Re-Vibe grounding, need your help

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Hauke Holm
Junior tube assistant
Posts: 1
(2/14/04 11:41 am)
  Re-Vibe grounding, need your help
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 Hi There,

I just finished a Re-vibe and I’m happy with the sound, but I get a ground loop problem. :(

I use a DPDT switch to connect the board ground to the chassis, I can lift the ground with the switch (51ohm in series with 0,01uf). All jacks and pots are isolated from the chassis, but even when I connect the ground thru the RC combination the hum doesn’t disappear.

I still get hum with no tubes in all sockets, but there is more hum with the tubes in. If I only put the 6V6 in, the hum increases. I use the negative rectifier turret as main grounding point. I’m sure that the hum source are not the filaments from the tubes. It looks like a power supply problem.

Does somebody has an idea where to connect the grounds to get the problem solved? I think I need a new grounding scheme for my re-vibe.

Looking forward to your suggestions.

Hauke

PS: Please forgive me my small English, I’m still learning….

 
Rotting27
Junior tube assistant
Posts: 111
(2/14/04 1:14 pm)
  Re:
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 Connect ALL the ground together and make sure ALL of them are isolated from the chassis. That means ground lugs on pots, the PT centertap, all jacks--including rca jacks.

In other words look at the project and determine ALL the grounds and isolate them from the chassis, then from any one point, connect that ground "bussing" to your ground lift switch. Then, bolt one wire to chassis ground from the other contact of the liftswitch.

I use this method exclusively and can tell, authoritatively, that this method is incredible at killing ground noise problems.
 
bnwitt
Senior tube assistant
Posts: 284
(2/14/04 1:56 pm)
  Re: Re-Vibe grounding, need your help
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 Or, try one of these:

www.ebtechaudio.com/new.html
 
Hauke Holm
Junior tube assistant
Posts: 2
(2/14/04 1:57 pm)
  Re: Re-Vibe grounding, need your help
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 Thanks Rotting27,

I still have some questions.

I use Dougs board layout, so I have 2 ground buss wires on the board and a pot buss wire which is also connected to the jacks. Should I solder them altogether at the main ground point at the rectifier turret?

So far I connected the main filter caps (C1,2,4) to that point, C3, 5 are soldered to the ground buss there this caps are used. In which way would you setup the "different" grounds in such a project?

I do not have any ground connection to the circuit ground until I use the ground switch. I don't have a PT center tap, is it heplfull to create an artificial center tab, like i do it with the filament voltage?

Thanks
Hauke
 
Rotting27
Junior tube assistant
Posts: 112
(2/14/04 7:23 pm)
  B
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 For your ground lift switch to work...properly, you need to be sure that all grounds are isolated from the chassis, except the ground from one lug on the groundlift switch.

This means that the ground busswire that you have across the pots is almost surely making contact with the chassis. So, disconnect the buss from the pots, then just link from point to point with an individual wire ALL the grounds. Remember they MUST be isolated from the chassis. SO, do NOT solder the ground lug from any pot to its casing or to a busswire that is connected to it's casing. The easy way to tell this is to put the switch on the lift position and check the resistance from chassis to each and every ground point in the circuit. You should get a high reading. A 0 or very low (2 ohms or less) reading will tell you that a ground is in contact with the chassis.

Just wire a wire underboard linking the two busses on Doug's board layout. The way I do it is jack ground to pot ground to next pot ground, one wire from last pot ground to buss ground on the board (which is now one big ground buss), CT from PT secondaries (if there is one) to ground, then the grounds from the filters all tied together and wired to another point on the board ground buss. You get the point. EVERY ground connected together EVERY ground isolated from chassis. Then one wire to the switch, the other lug of the switch is the ONLY wire going to chassis ground.

Also, I would install a three-wire power cord. And connect the earth wire to the chassis. If you have no CT on your PT I assume you're using a FWB, and if so, don't worry about my comments for using connecting the CT to ground.

So, to recap: All grounds isolated from the chassis with 2 exceptions: Earth from power cord, and 1 wire from your groundlift switch. Everything else connected together.

