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In Reply to: RE: CS8412/14 upgrade posted by GTCharlie on January 09, 2008 at 00:33:29
I hope you keep it DIY, and post more information.
I have scrapped the original output board and gone to cathode follower tube stage with AN output transformers. I have made many upgrades to my DAC and thought I had done as much as I could have with my level of knowledge, but the shif register change is new to me.
Tom R.
I did nothing drastic : wound separate transformer for digital board to bridge, BG Super E; another transformer for the analogue B+ and 6922 filaments, into their own rectifier bridges. B+ is now L-C-L-C. Using oil cans for the C, and Tamura 30Hy for the L. K-bypass cap for the SRPP 6922 is now super-e. Output is still cap-coupled. I didn't measure the original iron, but my present irons run and never get beyond a degree or two above room temp. I left as is and didn't alter AN's cascaded transformers - the four cylinders - to lop off high frequency grunge. I am curious about your "cathode follower" Did you parallel the 2 halves of the dual triodes, and tapped into the cathode? or did you cascade the 2 halves ? WHat's your plate and cathode voltage? Current? I didn't touch the SRPP anymore because it was handling minuscule signals anyway ... but your amendments might be superior to the original.
GT Charlie,
I will have to reply at a later date as I am burned out from work and have to work Saturday and Sunday, but if you look in the "Imamate Systems" under "John PA, my one and only", read the section on his AN DAC 1.1
John's DAC is very close to mine, actual John's did the original research and he helped me modify my DAC 1.2
Link:http://cgi.audioasylum.com/systems/961.html
I have not changed anything for a year or so as I have gotten interested in speaker projects.
Cathode follower: If I remember correctly, I tied the two halves of the triode together, with a cap and resistor from ground to the cathodes in parallel. I will try and get a better for you and post it in a few days
Tom R.
http://cgi.audioasylum.com/systems/961.html
Just so you know I an not a engineer so what I describe hear is correct to the best of my knowledge, but others may have a different opinion. Anyway….
As I stated, I scrapped the original output board in favor of transformer output stage. I purchased from AN Output Transformer number 011/01-A to be the heart of the new output stage. AN OPT number 011/01B can also be used, this is a better OPT but also the cost is almost double.
I also used a 6N1P as an output tube, it is a duel triode. So I parallel the two sides together for each channel.
Cathodes pin # 3 and 8 were tied together. From ground I added a 180ohm Tantalum cathode resistor, bypassed with a 470uF black gate cap. This resistor/cap feed the two Cathodes tied together. This will give 12mA to the tube or 6mA per side.
Signal from the digital board is fed to grid pins 2 and 7 – with 120 ohm grid “stopper resistors”
The two anodes pins 1 & 6 are tied together and are connected to the OPT transformer 160 VDC B+ supply coming through a LCLC network from the power supply board.
Very simple design with no caps in the signal path. Works great.
Tom R.
Fantastic... that's somewhere Level 4 ??? in the AN DAC line-up. The parallel 6n1p should sound better than the original SRPP.
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