First Build, 5E3, strange problem, help please

[cfidave]

I am new to the forum, but have already learned a great deal from many of you. I have completed my first 5E3 build and have run into a strange problem.
The amp is virtually silent with no guitar plugged in. Almost no hum, and a little white noise with volume & tone at 12. So far so good. Plugging in a guitar, any guitar, and I get a loud buzz that increases with volume, and more so as the tone knob is increased. Much more noticable on the two #1 inputs. Touching the guitar strings, quiets it a little, but does not eliminate the buzz. It is not the guitar, cable, or any of the tubes, as all have been swapped, and the buzz persists. I have used the Hoffman buss bar grounding scheme, and checked grounds which seem solid on the DVM. I am wondering if either or both of the tone caps ( 500pf & 0047uf) being bad could cause this. I have no way of checking those caps. All resistors read the correct value. Seems like a grounding issue, possibly at the input jacks, but they check out O.K. Any help would be appreciated. Thanks much.

[tubeswell]

Got any pics of your build you can post here? (Helps with trouble-shooting). If not, maybe some of these things might be useful:

1) You could try a split-ground (run separate wires from all all pre-amp ground return points - including the pre-amp filter ground - to one of the input socket ground lugs. I find keeping the PI grounds with the pre-amp grounds in this scheme is quieter than grounding it with the output stage grounds. Then run the all the output stage ground returns - including the 'plate & screen node' filter grounds - and your PT 2ndary CTs, via separate wires to another ground point on one of your PT chassis bolts (with a solder tag terminal).

2) How are your heaters wired? Do you have a heater winding Centre Tap, or have you used 100R-to-ground from each 6.3VAC lead, or have you done it the way Fender shows on most of their schematics? This can make a difference in hum

3) In your amp, are the wires neatly organised, or are they all over the place like spaghetti? If it is the latter, you could have unwanted coupling from hotter wires going into more sensitive parts of the circuit, which can induce hum. Where possible keep all wires up against the chassis (this 'eats up' the EMF radiation around the wires). Keep wires physically seperate, and keep supply wires away from signal wires by about 1" min if possible - where it is necessary to cross other wires, keep them at right angles to each other. Keep AC pairs of wires (from the PT secondary windings) twisted around each other - this cancels out the EMF around those pairs.

4) For sensitive signal wires (such as input wires going to grid of first stage), have you tried using shielded cable (with the shield grounded at one end only - to avoid stray capacitance induced hum)?

[txstrat]

Have you already tried to pull the tubes one after another to figure where in the circuit the hum consists.
If you pull a tube and the hum disappears the reason for the hum is before that tube (or the tube itself, but you swapped them already).

Hope this helps

Matt

[cfidave]

Thanks for the quick reply guys. Here are some pics, of my build. As far as grounding goes. All power supply filter grounds, the bias supply ground, both center taps, ( including heater winding Centre Tap) and the green AC wire are grounded at the PT studs. All other grounds are to the buss bar on the back of the pots. I have trouble, at this point knowing & identifying what you mean by " pre-amp filter ground" and " PI ( phase inverter?)ground. I not sure if my grounding is what you are talking about. BTY, I used Mercury Magnetics transformers, if that helps.

As far as pulling the tubes goes: humming goes away with removal of either
V1 or V2. With V1 & V2 installed, humming returns and is not affected by removal of power tubes. I think that tells me it is in the preamp stage. BTY, the sound of this guy is amazing, I just need to track down this problem.

[hasserl]

In my experience you cannot beat the brass grounding plate for Fender style amps. It is a brass plate that mounts between the input jacks/pots and the chassis, all grounds off the board are fed to it. My first 5E3 I tried to incorporate a star ground, and I just couldn't get it to be as quiet as it should be. Went back to the brass grounding plate and all my noise issues went away. I've used it on all other Fender style builds since then and I've never had ground noise issues. My suggestion is that you get one of the brass grounding plates for these amps and install it, chances are very good your noise issues will go away.

[cfidave]

Thanks, I may need to try the brass grounding plate. I keep checking evrything I can think of, with no luck. I am going to try shielded cable between the pin 2 of the AX7 & the volume pot, as a last resort.

