Express layout question?

[joebob]

On the layout; the top of resistors; r7, r5 and r8 have seperate ground wires going to the ground buss. Why not short or interlace a wire between the three resistors (still have the 3 turrets or eyelets) and run ONE ground wire to the ground buss.

Dave

[paulster]

Because it's a ground buss scheme, so the idea is that everything is locally grounded to the buss, which is nice and chunky to be a very low resistance from end to end, such that you don't end up with even small potential differences between various ground points.

Not that joining those three resistors locally and then tying them to the ground buss is likely to introduce a different potential than tying them individually but the theory is there.

[joebob]

Well I was thinking that having 3 wires run in parallel would introduce stray capacitance between the wires. Also having just 1 wire is better than have 3 wires, no stray capacitance between wires. I don't think have 3 ground wires is an advantage trying to acheive better tone. Reduce the number of wires, reduce the lenght of the wires any where you can is good engineering.

dave

[Structo]

These guys have built a lot of Trainwreck amps.

I would listen to them.

[Richie]

I don't think have 3 ground wires is an advantage trying to acheive better tone. Reduce the number of wires, reduce the lenght of the wires any where you can is good engineering.

Might be true, but not always. Look at some Ampeg V4s and SVTs..
Look at the ground leads,and think ,wonder why that cap has such a long ground lead. And then make a short direct ground connection, and remove the long lead it had.. Flip the amp on, and hmmmmmm. Sometimes its not the length of wire, but where it connects is all the difference.

But yes, in most situations it is great to use short leads if possible.
Signal, power,crossing, placement , twisted, AC-DC.. High gain, low gain. etc.. It can all make a difference.

[ckpop]

Over the years of building amps grounding locations or how you do it can be a funny thing. The Trainreck amps are a funny beast and the simple design makes more of a difference.
There has been several times I have moved cathode bypass grounds less then an inch and got a different result. I would of never thought it would make a difference but does.

[paulster]

You'll notice that Ken used a particular grounding scheme, which is why the grounds aren't all shared between the power supply caps.

He was quite specific about tying all nodes to the corresponding caps and then to the chassis for that particular node, so there's preamp and pi, screens and plates all with individual grounds.

Arguably you'd have the PI separate and possibly the first or third stage too, but the theory is sound in how Ken's done it.

[geetarpicker]

Ever look under the cap can on a blackface or silver face Fender? Even in these low gain amps Fender went to a bit of trouble to run separate ground wires to different points on the chassis. They could have done things simpler and more direct, however it works the way they did it. An old Blackface or Silver Face Fender tends to be one of most quiet amps ever made in the hum department. Usually the bias circuit (which has a filter cap that's a little undersized in stock form) induces some hum into the circuit well before any issues due to the grounding scheme.

Grounding is a tricky thing in tube circuits. Also another odd area is shielded wire. I've seen cases where shielded wire added to a tube circuit can make it hum worse, not less.

In regards to Trainwreck clones I think the best way to build one at first is to follow the way Ken did it to the T. Once it works nicely then and only then would I consider modding it. I've seen SO MANY threads started here where folks combine the same two basic sentences. One starts out with how they have hum, noise, and instabilty issues let alone tone problems. Sentence two is where they mention about the changes they made in layout, lead dress, grounding, etc...

[mcrracer]

Glen, since you mentioned cap cans. ... I am planning an Express build with VVR. The threads where the guys talk about it says to use two cap cans, 50/50 and a 40/20/20/20. Have you any experience with an Express with this configuration? Any opinions? The guys who have done it says it works OK. Thanks

[geetarpicker]

I'm not sure how the VVR would be related to cap cans. I think Richie has had more experience running cap cans so he might chime in.
I built my two amps with original spec Mallorys.

[Jackie Treehorn]

On the layout; the top of resistors; r7, r5 and r8 have seperate ground wires going to the ground buss. Why not short or interlace a wire between the three resistors (still have the 3 turrets or eyelets) and run ONE ground wire to the ground buss.

Dave

I think the way Ken laid it out makes sense given his perfboard/flea clip constuction; he could easily move components horizontally along the board without running out of slack on a ground wire.

However, what you're suggesting strikes me as just as valid. You're essentially just doing the buss on the end of the board. I never do the buss. I prefer to tie each stage to its filter cap and then do a two point star. You can achieve an extremely quiet amp this way. I'm sure the bus works fine, too.

Something to keep in mind is just making your amp look like the pictures doesn't mean it will be as quiet or sound as good. Don't make shortcuts on working the layout.

[mcrracer]

I'm not sure how the VVR would be related to cap cans. I think Richie has had more experience running cap cans so he might chime in.
I built my two amps with original spec Mallorys.

Sorry Glen, I should have been more clear...with the VVR it is suggested to use cap cans. I was just wondering if you had any experience with that arrangement.

[geetarpicker]

Yo... Richie

[ampgeek]

There is a very good discussion of cap cans and VVR's for the Express here:

http://ampgarage.com/forum/viewtopic.ph ... +regulator

Dave O.

[Richie]

here are a couple more links to threads about can caps, and pics.

one link is Dana's Liverpool/Rocket which uses can caps and VVR.
The other link is an amp i built using 6v6s and VVR and can caps.

The layout works, its quiet, not much difference except you don[t have the stack of caps,so it free's up space to make room for the VVR on the front panel.
Basicly its very close to being the same,maybe just a tad different in UF value using the can caps. But i'm sure if you measure most caps,they will measure a bit more or less uf than the value they are supposed to be.
Some other things added using the VVR. The VVR can be put in place of the standby switch,and use a switch that is 3 position for ON-Standby-Off on the one switch.

http://ampgarage.com/forum/viewtopic.ph ... light=caps

http://ampgarage.com/forum/viewtopic.ph ... hlight=cap