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PostPosted: 18 May 2019, 21:13 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Continuing my Wood Cheek series (seven in all and still have five) here is an assembled but not fully wired hybrid headphone amp. 4SU front end and OPAMP (like CMoy) backend. External PS is complete with three voltages; HT, filament and B+ for the OPAMP section.
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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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PostPosted: 24 May 2019, 20:04 
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Location: Australia
Here is a shot from underneath and some updated outer images. I wired the first socket wrong so added another and rewired it to the first correctly this time. Apart from a few poorly soldered socket pin connections on the second socket the amp worked perfectly. The limiting R to the 6V reg has been finalised to 1K which puts just under 10V on the input to the reg to give me a steady and overly well filtered 6.02V at the PT2308. The chip max V is 7V. Chip (Class AB) draws 12mA.

This is the best piece of audio gear I have ever built in 50 years of this hobby. My second pick would be the recently constructed Chuguang 6SN7 50 year treasure, active load, preamp ("Icon"). The preamp outperformed the far more expensive Elite with its PsVane Globes.

With the inputs shorted and my new meter on 200mV scale (displays in RMS) I got 0.0uV of noise on the output with pot (blue velvet) fully open. On my Sennheiser 700s there is no hum, hiss or noise of any kind. The blackest blacks. The current tube is a new Tung Sol gold pin which when flicked has NO ringing at all. Great tube and a pair have sat in the draw years. Music through the amp and 700s is absolutely sublime. I just forget I'm on phones and get totally lost in the music. This amp beats the last two all tube HP amps - Sanctum and Sanctorum absolutely hands down. Stunning is the only word to describe the music. Gain is more than sufficient when you consider in the 4SU stage there is no Ck(s) and the chip stage only has a gain of 3db.

The external PS has a triple Pi choked (5H Hammond) filtering stage; C-L-C-R-C-R-C. There is over 400uf for high voltage caps for filtering. Last cap right at the tube section is a 4uf PIO (snubbed). Very clean DC (near 10,000uf of Pi filtering) on the filaments and triple filtering and regulated DC to the chip. All LESR caps on the chip and the poly output cap from the tube section is fed direct to the chip. Pots on the front so no input on the chip I just share the output cap of the 4SU stage. There is a 100uf LESR output cap from the chip. I thought of a NP but way to big and I'm not sure it would have improved the sound. Very, very happy.

I could go on...

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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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