I'm adding a shunting relay to mute the output of a tube preamp. The issue is mostly at power down, I get a big bump on the output. I've read all the threads on this, but my question is a little different.
My chassis is already extremely tight, so I have room for a mini relay and maybe a resistor and diode that's it. I don't wish to create any elaborate circuits. I'm choosing only to address the turn-off bump at this time because it's most egregious. My power amp has a delay turn/on function when using a trigger, so any noise coming from the preamp associated with the slow B+ climb are solved enough for now. Turning off the amp via the trigger does not happen fast enough to avoid the turn-off bump from the preamp however.
I have a small 12VDC power supply already in the chassis for a 12V trigger, and LEDs and such, so I can use this to control the relay. Because the power-off bump happens so quickly after I turn off the amp (or physically unplug it), I need the relay to de-energize very quickly, before the B+ collapses, in order to shunt via the NC contact.
I'm thinking to use this relay. Like most relays, it energizes at 80% of rated V, and de-energizes at 10% which is way down at 1.2V.
QUESTION
Can I make the relay de-energize more quickly and at a higher V, like lets say 8V, by using a zener somehow? Will the attached sketch work? I may totally be misunderstanding how zeners actually work, so pardon if this is a silly question. I'm a little unclear if the zener conducts the full voltage from cathode to anode when reverse biased, or if it drops the full voltage equivalent to the breakdown voltage.
My chassis is already extremely tight, so I have room for a mini relay and maybe a resistor and diode that's it. I don't wish to create any elaborate circuits. I'm choosing only to address the turn-off bump at this time because it's most egregious. My power amp has a delay turn/on function when using a trigger, so any noise coming from the preamp associated with the slow B+ climb are solved enough for now. Turning off the amp via the trigger does not happen fast enough to avoid the turn-off bump from the preamp however.
I have a small 12VDC power supply already in the chassis for a 12V trigger, and LEDs and such, so I can use this to control the relay. Because the power-off bump happens so quickly after I turn off the amp (or physically unplug it), I need the relay to de-energize very quickly, before the B+ collapses, in order to shunt via the NC contact.
I'm thinking to use this relay. Like most relays, it energizes at 80% of rated V, and de-energizes at 10% which is way down at 1.2V.
QUESTION
Can I make the relay de-energize more quickly and at a higher V, like lets say 8V, by using a zener somehow? Will the attached sketch work? I may totally be misunderstanding how zeners actually work, so pardon if this is a silly question. I'm a little unclear if the zener conducts the full voltage from cathode to anode when reverse biased, or if it drops the full voltage equivalent to the breakdown voltage.
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If you have DC filaments, the fastest way to mute would be to run the relay coil from
the filament supply, so the voltage on the coil will collapse quickly when turned off.
You'd use a normally closed relay for this.
The switching supply may not collapse quickly enough for your purpose, test it and see.
the filament supply, so the voltage on the coil will collapse quickly when turned off.
You'd use a normally closed relay for this.
The switching supply may not collapse quickly enough for your purpose, test it and see.
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Here's a better sketch of what I'm planning to add (minus the zener idea).
Unfortunately, I'm not using DC heaters. Just elevated AC
"The switching supply may not collapse quickly enough for your purpose, test it and see. "
That's why I'm thinking if I didn't have to wait till it got all the way down to 1V, rather just 8V or so that would save precious ms.
Unfortunately, I'm not using DC heaters. Just elevated AC
"The switching supply may not collapse quickly enough for your purpose, test it and see. "
That's why I'm thinking if I didn't have to wait till it got all the way down to 1V, rather just 8V or so that would save precious ms.
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If you have a back EMF suppression diode across the relay's coil, that slows the turn-off time by providing a path for current to flow as the coil's B field collapses. Removing that will speed up turn-off but will of course allow damaging voltage surges upon turn-off, which is a no-no. If you place a Zener in series with the back-EMF diode, say 12V or so, that allows the back EMF voltage to rise a bit, to within safe levels, and that will somewhat speed up the turn-off cycle.
Then try powering the NC mute relay coil from the SWPS and see if it's fast enough.
That's about the only option. If you want to try a series resistor with the coil, keep
the relay coil voltage above half its rated voltage, or it may not work well enough.
That's about the only option. If you want to try a series resistor with the coil, keep
the relay coil voltage above half its rated voltage, or it may not work well enough.
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Maybe something like this operated directly from the 6.3VAC windings? Not a signal relay but maybe it doesn't matter for shunt function. Looks like around 10ms release time.
https://www.mouser.com/ProductDetai...GAEpiMZZMtGt%2Bn33CgIP68tht9FRr44rZk6En2Yzl4=
https://www.mouser.com/ProductDetai...GAEpiMZZMtGt%2Bn33CgIP68tht9FRr44rZk6En2Yzl4=
I think you're probably right, but I'm a little overwhelmed by the options. I don't mind using a small dip package either. Could you help me select one?
https://www.mouser.com/Electromechanical/Relays/Solid-State-Relays-SSR/_/N-ay0ti
It would be great to control from 6VAC, but otherwise 12VDC may have to be the option
If it will run on the AC voltage for the filaments, then the DPDT version should work.
https://www.mouser.com/datasheet/2/307/en_g2r-1670578.pdf
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Mute output with a FET, WAY faster than any mechanical thingie.
Or do what I do in similar situations: add a switch across output terminals, label it "mute" or even "standby", add a little label besides it:
"
Highest Technology, it only needs a Million Dollar Microprocessor, called B.R.A.I.N. 9000
Not kidding, it saved my bacon 1000 times at "any noise is unacceptable" places such as Opera houses, meditation centers, etc.
Or do what I do in similar situations: add a switch across output terminals, label it "mute" or even "standby", add a little label besides it:
"
Works like a charm, better than any other solution on Earth, because it PREDICTS THE FUTURE, and Mutes BEFORE click/pop/thump is even *created* , go figure.
Highest Technology, it only needs a Million Dollar Microprocessor, called B.R.A.I.N. 9000
Not kidding, it saved my bacon 1000 times at "any noise is unacceptable" places such as Opera houses, meditation centers, etc.
As for the FET solution, I need a circuit accompanying it to allow for NC operation I believe. Otherwise a depletion mode PNP or something but I haven't been able to figure it out. Do you have very a simple circuit that operates in this way? Otherwise yes its a cinch to create a mute with an enhancement mode NPN and 5V available after the amp turns off.
I'm aware of the manual switch option, but I prefer not to make equipment that only I can operate. Just because it's tubes doesn't mean you should need a license to turn it on.
I'm aware of the manual switch option, but I prefer not to make equipment that only I can operate. Just because it's tubes doesn't mean you should need a license to turn it on.
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BTW, I added this relay K10P-11A15-6, exactly as drawn in my post #3 (except wired to 6.3VAC rather than 12VDC), and it absolutely solved the problem of the turn-off bump. Totally silent when I cut the power to the preamp.
I ended up using a 6VAC power relay, powered to the 6.3V heater winding. It's not really passing audio. It just kicks in at shutdown, and shorts the output to ground through a 100R resistor.