Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on September 12, 2010, 04:18:52 pm
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Never goes a long time since we discuss about standby and the opportunity to put one in an amp
very often many people say it is not necessary and also it comes with some problems
(we can short the life of a tube rectifier if we place it before the tube, also often on/off action causes pop or other noise)
but many people want a standby switch, so I was thinking if it will be better to use a mute circuit instead of a standby switch
which is your opinion ??
I've seen that in some Mesa they put a mute switch disconnecting the cathode of the PI from ground, but PRR explained me that in that way big spikes will be put in the circuit and that isn't a wanted feature
Some time ago (if I remember well) Geezer discuss about an idea about power lowering connecting the final tubes grids to ground and (also if I remember well) that method give the way to mute the amp if all the grids of the final tubes were connected to ground
Which do you think is a best way to give a mute to a guitar amp ?
Many thanks for sharing your opinion
Kagliostro
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Turn amp's Volume or Gain to "0"?
Turn guitar's volume to "0"?
Have a pedal which mutes the guitar signal and turns on your tuner at the same time? I like that one and plan to build the pedal someday, including switching on power to the tuner.
The setup at the bottom of THIS Page (http://www.freewebs.com/valvewizard1/standby.html) on Merlin's site is interesting. Heaters at 1/2 normal voltage and a trickle of current onto the power rail. If it's not complete mute, it has to be close. Plus it addresses whatever boogie men might make you want a standby switch.
Seems to me that grounding the input to the PI would a perfectly acceptable mute if that's what you want. Single pole/single throw switch too.
If you want to play with a cathode (or power tube cathodes), you could simply put a relatively big resistor in between the cathode & ground. Bypass it for "play", bias the power tubes ultra-cold for "mute".
Respectfully,
Chip
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Thanks Fresh_Start
I know very well Merlin Web site
a very important stone in my knowledge about circuits (I've no study in the matter)
but there are not <mute> circuits options
he largely discuss about <standby>
my actual interest was go on deeper in <mute> circuits options
thanks again
Kagliostro
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Just use a switch to ground the grid of one of the preamp stages.
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Thanks Merlin
So I must use a SPST or a SPDT ? not sure about :undecided:
to prevent pop a large (say 1M) resistor in parallel with the switch ?
Thanks again
Kagliostro
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So I must use a SPST or a SPDT ?
I don't think it matters. Just try to avoid any really long wires leading from the board to the switch.
to prevent pop a large (say 1M) resistor in parallel with the switch ?
That job is already performed by the other resistances that are already in the circuit (gain pot / grid leak etc.)
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Maybe an easy way to mute would be to mount a switch next to the volume control and connect the switch to the volume control wiper and ground lug. You may even want to replace the volume control with a pot that has a 'pull on' switch mounted on the back of the pot. You may even consider just turning the volume down.
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If it's a performance option, i.e. something to shut things up while you're switching guitars, tuning, etc., then you'll likely want it on a foot switch along the lines of what Fresh_Start is talking about. If so, you could use an A/B box in the effects loop. Hook it up backwards so that the signal from the "SEND" loop jack can either be directed to the "RETURN" loop jack in the "A" position or to nothing in the "B" position. That always leaves a possible tuner option or even a path to another audio device, like a power amplifier, direct box, etc., if you decide later you need it. Usually, loops are buffered at least well enough to keep mechanical switches silent. I'd opt for an electronic one anyway and power it from a 9V or external pedal supply with the rest of my pedals. YMMV...
I think daGeezer or somebody else had a good A/B schematic posted here a while back. It may have been a good while back, so try searching and having a look in the Effects section here (http://www.el34world.com/Forum/index.php?board=8.0).
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Many thanks to all friends for councils
I like the the idea to use a pot with a "pull on" switch for volume
the only problem is to find an adequate one
also I like the idea to act the mute via a foot pedal (may be a relay in parallel with the "pull on" switch
Kagliostro