5E3 Help

[valco]

Hi all, I'm hoping I can get some help from you guys on this. Its my first amp build. A 5E3. I used the mojotone layout, except I used the more standard input jack and PT wiring.

It all sounds and works beautifully. Very little noise, and overdrives beautifully. But there are 2 problems I'm having:

1. Adjusting the volume pot on any guitar (using any cable) causes a static/woosh sound.
2. If I put a buffer between the guitar and amp, the static/woosh sound completely goes away.
3. Switching any pedal on or off causes a loud popping sound.

I've posted on another forum and the people have been incredibly helpful, but no success so far. I'm hoping maybe some of you can help me out.

I've tried swapping V1 and V2, and fe-flowing solder joints all over the board. No help.

Here are some pics. The wiring was much nicer before I started trying to solve these issues. Anyway, any and all help would really be greatly appreciated. I'm so close to having this amp be 100%.

I will post a number of photos now.

[valco]

1

[valco]

2

[valco]

3

[valco]

4

[valco]

5

[valco]

6

[valco]

7

[valco]

8

[valco]

Layout (used standard input jack and PT wiring, rather than what is seen on this layout)

[valco]

Factory Schematic

[eleventeen]

Looks pretty good, and fine for your first effort!

As far as the "whoosh" on the volume change, looks to me like you are relying upon the "frame" (meaning, the threaded bushing that goes thru the chassis) of the input jacks and the resulting mechanical connection that bushing makes with the chassis for your signal ground. You say [changing the volume on] "any guitar, any cable" causes the whoosh...and thanks for having thought to test that....I am not much of a builder of the older tweed style amps because I am a blackfacer, not a tweeder...but I would start by improving the ground connection between the input jacks and signal ground.

Point being, if this goes away with your buffer inserted in-line, it's almost gotta be a grounding problem....but not a "hum-causing" gnd problem...a more subtle variety. Connect a real, soldered wire from the ground terminal on the inputs jack(s) to real, actual signal ground...don't rely on the chassis. Yeah, I know, plenty of those old amps seemed like they could get away with this, but they had magic working for them!

[valco]

Thanks so much for your help!

Where would you recommend I run the input grounds to, that is not connected to chassis?

I tried to follow the grounding scheme that so many have had succes with. Which is to ground all the input jacks, preamp, and pots together on a ground bus. And a separate ground for the PT, Lamp, AC, 25uf/220ohm cap, and the first 16uf cap.

[Willabe]

Eleventeen may be on to something but I think it's this;

I'm not sure but it looks like you have your input jacks, which are already grounded at the chassis through the jack's frame bushing hooked/wired up to the ground buss and then the ground buss is hooked/wired up to the PT CT/chassis?

If so that's a ground loop through the chassis because it goes from the input jacks to the ground buss, which has all the preamp, PI and control grounds on it, to the 3 filter caps to the PT CT chassis ground then back through the chassis to the input jacks bushing chassis ground, and round and round it goes.

Try disconnecting the ground buss from the PT CT chassis ground and see if that helps. And you have to disconnect the 3rd filter cap's (from the left to the right) ground from the 1st and 2nd filter cap's ground. From the left 1 and 2 stay with the PT CT chassis ground and the 3rd goes to the ground buss. That will break the loop and may fix it.


            Brad        

[valco]

Thanks for the help!

However, I dont see where I'm connecting the ground bus to the PT ground. I have the 1st and 2nd caps at the PT ground. Then the rest of the board grounds, along with the jacks and pots on the bus ground.

However, since the PT ground is on the chassis, and the ground bus contacts the chassis throught the jacks, dont they then share a ground?

[Willabe]

However, I dont see where I'm connecting the ground bus to the PT ground. I have the 1st and 2nd caps at the PT ground. Then the rest of the board grounds, along with the jacks and pots on the bus ground.

I see 2nd cap's (screen) ground to buss and KR/KC, 1st, 2nd and 3rd filter caps grounds all connected together under the eyelet board. 

Look at the red circle.


       Brad      

[Willabe]

However, since the PT ground is on the chassis, and the ground bus contacts the chassis throught the jacks, dont they then share a ground?

Yes but that does not make a loop. As long as the ground buss is only connected to the chassis at 1 point and nothing else it's not a loop. If you re-read what I described you'll see the difference.


             Brad     

[valco]

The middle cap there with the lead to the ground bus is connected to the cap to the right on the back of the board. It is not connected to the cap to the left.

My board is wired exactly like this image.

[Willabe]

That green wire sure looks like it goes from the ground buss to the 2nd filter caps (center cap) eyelet. But if you say it doesn't ok.

Oh, I see now. I thought all 4 of the end ground eyelets were wired together under the board.

I wouldn't run the screens filter cap ground with the buss. I would run it with the PT CT filter caps ground.


                 Brad    

[valco]

Okay, I am not entirely sure how to describe this stuff. So I will do so very planely (and ignorantly). Please bare with me.

