... Wink

You'll like op-amps Smile Get to know them.

In that circuit the op-amp acts as a buffer - so what you are plugging into the inputs does not adversly affect the output - It presents a constant impedence at the output...
There are two sections so the signal comes out the same way it goes in... The first op-amp section inverts the signal...the second flips it back around. I don't think you are looking at any gain from that circuit... but you could change that by messing with the feedback resistor (R13) a higher value resistor = more gain...you could also add a pot in there for a 'master' volume control...

Actually - I just used a passive mixer for my first Lunetta and it worked fine in that application. ('Course, it was a tad quirky by design.. Laughing )

bruce

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-minus-



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PostPosted: Wed Jul 07, 2010 7:44 am    Post subject: Reply with quote  Mark this post and the followings unread

HA HA HA!! Had to laugh about keeping the riff-raff away from DIY!! Laughing That's me, Bruce!

Ok, so I'll take your word for it and believe op-amps aren't just empty black boxes with little legs poking out each side for keeping the riff-raff at bay, or for those who have a soldering fetish, or those who like to impress their friends with the amount of IC's in their machines, or whatever...

I have a few of these TL072 and TL074 thingies so I guess I better use at least one of them! I'll try and be a bit more serious about this DIY thing. Don't want my E-M membership cancelled! And I shall try and get to know these op-amps. Thanks for your help! I might start by increasing the feedback resistor and see what happens... maybe then I'll understand and see op-amps as something more than an placebo IC!


EDIT: 5 minutes later... well, increasing the resistor actually decreases the volume output. Question In fact, pulling the resistor out completely = the most volume! Hmmm... placebo IC anyone? Don't you love DIYers who don't have a clue about what they are doing! Laughing
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DGTom



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PostPosted: Wed Jul 07, 2010 7:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Try dropping the voltage of the signals before they hit the mixer, say a voltage divider of 10K & 1K to ground, then use a pot as the feedback resistor so you can hear the op-amp working - the problem with feeding rail to rail squarewaves into an op-amp that doesn't have a rail to rail voltage swing is you might not actually hear it do anything as everything is just a big clipping mess.

Try breadboarding a basic Twin T filter around an amp in a 072, again, make sure if you are feeding it CMOS squarewaves they are attenuated before going in.
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PostPosted: Wed Jul 07, 2010 8:27 am    Post subject: Reply with quote  Mark this post and the followings unread

well, I clearly have a LOT more to learn: Voltage divider, Rail to rail, Voltage swing, Twin T filter, Attenuated... Rolling Eyes

Without knowledge of such things, it is no wonder I run into difficulties! I shall research what all this means... And report back later!

EDIT: 5 minutes later... Voltage divider! Just worked out what that is! ...A T T E N uated... hmmm....
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tjookum



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PostPosted: Wed Jul 07, 2010 9:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Without knowledge of such things, it is no wonder I run into difficulties!


Haha, exactly how I feel. What might seem perfectly logical to someone sniffing solder for a good part of their life is total magic to me sometimes. Getting my first bleeps out of my lunetta was a great victory, I never imagined that I would be able to make a soundmachine like that. But now Im getting into more advanced circuits I keep on running into all kinds of problems. I have been spending a lot more time reading and understanding than I am building. I guess Ill just have to keep with the basics for now and get back to building Smile .

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-minus-



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PostPosted: Wed Jul 07, 2010 10:01 am    Post subject: Reply with quote  Mark this post and the followings unread

HA HA! YES! I know what you mean... Sniffing solder! Laughing

I have put voltage dividers on the inputs and I can now hear what the feedback resistance is doing with the pot. So I'm making some progress...

