Express touchy?

[Franc]

Finished my first Express and I am impressed with the sound.

Most of my experience is with building Marshall-like amps so this was a challenge at first (everything being mirrored and all).

But, I can clearly hear when I touch the string or any metal part on the guitar that is plugged in. It's not making a lot of noise at all, but it gets more quiet when I touch the guitar. Is something wrong or is it just the way it is? Never noticed that on my Marshall builds...

So before I start looking for a fault that isn't there....what's your experience?

Thanks,

[Darkbluemurder]

Don't worry, that is perfectly normal.

Since the strings and bridge on a guitar are usually grounded whereas the human body is not, once you touch the strings or the guitar bridge your body is grounded and acts as a shield thus making things quieter.

[Jack]

On any amp: if you unplug the cord at the GUITAR (and no the amp) and the problem gets WORST, it may be a poor input ground/shielding. If the BETTER, it migh be the guitar's fault.

If you un plug the cord and everything is fine, then it's the input jack. If not either it's the nature of the beast of it's some noise problem further down the chain (but usually in the first stages).

What is your grounding scheme?

[riscado]

I'm sorry but if he unplugs the chord of the guitar, it's bound to get noisy... it would be strange if it didn't, after all the input jack won't be shorting!

[Franc]

Jack, not sure if I follow.

If I unplug the cord from my guitar and leave it in my amp, I always get a loud noise when I touch the plug. On any amp.

This is the layout I used:

http://www.ceriatone.com/images/layoutP ... iatone.jpg

[Jack]

Jack, not sure if I follow.

If I unplug the cord from my guitar and leave it in my amp, I always get a loud noise when I touch the plug. On any amp.

This is the layout I used:

http://www.ceriatone.com/images/layoutP ... iatone.jpg

Exactly. HOWEVER, if the noise is LOUDER than when the guitar is plugged, it means your guitar ground is OK. If not, it means the guitar ground is bad. Why? Because the cord alone is a worst antenna than the pickups. If the guitar is proprelly grounded, it's a worse antenna than the cord. There may be nothing to do about it.

To cure this (assuming it's a jack ground issue) you can hook a small cap between input ground and chassis or ground the input at the chassis as close as possible to the physical input ground.

[Rick]

The touchiness is part of what makes these amps so great. It's articulate, sensitive, subtlties are expressed. The guitarist has an instrument that reacts immediately to whatever he/she does. A lot of commercial amps are dull and dead or muffled sounding in comparison it seems to me.

I would add that as it has often been stated, this is an amp where you really need to run your guitar volume knob to make the amp do what you want it to do.

Another trick I use is to ground the input tube cathode directly to the ground of the input jack, that should eliminate ground loop hum on that jack.

[Franc]

Thanks for the response guys.

I guess it's nothing to worry about, just something I didn't notice on my 'Marshalls'

I tried 4 different guitars and the 'noise' is different for everyone one of them, on one of them I didn't hear it at all so it's probably the guitars' fault anyway.

Thanks again!

[iwo]

...

Another trick I use is to ground the input tube cathode directly to the ground of the input jack, that should eliminate ground loop hum on that jack.

excuse me, as i'm having hum issues with my clone... can you even do that? I mean, cathode has some components before it goes to ground does'nt it? If you connect cathode directly to ground will it not basicly remove the resistor and capacitor from the circuit?or do i understand something completely wrong here?

Ivo.

[LeftyStrat]

He means the ground side of the components. Here's a gut shot of one of Paul Ruby's amps:

http://paulamps.com/MiriamGuts2.jpg

Since he is using an isolated input jack, he put a ground lug right next to the jack. Then the ground of the jack and the ground of the cathode cap and resistor also connect to this point.

[iwo]

Ok, so I did that, I connected the cathode side to the input jack ground and it did not help. I put 39 Kohm resistor to the input pin and soldered input coax cable to that.. it didnt help either .. only I seemed to have a feeling that the amp didnt sound as transparent as before... but the hum issue is still going on... My hum problem decreases a lot when I touch the strings. I tried tu insert just an 6,3 mm/RCA plug to the input and it is bit qiueter then but im quite sure that it hums too muchIll post a picture of my seriatone TW inspired amp here so but if you can see or suggest something and also i recorded a clip of the hum I'm getting (first there is the hum when not touching string, then i'll touch the strings and then i turn down the gain and then the master volume). The picture was taken before I added the 39 Kohm resistor and tied the input cathode to the input jack. Any suggestions? I have 3 weeks to solve the problem until I have my first show... I have steel metalplate about 1 mm thickness for the bottomplate.

[iwo]

seems I cannot add soundfile as an attachment

[iwo]

so i had a chance to put the soundfile up now if it could help:
http://www.leechband.net/iwo/
and there hum1 file, in .ogg format as my computer did not wish to convert the wav file to anything else at the time.
So first there is the hum when i'm not touching strings, then i touch them and hum decreases considerably... then I turn down the gain knob and then master volume knob. I have there 39 Kohm resistor on the input grid and cathode ground to the input jack ground.
The two switches you see between the filter caps and output impedance switch are half/full power switch and OT primary impedance switch 5,2 Kohm/6,6 Kohm.

Ivo.

[drz400]

Finished my first Express and I am impressed with the sound.

Most of my experience is with building Marshall-like amps so this was a challenge at first (everything being mirrored and all).

But, I can clearly hear when I touch the string or any metal part on the guitar that is plugged in. It's not making a lot of noise at all, but it gets more quiet when I touch the guitar. Is something wrong or is it just the way it is? Never noticed that on my Marshall builds...

So before I start looking for a fault that isn't there....what's your experience?

Thanks,

That means your guitar isnt shileded very well.
This isnt an amp problem it is a guitar shielding problem