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Resistor w/cap or LED or battery bias?


Paid Member
2009-02-11 12:58 am
LED vs Resistor+Cap: In applications where a triode is loaded by a CCS, I find the LED gives the lowest distortion and best sound.

I have not tried battery bias. The dynamic resistance of a battery depends on all sorts of variables and I'd rather not open that can of worms. The dynamic resistance of an LED is fairly constant by comparison. If you want a clean tone, I doubt battery biasing would be desired.



2008-08-23 7:28 pm
LED will give You low distortion and constant mode, but pressed and dry sound...I tried and heard with full range speaker 96 dB. I will use only resistor and shunt cap with Hi quality. IMO, every SS in plate, in cathode, electr. choke in PSU / I use only iron choke/, in....will dry the sound and press dynamic. I make compromise only with fast rect. diodes. But choice is Yours....
If you are talking about phono and linestage applications as opposed to output tubes, I have found an unbypassed resistor sounds best with a plate CCS. LEDs with a CCS can sound slightly harsh and edgy. The resistor quality is very important---my favorite is 2W Audio Note tantalums. For a plate choke or plate resistor, I use both LEDs and cathode resistors with a bypass cap. Both can sound good. I have also had good results with battery bias, but in each case I eventually went to LEDs instead. Batteries can be very smooth sounding but lacking some drama and excitement.
I'm using battery grid bias in my 26 preamp with a CCS on the plate and really like the sound. I'm applying it through an input transformer so I don't need a DC blocking cap in series. The transformer also lets me invert the signal polarity, drop the gain in half, and eliminate ground loops. See schematic.

I've also used diode bias in the cathode of my 7193 preamp with a CCS on the plate, and I've found I like the Cree SiC schottky diodes over LEDs in that application. Both sounded better to me than a resistor with cap.


  • 26 preamp grid bias.jpg
    26 preamp grid bias.jpg
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