Metropoulos Forum

Bare Bones chassis kit from Metro (plus parts), Turret Board from Brian H, Caps from Sparky.
Transformers ordered next week.
Advice from Will (Thousandshirts).

Decals & Snubber Cap on the way (hopefully) from Steve (S. Marshall).

Gawd - this is an expensive hobby !

Wayne

So the micalex powertube sockets fits in this chassis? I think i once heard that only the amphenol sockets did or something like that....

What transformers you using, Wayne?

it really looks good. although it is not historically correct, I would consider using larry's grounding scheme. it really reduces noise and ghosting. the original schemes were not so great

+1 on the grounding layout. It took my amp from great to astounding! Maybe the older ones had better quality filter caps than we get today and didn't really "need" the improved grounding, but it really made a difference in mine.

Vegard wrote:So the micalex powertube sockets fits in this chassis? I think i once heard that only the amphenol sockets did or something like that....

NOPE ! They don't fit. I found that out the hard way.
They are just slightly too big. I had to enlarge the holes a bit. This is easily done though with a half round file & it is only aluminium. If i did this again i would just buy the amphenol sockets.

BrianH wrote:What transformers you using, Wayne?

Maybe Marstran. I haven't heard back from Brian on the shipping costs (Australia !!)
Will (thousnadshirts) put me onto another brand worth looking at too.
I'd go Metro if the shipping was less. It's around $200.00 US !!!

We'll see - but i'll be ordering next week.

Anyone got a link to larry's grounding scheme topic ??

I'll have a look before i get to far into this.

Thanks

Wayne

shakti wrote:+1 on the grounding layout. It took my amp from great to astounding! Maybe the older ones had better quality filter caps than we get today and didn't really "need" the improved grounding, but it really made a difference in mine.

c e r r e m claims that the original also had this problem, esp. the PA amps. he said that you often have to change the grounding scheme in order to avoid ground loops

Roe wrote:

shakti wrote:+1 on the grounding layout. It took my amp from great to astounding! Maybe the older ones had better quality filter caps than we get today and didn't really "need" the improved grounding, but it really made a difference in mine.

c e r r e m claims that the original also had this problem, esp. the PA amps. he said that you often have to change the grounding scheme in order to avoid ground loops

At the very minimum at least be sure to ground your mains and screens filters separately

larry grounding:
http://forum.metroamp.com/viewtopic.php ... ng#p252117http://forum.metroamp.com/viewtopic.php ... ng#p250168http://forum.metroamp.com/viewtopic.php?f=4&t=25351http://forum.metroamp.com/viewtopic.php?f=4&t=25351

OK, I understand most of the reasoning for Larry's scheme.
The AC supply ground right below the IEC and the main filter and screen filter caps separate. Most guys do that.

The one that kind of bugs me though is the heater CT.
Just seems strange to run an 60Hz AC heater wire (even though it doesn't have that high of potential) up through the preamp area and ground it to the input ground.

I usually run a ground buss wire above the pots and tie my inputs, preamp cathodes and the various pot grounds to it.

How is having those three separate grounds in the front of the amp better than the buss?

I thought the theory was to have as little difference in potential between the grounds of the preamp stages as possible to avoid loops and humming?

I understand you guys saying it works, but can somebody explain to me why it works better than the general grounding scheme most amps including Marshall use??

Thanks, Tom

the ordinary grounding scheme creates a ground loop. the pots for instance are grounded both on the back and to the chassis (since they touch the front of the chassis)

Structo wrote:OK, I understand most of the reasoning for Larry's scheme.
The AC supply ground right below the IEC and the main filter and screen filter caps separate. Most guys do that.

The one that kind of bugs me though is the heater CT.
Just seems strange to run an 60Hz AC heater wire (even though it doesn't have that high of potential) up through the preamp area and ground it to the input ground.

I usually run a ground buss wire above the pots and tie my inputs, preamp cathodes and the various pot grounds to it.

How is having those three separate grounds in the front of the amp better than the buss?

I thought the theory was to have as little difference in potential between the grounds of the preamp stages as possible to avoid loops and humming?

I understand you guys saying it works, but can somebody explain to me why it works better than the general grounding scheme most amps including Marshall use??

Thanks, Tom

Going to ressurect an old thread here.

I too am a little confused as to the Larry Grounding scheme.

For the most part, it seems logical to group each preamp stage into a sub-star in order of where current is flowing.

But why on earth (pardon the pun) would you ground the Heater CT at the input stage? I can't see the logic, but I am sure there is some and I am trying to quench my thirst for knowledge!

Anyway, I don't believe the original post's question was answered......