I built the following in two sections to use as a buffer for the line outs of less expensive CD/DVD/SACD players. Seems to add to the weight of the sound, softens the high end hash and images nicely going through an Aikido preamp and two EL84 based monoblocks.
Any comments or critics.
dr._sleep
Any comments or critics.
dr._sleep
How are you biasing the CF? For best linearity and dynamic range the voltage at the midpoint between the plate of the source and the cathode of the CF should be right around 1/2Vs or 90V..
I would use a high mu triode in both positions and bias the source close to ground using a cathode resistor of just a couple of K ohms, and a fixed voltage source of a few volts.. An ECC83 with a 2.2K cathode resistor biased for 1 - 2mA standing current would give you an rp of > 250K ohms which for this application is more than enough.
IMHO I would run this circuit off of a higher supply voltage with typical high mu triodes, something on the order of 300V seems warranted.
Kevin
I would use a high mu triode in both positions and bias the source close to ground using a cathode resistor of just a couple of K ohms, and a fixed voltage source of a few volts.. An ECC83 with a 2.2K cathode resistor biased for 1 - 2mA standing current would give you an rp of > 250K ohms which for this application is more than enough.
IMHO I would run this circuit off of a higher supply voltage with typical high mu triodes, something on the order of 300V seems warranted.
Kevin
Oops. my bad. The cathode resistor is 5.6K NOT 22K.
The 13.22 volts must also be in error. I'll re-measure when I get home.
The valves in use are 12AU7's, very nice Bugle Boys. I wanted to put this together using a 5X7x2 project box with the power tranny under the chassis, so the secondary is 120V. I am able to get 190 V on the plates after a bridge rectifier, CLC filter (33uF, 9H choke, 33uF).
Actually, it sounds good. I have a Decware 685 player with the tube output stage and with the buffer attached to the stock outputs it rivals the smoothness and punch of the modded outs.
Thanks for you inputs, I'll recheck that voltage and post later.
dr._sleep
An externally hosted image should be here but it was not working when we last tested it.
The 13.22 volts must also be in error. I'll re-measure when I get home.
The valves in use are 12AU7's, very nice Bugle Boys. I wanted to put this together using a 5X7x2 project box with the power tranny under the chassis, so the secondary is 120V. I am able to get 190 V on the plates after a bridge rectifier, CLC filter (33uF, 9H choke, 33uF).
Actually, it sounds good. I have a Decware 685 player with the tube output stage and with the buffer attached to the stock outputs it rivals the smoothness and punch of the modded outs.
Thanks for you inputs, I'll recheck that voltage and post later.
dr._sleep
Here is the finished product, 12AU7 based current sourced cathode follower. I have dropped the cathode resistors to 4.6K and the grid is at +4.9 volts.
The insides
Scope shot with an input square wave .5 volts @1000 Hz, the lower field is the input side the upper the output.
Final Schematic
Very pleased with the sonic results also.
dr._sleep
An externally hosted image should be here but it was not working when we last tested it.
The insides
An externally hosted image should be here but it was not working when we last tested it.
Scope shot with an input square wave .5 volts @1000 Hz, the lower field is the input side the upper the output.
An externally hosted image should be here but it was not working when we last tested it.
Final Schematic
An externally hosted image should be here but it was not working when we last tested it.
Very pleased with the sonic results also.
dr._sleep
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