electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software
Buchla Matrix Mixer Clone
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 2 of 3 [71 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: Previous 1, 2, 3 Next
Author Message
widdly



Joined: Jun 25, 2007
Posts: 268
Location: singapore
G2 patch files: 2

PostPosted: Sat Nov 08, 2008 1:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

The opamps are inverting...so two in row will be non-inverting.
Last edited by widdly on Thu Aug 05, 2010 10:04 pm; edited 1 time in total
Back to top
View user's profile Send private message
gogmagog



Joined: Nov 08, 2008
Posts: 19
Location: Nashville, TN

PostPosted: Sat Nov 08, 2008 1:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the speedy reply, and sorry for digging up an old thread (didn't notice the date until it was too late).

Anyway, I'm still wondering what the practical purpose of using two inverting opamps in this scenario is versus using one non-inverting opamp. I'm thinking of implementing a mixer like this, but on a much larger scale as a patchbay...
Back to top
View user's profile Send private message
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

gogmagog wrote:
sorry for digging up an old thread (didn't notice the date until it was too late).


That's ok, we do it all the time Laughing

welcome aboard.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 1:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is not even an old thread Shocked it's from June, this year even Exclamation
_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 1:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

gogmagog wrote:
Anyway, I'm still wondering what the practical purpose of using two inverting opamps in this scenario is versus using one non-inverting opamp.


The first opamp is a summing node, the non inverting buffer would not be suitable for that. Penalty is that an extra opamp is needed to reverse the phase. I just saw that the Ken Stone circuit has an interesting feature, the bipolar/unipolar switch ... but maybe Moog has that as well.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
gogmagog



Joined: Nov 08, 2008
Posts: 19
Location: Nashville, TN

PostPosted: Sat Nov 08, 2008 2:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, thanks for the explanation. Looks like I need to hit the books some more Sad
Back to top
View user's profile Send private message
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 2:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

gogmagog wrote:
Ok, thanks for the explanation. Looks like I need to hit the books some more :-(


You want that 2nd opamp out?

Guess you could make the ingoing buffers inverting, that way the outgoing inversion would be a feature really.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
gogmagog



Joined: Nov 08, 2008
Posts: 19
Location: Nashville, TN

PostPosted: Sat Nov 08, 2008 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Not really so concerned about having a second opamp per output, so much as I am about the fact I don't know why it needs to be inverting in order to function as a mixer.
Back to top
View user's profile Send private message
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok ... well let me try to explain ... the inverting summer has a special property in the minus (-) input of the opamp being at virtual ground (due to the feedback regulating the - input to the same level as the + input), this results in the inputs being virtually short circuited with no possibility of the signal from one input going back into another. When you'd try to sum on the + input you'd not have that feature and signals would influence each other back through the matrix in this case.
_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://www.engineering.uiowa.edu/~bme080/supplementary_info/BBTI_AppCkts.pdf might be useful.
_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
blue hell
Site Admin


Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat Nov 08, 2008 4:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

or http://www.williamson-labs.com/480_opam.htm
_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
gogmagog



Joined: Nov 08, 2008
Posts: 19
Location: Nashville, TN

PostPosted: Sat Nov 08, 2008 4:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Aaaaah! Now I get it. The negative feedback essentially cancels out the signal behind the opamp, yes? I had actually wondered about input signals bleeding into each other, but was ready to ignore the consequences, since I had seen some patchbay designs (like this one: http://monopole.ph.qmw.ac.uk/~thomas/synthdiy/patchpanels.htm) ignore it too.

Thanks a bunch for clearing that up for me.
Back to top
View user's profile Send private message
doctorvague



Joined: Mar 14, 2007
Posts: 281
Location: new mexico
Audio files: 2

PostPosted: Sun Nov 09, 2008 6:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan. That answers some questions for me too. Appreciate your input on things like this - I've learned a lot from you - in bits in pieces Smile

Cheers
Phil

_________________
doctorvague's youtube channel
Back to top
View user's profile Send private message
neandrewthal



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

PostPosted: Sun Nov 09, 2008 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

So, now that everyone is happy, can I ask a question? Smile

Can I build a matrix mixer using these CGS DC mixers (with the optional attenuverting circuitry shown in red)? The official CGS matrix mixer has input buffers to "avoid loading your output" I'm not too sure what this means, but I'm wondering if I can get rid of them for simplicity's sake since I will be need 12 of these circuits for my intended project. Getting rid of the buffers would save me 32 op-amps

Posted Image, might have been reduced in size. Click Image to view fullscreen.

