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Old 7th November 2011, 12:17 AM   #1
Bicolor is offline Bicolor  Sweden
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Default Tubing Arcam Delta Black Box 3 for fun?

I have an old BB3 laying around and started thinking about doing some mods to it. Maybe it can get a bit better, I sure hope so.

Started reading up on it, got hold of the service manual and quickly discovered that it was a bit too new to have the d/a chip that I really was hoping for, the classic 1541A.

Nope, this beast has dual bitstream dacs, one handling the "left+" and "left-" -signals and the other dac does the same for the right channel.
The signal then passes through no less than five caps to get rid of the noise, and then goes to diffrential amplifiers (lm627) to make the signal single ended. Phew!

If I am going to be mad enough to try to convert it to a tube output stage, where on earth would be the best place to steal the signal? I am guessing after the lm627.

This may be a good moment to laugh, as I am a beginner, but eager to know more.

Maybe just easier to get an older cd to experiment on. But, the BB3 is "free" since I already got it, and there is sufficient room in the box to fit more stuff in it, so why not give it a try.
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Old 9th November 2011, 02:04 PM   #2
poynton is offline poynton  United Kingdom
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I tried a modified version of "Thorsten's" output stage with the Marantz CD63 with excellent results


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Old 9th November 2011, 04:16 PM   #3
Bicolor is offline Bicolor  Sweden
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Thanks for the input! Today I located a place closer to the chips where I can steal the signal. The place where I intended to take the signal in the first place seems like a bad idea, the signal was already amplified a lot there.
Where can I find a schematic? I am a beginner, but I do know how to follow a schematic.
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Old 10th November 2011, 07:38 AM   #4
poynton is offline poynton  United Kingdom
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Usually, the DAC will be a voltage output followed by some filtering before the opamp.
So before the opamp is the place for taking the signal unless you are into filter design.

What are the DAC chips?



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Old 10th November 2011, 09:59 AM   #5
Bicolor is offline Bicolor  Sweden
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They are SAA7321GP. I have located the outputs (two per chip), called INTL and INTR.
Any ideas if it matters which ones I go for? I guess it doesnt really matter as long as I use the same output from both chips so that they dont get out of phase.
Where can I find out if it is a voltage output or current output?
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Old 10th November 2011, 10:48 AM   #6
Bicolor is offline Bicolor  Sweden
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If I have read correctly it is a voltage output.

Anyone with a good schematic?
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Old 18th November 2011, 03:15 PM   #7
Bicolor is offline Bicolor  Sweden
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I have now started this project by removing old rca jacks, drilled holes for the tube sockets. The power supplies are also soldered.
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