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Old 24th February 2004, 05:54 PM   #1
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Question tube buffer for TDA1543 based dac

Hi to all!

Did anyone tried to add tube cathode follower or something with tubes to the CS8412 and one TDA1543 dac after the IV resistors and coupling cap?

I am strugling to open my dac in highs for months and now I think I might try to add some tube buffer at the end. Maybe some White cathode follower or something. I could use 5687 or 6DJ8 for that.... Any ideas...
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Old 24th February 2004, 10:18 PM   #2
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Hi,

Quote:
I am strugling to open my dac in highs for months and now I think I might try to add some tube buffer at the end.
You mean you'd like to add some "sparkle" to the highs?

A buffer's not going to help here...

Quote:
CS8412
IME that's more likely to be the cause + possibly some lousy coupling caps along with it.

Cheers,
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Old 24th February 2004, 10:32 PM   #3
EC8010 is offline EC8010  United Kingdom
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I think you may be trying to polish something unpolishable. The CS8412 could well be responsible as it's an early receiver chip. Further, I'm afraid that if you read the data sheet for the TDA1543, you will find that it is distinctly second-rate.

On the other hand, if you want to learn about how to tack a valve stage onto the back of a DAC, then an unfortunate accident won't cost you much, and the experience would be valuable later on if you use some more recent DAC chips.

Note, however, that the TDA1543 (and 1541) won't tolerate much of a voltage at their outputs before their distortion rises. You're not so much looking for a cathode follower as an MC input stage (without RIAA, of course).
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Old 24th February 2004, 10:35 PM   #4
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Hi,

Quote:
You're not so much looking for a cathode follower as an MC input stage (without RIAA, of course).
IOW, a valved I/V convertor. A prime candidate for that line of work is the obiquitous E88CC/6922 IMHO.

Do not use the USSR 6N1P here, it's not the same valve at all.

Cheers,
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Old 24th February 2004, 10:56 PM   #5
Jax is offline Jax  Sweden
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Has anyone tried a grounded grid I/V here?

Sum the bias and DAC currents at the cathode, voltage out at plate.
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Old 24th February 2004, 11:03 PM   #6
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Hi Jan,

Quote:
Sum the bias and DAC currents at the cathode, voltage out at plate.
That's another possibility but I can't say I've seen this done yet.

Have you done this?

Cheers,
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Old 24th February 2004, 11:29 PM   #7
Jax is offline Jax  Sweden
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I have been pondering about it. I have a bunch of PCM63 K-grade and they are a good candidate for an experiment.

I have a bunch of direct heated pencil tubes laying around like 6286 and 1AD4. Triode connected of course.

DCC90 would be another sleeper.
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Old 24th February 2004, 11:32 PM   #8
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by fdegrove
A prime candidate for that line of work is the obiquitous E88CC/6922 IMHO.
Exactly. And the more gm, the merrier.

Quote:
Originally posted by Jax
Has anyone tried a grounded grid I/V here?
It looks attractive until you wonder where the cathode current goes. I expect that's why we haven't seen one yet. (Cue: Loads of outraged posts saying, "I've done it, and it works.")
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Old 25th February 2004, 08:11 AM   #9
Jax is offline Jax  Sweden
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Quote:
Originally posted by EC8010
It looks attractive until you wonder where the cathode current goes. I expect that's why we haven't seen one yet. (Cue: Loads of outraged posts saying, "I've done it, and it works.")
Sounds like a challenge then

The problem is that the DAC current comes from its reference voltage source.

Or use a tube with antimatter electrodes where positrons are flowing

Anyway, a cathode follower with 6922 with its cathode resistor tied to a negative source should suit the 1543 well I think.
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Old 25th February 2004, 06:03 PM   #10
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Hi all!

I know that 6N1P is not hte same as 6dj8 but it is not bad tube...
Maybe to use it like this?
Vref is measured from my dac that is currently working- not right as in datasheets but o.k.
daniel
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