plumsolly

Solo-in-place schem?
« on: March 05, 2010, 02:52:26 PM »
I am trying to implement a solo-in-place system in my console. I came up with this:
What do you think? Thanks, Ben


JohnRoberts

Re: Solo-in-place schem?
« Reply #1 on: March 07, 2010, 10:51:49 AM »
First there are two kinds of solo.. One is destructive to the two-mix and the other not.

The former is a mute everything but the solo'd channel(s), the latter routes an AFL (post fader) feed from the solo'd channel to just the control room monitor output so you can isolate and listen to a channel without trashing your mix.

The former is slightly more useful for troubleshooting how an input interacts with effects too, while any mix muxt be started over. So the depending on how you intend to use this one way is more desirable than the other.

The former is basically a layer of logic applied to active mute circuitry. The latter requires an additional two-mix bus and electronic signal routing circuitry in the master section.

JR 
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

plumsolly

Re: Solo-in-place schem?
« Reply #2 on: March 07, 2010, 01:24:07 PM »
Thanks John -
The former is basically a layer of logic applied to active mute circuitry.
This is exactly what i was going for. Does it look like it will work? Here is a copy of the schematic of the channel. It was originally set up for a separate mono solo buss, but the master section has been removed completely.
Thanks, Ben

JohnRoberts

Re: Solo-in-place schem?
« Reply #3 on: March 07, 2010, 02:05:53 PM »
Well that is using a mechanical switch for the mute...  That would have to be changed to a relay or fet switching to perform mute in response to a logic signal, then add logic between solo and mute logic to generate the different result for different modes.

That board is set up for non-destructive solo using a separate solo signal bus and (most likely ?) CR routing responsive to solo logic. 

JR

PS: One of us is spelling bus wrong. I don't think it's me.
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

plumsolly

Re: Solo-in-place schem?
« Reply #4 on: March 07, 2010, 03:39:13 PM »
Hey John,
Well that is using a mechanical switch for the mute... 
I meant the green box with the coil and switch in it to represent a relay. That relay is controlled by either the 'on' (mute) switch or the solo logic bus. When any channel is soloed it will put 24v common on the solo logic bus activating the relays and muting all other channels unless they are soloed. When a channel is soloed, it's mute relay is no longer connected to the solo logic bus, so it stays unmuted unless the channel on button is not depressed (mute).
That board is set up for non-destructive solo using a separate solo signal bus and (most likely ?) CR routing responsive to solo logic. 
Yes, thats all gone now - all the modules relating to it have been removed, hence the new arrangement.
PS: One of us is spelling bus wrong. I don't think it's me.
I've seen it both ways, but more often with only one 's'

Thanks, Ben

analogical

Re: Solo-in-place schem?
« Reply #5 on: March 07, 2010, 04:40:02 PM »
Similar vein, quite simple if you don't care about destructive mutes:


analogical

Re: Solo-in-place schem?
« Reply #6 on: March 07, 2010, 04:43:35 PM »
"PS: One of us is spelling bus wrong. I don't think it's me. "

Well, that all depends on what period of time you began publishing things.  =P

ChrioN

Re: Solo-in-place schem?
« Reply #7 on: March 07, 2010, 05:16:04 PM »
12vdc in the audio path? I don't get the schematic.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

plumsolly

Re: Solo-in-place schem?
« Reply #8 on: March 07, 2010, 05:22:49 PM »
Thanks analogical,
Similar vein, quite simple if you don't care about destructive mutes:



Yeah - thats really similar to what I have, except that the switching on yours is done on the + side of the relay. I think they will both accomplish the same thing. Thanks for the scheme.

12vdc in the audio path? I don't get the schematic.

He doesn't have audio on that schematic at all, just logic. The relay switches the channel mute on and off.

- Best, Ben

JohnRoberts

Re: Solo-in-place schem?
« Reply #9 on: March 07, 2010, 07:35:06 PM »
"PS: One of us is spelling bus wrong. I don't think it's me. "

Well, that all depends on what period of time you began publishing things.  =P

I was first published in the '70s.

I learned the correct spelling for bus in the mid '80s.  ???

I spelled it wrong in an article I wrote in 1980. :-[

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.


analogical

Re: Solo-in-place schem?
« Reply #10 on: March 07, 2010, 08:35:30 PM »
Hehe I've also seen you attack yourself for that misspelling in more than one thread,
So I was just exploiting your sensitivity to that!

I think that article of which you speak of is required reading for anyone who wants to learn about summing.
It's like a permanent fixture/coaster on my nightstand.

 /cheers

plumsolly

Re: Solo-in-place schem?
« Reply #11 on: March 13, 2010, 01:47:13 AM »
I implemented this scheme on one channel and it worked like a charm (it mutes when any other channel is soloed) I am ready to install it on each channel, but I wanted clarify a couple of things first: In his console design article, Steve Dove warns against using relays because of the noises (click and pops) that can result - I didn't have any problem with this, but should I worry about what will happen when they are on each channel and all switching simultaneously? Secondly, in Joe Malone's Pm2000 solo mod circuit he has got a transistor, which I presume is to drive the relay (I haven't been able to get in touch with Joe to get a schematic) Steve Dove also talks about drive circuits for relays. When is this needed? Again, I didn't have any problems with the one I installed, but It would be a debacle if I installed them in each channel only to find that there was a problem that arose from having many all switching at once. Thanks very much, Ben

JohnRoberts

Re: Solo-in-place schem?
« Reply #12 on: March 13, 2010, 10:55:41 AM »
Steve Dove is right.. (easy to say). 8)

Not only is switching relays subject to noise, they draw a relatively large amount of current for what they do. In console design we also have to think about X mA times 36 or 48 channels or whatever.

