seppomans building information;ssm2164_pcb
the following informations are take from the midibox forum, its a collection of infos, without the claim to be 100% true, i will try to test the given information.
not found anywhere…
also reverse engeniering/understanding/troubleshooting/moding is nearly impossible when the pcbs are stuffed, because most of the traces are on the component site… or hidden behind the black paint\
— first i want to know for what are those POTs? Input Gain of Audio? or of CV? or some BIAS? seppoman said nothing…
POT P1 middle & right Pin connected to VCC-
POT P1 left Pin connected to a 27K Resistor and this resistor to a nother 27K Resistor which is connected to CV1+ Input. the middle point of this2xresistors is going to the TL74-OP-Amp Pin1 which is a inverting input…
The Output of this TL74 Stage is Pin1: its connected to Pin 6 SSM2164, which is the CV-Input
When i measure Pin6 to Ground, and Turn P1 most left:1,8V… Turn P1 most right: 2,47V
so what does it? no one said: its a zero offset for bipolar cv? or is it gain-control?
+ GND -
J5 is obviously the only connector where you could come to the conclusion that it might have something to do with power supply.Just like the:
AOUT(NG), the 2044 board, the MB_FM module etc, it expects a bipolar power supply of +/- 12 V and GND.
as a general rule of thumb you can assume that everything that doesn't specifically mention a bipolar control voltage will expect an unipolar CV.
In the case of this module, IIRC the dynamic range of the regular CV range (0 .. 11.67V) (uni-polar!) is about 65 dB, with 0V being “silence” and 11.67V being unity gain.
I have never thought about what happens if you apply a negative voltage to the CV input…
Note also that generally a bipolar control voltage (CV) still doesn't mean that there are more than two wires involved,
just the one signal can be above or below GND.
if you followed aout_ng built plan you will get following Stock-CV-Voltages @+-12V PSU:
Uni-Polar CV-Range: 0-11,4V
Bi-Polar CV-Range: +-3V
SSM2164 & Stock AOUT_NG:
As the SSM2164 is UniPolar, and seppoman designed it as a couple with AOUT_NG. stock is ok
SSM2044 & Stock AOUT_NG:
As the CUT-Off-CV is UniPolar, and seppoman designed it as a couple with AOUT_NG. stock is ok
I guess for proper +/- 5V operation I'll have to try out a few other resistor values on the SSM module,
but this will only apply if you if you're using a different CV source than an AOUT_NG.\\
If you need more CV-Range:
for more distortion, drive, range, or other modules:
if you sum two voltages through two resistors of same value, you'll get (V1+V2) / 2 as a result…
R9…R16 > 5.6k (only on the channels that are setup for bipolar mode)
+-3.5V to +-5.8V Bi-Polar calibration range
Pro: easy job, still have a decent precision when calibrating.
Con: “just change the jumpers if you need some channel in bipolar mode” thought will not work. ( really?)
we came to the conclusion that it's probably much easier to have the AOUT only output unipolar 0 to 10 volt, and design a simple -5v level shifter board that can be used as an add-on (or separate module with hands-on access to the level shifting) to shift the output to -5 to +5 volt where needed.
Things to consider are:
- not a lot of equipment actually makes use of negative voltages
- equipment that needs bipolar CV input can be retrofitted with a fixed level shifter at the input to make it compatible with your other modules
- negative voltages can be used for CV modulation purposes (modulate one CV source with another) so it's certainly not useless
R1…R8 > 10k
R9…R16 >2.2k (on all channels). (QUESTION WHY ON ALL? )
+9.5V to +22V Uni-Polar calibration-range
+-2.4V to +-5.5V Bi-Polar calibration-range ( dont think so )
Pro: preserve the “just change the jumpers if you need some channel in bipolar mode” thought behind this option.
Con:dramatically increase the calibration range, i.e. exactly calibrating the outputs will get harder because the same angle of turning the pot will have much more impact.
SSM2164 Pin 1 (the first pin) sets the “Mode”
Pin 1 is Open, no Resistor to +12V (PCB Default)
Lower current results in higher distortion/lower noise.
—i do want distortion and dont care about noise— so i do not change anything, the pcb is fine.
Pin 1 is Connected to +12V via a Resistor
Higher current results in lower distortion/higher noise
lets look in the datasheet:
Figures 11 and 12 show the THD and noise performance of the SSM2164 as the bias current is adjusted
I_MODE = ( (V+)−0.6V )/ RB
1,52mA = (12V-0.6V) / 7,5K
Leaving the MODE pin open sets the SSM2164 in Class AB with 30 μA in the Gain-Core