How important is layout to the TW tone?

[paulruby]

Bob, you might ask Paul Ruby, I know he uses his own layout and has the iron positioned much like a Marshall.

I'd say his builds sound like Trainwrecks to me, and I own the one featured on his site in spalted maple (Elvira).

I'd also agree that the way the tone controls are laid out makes the most importance, and Paul has that pretty similar to Ken's. However his power supply is more like a Marshall in layout if I recall... He has gut pics of my amp on his website...

Dave

EDIT

Link to the guts shots of my amp on Paul's website:

http://paulamps.com/MapleWreckGuts.html

By the way, that was the first express I ever did and I did have some trouble with rectifier noise. The circuit loop of the PT, recto and first filter cap is too big and posed a problem and I had to add some series resistance with the diodes to tame the buzz. This is the nature of doing your own layout. There may need to be some tweaks.

My following amps moved the first filter cap and diodes to a separate board mounted right on the PT. This completely solved the buzz issue with no need for any other solution.

Latest layout examples:
http://paulamps.com/Marta.html
http://paulamps.com/Miriam.html

[gearhead]

Interesting read from the Pre-Francesca days:

https://tubeamparchive.com/viewtopic.ph ... grid+noise

Jackie's second wiring scheme got him excited.

[rfgordon]

The new issue of Guitar Player has several shots of Brad Paisley's Z Wrecks, and at least the control spacing varies from Hattie Mae, his Liverpool. No clue how the guts may vary.

[Bob-I]

Thx guys, especally Paul for the great gut shots.

I'm drawing up a layout for my "Bass-Wreck" or the "Wrecked Bassman". I'll post it when I'm done. My plan is to use the stock Fender xformers, gut everything else and build an Express. I may need to lower the B+ with a zener.

I'm concerned about the xformer impedance since it only has one output tap. Once I get this I'll measure and see what I get. I'm afraid that I'll need a 4 ohm load, but every cab I own is 8 or 16.

[Mark]

I had to add some series resistance with the diodes to tame the buzz.

Dear Paul

What was the nature of this buzz?

Was it mains buzzing, or was it buzziness in the tone of the amp?

[paulruby]

I had to add some series resistance with the diodes to tame the buzz.

Dear Paul

What was the nature of this buzz?

Was it mains buzzing, or was it buzziness in the tone of the amp?

It was the typical mains buzz you get from solid state rectification. When solid state recto is used, there are very large charging current spikes every 8ms to refill the first filter cap. This current flows in the circuit loop formed by the PT, diodes and first filter cap. That loop physically forms an AM radio antenna that transmits RF noise to the rest of the amp, which can be picked up by your input stage. Avoiding this consists of the following:

Make the physical loop of PT, diodes and 1st filter cap as tight as possible. This minimizes the AM antenna.

Keep the PT, diodes and 1st cap as far to the end of the chassis opposite the input tube as possible. Maximizes transmission distance.

Include no grid stopper on the input stage. Minimizes grid node impedance and makes it least prone to picking up the noise transmitted. But, this change also makes the input stage suseptible to radio signals coming in on the guitar chord shield.

So, make your connection of circuit ground to chassis ground right at the input socket. This is easy to do with an un-isolated input jack. Since I use cliff jacks, I add a ground lug to the chassis right next to the input jack.

Finally, use shielded line from the input jack to the first tube to avoid the noise transmitted.

You can see the ground lug right next to my input jack in this pic.

http://paulamps.com/MiriamGuts2.jpg

[paulruby]

Interesting read from the Pre-Francesca days:

https://tubeamparchive.com/viewtopic.ph ... grid+noise

Jackie's second wiring scheme got him excited.

I just re-read this and tried it in my liverpool and it makes a difference. Clarity is improved if the wire from the treble cap to the treble pot runs in "free air" to avoid any parasitic capacitance to the other tone wires or to the chassis. This seems to have a larger effect on the liverpool since the treble cap is only 50pf. That wire is higher impedance and is the path for all the top end of the amp, so is a key point in the circuit where you want to avoid parasitic capacitance hurting the top end.

http://paulamps.com/FreeAir.jpg

The red arrows point to the wire that needs to be in free air.

Green arrow points to an added cap to get the coupling cap between 2nd and 3rd stages up to 7nf.

Blue arrow is the shunt resistor after the coupling cap to get the proper volume knob range. I ended up with 22K here so I could get the sweet spot of the volume knob up to ~12 o'clock. (I like the way the bright caps work when the volume sweet spot is between 10 and 1 o'clock on the pot).

