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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Hi Bob,<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Well, there’s theory and practice…<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>In your case, there are two things to consider:<o:p></o:p></span></p><ol style='margin-top:0cm' start=1 type=1><li class=MsoListParagraph style='margin-left:0cm;mso-list:l0 level1 lfo1'><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>There is no such thing as ground<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0cm;mso-list:l0 level1 lfo1'><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>You are making essentially a power amp (big current)<o:p></o:p></span></li></ol><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Point 1) means that you the second you pass any current through a conductor, it ceases to be a ground reference. Point 2) means that you are going to be dumping an amp say (if it’s a decent studio headphone amp) through your ground return – it really will stop being a ground.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Typically if you’ve got a nice metal box, you can treat this as a chassis ground for RFI. Relatively low level currents will circulate around the chassis, and you can tie pin 1 to this OK. The chassis will float to a potential due to the RFI currents, and all of the pin 1’s will mostly be shorted together. Every input can be connected to a differential amp, balanced, or unbalanced, so the inputs are all sorted.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>However, your power amp is unbalanced. If you connect the return of your headphones to this chassis by shorting the output “ground” to the chassis, it will all go Pete Tong, because you’re now dumping 1A through the chassis.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>The current flow goes, 1A through the transformer secondary, ref the 0V of the secondary, via the regulators to the power amp, via the output transistors, via the headphones, back down the return ground. This return ground needs to be connected to two points. 1 to the power amp ground reference differential pin, because the power amp output is referenced to this, and 2 directly to the 0V tap of the secondary, and nowhere else.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>You can connect the return ground to pin 1/ chassis via a 10N ceramic if you want some RFI attenuation however.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Finally, you need to connect your 0V secondary to the chassis at one point, and one point only. This ground partitioning will give you the best RFI and audio performance. Digital grounding is different however. <o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Note mass production often uses ground planes. These are convenient, but do not provide a good analogue ground, especially if you’re dumping any current through them.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'>Hope this helps.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>Kind Regards</span><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='mso-ligatures:standardcontextual'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>Crispin Herrod-Taylor</span></b><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:black;mso-ligatures:standardcontextual'>Managing Director, Crookwood</span></b><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p><p class=MsoNormal><span style='mso-ligatures:standardcontextual'><a href="http://www.crookwood.com/" target="_blank"><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif'>www.crookwood.com</span></a></span><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'> </span><span style='mso-ligatures:standardcontextual'> <o:p></o:p></span></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>Tel: +44 (0)1672 811 649</span></i><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Segoe UI",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>Mobile:+44(0)7910 637 634</span></i><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Arial",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'> </span></i><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p><p class=MsoNormal><b><i><span style='font-size:10.0pt;font-family:"Arial",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>Sign up for our great newsletter </span></i></b><span style='mso-ligatures:standardcontextual'><a href="http://crookwood.com/newsletter/" target="_blank"><b><i><span style='font-size:10.0pt;font-family:"Arial",sans-serif'>here</span></i></b></a></span><b><i><span style='font-size:10.0pt;font-family:"Arial",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>!</span></i></b><span style='mso-ligatures:standardcontextual'> </span><b><span style='font-size:10.0pt;font-family:"Arial",sans-serif;color:#1F497D;mso-ligatures:standardcontextual'>and keep up to date with the audio world</span></b><span style='mso-ligatures:standardcontextual'><o:p></o:p></span></p></div><p class=MsoNormal><span style='font-family:"Segoe UI",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US>From:</span></b><span lang=EN-US> ProAudio <proaudio-bounces@bach.pgm.com> <b>On Behalf Of </b>Bob Katz via ProAudio<br><b>Sent:</b> 02 December 2023 17:21<br><b>To:</b> proaudio <proaudio@bach.pgm.com><br><b>Subject:</b> [ProAudio] Muncy Revisited: Pin 1 to chassis through a capacitor?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p><span style='font-size:18.0pt'>Hi, Pro audio! Happy Holidays from Bob.</span><o:p></o:p></p><p><span style='font-size:18.0pt'>Naturally, I started a firestorm on facebook asking a question about grounding in a headphone amplifier I'm building. </span><o:p></o:p></p><p><span style='font-size:18.0pt'>I made a mistake by forgetting to show the connection between the 0 volt (transformer center tap) and chassic ground... oops, so the conversation went downhill and even after I revised my diagram some people were responding to my first diagram with the error :-(</span><o:p></o:p></p><p><span style='font-size:18.0pt'>I insisted (and still insist) that EMI/RFI interference at the audio input is ameliorrated in Muncy's "rule 2": by connecting pin 1 to chassis directly at the audio input. This is the centerpiece of Muncy's seminal article "Noise Susceptibility in Analog and Digital Signal Processing Systems"</span><o:p></o:p></p><p><span style='font-size:18.0pt'>I know this from experience as well as theory, having successfully installed a microphone preamplifier on the 101st floor of the World Trade Center in 1995 or so. </span><o:p></o:p></p><p><span style='font-size:18.0pt'>Now on Facebook, a genuine expert in power supply regulation design said "that will make the regulator unstable cause it sees every ground current as an error".</span><o:p></o:p></p><p><span style='font-size:18.0pt'>I'm not expert enough to either verify or refute the above statement, but perhaps my response to his statement could be to recommend connecting pin 1 to chassis through a capacitor. </span><o:p></o:p></p><p><span style='font-size:18.0pt'>Would the experts on this group please comment on these thoughts? Thanks.</span><o:p></o:p></p><p><span style='font-size:18.0pt'>I think that this reflector does not permit attachments, so here is a link to my simple block diagram, which is essentially a simplification of Muncy's Figure 1 in his paper if you'd like to refer to the diagram:</span><o:p></o:p></p><p><span style='font-size:18.0pt'><a href="https://crush.digido.com/?u=pro_audio&p=muncy">https://crush.digido.com/?u=pro_audio&p=muncy</a></span><o:p></o:p></p><p><o:p> </o:p></p><p><span style='font-size:18.0pt'>Thanks in advance,</span><o:p></o:p></p><p><o:p> </o:p></p><p><span style='font-size:18.0pt'>Bob</span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.5pt;font-family:"Arial",sans-serif;color:#1C1E21'><o:p> </o:p></span></p></div><div><p class=MsoNormal>-- <o:p></o:p></p><pre><span style='font-family:"3D"Courier"",serif'><o:p> </o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'><o:p> </o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'>If you want good sound on your album, come to<o:p></o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'>Bob Katz 407-831-0233 DIGITAL DOMAIN MASTERING STUDIO<o:p></o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'>Author: <b>Mastering Audio</b><o:p></o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'><a href="https://www.digido.com/">Digital Domain Website</a><o:p></o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'><o:p> </o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'>No trees were killed in the sending of this message. However a large number<o:p></o:p></span></pre><pre><span style='font-family:"3D"Courier"",serif'>of electrons were terribly inconvenienced.</span><o:p></o:p></pre></div></div></body></html>