Aux sends and returns in a mixer project- what's your opinion?

[Newmarket]

Ian , sorry to be pedantic but I guess that when you write:

"The downside of solo is that it is pre-fader so it is great for checking gain staging but no good for checking individual levels in a mix. "

You actually mean "The downside of PFL..." ?

 

[abbey road d enfer]

Edit: Trying to wrap my mind around this one.  We are talking about the aux bus solo correct? 

I refer using the term "aux(iliary) group"; bus is an engineering concept. Same difference as between a gearshift and a gearbox. I'm talking about PFL - obviously not SIP (destructive Solo In Place) - on both send and receive ends of the FX path. PFL on the Aux groups and PFL on FX returns.

Not channel aux pfl. Channel aux pfl is clearly essential.

??? PFL on Aux sends? You lost me...

I'm trying to figure out how to solo the aux bus and have it retain the channel signals.

You just can't do it simply.
You would have to have a Mute that doesn't mute the aux sends, just the group and mix feeds. Too complicated.

 

[abbey road d enfer]

PFL switch routes a pre-fader signal to the PFL bus and a dc signal to the dc PFL bus. THe output of the PFL bus amp feeds the monitor section where a relay, operated by the PFL dc, switches the studio monitions away from whatever the are selected to, to the PFL bus. Hence PFL does not affect the main mix so it is safe to operate anytime during a session. It only affects what is fed to the monitors. Rarely if ever do you press more than one PFL button at a time., The downside of solo PFL is that it is pre-fader so it is great for checking gain staging but no good for checking individual levels in a mix.

PFL is essentially used for ensuring signal integrity, not for balancing levels.

That is where Solo comes in. There are two  basic types of solo. Destructive and non-destructive. The non-destructive version is much like PFL except it is taken after the fader, usually from the pan pot. So in this case  the Solo button feeds a stereo bus and a dc bus and is connected to the monitors exactly the same as PFL. So you get to hear the channel exactly as it is being fed to the main L/R buses but, like PFL ir does not affect the mix.

I would think non-destructive Solo is commonly referred to as AFL (After Fade Listen), which removes any ambiguity. Actually, not many mixers have AFL inplemented, since SIP is much more significant.

The only advantage of destructive solo is it is cheaper to implement.

Sill many mixers do not include SIP because it involves a DC controllable Mute switch.

 

[ruffrecords]

Ian , sorry to be pedantic but I guess that when you write:

"The downside of solo is that it is pre-fader so it is great for checking gain staging but no good for checking individual levels in a mix. "

You actually mean "The downside of PFL..." ?

Correct. I have fixed the post.

Cheers

Ian

 

[ruffrecords]

PFL is essentially used for ensuring signal integrity, not for balancing levels.

Agreed but PFL is also usefull for setting levels provided it is metered as well as listened to.

I would think non-destructive Solo is commonly referred to as AFL (After Fade Listen), which removes any ambiguity. Actually, not many mixers have AFL implemented, since SIP is much more significant.

It is unfortunate that there is no real agreed terminology here. In my days at Neve, AFL was the same as PFL but after the fader i.e it was mono. The non destructive solo I described reaches the monitors in exactly the same way as PFL or AFL but it is in stereo, That was what we called SIP.  Destructive Solo did not exist - far too easy for some plonker to accidentally hit a solo button and destroy a carefully crafted mix.

Sill many mixers do not include SIP because it involves a DC controllable Mute switch.

Sorry, I don't understand that. Can you please explain.

Cheers

Ian

 

[abbey road d enfer]

Agreed but PFL is also usefull for setting levels provided it is metered as well as listened to.

Agreed; PFL is essential; I just pointed out it can't be useed for balancing a mix since it's pre-fade.

  It is unfortunate that there is no real agreed terminology here. In my days at Neve, AFL was the same as PFL but after the fader i.e it was mono.

That's where we see the limits of terminology. 

