boji

L + R button panpot circuit
« on: January 03, 2019, 08:01:16 PM »
Hello friends.  I was thinking of using relays to engage a panning circuit when both 'left' and 'right' buttons are pressed in my group cards.
When either left or right are pressed (but not both), it removes the pan circuit, and sends L or R output directly to program bus.

I think Ian mentioned Neve used this method back in the day, but they had a trick way to do it (possibly created by Ian?) in that it avoided relays.  Ian, if you're out there, do you recall how they did it? If not or if it requires 6 pole switches I'm comfortable going with relays.

My question is, does anyone see a problem with circumventing the pan circuit with regards to volume level?  I imagine signal hard panned would be quieter than a left or right direct output going to program bus.  Should I offset that with attenuation resistors or just leave the louder (slightly less noisy?) signal in play and pull down the fader if required?
« Last Edit: January 03, 2019, 08:12:20 PM by boji »


Re: L + R button panpot circuit
« Reply #1 on: January 03, 2019, 08:47:37 PM »
I've never designed a panning circuit but I think it depends on whether the source signal in question is mono or stereo, ie. whether you're sending it to the left channel only or just the left channel (since it may contain a very different level signal than the right)

In mono operation you'd essentially be splitting the signal in two paths and varying their resistance and their sum would be (depending on the taper used) very close the same with a linear pot.

With a log pot in theory you'd have the "middle" somewhere around 1-2 o' clock. I've seen special taper pots being sold (S-taper, anti/reverse log etc) which are specifically designed for panning, but they're no use to you since you're looking to L/R with switches/relays.

john12ax7

Re: L + R button panpot circuit
« Reply #2 on: January 03, 2019, 09:50:17 PM »
You could do it with DPDT switches. See attached for one conceptual way (you could take the pan circuit send from either switch).

For the panning,  first decide a pan law,  3dB is common,  then make all the levels match, L switch and hard panned L should be the same level.  You could use different size bus feed resistors to match the levels if necessary.

I like the idea of bypassing the pan pot,  but maybe implement center as well?
« Last Edit: January 03, 2019, 10:00:00 PM by john12ax7 »

Re: L + R button panpot circuit
« Reply #3 on: January 03, 2019, 11:49:52 PM »
I like the idea of bypassing the pan pot,  but maybe implement center as well?

I've read people do the center dent with blobs of solder.. bypass is in my opinion sort of useless.

boji

Re: L + R button panpot circuit
« Reply #4 on: January 04, 2019, 12:13:00 AM »
Thanks  Efinque and 12AX for your ideas!

Quote
You could do it with DPDT switches. See attached for one conceptual way (you could take the pan circuit send from either switch).

Thank you for the diagram!  If I am looking at it correctly, engaging either left or right switches would leave the panpot outputs still in circuit with a return path to ground. However i'm not confident a 'true bypass' would be entirely beneficial. I'll draft up what I have so far and post it in a bit, that way we can appreciate how simple and clean yours is in comparison.  :)

Quote
maybe implement center as well?
You know, I hadn't even considered that, thanks! Yes why not, since I'm already going whole-hog with bypass.


john12ax7

Re: L + R button panpot circuit
« Reply #5 on: January 04, 2019, 12:16:58 AM »
bypass is in my opinion sort of useless.

Depends on your intended goal. The advantage would be not going through additional circuitry, extra noise and distortion which can add up over multiple channels. Plus you get true and precise panning with switches, which is often not the case with a pan pot.

john12ax7

Re: L + R button panpot circuit
« Reply #6 on: January 04, 2019, 12:38:32 AM »
If I am looking at it correctly, engaging either left or right switches would leave the panpot outputs still in circuit with a return path to ground. However i'm not confident a 'true bypass' would be entirely beneficial.

Yes the pan outputs would still be connected, it was more a quick sketch to show the sending part. With pushbutton switches you can get more poles and use them for a true bypass, which is probably a good idea, one less stage adding noise.

boji

Re: L + R button panpot circuit
« Reply #7 on: January 04, 2019, 02:09:39 AM »
Thanks John. Ok shooting for center and true bypass,  I rushed this and it's late, but draft attached:





boji

Re: L + R button panpot circuit
« Reply #8 on: January 04, 2019, 02:21:48 AM »
I suppose I could do without the two extra input relays, instead just connect to switches.   ::) ::) 

Like I said it's late.  ;D I suppose the only value would be the panner is way on the other side of the card near the TX output,  far from the switches. Relays would reduce the signal trace length and remove vias.

Edit: Ah! Not if I move the pan switches above the panpot!  Hmmm
« Last Edit: January 04, 2019, 02:27:05 AM by boji »

boji

Re: L + R button panpot circuit
« Reply #9 on: January 04, 2019, 02:32:50 AM »
Also (just spitballin')  maybe it's more intuitive to have buttons off mean the panpot is engaged, and both L/R buttons on, be center?


