Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: markmalin on September 04, 2026, 02:41:53 pm

Title: Is the ground reference for Presence the preamp or power amp?
Post by: markmalin on September 04, 2026, 02:41:53 pm

Hi, all


I'm building Robinette's 1 Watt Soldano SLO (schematic attached).  In my chassis layout I want to attach the presence control's 4k7 Ohm resistor and 0.1uf cap directly to the ground bus of either the preamp or power amp.  It's just not clear to me which is best for its reference point (ground).  My thought is the power amp's ground bus because it's close to the PI circuit.  Can someone shed some light?


Thanks
Humbly,
Mark

Title: Re: Is the ground reference for Presence the preamp or power amp?
Post by: pdf64 on September 04, 2026, 03:00:41 pm

Quote from: markmalin on September 04, 2026, 02:41:53 pm

... the presence control's 4k7 Ohm resistor and 0.1uf cap ...

That, and the OT secondary common, are the 0V reference point for the power amp NFB loop.
Merlin's document on the topic is fantastic https://www.valvewizard.co.uk/Grounding.pdf
If something there doesn't make sense, many Modulus layouts show how Merlin's principles can be real world implemented https://www.mediafire.com/file/yj9xfz7l2wx1dc8/DF_Mrs_Layout.pdf/file