NY Dave 600ohm mixer build completed

Here's my version of NY Dave's passive 600 ohm mixer.  I extended the number of inputs to 10 and added auxiliary sends for each channel.  There's also a second set of 4 auxiliaries hard assigned to channels 1-4.  I haven't bothered tracking down a coherent set of knobs for this yet but it's been in regular use since the last solder joint was laid down.


Very handy mixer to have if you like the idea of having a tube or vintage style mixer.  The idea here is simply to use your arsenal of outboard preamps, line amps, EQs, Limiters etc to form the input channels of your choosing.  I still do a lot of work from 8 track analog and this mixer is ideal.  Thanks to NY Dave where ever you are!

Original forum thread & schematic:  http://www.groupdiy.com/index.php?topic=1298.0

Nice one Congrats!

yeah, that's very cool! Thanks for sharing!

anyone able to work out the R changes for a 16 ch version?

buschfsu said:

anyone able to work out the R changes for a 16 ch version?

Click to expand...

It's shown in Dave's 5th post down in the original thread   

NewYorkDave said:

OK... You can use your transformers in whatever preamp or line-amp circuits you like. Here's a simple mixer circuit that should do well with any amps that are designed to work from/into 600 ohms.

A typical implementation would have the left/right outputs going into the 600-ohm inputs of preamps, with their gain controls acting as the master faders; or, into preamps, followed by master level controls, then line amps.

Good luck!

Click to expand...

how are the auxs figured in?

Aux sends were generated with simple passive splitting before the hitting the input of the mixer.  Schematic shows how a single aux send was derived.

The insert points shown for the DPDT switch were for generating an alternate aux send.  I included the alternate aux send on ch 1 - 4.  Note:  This would mean that on ch 1 -4 you have a choice between one aux or the other - but not both.  So, there is only one single aux send available per channel, but by having ch 1 -4 fitted with an alternate aux send you could have the use of two different aux send paths overall - but only one at a time per channel. (Actually it would be 5 different overall paths if needed but I only did it this way to be able to send up to 4 channels to another 4 X 1 outboard mixer with its own FX loop).

It would be fairly easy to create more aux sends per channel - just a matter of changing the resistor values in the dividing network.  Without doing the math, I suspect having 2 sends per channel would increase the total loss another 6db or so.  Either way you'd still be using an outboard line or buffering amp of some type so an extra 6 or 12db shouldn't be a problem.

Very Nice ! and im sure very usefull as well ...im sometimes mising the paning on my passive mixer..

How is the noise on these things? What do you normally use for make up gain? And how well does it interface with modern stuff? Any problematic gear you've run into?

thanks!

mitsos said:

How is the noise on these things? What do you normally use for make up gain? And how well does it interface with modern stuff? Any problematic gear you've run into?

thanks!

Click to expand...

Hi mitsos,


I've got a pair of Neve 3405s and a pair of RCA BA-2 clones that I mainly use for make up gain - oh, and whatever compressor follows those if I'm using one.  Neither of those I suspect quite meet the optimal bridging impedance but I've been happy with the results so far.  I plan on doing some A/B comparisons with a bridging pad in front vs going straight into the transformer.

I haven't had an opportunity to use it with a converter interface.  As long as the input source can drive 600ohms ok I suspect it would behave fine.  Being all passive I would imagine the noise of whatever make up gain amps used would swamp any self noise of the mixer . 

I use a couple of digital reverbs on the aux sends and they work great.  Though I generally keep a small compressor in front of the reverbs for gain control, I usually have enough of an input signal to drive them just going straight from the passive aux send jack.

Thanks for the reply. I've been needing (read: wanting) to build a little mixer and this looks to be the simplest method, so quite appealing..

re noise, that's what I thought.  I was worried about all the attenuation and having to use lots of gain to bring that back up, but I guess it's not much more than a pultec..

cool, but now I have to make a case for mine....  Did you make yours or is it off the shelf?

cheers!

The case was a Hammond.  Great bang for the buck - think it was around 38 USD.  Probably big enough to do a small sidecar of some type too.



http://www.hammondmfg.com/dwg16.htm

wow, even better!  Awesome! thanks!

