Metro Marshall MOAB+ build thread

[RedPlated]

Thought it would be fun to post a build thread on this Metro clone. It’s a super lead build with Heyboer transformers and what appears to be a Metro chassis and turret board.

This one belongs to @grimmchaos.

This amp will be getting a full MOAB+ mod with my Add-a-Stage added tube gain stage PCB, 3 way Mid Structure switch and 3 way Ultra Tight switch.

Now, for the extra fun part… this particular amp will be getting a brand new product I haven’t announced yet which will add a full clean channel. It will be foot switchable and include a full EQ, bass, middle and treble, with a 3 way bright switch.

The amp will use a two button foot switch and switch between 3 and 4 stages on one side, and between gain and clean channels on the other side. Making it ideal for live use.

Here is the amp as it arrived. I’ll post updates as I complete the mod. Going to be A LOT of work but I will be grinding away at it asap.

 

[RedPlated]

So I’ve measured all the internal voltages, tested all the tubes, and all looks good.

I replaced the attached power cord with an IEC. Replaced all screen resistors, which revealed a fragile pin on one socket. So I replaced that tube socket.

I’ve stripped all the old components off the board, added some of the new ones, removed all pots and input jacks, and AC heater wiring for the preamp tubes.

I’ve marked the back panel spacing for the loop, atten-u-hater, NFB, Depth, etc… and will drill those holes next. Then add DC heaters. After that, lift the board and re-do all the grounding points.

 

[Trevor]

Love this

 

[rallyfingers]

Noticed the Metro has "Neutral" fused as well as your IEC, I'd swap them wires & fuse the "Hot" for safety/code reasons.

 

[RedPlated]

Noticed the Metro has "Neutral" fused as well as your IEC, I'd swap them wires & fuse the "Hot" for safety/code reasons.

You’re right. I caught it too. The whole time I was taking the cord out, I was telling myself to wire hot to the fuse. I guess I’m getting old and delusional sometimes.

 

[RedPlated]

Holes are laid out and drilled in the chassis. This will be for fx loop, NFB/ depth, atten-u-hater, clean channel controls/ bright switch, Ultra Tight switch and Feel switch.

 

[retrorack]

Pretty soon you’ll have a bread board on the back. The possibilities will be endless.

 

[ilikehats]

@Sixstringflannel GET THE HELL IN HERE

 

[Sixstringflannel]

Here for it bro! Keep the updates coming - this is bad ass!

 

[RedPlated]

Board lifted, making connections underneath and adding new ground points along the chassis.

New pots going in, DC heaters installed and wired. Back panel labeled. You can see how the layout looks. Pretty killer on this one. Fully loaded.

Added one of my single relay boards to switch the output of clean and gain channels into the loop. There will be a total of 3 relays in the amp to handle the switching duties.

And a pic of the 6 way Gain Style switch being built. Selects from 6 different value diodes / transistors for different dynamics and response.

Still a long ways to go…!

Side note…whoever built this amp put a sleeve of shrink tube on the end of every single wire in the amp. No idea why.

 

[SpiderWars]

Side note…whoever built this amp put a sleeve of shrink tube on the end of every single wire in the amp. No idea why.

I noticed and I assumed it was pre-emptively preventing the insulation melting and looking bad.

Are you making/selling those relay boards or is that something already available?

 

[RedPlated]

I noticed and I assumed it was pre-emptively preventing the insulation melting and looking bad.

Are you making/selling those relay boards or is that something already available?

Yes I have a bunch of them. I designed my own. They’re pretty compact, which is nice. The last ones I used had solder pads for resistors to prevent popping, but those have never worked for me, and I don’t have popping issues anyway, so I’d rather have a smaller foot print and leave that off.

I can sell the relay boards. I’ve been meaning to add them to my site. They will be necessary with the clean channel setup I’m about to release.

 

[glpg80]

Love the build progress. At least it’s getting the spa treatment it deserves!

 

[grimmchaos]

This is awesome. Love watching this come together!!

 

[DredFryer]

Footswitchable clean? I'm in.

 

[RedPlated]

Footswitchable clean? I'm in.

And wait till you see the clean channel circuit. It’s awesome.

 

[RedPlated]

Here’s where I wrapped up at around 2am this morning. Pictures just cannot convey the amount of hours and work that goes into these mods. Every wire, solder joint, capacitor, resistor, etc, etc… it’s a ton of effort. But I do enjoy it. I love seeing an amp transform into something so much more useful and dynamic.

All pots are in, fx loop installed, board back down and buttoned up, new input jack, foot switch wired to gain and Aura push pull pots for channel switching and 4th stage switching.

Still plenty more to do. Hopefully I can jump back on it later tonight or tomorrow.

 

[RedPlated]

Here’s a teaser for the clean channel

 

[RedPlated]

Made some good progress today. Switches and front panel wired, Add-a-Stage (4th gain stage) installed. Getting ready for clean channel install.