2204 chassis layout diagram

[mdc1]

Reworking my 2204 with a Metro board. I have the Billy Batz layout, the SDM layout, and the Ceriatone. Which layout promotes the best noise immunity and also includes the best coverage of the power section and output stage wiring (Batz omits)? Adding new caps and an MM output transformer.

[Mars Hall]

Reworking my 2204 with a Metro board. I have the Billy Batz layout, the SDM layout, and the Ceriatone. Which layout promotes the best noise immunity and also includes the best coverage of the power section and output stage wiring (Batz omits)? Adding new caps and an MM output transformer.

This can be found in the Wiki section of this forum.

http://metroamp.com/wiki/index.php/2204_chassis_layout" onclick="window.open(this.href);return false;

[skidbrake]

I just finished a JCM800 2204 build using nearly the same layout as this. I cobbled my scheme together using layouts from Joe Popp, Nik at Ceriatone, Metro forum members SDM and S. Arledge, and Marshall schematics. I chose to go with lower filtering on the PI (32x32) and a bass spec tone stack (56k/250pF), and a 50KL middle pot, blending a bit of the 86 spec warmth into the grit and gristle of a 50W 80's-style Marshall. I play Strats and was going for Jimi bluesy tones at the edge of breakup, but to also be able to roll up the guitar vol pot to belt out some rib-cracking chords. I got it with this circuit -- and without a lot of high priced parts, which was a revelation to me.

For trannys, I ordered Mojo's private-label JCM800 PT/OT/choke set, which were reasonably priced. I wasn't sure what to expect in comparison to MM, Heyboer, ******, RS, Metro and other era-correct brands, but thought I'd give Mojo's iron a shot. (I imagine they're made by Heyboer?)

I scrounged up some Alpha pots and a steel 50W chassis, I hand-drilled a PTP using some black Garolite sheet I had, gathered some PTFE wire, a mix of CC, CF and MF resistors (I only used CC on the NFB circuit). Nothing fancy. The only place I splurged was on the caps (F&T and Sprague), because I've learned the hard way that you can't go cheap on filter cans, and I used Sozo coupling caps for tone. Other than these, this was largely a spare parts build, in true DIY spirit!

This was my fifth build and I've struggled with ground loop noise on my earlier efforts. I've tried star grounding to single point, buss grounding, dual-point stars on busses that separate power and signal, all with mixed results. When I read about the Larry Grounding scheme (search for this on the Metro forum), I thought I'd give it a try. Holy cats, man, it works! When I fired up the 2204 tonight, it was resting under two nasty banks of buzzing fluorescent shop lights, and the amp hissed so quietly I thought the speaker cable was unplugged. The only time I can get it to buzz is when I hold my Strat up to the face of the amp, otherwise it's dead quiet. This is how I will ground my amps from now on.

On to the tone ... I was expecting more raunch and grind from the MV and diode rectification, and less of the sweet woodiness and chime of earlier era Marshalls. I was willing to compromise in order to get MV breakup at bedroom volume levels, and assumed I'd pay for that by giving up some tone coloration.

My shop speaker cab has a Celestion G12H in it, my Strat is a Jeff Beck, and when I flipped the switch I was stunned. Jacked into the Hi channel, MV set on 5, Treb on 3, Middle on 8, Bass on 5, Presence on 2. I started playing "Little Wing" and couldn't believe my ears.

I dimed the MV, set the Vol on 5 and started playing with the guitar's volume knob to see what it could do. Gorgeous shimmer, wood, smoke, ash, all of the colors of a Strat/Marshall union coming out, and it roars when it's opened up. I can't wait until the caps and tubes settle in to see what else it has.

So the point of this little essay is: To share what I was able to do with non-vintage, after-market parts that are affordable and available, to recommend the Larry 6-point grounding scheme, and, most importantly, to express my gratitude to Larry, Joe Popp, Velvet George, SDM and the many others who generously share their expertise and ideas on this forum. With your counsel and encouragement, and access to the vast repository of advice and tips provided in your many postings, I've been able to reverse time by bringing back the sounds of my youth, and with it the energy and optimism I felt when I was a younger man. Thank you, all.

[skidbrake]

Here are notes from my build journal for those who are interested. These are the changes from the JCM800 2204 stock spec:

>> 47k instead of 100k on NFB to give the tone more wood, and wire NFB to the 8Ω tap
>> 0.022uF PI caps instead of .1uF, to reduce bass response
>> 1k bias resistors ground to lug #5, not their octal bolts
>> Added 330pF ceramic cap across each 68k input resistor (V1-2 and V1-7) to beef up tone
>> Tone stack is 56k/250pF to give it more midrange beef; may also try 47/500 and 47/250
>> Used a 50KA Middle pot for more midrange flexibility
>> No bright cap
>> Larry grounding scheme ... with amazing results
>> 50/50uF mains; 32/32uF for screens & PI. Dual 33 on the board for pre filtering

>> Carbon comp resistors on:

V1a cathode
V1b cathode
V2a cathode
V2b cathode
Tone stack
NFB

>> Metal film and metal oxide resistors everywhere else
>> Tubes are Mullard RI EL34, Tung-Sol 12AX7, which I understand were spec for this amp (though Im not positive about this)

I'll post some pics soon, and some sound clips using an H2 Zoom.

[vanhalen5150]

Pic's?