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ackcheng 9th January 2004 06:04 PM

Tube output stage for DAC
2 Attachment(s)
Dear all high hand,

I have a kit for CS43122 but I would like to modify the analog output stage to use tube output lilke the picture shown. Unfortuately, the CS43122 output is balanced with Vout+ and Vout-. How should i readjust the ciucuit accordingly?

nonik 9th January 2004 07:19 PM

DAC output with tube

As the output of the DAC is balanced and needs to have at least a 12dB/oct. low-pass
I propose you experiment with a dual triode
( one half for the phase and one for the antiphase output ) followed by another dual
triode that is charged with an output-transformer. ( balanced )
Not a power output transformer !


nonik 9th January 2004 08:13 PM

DAC-valve output
2 Attachment(s)
Did a quick drawing of my idea.
Sorry for the clumsy quality, my CAD had no
symbols of valves so I used OO-draw.


runeight 10th January 2004 03:43 AM

Say, do you want a balanced output from the tube stage or a single ended output?

ackcheng 10th January 2004 03:52 AM

A single ended output as I have RCA only!

ackcheng 10th January 2004 03:55 AM

Thanks nonik for your schematics very much.

agent.5 10th January 2004 04:10 AM

Just use a transformer. No modification to the circuit will be required.

runeight 10th January 2004 05:13 AM

I agree that, if the output voltage is sufficient, a good audio transformer would be easiest. However, if you really want a tube output stage and if you don't mind cathode followers, the circuit on this link will convert from balanced to single ended:

Broske Cathode Follower

If you need gain, it should be easy to add a tube gain stage.

nonik 10th January 2004 11:15 AM

The idea of just using a transformer on the
output is very attractive, as fewer parts could
only improve quality.
However, every DAC needs a low-pass on
its output even if they use digital brick-wall
filters in the DAC.
You cannot rely on the roll-off of the transformer as, a quality audio transformer
could go as far as 100kHz. ( but i assume
that is known by valve enthausiastics )
however the low-pass needed should match
the fs used in your DAC.

So you need to add some passive filtering
wich has to be designed very carefull,
incorporating the specs of the transformer.
Remember that the complex load of such combination together with any load "on the
other end of the output-cable" will directly
charge the DAC-output.

So I would prefer to use some buffer.
A valve as ackcheng asked for.

btw the circuit i proposed is for one channel
and the output does not necessarily be balanced. just tie one end to GND !


fscarpa58 14th January 2004 11:19 AM

The Broskie Cathode Follower is an exceptional performer.

Moreover, with a balanced supply the output condenser can be avoided but, in this case, a bias adj. resistor will be required.


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