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Planning a Tube Buffer based on 12Au7

Wharfedale EVO 4.1 4.2 Speakers

Hari Iyer

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This project was on my mind for quite some time and looks like it will find the light of the day. Some background of this project of why i want to go for a tube buffer that too a DIY when many tube buffers are available of the shelf for as low as INR13,000/- + which looks very fancy.

1. Most tube buffer kits available in eBay are not tube buffers so to speak but are some kind of a pre-amplifier with gain and negative feed-back.
2. Kits component quality are shoddy and i pay extra $$$ for a lousy list of components which will be required to be anyway scrapped.
3. Finished products also dont have the flavour of the tubes that i am looking for and are around cheap tubes.
4. I had reviewed many tube CD players like Shangling, Yaqin and the likes and most of them used a tube buffer after the low pass filter to give a tube signature to their CD player. These players are costing 65K+ after considering landed cost which is way above my budget.
5. I already have a decent cd player which i have been using now for 7+ years and already have the BB PCM1796 DIY DAC. The only thing missing in the output stage is a tube buffer which is very easy to design and built. In addition i can now give tube signature to all my source (phono preamp, tapes, DACs, youtube from TV etc.) as i will be using this just before the power-amp.
6. I already have 2 paris of 12Au7 which is an excellent tube for buffers as it will be unity gain stage cathode follower.
7. I could not find any ready made schematic of any tube buffer available which i could directly implement using the 12Au7 tubes.

I finally decided to design my own cathode follower using the 12Au7 tubes with the following details,

1. B+ will be 200V,
2. Cathode current will be 21mA
3. Output impedance will be around 320 ohms
4. Input impedance will be around 1M ohms.
5. Gain will be less than unity around 0.95
6. Heater will be parallel wired with AC voltage.

Attached is the schematic for DIY review. In case of any issues in the same, do let me know.
I am going for a point to point wiring for this project as i want to keep minimum cost for this project and hence avoiding any PCB. Will built a prototype first to check out how this goes and maybe in future built with a PCB.
 

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Hari Iyer

Well-Known Member
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Feb 8, 2010
Messages
3,111
Points
113
Location
Mumbai
After couple of interactions with FM Prem, i may not go ahead with this project to keep the source to amp chain simple and minimum. Will update this post whenever i plan to built one.

Thanks for looking.
 

robin3989

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Dec 30, 2019
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Hello @Hari Iyer sir, hope you are doing well!
I have an integrated amplifier, which is good and there are no issues. Just having an urge to experience the sonic changes tubes bring to the overall sound. And basically interested in adding tubes in the input, as a buffer after the DAC.
I understand that the project didn't take off, but your opinions mean a lot, for me to decide if introducing a tube gear in the input worth it.
I wanted to find designs based on 12AU7, and landed in this thread.
 
Last edited:

tnvijay

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Oct 10, 2014
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Hi,
In my opinion, a tube buffer will sound good if wired as a cathode follower. I assembled a 12au7 cathode follower with a class AA opamp technics circuit. Details in the following link

Also, a 6j1 tube,when wired as cathode follower with high voltage ( yaqin cd2 schematic) also sounded good to me.
 
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