Neve 80 series Console Build

[remsouille]

EDIT: this project turned into a full scale neve console build. yup.
Hi folks,
I'm about to start building a Neve inspired monitor mixer to be able to monitor my tape returns.
My Amek BCIII is not in-line and until then, I managed to monitor my 8 track A80 with unused line-in channels. Not the most intuitive monitoring system, and now with that 16 track 2" coming in next week ( 8) ), the monitor mixer becomes a necessity.

I'm planning to build a neve 8014ish console in the next couple (dozens) of years, so I figured, let's do that monitor mixer right, so I can fit it in the big one when (if it ever) happens, and also be able to use it as 16 additional inputs at mixdown.

I'm going all passive summing, 70's neve style, with 1272s and everything.
What I need is transformer inputs to unbalance the signal,  mute switches, PFL switches, faders (P&G 1520), pan pots with disengage switches, and 2 aux sends with pre fade/post pan switch. I really want the post pan feature for cue purposes, so both the musician and I can listen to the same mix right away. Time saving.
I'm only splitting the signal once, for the aux sends, so I shouldn't need an amplifying stage, should I? Or are the aux pot and the fader going to suck up too much volume?
I came up with this, and would appreciate if anyone could have a look and tell me if i'm missing something. Note that I'm really going for the Neve way of summing, so I really don't want to improve anything over the way they would have done it.

EDIT: Ok, I realize now how naïve I was, thinking I could make this work without gain stages.. I'll come up with something a little more realistic in the next couple of days... I will probably follow the 1883 routing module schematic and stuff a couple of BA183s in there...

 

[ruffrecords]

I don't think you are too far away. The 31267 gives you a low Z source so you can use a 1K fader. The rest should be OK.  The only thing I would not do is switch the bus with the police relay. Instead,  switch the police after the first stage of the 1272.

Cheers

Ian

 

[remsouille]

I don't think you are too far away. The 31267 gives you a lot Z source so you can use a 1K fader. The rest should be OK.  The only thing I would not do is switch the bus with the police relay. Instead,  switch the police after the first stage of the 1272.

Cheers

Ian

Thanks for your input, Ian!  I just talked to Geoff Tanner, he said that I should stick to the 1883 schematic and use 2 ba183am, and that I couldn't keep loads hanging to the fader, or the 31267...
I suppose that would also improve the crosstalk and noise figures, wouldn't it ?

 

[ruffrecords]

Crosstalk depends on the source impedance driving the pan pot so Ba183 after the fader can provide that.  There are no crosstalk issues for the auxiliary sends as rhey are mono. The ba183 will add a little noise but not enough to worry about. The BCM10/2 uses a schematic similar to yours.

Cheers

Ian

 

[remsouille]

Crosstalk depends on the source impedance driving the pan pot so Ba183 after the fader can provide that.  There are no crosstalk issues for the auxiliary sends as rhea are mono. The ba183 will add a little noise but not enough to worry about. The BCM10/2 uses a schematic similar to yours.

Cheers

Ian

You don't happen to have the 1895 schematic, do you?  What you're saying is that I could skip the input amp and just drive the output with a single BA183 right after the fader?

 

[ruffrecords]

Here you go:

https://drive.google.com/file/d/0B_n67A1hN3qtUi1IZHFJUHBidW8/view?usp=drivesdk

Cheers

Ian

 

[remsouille]

Thank you Ian, this is very interesting.  So if I get it right, the 1895 takes an unbalanced output from the Input module and then that ba106 is there  to carry the output loads, right?
But waht if I really want a 31267 Input trafo and 1520 faders? How do I load them properly . I'm sure this is not very complicated, but still over my head as of now. I need education

 

[ruffrecords]

From the schematic it looks like it takes the unbalanced output  via the ba106 and sends it to the fader. Post fade buses, including pan, are fed direct from the fader.

Cheers

Ian

 

[remsouille]

From the schematic it looks like it takes the unbalanced output  via the ba106 and sends it to the fader. Post fade buses, including pan, are fed direct from the fader.

Cheers

Ian

But doesn't the fader have a HI-Z output? How can it drive all this? Does the BCM10 have the usual P&G 1520 10K faders? I presume yes...

 

[ruffrecords]

But doesn't the fader have a HI-Z output? How can it drive all this? Does the BCM10 have the usual P&G 1520 10K faders? I presume yes...

The 1520 comes in various values including 600 ohms. If a 1k version was used, the fader plus the pan pot and auxes would probably be close to 600 ohms but I am not sure if the emitter follower  can drive that low a load. The worst case source impedance of a 1k pot is 250 ohms which is plenty  low enough  to drive the pan pot.

Cheers

Ian

 

[remsouille]

The 1520 comes in various values including 600 ohms. If a 1k version was used, the fader plus the pan pot and auxes would probably be close to 600 ohms but I am not sure if the emitter follower  can drive that low a load. The worst case source impedance of a 1k pot is 250 ohms which is plenty  low enough  to drive the pan pot.

Cheers

Ian

Well I've never seen 1K 1520s, and Dan Alexander doesn't have any, so as far as availability goes, I guess I'm stuck with 10Ks. Which means I should in fact need an output stage... right?

 

[ruffrecords]

Well I've never seen 1K 1520s, and Dan Alexander doesn't have any, so as far as availability goes, I guess I'm stuck with 10Ks. Which means I should in fact need an output stage... right?

600 ohms ones do exist, there are some on eBay right now.  Do you have to use 2520s?

If you want to have 10dB in hand on the fader then you definitely need an amp. I think it would be a better design with a post fader amp.

Cheers

Ian

 

[remsouille]

I think they (600ohm 1520 faders) were  typically used in the monitor section before the days of in line consoles. The tape return entered via a 31267 10k:600 transformer and was fed direct to the fader. The fader  fed a pan pot and then the monitor buses.

I think they may also have been used in the BCM10/2 mixer in a similar configuration.

Cheers

Ian

I'm certain you actually wanted to post this in here, right?
This is great! This means I can go 31267>600ohm fader> BA183>pan pot>outputs, right?

 

[ruffrecords]

I'm certain you actually wanted to post this in here, right?
This is great! This means I can go 31267>600ohm fader> BA183>pan pot>outputs, right?

Yup.

Ian

 

[remsouille]

Great! Let's start building some ba283s, then !

 

[remsouille]

And what if I used a 10K:10K input transformer? Wouldn't this allow me to use a more available 10K 1520 without having to change anything else in the circuit?

 

[ruffrecords]

And what if I used a 10K:10K input transformer? Wouldn't this allow me to use a more available 10K 1520 without having to change anything else in the circuit?

The problem with a 10k fader is that the pan pot now loads it too much. With the pan pot hard panned it presents a load of about 1.5k ( two parallel 10k in parallel with 2k). If you want to use a 10k fader you need to increase the pan pot value to 50k, change the padding resistors from 2k2 to 11k and raise the bus feed resistors to 47k. These are the values I use on my tube mixer auxes returns.

Cheers

Uan

 

[remsouille]

The problem with a 10k fader is that the pan pot now loads it too much.

But doesn't the ba283 between the fader and the pan pot make up for that?

 

[hitchhiker]

If I understand it right, there is no need for an amp there if you use a 600 or 1000 ohm fader.

 

[remsouille]

If I understand it right, there is no need for an amp there if you use a 600 or 1000 ohm fader.

I think you're right.  No need for amplification with a 600ohm fader. But if I were to use a 10K fader, the amp would take care of the pan pot load, right?