A relay may be justified for high quality switching of line level signals, but for say a simple mute, who cares if a JFET is not perfectly linear, while it's shunting a signal node to ground?

I never used a relay in a console, and only a few times in higher end rack mount gear as a robust signal bypass when power is removed.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

plumsolly

Re: Solo-in-place schem?
« Reply #13 on: March 13, 2010, 05:20:08 PM »
Thanks for the insight John. I am only working with 16 channels and it looks like these relays draw ~.02A at most when switched, so I should be set current-wise (I have 4A and I am only drawing ~.5A with every led on). As far as click/pops, as it is, with just the one channel, its absolutely silent when switching - I hope that will still be the case when they are all installed. How about the driver circuitry? When is that used, and for what? Thanks, Ben

JohnRoberts

Re: Solo-in-place schem?
« Reply #14 on: March 14, 2010, 11:38:13 AM »
There should be a lot of examples around showing how to drive relays and dealing with coil inductance (clamp diodes etc).

In the context of a low noise console environment, it is not unheard of to use a separate power and ground feed to keep the relay noise out of general PS grounds and rails. I haven't seen this actually done for relays, but I have seen separate PS for LEDs in larger consoles. This also allows you to dial in the PS to be a better voltage match for relay (or LED) needs.

Of course the PS can not be completely floating as that would complicate control logic. Just watch where the heavier current is flowing.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Mark Slocombe

Re: Solo-in-place schem?
« Reply #15 on: March 14, 2010, 01:53:01 PM »
A lot of the electronics I build are used in sound contracting situations where 24vdc is common. I've been building heavily with relays since 1981, I love them for their reliability. In my mixing console designs I have a separate 24vdc supply and ground, I use this for LED displays and powering relays.

I put a diode across the relay coil to snub the coil discharge. By implementing the separate power supply and the diode I have zero pops and clicks.

If you are switching audio with relays look for sealed relays with precious metal contacts that are bifurcated, gold contacts are best. I have one large installation I built in 1984 with these parts, they are "ON" 24/7 and have never had a failure.

I personally like destructive solo where everything drops out except what is solo'd. I never solo anything when I'm doing a final mix so destructive is fine. I also like doing it this way because it keeps me focused on the mix and hearing what each track or effect is contributing.

Best of luck with your construction project.
Mark Slocombe

analogical

Re: Solo-in-place schem?
« Reply #16 on: March 14, 2010, 03:14:16 PM »
Quote
...say a simple mute, who cares if a JFET is not perfectly linear, while it's shunting a signal node to ground.
Mr. Roberts, would you be so kind as to steer us towards an example?
I'm all for simplifying mechanical aspects of my project if the audio signal remains as clean as it would otherwise.

Thank you!

JohnRoberts

Re: Solo-in-place schem?
« Reply #17 on: March 14, 2010, 06:26:38 PM »
Googling JFET and mute turns up this, as one of the first hits. 

http://www.edn.com/article/CA468422.html

Of course you could substitute a P-channel JFET and use opposite polarity voltage to turn it on/off.

If you want to get fancy there is a technique to reduce distortion when the FETs channel resistance is conducting, by adding 1/2 the AC voltage at the drain back into the source.  (See note about half way down this link.)
http://freespace.virgin.net/ljmayes.mal/comp/vcr.htm

In general I would cap couple (r2) to keep gate control DC out of audio, and maybe buffer if changing the gate voltage quickly.

I seem to recall a good treatment of this in an old National semi app note, but i couldn't find it on google very easily. Bob Cordell's classic low distortion THD set, used a variation on this linearized FET in his sine wave oscillator AGC loop gain control.

If you google more you can probably find some console circuit to copy.

Cheap consumer gear, sometimes used bipolar transistors as audio (shunt) mutes, but these will not be as clean, so I would stick with JFETs.

I haven't looked at this for a few decades so there may be better modern parts than what I messed with back in the day.

=====
Note: ignoring possible noise problems from relay coil current, it will be easier to get a hi performance audio result with a relay. For a one off project it may not be worth the learning curve to design a JFET mute from scratch.

If you decide to figure it out, things you need to look out for is signal swing wrt JFET breakdown voltage and when a mute is turned off, the gate voltage needs to be held far enough away from the signal peaks that they don't turn on the channel again.

In production a JFET solution will be much cheaper.  Relay is perhaps better if your time is worth more than your money for parts.

JR

Visit https://circularscience.com to hear what properly "cleared" drums sound like.

analogical

Re: Solo-in-place schem?
« Reply #18 on: March 15, 2010, 12:04:36 AM »
Thank you for your time. Much appriciated.

jsteiger

Re: Solo-in-place schem?
« Reply #19 on: March 15, 2010, 09:38:05 PM »
Hey Ben,

I have been using the following control circuit that I discovered in my console. Kinda like John mentioned!  ;)  Anyhow, it is for mute and destructive solo. Some minor rework would easily provide a dedicated stereo solo bus for non-destructive SIP. The parts are cheap and plentiful. Works like a dream. I like the TQ2's. Q1 is an NPN.



Oh, and out of respect for JR, I always try to spell bus correctly.  8)

Cheers, Jeff
« Last Edit: March 16, 2010, 09:30:46 AM by jsteiger »
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