Don't doubt, just pot them together and keep away from fluctuating temperatures, and that will take doubt away. Even Silonex will tell you if you care to ask, they are temperature sensitive.
No need to pot the whole board/case, just the section with the LDR's, in the early days I used a Tick Tack container cut in half to sit over the LDR's to pour the potting mix into, when set just squeeze the container and it slip off.
Hint don't have the wax too hot, just when it melts so it's a little thick and not too runny.
Cheers George
No need to pot the whole board/case, just the section with the LDR's, in the early days I used a Tick Tack container cut in half to sit over the LDR's to pour the potting mix into, when set just squeeze the container and it slip off.
Hint don't have the wax too hot, just when it melts so it's a little thick and not too runny.
Cheers George
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This wax idea sounds like a nightmare to have in a hot amp George. I dread to think how it will all look in 5 years time. Surely there's a better way to pot the LDRs, like a small aluminium box, for example, filled with good old air, and insulated wires through small holes. Wouldn't that make more sense?
You could use a Peltier Junction and external heatsink to cool your aluminium box to make it the first cryogenic preamp, and don't forget to insulate the outside surfaces to make it efficient . . .
Peltier Junctions | AllElectronics.com
Another way to reduce temperature sensitivity is to make an oven, just like a crystal oven, for the LDR's - a thermally insulated box with a heating element (big resistor) and temperature sensing element - control circuitry power the element to bring the temperature up to a desired value (warmer than ambient would ever be, maybe 95F for a stand-alone box, perhaps warmer for the inside of a power amplifier). Of course it would have to be calibrated warmed up, and when powered on may take a couple of minutes for the temperature to stabilize.
Your system is compatible for a Lightspeed without buffer, you may enjoy it even more, as it will not have an transistor preamp thinness to it, as in a "hot" shot at you type transients. The transients the Lightspeed have has more body to them and sound more relaxed yet it will extend higher and lower than your tube pre.
If you feel the need for a tube buffer after it, this is the one that sounded best to me tube or transistor
Cheers George
If you feel the need for a tube buffer after it, this is the one that sounded best to me tube or transistor
Cheers George
Attachments
It is a buffer that Tektronics used in their top tier tube Occilloscope of yester year and called the "SLCF" Super Linear Cathode Follower, and yes it was reborn. For a tube buffer it has a nice low 100ohms output impedance, shame about the coupling cap thou.
Cheers George
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rise and decay times
Hi all
I don't doubt that the lightspeed attenuator works well and like the concept but am struggling to understand how the optocouplers with a rise and decay time of 5 and 80ms respectively can follow an audio signal of 20kHz-can someone please help me with this...I'm but a mechanical engineer dabbling in electronics...
Thanks
Chris
Hi all
I don't doubt that the lightspeed attenuator works well and like the concept but am struggling to understand how the optocouplers with a rise and decay time of 5 and 80ms respectively can follow an audio signal of 20kHz-can someone please help me with this...I'm but a mechanical engineer dabbling in electronics...
Thanks
Chris
the operator sets the "volume" by adjusting the current fed to the LEDs.
The LDRs adjust their resistance (slowly) to follow the light output of the LEDs.
After your time constant or seven have passed the LDRs have reached their final resistances.
These final resistances attenuate the Audio Signal that passes through the LDRs.
The Audio Signal does not pass through the LEDs.
If the design can hold the LEDs light output more constant then the resistances of the LDRs will be more constant. That's where regulation and capacitors come to our aid. To help fix the LED currents.
The LDRs adjust their resistance (slowly) to follow the light output of the LEDs.
After your time constant or seven have passed the LDRs have reached their final resistances.
These final resistances attenuate the Audio Signal that passes through the LDRs.
The Audio Signal does not pass through the LEDs.
If the design can hold the LEDs light output more constant then the resistances of the LDRs will be more constant. That's where regulation and capacitors come to our aid. To help fix the LED currents.