<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 25 May 2017, at 17:48, John Speth <<a href="mailto:john.speth@andrews-cooper.com">john.speth@andrews-cooper.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple" style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class="WordSection1" style="page: WordSection1; "><ul type="disc" style="margin-bottom: 0in; margin-top: 0in; "><li class="MsoListParagraph" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">PWM is noooisy.....<o:p></o:p></li></ul><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="">So true. I recently abandoned a design that tried to PWM a vactrol with the intent of "linearizing" response. PWM noise was everywhere. It wasn't worth the expense to try to eliminate it. Another lesson learned.<o:p></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><span style=""> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="">JJS</span></div></div></div></blockquote><br></div><div>I've had different experiences. Perhaps you have to be careful with PWM, but noise "everywhere"? Nope, not at all. Perhaps it depends how the PWM is generated?</div><div><br></div><div>It's a very good fit for vactrols or LEDs. Running a LED from a PWM gives you a good control over the LED brightness without needing some sort of current drive. I've seen circuits where people add an op-amp just to drive an LED, which seems like total overkill.</div><div><br></div><div>I've used PWM for LFO output for years now. Running that to a vactrol controlling op-amp gain gives you a dead-simple tremolo circuit. The vactrol's slow LDR response acts to filter the PWM. You can't beat it for features in few parts.</div><div><br></div><div>Tom</div><div><br></div></body></html>