Schematic Overview:Voltage Controlled Amplifier
Inputs:
VoltageControlledFilter Audio
EnvelopeGenerator Gate
EnvelopeGenerator Envelope
EnvelopeGenerator Accent
Outputs:
HeadphoneAndMixer Audio
The BA6110 comes in SIP and DIP (BA6110FS) packages. The x0xb0x ships with the SIP version, but the DIP pinout is provided for reference in case you need to replace it, and you can't find the SIP.
| SIP | DIP Pin | Function |
|---|---|---|
| 1 | 1 | Positive Input |
| 2 | 3 | Negative Input |
| 3 | 5 | GND (input bias?) |
| 4 | 7 | Control Signal (envelope) |
| 5 | 9 | GND (Vcc) |
| 6 | 11 | unbuffered VCA out |
| 7 | 12 | buffer input |
| 8 | 14 | buffered output |
| 9 | 15 | PWR |
the vca envelope generator is created by this same pulse and by the gate signal created by q36
the gate signal merely turns on the vca circuit
the pulse signal generates the attack and decay via q32 and q31
q31 creates the current that controls the amplitude of the vca
q1 through q4 are merely current mirrors to reflect this current appropriately to the 6110 since it is different than the 662
The output of the BA6110 is a few dB hotter than the BA662, I measured as much as 5dB. If using the BA6110 changing R155 to 100k will give the same performance as a tb-303. There will still be some distortion with higher settings of volume and accent - the tb-303 does it too. Or you can simply turn down the volume control down until it doesn't clip (the 'mixer' stage is after the volume control).