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It is currently 22 Jun 2018, 04:28

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PostPosted: 17 Jun 2018, 17:15 
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Joined: 11 Apr 2018, 21:00
Posts: 5
Location: Niceville, FL, USA
I have started design and construction of a new preamp:
It will have Analog, SPDIF, Bluetooth, and I2S inputs.
Tube design based on the late Fred Nachbauer design for his RA100 tube amp. [http://www.dogstar.dantimax.dk/tubestuf/ampindex.htm].
I am presently constructing the PWB's for the six tubes.
No RIAA phone input will be there, but I want to use the tube-equilivilant OpAmp design of that design as an amplifier for the DAC preamp. I do not intend to attempt to brick-wall filter the 44.1Khz sample frequency, but will "see what happens".

My first boards (the four amplifiers) are complete. I have reversed the board layouts so I can put the tubes on the wiring side, mounted beneath the chassis top. and the components on the bottom. This allows me to hide the components (except the tubes) for a clean look. I shaved a dimension or two to allow it to fit into a 2 inch tall chassis. I am expecting a 12 inch wide, 10 inch deep package.
Trying to use google photos for the first time: Hope this works--I'm a HARDWARE guy!!

https://photos.google.com/photo/AF1QipN ... dMHJH6lNWx


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PostPosted: 21 Jun 2018, 16:31 
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Joined: 11 Apr 2018, 21:00
Posts: 5
Location: Niceville, FL, USA
Here's a progress picture, my layout for the chassis. looks like 10 X 12 X 2 will work. Now selecting the power transformer (s): I don't like the back to back filament transformer from the original design, and want a separate winding for the digital devices anyway. (Thanks to Bruce Heran for the cast aluminum box idea for the power supply). My DIY Pavouk preamp (Black box in the lower left) will be repackaged with a i2S switch between the SPDIF and DAC sections.

I also found that the tone feedback card artwork in the Nachbauer article is incomplete (the poor man was dying of cancer and probably had more important things to do). I had to do some cut & jumps to match the schematic, and also added a miniature DPDT 5V. relay to each board for the tone bypass switching. (couldn't find a suitable 4PDT switch that would have looked good on the front panel). When I have the time I will redo the artwork to reflect what should be etched, but will live with the cut and jumps for my developing project. Going on vacation for a while, so there will be a pause in construction.

https://photos.google.com/album/AF1QipM ... aQW6Y5P4dt


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