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[Quoting amb]

dBel84, measure across the D1 zener and see if you have ~24V.

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I thought as much. I was getting a 60V ptential which I couldn't make sense of - I will look for another 24V zener and try again. Thanks AMB ..dB

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[Quoting heady]

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[Quoting amb]

You really didn't provide enough information for me to even guess. What is "dead"? Did you go through the ε12 initial setup as documented at the website?

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Amb, I don't know myself what is dead. I forgotten the readings I got from the tests I did but I will redo them and post them. The board just doesn't work, nothing happens when power is supplied.

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Supply voltage is a spare 12VDC wall wart I have. I get 12.4V from V+ and V-. Pin 4 and 7 of U1 is 2V. It's the same even when I removed the opamps.

Are Q1 and Q2 gone? It is possible I shorted pin 6 and 7 while measuring the voltage the very first time I test this before it went dead.

Hope this is enough info.

Thanks.

That said, you should have more than 2V across the opamp's pins 7 and 4. Check your Q1 and Q2.

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[Quoting amb]

Heady, you need to have at least 24V... 12V is not enough voltage to power the circuit in its defauilt configuration.

That said, you should have more than 2V across the opamp's pins 7 and 4. Check your Q1 and Q2.

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Thanks amb, I guess as much 12V isn't enough but I haven't got access to a higher voltage power supply at the moment. I don't know how to check Q1 and Q2, but I will just replace them, as I have spares. Thanks again.

[Edited by helzerr on 02-09-2009 at 04:42 PM.]

[Edited by Mister X on 02-09-2009 at 04:44 PM.]

Using mains switch of σ22 configured for ±30V, no problems for several on/off cycles.

I got lazy, since this project is still on the test bench, and used the alligator clip lead as the switch. It seems the sudden inrush of current or arcing of the clip before full contact somehow blew D1, Q1 and Q2. Q2 was visibly destroyed, while D1 and Q1 were deemed to be bad upon further inspection.

Thankfully I had another 1N5252B on-hand, and the local surplus parts shop ought to have 2N3904 & 2N3906 parts.

Initial DMM checks indicate everything else survived

[Edited by helzerr on 02-09-2009 at 08:30 PM.]

My problem is that the ε12 switches off at loud kettledrums. It's not possble to set the zero-reference to a value there it switches when the amp is cold or warm and does not switch off at loud kettledrums.

[Edited by rille on 02-18-2009 at 12:55 PM.]

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[Quoting rille]

How can I make the ε12 less sensitive? Reduce R9?

My problem is that the ε12 switches off at loud kettledrums. It's not possble to set the zero-reference to a value there it switches when the amp is cold or warm and does not switch off at loud kettledrums.

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From what I can see from the schematic, increasing the value of R7 and R8 will make the ε12 less sensitive and increasing the value of R10 will make the ε12's behavior/reaction a bit slower (larger RC value). May be Ti can verify this for me?

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[Quoting rille]

How can I make the ε12 less sensitive? Reduce R9?

My problem is that the ε12 switches off at loud kettledrums. It's not possble to set the zero-reference to a value there it switches when the amp is cold or warm and does not switch off at loud kettledrums.

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Yes, you can reduce R9 but make sure to increase C5 as much as you can (board space permitting). Try to get the lowest corner frequency you can.

The problem may not be the sensitivity of the circuit so much as the corner frequency being too high and 'mistaking' music signals for DC.

[Edited by moodysteve on 02-18-2009 at 03:02 PM.]

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[Quoting moodysteve]

Yes, you can reduce R9 but make sure to increase C5 as much as you can (board space permitting). Try to get the lowest corner frequency you can.

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[Quoting rille]

If I reduce R9 to 50 kOhm I would get half of the sensitivity? Then I would increase C5 to 2µF for the same corner frequency.

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[Quoting helzerr]

Thankfully I had another 1N5252B on-hand, and the local surplus parts shop ought to have 2N3904 & 2N3906 parts.

Initial DMM checks indicate everything else survived

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Sure enough, a replacement pair of Q1 / Q2 from the surplus shop plus the D1 I had on-hand and all is well with my ε12

[Edited by helzerr on 02-28-2009 at 05:47 PM.]