Tube output for Rotel RCD-971 - diyAudio
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Old 10th August 2015, 02:29 AM   #1
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Join Date: Sep 2008
Location: Pennsylvania, USA
Default Tube output for Rotel RCD-971

This is the story of a lampizator project which kind of got out of control. I had followed Lukas the Fig's instructions and tubed a cheap Pioneer Elite (PD-59 - definitely el cheapo compared to the PD-65) player with an SRPP stage. It sounded good but it was noisy, so I switched over to a Broskie Cathode Follower configuration, which was quiet and beat the pants off the more expensive Rotel RCD-971, which I had modified & thought sounded pretty good. So I looked into tubing the Rotel, thinking I'd do the BCF thing again, but no go - it has two PCM63 chips with single ended outputs. I didn't want to follow Lukas' recommendation of a resistor as an I/V stage, so after some looking around settled on the Pass D1 I/V since it was designed to go with this chip. This requires +/-30V, and I had an extra Salas shunt reg I had bought just in case I needed it. The Broskie Aikido noval stereo provided the tube stage. I wanted more gain since I planned to use it with a Lightspeed clone, and the Pioneer/BCF didn't really have enough output. This is powered with a Salas high voltage shunt reg, which is preceded by a CLC filter using parts left over from aborted projects.

The tubes are PCC88, which are specified for 300 mA heater current (sometimes given variously as anything from 7 to 7.6V) so I wired them in series (had to cut a trace on the Broskie board) and made an LM317-based CCS for the heaters, fortunately out of parts I already had.

Connection with the Rotel is made through silver wires soldered to ground and close to the I out pins of the PCM63 - I just found nearby jumpers to lift. To the wires I attached male RCA connectors I scrounged from a dysfunctional pair of Audioquest interconnects.

The top plate is from Front Panel Express, and my brother did the case. It all turned out OK in spite of all the goofs I made along the way (the more sharp-eyed among you might spot a couple right off the bat). With a pair of Telefunken and another pair of Valvo tubes it sounds great, better than the tubed Pioneer, Hagerman Chime DAC or Lampucera/BCF DAC. And cheap, too, for the sound I got - except for the top plate, which was a little pricey.

Downside? It weighs 26 lb.
Attached Images
File Type: jpg Rotel RCD-971 output top 1.jpg (238.9 KB, 48 views)
File Type: jpg Rotel RCD-971 output top 2.jpg (226.4 KB, 47 views)
File Type: jpg Rotel RCD-971 output case.jpg (175.2 KB, 49 views)
File Type: jpg Rotel RCD-971 output bottom.jpg (283.7 KB, 48 views)

Last edited by schubert; 10th August 2015 at 02:50 AM. Reason: error
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