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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Ultra Simple Mono Mixer - how many inputs?
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mark_olson



Joined: Oct 26, 2006
Posts: 177
Location: Lawrence, Kansas

PostPosted: Tue Jan 11, 2011 9:34 am    Post subject: Ultra Simple Mono Mixer - how many inputs? Reply with quote  Mark this post and the followings unread

I built one of these with four inputs:

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

I needed an ultra simple mono mixer and this one is just great.

So now I am thinking I'll build another and I am wondering how many inputs the TL084 will really take. There is a note on the schematic that says "Additional Input Channels if desired.", but I assume there must be a functional limit.

How do I calculate the number of inputs I can really add?

Thanks for any advice.

Mark
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adamon



Joined: May 15, 2009
Posts: 95
Location: Lawrence Kansas
Audio files: 3

PostPosted: Tue Jan 11, 2011 9:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Mark, glad to see you're still building!

The number of inputs really shouldn't matter too much; at least not for a realistic number of inputs. I don't think you can really do any harm to the op-amp itself by having too many inputs. I imagine you'd get some signal degradation when you start summing a lot of inputs.

Might be able to find some info on the data sheet as well.

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mark_olson



Joined: Oct 26, 2006
Posts: 177
Location: Lawrence, Kansas

PostPosted: Wed Jan 12, 2011 7:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Damon,

Thanks for the reply.

Yes, I'm still building, but very slowly; I added six modules last year and am now sourcing parts for another six or seven.

Anyway, reading the datasheet for the TL084 I am reminded that in spite of my relative success building stuff my actual grasp of the underlying engineering is quite feeble.

Now I'm thinking I'll just build one with more inputs (eight?) and if it falters I'll prune inputs until it's happy.

Mark
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emdot_ambient



Joined: Nov 22, 2009
Posts: 669
Location: Frederick, MD

PostPosted: Wed Jan 12, 2011 8:58 am    Post subject: Reply with quote  Mark this post and the followings unread

You should have no problem with 8 channels. I'm using Ken Stone's CGS04 DC Mixer, which only has one mono out with no stereo headphone circuitry. The schematics on their web page shows the circuit with 6 inputs, but if I'm not mistaken, the newer PCBs actually had 8 inputs. Anyway, it uses a single TL072.

You're good to go!
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negativspace



Joined: Dec 25, 2010
Posts: 17
Location: Manhattan, Kansas

PostPosted: Wed Jan 12, 2011 12:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yep, there's 8 inputs on the new PCBs.

Also, hi Kansas. Shocked
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mark_olson



Joined: Oct 26, 2006
Posts: 177
Location: Lawrence, Kansas

PostPosted: Wed Jan 12, 2011 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for that emdot.

And thanks negativ for the confirmation.

Yeah, Kansas, I see that so far this thread is 75% Kansan!

I also see that a welcome is in order for you negativspace!

Glad you're here!

Mark
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negativspace



Joined: Dec 25, 2010
Posts: 17
Location: Manhattan, Kansas

PostPosted: Wed Jan 12, 2011 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the welcome, Mark!

I've migrated over from the Muffwiggler's, so I may look familiar to the double-members among us. But the modular has sucked me fully into SDIY and it was time to get an account here. It's great to see Kansas so well-represented in this community... who'd have figured? Very Happy
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kkissinger



Joined: Mar 28, 2006
Posts: 1221
Location: Kansas City, Mo USA
Audio files: 29

PostPosted: Wed Jan 12, 2011 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Mark,

I have a similar mixer to which I have 11 inputs with no problems.

The mixer already has input capacitors so you don't have to worry DC bias from the inputs.

The worst that can happen is that you'll get clipping. If you reduce the value for the input stage's negative feedback resistor (the 39K resistor) that will reduce the gain of the input stage and reduce clipping.

If you do this, you may want/need a corresponding increase for the value of the negative feedback resistor in the output stages (the 100K resistors connected in series with the 22pf capacitors).

Interestingly -- the line output for this mixer inverts the inputs -- and doesn't include a stage to invert the output from the first stage.

If you aren't using headphones, you may want to use one of the headphone stages to drive the line out -- that way you will output a non-inverted signal and you can adjust the overall gain with it's feedback resistor.

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mark_olson



Joined: Oct 26, 2006
Posts: 177
Location: Lawrence, Kansas

PostPosted: Wed Jan 12, 2011 8:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

I appreciate your insights, Kevin.

Now you have me thinking I'll bump up from 8 to 10 inputs.

I actually have been using the headphone output, it's cleaner than the one on the tired old keyboard amp I'm using and headphones do help keep the peace in the household.

Mark
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jgoulds



Joined: Sep 25, 2012
Posts: 10
Location: bristol, va

PostPosted: Mon Mar 25, 2013 3:52 pm    Post subject: Power Source for the mixer Reply with quote  Mark this post and the followings unread

I know it's off the subject, but I'm wondering if this circuit (Simple Mono Mixer) will function with +/-9V. Anyone know? Thanks!
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Zodiak



Joined: May 20, 2007
Posts: 245
Location: Gillingham, Kent UK

PostPosted: Sun Mar 31, 2013 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Shouldn't be a problem. I built one similar to this with 6 inputs that ran on just one 9V cell, and that's fine. The only restriction is that you won't be able to get signals quite as loud from it, but as it is already way above what most audio circuits need that shouldn't be a problem.
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