Why is the input cap value to PI stages much lower than the FB input?

[nevetslab]

I haven't drawn up the revised circuit on the amp yet. This is the stock Traynor YBA-1A below. I moved capacitor C9 ahead of the Presence Control R6A, with the wiper going to Ground. R20, the bottom of the 'tail' still goes to ground. Traynor labeled the Presence Control 'High Range Extender' The LTPI shown here as still the same as I have, apart from C7, which I increased to 0.1uF from 0.022uF.

YBA-1A Bassmaster MK II.pdf

[pdf64]

The YBA-1AMkII has an additional resistor, R20, compared to the 5F6A, which may address Chuck's query.
Pete

[Enzo]

With the cap in series with it, the presence control no longer has DC across it, so shouldn't scratch. That is what R20 does.

With a pot and cap in series, C9 and the pot, I don;t see how it matters which end of that is grounded. Either way there is no DC path to ground, and it is a simple RC circuit. The DC path is through the parallel resistor.

[nevetslab]

Right.....the 59 Bassman circuit has that as well. I meant to pull that schematic up instead, as its' LTPI IS the same as the Traynor. I had mentioned that in an earlier post on this thread. My oversight.

[nevetslab]

Traynor YBA-1A Power Amp/Pwr Supply Schematic 7.30.14

I've attached a fresh drawing of the power amp & power supply stages of the Traynor YBA-1A MK II as I currently have it built. I haven't made any changes to the preamp section, but also have not drawn it.

YBA-1A PWR AMP PWR SPLY-1.pdf

[nevetslab]

It could be with the original circuit components, that cap attached to the wiper of the presence control was leaky. It was 44 yrs old, but all that got pulled & replaced. I just put the cap ahead of the pot, wired as a rehostat to Gnd, and it's dead quiet. I just posted the current schematic of the mod's Traynor's power amp & power supply section.