no volume on weber 5e3

[blodviol]

I just finished my weber 5e3 kit and hooked it up to a speaker. It seems to be working ok, if it was suppused to be a 1/2 watt amp. Clean when low, gets alot grittier, and loads of sag on 12. But not at all loud. my battery-powered marshall MS-2 is easily twice as loud.

There is also a little hum. Hard to tell how loud it is since the amp is so un-loud, but more hum than you'd want in a studio. I swapped the chinese 6V6's for some (almost) NOS tubes I have, and it hummed less, and got a smidgen louder, maybe.

This is my first build, and i really don't know where to start debugging.

Any thoughts?

Tríste

[blodviol]

I posted in the weber forum, and he (Ted) said it might be me plugging into the wrong jack. not the case, but i checked out the jacks and found all connections were ground. Both switched (of course) and not. Thought it could be faulty jacks, so i cut them out, and checked the green and black wires coming out of the OT. They are the same point, so i guess that's where the problem is.

Should i just get a new OT?

Tríste

[hasserl]

Whoa, whoa, slow down. Don't be condemning transformers just yet. Have you taken any voltage readings? One of the most common problems with these kit builds is incorrect wiring on the input jacks. This seems to be due to people following the layoutr diagram and not really understanding what they are doing or why. I suggest you really study the input circuit and make sure it is wired corectly. Use the schematic, not the layout diag. Check the voltages and post them here.

[blodviol]

Whoa, whoa, slow down. Don't be condemning transformers just yet. Have you taken any voltage readings? One of the most common problems with these kit builds is incorrect wiring on the input jacks. This seems to be due to people following the layoutr diagram and not really understanding what they are doing or why. I suggest you really study the input circuit and make sure it is wired corectly. Use the schematic, not the layout diag. Check the voltages and post them here.

Yeah, i figured that too... I guess the OT is sort of a voltage supply and SHOULD have a low internal resistance... measured it to 0,7ohms. But i found the problem elsewhere. it was a loose wire. From pins 4 on the 6V6's...

But it still hums rather annoyingly loud. Thinking it could be mains hum, and i'm thinking of upping the filter caps to 40uF. But i haven't had the possibility to check the voltages yet. I'll surely do that first.

Thanks

Tríste

[Jeff E]

The stock filtering is perfectly adequate if everything is wired right, so adding filtering is a bandaid which probably won't help. Power supply ripple isn't your problem; most likely grounding is.
The layout diagram doesn't really spell out grounding schemes, and there are a number of possibilities as to how it can be done. It only takes one connection to create a ground loop. Maybe you could describe your grounding scheme and we can go from there.

[hasserl]

In this amp/kit I've found it's best to use the brass grounding plate suplied with the kit. It seems crude, but it works.

[blodviol]

The stock filtering is perfectly adequate if everything is wired right, so adding filtering is a bandaid which probably won't help. Power supply ripple isn't your problem; most likely grounding is.
The layout diagram doesn't really spell out grounding schemes, and there are a number of possibilities as to how it can be done. It only takes one connection to create a ground loop. Maybe you could describe your grounding scheme and we can go from there.

Yeah, i didn't even think of that. That's probably it.

I grouped the board grounds and connected it to the case of the bright volume pot, together with the left lug of that same pot. the other vol to its case. the tone cap is grounded to the case of the bright vol too.

The input jacks i didn't ground other than screwing them to the chassis.

And then i guess i made the fatal mistake of grounding the mains ground and red/ylw and green/ylw to the bolt and nut securing the PT adjacent to the standby switch. I didnt solder this, but used an eyelet (dunno if that's what it's called, here it's called a "cable-shoe") between the chassis and nut.

I checked all the ground connections against the brass plate, and they seemed to be all right. I can't work on the amp 'til Monday, but is this likely to be the issue? In case it is, any suggestions to how it should be done? This is my first build and i really appreciate your help.

