<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="">Agreed, can you post a screenshot of your sim somewhere?<div class=""><br class=""></div><div class="">Thanks,</div><div class="">Tom</div><div class=""><br class=""><div class="">
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">==================<br class=""> Electric Druid<br class="">Synth & Stompbox DIY<br class="">==================</div></div>
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<div><br class=""><blockquote type="cite" class=""><div class="">On 17 Mar 2020, at 18:13, Neil Johnson <<a href="mailto:neil.johnson71@gmail.com" class="">neil.johnson71@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="">Too many words, need picture :)</div><div class=""><br class=""></div><div class="">Cheers</div><div class="">Neil<br class=""></div></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, 17 Mar 2020 at 17:23, Ben Riggs <<a href="mailto:benalog1977@gmail.com" class="">benalog1977@gmail.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi all,<br class="">
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I’ve been playing with differential driver circuits as part of a larger synth circuit I’m working on to seek a simple solution, what I’ve come up with just seems wrong but the sim has it working exactly as I need.<br class="">
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To start, I played with 2 cross-coupled input stock-standard differential op-amp circuits, then adding the “Superbal” feedback to both inverting and non-inverting, then I ended up playing with the MCI cross coupled output driver to reduce parts-count (drv135). With the MCI circuit, all reference to the output resistor of the MCI in my research was about output impedance (being quasi-floating was for short circuit current when one input was tied to 0V), I recall in other reading years ago it was also to reduce the cross coupled gain below 1 for stability, but then in another ESP article Elliot compensated for the loss in gain?? I’m not interested in the quasi-floating aspect and won’t be tying either output to 0V so I dropped that output resistor. Then I realised that the cross couple non-inverting resistor divider is (basically) in parallel with the inverting Rin/Rf on the visavi cross coupled op-amp so I reduced them and ended up with 2 basic inverting amplifiers with the op-amp inputs cross tied directly. A resistor tied from each output to ground to keep the output symmetrical, 2 op-amps and 6 resistors.<br class="">
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I hope that description makes sense.<br class="">
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The sim has 1V differential in = 1V differential out, 1V single ended in (one input tied to 0V) has symmetrical .5V on the non-inverted and -.5V on the inverted. This is exactly what I need!<br class="">
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It just seems wrong, and I’ve tried deliberately unbalancing the whole circuit in the sim, interchanging mix-matching op-amps and deliberately mismatching resistors but I think the SIM is failing me.<br class="">
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Is this actually a “stable” circuit, or is the simulator just telling me what I want to see? Surely life isn’t that simple..<br class="">
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Regards,<br class="">
Ben.<br class="">
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