from jhulk on muffwiggler: As a summary, I suggest:
Synthesis Input and Compander
Levels:
R2610 (Potentiometer on front panel)
R2612=39K (to add 6dB of extra gain)
R2659 (Switch ExcMode and S_Mode OFF and Ns_Mode ON and adjust the trimmer R2659 for 1.23VRMS at U2606B output. Pin 7) (R2659 could also be on the front panel)
R2645=20K
R2649=7.5K
R2654=10K*
R2655=1.8K*
C2626=47nF*
R2657=20K
R2656=JUMPER
*PCB's Layout says 100K, 18K and 4n7 respectively. Schematics say the suggested values.
Switches:
C2622=100n
C2623=100n
C2624=100n
(These values attenuate “pops” when switching, these are noticeable when unvoiced signal turns on Ns_mode Switch for example.)
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Voiced/Unvoiced Detector
Filter's Cutoff Frequency:
I placed high-pass filter cutoff at 5000Hz and low-pass filter cutoff at 2000Hz.
R2311=33K
R2312=150K
R2309=56K
R2310=24K
Instability Preamp Protection:
Noise or high frequency oscillations in the preamp section will turn ON the unvoiced section.
To achieve protection to this, I considered to use the channel 17 analysis output instead of the high pass-filter, or convert the high-pass filter in a band-pass filter. However I found a more easy solution:
Place a 470pF capacitor in parallel with R2302 and
R2303=JUMPER
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Speech Input Amplifier
I noticed instabilities in this section.
TONE Network:
U2102A's inverting input has long trace and also it is the center leg of the TONE potentiometer. It will be recommendable take special care of this when assembling the Vocoder to the front panel, like to use a short length and coaxial cable (shell grounded).
A tested and working solution is to place a 100pF capacitor parallel to R2120.
An extreme solution could be bypass the tone section. In this case: do not place all components related (Blue labels on the attached picture) and C2111=JUMPER, R2117=20K, TONE 5 pin connector (pin 2 to 3)=JUMPER, R2120=20K with a paralleled 220pF capacitor. This is by now untested.
Preamplifier:
I'm using the chip THAT1510 instead the SSM2019.
My suggested values are R2101=10R, R2102=10R, R2103=1K, R2104=1K, RG0=OPEN, RG1=5R, RG2=Capacitor Electrolytic 10V 3300uF (will cut about 10Hz).
Limiter:
RLIM =6K
RG3=22K
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this is what was recommended for tuning the pcb
and some one asked about the values for resistors on the pcb values if they were correct and the answer was yes apart from the tuning values above |