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Sun Nov 09, 2008 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

For each input you connect a single output to, the input impedance goes down because the input resistors are in parallel. This happens any time you use a multiple module or connect 1 banana output to several inputs.

With a matrix mixer each input channel is always connected to N inverting summers, so the input impedance goes down quite a bit. Assuming 100kohm input resistors the effective input impedance is:

2 channels: 50kohm
3 channels: 33kohm
4 channels: 25kohm
5 channels: 20kohm
6 channels: 16kohm
7 channels: 14kohm
8 channels: 13kohm

What this means is that the signal that is input into the matrix mixer will start to droop. Assuming 100kohm input and 1kohm output resistors:

1 channel: 1% error
2 channels: 2% error
3 channels: 3% error
4 channels: 4% error
5 channels: 5% error
6 channels: 6% error
7 channels: 7% error
8 channels: 7% error

For audio the error is not too significant, less than 1dB attenuation. But for CV, especially accurate 1 V/octave signals you will have tuning issues.

Smile
Back to top
View user's profile Send private message
neandrewthal



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

PostPosted: Sun Nov 09, 2008 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag wrote:
For each input you connect a single output to, the input impedance goes down because the input resistors are in parallel. This happens any time you use a multiple module or connect 1 banana output to several inputs.

With a matrix mixer each input channel is always connected to N inverting summers, so the input impedance goes down quite a bit. Assuming 100kohm input resistors the effective input impedance is:

2 channels: 50kohm
3 channels: 33kohm
4 channels: 25kohm
5 channels: 20kohm
6 channels: 16kohm
7 channels: 14kohm
8 channels: 13kohm

What this means is that the signal that is input into the matrix mixer will start to droop. Assuming 100kohm input and 1kohm output resistors:

1 channel: 1% error
2 channels: 2% error
3 channels: 3% error
4 channels: 4% error
5 channels: 5% error
6 channels: 6% error
7 channels: 7% error
8 channels: 7% error

For audio the error is not too significant, less than 1dB attenuation. But for CV, especially accurate 1 V/octave signals you will have tuning issues.

Smile


Would a trimpot in series on one side of the pot help to "center" it? I don't care if the scaling is 4% off, as long as the "off" position is at 12 o'clock on all the pots. Maybe center detent pots would get rid of this issue?

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Sun Nov 09, 2008 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well I think you could up the gain a little bit by increasing the 100k* resistor between nodes A and B. What is the output resistance of your other modules? If its 1kohm like I assumed above and you have a 4 channel mixer you could add a 4kohm resistor in series with 100k*. If the output resistance of each of your modules isn't 1kohm this trick won't work. That's where the input buffers come in. Wink
Back to top
View user's profile Send private message
neandrewthal



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

PostPosted: Sun Nov 09, 2008 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, my output impedance is 1k for just about everything. So, all I do is use 101k for channel 1, 102k for channel 2, 103k etc...?

Sounds easy. I can build 8 separate adding/subtracting mixers that cascade into a big matrix with only 4 TL074's Very Happy

But, what if I happen to plug in a module with a 10k impedance?

None of this would change the center point of my pots, would it?

If I have a 4% drop on channel 4 and it just means that -5-+5 signals are now -4.8-+4.8 and 0-10 signals are now 0-9.6 that wouldn't bother me the slightest bit, as I'm building a separate mixer specifically for v/oct voltages

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Sun Nov 09, 2008 5:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK looks like I have caused some confusion above, let me try and straighten things out. The error will be constant across all channels of the matrix mixer, but the error will depend on how many channels your mixer is. If you make a 4 channel mixer only look at that row in each of my "tables".

