PFL solo signal question, ok to float?

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boji

Well-known member
Joined
Jan 6, 2010
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Location
Maryland, USA
So after reading gdiy kindly wisdoms on the benefits of PFL, I feel I should add it to my input card.
I have no circuit references, so I'd like to ask a few questions about it if that's ok.

I get that AFL is just a cv telling all other channels to mute. That part I have wired right. WIth respect to API type circuits, should the PFL signal be pulled from A1's TX out AFTER the insert point, sent to a 47k resistor, and then passed on to the backplane, just like an aux or group bus?

What should it do when it's not activated-- may it just float open off a relay, not connected to anything?

Also this may seem obvious, but to be clear, when activating PFL, I want the stereo program bus muted to the monitors, but leave that same signal free and clear going to DAW, and possibly with the same relay, switch monitor input over to the solo bus, kind of like an insert?

Thanks for your thoughts,
-Boji
 
Perhaps I'm over thinking it.

For example, I chose to go with a Grace Design's m905 and it has some aux in's, one of which is stereo unbalanced.  Maybe I should just send the solo bus to this input and when needed, select it? This is to say that the solo bus would always be active,  and hearing pfl would would be about choosing PFL (disarm destructive AFL) on the console, soloing the channel needed, and then select the solo bus input on the m905 controller?

Edit: I think this means AFL would simply hit the main monitor input, not the solo bus, unless I'm misunderstanding something.

Forgive the hand-holding  type language, but confirmation from someone familiar with large format consoles would help me know I'm going about this right and continue with layout of the PCB's.

Thanks again for your advice!

 
After fade listen (AFL) and pre faderlisten (PFL) seem to have rather vague meanings these days. Back in the 70s at Neve there was no confusion. The clue is in the name;  'listen' being present in both means you want to hear the channel through the control room monitors. AFL was a mono feed after the fader and PFL was a mono feed before the fader. Both went to a mix bus of their own. They also had a dc bus which activated a relay that switched the AFL or PFL bus amp output to the monitors instead of whatever was currently selected. Group and main bus outputs were unaffected. At Neve we used passive mixing so 'off' inputs had to be grounded but if you are using virtual earth mixing you can either ground them or leave them floating.

What you described as AFL I would have called solo or maybe solo in place (SIP) where selecting solo causes all other channels to mute and so affects the bus outputs directly. What you hear depends on what the monitor input selector is set to.

Of course, these terms are not set in stone so over time their meaning tends to change.

Cheers

Ian
 
Indeed precise definitions are a little squishy, I used a separate stereo bus for solo in my big mixers, but it was all kept separate for presentation only in the control room monitors, and did not step on the final stereo mix output.

PFL is generally grabbed before channel fader and pan (so mono), and also not destructive, so you could PFL or solo a channel during a mix without trashing it.

JR 

 
boji said:
I get that AFL is just a cv telling all other channels to mute. That part I have wired right. WIth respect to API type circuits, should the PFL signal be pulled from A1's TX out AFTER the insert point, sent to a 47k resistor, and then passed on to the backplane, just like an aux or group bus?

Hi Boji
just to add to Ian's and John's replies, the "control voltage telling other channels to mute" is only applied to a channel if its AFL/PFL is not active.  This is why, as Ian points out, AFL and PFL circuits are mix buses in their own right so that you can listen to multiple channels on them.

Cheers

Mike
 
madswitcher said:
Hi Boji
just to add to Ian's and John's replies, the "control voltage telling other channels to mute" is only applied to a channel if its AFL/PFL is not active.  This is why, as Ian points out, AFL and PFL circuits are mix buses in their own right so that you can listen to multiple channels on them.

Cheers

Mike
I've never done this***, but I think the selective channel muting is what's called "solo in place" . The solo in place keeps the effects sends active, while muting all other inputs, so you can better listen for subtle problems in a channel including it's isolated send to reverb or whatever.

The obvious downside to this approach is that this trashes any existing stereo mix or tracking going on at the same time. IIRC this is called a destructive solo. The popularity of dual use mixers for recording and live, rules out incorporating such easy ways to screw up a live mix during a show.  ::) 

For dedicated recording use, do what makes most sense for your needs.

JR

**** while not technically "solo in place" I designed a novel mute group approach for a friend's custom console back in the 80s. As I recall we used an 8 position selector switch on every channel that assigned that channel to one of eight groups. These groups could be muted as a group, or solo'd as group (effectively muting everything else). This was like solo in place, but my friend used it for mixing reggae bands, where he would group similar inputs together to mute or solo as a group during the actual mixdown. 
 
JohnRoberts said:
Indeed precise definitions are a little squishy, I used a separate stereo bus for solo in my big mixers, but it was all kept separate for presentation only in the control room monitors, and did not step on the final stereo mix output.
Yes we did that too on some of the early big Neve desks. You can step on what is coming out of the monitors but not on the master buses. I am not sure when destructive solo first came in

Cheers

Ian
 
ruffrecords said:
Yes we did that too on some of the early big Neve desks. You can step on what is coming out of the monitors but not on the master buses. I am not sure when destructive solo first came in

Cheers

Ian
I'm thinking it might have been an SSL thing after they had digital control over more discrete functions (but don't hold me to that).

JR
 
Thanks for the advice and philosophy gents. Very helpful.

