Layout!

[Jackie Treehorn]

A couple days ago, there was a topic at the gearpage regarding building express clones. I had said that I felt my build was lacking in the harmonic feedback department, not that I've ever played a wreck. However, I've read they give a lot of feedback, etc.

Anyway, Mark Abbott's layout diagram for the liverpool/express preamp had kind of an unusual wiring of the tone stack. I have experimented with the wiring of the tone stack, specifically the interaction of the wire from the treble cap to treble control with the mid/bass wires. With a scope hooked up to the output of V2, there was this extra blip on the sine wave. At one point, I was able to drastically subdue it by actually twisting the treble cap wire with the adjacent wire to the mid pot. This sounded terrible. The amp was really dead. So, I went back to kind of having the wires spread out a bit.



That's one iteration. I had wanted to try running the mid/bass wires per Mark's layout, but had run out of the Kimber wire I like to use in amps. I recently got some more. Here's how I ran the wires this time...



I am absolutely blown away with how much harmonic feedback I can get with just this layout change! It's almost too much. This change is easily as big as changing a component value in the circuit. The two little jumpers between the tone control pots can affect the tone dramatically, too. Also, the distance between the mid and bass wires affects the tone and feedback considerably; if they are too close, the amp got very bright and piercing. I ran them as close as possible, while still retaining warmth. I did the layout change on Wednesday, and have been really excited about how much better the amp is. I waited a few days to post just to make sure I wasn't imagining the effect. At one point, I was getting so much response through the strat, it was like the whole neck was vibrating in my hand! I feel this layout change was the last piece of the puzzle. I highly recommend taking a look at Mark's layout in the files section, and thanks to Mark for drawing it out in the first place!

Anyway, if anyone else has some layout tricks to contribute, let's make this thread a place to put them!

[gnugear]

WOW!! That little change made that much of a difference?

I've got some work cut out for me!!

Nice pics

[gnugear]

What kind of tubes are you running, and are those the Japanese resistors?

[Dai H.]

WOW!! That little change made that much of a difference?

I would guess because those are high impedance runs (which makes them more sensitive to small changes in length, position--like the wires to the pots in a Marshall).

thanks for the report JT! What it looks like to me is that by laying the wires flat against the chassis, you are getting better wire to wire isolation by increasing the respective wires capacitive coupling to ground and thus lessening their coupling to each other. Plus by making them longer and putting them against the chassis, the impedance for the high frequencies should be increased, making the highs harder to get through. Assuming that you could hear it, that's something that you could play with (not just in Trainwreck clones). Length, position of wires to ea. other (farther, closer, twisted together, right angle cross), position of wires relative to chassis, use of shielded wire, etc.

[Jackie Treehorn]

Yes, it's a big, very real difference. I don't know why, either.

The resistors are the Japanese Riken-Ohms. I got them from Angela Instruments. They sound pretty nice and are very quiet. I've got a Tungsram in the first preamp position, Mullards in the other two, and JJ 6V6's as power tubes at the moment. The 6V6's surprisingly sound pretty good and let me use a less extreme setting on the airbrake at rehearsal.

[Jackie Treehorn]

WOW!! That little change made that much of a difference?

I would guess because those are high impedance runs (which makes them more sensitive to small changes in length, position--like the wires to the pots in a Marshall).

thanks for the report JT! What it looks like to me is that by laying the wires flat against the chassis, you are getting better wire to wire isolation by increasing the respective wires capacitive coupling to ground and thus lessening their coupling to each other. Plus by making them longer and putting them against the chassis, the impedance for the high frequencies should be increased, making the highs harder to get through. Assuming that you could hear it, that's something that you could play with (not just in Trainwreck clones). Length, position of wires to ea. other (farther, closer, twisted together, right angle cross), position of wires relative to chassis, use of shielded wire, etc.

Dai, thanks for the explanation. That makes a lot of sense.

[erigm]

Funny how the Komet's tone stack leads look pretty "normal". I wonder why that amp didn't run the wires "trainwreck" style.

[gnugear]

So the harmonic feedback increased with the longer wires and pinning them against the chassis (just trying to get it straight)?

Also, where did you get your board material? I like the brown.

[Jackie Treehorn]

So the harmonic feedback increased with the longer wires and pinning them against the chassis (just trying to get it straight)?

Also, where did you get your board material? I like the brown.

Yes, that's exactly what happened. I had previously been fiddling with the wires from the board to the preamp tubes. Running the wire from V2's cathode parallel, slightly spaced from V2's plate wire helped the sound & feedback, too. If you look at the Ginger pictures, there's a shot of the full chassis and the shielded wire coming from the output of the tone stack, the plate wire to V2 and the cathode wire from v2 all converge and run parallel a little. Fixing the tone stack, however, was like unleashing the amp and much more dramatic. Perhaps it's a combination of the two.

Yes, the Komet looks more conventional in the tone stack wiring. Ginger also doesn't have the wires run per Mark's layout. I guess Ken could tweak the layout for each amp. Who knows? I think it's worth trying both ways, though.

Gnugear, I sent my layouts to Ray D. http://smallbox.freeservers.com/index.html and he cut the boards and installed the old Marshall style turrets. He did a great job. The boards are incredibly thick! They looked much better before a year or so of soldering, desoldering, etc. etc.

[Mark]

Dear Jackie

I'm glad the info I provided was able to help. I do have an "exact" layout for an Express/Liverpool amp. I have been meaning to forward it on to Omar, but work is getting the better of me at the moment.

Should you want a copy, just send me an email. there is also a layout of the Express style power supply floating around too. Once you see it you realise why no one copied it. The Komet layout is far better (looking.)

I'd also love to see the Two Rock transformer spec sheet and be able to compare the Heybour transformers with them. Then I think we'd have all of the puzzle. Though I wouldn't be surprised if no one heard any difference.

P.S. Jackie, I'd love to hear a clip of your amp.

[gnugear]

I'd love to see it (if I don't have it already!!).

c.larralde@verizon.net

[erigm]

Mark,

What kind of file is your layout (pdf, jpeg, gif, illustrator, corel, etc.)?

[Dai H.]

Dear Jackie
Should you want a copy, just send me an email. there is also a layout of the Express style power supply floating around too. Once you see it you realise why no one copied it. The Komet layout is far better (looking.)

you know iirc--about the amp I believe JT's amp is copied from (those enhanced pics)--Hogy from Komet was saying something about--or the gist of what he said was that that Ken wasn't finished w/that design, so it may have looked differently when he presumedly did finish tweaking out the design... Or it could have been disinformation, lol (which I wouldn't fault him for though).

[Allynmey]

Hi Mark, con you e-mail the layout please?

Allynmey

allynmey at aol dot com

[Omar]

Jackie,
Thanks for the great info. Can't wait to try this on my T-wreck clone.

Btw, I know I've told you before, but your amp look fabulous!!

Omar