12B4 Battery Bias from (Preamp: Foreplay or 5687 or 12B4 ) - diyAudio
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Old 31st July 2004, 06:17 PM   #1
DougL is offline DougL  United States
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Default 12B4 Battery Bias from (Preamp: Foreplay or 5687 or 12B4 )

I agree with you about removing the cathode bypass cap, .. I'm guessing it's responsible for the slightly flabby bass. I will get around to it one of these days, .. was actually thinking of replacing it with an IXYS CCS (battery bias seemed too intimidating considering the preamp was biased to provide 20mA current per channel), .. any opinions.on this idea . What's the difference / pro / con of implementing the CCS on the plate vs. the cathode, ..or can both be used simultaneously (don't think it's practical due to potential imbalance, but i had to ask)
If you want to do battery bias, what about replacing the cathode resistor and bypass cap with4 red LED's?
This should give you about 8 volts, which should word out to a bit over 14 ma in your circuit.

Just a thought.

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Old 31st July 2004, 10:41 PM   #2
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Good idea, Doug.

Any idea where to find relevant info on how to choose the appropriate LEDs for the job?

It was rather dissapointing to find so little data from the manufacturers of these devices.

Does their noise affect performance in any way?


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Old 2nd August 2004, 05:48 PM   #3
DougL is offline DougL  United States
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You are right about practical information on LED's being in short supply.

My guess it the major noise determiner is the substrate material and doping recipe. Since virtually all the red ones I have any data for are made on the same process, they have a similar noise figure.

I would be interested if anyone else has a source of information.

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Old 2nd August 2004, 06:06 PM   #4
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Steve Bench has some studies compairing battery bias with
bypased cathode rersistors. On the other hand I tended to
think that a 6c45pi sounded better with a cathode rersistor
using a blackgate bypass cap than just using a led. I have yet to try a battery or a a led with a bypass cap.

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