Hi Shun. Haven´t found it either, but I´m sure it´s a stripped down version of its big brothers, so having it´s brothers schematic in front of you should be help enough. Start by checking that TRS single-jack effects loop. You might have a problem there.
Bye.
J M Fahey

Hi Pelanj. I think that unfortunately today the speaker is still necessary; we should experiment some more until it can be fully emulated. I´ve tested a lot about SS reamping a tube amp. To begin with, with a resistive load it sounds  different (not bad at all, similar to a very good pedal) ; but a real speaker load provides the real thing. Let me define exactly what i´ve found, and which basically agrees with your experiments: if I get a certain voltage waveform (from a tube amp) across the speaker terminals of, say, a Vintage 30 mounted in a certain box, and I reproduce that *same* voltage waveform, across one or many V30s mounted in similar boxes, at *higher or lower* levels, I get the exact same sound with the important advantage that the original tube sound was obtainable at only a fixed volume while this "clone waveform" can be reproduced at any volume, with only two caveats:
1) at lower volumes, *my ear* hears less bass , and
2)The SS final amp must be powerful enough to *NEVER* clip at rehearsal or stage levels.
The Weber mass is 70% of a speaker .... and provides 70% of the sound. Obviously, it´s almost there, but it still lacks emulation of 2 smaller but still important physical aspects of real speakers:
1)the short voice coil of a typical guitar speaker travels outside the gap often, mechanically "clipping" peaks, and that in a frequency dependent way, which I at least coudn´t emulate with diodes. (Well, I could do it at a fixed frequency, say 90 or 100 Hz, but not across a usable range of frequencies). As a by product, the V. Coil leaving the gap loses inductance brutally and in an unsymmetrical way (because magnetic circuits are unsymmetrical), modulating the high frequency response.
2)Reactive load boxes emulate only the main resonance (80/110 Hz) and one or two also emulate the impedance increase above 500 Hz, but none to my knowledge emulates other smaller but audible resonances which are mechanical in nature and are generated by the paper cone itself.
Also a myriad peaks and dips are lost.
That´s why I say that for a perfect response a speaker (even in an isolated box) is still needed, but with patience and hard work that will be emulated too.
As for a Randall, it does NOT sound like a tube amp, it´s very good but on it´s own SS way, which is commendable.
In that case, just hook a Randall preamp to a Big power unit and let it loose.
Bye and keep experimenting (and don´t forget those MP3s)
J M Fahey

Dear Phatt, that´s exactly the relatively no pain but precise way to go.
To summarize it, and compare it what´s available "out there":
the signal chain should be:
1)Active mics/active electronics in guitar/inline clean preamp
Al three amount about to the same end result: powerful, clean guitar signal; sent into:
2)Some GOOD distortion/overdrive that you like; sent into:
3)Good clean preamp, Fenderish or Marshalish or Voxish (your choice) which can be Tube (the classic solution) OR SS which sounds the same *when clean*;  driving:
4) Some *Power* tube, which can be overdriven and Transformer coupled to a real-world speaker , with all its quirks, resonance, impedance and phase shifts, nonlinearity, etc.
Here's where the real Witches Brew cooks, in that complex interaction between those three actors.
I agree with you that a PP amp is best, but even a humble Champ can prove its worth there (I´ve already tested that).
That signal should be suitably padded and re-amplified by
5) A good SS amp driving guitar speakers.
5)Your inclusion of a Graphic between 4) and 5) allows for fine tweaking of the sound, but must be used subtly and carefully to avoid destroying the sound you already have.
I agree that that´s the way to get World Class sound in a very practical way.
Congratulations!!
Please post some MP3s
Bye.
J M Fahey

>>and thank you for your book. You should recieve some kind of >>ssguitar.com medal... (2)
Agree fully.

Hi Wooji, I think that as a final safety test, you can use a 100W series lamp, play quite lous for 1/2 or 1 hour, and if everything still looks OK, you're done!
Power it straight without the lamp, play sometime while checking it now and then, and that's it!
Congratulations on your servicing skills.
Bye

Teemu and others: thanks a lot for the myriad links and excellent books suggested.
I myself got into this thanks to Jack Darr´s book; my first guitar amp was a Gibson GA-5, then a Fender Bassman 2x6L6, then an Ampeg BT-15, and from there on. I had also built Popular Electronic´s 60 W guitar amp published in 1968. Thanks again.

