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Re: some i/v options for current output DAC chips (technical sugestions)

Posted by MBK (A) on March 19, 2002 at 18:14:00

In Reply to: some i/v options for current output DAC chips (technical sugestions) posted by jcox on March 19, 2002 at 16:18:02:

>while not difficult for op amps over audio range, ideally the i/v circuit would have low input Z into the MHz range to "soak up" switching glitch spikes, preventing possible intermodulation distortion

>i feel a common misunderstanding of op amp i/v requirements leads to tweakers often calling for ultra hi slew rate op amps, if at least one pole of the image rejection filter is incorporated in the i/v stage there is little need for high slew rate -- lose the glitches don't reproduce them

That was my reasoning too. The circuit lifted from BB appears in app note SBOA046 "IMPLEMENTATION AND APPLICATIONS OF
CURRENT SOURCES AND CURRENT RECEIVERS", page 27, Figure 61; I recalculated for 22 kHz cutoff and the final implementation with values I had handy was: R2=511R; R3=20R; C1=0.01µ; C2=0.22µ

SBOA046 also notes noise gain and the peaking you mentioned, but still eventually a good cutoff at HF.

Now sound wise: I used parts I had lying around: OPA2134 SMD, carbon R, ceramic caps and RS polypropylene caps, haha, (though for HF filtering to GND why not) and it sounds decent, very dynamic with very good bass BUT a bit "bland"; then again downstream sits a Rotel integrated amp used as a pre whose headphone out feeds my active speakers; so maybe that solution achieves a resolution I am unable to appreciate with the compromised "pre" solution. The simple resistor solution, albeit with 20R, so outside compliance V, had sweet imaging and microdynamics but awful transients, no highs and no bass.

MBK

• BB application note SBOA046   (Open in New Window)

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