Thanks,

Tríste

[blodviol]

Dunno if it's important, but the hum is an octave higher in the bright chnl than the normal chnl. i guess that's because the bright chnl is basically a hi-pass filter. Am i right?

Tríste

[Jeff E]

I'll try to keep it short for simplicity's sake. First, although you see pot cases used as part of the ground plane in guitars, I would avoid it in amps. You are relying on a mechanical contact which may become loose. Instead, use the brass plate as your primary ground plane. Run each preamp ground (cathodes, vol/tone stack, input jack) separately to the closest point on the brass plate.
Referring to the Weber layout diagram, you can do it pretty much as depicted, except for using the pot cases as grounding points. Instead, tie those points to the plate next to the pots. That will give you a more reliable connection without ground loops. Don't worry about grounding the pot cases to anything - the mechanical contact will suffice for shielding purposes.
Also, a lot of builders will run the first filter ground (the one that is tied in with the output tubes' cathode grounds) to a power transformer bolt instead of the brass plate. The thinking is, low current grounds to the brass plate, the high current grounds to the PT bolt.
Soldering to the ground plate is next to impossible when it is installed in the chassis, which acts as a huge heat sink. Instead, identify the locations of all the places you wish to solder to, and use a stove burner to heat the plate enough to melt some solder to each grounding point. Then you can insert the pots and jacks into the plate and complete the soldering job before installing the assembly into the chassis and tightening everything up.
Also, if you used shielded cable in the amp, be sure the shield is grounded at one end only.

[Tom Phillips]

Dunno if it's important, but the hum is an octave higher in the bright chnl than the normal chnl. i guess that's because the bright chnl is basically a hi-pass filter. Am i right?Tríste

Nope. A filter difference will not change the pitch. The only explanation I can think of is that the hum in the bright channel is originalting from the power supply rail which will be 120 Hz and their is more 60 Hz getting into the normal channel.
Anyone have other ideas?
Tom

[Stone]

I'm certainly no expert, but I had a very similar problem with my first amp. It turned out to be a bad solder joint at one of the input jacks. The joint looked good at a glance but wasn't. The wire would move very slightly within the solder.

[blodviol]

Nope. A filter difference will not change the pitch. The only explanation I can think of is that the hum in the bright channel is originalting from the power supply rail which will be 120 Hz and their is more 60 Hz getting into the normal channel.
Anyone have other ideas?
Tom

Well, actually, it sounds to me like 100Hz and 200Hz (we have 50Hz mains here in Europe), but i haven't measured it.

Tríste

[blodviol]

Thanks Jeff,
I have some questions:

-should i ground the wires from the PT seperately from the ground from the mains cable?

-I'm not sure what you mean by cathode ground, but I guess you mean the two rightmost grounds on the board. (Looking at the layout)

-Where should i ground the output jacks?

-The first filter ground is the leftmost ground on the board? (Again, looking at the weber layout.)

I'm sorry i don't understand all the terminology and the nature of ground loops. I've been reading only about tube amps for some years and accumulated a limited knowledge that way, but the best way to learn is by trial and error. Your help (all of you) is truly appreciated.

Thanks,

Tríste

[Jeff E]

-should i ground the wires from the PT seperately from the ground from the mains cable?

Yes, ground the mains cable at the PT bolt closest to its entry point.

-I'm not sure what you mean by cathode ground, but I guess you mean the two rightmost grounds on the board. (Looking at the layout)

Yes, those are the cathode resistors and bypass caps. They connect the preamp tubes' cathodes to ground.

-Where should i ground the output jacks?

Run a wire from the output jack sleeve terminal back to the common ground point at the PT bolt. It isn't necessary to use an isolated jack, but you can if you want.

-The first filter ground is the leftmost ground on the board? (Again, looking at the weber layout.)

Right again!

If you want to learn more about the star grounding concept, go to http://aikenamps.com/
Go to Technical Papers=>Advanced=>Star Grounding