<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 18 Sep 2021, at 7:34 am, Antti Pitkämäki via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">The pitch of the strange oscillation changes when changing filter cutoff frequency, and it ends if the filter cutoff frequency is changed considerably. Also turning down the resonance ends the weird oscillation, after which everything works normally.</span></div></blockquote></div><br class=""><div class="">Antti, a couple of thoughts:</div><div class="">• there’s no garbage anywhere on the filter PCB, you’ve cleaned, inspected etc etc?</div><div class="">• have you been through the calibration procedures for the filter ? (around page 47 in the SM you linked) How does it respond? </div><div class="">• you say there are very specific conditions for the oscillation to start: set those conditions up and examine the VCO and MOD boards as well with your scope. It may seem like it’s the filter board but as you say, unlikely both filter circuits would be faulty…</div><div class=""><br class=""></div><div class="">A</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><img apple-inline="yes" id="73D5FBD8-4F43-41CD-9AF9-10FBBB43ED31" src="cid:CE88D162-EA63-4F7D-BD7F-5852110ACFAF" class=""></div></body></html>