[Bob-I]

Green arrow points to an added cap to get the coupling cap between 2nd and 3rd stages up to 7nf.

I believe that parallel caps like this sounds different than a single cap of the same measured value. I'm not sure why, maybe the ESR of the 2 caps is different than a single, but bottom line, find what sounds good.

Thx for the info Paul. Great stuff!!

[mhuss]

Make the physical loop of PT, diodes and 1st filter cap as tight as possible. This minimizes the AM antenna.

Hmm, this adds another angle to the "where is the best place in the circuit for the standby switch" discussion.

Otherwise, I followed all your advice already (except for the input grid stopper).

Something else to experiment with...

--mark

[paulruby]

Make the physical loop of PT, diodes and 1st filter cap as tight as possible. This minimizes the AM antenna.

Hmm, this adds another angle to the "where is the best place in the circuit for the standby switch" discussion.

Otherwise, I followed all your advice already (except for the input grid stopper).

Something else to experiment with...

--mark

I use a twisted pair between the diodes and cap most of the time. The stand-by switch is right there with the other stuff, so isn't a big deal. In the following pic, you can see my transition from one method to another. The power supply board has a spot on it for a resistor in series with the recto. But, following the other "rules" above made that obsolete. So, there is a grey wire in that position. Then there are a couple very short leads to the stand-by switch between the recto and filter cap.

http://paulamps.com/MartaGuts2.jpg

In my latest builds, that spot for a series resistor is gone and a twisted pair under the board goes to the stand-by switch.

This is the original layout that had an issue. Adding series resistance to the diodes tamed the buzz.

http://paulamps.com/WreckChassisGuts.jpg

[rhinson]

i believe one general wiring "rule" is to try to make the hv sec winding wires distance to whatever rect. as short as possible to avoid any sort of buzz. this is one thing the original style did. of course pretty much any layout could be accomodated to this concept. the "standard" fender layout for parts generally makes use of this idea. rh

[Allynmey]

Bob, I think layout is key more for stability and noise as opposed to tone.

Hold the phone a moment... For a relative novice who is still trying nail down the finer points of this amp building thing, that's a bit like saying that there is no Easter Bunny. I had always thought that layout was ESSENTIAL for a good tone, especially in a high performance amp like a trainwreck. Should I wrote that off as a fools quest and spend time on other considerations? I know noise is a prime consideration when layout is concerned, but I thought there was more to it than that. I've rebuilt my champ probably 4 times with different layouts (exact same circut); some of them sucked, some didn't.

Please don't think that I'm writing this to challenge your statement, I just thought I had somewhat of a grasp on this layout thing and this is something new and different. I'd always held that layout was essential for controlable feedback, bright articulate high end, and the "fighter jet" edge of stability quality that Ken touches on in his interviews.

(Plus, I made an embarassing attempt at a liverpool with a different layout a while back. It was not noisy, just sucky.)

Tom, as someone who is guilty of making "exact clones", I understand your layout concerns. Bob is quite an experienced builder and understand a lot about layout and stabilizing an amp. Paul Ruby's layout is different but again, a very experienced builder can stabalize an unstable circuit with his knowledge. My point is there is not only one way to layout a wreck rather, there is one way to layout a wreck if you want consistant results without having superior knowledge of how to stabilize a circuit. The people that ask me to build them one usually ask for an "exact" build as shown in my build pics that I post as a w ay for people to get a look on how a real wreck is laid out. Many times I will be asked by wreck owners to clone their amps and I do. They ask not to share pics of their amps but, have no problem with me posting pics of my exact clone of their amp...get it? This way I can share the guts of many real wrecks with the owners blessings without having to post real pics!

[Bob-I]

My point is there is not only one way to layout a wreck

In other words, there's more than one way to Wreck a Bassman.

[mhuss]

After reading Paul's post above, I made a few changes last night:

1) Got rid of the input grid resistor; this made it noticeably quieter.
2) Got rid of the parallel switch -- the buzz would increase if I even touched the toggle , one less antenna...
3) Added a 10 ohm 5w resistor in series with the diodes to limit the peak charging current pulses.
4) Twisted the already short wires going from the PS board to the standby switch.
4) Moved the first-to-second node 1k resistor off the PS board -- after running cranked for a while, it was getting too hot to touch, and I don't want to prematurely dehydrate my electrolytics.

Now the hum is at least on a par with the hiss level.

--mark

[drhulsey]

... there is one way to layout a wreck if you want consistent results without having superior knowledge of how to stabilize a circuit...

This is a key point It is me or it is I, which ever is correct Those who know the route can stray farther from the path and reach the same destination