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Old 18th May 2002, 02:28 AM   #11
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Quote:
The 50K R11 is the attenuator.
Its not a attenuator. It is a regular resistor. The pin two of R11 is unused.
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Old 18th May 2002, 02:42 AM   #12
jwb is offline jwb  United States
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Don't pick nits. I used the symbol b/c its in the library. The attenuator isn't a pot, it's a stepped attenuator with 24 positions, where V+ is connected to GND and V- is connected to OUT. Sound backwards? Think it over for a while.

[ time passes ]

I only need two terminals of the attenuator because it works backwards in this circuit compared to a normal attenuator circuit. With the switch all the way up, I want the maximum resistance, and with the switch all the way down I want zero resistance.
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Old 18th May 2002, 04:29 AM   #13
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Sounds lazy because you didn't draw it correctly.
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Old 18th May 2002, 05:30 AM   #14
jwb is offline jwb  United States
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I'll be sure to report back here if that has any effect on the audio quality.
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Old 18th May 2002, 06:23 AM   #15
tiroth is offline tiroth  United States
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Originally posted by Jocko Homo
Ignore the guy from Pittsburgh. [joke]
Jocko
:P

I've been doing some work on my own variation on the D1 theme if anyone is interested. Nothing special, but closer to normal supply voltages.

link

If the part count seems high, consider that the capacitors are really optional (but a very good idea).
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Old 18th May 2002, 05:58 PM   #16
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The DAC wants to see a virtual ground, and at zero volts. How are you ensuring the latter?

Jocko
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Old 18th May 2002, 08:48 PM   #17
tiroth is offline tiroth  United States
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The design is for a DAC with virtual ground between 0v and AVdd. You could use it on a DAC like the 1704 by making the circuit's "virtual" ground the real ground and adjusting the trimming resistors appropriately.

The diagram is confusing...here is an update:
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Old 19th May 2002, 08:08 PM   #18
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Not quite the way I would have done it. Remember I don't like MOSFETs, especially there. Should work though. Try to get the Z as low as possible. Yes, I know it will work if it is >0, but the lower the better.

(Hint: try a BJT.)

Jocko
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Old 19th May 2002, 08:14 PM   #19
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Default Mosfet

Or you could put some feedback around mosfets gate to source to lower the impedance seen by the DAC. Or you could use inferior sounding BJTs.

H.H.
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Old 19th May 2002, 10:51 PM   #20
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How could you ever listen to those inferior things, Harry.

Jocko
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