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4 channel mini line mixer


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I’ve been working on a design for a small line mixer since January, on and off. I’m getting pretty close now- I’ve got a working circuit and managed to get the enclosure design working. I need to make a few tweaks to the board design, as some components need to be moved in order for it to fit in the box

20130508_173901.jpg                                        20130508_173909.jpg

This particular one is an unbalanced design, with 4 inputs over 2 mini XLR inputs, outputting to a single mini xlr output. The reason for this is to work with my Sonosax recorder and mixer, in order to be able to be able to add the recorder’s 4 XLR inputs to a mix (on the bus in for the mixer) and still record pre-fade ISO tracks.

The holes at the top are for L-C-R panning switches, which will need to be glued into place (one’s actually on the table in the photo above to the left).

I’ve made sure to use high quality components in the circuit- resistors on the inputs are matched within 0.1% tolerance and high quality op-amps have been used. The most expensive parts were the sfernice conductive plastic potentiometers, though.

There’s no internal batteries, but it will run on sources from around 9-16V, with the internal regulator providing +15 and-15V for the op-amps

Here’s how it fits in the bag.

20130508_174328.jpg

It shouldn’t be too different making a balanced design using 5 pin mini XLRs- I went through one in the design process. There’s also a headphone amp on the board, I’m wondering where I can squeeze a 3.5mm jack and a small level pot in there.

As the boards are being fabricated I may be able to sell some of these as kits, if it’s useful to anyone else

http://rtsound.net/?p=330

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Looks real good to me! 

I can't seem to wrap my head around what you really need it for, is it to be able to mix the direct outputs back into the recorder? Didn't really catch that... But the box looks great! This is the box I see when I hear people saying they want to record four tracks on a XDCam.. With this little dingy, if it outputted AES, it could be the return signal so you'd be able to hear all four channels from the camera. Great work!

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Looks real good to me! I can't seem to wrap my head around what you really need it for, is it to be able to mix the direct outputs back into the recorder? Didn't really catch that... But the box looks great! This is the box I see when I hear people saying they want to record four tracks on a XDCam.. With this little dingy, if it outputted AES, it could be the return signal so you'd be able to hear all four channels from the camera. Great work!

XDCAM cams can not output 4 channels as far as I know. But great little summing box indeed!
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It's so that I can actively mix from the recorder's inputs, (the SX-R4 only has gain control and can't fade to -infinity) and send it to camera or wherever (so I've effectively got a 7 channel recorder and mixer in that small bag). 2 of the channels do come from the recorder's headphone out, though

 

It'll also work as a 4 channel RX emergency type device, to add extra inputs to a mixer- although it's active, so losing level shouldn't be an issue.

 

Might have a look at analogue to digital converters, after seeing that DIY one...

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Nice looking box, good for you.  This should shame Sonosax into including something like this in a firmware update.  

 

Not as nice as your box, but I had thought of repurposing/repackaging 2 of these for a "Q+D" monitor mixer:

 

(Behringer MX400)

 

philp

 

Thanks Philip,

 

Sonosax have discontinued the R4, in order to make a replacement- I'd expect faders would be a hardware addition (and probably a colour screen etc).  There's also an RS422 port on the accessory port for "future use", and was wondering if some kind of digital controller (ala CL8/CL9) may have been in the works at some point.

 

What's "Q+D"?

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Very nice work Richard. Its a shame Sonosax didn't do the necessary for the R4 to make it more of a stand alone contender, as zaxcom's development of the maxx shows, a small multi-track with 4 pre-amps and aes options can make a very nice, lightweight set-up to have (especially if it mixes). I used an early R4 for a job, and liked a lot of it, i'll be interested to see what they replace the R4 with. Your mixer box may work quite nicely with my dr-680 (maybe with aes or balanced O/P) any ideas on pricing for the mixer as it is?

RE headphone O/P and gain - how about going for 2 more pins on your O/P connection (eg 7 pin xlr) and put a flying lead with HP socket on the end, you could use a screwdriver pot for gain if you want to keep it small.

 

All the best,

 

dan.

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Thanks Philip,

 

Sonosax have discontinued the R4, in order to make a replacement- I'd expect faders would be a hardware addition (and probably a colour screen etc).  There's also an RS422 port on the accessory port for "future use", and was wondering if some kind of digital controller (ala CL8/CL9) may have been in the works at some point.

 

What's "Q+D"?

Quick and dirty.

 

I agree that Sax should have realized that users would want more out of the R4--I guess that's why they made the 62, but that thing is very expensive in the USA.  I looked very hard at the R4 but felt it was missing too many things I wanted, but didn't want to have outboard.  It sounds pretty great though.

 

philp

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Very nice work Richard. Its a shame Sonosax didn't do the necessary for the R4 to make it more of a stand alone contender, as zaxcom's development of the maxx shows, a small multi-track with 4 pre-amps and aes options can make a very nice, lightweight set-up to have (especially if it mixes). I used an early R4 for a job, and liked a lot of it, i'll be interested to see what they replace the R4 with. Your mixer box may work quite nicely with my dr-680 (maybe with aes or balanced O/P) any ideas on pricing for the mixer as it is?

RE headphone O/P and gain - how about going for 2 more pins on your O/P connection (eg 7 pin xlr) and put a flying lead with HP socket on the end, you could use a screwdriver pot for gain if you want to keep it small.

All the best,

dan.

Thanks Dan

I'm thinking it's going to be around £150-£200, a balanced design would be a similar price. AES out is quite a bit more complex and I'd expect I'd have to go surface mount to fit the board in.

I'll see about getting a revised test board done this week and see how that goes.

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