The non destructive solo I described reaches the monitors in exactly the same way as PFL or AFL but it is in stereo, That was what we called SIP. 

That's what I call AFL. And what you call destructive solo is SIP for me. Another example of being separated by a common language.  8)

Destructive Solo did not exist - far too easy for some plonker to accidentally hit a solo button and destroy a carefully crafted mix.

In a well designed mixer there would be a Global Solo Safe facility, either a button or a logic related to the console status. Basically, in Mix mode, destructive solo is inhibited and defaults to AFL. That's what it was on the big Soundcrafts, Cadac and SSL.

Still many mixers do not include SIP because it involves a DC controllable Mute switch.
Sorry, I don't understand that. Can you please explain.

For me SIP is destructive solo, which requires the channels to include some king of DC-controlled switch. A feature that cannot be included in small (cheap) mixers because of the cost.

 

[boji]

Ian, I appreciate the 'first principals' that you build upon to get up to speed on the aux groups. Thanks!

Abby!  I slept on it, read each of your replies, and realized conceptually I was not treating the AFL/PFL bus as a separate monitor mix, but as signals that would be occasionally monitored on the main pgm bus.  It was then I realized in my pcb revision I shorted the afl & pfl bus to acom when not in use, so not only have y'all helped me figure out how to monitor aux groups but you have been quite helpful in preventing some frustration come testing time.  ;D ;D

Thank you!!!!!

??? PFL on Aux sends? You lost me...

Oops, I meant prefade selection of auxs for cue mix.

Edit: just as an aside, I think the routing confusion had to do with the split pcb design. My afl/pfl relays are not on the same card as the edge connector.

 

[boji]

Global Solo Safe facility, either a button or a logic related to the console status.

Ian, fyi, I elected to go with arduino's for logic, instead of running logic across the backplane as it allows for some options, including SIP/solo safe and solo/mute group logic with global defeat.

Embarrassing how old this is but I'll enjoy getting back to it...eventually...
https://www.youtube.com/watch?v=9ysyU8XKjFI

'Prodigy Pro forum'... man how time flies.

 

[JohnRoberts]

Agreed but PFL is also usefull for setting levels provided it is metered as well as listened to.

Setting levels is different from balancing levels (aka mixing).

PFL can be used to check for adequate headroom and that a quality signal is present.

This is only one of many terminology differences across the console community.

Viva la difference.

JR 

It is unfortunate that there is no real agreed terminology here. In my days at Neve, AFL was the same as PFL but after the fader i.e it was mono. The non destructive solo I described reaches the monitors in exactly the same way as PFL or AFL but it is in stereo, That was what we called SIP.  Destructive Solo did not exist - far too easy for some plonker to accidentally hit a solo button and destroy a carefully crafted mix.
Sorry, I don't understand that. Can you please explain.

Cheers

Ian

 

[boji]

Ian, have you any interest in aux group send volume in addition to returns volume?

 

[ruffrecords]

Ian, have you any interest in aux group send volume in addition to returns volume?

Yes, just like any other bus, aux sends usually have an overall send level control. Most mixers have them.

In a the monitor section it would be normal to have switching that allows the aux send outputs to be monitored (at least on meters.

I like to keep the main switching in the monitors s simple as possible. It would normally be a three position switch labelled 2T Playback, Master Bus and Meters. The first two are self explanatory.  The third position routes whatever the meters are connected to, to the monitors. I usually have a separate switch for the meters. This is usually arranged to allow the meters to be connected to any of the buses to check levels and if you need to make a listening check you can quickly switch the mionitors to meters.

Cheers

Ian

 

[ruffrecords]

Ian, fyi, I elected to go with arduino's for logic, instead of running logic across the backplane as it allows for some options, including SIP/solo safe and solo/mute group logic with global defeat.

Embarrassing how old this is but I'll enjoy getting back to it...eventually...
https://www.youtube.com/watch?v=9ysyU8XKjFI

'Prodigy Pro forum'... man how time flies.

