<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Hello,</div><div>I have this lovely Univox JR-5 rhythm machine I have modded with knobs to control the sound mix. The original circuit was high gain but impedance sensitive so it summed current, not voltage and was very </div><div>I added a simple op amp to handle the mix. When power is turned on there is a horrible thump that sounds like it is 100x too loud. </div><div>I have been looking for a simple muting circuit. When I was repairing a Roland MC-909 I saw the muting circuit was little more than a pair of BJTs shorting the signal path. </div><div>I also saw this novel patent which attenuates the signal without much voltage offset, maybe?</div><div><div style="display: block;" class=""><div style="-webkit-user-select: all; -webkit-user-drag: element; display: inline-block;" class="apple-rich-link" draggable="true" role="link" data-url="https://patents.google.com/patent/US4288753A/en"><a style="border-radius:10px;font-family:-apple-system, Helvetica, Arial, sans-serif;display:block;-webkit-user-select:none;width:300px;user-select:none;-webkit-user-modify:read-only;user-modify:read-only;overflow:hidden;text-decoration:none;" class="lp-rich-link" rel="nofollow" href="https://patents.google.com/patent/US4288753A/en" dir="ltr" role="button" draggable="false" width="300"><table style="table-layout:fixed;border-collapse:collapse;width:300px;background-color:#E3E3E3;font-family:-apple-system, Helvetica, Arial, sans-serif;" class="lp-rich-link-emailBaseTable" cellpadding="0" cellspacing="0" border="0" width="300"><tbody><tr><td vertical-align="center"><table bgcolor="#E3E3E3" cellpadding="0" cellspacing="0" width="300" style="table-layout:fixed;font-family:-apple-system, Helvetica, Arial, sans-serif;background-color:rgba(227, 227, 227, 1);-apple-color-filter:initial;" class="lp-rich-link-captionBar"><tbody><tr><td style="padding:8px 0px 8px 0px;" class="lp-rich-link-captionBar-textStackItem"><div style="max-width:100%;margin:0px 16px 0px 16px;overflow:hidden;" class="lp-rich-link-captionBar-textStack"><div style="word-wrap:break-word;font-weight:500;font-size:12px;overflow:hidden;text-overflow:ellipsis;text-align:left;" class="lp-rich-link-captionBar-textStack-topCaption-leading"><a rel="nofollow" href="https://patents.google.com/patent/US4288753A/en" style="text-decoration: none" draggable="false"><font color="#000000" style="color: rgba(0, 0, 0, 1);">US4288753A - Muting circuit with operational amplifier - Google Patents</font></a></div><div style="word-wrap:break-word;font-weight:400;font-size:11px;overflow:hidden;text-overflow:ellipsis;text-align:left;" class="lp-rich-link-captionBar-textStack-bottomCaption-leading"><a rel="nofollow" href="https://patents.google.com/patent/US4288753A/en" style="text-decoration: none" draggable="false"><font color="#A2A2A9" style="color: rgba(60, 60, 67, 0.6);">patents.google.com</font></a></div></div></td><td style="padding:6px 12px 6px 0px;" class="lp-rich-link-captionBar-rightIconItem" width="30"><a rel="nofollow" href="https://patents.google.com/patent/US4288753A/en" draggable="false"><img style="pointer-events:none !important;display:inline-block;width:30px;height:30px;border-radius:3px;" width="30" height="30" draggable="false" class="lp-rich-link-captionBar-rightIcon" alt="favicon.ico" src="cid:52E20B6A-97BA-4365-BFE5-85DFF55E7062"></a></td></tr></tbody></table></td></tr></tbody></table></a></div></div><br></div><div>I really just need to prevent that initial thump. I’ll pick up a relay if that is best. </div><div><br></div><div>Is there an easier solid-state solution? I don’t mind adding another buffer stage at the output.</div><br id="lineBreakAtBeginningOfSignature"><div dir="ltr">Benjamin Tremblay</div></body></html>