A Ground and Offset Voltage problem ......

Rykhaard · Joined: Sep 02, 2007 Posts: 1290 Location: Canada

Wow. Have I run into a problem that I have no clue for sure, as how to solve. Sad

I found yesterday, that I had a 17-20mV offset between ALL of my 4 step Semitone Sequencers and my single 4 step Octave Sequencer. Sad

In mapping everything out yesterday, each of the Semitone Sequencers has the exact same circuitry. Except for the Initial Voltage from the Voltage References, so does the Octave Sequencer. (Same as the Semitone Sequencers.)

But - in checking the Ground plane on the Semitone Sequencer's PCB and the Vertical Sequencer's PCB - both of their Ground planes (connected together)n showed a 20mV Offset, as compared to the Ground plane from the VCO (close to the +/-15V power supply) that I am pulling Ground from, for my audio output, at the moment.

20mV difference between 2 points of Ground??? scratch

I changed the VERY long (about 8 feet) power cable for the Semitone / Vertical Sequencers pair, to a 3 foot long cord. No change in the mV offset. scratch

I used a pair of alligator clips to connect the Sequencer's Ground plane pair, directly to that VCO that's closest to the power supply. This, dropped the mV offset to approximately 6mV.

But - why an offset STILL??? I am completely stumped - having nowhere nearly enough theoretical knowledge, as to Ground planes and their troubles. Sad

Every single PCB that I make myself, has a Ground plane around the ENTIRE PCB. I don't know if this could cause a problem in any way.

Off on another problem - today as well - I've noticed that 2 of my 4 VCOs are sporadically drifting over quite a few semitones, at an unpredictable rate. I'll track that one down myself later. My main concern right now - is the mV Offset between different areas of Ground. Sad

Oh yeah. And when I hooked up the new power cord to the Semitone / Vertical Sequencers, I hooked it up to the Digital Only, +/-15V power supply. (Who's Ground itself, is connected to the Analog Only, +/-15V PS.)

Thoughts, anyone? Greatly appreciate any tips / eye openers on this one. Surprised

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

perhaps put this in the DIY section rych