There are 3 large blue caps. I thought the middle large blue cap and other large blue to the right should be grounded to the ground bus. They are both connected on that back of the board. The middle large blue cap IS wired to the ground bus. Which would mean that the large blue cap to the right is also grounded there.

THEN, the 1st large blue cap on the left is connected on the back to the small 25uf cap/220ohm resistor. These are connected to the PT ground.

This is how I currently have it wired up. Is this wrong?

[Willabe]

Yes I see it now, I'm sorry.

There are different schools of thought on how to wire up grounds in an amp.

For me I would not run the screen cap ground with the preamp grounds. I would run the screen over to the PT CT filter cap ground.

But I don't think this would fix your problem.   

Eleventeen might have nailed it. Are your input jacks snugged up nice and tight? Do they have nice star washers between them and the chassis so they cut into the chassis and get a nice ground?


             Brad     

[Willabe]

I don't know if you've read this, if not this may help you with grounding?

http://www.valvewizard.co.uk/Grounding.html

Our host Doug has a grounding schem that is well loved by many. You can find examples of it in his tube amp library of information.


               Brad     

[Madison]

+1 on the Hoffman Library of Information.
Read it, read it all, and refer to it often.
I do.

There are a few ways to ground a 5E3.
Try this way.
Do it first with alligator clips so you can try different grounding schemes if it doesn't work.

Also, solder a buss wire to the back of the pots and ground the pots to it.
Take a small file and go over a corner on the rear of the pot corner to get a decent surface to solder to.
Since your pots are already installed get out the vacuum as you are filing to suck up any shavings.

I do all the grounding last on amps anymore with alligator clips to get the "right" scheme down and then permanently solder in later.
Since it seems every amp (I make) has quirks and surprises.
 
Hope this helps.
Good luck.

  

[Madison]

pic

[valco]

Thanks you all for the help. Its greatly appreciated!

I put star washers on and cranked down the nuts on all 4 jacks. No improvement.

I then tried this new grounding scheme. No improvement.

I checked just now for DC on the input jacks and I'm getting 0.08 DCV. Is that enough to cause problems?

[Willabe]

I then tried this new grounding scheme. No improvement.

And what was the new grounding scheme?



                     Brad     

[Madison]

I then tried this new grounding scheme. No improvement.

And what was the new grounding scheme?



                     Brad     

+1

[valco]

The one Madison posted about 3 posts up.

[PRR]

> DC on the input jacks and I'm getting 0.08 DCV. Is that enough to cause problems?

Small problems; but we expect less DC. Like 0.01V (10mV).

Swap the two small tubes. Is it still 0.08V?

[valco]

Hey Fellas,

Just an update that the amp is now working 100% and sounds fantastic. It was just some grounding issues. Thanks to everyone who helped out!

 

[Willabe]

It was just some grounding issues.

Hi valco, glad you fixed it!     

But, if would you mind sharing with us just what the grounding issues were that you fixed it would help us all.     

We ALL have made mistakes both simple and sometimes more complex and when, with help the from our fellow forum members we find and resolve the problems we share what they were. This way we give back to the community for the common good of all.


               Thanks,    Brad         

[valco]

Sure thing!

Well, I was going completely crazy with my head in the chassis for about two weeks with no luck solving the noise problems. So I finally gave up and handed it over to a local amp tech. He fixed it right away. Here is what he had to say:

----

"I removed the cap and never got the DC voltage you brought it in for. The good news is I found a few reasons why you would of had it there. A filter cap did not have a ground so besides a hum when you turned up, the amp was way under filtered and that could cause it. Also I know you tried grounding every way under the sun, but the input jacks were the ground point for the power supply and pre amp. I know I have seen kits with this before (that didn't work and had DC on the jacks with hum) . This is a bad idea. All that voltage dumping to a input jack in the front end could induce voltage right there. Also you don't need all those grounds on the jacks, it can create a ground loop. The chassis ground from the jack itself is fine. Thats how the originals were. So i got the filter caps dumping to the main ground, the pre amp grounded to the pots and the jacks grounded all to themselves. Its been on all night and no problems."

----

Its weird that he found one of the caps ungrounded. I had a ground wire connecting to that cap and I reflowed it many times. Anyway, this was my first amp build, and everything actually went pretty smooth except for the noise stuff I was having. So I'm glad it finally got worked out. Amp sounds great now. The tech agreed that the amp sounds great. However, he mentioned that he really likes the yellow Jupiter caps in a 5E3 (instead of my Orange caps.. To be honest, I've never quite believed all the cap-mojo hype. Would the Jupiters really "improve" the sound?

The Cannabis Rex speaker may be a little too "thick" sounding for this amp. Not sure yet. I have to gig with it a bit to know for sure. You guys have a prefered speaker for this circuit? I'd love to hear your opinions!

As always, thanks to you all for your input, help and support!