So much to learn with this! I spend far more time reading than building, and even less making 'music'... Eventually though this obsession seems to end up occupying at least a wall, if not an entire room of knobs and patch leads everywhere! That's when we get to answer questions like "Does it matter which way a resistor goes around?" Laughing

...and if Draal doesn't get a mixer built in the next 3 or 4 days, he probably won't get another opportunity for at least two years!! ...I'd go with a passive one Draal! Laughing
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tjookum



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PostPosted: Wed Jul 07, 2010 10:53 am    Post subject: Reply with quote  Mark this post and the followings unread

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


Finally got around to breadboarding these 2 circuits, amazingly simple stuff! I didn't really like the diode mixing because I noticed the 2 signals were gating eachother. The resistor one works fine for me, I think I'll keep the output open so I can always attach the op-amp buffer if I get around to it. Thanks everyone for shedding some light on your designs.

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PostPosted: Wed Jul 07, 2010 11:16 am    Post subject: Reply with quote  Mark this post and the followings unread

GREAT TO HEAR GENERAL TJOOKUM! On this side of the earth the op-amp war is far from over, over. Sustaining massive brain damage, over... Got bleeding on all inputs!

Well actually, I think your reasoning is good. Why f**k around with this op-amp conspiracy when it can be done an easier way! I'm thinking I may go for the passive option too. If information leaks down via the Lunetta hierarchy ( king ) in terms of a tried and tested schematic, then I'll hook up onto it. Until then I'll go with the resistors. I'm actually getting better results from my little red resistance mixer than the op-amp, in terms of one pot NOT f**king around with the other input signal every time it's moved.

Anyway, sunrise soon... and I have to retire to my trench before the TL072 mortars hit! salut
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Draal



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PostPosted: Wed Jul 07, 2010 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

-minus- wrote:
...and if Draal doesn't get a mixer built in the next 3 or 4 days, he probably won't get another opportunity for at least two years!! ...I'd go with a passive one Draal! Laughing


Laughing Indeed! Finished soldering up a mixer, melody generator and I'm working on the 4040 today. Haven't tested much...brain is on overload and may crash any moment! 8 days till baby! Must..build...more...modules...GASP!
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tjookum



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PostPosted: Wed Jul 07, 2010 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Got bleeding on all inputs!


Laughing hahaha, I love your style minus! Keep it coming...

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PostPosted: Wed Jul 07, 2010 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah well I'm a bit of a shit stirrer really Wink

I'm still not in the trench yet General! The battle may be over for the day, but the war has yet to be won!

I have just implemented your mixer... Yes it works but I was still having interactions... when one pot was turned right up, the other signal would cut out. I have put another resistor after the cap before the pot (in between). This seems to stop the supplies being cut off, over...Can't tell you what value as it is not yet daylight and visibility is low... Fog of war? It's one of those dastardly blue critters with enemy markings! Seem to be flanked with five bands of colour... over? Unable to decipher the enemy code, over. But rest assured, our chaps are working on cracking the code. Will transfer the coordinates at 0900 hours, over...

Chin up, old bean! The Lunetta war will be over soon..... Then it will be cigarettes all round, dancing girls with garters, ticker tape parades in the streets, freshly baked bread with lashings of REAL butter!!! Meet you at check point Charlie! .........over and out!
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Rykhaard



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PostPosted: Wed Jul 07, 2010 3:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

-minus- wrote:
Yeah well I'm a bit of a shit stirrer really Wink

I'm still not in the trench yet General! The battle may be over for the day, but the war has yet to be won!

I have just implemented your mixer... Yes it works but I was still having interactions... when one pot was turned right up, the other signal would cut out. I have put another resistor after the cap before the pot (in between). This seems to stop the supplies being cut off, over...Can't tell you what value as it is not yet daylight and visibility is low... Fog of war? It's one of those dastardly blue critters with enemy markings! Seem to be flanked with five bands of colour... over? Unable to decipher the enemy code, over. But rest assured, our chaps are working on cracking the code. Will transfer the coordinates at 0900 hours, over...

Chin up, old bean! The Lunetta war will be over soon..... Then it will be cigarettes all round, dancing girls with garters, ticker tape parades in the streets, freshly baked bread with lashings of REAL butter!!! Meet you at check point Charlie! .........over and out!


