Build Log - John Mayer Amp Clone

[Johnny_Boy]

I've been sitting on parts that I've gathered for several years now and finally got around to start on it over the Christmas through New Year holidays. I am going to write up the build log here, as I've had a lot of issues that I had to work through, so others can benefit from it.

What I am trying to build

• Two Rock John Mayor Signature Amp - Front
  JM front.jpg

• Two Rock John Mayor Signature Amp - Back
  JM back.jpg

• Production photo inside
  JM production inside 2.jpg

Build Background Information
I am building it based on many details found around the internet, but mostly from

• AN Wonderland/JM 100w layout thread on this forum - https://ampgarage.com/forum/viewtopic.php?f=4&t=29774

• The Tone Geek blog - https://www.thetonegeek.com/post/2019/0 ... -amplifier

• Two Rock John Mayer Signature Manual - https://www.two-rock.com/ownermanuals/trjmsmanual.pdf

Layout and Schematic

• Amplified Nation Wonderland amp layout by Taylor
  Wonderland 100w jan2017.jpg

• John Mayor Proto Schematic by Aaron
  TR JM Schematic.jpg

[Edit - the prototype schematic has too many differences from the layout. Use the updated schematic down below in this thread]

[Johnny_Boy]

Additional Photos of Previous Builds that I've Cross Referenced

• Someone? (Amplified Nation?) 50 watt build
  Two Rock John Mayer.jpg

• TR JM Prototype inside photo
  Guts Proto.jpg

• MHartman's build
  MHartman Mayer Clone DSC_0458.jpg

• Two Rock Classic Reverb inside photo
  Two Rock Classic Reverb.jpg

[Johnny_Boy]

Chassis Info
Chassis build information from Taylor Cox from Amplified Nation

• CAD rendering
  WO-03a.JPG

• Dimensions and layout
  WO-03.JPG

[Johnny_Boy]

Faceplate Design
Here is my "Tow Rack Jon Mayor" faceplate design.

• Tow Rack Jon Mayor - front.jpg

• Tow Rack Jon Mayor - Back.jpg

I don't have a way to silk screen print at home. So I am going to print on my color inkjet pigment photo printer and then put it behind Plexiglas (i.e. Marshall Plexi panel look). Hopefully it will turn out OK

If you plan to use the above, you might have to do a trial and error to move the hole alignments to the proper place. I've aligned them to match my chassis, but depends on how the chassis was built, it might not align.

Originally I've made these faceplate design, but I wasn't sure if I should use it, mainly due to the trademark issue, though I am not using it for commercial use, but just my personal fun.

• Two Rock John Mayer - front panel.jpg

• Two Rock John Mayer - Back Panel.jpg
  [notice the serial number #26 for the Limited Edition of 25 ]

[Johnny_Boy]

Bill of Materials

Ugh, I had to order like 10 different orders from varying places to get all the parts ordered over multiple weeks! I hate that. Keeping the placeholder here, so I can list out the parts for those who want to order it in one shot in the future.

Transformers
Basically I've ordered the whole ClassicTone Twin Reverb set.

• Transformers.jpg

[Note - I ordered 40-18004 instead of 40-18005, per the schematic that I used, for the power transformer and didn't realize until I was ready to build it. Main difference is 18005 has 330VAC while 18004 has 320VAC, so your B+ might come out slightly lower. Also the bias tap is 60V instead of 50V, but you can use the bias trim pot to adjust this later, so I don't think it matters. Though I ended up using a higher value resistor (6.7K ohm instead of 1 ohm) to reduce it to 48V eventually, but I don't think that was necessary at all]

Orange Drop Capacitors

• OrangeDrops.jpg

I've built a few Hi-Fi amps before but never a guitar amp, so I was totally against using Orange Drops for any kind of signal path coupling capacitors, but after doing some research it looks for guitar purpose you do want the coloration that comes from the Orange Drop capacitors.
[Side note - polypropylene vs polyester orange drop. Of course when I was building hi-fi amps, I would pick polypropylene over polyester any days, as it give more "hi-fi" sound. I didn't realize for guitar amp builds most people prefer the polyester orange drops instead. By the time I've learnt this I've ordered and soldered half of them in, Ugh. I might have to switch them out later if the amp sounds too pristine.]

Sprague Atom Capacitors

• c-sa_group_0.png

These for the power supply section. Yikes, since when these become so expensive? Mouser.com had crazy expensive prices for these. I ended up going with a mixture of Sprague Atom, F&T (which are popular among Hi-Fi builders) and JJs.

[To be further edited as I go along here...]
Attached the Excel file of parts that I purchased.

Two Rock John Mayer Parts List (1).xlsx

[Johnny_Boy]

Cabinet Box Build

Dimension of the Amp Cabinet shared by Amplified Nation. This is what I've used.

• TAG drawing.jpg

3D Rendering of the cabinet. Courtesy of The Tone Geek.

• Cabinet CAD from Tone Geek.jpg

After spending 8 hours making two boxes (just the wood part, not wrapped) at my father-in-laws shop, I am thinking I should have just bought the built cabinet instead from Taylor at https://amplifiednation.com/cabinets

Here is my built box.

• TRJM Box1.jpg

• TRJM Box2.jpg

I've decided not to do finger joints as that would taken me even longer. I've used pocket hole joints instead. While it will not be as strong, I think it should be plenty strong for my use.
I've sprayed painted inside with black paint.

