VB-2 Ramp Function

[rthryhorysak]

So I was looking at the ramp function that the Boss VB-2 has, and based on the knowledge (or lack thereof), it seems to be a VCA controlling the voltage depth of the LFO. Correct if I am wrong about that, but I wondering about the other part of the ramping. So is that ramp circuit outputting a voltage that completely opens the VCA and the rise pot in conjunction with the diodes delaying that voltage? I am not familiar with anything similar to it so if someone could explain it to me I would greatly appreciate it, and if there is a way to simplify it as well. Thanks

This is the schematic from BYOC, the boss is a little different, but I assume that's because of the bypassing of the boss. Also sorry for the poor quality.

[anotherjim]

D5 and D6 are acting as steering diodes (If I read numbers correct).
With increasing control volts, C26 charges via D5 at a rate set by VR3. When control falls, C26 discharges at a fixed rate via D6.

[rthryhorysak]

D5 and D6 are acting as steering diodes (If I read numbers correct).
With increasing control volts, C26 charges via D5 at a rate set by VR3. When control falls, C26 discharges at a fixed rate via D6.

Ok, interesting, thank you. What is that transistor network on the control input of the VCA?

[anotherjim]

Q10 & Q11 = current sink.
Q12 & Q13 = current source mirrored from Q11.
? That's my guess, I've never seen so much in an OTA control before. Some Boss circuits look like they were trying to clear a surplus of parts, though I'm sure there's a good reason for it really.

[rthryhorysak]

Well this is the BYOC schematic. On the Boss schematic R55 (33k) goes right to the control input of the OTA

[armdnrdy]

On the Boss schematic R55 (33k) goes right to the control input of the OTA

That is because the original Boss circuit uses the BA662 which is very rare these days...

The "extra" transistors are due to making the BA6110 work in its place.
I believe that synth guys working on a BA662 replacement for the x0xb0x came up with this work alike.

[anotherjim]

AH, Thanks Larry.

[rthryhorysak]

On the Boss schematic R55 (33k) goes right to the control input of the OTA

That is because the original Boss circuit uses the BA662 which is very rare these days...

The "extra" transistors are due to making the BA6110 work in its place.
I believe that synth guys working on a BA662 replacement for the x0xb0x came up with this work alike.

Is it possible to use something like an LM13700 or a CA3080 in place without having to rework the BYOC schematic? I cannot find a datasheet for the BA662, but I was reading some forum posts saying the 3080 is a good replacement for the BA662 despite the sonic quality. However, since it doesn't process the audio signal at all, not a big deal, and the 13700 is close to 2 3080s...

[Fender3D]

Ok, interesting, thank you. What is that transistor network on the control input of the VCA?

Maybe this? http://www.diystompboxes.com/smfforum/index.php?topic=117220.msg1088054#msg1088054

[rthryhorysak]

For anyone interested, I picked the Behringer clone and they are using a V13700M for the OTA with the 33k resistor going straight to the Bias Input.