First Build, 5E3, strange problem, help please

[dai h.]

Hey thanks guys. I ran shielded cable from the first volume pot to pin 2 of V2.
grounded just on the volume pot. No real change.

The whole grounding thing has got me confused. I grounded it the way you see it on advice from Hoffmans web site,

http://www.el34world.com/charts/grounds.htm

Apparently, it is not the way to go. Changing it is no real problem and worth a try.

the way as described on the Hoffman site probably works fine. If you notice where it says "1, 2, (and) 3" if you put your preamp filter(s), or your "3" points along with the "1", and "2" points you didn't do it the same way as shown in the diagram.

[cfidave]

Yeah, I think I understand where I went wrong. Here is what I am going to do:

1st power supply filter cap ( the one closest to the PT) to be grounded to PT lug.

2and or middle filter capacitor grounds to buss bar ( which grounds to backs of pots)

3ard filter capacitor, closest to preamp tubes, grounds to buss bar

Power tube bias supply ground, goes to buss bar

Green AC from plug, goes to PT lug

Center taps go to transformer lug, ( actually I have the heater supply center tap ground, going to pin 8 of a power tube) to elevate the heater supply.

Of course all the grounds from the preamp side of the board are at the buss bar as well. I really have trouble getting my head around this whole grounding issue, thanks much for everyones patience. If any of the above is incorrect please let me know.

[Mandopicker]

Beautiful job. (I apologize for chimming in so late, but the topic is quite interesting.) Even the grounding looks sufficient to keep it quiet...IMHO.

But looking at one of the photos myself, I can't help but think about something G. Weber writes about in one of his books related to Deluxe amps.

It has to do with the location of the input jacks relative to the capacitors on the board and an oscilation that can occur. Your situation doesn't exacly fit the description, but consider this...

Perhaps when inserting a cable into the jack, the hot side looks as though, it moves slightly closer to the solder joints on the board. In the photo it looks like this is the area over top of the 2 x 68k resistors.

You might try rotating the two jacks closest to the board so that the hot lead is as far away from the board as possible.

May not solve the problem but seems like a resonable experiment.

Good luck.

[bnwitt]

You cannot go wrong with a Hoffman grounding system especially if you couple it with a Hoffman layout. You also cannot go wrong sticking to the Fender layout with grounding plate. Either one of these makes a pretty quiet amp. The Hoffman layout and grounding scheme makes a dead quiet no hiss no hum amp. You have something wrong for sure. Since you have chosen a Fender board layout, stick with the fender layout 100%. Do it exactly like Fender and you will have a quiet amp. I think the real problem here is you have mixed two different layouts and have created ground loops.

[cfidave]

Mandopicker, I think you may be on to something. After moving around the grounds as recomended, no change. I do not think I have a grounding issue. What I did notice was that the tip of the jack is very sensitive to noise. I plugged the guitar in, amp on, and moved my finger close, but not touching the tip of the input jack. The hum got louder in volume, the closer I got to the tip. I also noticed I am not getting near as much hum & noise on the other jacks.

I decided to pull the board and check all the jumpers under the board, just to make sure I did not have a broken wire or short. I am in the process of putting it back in. I will try moving that jack so the the guitar cable tip is as far away from the 68K's as possible. Thanks again to all who have made suggestions, great forum, I am learning a great deal.

[bnwitt]

Well let me tell you what I see. I see 1 of 4 input jacks grounded to the grounding buss across the back of the pots and the other 3 simply grounded by there face contact to the chassis. If I'm not missing some hidden wires, then that is a perfect set up for ground loops. You should either have no buss bar at all or the buss barr should connect the remaining three inputs as well and then have a wire to the chassis from the jack end. This is what I meant when I said you have mixed two grounding schemes.

[cfidave]

bnwitt, thanks. If I did what you say on the jacks, wouldn't I have to use isolation washers on the jacks? It would seem to me that all the jacks would still see ground through the chassis, since they are chassis mounted.

[bnwitt]

bnwitt, thanks. If I did what you say on the jacks, wouldn't I have to use isolation washers on the jacks? It would seem to me that all the jacks would still see ground through the chassis, since they are chassis mounted.

No. With the grounding buss connecting all pots and jacks and then going to the side of the chassis you have a parallel ground with the face contacts but it doesn't produce ground loops anymore than the brass plate does. I have built over a hundred amps with the Hoffman/Marshall ground buss assembly and never had a ground loop issue. That being said, if your amp is completely quiet with no guitar plugged in I don't think your problem is a ground problem. I would think something is wired wrong at the jacks. But the pictures look good. Is it possible you have a bad guitar cord? Have you tried the amp in another room?