For the wrap part, I've ordered the carbon fiber tolex from Parts Express. Unfortunately they ran out and sent me less than half of what I've ordered which was not long enough.
https://www.parts-express.com/parts-exp ... --260-7612. But you can purchase it from other places like Mojotone (I didn't go with them as the shipping cost was a bit crazy).
OK, so after spending about 5 hours (e.g. cut,wrap, wait for the glue to dry, go get some food, and repeat) I finally got it all wrapped.

• CFWraptooshort.jpg

I've never done Tolex covering before, so I had to do some quick YouTube watching . I liked the video from Uncle Doug (and Rusty)

• 
  

[pompeiisneaks]

Wow great stuff, thanks for the detail. Can't wait for the full thing

~Phil

[Guy77]

Your build is looking great! Its a great sounding amp !

Lots of room to customize. I have done things like put the 68K voltage divider in the tone stack on a switch and go from 68k to 140K ( by adding another 68K resistor). And placing the negative feedback resistor on a pot for variety!

Enjoy

Cheers!

Guy

[rootz]

That reference classic reverb signature is the odd one here. Yes, mostly like the famous JM amp, but with FET, PAB, gain structure. No idea what the left relay board does. Not a clue either why there are a cap and trim pot on the PAB relay board. Might be nice additions to the JM amp though.

Must say I really like this thorough and pro approach in this build log.

[Johnny_Boy]

Question #1 - How do you Tolex wrap the inside round corners of the back cover?

Any tips on how to do this? I can't figure out how to wrap it in a way it looks totally professional. Here is what mine looks like now.

(ignore the ugly staples they are there to hold it in place while the glue dries. I will pull them out later or replace them with real thick staples)

• insidecorner1.jpg

• insidecorner2.jpg

I used a single piece to wrap this thing. Once I realized that the cut wrap could not cover half circle, I've put another piece of tolex that covers the inside half circle first and then wrapped those "pizza slices" over it. Not sure if that was the best way. you can't tell from 3 feet away, but if you go close, you will see how it is done, which is not pretty.

On a side note, these fake carbon fiber look tolex are not very sturdy. A slip of the screw driver drill cut right through the tolex. Ugh . (filled it in with a black Sharpie pen to hide my sin there... )

• Ding.jpg

[norburybrook]

I tend to make the rear panels only 1/2 inch instead of 3/4 inch plywood for this reason. Also I heat it with a hair drier and stretch it before I cut the 'pizza' slices and I usually cut them finer than yours..i.e more slices.

Black is the easiest colour to hide as you paint it black first so you don't see any small triangles of uncovered wood underneath. I also route the edges as well the same radius as the cabinet edges.

so 1/2 inch ply and the hair drier to stretch is the way to go. IMHO





M

[rootz]

Haha been there, done that. First time I wrapped a rear panel I had the same problems. Last time I made the panel from 12 mm birch ply, that is the same 1/2” Marcus used. Problem solved. I painted the inside of the curve black with water based paint. Great stuff, covers the wood in one go without an undercoating. Only downside is that the glue I used doesn’t really stick to it well. So left the backside where the triangles go unpainted. I also noticed that sticking the triangles down properly goes better when you chop their tops of with a pair of scissors.

[alkuz1961]

I also use water-based paint, but I just paint open area after the tolex gluing works are finished.

[Johnny_Boy]

Updated & Corrected Schematic
The prototype schematic noted above is quite a bit off from the layout graphics of the production amp. It took me hours to reconcile it.
Then I noticed that Sonny ReVerb's file was much closer to the production amp. So, I've used Sonny ReVerb's Wunderbar 50 schematic as the baseline,but modified to match the layout file.

Two Rock John Mayer Production Schematic.jpg

I've marked RED for the ones that I've added or changed.

Notes
- for the power transformer, since I used 18004, instead of 18005, it ha extra "SS" tab, which I drew it in the schematic. You will not have that if you use 18005 transformer.
- Same thing with the heater center tap. 18004 do not have it but 18005 does.
- I missed updating pin #8/cathode on tube V6 ad V9. Instead of them going to ground directly, it should be tied to the 1 ohm resistor on pin 8 of V7 or V8 6L6 tubes.

1. Can someone check to make sure it looks right?
2. Any idea why there are 100 ohm resistors on the heater wires for V7 and V8?
3. Also why would you use two different values, 110K and 120K for R49 and R50? Is it intentionally to not match them? Maybe related to #2 question above?

[norburybrook]

Updated & Corrected Schematic
The prototype schematic noted above is quite a bit off from the layout graphics of the production amp. It took me hours to reconcile it.
Then I noticed that Sonny ReVerb's file was much closer to the production amp. So, I've used Sonny ReVerb's Wunderbar 50 schematic as the baseline,but modified to match the layout file.
Two Rock John Mayer Production Schematic.jpg

I've marked RED for the ones that I've added or changed.

1. Can someone check to make sure it looks right?
2. Any idea why there are 100 ohm resistors on the heater wires for V7 and V8?
3. Also why would you use two different values, 110K and 120K for R49 and R50? Is it intentionally to not match them? Maybe related to #2 question above?

100r Resistors are artificial center tap for the heaters (stops hum).If your PT has a center tap on your heater winding you don't use these.

R49 and 50 and the PI plates so they're intentionally mismatched to add a bit of harmonic content.

M