# My JCM800 build project



## Emohawk (Feb 3, 2006)

Hey folks,

Just finished my JCM800 scratch build on the weekend. Just waiting for the cabinet from Trinity (JTM45 style). Here's a couple pics.


















Here's the details...

- Chassis, naked board & faceplates from Nik Azam at Ceriatone
- JTM45 style head cabinet on order from Stephen Cohrs at Trinity Amps.
- Sozo coupling caps
- Alpha pots
- Carling switches
- Cliff jacks
- F&T & JJ can caps
- Sprague Atom filter caps
- primarily 1-watt carbon film resistors
- Heyboer Drake clone transformers

Mods from stock JCM800:
- Cathode resistor on V1A reduced to 5.6k (increased gain on high input)
- all three "bright/high treble" circuits removed (fatter/warmer tone at low volume)
- plexi-style input jack wiring (directly to V1 with 68k resistors)
- increased gain to 3rd/4th gain stages (input resistor to V2a lowered to 270k from 470k)
- old Marshall style presence wiring (8-ohm tap, 27k resistor, 5k pot, .1uf cap from wiper to leg, to ground)
- Fender-style jewel lamp

I basically used Joe Popp's modified version of Nik Azam's Ceriatone layout with the aforementioned mods. Thanks to both Joe & Nik for the inspiration on this one!

I haven't decided on the pre-amp tubes yet. Have an old Mesa branded Chinese 12AX7 in V1 and Sovtek 12AX7WA's in V2/3.

I have tried both JJ KT-77's and EH EL-34's in the power side, both biased to just over 60%. 

With the KT-77's there's a bit more bottom end, later breakup, and an overall slightly warmer tone. Through the lo input this gives a warm, punchy clean tone that just starts to break up toward the top end of the master volume. It's killer for jazzy stuff and is actually a really sweet clean. Through the high input it's a thick tight overdrive, but maybe just a hair too bottom-heavy.

With the EL-34's the breakup is quite a bit earlier. The tone through the hi input is more middy/crunchy - 80's hard rock heaven (exactly what I built this amp for). The lo input gives a more laid back tone, but again breaks up much earlier giving an AC/DC-ish crunch when wound out.

I'm really pleased with the result. I hadn't expected it to sound this killer! :rockon2:

Kirb


----------



## greco (Jul 15, 2007)

WOW...CONGRATULATIONS !!

Thanks for posting the pics.

Great looking amp....very nice work.

Dave


----------



## Emohawk (Feb 3, 2006)

Thanks man. It was great fun (for me at least!). I'm hooked on the DIY thing however. Like I needed another expensive toy habit!!!


----------



## Greg Ellis (Oct 1, 2007)

That's impressive!

Can you give us a wild guess on total time and money spent?


----------



## Emohawk (Feb 3, 2006)

No idea regarding time spent. It's been an off & on thing over the last month or so between work, life, waiting for parts to arrive, etc.

Money wise I think it'll come in at about $1150 CAD including taxes, shipping, duties, etc. That's for the complete amp including the head cabinet Trinity is building for me.


----------



## Guiary (Oct 10, 2007)

Wow nice work! Looks clean! You should head on over to BYOC and start making yourself some pedals! If you haven't already.

My damn chorus pedal!! I can't figure out why my LED won't work!!! Phaser was an easy build.


----------



## Emohawk (Feb 3, 2006)

Thanks!

I already have 4 BYOC's! 

Heavily modded Screamer
Heavily modded Analog Chorus (built to "Fully Loaded" specs)
"Stock" Phaser
Octafuzz with octave lift switch


I had a problem with the LED on my chorus also (after I modded the heck out of it). It turned out the leads were reversed.


----------



## Guiary (Oct 10, 2007)

Ya I tried swapping it around... many times and still nothing. I know the LED is good cause it works with an external power source. Who cares really I just have to remember when I turn it on... and off.

How does the heavily modded one sound compared to the stock one?


----------



## Emohawk (Feb 3, 2006)

Similar. I took the BYOC "Fully Loaded" design & changed the layout a bit - I like the horizontal layout better. On the width/intensity 4-way switch I used the stock setting (150pf cap), one setting below (around 65pf I think) and two above (220pf & 500pf). I also did the "speed" mod (switchable) and that takes it from the max stock speed up to basically a buzz. It's almost ring-mod in between. I added the Vibrato mod (again switchable).

So, it can sound stock plus a less crazy chorus on the bottom of the width/intensity switch up to crazy watery warble on the top 2 settings. It's a pretty wide variety.

One thing I have found is it REALLY doesn't like being in front of an amp now. I get the clock noise plus some white noise. If I put it in the loop it's fine.

BTW, with your LED problem, did you only put one of the three resistors in? I think there's a 4.2k, 42k and maybe a third one (something like that)? If you put more than one in the LED won't work. I think they're in the middle of the board closer to the leads end (at least on the version I have).

(edit) The two resistors are 4.7k & 470. There's a 47 ohm right below them next to the pos & LED pads.


