Current Sourced Cathode Follower

dr._sleep · 20th February 2006, 06:40 PM

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

darkfenriz · 20th February 2006, 07:14 PM

what's the voltage on lower triode's anode?

(sorry)

dr._sleep · 20th February 2006, 11:56 PM

13.22 volts on the anodes of the lower triode.

dr._sleep

darkfenriz · 21st February 2006, 09:17 AM

that's very low =low current sourcing
is it ecc83 ?
I think you create high harmonic distortion, which sometimes could mask imperfections of cheap dacs.

reinhard · 21st February 2006, 03:35 PM

that can´t be real, the grid is at 40 + Volts, so the Anode is more positive.

Reinhard

kevinkr · 21st February 2006, 04:26 PM

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

dr._sleep · 21st February 2006, 05:15 PM

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

dr._sleep · 27th February 2006, 08:06 PM

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

dr._sleep · 27th February 2006, 08:46 PM

SORRY ----R2 is 100K. Not 412K

Sleep

20th February 2006, 06:40 PM	#1
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	Current Sourced Cathode Follower 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

21st February 2006, 04:26 PM	#6
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	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 __________________ www.kta-hifi.net

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20th February 2006, 07:14 PM	#2
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	what's the voltage on lower triode's anode? (sorry)

20th February 2006, 11:56 PM	#3
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	13.22 volts on the anodes of the lower triode. dr._sleep

21st February 2006, 09:17 AM	#4
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	that's very low =low current sourcing is it ecc83 ? I think you create high harmonic distortion, which sometimes could mask imperfections of cheap dacs.

21st February 2006, 03:35 PM	#5
reinhard diyAudio Member Join Date: Dec 2000 Location: Germany	that can´t be real, the grid is at 40 + Volts, so the Anode is more positive. Reinhard

21st February 2006, 05:15 PM	#7
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	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

27th February 2006, 08:06 PM	#8
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	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

27th February 2006, 08:46 PM	#9
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	SORRY ----R2 is 100K. Not 412K Sleep

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