"improved" standby switch

[pjd3]

Thought I'd just toss this up for discussion and feedback.

While building my 3rd amp (2204 with a few mods) I came across the improved standby switch mod/upgrade. To me, it really seemed like a transforming of the standby switch into a soft start of sorts.
I placed about 50K across the standby switch contacts and added one more diode after the standby switch. It seems as though that the diode after the "standby switch" helps keep the switch within a statistically more AC environment that keeps arcing minimized (as opposed to always seeing a solid high V DC from the big filter caps when switched).

Following this modification and across the 1st filter cap, I measured about 35 volts after 1 second, 70-80 volts after 2 seconds, 150 volts after a few seconds and may around 300vdc or more after 5 seconds or so. As expected, the voltage would instantaneously rise to the B+ voltage upon switching the "standby switch". (about 400vdc)

Well, I was at least left fairly convinced that the PT, Diodes and Main filter caps were no longer seeing an instantaneous low impedance upon power up and hitting the standby switch and thus trying to deliver a stressfully high instantaneous current, that my amp was likely all the better for it, particularly in the long run. Of course, one might ask if there are any drawbacks or unseen prices to pay for any "upgrade" that takes place so, it would very interesting to hear a bit about your take on this modification.

Thanks for your time.
Best,
Phil D

[tmknight]

I've implemented this as well (though sans diode as I use a full bridge rectifier) and I opted for a higher resistor so that you don't get signal bleed-through (a-la Fortin Sigil standby farting drama) - through trials, I settled on 220K to achieve full muting in my circuit.

Merlin discusses this here

[pjd3]

Interesting tmknight.

I had just accepted that I wasn't going to have a full mute condition and was willing to live with that. Others had mentioned about the "fart" syndrome that occurs in the new "standby" condition with 47K ohms but I figured it was worth it.

So sure, if increasing the resistance will get you both a soft start and a full mute then why the hell not. Its very rare that there would a situation where time was at such a premium that I couldn't let the caps leak in for a minute or two.

Thanks, that a good point you've shown.

Best,

PJD3

[Roe]

Interesting tmknight.

I had just accepted that I wasn't going to have a full mute condition and was willing to live with that. Others had mentioned about the "fart" syndrome that occurs in the new "standby" condition with 47K ohms but I figured it was worth it.

So sure, if increasing the resistance will get you both a soft start and a full mute then why the hell not. Its very rare that there would a situation where time was at such a premium that I couldn't let the caps leak in for a minute or two.

Thanks, that a good point you've shown.

Best,

PJD3

agreed but check the voltage rating of the 220k resistor. 350v may not do.

[wpaulvogel]

Adding a bleed resistor to the first filter cap can help with the rise time and “amp on” behavior but it’ll never be completely silent. I’ve done this same addition before. I use a 1Meg across the switch and a 470k bleed resistor.

[W5FH]

I believe you are discussing the standby circuit published by Mr. Blencowe. I have used this in several builds. I have remained with the 47K series resistor. My voltage at preamp nodes is around 130 VDC to 180 VDC from checks in the several builds. Residual sound from amp has not been an issue yet. Not sure why my voltages are lower, my only bleeder is a 220K at main filter cap. I do use a large amount of capacitance in amps, from between total of 100 to 200 uFD in main filter (10 Hy series choke following main filter for secreens and preamp) plus around 150 -200 uFD total for screens/preamp section string.