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<P CLASS=DESC>Regarding the quality of the "discrete DAC" outputs it should be mentioned, that it directly depends on the chosen resistors. The tolerance should be 1% or lower (Metalfilm) and stable over the typical temperature range. The results can be dramatically improved by selecting the best matching resistors: just buy a set of 100 pieces (e.g. at <A HREF="http://www.conrad.com" TARGET="_blank">Conrad</A>: a set of 100 * 10k metalfilm resistors for 1.33 EUR, part number #408280), measure the resistance and take the ones with the best matching values for the ladder circuit.</P>
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<P CLASS=DESC>Regarding the quality of the "discrete DAC" outputs it should be mentioned, that it directly depends on the chosen resistors. The tolerance should be 1% or lower (Metalfilm) and stable over the typical temperature range. The results can be dramatically improved by selecting the best matching resistors: just buy a set of 100 pieces (e.g. at <A HREF="http://www.conrad.com" TARGET="_blank">Conrad</A>: a set of 100 * 10k metalfilm resistors for 1.33 EUR, part number #408280), measure the resistance and take the ones with the best matching values for the ladder circuit.</P>
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<P CLASS=DESC>Another typical problem of cheap DACs (not only of this circuit, but also for cheap integrated DACs) is, that there is some "zipper noise" each time a new voltage is selected. The intensity of this noise depends on the bits which are toggled when a new voltage is selected - the leftmost bits (most signifigant bits) will produce the highest zipper noise. Even I can see this noise on my scope, I haven't noticed an audible effect with a discrete Moog- and CEM3378 filter, yet. Also CV controlled Korg MS-20 oscillators are working well with it. However, this is an explicit warning for those who expect perfect results! The zipper noise can be completely eliminated by adding a S&H circuit behind the DAC. By using the <A HREF="mbhp_shx8.html">NJU7304</A> this would also increase the number of available channels - on the other hand this solution requires once again a special IC or a lot of additional discrete ciruitry - it's a disaster! :-/</P>
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<P CLASS=DESC>Another typical problem of cheap DACs (not only of this circuit, but also for cheap integrated DACs) is, that there is some "zipper noise" each time a new voltage is selected. The intensity of this noise depends on the bits which are toggled when a new voltage is selected - the leftmost bits (most signifigant bits) will produce the highest zipper noise. Even I can see this noise on my scope, I haven't noticed an audible effect with a discrete Moog- and CEM3378 filter, yet. Also CV controlled Korg MS-20 oscillators are working well with it. However, this is an explicit warning for those who expect perfect results! The zipper noise can be completely eliminated by adding a S&H circuit behind the DAC. By using the <A HREF="mbhp_shx8.html">NJU7304</A> this would also increase the number of available channels - on the other hand this solution requires once again a special IC or a lot of additional discrete ciruitry - it's a disaster! :-/</P>
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<P CLASS=DESC>For those who don't feel disappointed yet, here two audio examples which demonstrate which results can be expected when the AOUT_LC module is connected between a MIDIbox SID and a CEM3378 filter: <A HREF="http://www.midibox.org/forum/index.php?topic=5538.0" TARGET="_blank">Forum Posting #1</A>, <A HREF="http://www.midibox.org/forum/index.php?topic=5633.0" TARGET="_blank">Forum Posting #2</A>.</P>
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<P CLASS=DESC>For those who don't feel disappointed yet, here two audio examples which demonstrate which results can be expected when the AOUT_LC module is connected between a MIDIbox SID and a CEM3378 filter: <A HREF="http://midibox.org/forums/topic/5158-cem3378-filter-first-impressions/" TARGET="_blank">Forum Posting #1</A>, <A HREF="http://midibox.org/forums/topic/8846-cem3378-schematic/?p=67098" TARGET="_blank">Forum Posting #2</A>.</P>
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