So hopefully now you've got the idea that the "error correcting" resistor should be constant across all channels of the matrix mixer.

Smile

I don't think you'll have any modules with a 10kohm output impedance, but maybe a designer could choose 100ohm instead of 1kohm. In this case the errors will all a magnitude smaller, 1% -> 0.1%, 2% -> 0.2%, and so on. So if you added a 4kohm resistor in series with the 100kohm resistor you'll have created a new error by adding 4% more gain for sources with 100ohm output resistors.

Your droop voltage numbers look correct. I'm not sure a separate matrix mixer for 1V/octave signals will help any unless you have buffered inputs. It will only really be a problem if you have a signal from a keyboard, sequencer, or MIDI -> CV and you have the mixing pot all the way clockwise (for no attenuation) in which case you wouldn't have correct scaling.
Back to top
View user's profile Send private message
neandrewthal



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

PostPosted: Sun Nov 09, 2008 5:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, thanks a bunch. Makes sense now.

I meant I'd build a regular mixer for mixing V/oct, just 2 in 1 out, not a matrix. Also, I already have a CGS cascade mixer, which is a matrix mixer for v/oct CV's Very Happy

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Sun Nov 09, 2008 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool
Back to top
View user's profile Send private message
Pehr



Joined: Aug 14, 2005
Posts: 1307
Location: Björkvik, Sweden
Audio files: 2

PostPosted: Mon Nov 10, 2008 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

I got to build this mixer. Would it work with 10k pots?

EDIT: Yes, it will Smile http://cgs.synth.net/modules/cgs33_matrix_mixer.html

_________________
YouTube channel
flickr photostream
http://loxodrom.blogspot.com
http://www.garageband.com/artist/loxodrom
http://soundcloud.com/loxodrom
Back to top
View user's profile Send private message
noisedeputy



Joined: Nov 15, 2008
Posts: 17
Location: Boston, MA

PostPosted: Sun Nov 16, 2008 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

so is this just 8 ins and 8 outs?

I want to make something like the aux pander, with 8 fx sends.
Back to top
View user's profile Send private message AIM Address
vtl5c3



Joined: Sep 08, 2006
Posts: 425
Location: PDX
Audio files: 13

PostPosted: Sun Nov 16, 2008 6:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's how I built it, but you can really do any number of inputs and outputs. Not sure what the aux pander is, but I built it thinking of it as an 8 way effect send, where any of the 8 inputs could be sent to any of the 8 outputs in varying amounts.

noisedeputy wrote:
so is this just 8 ins and 8 outs?

I want to make something like the aux pander, with 8 fx sends.
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3950
Location: Germany
Audio files: 23

PostPosted: Wed Jan 21, 2009 8:16 am    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag wrote:
OK looks like I have caused some confusion above, let me try and straighten things out. The error will be constant across all channels of the matrix mixer, but the error will depend on how many channels your mixer is. If you make a 4 channel mixer only look at that row in each of my "tables".
[...]
I don't think you'll have any modules with a 10kohm output impedance, but maybe a designer could choose 100ohm instead of 1kohm. In this case the errors will all a magnitude smaller, 1% -> 0.1%, 2% -> 0.2%, and so on. So if you added a 4kohm resistor in series with the 100kohm resistor you'll have created a new error by adding 4% more gain for sources with 100ohm output resistors.
[...]
I'm not sure a separate matrix mixer for 1V/octave signals will help any unless you have buffered inputs.


i read thru the thread. and i was thinking of the following: an inverting opamp buffer at each input, and an inverting opamp mixer at each output row - this way i would have buffered inputs (no error), a non-inverting matrix mixer and lower part count. with selected resistors it should be suitable for keyboard voltages too (but what different keyboard voltages should one want to mix?).
an inverting input buffer would actually be the same thing as an inverting mixer with just one input Wink

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 2 of 3 [71 Posts]
View unread posts
View new posts in the last week
Goto page: Previous 1, 2, 3 Next
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use