"At Neve we used passive mixing so 'off' inputs had to be grounded but if you are using virtual earth mixing you can either ground them or leave them floating."
Excellent, thank you.


"Dual use mixers for recording and live, rules out incorporating [destructive SIP] to screw up a live mix during a show."

Desk plans were for tracking and pp, but I think I'll nonetheless go for safety and keep it AFL.
Switching logic is digital and entirely separate from the backplane, so SIP could be coded in at a later time if truly necessary.

I suppose the only question left is why AFL & PFL would each need their own rails if switched within a channel.  I'll take your word on its importance.

Edit: Duh, I guess it's so if you want to solo more than one channel but also want pre/post fade flex. Not sure how the monitor input would handle that.

 
PFL can serve several uses. First it can be used for correct gain staging. Look at the level on a meter and set mic pre gain accordingly. Second it was often used for cueing in broadcast applications. A lot of broadcast desks used fader over-press operated PFL. Sometimes PFL was not routed to the monitors but to a small cue speaker in the meter bridge.

Cheers

Ian
 
Ruff, you've given me an idea and everyone here has helped me appreciate the value of their use:

The code I had pre-written for nonlatching solo button was, long press = add to solo grouping (similar to JR's Reggae console), short press = SIP.

After this very helpful thread I'll instead go with Long press PFL, short press AFL.  This way, to keep in line with your example of gain staging, I can set and forget one channel, hit AFL on it,  then use it as a baseline to stage another solo channel in PFL, that way the faders generally stay at unity while adding inserts until/unless the song demands changes later.  Very cool! Thanks!

Edit: By the way if this method is totally obvious to seasoned mixers, forgive me! Not having time on big desks, this is all being worked out in my wee little head...
 
JohnRoberts said:
**** while not technically "solo in place" I designed a novel mute group approach for a friend's custom console back in the 80s. As I recall we used an 8 position selector switch on every channel that assigned that channel to one of eight groups

SSL 4000E had thumbwheels on each channel to select a VCA group. Each group had a fader, Cut button & Solo button. These Solo & Cuts - being destructive - became the de facto way to do 12" mixes

Nick Froome
 
pvision said:
SSL 4000E had thumbwheels on each channel to select a VCA group. Each group had a fader, Cut button & Solo button. These Solo & Cuts - being destructive - became the de facto way to do 12" mixes

Nick Froome
Looks like ancients are still stealing our ideas....

JR
 
boji said:
I get that AFL is just a cv telling all other channels to mute.
No; what you describe is Solo In Place (SIP).
AFL is similar to PFL, except the signal feeding the listen bus is taken After Fader (as the name implies).
Both AFL and PFL involve switching the monitor source from Mix to the output of the summing amp fed by the PFL or AFL bus.
In mono channels PFL is a mono signal, but PFL can be either mono (After Fader but Pre PanPot) or stereo (After Fader After pan).
 
Yessir, good Abby.  JR, RR and MS have set me straight as well.  :)

Thanks again everyone.

Edit: If only our politicians received such generous, manifold instruction...
 
JohnRoberts said:
Looks like ancients are still stealing our ideas....

JR

The only genuinely new (I hope) audio related invention I made at Neve was the exclusive OR pan control. Usual two buttons for routing a channel to L or R. But, if you pressed both, the pan was automatically switched in. With both out, the channel was muted. I was only a couple of years out of university when I came up with this. I remembered the lecture on truth tables for various logic gates.

Cheers

Ian
 
Almost done adding PFL/AFL.

Quick question: On the API 536 skiz, there's a 4.7k resistor that goes to the prefade Echo's single 5k pot.

I'm not fully certain why it's there. Does it have something to do with compensating for the cue's two 5k's or is it matching gain for A2 postfade? Following this, if I'm instead using six 20k pots for cue/aux's that can be selected prefade, should I dispense with the 4.7k?

Thank you again!
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boji said:
Quick question: On the API 536 skiz, there's a 4.7k resistor that goes to the prefade Echo's single 5k pot.

I'm not fully certain why it's there.
Neither am I... Could be intended to match the level with that of the post-fader signal (that would mean the fader has 6dB in hand... which I doubt ???).
This needs to be analysed with a full schematic of the whole mixer, particularly the summing amps and the control-room module...
 
ruffrecords said:
The only genuinely new (I hope) audio related invention I made at Neve was the exclusive OR pan control. Usual two buttons for routing a channel to L or R. But, if you pressed both, the pan was automatically switched in. With both out, theoplppyy channel was muted.
What's brilliant about that is that no instructions are required. It's pure logic and it works exactly the way you'd expect - the two things don't always coincide

Nick Froome
 
Neither am I... Could be intended to match the level with that of the post-fader signal (that would mean the fader has  6dB in hand..

That’s how it hooks up on the 538 schematic for my console.  When you track to tape, the fader goes to top of fader with mic selected.  When you mix there is a - 12 DB down  dot on the legend of the 440 fader face plate. 

What you show as an in jack on your drawing is the output of the 550 eq on my board. 

The actual prefade patch point is the output of the A1 amp through a transformer that’s 1/2 normals to the input of the 550 EQ.  It must be dropping the output of the eq out which is the prefade  high side of the fader to match the dropped output of the wiper which is set at the -12db down point of the fader when fader is in mix with A1 set to line in for tape machine playback.   
 

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