[michaelj]

Although it may sound "way" simplistic, you may want to try tube shields on your preamp tubes. This has made a significant difference for me both in my 5e3 build and in a el84 single stage pre / PP el84 pair build.

Mike J

[cfidave]

Tried the shields, no real change, but thanks for the suggestion. Grounding the heater center tap to pin 8 of the 6L6 has helped some. Since the amp is hum free with no input, even with controls at 12, I think I am picking up noise from the input ( guitar), that is being amplified. I am going to try and run some shielded cable ( gonna be a bear), and see if that helps.

[Chuck H]

You might also try isolating the input jacks from the chassis.

Also, Have double checked and are sure that the switch on either input jack is not lifting the ground with a cable plugged in?

Chuck

[dai h.]

my guess (since the layout looks stock and the workmanship looks clean) judging from the above is that the main problem is the grounding scheme. One of the things mentioned for example, about tying all the filter cap grounds together is wrong (preamp filter shouldn't be tied together with early filters, B+ winding, and filament ground). Probably (since the build is clean) there won't be too much to do to correct the situation and get the amp working as it should be.

[cfidave]

Chuck, not sure what you mean by lifting the ground. The number one input jacks are connected to the number two input jacks by tip of the #1 switch going to the switch of the number two jack, via the 1 meg resistor. That 1 meg resistor is connected to all 3 lugs of the number 1 jack.

[michaelj]

Sorry the shields didn't help.

After looking at your pics a bit closer, you might want to try "chopsticking" the leads on your pre and PI some. Seems like there are a fair number of parallel runs there, I have had better luck keeping the runs short and making sure that nothing [esp cathodes] runs parallel or too close to screens and plates.

I agree with the other guys re grounding runs. I don't use the brass plate myself but have installed "stars". Center taps and first filter to one PT bolt. AC ground to another. All the other grounds go to a separate "star".

Single coils [especially P90] still hum a bit but not enough to spoil the fun.

I also shielded my "back panel" with copper foil which helped even the single coil / P90 stuff.

Good luck..... It is a real clean looking build so I know you will sus it out.

MikeJ

[tubeswell]

Originally Posted by cfidave

I have trouble, at this point knowing & identifying what you mean by " pre-amp filter ground" and " PI ( phase inverter?)ground.

'Pre-amp filter cap ground' is the ground side of the decoupling/filter cap for the pre-amp supply (the filter cap nearest the pre-amp plates). This should be grounded with your pre-amp grounds for minimal hum - and not linked to your other filter cap grounds

PI = Phase inverter/splitter - the ground for this is the cathode resistor/bypass cap ground (and any grid bias resistor ground). I find its better to ground these with the pre-amp grounds as well.

[cfidave]

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. I also noticed that when I plug a speaker cable in, the tip of the plug sees signal as well as ground. I am using the Mercury Magnetics output transformer that has no speaker ground wire, just the yellow wire that goes to the tip of the jack. Anyone know if it is normal to see ground at the tip of the plug. Thanks much for the help!

[txstrat]

I usually run a rather strong wire over the pots bodies as a replacement for the brass ground plate. I put ALL preamp grounds (including the filter caps in the preamp section) and the PI ground (including filter cap) to this wire.
All other grounds (power tubes, 100 ohms resitors for the heaters etc.) I put to a star ground at one of the PT bolts. That does the job in my amps. To be honest, I forgot about that in my recent 6G3 build (put all grounds to the star ground) and it hummed, until I changed the preamp as described.

Hope this helps

Matt

[dai h.]

Originally Posted by cfidave

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]

Originally Posted by 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.

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]

Originally Posted by bnwitt

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]

Originally Posted by 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.

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.

[cfidave]

dai,

I think you hit the nail on the head. As a first time kit builder, I was simply copying a layout that came with the kit. When that did not work, I was clueless on how to fix it. I did not understand the theory behind what I was trying to do. Most of the grounding layouts I looked at were not specific enough for me follow correctly. A prime example of this is from the Hoffman site:
"Make sure all Jacks and pots are bolted down firmly to the metal chassis. If you use plastic jacks, make sure all jacks are grounded to the pot buss wire".

