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Lightspeed Attenuator / Audiohm Optocouplers / LDR
http://diyaudioprojects.com/Forum/viewtopic.php?f=12&t=615
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Author:  JHtires [ 10 Dec 2012, 16:41 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

Hello redsky.
I´m working in the similar project and I´m very glad if I would can see the pics. I don´t know why don´t show me.
Best regards

Author:  jpchissitt [ 18 Nov 2013, 06:01 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

Hello All

I've now put one of these together, and am very pleased with the results, The only problem appears to be a massive increase in volume when I turn my amp off (I've plumbed it into my KT88 valve amp, and it runs off the heater supply), until the caps run dry. I assume it is something to do with the voltage regulator's behaviour when the supply is cut, but am guessing - any ideas?

Cheers

John

Author:  gofar99 [ 18 Nov 2013, 18:05 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

Hi, I would think it is related as the "gain" is a function of brightness in the LEDs and when the power supply is shutting down an unusual voltage condition would be expected that could cause brightness.

Good listening
Bruce

Author:  jpchissitt [ 19 Nov 2013, 04:56 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

I might stick a relay inbetween the regulator and the pot, just to cut the supply straight away when the amp shuts down. If I forget to turn off the source first, it wakes the whole house!

Author:  Gio [ 19 Nov 2013, 23:00 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

Hi John,
The attenuation should decrease with increasing current through the LED in the LDR. So it could be strange behavior from the regulator at the dropout voltage limit.

You have to watch that the heat from the tube amp does not heat up the LDRs. The resistance of an LDR will vary significantly with small changes in temperature. I had a similar arrangement but I eventually housed the attenuator in its own enclosure and separate power supply.

Cheers

Author:  sckma [ 07 May 2017, 21:33 ]
Post subject:  Re: Lightspeed Attenuator / Audiohm Optocouplers / LDR

Can anyone tell me where I can get a matched quad of LDP for building such Attenuator? Thanks in advance for your help!

Cheers

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