Purusha

Here is the mono summing section I took from MIDAS Venice schematics



Is there anyone who would do me a favour and draw a simple PCB layout from this?  I am not sure if the part with TL072s is needed in the mono summing or not.

I need to improve my monitor controller project where I implemented active mono summing based on NYD's schematics..



It works but I hear clicks when engaged and I have no idea how to solve this other than to try another active circuit.
Regards as always, Purusha


Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Mono summing schematics from MIDAS Venice ... looks nice
« Reply #1 on: May 23, 2007, 01:42:35 AM »
Quote
It works but I hear clicks when engaged and I have no idea how to solve this other than to try another active circuit.

Just randomly trying different collected circuits is unfortunately not a very promising route for proper design if you ask me--I'd rather suggest you post the current schematic (I mean the entire one, not just the mono section) with which you hear clicks so we can have a lock at it and suggest how to get rid of the clicks. Perhaps the solution is to use another circuit but first you need to know what your problem really is before you can solve it.

BTW, why do you need a PCB for this? This circuit is so simple that you can easily build it on perfboard.

Samuel

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #2 on: May 23, 2007, 04:18:02 AM »
Regarding my mono circuit there is nothing more to it than whats on NYDs schematics above except two relays which route the signal through the mono circuit...


Here is the full Midas schematics if someone needs to look into it.


Quote
BTW, why do you need a PCB for this? This circuit is so simple that you can easily build it on perfboard.


I am not sure if the TL072 part is needed for mono summing or not.
Regards as always, Purusha

emtee

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #3 on: May 23, 2007, 05:12:13 AM »
Quote from: "Purusha"

I am not sure if the TL072 part is needed for mono summing or not.


The Tl072 part is for the mono summing. L&R are summed through the two 15k resistors R30 & R31

NewYorkDave

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #4 on: May 23, 2007, 08:34:54 AM »
You're blaming the audio circuit for something that's obviously the fault of the switching circuit--or how the switching circuit is implemented, anyway. And you never posted the switching circuit.

Svart

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #5 on: May 23, 2007, 10:04:59 AM »
Summing circuits need fast opamps too..  I would just bread out Fred's summing circuit and be done!
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

NewYorkDave

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #6 on: May 23, 2007, 11:04:40 AM »
That still won't take care of switching clicks. I say again: he has to look at his switching arrangement, then worry about the rest (if it even needs worrying about, that is).

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Mono summing schematics from MIDAS Venice ... looks nice
« Reply #7 on: May 23, 2007, 12:26:55 PM »
Quote
I say again: he has to look at his switching arrangement, then worry about the rest (if it even needs worrying about, that is).

That's very much my point. I suspect that there is either some DC on the switched signal or some unhappy relays configuration.

Samuel

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #8 on: May 23, 2007, 03:33:14 PM »
Quote from: "NewYorkDave"
You're blaming the audio circuit for something that's obviously the fault of the switching circuit--or how the switching circuit is implemented, anyway. And you never posted the switching circuit.


I did post this PCB layout in the other thread after you mentioned this... but you never answered  :roll:

My switch fires both relays at the same time ...



Quote from: "Svart"
Summing circuits need fast opamps too.. I would just bread out Fred's summing circuit and be done!


I don't mind where the circuit comes from as long as I don't have this clicking problem. I don't know if my Midas board is using
any relays or not but there are no clicks when mono is engaged... just slight volume drop.
Regards as always, Purusha

NewYorkDave

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #9 on: May 23, 2007, 03:43:32 PM »
Some of us don't have enough free time to decode a PCB layout. Why not just post a schematic?


Svart

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #10 on: May 23, 2007, 03:55:40 PM »
Quote
That still won't take care of switching clicks.


oh, I'm not even talking about those clicks.

Quote
I don't mind where the circuit comes from as long as I don't have this clicking problem. I don't know if my Midas board is using
any relays or not but there are no clicks when mono is engaged... just slight volume drop.


Then they likely had a set of coupling caps around a relay or they just used a JFET array.
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #11 on: May 23, 2007, 03:55:59 PM »
OK, maybe I can explain it quicker than drawing the schematics now...  :wink:

Imagine one relay in front and another after your (NYD) circuit. They are both engaged with the same switch.
When they are not engaged the signal bypasses the mono circuit completely. I am using a balanced controller
so one mono circuit handles the positive L/R signal and second the negative. I think this should clear how I did it.

NYD, If you still want I can add the drawing to your schematics.
Regards as always, Purusha

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #12 on: May 23, 2007, 03:59:21 PM »
Quote
Then they likely had a set of coupling caps around a relay or they just used a JFET array.


Any schematics you can point me to?
Regards as always, Purusha

AudioJohn

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #13 on: May 23, 2007, 04:16:37 PM »
It is not apparent from the PCB extract you have shown how the power for the relay is derived.

If it shares the same supply rails as the op amp - there is quite likely to be a click when the relay operates - as there will be some back emf injected back into the supply, even with the diode across the relay coil.

More information - or full circuit schematic please!

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #14 on: May 23, 2007, 04:40:45 PM »
I am using Mnats PSU boards for +18V/-18V and this PSU is feeding all my active stuff in the Monitor controller.
My relays are 12V so I am using a resistor to drop the +18V line for the relays and another resistor for voltage
drop to feed all my LEDs... so the positive side of the Opamp, Relays and LEDs are fed from the Mnats +18V PSU side.

BTW, every switch also provides voltage to each LED next to it...
Regards as always, Purusha

AudioJohn

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #15 on: May 23, 2007, 05:06:04 PM »
There are plenty of possibilities for clicks with the method you have outlined.

When relays and LED's are switched there is a sudden increase of current, which might cause the +18  supply to drop momentarily if it is not well regulated and of very low impedance. Similarly the return for the current looks as though it will be via 0v (or earth) - so the PCB track routing will have an effect if not very carefully laid out. Ideally take the relay and LED returns directly to the 0v common point (same principle as star earthing).

In many mixers -  LED indicators (for solo, mute, channel on etc) will be connected in series and fed with a constant current (say 10mA) - then  the LED's can simply be shorted with a switch contact to turn it off. This does not alter the current - so no clicks can be induced into the audio circuitry.

Relays are usually lovely things - when used appropriately. The contact side is simple to implement - but the coil switching needs care in design.

If using many relays - then a separate supply is warranted, but in this case ensure that the resistor dropper has a capacitor to earth to help with switching transients.

Finally - could there be any DC on the signals coming into points C & D on your PCB? (Measure with a multimeter or scope) - if there is - even a tiny voltage - there will be a click when the channels are combined when the relays operate....

This can (and will?) - be fixed......!

Purusha

Mono summing schematics from MIDAS Venice ... looks nice
« Reply #16 on: May 23, 2007, 05:12:51 PM »
Thanks AudioJohn for this nice explanation  :thumb:

I will check your points against my layout and do some tests in the following days and report back for further troubleshooting (if necessary). Thanks again.  :razz:
Regards as always, Purusha


 

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