Since I used metal jacks, I simply did what the site said not knowing I was setting up a potential ground loop, by not grounding all jacks to the buss wire. I have learned a lot from this thread, thanks to all the advice. It would have been much better to have had at least a basic understanding, of what grounding is all about, before starting the build. Lesson Learned.

[hasserl]

Originally Posted by 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.

I never said the Hoffman ground system was a star ground, you read that into what I wrote. You're right that I've never used the Hoffman ground, I've never even checked into it or know the layout is. What I do know is there have been several threads over the years here with people grounding their amps with what they picked up off the Hoffman website and they've had noise issues. Whether they followed the layout correctly or not I really don't know or care.

Like I said, it's a simple circuit and it works fine just as Leo did it. There's no need to reinvent the wheel, IMO. If you just layout it out like a Fender and use the brass grounding plate you won't have ground related noise problems. Simple circuit, simple layout, don't complicate something that doesn't need to be complicated. Save your time and creativity for something that will make a real difference.

[bnwitt]

Originally Posted by hasserl

I never said the Hoffman ground system was a star ground, you read that into what I wrote.

Maybe not but you insinuated that it was like a star ground in the fact that it too had noise complaints associated with it.

Originally Posted by hasserl

You're right that I've never used the Hoffman ground, I've never even checked into it or know the layout is.

And yet you completely dismiss its potential improvement in noise floor reduction over the standard Fender 5E3 layout.

Originally Posted by hasserl

Whether they followed the layout correctly or not I really don't know or care.

Not interested in factual comparisons I guess.

Originally Posted by hasserl

Like I said, it's a simple circuit and it works fine just as Leo did it. There's no need to reinvent the wheel, IMO. If you just layout it out like a Fender and use the brass grounding plate you won't have ground related noise problems. Simple circuit, simple layout, don't complicate something that doesn't need to be complicated. Save your time and creativity for something that will make a real difference.

Well my experience is somewhat different. I have had my hands on numerous original Fender deluxe and other tweed era amplifiers and they all have had some amount of hum present at zero signal. I have also built at least 9 or 10 5E3's with the Fender layout and the brass plate grounding and they too had some hum at zero signal. Once I tried the Hoffman layout on my first 5E3 there was no turning back. Now I will admit that I have added a few changes to the current Hoffman scheme like running a ground to each input jack and then wiring the whole preamp section to a chassis ground bolt, plus I never use a PT bolt for power section or center tap grounding. The result is a 5E3 with no hum at any volume level period. Sometimes a little tube hiss on full volume but that has nothing to do with grounding. I have had so many customers tell me that they thought some hum was just part of tube amp life and are really surprised that it doesn't have to be.


I really think you should try a Hoffman ground scheme before you summarily dismiss its value. Remember, it took a long time for folks to except that the world was round and not flat. Experimentation is a great thing. Saying the way its always been done is just fine prevents new discovery.

[hasserl]

Originally Posted by bnwitt

Maybe not but you insinuated that it was like a star ground in the fact that it too had noise complaints associated with it.

Yes, in that people have come here looking for help with a noisy amp after having tried both of those schemes'.

Originally Posted by bnwitt

And yet you completely dismiss its potential improvement in noise floor reduction over the standard Fender 5E3 layout.

Again, you're adding to what I said. I didn't completely (or summarily) dismiss it, I said this isn't the first time someone used the scheme then came here looking for help with noise, and I posted that the stock arrangement works fine and IMO is what a builder should use, in particular a new builder that will typically have plenty of other things to occupy their attention.

If you've built 40 5E3's, I don't blame you for moving past the stock layout, or circuit for that matter. But if it's your first amp, the smart thing is to stick to the tried and true circuit/layout. IMHO of course.

You seem rather defensive, no need to insult or assume things about me. Where are you at in Southern Cal? I'm local, in Orange Co, perhaps this would be better discussed over a beer.

[cminor9]

Originally Posted by hasserl

I'm local, in Orange Co, perhaps this would be better discussed over a beer.

Discussing religion (grounding schemes, same diff) over a beer?!? What, are you trying to start a barroom brawl?



I kid! I kid!