Hi Wooji.
So far so good: you can play, clean and dirty, only not terribly loud because of the lamp limiter. Good!
The lamp glowing brighter on higher power, specially on bass notes, is what´s expected.
The only thing that stil worries me a little is the "getting brighter after 20 minutes" which might indicate some thermal riunaway.
As Teemu pointed, quoting Fender literature, there seem to exist some cases of bad thermal tracking (the diodes not making good contact with the heat sink); check that.
You might also play (still with the lamp) for 20/30 minutes, until you feel heatsinks at least warm, and then turn down the volume but not powering it off. If after one hour of not playing it´s still hot (or, worse still, hotter) and/or the lamp keeps getting brighter, then you have thermal runaway.
If everything appears normal but you still aren´t sure, replace the series lamp by a 100 Watt one, which will let you play quite loud, and still offer some protection. Bye.

Hi One Way.
I think I must rephrase my earlier answer. In fact the toroid *does* supply 25+25 Volts A.C. , and it´s correctly labeled. What I should have added more clearly  it that such a transformer, *hooked to a bridge rectifier and 2 capacitors* will supply 35+35 Volts D.C. , which is the peak value of the 25+25V senoid. You suspect right, that voltage goes down somewhat with high volume (up to 20%), but don´t worry, that's  accounted for in the design. Engineers must live in and design for the "real world". Good luck.

Dear VA3UX. What I see is that Marshal, fed up with everybody copying them, resorted to use obscure, relatively unavailable chips. That way, it´s difficult for anybody to copy them, and in case you do, it´s very easy for them to prove it : you just can´t argue: "I was just tinkering in my Lab and ¡Oh my God, don´t tell me that by sheer chance MY design somewhat resembles Marshall´s"and they have your hands tied. I can tell you,  that ordering  a couple of them is easy , but asking for, say, 50 or 100 of them raises paranoia. "Hey, you aren´t trying to copy us!, are you ? Today they are using an even more obscure switcher, I think it´s "DG212" or something like that, not sure. It´s pin-compatible with other CMOS types, but it handles full +-15V (30V total); any substitution dies instantly. Other important point: M5201 is basically an TL072 + an internal switcher; it can´t cost more than 50 cents (or even less) in bulk amounts, but Matsushita won´t sell them to you, so Marshall can charge  3 to 4 Euro each. Whenever I tried to deal directly with Japanese companies, they often said they could supply me, but: 1) they never have stock, not even samples, 2) I must sign a "Buying Plan" stating, say, "I need 1000 in February, none in March, 2000 in April ..."and so on (they call it "Just In Time Production": JIT); 3) minimum quantity 10.000 units of each. Well, they're Japanese giants !!! Their terms are easy to meet for Fender, Marshall, Crate, etc. but impossible for us mere mortals. Good luck. PS: ¿Vous êtes Francophone?

You found a big one there!! Probably somebody tried to repair it and didn´t bother to use micas there.
As Teemu points, some units used silipads insulating rubber.
I never trusted it, mica/grease works much better.
Go on slowly and carefully with your servicing.
Good luck.

Hi. If that´s what you want, good.
Your toroid supplies +-35V.D.C, which is great for an LM3886. I think you already have something like that.
A commercial preamp I suggest you copy is Marshall´s Lead12, a killer 12 watter from the 80´s. I think the schematic was called "3005" or something like that.
It was so good that Billy Gibbons (ZZ Top) rackmounted one of them, to use it live.
It only uses an LM1458 (you can use RC4558 or TL072), and will easily drive your power amp.
Bye.

Hi Ray: short answer: the hum comes from your guitar. The clean channel doesn´t bring it forwars very much, but the hi-gain channel shows it in all its beauty. If the hum all but dissapears when zeroing your guitar´s volume pot, that´s it
Just to make sure, short a plug , insert it in the amp input and switch channels.
Very probably you´ll have very little hum, only hiss.
Bye.
PS: if (very unlikely) your amp hums badly, then you have anther problem. Filtering ... internal grounding ... Hard to tell without seeing the amp.

Congratulations, very interesting amplifier.
When possible post some clips.
Bye.
J M Fahey

INCREDIBLE STUFF !!! Unbelievably good. You guys deserve a prize. What a great range of products. Best of all, besides looking very professional they are very creatively packaged and veeeeeeeery FUN!!
Congratulations.

Hi One Way
Being an Engineer surely helps !!
Having access to some kind of metal shop is even better.
The worst problem for experimentors and hobbyists is the "mechanical" part.
"Small" projects, those which can be built on one board, powered by batteries or some wall-wart and which can work without an enclosure or which are happy with some kind of plastic case, are best.
I suggest you download Teemuk´s *excellent* book; various datasheets as needed, and make an "universal" chassis, with a lot of holes for pots, jacks and switches in the front panel.
That way you can mount firmly your power amp and supply, and experiment at will with various preamps, effects, etc.
If possible use aluminum: easy to work, doesn´t rust nor need paint or other protection,etc.
I found this veroboard PCB designer software very useful:
DIY Layout Creator:
http://www.storm-software.co.yu/diy/
It already comes with a lot of useful projects already designed and tested.
Bye.
J M Fahey