[silent:arts]

Re: L + R button panpot circuit
« Reply #10 on: January 04, 2019, 03:27:33 AM »
Also (just spitballin')  maybe it's more intuitive to have buttons off mean the panpot is engaged, and both L/R buttons on, be center?
I find it most intuitive like it is done in a VR Console:
One button for each bus, and one button to activate the panpot.
« Last Edit: January 04, 2019, 04:42:11 PM by [silent:arts] »

ruffrecords

Re: L + R button panpot circuit
« Reply #11 on: January 04, 2019, 04:32:52 AM »
I did indeed invent such a circuit back in the mid 70s. Even in those days, front panel space was at a premium especially on custom consoles. The standard set up at Neve at that time was routing buttons plus a pan button plus a mute button. I was a year out of university and we had been taught all about these new fangled logic circuits. So I drew up a truth table and worked out the switching to achieve it. Attached is a schematic of the version I used in the EZTubeMixer design using toggle switches. With both toggles up the channel is muted. With either one down the channel is routed straight to a bus. With both toggles down the pan pot is engaged.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

boji

Re: L + R button panpot circuit
« Reply #12 on: January 04, 2019, 03:56:32 PM »
Quite a sleek and simplifying circuit.  I appreciate it Ian!

As an aside, my channel cards are packed too tight, but group cards are the opposite, with lots of empty faceplate- almost too much...  It has me leaning towards the extra pan button now.  ::)

I wish I could backtrack and increase the face plate size of the channel cards, as I'd definitely have added your pan idea to it.
I'm sure I'll return to it for another project down the road.

Thanks again for sharing it!

Re: L + R button panpot circuit
« Reply #13 on: January 04, 2019, 05:00:35 PM »
VCA panning circuit?

Don't listen to me though, I've never built one.. you'd probably need a control voltage to an IC or something but at the cost of fidelity (and it sort of makes things complex, as well as some basic IC's only have mute)

Pan pots can get very crackly as they age though (I have a DJ mixer from the 90's)

Gareth Connor

Re: L + R button panpot circuit
« Reply #14 on: January 04, 2019, 07:15:54 PM »
VCA. No reason not to use VCAs.
With a bit of thinking, you could use a pair of VCAs to do fader, pan and mute. It's a matter of getting your control voltages correctly scaled for the required functions. If you get really clever, feed the VCAs from a dynamics sidechain as well.
Gareth.

EmRR

Re: L + R button panpot circuit
« Reply #15 on: January 04, 2019, 07:54:08 PM »
JR and Wayne had some detailed musings on an all VCA approach to pan/fade/mix over at proaudiodesignforum.com several years back. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

boji

Re: L + R button panpot circuit
« Reply #16 on: January 05, 2019, 03:10:24 AM »
Quote
VCA. No reason not to use VCAs.
I guess I've had this running belief that VCA's have not improved over the years.   :D

Quote
JR and Wayne had some detailed musings on an all VCA approach to pan/fade/mix over at proaudiodesignforum.com several years back.
Thanks I'll try to locate the thread. 

I must confess keeping it mechanical has an appeal to me that fits with my level of competency while also ensuring a clean signal path.

boji

Re: L + R button panpot circuit
« Reply #17 on: January 05, 2019, 03:13:57 AM »
Quote
If you get really clever, feed the VCAs from a dynamics sidechain as well.

I can't even imagine what that would do!  Are we talking dynamic pan/width ? Or just that it allows you to also have a dynamics processor included as part of the bargain?
« Last Edit: January 05, 2019, 03:18:53 AM by boji »

abbey road d enfer

Re: L + R button panpot circuit
« Reply #18 on: January 05, 2019, 03:29:54 AM »
I guess I've had this running belief that VCA's have not improved over the years.   :D
That is not true. The 2181 is actually significantly better than the 2151 of yore.

Quote
I must confess keeping it mechanical has an appeal to me that fits with my level of competency while also ensuring a clean signal path.
IMO you're making it too complicated. There is nothing wrong with having the panpot permanently in circuit.
The only possible issue is that attenuation of opposite side when panning hard is not sufficient. That's where the active panpot created by Doug Self excels.
EDIT: I see you use a weird panpot arrangement that is in shocking contrast with the level of dedication you put in this project.
« Last Edit: January 05, 2019, 03:33:54 AM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
"The important thing is not to convince, but to give pause for thought." (B. Werber)
Star ground is for electricians.

boji

Re: L + R button panpot circuit
« Reply #19 on: January 05, 2019, 03:51:14 AM »
I guess I've had this running belief that VCA's have not improved over the years.
Quote
That is not true.

Figured as much.  Superstition is not a positive personality trait.

Quote
IMO you're making it too complicated.
You're right.   I have the compulsion to add buttons since the group card looks naked in comparison to the input card. 
(>.<)
« Last Edit: January 05, 2019, 04:28:12 AM by boji »


 

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