EDIT: I saw they even have sloped tops on some... and walnut sides... that's even cooler! 

Found this one via the "thank you NYD" thread, nice! If I was to put an Ian's poor men's eqp1 on the output, would his tube gain make up stage be enough for both mixer and eq?

Running direct into the EQ would probably not be the optimal way to interface since there is considerable loss in the mixer.  I measured about 36db loss from input to output.  So you would need to use a set of booster amps of some kind before the EQ to get best S/N performance.  I use a pair of 40db tube mic pres for make up gain and don't even have to use the pads on the mic pre.  I then run into a pair of Pultec clones and this works excellent.

Does anyone have a copy of these schematics?  It's a real shame all of these NY Dave schematics are gone!  This mixer looks really nice, and the hammond chassis is still cheap. 

I'm thinking of using the 600 ohm outs from my UAD apollo to start mixing OTB so I can do panning effects and use some of my outboard more easily while mixing

Are you planning on using outboard line amps during mixdown?   

The reason I ask is that it sounds like you're just looking for a good passive outboard mixer to run straight from your converter interface?  In that case you'd really only need a bridging input, so a high impedance mixer might be a more flexible choice if you're not using amps that want to see a 600 ohm load.

The 600r mixer was designed primarily for using with vintage line amps that expect to see a 600 ohm load on their output.  I used mine with 8 tube line amps in front coming off an 8 track analog machine (or sometimes from DAW interface outputs).  The UAD Apollo may work just fine driving 600 ohm loads, but doesn't require them like some vintage line amps do.  NYDave also had a schematic for a high impedance version of his mixer up at one time too.  I think he posted it a bit before the 600 ohm version.  Seems like there was a thread about it way, way back there - like 2004 or 2005. 

don't know if this helps:

lassoharp said:

Are you planning on using outboard line amps during mixdown?   

The reason I ask is that it sounds like you're just looking for a good passive outboard mixer to run straight from your converter interface?  In that case you'd really only need a bridging input, so a high impedance mixer might be a more flexible choice if you're not using amps that want to see a 600 ohm load.

The 600r mixer was designed primarily for using with vintage line amps that expect to see a 600 ohm load on their output.  I used mine with 8 tube line amps in front coming off an 8 track analog machine (or sometimes from DAW interface outputs).  The UAD Apollo may work just fine driving 600 ohm loads, but doesn't require them like some vintage line amps do.  NYDave also had a schematic for a high impedance version of his mixer up at one time too.  I think he posted it a bit before the 600 ohm version.  Seems like there was a thread about it way, way back there - like 2004 or 2005.

Click to expand...

Thanks for the help and thoughts, and thanks shabtek for the schematics

The apollo has 600 ohm outs, which is why I said that.  I still don't understand impedance bridging, I should research that.

My plan was to run the 8 600 ohm outs of the apollo into a simple mixing board, with some outboard in between for some channels- for instance a spring reverb, an echoplex, a plate reverb if I ever get around to building it, a compressor or two, etc.

It would be something like:
Output 1 - Bass out to 1176 into mixer channel 1
2 acoustic guitars (summed in DAW) into mixer channel 2
3 rhythm guitar (panned left) into mixer channel 3
4 lead vocal out to echoplex into mixer channel 4
5 and 6 drums (summed in DAW) into mixer channels 5 and 6
7 lead guitar with panning effects into mixer channel 7
8 reverb sends summed from DAW out to reverb unit into mixer channel 8

Then plug the stereo out of the mixer into two mic pre channels and record the mix/mixes back into the DAW

I have two spectrasonics model 101 cards I have been planning on using to build mic pres with, but I could use them as line amps for the output of this mixer - especially if I use it all the time.  I could wire it in "permanently" into two line in channels in the apollo.

Would it be best to keep this balanced?  in the schematic the first transformer is just converting the input to unbalanced, right?  what would the input impedance of this on be?

I'm also thinking of adding another apollo at some point to get more UAD processing power, and I could use that to expand this whole rig to 16 track outs, but I think it would be best to design and build another mixer then after learning from mixer 1.

So what should I do for this?