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fitz

fitz

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New empty amp chassis day.

Got this gutted Madamp G3 chassis for a couple of bucks.
Came with 3 Cliff jacks, the power switch and a fused IEC power cord socket.
The little doodads are worth what I paid.
No cover, but I have a plan... :hmmm:

m2-1.jpg

Low watt amp build?

Nope.

New smaller case for my John H M-2 attenuator.
The back will be the new front, and I'll cover the power socket with the vanity plate.
Need to enlarge the 2 existing jack holes and add one more for the stage switches.

m2-2.jpg

Front will be the back.
Power switch will be reused for the fan.
Control pot holes will be enlarged for a 9v power cord jack and 4 speaker jacks.
(amp in - 8Ω / 2x16Ω parallel jack - main 16Ω out - and a 2x8Ω series jack)
The existing input hole will just get a button cover.

m2-3.jpg

Disassembly of the current M-2 is underway.
I think I can remount everything with only a few wiring modifications.

m2-4.jpg

Yesterday I prefabricated a new top cover - drilled & mounted the fan and vent.
Along with the aforementioned plan....

I've since decided (after I did the drawing) to swap the front to back for less new holes and just the one unused existing hole.

m2-5.jpg

Let the games begin!
 
fitz said:
New empty amp chassis day.

Got this gutted Madamp G3 chassis for a couple of bucks.
Came with 3 Cliff jacks, the power switch and a fused IEC power cord socket.
The little doodads are worth what I paid.
No cover, but I have a plan... :hmmm:

View attachment 106732

Low watt amp build?

Nope.

New smaller case for my John H M-2 attenuator.
The back will be the new front, and I'll cover the power socket with the vanity plate.
Need to enlarge the 2 existing jack holes and add one more for the stage switches.

View attachment 106733

Front will be the back.
Power switch will be reused for the fan.
Control pot holes will be enlarged for a 9v power cord jack and 4 speaker jacks.
(amp in - 8Ω / 2x16Ω parallel jack - main 16Ω out - and a 2x8Ω series jack)
The existing input hole will just get a button cover.

View attachment 106734

Disassembly of the current M-2 is underway.
I think I can remount everything with only a few wiring modifications.

View attachment 106735

Yesterday I prefabricated a new top cover - drilled & mounted the fan and vent.
Along with the aforementioned plan....

I've since decided (after I did the drawing) to swap the front to back for less new holes and just the one unused existing hole.

View attachment 106736

Let the games begin!
Click to expand...
Are the jacks stamped "UK?"
Or are the jacks stamped "Cliff," without the "UK?"
 
Last edited:
Initial surgery seems to be successful.
I think everything is going to fit with minimal rewiring.
The new series jack will need incorporated into the circuit.

Next is making a new mounting plate for everything now that I have the switches and jacks located.
1/4" aluminum also acts as a heat sink, mounted on some offset risers
Might need to do a little more measuring and thinking - possibly a new drawing before cutting and drilling.

m2-6.jpg

Back view.
When I made the top cover, I also made a blank to go on the bottom to cover the tube sockets and other holes.

m2-7.jpg
 
I cleaned up the layout a bit to get everything to fit.
Cut a new 1/4" aluminum mounting plate.
Haven't cut a wire yet...

m2-8.jpg

Laid out the holes and spent some time at the drill press.
Just dropped the little bolts in for a test fit.
Couldn't find any thermal past so that'll be here tomorrow.
Gotta make some shorter spacers for under the mounting plate, or possibly carve out the corner by the coil.
It's going to mount on its own spacer and attach directly to the chassis.

m2-9.jpg

Here's a gut shot of how it used to be if you're curious.
Lots more room in a 17 x 8 x 3 chassis.

m2-10.jpg

I think that's a wrap for today.
 
syscokid said:
Fricking awesome! What does that reddish coil do for the circuit?
Click to expand...
It's the inductance coil.
Paired with the main resistor, it presents the amp with a constant desired impedance and appropriate load.
The other 2 big resistors start dropping the power output.
Additional stages are pairs of resistors engaged by the switches that further reduce the output.
The other small resistor near the middle is a tone compensator for an 8Ω (2x16Ω) load.
The amp always sees 16Ω with this version.
I'm adding in a series jack to run a pair of 8Ω cabs.
 
If I'm not mistaken, the inductance coil acts like a speaker coil giving a "reactive" load to the amp so it not just a pile of resistors.
My Weber attenuator has an actual speaker coil & magnet in it. (thought I had a gut shot of the Weber, but can't find it)
 
fitz said:
I cleaned up the layout a bit to get everything to fit.
Cut a new 1/4" aluminum mounting plate.
Haven't cut a wire yet...

