<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">(Sorry, just saw that the Recom has quite a bit of noise on its output. The CUI P7805B-1000 is a better choice.)<br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 4 Feb 2025, at 23:26, Ben Stuyts <ben@stuyts.nl> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;">One more thought:</span><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><br></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;">There are DC/DC converters with the same pinout as a 7805. So what you could do is:</div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><br></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;">- remove the 7805 and rectifier for the 5V section.</div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;">- Put a DC/DC converter in it’s place, e.g. a Recom R-78E5.0-1.0 (input is 8-28V, output is 5V, 1A max)</div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;">- Wire the input to the +20V input of the 15V section.<br id="lineBreakAtBeginningOfMessage"><div><br></div><div>DC/DC converters are very efficient and can handle the drop from 20 to 5V easily without breaking a sweat. An analog part like the 7805 would dissipate a ton of heat.</div><div><br></div><div>Ben</div><div><br><blockquote type="cite"><div>On 4 Feb 2025, at 23:15, Ben Stuyts <<a href="mailto:ben@stuyts.nl">ben@stuyts.nl</a>> wrote:</div><br class="Apple-interchange-newline"><div><div style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Yes, that should work for the lower part, the +/- 15V section. It can deliver 1.67A when the windings are in series, not 3.34A. But that is more than plenty for this application.<div><br></div><div>For the 5V you need a separate winding, for the reasons Bob explained. You can use a separate transformer for this, it doesn’t need to come from the same transformer. Looking at the schematic, a 5VA or 10VA type should be sufficient.</div><div><br></div><div>Another possibility without an added winding is to add a small DC/DC converter on the +20V line, and pre-regulate it to 8V. A 5W type is probably enough. Feed this into the input of 7805. You could even take out the 7805 and use a DC/DC converter which outputs 5V directly, depending how purist you are. ;-)</div><div><br></div><div>Ben</div><div><br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 4 Feb 2025, at 23:05, Todd Sines <sines_list@scale.la> wrote:</div><br class="Apple-interchange-newline"><div><div fr-original-style="" style="box-sizing: border-box;">I have a Triad VPT30-1670, which is a dual 15V output toroidal transformer at 3.34 A.<br fr-original-style="" style="box-sizing: border-box;">I would think that would work, but maybe I'm missing something?<br fr-original-style="" style="box-sizing: border-box;"><br fr-original-style="" style="box-sizing: border-box;">The schematic is here:</div><div fr-original-style="" style="box-sizing: border-box;"><a href="https://www.synthxl.com/wp-content/uploads/2020/01/Roland-CMU-800-Compu-Music-Schematic.pdf" target="_blank" id="isPasted" fr-original-style="" style="box-sizing: border-box; color: rgb(76, 140, 246); text-decoration: none; background: none; outline: currentcolor; cursor: pointer; transition: color 0.3s; touch-action: manipulation;">Roland-CMU-800-Compu-Music-Schematic.pdf</a></div><br fr-original-style="" style="box-sizing: border-box;"></div></blockquote></div><br></div></div></div></blockquote></div><br></div><br class="Apple-interchange-newline"></div></blockquote></div><br></body></html>