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Old 4th September 2011, 11:31 AM   #1
kjb is offline kjb  Sweden
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Default ESP Project 104 muting problem

Hello!
I'm trying to finish a Linkwitz Orion ASP upgrade and adding a mute circuit. There is a problem when cutting the power it wont mute.

The circuit Project 104 - Preamp/ crossover muting circuit

Click the image to open in full size.

The problem is that there is a voltage on pin 1 to the AC trigger part despite the fact that the ac is cut. It has to go low before the circuit mutes . (should happen 50ms after ac is cut)
Its two diodes between GND and positive rail. In the middle there is pin 1. It seems like i get half voltage (like a voltage divider) between GND and +5.5 V (I'll use a 5.5V zener) The level is always high. I can mesure ~2.8 V slowly decreasing when the external filter caps drains.

I use full rectifier bridges. two instead of only one described in the article.
Anybody knows whats I'm doing wrong? This is driving me mad
Thanks for all suggestions!
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Old 4th September 2011, 11:57 AM   #2
Mooly is offline Mooly  United Kingdom
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Just some thoughts...

The 100k to pin 1 has to be "ground referenced" which would normally be via the transformer. In other words the left hand end of R1 should read essentially zero ohms to ground. Check it ? Have you got it connected to the AC on the tranny and not the rectified rails ?

Without seeing how you have wired it up it's hard to say.

Check the remainder of the circuit...

If you lift D3 the circuit should mute/unmute as you short out C1.
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Old 4th September 2011, 01:22 PM   #3
kjb is offline kjb  Sweden
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That's was the problem I had hooked it up like this. Click the image to open in full size.

The ac was from one of the secondaries, and the positive rail is taken from the same rectified secondary, same with the GND.

I removed one bridge and connected it like it should and now it works perfectly.
But now the regulation is worse i guess. But i will use superregulators so thats probably not a problem
Thanks!
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Old 4th September 2011, 05:50 PM   #4
Mooly is offline Mooly  United Kingdom
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Thanks for the update...
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Old 4th September 2011, 06:27 PM   #5
AndrewT is offline AndrewT  Scotland
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This may solve the problem of not recognising the "loss of AC"

Tap directly to one secondary. Use a diode to rectify that AC.
Connect the half wave rectified signal to the 100k.
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