View attachment 106739

Laid out the holes and spent some time at the drill press.
Just dropped the little bolts in for a test fit.
Couldn't find any thermal past so that'll be here tomorrow.
Gotta make some shorter spacers for under the mounting plate, or possibly carve out the corner by the coil.
It's going to mount on its own spacer and attach directly to the chassis.

View attachment 106740

Here's a gut shot of how it used to be if you're curious.
Lots more room in a 17 x 8 x 3 chassis.

View attachment 106741

I think that's a wrap for today.
Click to expand...
Man, you have the best ideas Fitz. I love that you repurposed the chassis. It looks like it was made for the attenuator.
 
ibmorjamn said:
Man, you have the best ideas Fitz. I love that you repurposed the chassis. It looks like it was made for the attenuator.
Click to expand...
Thanks, I was actually searching the Reverb junk pile (used, non-functional) for an enclosure for this very purpose.
This chassis was listed as an "amp enclosure", and 10 x 6 x 2 seemed like a good size.
It had been sitting for 9 months with just a few dozen views, so I lobbed a low-ball and they snatched my offer.
 
Thermal paste was delivered today, so I got everything bolted to the new mounting plate.
Inserted the series jack into the speaker options.
Decided the coil fit best vertically, so I cut a notch in the plate for a little mor clearance.

m2-14.jpg

Wired up the fan, switch and 9v jack.

m2-15.jpg

Waiting for paint to dry...

m2-16.jpg
 
Got it put together and added some labels.

m2-17.jpg

Back view

m2-18.jpg

Mostly working as expected.
Fan was working until I put it in the box - might have knocked a wire loose or it's grounding on something.

My series jack is giving a strangely high (double) resistance reading, but normal with the Palmer on the outside to the 16Ω jack.
I'll recheck the wiring tomorrow, and possibly touch base with John H.

Need to find some feet, so it's sitting on a towel.

m2-19.jpg
 
fitz said:
Mostly working as expected.
Fan was working until I put it in the box - might have knocked a wire loose or it's grounding on something.

My series jack is giving a strangely high (double) resistance reading, but normal with the Palmer on the outside to the 16Ω jack.
Click to expand...
Did you ever get these little gremlins figured out?

This thread has pumped me up with enough GAS to consider trying a project like your John H M2 attenuator build. At the Marshall forum, I’ve been heavily checking out the two huge threads regarding the building of, and completed John H attenuators. The sound clips is what really sold me to pursue this project further.

I can’t tell from your last pic of the internals, but how are you securing that coil inductor assembly in your build?
 
syscokid said:
Did you ever get these little gremlins figured out?

This thread has pumped me up with enough GAS to consider trying a project like your John H M2 attenuator build. At the Marshall forum, I’ve been heavily checking out the two huge threads regarding the building of, and completed John H attenuators. The sound clips is what really sold me to pursue this project further.

I can’t tell from your last pic of the internals, but how are you securing that coil inductor assembly in your build?
Click to expand...
Yes, I rewired the series jack to split the tip instead of the sleeve - if that makes any sense.
I can provide a diagram if anyone wants to do something stupid like that...
I think the fan was just hitting a wire that physically kept it from spinning.
All is working as planned.
I have the coil mounted to the back side of the front panel on an insulating piece of wood, and held in place with some double sided sticky strips.
 
fitz said:
Yes, I rewired the series jack to split the tip instead of the sleeve - if that makes any sense.
I can provide a diagram if anyone wants to do something stupid like that...
I think the fan was just hitting a wire that physically kept it from spinning.
All is working as planned.
I have the coil mounted to the back side of the front panel on an insulating piece of wood, and held in place with some double sided sticky strips.
Click to expand...
I might have used liquid sodium and a cooling tower instead of the fan...(keeps the noise down).
 
fitz said:
I have the coil mounted to the back side of the front panel on an insulating piece of wood, and held in place with some double sided sticky strips.
Click to expand...
Nice… and thanks!

If I build one of these, it’ll be the 8 ohm/50 watt version. No fan. And a Hammond 1590F enclosure: 7.4" x 7.4" x 2.65", which should have plenty of real estate without being overly huge.
 
syscokid said:
Nice… and thanks!

If I build one of these, it’ll be the 8 ohm/50 watt version. No fan. And a Hammond 1590F enclosure: 7.4" x 7.4" x 2.65", which should have plenty of real estate without being overly huge.
Click to expand...
If I was doing a scratch build, I'd invert the coil spool and mount it with the non-conductive screw like it was in my larger enclosure.
Because of the lead wires on the existing connections, I kinda did what I did to minimize re-wiring.
The piece of wood is more of a spacer than an electrical insulator as the coil can act like an induction heater next to the enclosure metal if you put enough juice through it ...
 
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