Edited by: Rotting27 at: 2/14/04 7:25 pm
 
bnwitt
Senior tube assistant
Posts: 287
(2/14/04 9:54 pm)
  Re: B
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 Did anyone ever see that Carol Burnett episode where she was complaining to her friend that she felt she was invisible and that no one paid attention to her and while she was telling her friend this at lunch the waiter was taking her friends order and completely ignoring her? Well that's how I feel in this thread.

Edited by: bnwitt at: 2/14/04 11:52 pm
 
Rotting27
Junior tube assistant
Posts: 113
(2/14/04 10:22 pm)
  Re: B
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 Yeah, spend 10 bucks and 30 minutes working on your amp vs. shelling out 100 dollars for whatever the hell that thing is. That's a hard decision for me.

While we're at it, why even build a PTP handwired AC30 when you can buy one from Vox for 4 grand?
 
bnwitt
Senior tube assistant
Posts: 288
(2/14/04 10:32 pm)
  Re: B
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 Ah rotting, your true self......no open mind at all, just the great God of tube. Ahhhhmmmmmmmm.
Yes you could work on every amp you own for that 10 bucks and the 300 bucks of your time it takes to implement until it becomes thousands of dollars, or you could get one of these devices to use for every time you A/B with multiple units and be done with it. Oh yee of narrow mind. Just one more thing..... you started the insults dude, and boy are you so smart.
 
Rotting27
Junior tube assistant
Posts: 114
(2/14/04 10:48 pm)
  Re: B
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 Seriously, what is your problem? I started the insults? So, I took the same sarcastic tone that you started, so now I'm insulting people? Like "yee of narrow mind" and "you're so smart"? Whatever, champ.

The dude was obviously wondering what he could do to solve his grounding problems in terms of rewiring his amp, and by his lack of interest in your suggestion to spend $100 on the Ebtech cureall, and his interest in the way I and several other people on this board ground their amps, I don't think that makes me elitist. I guess using DC referenced heaters, and individual bias circuits for each power tube makes me a real tube asshole?

By the way, have you ever used one of the Ebtech ground-problem-solvers? Do you know what's inside or how it works? Are you positive that it will cure all grounding issues? If so, let us know.

Like I've said before, if someone were building an amp from scratch there is no added time put into implementing the grounding scheme I described. Instead of drilling 3/8" holes for jacks you drill 1/2", then simply wire things differently. The only added cost is 8 bucks for a switch and 2 bucks for shoulder washers and a cap and resistor. Also, I don't charge myself money for time spent on working on my own amps. And if I started doing that, I really wouldn't know how to ascertain the hourly charge. So $300? I think I'd give myself the family-member-discount.
 
bnwitt
Senior tube assistant
Posts: 289
(2/14/04 11:03 pm)
  Re: B
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 You are so funny.
I was just kidding around on the Carol Burnett post but obviously you don't take afront to your guru status very well. Yes I have used the ebtech product. I include one with every amp/revibe unit I sell because of this same problem....so..... about 8 so far just on that. I have also used them with multiple units like a Plexi 50 and a VG-88 in series, the Bassman and a pod in series, a Bassman and a Plexi 50 on an A/B switch, and in fact anytime you use two units together, there is a potential for this ground loop hum thing to happen. Me, I just like tube amps, but, my customers want to marry them with all sorts of crap solid state stuff. For one single purchase of an Ebtech unit ( I have been using the 2 channel hum eliminator for quite a while) a player can fix this problem with lots of dual setups. You need to lighten up bud. Maybe change your handle from rotting to something a little less nasty. Maybe "Ripening" would be a better handle to keep you in a more friendly state of mind.
Cheers
 
Rotting27
Junior tube assistant
Posts: 115
(2/14/04 11:17 pm)
  Re: B
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 More power to you. If buying the Ebtechs and including them for your customers gets the job done, then keep on truckin'.

Personally, I'd chassis-isolate the grounds in my amps and add a switch and save the money on the Ebtech. I'll keep on truckin' this way.

We both win.
 
bnwitt
Senior tube assistant
Posts: 290
(2/14/