Hi, i got my midibox sid working. using the 8580 chip and a c64 psu (optimized).
now i am looking at ms20 filter clones: the filtered coffee from analogue solutions
there is CV in for HPF and LPF, is in the range of +12V/-12V.
what i wonder is if adding an AOUT_LC or an AOUT_NG would allow me to have CVs out in the range +12V/-12V? (or will i need to modify the midibox sid psu also ?)
I have been looking at the AOUT pages, and the AOUT_NG wiki, but i could not find the answer.
more generally should that setup work well with this ms20 clone? i need your advice as i have never used CV before…
i have also been looking at the sid documentation. but i could not find definite references to the voltage range (i saw somewhere +5V/-5V but not +12V/-12V)…
Its set up for ±15 but I think ±12 would be ok also. Someone who knows more about what they are talking about could confirm that. But if you built the sid…you might get more joy by diyin’ the filter also.
The range is stated as 10V maximum =range=, and that range can be shifted around via the configuration to be bipolar, specifically for controlling external filters. I don’t remember the exact offset possible, it was something like -2V to 8V. I don’t remember the page I on which I found the information.
so my question is: for people building the aout in a midibos sid, do they need to build circuit 2 of the bipolar_12v_psu and connect it to the 14V out of the sid optimized psu?
not sure what is a “center tap transformer” mentioned in schema 1, but we don’t have that in a midibox sid right ?
it isn’t possible to drive AOUTs only from a C64 PSU, you definitely need an extra center tapped or at least 15V AC transformer. The C64 PSU only provides 9V AC which is not enough.
regarding output range: with the default values, the AOUT_NG has a max output range of around 0..11V or -5.5…5.5V depending on your calibration and resistor tolerances. But this range only comes from the resistor values chosen for good fine calibration in the popular use cases, i.e. V/Oct or +/-5V bipolar. if you need a higher range, this is possible by calculating a different gain ratio for the TL074s, i.e. using different resistor values.
Another problem: the TL074 amps are not suitable for rail-to-rail voltages, i.e. even with a correct gain ratio, you won’t reach the max/min +12 or -12V value. Maybe ±11V is possible. If that’s enough for your application, then fine. If not, you need to power the NG from a ±15V supply and change the bipolar option’s resistor values, too. Or you use LM324 amps instead that can reach near rail-to-rail operation (but these have slightly higher nonlinear properties and therefore are not a standard recommendation).
so i think i will change my plan and make an external box for the AOUT (and using a 15V psu for it).
so could I use the midibox sid either connected to an AOUT box (to send CV to my external filter) or disconnected from the AOUT ?
sure you could - the core can’t detect if the AOUT is present so it’s no problem to have the driver activated all the time. If there are physically independent PSUs, just take care that both units (and also the external filter) are powered from the same mains outlet to avoid large ground loops.
Sun shines on my Midibox project at the moment, first USB/midi -chip and now this! Separate CV -module - I will adopt this idea right away.
I am just finishing my MidiboxSidv2 and I was about to put the AOUT inside the SID -case. I think I rather do a CV -module with a connector cable to the main unit and stuff all the AOUT jacks, power unit and circuitboard to this one unit rack-case I got from a friend yesterday.