[cfidave]

No. With the grounding buss connecting all pots and jacks and then going to the side of the chassis you have a parallel ground with the face contacts but it doesn't produce ground loops anymore than the brass plate does. I have built over a hundred amps with the Hoffman/Marshall ground buss assembly and never had a ground loop issue. That being said, if your amp is completely quiet with no guitar plugged in I don't think your problem is a ground problem. I would think something is wired wrong at the jacks. But the pictures look good. Is it possible you have a bad guitar cord? Have you tried the amp in another room?

I think I understand. I will try the jack grounding scheme you recomend. I checked & re-checked the jack wiring, I don't think that is the problem. I also tried several guitar chords & guitars, and different room locations, with no change. Just for the heck of it I put isolation washers on the #1 bright channel jack, and then ran its ground to the buss, with the current jack grounding scheme. It quieted down considerably. I think there might be a ground loop as you suggested. I also noticed that the #2 bright jack, the one that is directly grounded to the buss, is much quieter ( I know it is about 3db less volume then the #1), with far less hum.

[bnwitt]

just connect the other three jacks' ground lugs to the buss and then connect the buss to the chassis somewhere.

[Mandopicker]

Cfidave,

Here is another thing that I do... (Remove the 68k's, wires to the jacks, and wires connecting them to V1 from the board and replace with shileded cables and attach the 68k's directly to the socket.)

Get some real nice 2 lead shielded beldin cable for each pair of input jacks. Then tie two new 68k's together at one end for each pair of jacks. Now mount the joined end directly at the tube socket. Then connect one each of the two leads of the shielded cable to one end each of the resistors. Connect the other ends to the jacks and the shield to one of the input jack ground lugs. (Do this for each set of inputs.)

This works great and also eliminates any popping or interference that one might get from switching in effect boxes.

Continued luck to you...you'll get it!

[hasserl]

You cannot go wrong with a Hoffman grounding system especially if you couple it with a Hoffman layout. You also cannot go wrong sticking to the Fender layout with grounding plate. Either one of these makes a pretty quiet amp. The Hoffman layout and grounding scheme makes a dead quiet no hiss no hum amp. You have something wrong for sure. Since you have chosen a Fender board layout, stick with the fender layout 100%. Do it exactly like Fender and you will have a quiet amp. I think the real problem here is you have mixed two different layouts and have created ground loops.

Well this is not the first time someone followed the grounding scheme from the Hoffman site, or a star ground system, and posted here about noise issues.

This is a simple amp, and the simple Fender layout with the brass plate simply works. Use it.

[bnwitt]

Well let's be clear about two things my friend. This grounding scheme was not a Hoffman but an incomplete Hoffman. Big big difference. Secondly, a Hoffman grounding scheme is not a star ground scheme and Mr. Hoffman hates star ground schemes. you obviously need to do a little more research on the subject. And I'll say one more thing, I'll put my Hoffman layout and grounding scheme up against any brass plate Fender layout for quiet operation and kick The Fender's tail. I have a strange feeling you've never built a Hoffman layout/ground scheme amp. I've built 40 plus and every owner is amazed by how quiet they are. You should give it a try. No offense intended, just telling it like it is.

[dai h.]

that page on the Hoffman site looks more to be a description of "typical grounding" rather than a "Hoffman grounding scheme", so I think there is a misunderstanding there.

also, it matters less whether you use a buss, the brass plate, stars than hooking up the grounds correctly irregardless of the exact physical connections. If the grounds are done correctly, it'll work and it won't work if they aren't. I think it's that simple. A lot of people from what I observe don't really understand what is going on and are just copying (and mis-copying portions or maybe even a whole in cases) so maybe it shouldn't be a huge suprise when things turn out less than they should be. Not everyone wants to take the time to learn how (which I think is okay though perhaps not ideal) so (if you find yourself in this situation) I would try to copy something that is definitely known and confirmed to work (and probably a scheme where the points for the physical connections are shown very specifically). Also part of why grounding schemes cause problems for DIYers may be be due to physical layouts (factory Fender ones, etc.) not showing exactly how the grounds are connected physically in the chassis.

if anyone does want to learn more there is certainly no dearth of info on the subject(if you search), and IMO it is not that difficult to learn the basics--at least enough to improve, correct, or create a working grounding scheme for a relatively simple amp(champ, bassman, etc.).

[bnwitt]

dai,
I think you're talking semantics. The grounding layout on the Hoffman site is well known as the Hoffman grounding scheme. It is really his adaption of the Marshall grounding scheme with improvements. I have used Star, Galaxy, and every scheme out there but Doug Hoffman's scheme is the quietest. I only make one variance to it and that is I will not use a PT bolt for anything but a power cord ground point. I find there is a little noise injected if you use a PT bolt for the speaker jack ground like he shows.