amp buzz

[baddog]

This amy be a dumb question but what causes buzz in an amp when you take your hands off of the guitar strings? I think its a ground issue but I already star grounded the amp isolated the inputs and speaker jacks from the chassis. Any Thoughts or sudgestions welcome

ThanksBD

[tubeswell]

Yes - if you can 'deaden' it with your body, its a grounding buzz (but possibly accentuated by lack of shielding in your guitar body cavity). Is it different with different guitars? cables?

You can try different grounding schemes in the amp.

[izzybell2810]

Check the earth connection on your guitar.

[baddog]

Im playing through my gibson V and dont have the buzz problem with my silverface Bassman 50 . It must be something i did. Then amp I Built is a single channel bassman with a 5AR4 rectifier and cathode biased. It is built fron an old Knight phono amp and is roughly 35 to 40 watts . When i crank the amp i get the usual amplified noise and a little hum but its the static that i cant stand.
Im going to try removing the isolation washers at the input and see what happens.

When you star ground an amp all of the wires that would normaly go to ground go to one point and the from that point they will go to a single ground point that counnects to the chassis . Is this correct?

Any more sugestions welcome.

Thanks
BD

[tubeswell]

Hmmm... grounding - a tricky issue.

Some people here like using that single star-ground.

Myself, I prefer the split-ground system; where all the low-current/pre-amp grounds (including the PI and the pre-amp supply filter/decoupling cap ground) being all wired via their own separate wires to a single point on the chassis (which I do on the input ground); while all the high-current (i.e.; power amp) grounds (including the reservoir and screen node filter grounds) and the heater winding CT and high tension winding CT and bias winding ground etc go via their own separate wires to a single ground point at the other end of the chassis (I use one of the PT bolts).

However, I was recently discussing this with one of the local techs (Simcha Delft), who suggested disconnecting the common return point for the pre-amp grounds from the single chassis ground point and connecting a .01uF cap there instead, and them running a single wire from there back to the other (power-amp et al) ground. Maybe I'm going to try this on my next build.

[tubeswell]

Star Grounding (cont'd)

Despite all my ranting, there's R.G.'s statement on the matter...

[baddog]

For some reason i couldnt open your attachment.

thabks
BD

[tubeswell]

For some reason i couldnt open your attachment.

thabks
BD

Its just a .pdf - you might have to 'manually' open it from your desktop

[baddog]

When i open it their's no image
\

BD

[baddog]

i am still at a loss about the buzz. I just cant get rid of it. I am using a thick copper wire as a common grounding point. I have the copper wire soldered to a standard metal wire conector that bolts to the transformer chassis where the ground for the power cord connects. Should i buy copper conecters and replace the metal ones ? I have the input ground isolated and it goes to its own ground near the input. Any Thoughts welcome

Thanks
MD

[52 Bill]

When you unplug the guitar from the amp how much buzz does the amp make?

Is the power cord and chassis connected to AC ground?

[baddog]

Hi Bill

I have the green ground wire from the AC cord connected to the chassis via the power transformer lug. It does buzz when the guitar cord is inpluged. If i touch the chassis the buzz disaapears. My brother has the amp and is relaying the message to me over the phone.

thanks
Keith

[baddog]

I figured out the buzz problem my brother had the amp pluged into a power strip that was aperantly a piece of crap. He pluged it into the wall outlet and no more buzz.

thanks for the help,
BD