Speaker Turn On Delay and DC Protector Board Set (V3)

Folks:

I built the Speaker Protection board mentioned above (a V2 version, which I understand is virtually identical to the current V3 version other than connector options) and it appears to be working perfectly fine. After the amplifier has been on for a brief period, DC offset is 1.4 mV (L ch) and 0.9 mV (R ch) (I will be reducing it further). There is a problem, though: it seems that the Wolverine amplifier, when initially turned on, generates enough DC offset to trigger the Speaker Protection circuit. In short order the DC offset stabilizes and drops, but I'm guessing the Speaker Board isn't resetting or recognizing that DC offset has dropped to a non-threatening level. I'm no engineer, so please let me know if my speculation seems implausible. If it is a possibility, what changes to the board can I make that will cause the circuit, once triggered, to reset?

Thank you in advance for your guidance!

Regards,
Scott
T4 and T5 are your DC triggered switches. You can also add diodes ie 1N4148 to the emitters of T4 to T5 to raise detection threshold
 
How do you power this board?
I do not find it that easy after reading the hole thread! :)
Only one AC-in, the other for PSU-ground on the board.
For a set of 12VDC relays, do you just feed this with a 12-0-12VAC xformer with secondars coupled in series to the single AC-in for 24VAC??? Not having unused secondarys floating in the chassis....??

I run 90VDC rails, so I cannot tab the original xformer.

Best regards
 
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How do you power this board?

For 12 volt relays you need the rail voltage to be in the 20 to 24 volt range which means a single winding transformer (say a 0-15 transformer) or as @Plott suggests you can feed DC straight into the power terminals of the board.

I run 90VDC rails, so I cannot tab the original xformer.

90 as in -/+90 (so 180 :eek:) or 90 as in -/+45v or 90 as in a 0- 90 single rail design?
 
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I'm reading 180v a cross the poles on the PSU, so that'll be ±90VDC.

Thanks. Wow, that's a very high rail voltage indeed but if that's what it is...

A small transformer is the best option here I think, at least without knowing all the details of the amp it is going into. Can we ask what the amp is?

It might be possible to use one of the existing windings with a 'wattless dropper' arrangement using caps given that the current draw of the board and relays is pretty low. It's just a possibility at this point.
 
Thanks. Wow, that's a very high rail voltage indeed but if that's what it is...

A small transformer is the best option here I think, at least without knowing all the details of the amp it is going into. Can we ask what the amp is?

It might be possible to use one of the existing windings with a 'wattless dropper' arrangement using caps given that the current draw of the board and relays is pretty low. It's just a possibility at this point.
Acurus A250... 1kVA/123VAC xformer.
But it's an old model set to 220VAC at VAC-selector and we have 230VAC in EU today, that's why I'll end up with 90vdc instead of 85vdc as schematic
Screenshot_2022-12-27-20-41-50-88_965bbf4d18d205f782c6b8409c5773a4.jpg
 
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Interesting, thanks. So at -/+ 90 v rails the transformer is going to be putting out around 63-0-63 give or take.

Have you decided for sure on the relays (12v). I was just wondering over a wattless dropper. Not sure at this point.
 
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Interesting, thanks. So at -/+ 90 v rails the transformer is going to be putting out around 63-0-63 give or take.

Have you decided for sure on the relays (12v). I was just wondering over a wattless dropper. Not sure at this point.
Yes approx 63-0-63

Haven't decided on anything yet regarding the relays.
A wattless dropper(??), that's a new English word to me.. Don't know what it is :)
 
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A wattless dropper uses the reactance of a capacitor to limit current but unlike a resistor the capacitor dissipates very little power. Dropping 90 volts to 24 volts with a linear regulator (which is easy) would waste a lot of power in the scheme of things and would run hot.

The dropper idea would look something like this... values are just an experiment. The AC winding is at the top right and set to 90 v which is the peak of the AC voltage.

Screenshot 2022-12-27 200417.jpg
 
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It works in theory. A lot would depend on the relay coil resistance. The higher the better to minimise current draw.

I also wonder if a higher voltage version of the circuit would be possible, perhaps running on 50 volts dc with 24 volt relays. All ideas...

This shows the supply voltage with a wattless dropper and the relay current when the relays are active. In simulation it works but all this is just thinking aloud though at this point. The Zener gives a stable rail.

I'll look in again tomorrow :)

Screenshot 2022-12-27 200619.jpg
 
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