O-MFG! HAHAHAhahahahahhahahahaa. That's just brilliant! Very Happy HAhahaha. Takes me back to my similar days in about '86. (Happy memories of discoveries and diving for cover from exploding caps. Very Happy )

Also - '86 were the year that I built my first Lunetta machine, before I even knew what it were. Surprised (The one that I'd recorded the 30 minute 'hit' Wandering Minds / Wondering Doubts with ... and nothing else but effects.)

These latter portions of this thread also, have set off instructional inspirations for my Forum. Don't know when I'll begin, but I think they could help future Privates. Shall see. Smile (Mayhap - they could be a tie-in, to my intended future video trainings for the Lunetta world, as well.)
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Ajax



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PostPosted: Wed Jul 07, 2010 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

On op-amp mixers: http://www.colomar.com/Shavano/intro_opamp.html
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DGTom



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PostPosted: Wed Jul 07, 2010 9:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great link Ajax.

-minus- give it a read, but, yeah... if you can't get the passive mixer working 100% find out what you are doing wrong there before moving on.

tbh. if you are just mixing a load of 5V or 9V squarewaves together a passive mixer is all you need, the voltage drop isn't going to have much of an effect overall.

You are most likely clipping the op-amp to death. Make sure you get the Inverting & Non-Inverting inputs around the right way & if your power source is one sided & you are using a TL you set-up virtual ground Wink
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PostPosted: Thu Jul 08, 2010 1:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok... back on... reporting for duty!

Found a bit of passive resistor mixing info here:

http://electro-music.com/forum/topic-6386.html&postorder=asc&highlight=krunkus+ds7+stripboard&start=75

dnny mentions: the resistor values are not critical, but the summing resistors and pots should be about the same value, i.e., for 50k pots use 50k summing resistors

I might try that next and see what the results are. Thanks for the replies everyone! Onward we march... towards the inevitable!
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Ajax



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PostPosted: Thu Jul 08, 2010 12:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bah. Mixing for me has been an absolute nightmare. I've tried resistors, diodes, caps, messing with values... Ugh. Soon enough, I'll get it, but for now... Evil or Very Mad Evil or Very Mad Evil or Very Mad
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PostPosted: Thu Jul 08, 2010 1:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

You too Ajax eh? Join the club! I'm sure someone will come up with a solution soon. I was hoping it might have been you when I noticed a new posting. I'm going to do something else, like solder up a 4040 onto a bit of board instead.... I'm sure we'll see a breakthrough soon.

My tests with 100K pots and 100K resistors give much the same results as the 10K resistors. At full volume, one pot will cut out the others!!! With or without the 0.1uF caps before the pots.... I could sit here breadboarding, testing thousands of resistors at random until the sun comes up... wait a minute, the sun IS up! Going to be a very sleepy day for me today!

I share your frustration! Evil or Very Mad
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Draal



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PostPosted: Fri Jul 09, 2010 7:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Whew! Been working my butt off trying to get my mixer up and running as well as getting various ic's working. I settled on a design I found on the web. I am pleased Smile .

http://www.all-electric.com/schematic/simp_mix.htm

I changed some values:
1. 100k pots instead of 10k
2. 0.47uF caps instead of 1uf
3. Eliminated the 27p and 47p caps across the op amps
4. I did single, not dual mono and I used a 22uF cap and a 4.7k resistor instead of the 100r and 10 uF cap at the output.
5. I left out the 10k attenuation pot

It shares similarities with the mini mixer in some regards but I found the website provided plenty of insight into op amp construction. Is it perfect? Probably not, but I have very good control over my multiple volume pots without things going haywire. I used the TL074 ic. That allowed me to use 2 op amps for this mixer and another one for my R/2R ladder (with one op
amp to spare).

Time to rest... Wink


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PostPosted: Fri Jul 09, 2010 8:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

My my, Draal... YOU HAVE BEEN BUSY! Laughing

I have just skimmed through the link you posted. There is a lot of great info in here! I shall have a really goo read through of this and attempt reconstruction. I'll have a muck around on the breadboard first. If all goes well I shall post findings here.

Thanks for the research into this. It helps a lot to understand what these op-amps are actually doing!
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