Relay switching and transistor question; keeping it quiet

[R.G.]

Except that's a positive supply and there is no "chip output"? I'm dealing with a negative supply.

No biggie. See Enzo's note.

DCV from the PS after the resistor/before the relay is -13v ish, drops down to -10v ish with the coil grounded. That's with no transistor in there, I took it out for now.

That helps. If the power supply sags to 10V with 970R load, then the current in the relay is 10V/970R = 10.3ma. The power supply itself is acting like it has an internal resistance of (13-10)/10ma = 291R.

That is a massive change in nominally "-15V" power supply. So big, that my immediate concern is what else is powered by that supply? Unless you made this -15V just for the relay, any signal circuits running from it are getting positively hammered by the sudden drop from -13V to -10V on its "-15V" power supply.

"-15" is one of those signposts that almost screams "opamps inside". What kind of amp is this?
If -15V is derived from the bias supply for tubes in a fixed bias amp, simply the reflected change in the bias supply could be doing your click directly in the output tubes.

There are a whole lot of possibilities in addition to the relay coil itself causing the click. And of course, none of this thinking says the relay is not causing the click. But if one of the side effects are causing it, no amount of relay tinkering will fix it.

And the 10ma coil load is good. A trivial transistor like the 2N3904 will switch it fine. We can kibitz about the transistor drive circuit after we look at the rest of the amp and find out that there is not an elephant in the room.

[isaac]

Hey, I would think this problem is sorta like a true bypass switching click, in which case I would usually put a 1M resistor from the input lead of the switch to ground. Meaning the part of the switch that stays and goes between two other places. And if you are using both poles on the relay, do it twice.
I don't have my schematic software on this laptop, and I couldn't find a picture of it online already, so no diagram. Sorry.
Hope that helps,
-Isaac

[R.G.]

Hey, I would think this problem is sorta like a true bypass switching click, in which case I would usually put a 1M resistor from the input lead of the switch to ground. Meaning the part of the switch that stays and goes between two other places. And if you are using both poles on the relay, do it twice.

Yeah, we suggested that a couple of times. See reply #11, and others.

The OP has proven resistant to the suggestions that he post an accurate schematic, so we're all wandering around in the dark guessing at solutions from whatever pieces of the elephant we happen to touch.

[isaac]

Oh ok. The problem is sometimes the threads get so long you can't read em all, but I guess that is the only way to be informed, so IDK. Sorry... ;-) Yea it annoys me having no schematic, im a schem-junky. ;-)

[wizard333]

You want something like this then.

relay-drive.jpg

I think that's what I'm looking for, thanks!

What are you driving the transistor from? Is it some logic circuit or just a footswitch contact?

Footswitch contact.

Does it have a path for its input bias current during the few milliseconds between "break" and "make" when the relay's changeover contact is floating?

PI input blocking cap; Yes; referenced with 1M resistance.

I'm not "resistant" to posting a schem, I just don't have an easy way to do it. I'd have to scan in something hand drawn, and I don't have a functional scanner atm.

This is not a bias supply.

What would be the best way to isolate the PS and minimize sag? Diode? Regulator?

[R.G.]

This is not a bias supply.
What would be the best way to isolate the PS and minimize sag? Diode? Regulator?

To answer that, I'd need to know how the power supply is generated in the first place. Putting a diode, regulator, ore resistor in series with a saggy supply typically makes things worse. Sometimes, for a pulse load like switching a relay coil, you can put a BFC (big freaking cap) in parallel with the relay and driver right at the relay and driver. This stores enough current to switch the relay reliably before it sags, and helps eat the flyback pulse. In this case transistor emitter to top (0V) side of the relay coil.

This will make things better if the pop/click/whatever is being coupled to the rest of the circuit through the power supply or ground, as it keeps the relay transient off those wires.

Which begs the question - what else runs on that -12V? Anything that touches the audio signal? Opamps doing signal stuff with +/-12? Clicks can get in that way, too.

[Enzo]

No scanner? Can you take photos and post them? If so, draw a nice big circuit and take a photo of it. Poor man's scanner.

[isaac]

↑ +1 We can't do much for you, unless you can describe infinitely better than we can... , but without a schematic or maybe even layout, we can't help a whole lot, photos of the inside would be nice also.

[wizard333]

I'm waiting on some parts from Mouser at the moment, if what you guys have told me so far doesn't solve it, I'll hand draw the schem and post it.