Metropoulos Forum

Ok, so I built a plexi 100w superlead kit back in the day when they were selling 100w plexi superlead kits and I loved the sound. I've had a few problems over the years due to me bein' afflicted with the stupid, but now I think I have only three issues that keep me from being "record ready" with this amp. And since I have some parts that need recording, I need to solve those issues. I hope you guys can help me!

Issue # 1! I have a bad presence pot. I probably overheated it when I was soldering. It scratches when I turn it and after hitting it with gallons of pot cleaner, it still scratches when I turn it, so I am just going to replace it. So, there's that...

Issue #2 and maybe #3: I get a LOT of noise... so much so that the amp is unusable to record with now...

There is something microphonic going on with v1. When I tap the tube or the socket, I get amplification of that. I have swapped out the tube with several others and they all do it, so I am wondering if it is possible the socket is microphonic? If so, can I just replace it and where would I get a good replacement?

Issue #3 or just a continuation of issue #2: When I pull V2, all the noise stops... so I may also have an issue in that area...
or it is maybe just part of the microphonic problem...

here's a relevant picture:

http://s24.postimg.org/cn380v2xx/Board_Area.jpg" onclick="window.open(this.href);return false;

and one more:

http://s23.postimg.org/ojpubz0t7/Socket_Area.jpg" onclick="window.open(this.href);return false;

Any ideas on where to go with this would be awesome!

Thanks!

AG

Issue 1, not an issue. The presence control has DC on it by it's very nature. It does scratch in operation.

Issue 2, different story. Sockets CAN cause similar issues, as can dry or bad solder joints, or any components directly connected to it.

Issue 3, possibly a non-issue, since pulling V2 will stop everything that comes before it from passing. A bad tube in V2 will cause a lot of noise though.

I agree with checking for dry joints. When I look closely at the wires that come through the board onto your turrets - they are not tightly wrapped and I can see some daylight.

So first thing would be to use some snipe nosed pliers and tweak the wires and then reflow the solder (careful not to drown the terminals on the socket in case it drips down.

Make sure your grounds are good and that you have implemented a good grounding scheme too.

What preamp tubes are you using? It is nearly always worth investing in a high quality NOS (tested guaranteed etc) ECC83/7025 for V1 at least. Many of us have a box of all sorts of pres, I just swap in and out to find the best for an amp although I generally like Mullards or Brimars as a safe bet.

As above re presence, it is part of the charm of the design. If it really bugs you get a 25k pot and 4k7 resistor and wire it the post '73 Marshall style.

I didn't even look at the pics

I agree, there are quite a few joints on the turretboard that don't look very nice.
Quality of solder is often a very underrated thing. I personally love Kester 37/63. It gives lovely joints and doesn't leave much residue. A decent iron and tip is also a very good thing to have.

When making a joint, I always make sure I have a mechanically sound, and strong connection wherever possible, before soldering. I have a small set of angled point-nose pliers (with flat rather than serrated jaws) for exactly this purpose.

Thanks for the replies, guys! I will try to tidy up some stuff and report back...

AG