Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: acheld on May 12, 2019, 04:20:41 pm
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What is the "best practice" for grounding input jacks?
Referring to the pictorial for the Deluxe Reverb, the ground tab of the 12A jack is grounded via the ground bus.
However, if jack is mounted without insulation, the ground will be established BOTH through the ground bus and through the chassis. To me, this seems not desirable.
Are folks generally using an insulated jack in this setting? Fibre washers? Cliff jacks?
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read PRR's response here
http://el34world.com/Forum/index.php?topic=24680.0;topicseen
I personally bring all my pre stuff to the input jack, the input jack is NOT isolated
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This is how I do my input jacks. I'm not concerned that the jack provides it's own connection to chassis as well as having the sleeve lug connected to the preamp ground buss.
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This is how I do my input jacks. I'm not concerned that the jack provides it's own connection to chassis as well as having the sleeve lug connected to the preamp ground buss.
Better not upset the ground police :icon_biggrin:
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Sometimes the light bulb in my head does turn on. Maybe it takes a B+ jolt to get the neurons firing.
The first amp I built was Doug's Blues Junior, and I love it. Sounds great. I did use fibre washers on the input jack, but all of the pots are chassis grounded as well as through the ground bus. I did not think about it at the time, but it is a very quiet amp.
Sluckey's photo (that is beautiful wiring!) jogged my thinking.
What is the use of isolating the input jack, which is wired to the ground bus, which in turn is wired to the control pots, all of which are grounded via the bus AND the chassis?
I suppose you could isolate all the pots from the chassis . . . LOL, no, I'm not contemplating that.
Anyway, thanks!
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What is the use of isolating the input jack, which is wired to the ground bus, which in turn is wired to the control pots, all of which are grounded via the bus AND the chassis?
I think you overlooked the annotation in the center of my pic. "Pot buss (grounded at preamp ground lug only)". IOW, my pot buss floats above the pots and never touches them.
I soldered the buss to the back of the pots once. NEVER AGAIN! That's a waste IMO.
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NEVER AGAIN!
:thumbsup:
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OK you guys, yes I missed that.
I got it. That makes sense. TY.
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I know this a tad late.... Sluckey, out of sheer curiosity, can you show another angle of how that ground is implemented. Are you twisting the tab to accept the wire?
No worries if this is too late
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The buss is not physically connected to the jack. There is a short solid bare wire connecting the jack sleeve to the buss. The end of the buss is soldered to a ground lug that is secured to the chassis with a screw and kep nut. With that in mind, look at the pic again. I think you will see it more clearly.
Maybe this pic helps...
http://sluckeyamps.com/phoenix/p7.jpg
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sluckey,
May I ask were you acquired those two chassis? Most chassis I can find have the curled-under lip that makes tight work even harder.
Thanks!
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I soldered the buss to the back of the pots once. NEVER AGAIN! That's a waste IMO.
Is that because it’s unnecessary or it causes an issue?
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Soldering the bus wire to the back of the pots is perfectly acceptable.
However, many of us have found that later -- sometimes much later -- when you need to (or just want to) change a pot, it is a pain in the neck. Yes you can deconstruct the bus, but it takes quite an effort to do a clean job of it.
The alternative is to run the grounding bus just "behind" the row of pots as slicker (that is autocorrected sluckey ) has shown you in his Phoenix project.
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May I ask were you acquired those two chassis? Most chassis I can find have the curled-under lip that makes tight work even harder.
Those chassis came from Watts Audio, now out of business for shitting on his customers. Plenty on eBay. Mojo has a 17" chassis.
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I personnaly prefer run the ground bus from the input jack solidly bolted to the chassis. I usually take a ground wire from a length of a 14-2 household wiring. The end of that gnd wire is floating and isolated fromt the chassis and touches nothing else that the input gnd. The pots ground sides are connected to that bus but not the pots casings
The idea of grounding the bus at ONLY ONE SPOT is to prevent ground loops that otherwise would generate hum and noise.
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I usually take a ground wire from a length of a 14-2 household wiring
I did the same for years and it works fine. But another trick I got from Sluckey is to use 17 gauge galvanized electric fence wire - works even better. You can get it in several different spool sizes on that Really Big River place. Like many here, I do not solder to the back of pots and use a terminal bolted to the chassis right near the input jack.
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Wire straightening made simple
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Ciao Tubeswell
that method can be used (with caution) to twist heater wiring together
the use that is done on the video is prone to obtain wires that will broke easily,
so, excuse me, but I don't consider it good practice
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Larry uses a small brass pipe, so he can use it also as a shield for some sensible wires
(https://i.imgur.com/tOztteO.jpg)
(https://i.imgur.com/iN4acvc.jpg)
Franco
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Depends on the quality of the metal in the wire and how fast you twist it. I’ve done this numerous times with pliers and a vice - works okay for me
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Most copper #14, or #12 home use wire is used for a Buss, I would think twisting with the drill would weaken the wire somewhat..?
Why not put one end of say #12 household wire in a vice and hang a heavy weight on the other end, at least 10Lbs or more, let sit overnight.
This will take all the kinks out without twisting the wire, I do this all the time, works great. No vice, use a nail and had a heavy weight.
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ive been using this grounding scheme
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That's the "Larry" grounding scheme for Plexi-style circuits. How's it working out? A lot of guys on the Metro forum swear its the most quiet they've used.
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That's the "Larry" grounding scheme for Plexi-style circuits. How's it working out? A lot of guys on the Metro forum swear its the most quiet they've used.
it works well although i dont run the filament CT to the input ground, just seems silly. i always run elevated heaters with humdinger as well. Some of these jokers attach the input grid coax shield to the v1 plate. i wont risk it