Metropoulos Forum

Some time ago I built a jcm 800 2204 clone on jtm45 chassis. I had some big problems with noise, but after shielding the first stage it's gone. BUT. Some time later I realised that on higher volumes my amp is picking a radio. During the building prosses I was picking the information from the internet if I had any quastions or just wanted to be shure that what I doing is right. On youtube there is a TubeDepot channel, there is a video about how to build a jtm45 kit. The guy solders a buss wire on the back of the pots. Same thing I saw on other pictures in different amps. I used a CTS pots and they are metal from every side... I knew that if I'll solder the buss wire like that, I'll have many ground loops, but I belived more to the pictures and the guy from TubeDepot (he used Alpha pots and they are more or less like CTS). The Radio was gone when I removed that buss wire from the backs of the pots.
No radio but tiny bit of noise is left.
Than I had to put a shilded wire on the first half of V2 to see if it's helps. It's working, but not enough...
The last thing. A Sheet of metal on the bottom of a had cab! Strange that this thing is not there when you buy a new head cab...
It's like a cry baby pedal. When it's opened it picks every noise that you have, but when it closed - dead quite.

May be this will help to some one who is going to build and amp.

Thank you for haring your experience.

I was also checking the internet while building mine...

and while I was at it, someone suggested to incorporate Star/Larry grounding, and I did. I removed the buss from the Ceriatone board and I used 6 grounding points...

I've followed this thread. Make sure you check the SECOND diagram at the bottom of the page! Plus read the posts, their contain complementary info
http://forum.metroamp.com/viewtopic.php?f=45&t=31328" onclick="window.open(this.href);return false;

I also had squeals and noise without a cabinet. I still don't have a cabinet but I keep the chassis laying on a piece of cardboard covered in kitchen aluminium foil and it works very well for the moment and the hum level is very low, and inexistent when using an attenuator... Remember to use the metal side of the foil, not the plastic side, it must make contact with the chassis. Of course a proper head cabinet will have the foil too.

Apart from the foil shielding I also noticed that the wire going to V2 pin2 is very sensitive, so when I made my first mod (RR 1 wire mod) I shielded that wire too...
My only problem after the mod was parasitic oscillation when the bright volume was over 8 (no sound), but I only needed to move the input wire away from the remaining mixing resistor and pots to fix it.
Now I can crank both volumes to 10 when cascaded with no issues and I'm about to perform the SMAK mod .

I don't know if the larry grounding is making all the difference in this case, but everybody was recommending it so you might wanna try that in your next build.

Cheers

R