Balanced Mixing Network with AML Ez3415

[Tom snich]

Hello

Looking for some guidance before i spend a bit of money on some AML EZ 3415s.

http://www.audiomaintenance.com/downloads/ez3415_colourbook.pdf

I have read The Meta pages and done the math for the R shunt for an 8 input balanced mixing network and got 163 ohms output impedance. Then going into the AML EZ3415s, these have switchable inputs between 10k or 1.2k.
I'm thinking that selecting 1.2k is right?

I have a pile of P&G faders balanced 10KA  i would really like to use on the input level controls and also on the outputs of the AML EZ 3415s in-between the gain stages. The gain stages on the EZ3415s give a maximum of +18db or is it 18db + 18db = +36db?  I don't know how to work back from +18db or +36db to the signal loss for the values i have chosen in my schematic and if the +18db or +36db will do for make up gain after the Mixing network. From what i have read they seem like they would work.
Would adding a stepped gain switch here be a good idea?

I made a copy of New york Daves Mixing Network in CAD and added my own values i think will work, i have no problem experimenting, just want to get a good S/N ratio and minimum cross talk from the get go.
Could someone cast an eye on my schematic, those with experience, are these optimal values? Am i missing anything?

Regards
Ben

 

[ruffrecords]

1K2 inout impedance is the correct value for a passive summer of this type.

I cannot find NYD's original schematic but I seem to rememeber he used 1K dual fader pots in his design. Using 10K pots will increase interaction between the controls and increase the crosstalk. How many inputs do you have in total.

The 3415 has plenty of gain available for use as a bus amp - that was ehat they were used for at Neve.

Cheers

Ian

 

[Tom snich]

Hello Ian

I was hopping you would answer!

I am using this schematic from New York Dave, see pdf NYDbalansedsummer.
He is using 5KA balanced potentiometers i was hoping i could adjust values to accommodate my 10KA faders, i guess they wont work, or could there be a work around?

I am planning on doing 8 mono channels.
I have been reading alot about the 3415 glad its the right candidate.

Cheers
Ben 

 

[ruffrecords]

OK, thanks for the NYD schematic. The one I was thinking about had 1K pots at the front and 10K pan pots; hence the confusion.

So Dave used a dual 5K log pot at the input so the load it presents to the source and it effective source resistance should be identical to using a single 10K pot. Now NYD was very particular about design and he most likely used a dual 5K pot to preserve common mode rejection ratio (CMRR). But we are talking line levels here and short runs from the interface to the summer so I do not think CMRR is the major issue in this design. So I would recommend you use a single 10K fader in place of the dual 5K pot (this is exactly what I am doing in the Poor Man's Tube Mixer I am developing right now). Neve used a similar technique on monitor output pots so it does work.

Son the hot input goes to the top of the 10K fader and the cold goes to the bottom. The hot output is from the fader slider and the cold output comes from the bottom of the fader (yes the cold goes straight through). I would also keep the bus feed resistors at 10K as in NYD's design.

I think you bus slugging resistor is too low at 160 ohms. It never needs to be less than 200 ohms and in the interests of maintaining crosstalk you might as well make it 200 ohms. This will give you a bus loss of close to 40dB. Also, assuming you have all 8 inputs always driven by a very low source impedance then the reurn loss to the fader is about 20dB which gives you a crosstalk figure of around 60dB.

Cheers

Ian

 

[Tom snich]

Hello Ian

Thanks for taking the time to look this over you have been very helpful.

I will give this a go now, i have 2 Soundskulptor 1073 preamps to do a trial run before i commit but,
your tube mixer looks great too and you've got me thinking now.
The reason i am looking into a mixer is i got given an old French mixer AMIX CSL A.M broadcast mixer in bad condition but full of P&G faders 12 singels and 8 stereo, transformers and Ne5532s... the chassis looks like it could work with your tube mixer and i get to use those P&G faders!
I have got other projects to be getting on with, two Neumann W492 EQs, so i will wait and see how your mixer develops.


Cheers
Ben

Edit: I updated the schematic if it helps anyone else, i hope it's right.

 

[ruffrecords]

Looks good to me.

Cheers

ian