Cool video. Thay is a BIG console you are building.

The really nice thing about rolling your own is that you can include any features you like. Does not matter in nobody else wants them or does them differently, it's your console. Like a made to measure suit.

Cheers

Ian

 

[boji]

BIG console you are building.

Too big.  I bit off more than I can chew from the beginning, but hey shoot high, aim low.  Given discovery of all the time the aux bus and group modules will take, I think I'll pair it down to 18x8x2 for now. Maybe down the road if things magically take off, I'll add another bucket, but I'll be plenty busy building up 500 modules as I start to pass sound and get back to accepting clients again.
Thanks for watching!

 

[boji]

Just spit-balling here, but my guess is the below vol pot on NFB won't work since this is an inverting configuration.

Strapping a pot on the TX outputs was suggested, but I want the volume to pass balanced outs to aux sends. Any suggestions?

btw I selected 280R as the resistor to ground since in the Bo Hanson 312 mod (which is non-inverting) has a resistor that is a decade off from the feedback resistor, and I imagine that's on purpose.  But since the pot is 20k and not 28k, perhaps it's pointless keeping things consistent.

 

[ruffrecords]

Just spit-balling here, but my guess is the below vol pot on NFB won't work since this is an inverting configuration.

Strapping a pot on the TX outputs was suggested, but I want the volume to pass balanced outs to aux sends. Any suggestions?

btw I selected 280R as the resistor to ground since in the Bo Hanson 312 mod (which is non-inverting) has a resistor that is a decade off from the feedback resistor, and I imagine that's on purpose.  But since the pot is 20k and not 28k, perhaps it's pointless keeping things consistent.

Unfortunately you cannot alter the gain of an inverting stage that way. You could replace the 28K feedback resistor with a pot. This would allow you to reduce the gain to almost zero when the pot resistance is (almost) zero This is not a usually recommended method but for an aux send master control it might be OK.

What is the purpose of the aux ON switch?

Cheers

Ian

 

[boji]

Hey Ian, thanks for confirming my suspicions.  The post was a bit premature, but I'm head scratching.

I'll draft the below out clearly, and see if it is what you're talking about.  My only concern is it says 'trim' so it's not going to bring volume down to near zero, correct?

As for the Aux on switch, I figured a full break in signal would be the quietest approach. But I have not given that part any real thought yet, just trying to get some ideas down.

API 548 Echo module:

 

[abbey road d enfer]

Beware that the Aux sends will be out-of-phase if you don't add an inverter.

 

[boji]

Beware that the Aux sends will be out-of-phase if you don't add an inverter.

Thanks for the warning Abby. Am I wrong to think inverting the output pins of the tx would compensate?

Edit: Wait, that would only work if it was unbalanced?!? My head hurts.

Ian,  the on switch idea was initially coming from the 1608 block diagram:

Edit: Truth be told, living with unbalanced sends would make life much easier for volume attenuation. I just figured if I one day have my outboard rack 30feet away or so, I'd want the noise cancellation. I could add a differential output IC, but I feel like the tx's cmrr would go to waste.

 

[abbey road d enfer]

Thanks for the warning Abby. Am I wrong to think inverting the output pins of the tx would compensate?

Sorry; misunderstanding on my part. Was thinking Aux sends. Doh!

 

[boji]

Sorry; misunderstanding on my part. Was thinking Aux sends. Doh!

...Whew! Wuz feeling the walls close in on me there for a second!  ;D

So ok, below is a transcription of the 548's Input stage. Why what values are chosen here is...  :-[ beyond my comprehension.
Assuming it passes the sniff test, would substituting the 2k pot for a 1k still do the do?

Perhaps getting deep attenuation here is not so important, given overall volume can be adjusted at the return pot... I mean, why hit an fx unit weakly only to get more noise out of the bargain?

(Edit: ack, 2520 0v should go to pcom.)

Edit2: Ian, again regarding the Aux Group 'On' switch, are you thinking it is redundant given the mute later on?