Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on February 26, 2015, 02:31:57 am
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I was looking up info on the best way to tame standby pop and I found this (see below)
(This is where fender puts their standby switches)
A lot of people feel they're unnecessary?
Steve, on your deluxe lite there's a 220K 2W resistor in paralelle with the first two filter caps, is that to help with popping and make life easier for the choke?
Worst place for a standby switch:The worst place for a standby switch is immediately in series with a smoothing choke: When the switch is thrown one end of the choke is left completely unconnected to anything. Not only is this likely to lead to pop sounds, but the choke will develop a massive fly-back voltage which can cause serious arcing in the choke and switch, and may even break through the choke insulation. This could be allayed by adding a snubbing diode in parallel with the choke (as shown), but this is still a pretty poor design choiice.
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As far as I can know the best form of standby is ............... a mute switch
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A standby switch is better positioned when it is placed after the first filter capacitor
as an improvement you can add an in series diode next to the switch
(a fast one is to be preferred, as an example an UF5408 is better than an 1N5408)
K
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The 'pop' usually occurs because the switch contacts are arcing. Having the choke makes it even worse. Using a good quality switch such as Carling will help minimize the pop and may even eliminate it. I've seen a few attempts to minimize the pop, usually a cap across the switch or a cap and resistor in series across the switch. Sometimes it helps, sometimes not.
You'll have better luck by using a DPST switch to break the PT high voltage leads before they connect to the rectifier socket. The AC voltage is less likely to arc across the switch contacts than the DC voltage.
Do you have two parallel caps for your first filter and are they connected prior to the STBY switch like a typical Fender? If so, moving one of the caps after the STBY switch may help. You can test this idea by temporarily putting another 22µF cap after the switch but before the choke. BTW, that 220K resistor on my schematic is just a bleeder cap to help drain the charge when you turn the amp off. It doesn't help with the pop.
Best of all, just remove the STBY switch. I don't feel they are necessary in a small amp.
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Excellent! out it goes. it was a cheap switch anyway
Thanks yet again
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Excellent! out it goes. it was a cheap switch anyway
I bet a good Carling switch would help.