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Joachim Gerhard Filter Buffer for ES9022

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#427
Fran got the message. 🙂

Try to build this 100% yourself.
The PCB is easy, anyone can do.
Getting 8 FETs matched is not so simple, especially when they are SMD.
We already did all the difficult work for you.
Then Fran did the rest, making it almost too easy. (Many thanks Fran.)
The rest is also all there in the public.
I think it is not unfair to ask you to help yourself.

It is called DIY afterall ?


Patrick
 
#434
you could use this buffer, but it wouldnt be a very good choice IMO. performance is significantly lower in voltage output.

current sources typically have reasonably high output impedances, current output dacs typically have higher output impedance than the es9018/12/16, which is quite low; (195ohms in 2 channel/stereo mode) so if you present the dac with a next stage input impedance that is even a few ohms, you are already outputting voltage as well as current due to ohms law. and if that input impedance is higher than 195ohms, its ALL voltage, no current.

there is no 'current mode' or 'voltage mode' as some like to put it, only grey areas in between. there is a point where it effectively puts out all current (~3.9ma x 4 per channel at standard operating voltages in stereo balanced) and there is a point where its all voltage (with significantly reduced current)
 
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#437
hochopeper said:
If wanting to use this with ES9012/8 I would have an active IV stage THEN the filter/buffer board.
Click to expand...
why? any decent IV would remove the need for the filter/buffer, so you would be just adding noise, THD and complexity.

not because its a bad design, it isnt, but because its extraneous circuitry and anything added after whats needed adds noise, THD etc.
 
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#438
> why? any decent IV would remove the need for the filter/buffer, so you would be just adding noise, THD and complexity.

That I do not agree I am afraid.

Any IV stage merely converts the current signal to a voltage by the proportional constant R_iv.
It does not necessarily have any additional filtering to remove the digital noise.
Some IV circuits also have an additional RC filter. Our SEN is a good example.
This is actually equivalent to the built-in resistor of the 9022 and the external 4.7n film cap.

So any current-out DAC which uses a first order low pass in the IV circuit can still benefit from the passive filtering Joachim designed.
And because the passive filter is high impedance, you do need a buffer.
Hence this circuit.

Whether you like a simple RC filter, or the additional filtering as preferred by Joachim, is another matter.


My 2 cents,
Patrick
 
#439
It does not necessarily have any additional filtering to remove the digital noise.
Click to expand...
why? any decent IV would remove the need for the filter/buffer,
Click to expand...
I guess it depends on how you define decent. I consider that a decent IV circuit provides an optional low pass filter by default. if I wanted more than RC, I wouldnt add an entire additional buffer, just modify the existing integrated filter.
 
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