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Old 22nd November 2011, 01:44 AM   #1
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Join Date: Jun 2011
Location: Hobart Australia
Default How do i calculate the impedance?

Hi all!

I have been plugging away at a spring reverb project for a little while now and finally got the courage up to turn it on. After about 2 mins. I saw smoke coming from the input transducer coil. I have been using the provided schematic supplied by accutronics. my reverb tank is 9bb2c1b it has an input imp. of 190 ohms. I have used Q1&2 for low levels, and the resistances used are 2.2 ohms. I dont know enough to work out if there is an error on the schematic. could someone please help?

thanks!
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Old 22nd November 2011, 03:30 AM   #2
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Location: Canandaigua, NY USA
I don't see anything obvious, as the non-inverting input is correctly referenced to ground and the output shouldn't have any DC on it. Got to be a wiring error somewhere. Are you using the listed parts or substitutes? Do you have a true bipolar power supply?
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Old 22nd November 2011, 04:02 AM   #3
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Hi Conrad, thanks for the reply.

I have re checked the wiring its all good. No part has been substituted from the specified. and finally the power supply is a true +/- 15v i believe. I have a toroidal 15v + 15v 20va i have connected the two neg. wires together rectified full wave, then run that through a series caps and voltage regs. 7815 and 7915 then more caps. I have included a drawing.

Cheers Luke
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Old 22nd November 2011, 06:48 AM   #4
godfrey is offline godfrey  South Africa
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The circuits look OK. With smoke coming from the transducer, I'd expect Q1 and/or Q2 to be hot as well. Holding a finger on each as the unit warms up should give some clues as to what's going on. If you have a multimeter, it would be worth checking the voltage across the input transducer too.

For testing now before it's fixed, it might be smart to disconnect the transducer before more damage is done. Maybe replace the transducers with a couple of resistors to keep the rest of the circuit happy.
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Old 22nd November 2011, 08:35 AM   #5
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Join Date: Jun 2011
Location: Hobart Australia
Thank-you godfrey,

I Will have to get a multimeter. Good tip about replacing the transducers with resistors. Unfortunately I think the damage is done...

I have just looked a the circuit again. I had wired 2n3906 base as the collector and visa versa oops.

i will still check the circuit with a multimeter.

Thank-you! excellent!
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