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Main output Bus
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gusjdt



Joined: Apr 12, 2006
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PostPosted: Mon May 21, 2007 11:04 pm    Post subject: Main output Bus Reply with quote  Mark this post and the followings unread

I usually see a main output bus on most synths, or something that has the Master Volume control. Does that circuit take the output from VCAs or can you connect the output of a VCA straight into a keyboard amp and not get any weird results? If I _do_ need some sort of main output bus, does anyone know where I can find schematics for a circuit like that?
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Mikmo



Joined: Dec 01, 2005
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Location: Copenhagen - Denmark

PostPosted: Tue May 22, 2007 12:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I run the output of VCA's either directly to my Mackie mixer as a Line level signal, og to a smal (audio) mixer i have as a module that also expects line level signals.

So i think you can run it directly to your amp.

If it is too loud you can just turn the " initial gain" knob (or whatever it is called) on the VCA down.

I have a small 3 channel audio mixer in my modular to mix serveral VCA outputs before sending them to the mixer / amp. This is to avoid having too many cables going to the Mackie mixer, but it is also useful for other things, like splitting a sound, sending it to two different filters and combining it again. Or mixing the output of two VCO's and noise before sending it to a filter. Actually i'm going to build a couple more of these Smile

I just started the second cabinet of my modular. A lot of the space in it is going to be occupied by "utility modules" like audio mixers, CV mixers, mult's, an external input module with envelope follower and gate / trig. extractor, simple attenuators for CV. Not very fancy, but very usefull.

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doctorvague



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PostPosted: Tue May 22, 2007 3:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Mikmo wrote:
I run the output of VCA's either directly to my Mackie mixer as a Line level signal, og to a smal (audio) mixer i have as a module that also expects line level signals.

So i think you can run it directly to your amp.

If it is too loud you can just turn the " initial gain" knob (or whatever it is called) on the VCA down.

I have a small 3 channel audio mixer in my modular to mix serveral VCA outputs before sending them to the mixer / amp. This is to avoid having too many cables going to the Mackie mixer, but it is also useful for other things, like splitting a sound, sending it to two different filters and combining it again. Or mixing the output of two VCO's and noise before sending it to a filter. Actually i'm going to build a couple more of these Smile

I just started the second cabinet of my modular. A lot of the space in it is going to be occupied by "utility modules" like audio mixers, CV mixers, mult's, an external input module with envelope follower and gate / trig. extractor, simple attenuators for CV. Not very fancy, but very usefull.


Ditto almost all of what you said Mikmo.
And thus the modular cliche "you can't have too many mixers". I have 3 Blacet mixers and they probably get used more than any other modules I have. One I use pretty much as a dedicated output mixer as you describe. The Blacet Mixer/Processor kicks ass. His VCA mixer not so much.
It would be nice to have a dedicated final stereo mixer with pans and balanced outs and optionally sends and returns. I've seen a few out there in people's systems. I mean a module, not a Mackie.
Another simple utility module I'm going to build is a rotary switch selector to quickly select between CV sources for instance. Not too glamorous but seems like it would be useful. AND it can have a chicken-head knob Smile
Phil
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RF



Joined: Mar 23, 2007
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PostPosted: Tue May 22, 2007 5:57 am    Post subject: Reply with quote  Mark this post and the followings unread

This works great, and is easy to build. Just ignore the headphone segment if you want.

http://www.musicfromouterspace.com/analogsynth/monomixerschem.gif


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fonik



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PostPosted: Tue May 22, 2007 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

i am using a more simple mixer: just a unity gain inverting configuration without ac coupling. thus i can mix even control voltages... it may not be that special audio circuit but i never noticed any drawbacks.
if you need a PCB take a look at ken stones dc mixer:
http://www.cgs.synth.net/modules/mixer.html
Posted Image, might have been reduced in size. Click Image to view fullscreen.

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doctorvague



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PostPosted: Tue May 22, 2007 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

RF wrote:
This works great, and is easy to build. Just ignore the headphone segment if you want.

http://www.musicfromouterspace.com/analogsynth/monomixerschem.gif


Wouldn't this design have a maximum gain of around .5 due to the 20K input resistor and 39K negative feedback resistor ratio? I assume that's intentional...
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bugbrand



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PostPosted: Tue May 22, 2007 10:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Max gain of 2 surely? ... which, I think, is a standard for some people - good to have that bit extra, especially in a mixer.

I think you def. want an AC coupled mixer (ie blocking caps) for output to exterior world, but DC mixers are really useful within the system too. Just make sure you know which is which!


Q on:::: Headphone amps
Anyone got any good links?
I checked the PAIA one but don't currently have an NE5532s
Is a TL072 enough?? I did have a quick check through the datasheet for current driving capabilities... must check again..
Otherwise, LM386?

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bugbrand



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PostPosted: Tue May 22, 2007 10:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Also to note::
that MFOS one is inverting -- I'd recommend adding a further invertering unity gain stage..

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doctorvague



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PostPosted: Tue May 22, 2007 12:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

bugbrand wrote:
Max gain of 2 surely? ... which, I think, is a standard for some people - good to have that bit extra, especially in a mixer.

oops
you're right Bugbrand. My math was sdrawkcab

And extra gain is good sometimes Cool
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goodrevdoc



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PostPosted: Tue May 22, 2007 12:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Q on:::: Headphone amps
Anyone got any good links?
I checked the PAIA one but don't currently have an NE5532s
Is a TL072 enough?? I did have a quick check through the datasheet for current driving capabilities... must check again..
Otherwise, LM386?


Tl072 should do fine for NE5532. Also of note, try this:
Headphone Amp
It's for guitar, but could easily be adapted for modular use. Also, LM386 is a popular choice, just google to find stuff.
-justin
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gusjdt



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PostPosted: Tue May 22, 2007 12:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, I might just use a mixer at the end to mix the VCAs as mentioned before. Thanks for the replies!
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funkyfarm



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PostPosted: Thu May 24, 2007 6:41 am    Post subject: Reply with quote  Mark this post and the followings unread

bugbrand wrote:
Also to note::
that MFOS one is inverting -- I'd recommend adding a further invertering unity gain stage..


?!

it seems that mfos wasted half TL in order to to save a couple of resistors ?

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Coriolis



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PostPosted: Thu May 24, 2007 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

You mean: Why have a stereo headphone amp on a mono signal? Yeah - would it be possible to feed both channels with the same mono signal, but from one opamp?ยจ
It does look a bit like a waste...

C
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RF



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PostPosted: Thu May 24, 2007 12:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK - I admit it. I'm cheap. TL084 $0.78 each TL082 $.76 each (digi-Key)
The last mixer I made I used a TL082 and made it into a stereo mixer based on that MFOS circuit. The two pennies I saved on the op-amp paid for the two resistors for the second channel - and I'm better off 'cause I avoid the bad karma for leaving unused in/outs. Wink
As for inverted output - I'm using it to mix to my monitors, so I just listen while standing on my head.
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fonik



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PostPosted: Thu May 24, 2007 11:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

RF wrote:
OK - I admit it. I'm cheap. TL084 $0.78 each TL082 $.76 each (digi-Key)
The last mixer I made I used a TL082 and made it into a stereo mixer based on that MFOS circuit. The two pennies I saved on the op-amp paid for the two resistors for the second channel - and I'm better off 'cause I avoid the bad karma for leaving unused in/outs. Wink
As for inverted output - I'm using it to mix to my monitors, so I just listen while standing on my head.

what about TL07x? they are low noise. might be better for the audio path without being more expensive...

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