RCA BC-6B Console Project

[ruffrecords]

A Neve tube schematic. Not sure which one.

Cheers

Ian

 

[systemtruck]

A Neve tube schematic. Not sure which one.

Cheers

Ian

Thanks! Yeah i finally found that and ultimately figured out that it doesn’t have the transformer topology I’m working with, so I’m figuring to focus on ones that are closest and work from there...
The Collins 212B is pretty close to the setup i have sketched, minus pan, but it also has some interesting factors…
1- It uses the 600:600 T attenuator for volume.
2 - It DOES have the balanced bussing I’d mentioned. The T-attenuator only applies to the positive phase though. I don’t know enough about attentuator circuits to know why this works. But anyways, the balanced signal probably helps greatly with bus noise. That is awesome and very appealing to attempt. BUT… the Collins program amp is balanced the whole way through !! Kinda crazy to see. So the noise won’t be canceled out anywhere within the console…it will only be canceled out whenever said signal is finally made unbalanced again… so…. Back in the computer i guess. But one could just use an unbalanced Program Amp and the transformer at its input will cancel the bus noise.
3 - The summing resistor, 560 R, for any of the 7 channels, is disconnected from the summing bus when disengaged from that bus. It doesn’t hang with the bus, it moves with the preamp/attenuator. There is a second bus, which is Audition. When the Program bus is NOT used from the channel, a 1200R resistor is strapped across +/- signal path in its place. When the Audition bus is NOT used from the channel, a 2700R resistor is strapped across the +/- signal path in its place. I think the center position is just off/mute.
4 - The preamp does not have a volume control. It’s just a preamp. You adjust your level with the T-Attenuator after the transformer output from preamp. Makes total sense when you don’t care about fine tuning the way your preamp drives.

I’m going to think this over some more. Maybe my block diagram of values does work ok enough with gain losses and crosstalk and loading? Not sure yet. If anybody has thoughts about the values i chose, i would love to hear. But I’m also going to consider the Collins balanced summing approach. If there is a way to slap some panning into this Collins summing design, maybe that is the pot of gold at the end of the rainbow because that would probably sound so good. I would probably go ahead and use an unbalanced Program Amp so that the signal gets cleaned right away.

 

[ruffrecords]

One thing to bear in mind is that balanced busing complicates the pan control. A regular unbalanced pan needs a dual gang pot. Strictly speaking, a balanced pan needs a 4 gang. There is little if any benefit in balanced busing in a small mixer.

Cheers

Ian

 

[MidnightArrakis]

A Neve tube schematic. Not sure which one.

Cheers

Ian

This mixer looks to me to be like an old-style -- radio broadcast -- mixer. Maybe for "Radio Caroline"??? HA!!!.....



/

 

[ruffrecords]

This mixer looks to me to be like an old-style -- radio broadcast -- mixer. Maybe for "Radio Caroline"??? HA!!!.....

Strangely enough, virtually all the UK pirate radio ships used American AM broadcast consoles simply because at that time there was no local radio at all in the UK, just the three national BBC stations.

But I bet Rupert was aware of them and built his along similar lines.

Cheers

Ian

 

[systemtruck]

One thing to bear in mind is that balanced busing complicates the pan control. A regular unbalanced pan needs a dual gang pot. Strictly speaking, a balanced pan needs a 4 gang. There is little if any benefit in balanced busing in a small mixer.

Cheers

Ian

Alrighty, I’ll keep it simple (unbalanced).

I just have to decide if my drawn up block design of fading, panning, and passive mixing will function desirably enough.

Or, if I need to try something completely different for levels and panning, and then do the passive summing somehow isolated from that.

 

[inkster]

I've completely rebuilt 2 of those, modifying both for LCR and direct outs, one I built new outboard power supplies.
I like the performance of the original design overall and the clients are very happy with the results.
I started a PCB design for the cards...that was for quick service and long term as some of the cards did have some trace damage. Gotta go back in the archives to see if I finished that PCB design........good luck!