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====== AOUT_LC Module ======

{{ :neonking:mbhp_aout_lc.jpg?400 |}}

=====Introduction=====

The idea behind the AOUT_LC module was to **realize control outputs with parts that are easy to get in most countries**. After a discussion with Karl Dalen about the difficulity to find DIY friendly DACs with a serial interface. He proposed these **{{http://www.midibox.org/users/kd/KDdac.pdf|circuits}}**, and the discrete solution was selected because of the simplicity. 
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In difference to the [[AOUT_Module|AOUT]] or [[AOUT_NG]], **this project doesn't require a special (expensive and hard to get) DAC IC**, instead **resistors are formed to a discrete R-2R ladder network**. Building such a circuit means a lot of soldering effort, but as the MBHP is indented as a Do-It-Yourself platform, and not as a commercial product, this argument is very weak. However, **the resistor ladder could be replaced by a DAC with parallel interface** //(see Karl's schematics)//, this would still have the advantage, that the DACs are accessible via a serial chain (-> low number of uC pins are allocated), and that the software driver doesn't need to be adapted for a proprietary interface.
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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 , measure the resistance and take the ones with the best matching values for the ladder circuit.
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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! 

===== Parts List / Schematic =====

see [[aout_lc_board_parts_list|AOUT_LC Parts List]]

  * {{http://ucapps.de/mbhp/mbhp_aout_lc.pdf|Schematic}}<sup>UCapps</sup>

===== Resolution Adjustment =====

In order to increase the flexibility, the MBHP_AOUT_LC PCB provides two different resolution options. The first channel can either be controlled with 12bit or 8bit resolution, the second channel with 4bit or 8bit resolution:

{{ ::neonking:mbhp_aout_lc_res_options.gif |}}

The 12/4 bit option is used by MIDIbox SID (the filter is controlled with 12bit, the resonance with 4bit only).
In the MIDIbox CV firmware the resolution option is selectable. 8/8bit is enough if the module should control V/Oct CV inputs via Note or CC events. 12/4bit should be selected if channel #1 is connected to a Hz/V input, or if high-resolution events (NRPNs, PitchWheel) are desired.
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