Hard sync issue?

gdavis · Posted: Sun Nov 03, 2013 10:18 pm Post subject: Hard sync issue?

I'm trying to use the saw output of one VCO into the hard sync of a second VCO. I'm trying to makes it switchable through a DG413 (mosfet switch).

If I configure the switch to simply open or close to connect the output to the input, when the switch is open I apparently get a small amount of bleed-through that causes the two VCO's to sync up intermittently.

If I configure it to switch the sync input between the saw output and GND, when GND is selected it drops the output of VCO 2 by about 2V and pitches it up a bit.

I suspect that the second issue has something to do with putting R17 and R18 in parallel to ground, throwing off the switching threshold of the comparator, but I'm surprised the affect is this pronounced.

Any idea how I can implement this feature without adversely affecting the output?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

How do you power-up your DG413 ? Remember that the saw oscillates between a negative and a positive value, you must also power the DG413 with a negative and a positive voltage.

gdavis · Posted: Tue Nov 05, 2013 2:14 pm Post subject:

V+ and V- get +/-15V and VL is connected to another 5V supply. GND is common between all supplies.

I was just thinking, would I even need both of the 10K resistors? I can understand why you'd want that in a modular where the patch cord will be inserted or removed. But in my hard-wired system, could I just have one 10K resistor from the switch to the comparator and have it be switched between either the saw output or GND?