----------



## Michelle (Aug 21, 2006)

Great job Emohawk! A piece of art even! Glad you found good use for the phone book too. :smile: (work there)


----------



## Emohawk (Feb 3, 2006)

Michelle said:


> Great job Emohawk! A piece of art even! Glad you found good use for the phone book too. :smile: (work there)



Thanks Michelle! And as for the phone book, I work there too! :wave:


----------



## bcmatt (Aug 25, 2007)

Hey! Congratulations, it looks great!
I've had my 2204 kit for a couple weeks now and haven't even started it yet. I got a great deal on a vibro champ at the same time so I am building that first, but have been way too busy to do much on it.

I'm a little scared of the JCM (even though I've already done a DC30) because I've never had to bias tubes yet. I read about biasing all the time, but, Ive yet to see it done, or try it myself. Some people like cathode biased amps for the sound; I like them because it doesn't require any math, or confusing work with my dmm.


----------



## exhausted (Feb 10, 2006)

great job.

i think the amp building might be even more addictive than the pedal building. unfortunately, a much more expensive habit as well.


----------



## violation (Aug 20, 2006)

No idea what I'm looking at but I wanna hear it!


----------



## Emohawk (Feb 3, 2006)

bcmatt said:


> I'm a little scared of the JCM (even though I've already done a DC30) because I've never had to bias tubes yet. I read about biasing all the time, but, Ive yet to see it done, or try it myself. Some people like cathode biased amps for the sound; I like them because it doesn't require any math, or confusing work with my dmm.


Biasing really isn't that difficult, and the math's pretty straight forward. You just have to be careful. There's a lot of voltage pumping through there (444 volts with the KT77's in my 800). 

There's a good post on the Metroamp forum about it.

http://forum.metroamp.com/viewtopic.php?t=12286

And thanks for the comments! I worked hard on this sucker and I'm glad it shows.


----------



## Emohawk (Feb 3, 2006)

violation said:


> No idea what I'm looking at but I wanna hear it!


I'd love to post some clips...but I don't have a recording setup of any kind at the moment. Maybe when my roommate gets back we'll do something with his digital recorder (and he's a FAR better player than I am!!!).


----------



## Budda (May 29, 2007)

lookin good, get some clips!

a hair too bottom-heavy? what cab?


----------



## Emohawk (Feb 3, 2006)

exhausted said:


> great job.
> 
> i think the amp building might be even more addictive than the pedal building. unfortunately, a much more expensive habit as well.


Actually, lately building/modding has been more addictive than playing! If I spend half as much time with a guitar in my hands as I do a soldering iron I'd probably be an average player by now!


----------



## Emohawk (Feb 3, 2006)

Budda said:


> lookin good, get some clips!
> 
> a hair too bottom-heavy? what cab?


I did say "just a hair!". 

This is running through my V30 loaded closed-back Avatar 2x12. It's just a touch muddy in the bottom when driving the KT77's hard with a fair chunk of pre-gain. That said I haven't had it above 6 on the master using the hi input yet. This thing is freakin L-O-U-D, and any more volume might require police intervention. I haven't spent a great deal of time tweaking yet either. Just haven't had much spare time since I finished it.

Don't get me wrong...the thing does sound killer! Just needs some play time, time for the caps & tubes to burn in a little & some noodling with the knobs. When an amp sounds this good with the knobs basically at center you know good times are ahead...

Keep in mind too that I've just got old pre tubes in there at the moment. It will probably be even better when I do some tube swapping.


----------



## exhausted (Feb 10, 2006)

Emohawk said:


> Actually, lately building/modding has been more addictive than playing! If I spend half as much time with a guitar in my hands as I do a soldering iron I'd probably be an average player by now!


yeah, i know the feeling exactly. but at least i can solder when the house is asleep.


----------



## Budda (May 29, 2007)

Emohawk said:


> I did say "just a hair!".
> 
> This is running through my V30 loaded closed-back Avatar 2x12. It's just a touch muddy in the bottom when driving the KT77's hard with a fair chunk of pre-gain. That said I haven't had it above 6 on the master using the hi input yet. This thing is freakin L-O-U-D, and any more volume might require police intervention. I haven't spent a great deal of time tweaking yet either. Just haven't had much spare time since I finished it.
> 
> ...


ok, fair deal . attenuate the beast? I run my EQ pretty close to 5 all around on the JSX, which is pretty crazy haha. I want to play a cranked JCM800 some time, throw my TSOC in front of it and see what happens lofu


----------



## al3d (Oct 3, 2007)

Emohawk, what's the total part cost once it's finish for the head?..i'm curious, and will you mount it in a Marhsall looking frame?


----------



## Emohawk (Feb 3, 2006)

al3d said:


> Emohawk, what's the total part cost once it's finish for the head?..i'm curious, and will you mount it in a Marhsall looking frame?


As noted below, the total cost including shipping, taxes & whatnot will come to about $1150. That includes a Marshall JTM45 style head cabinet that the fine folks at Trinity Amps are building for me.


----------



## Emohawk (Feb 3, 2006)

exhausted said:


> yeah, i know the feeling exactly. but at least i can solder when the house is asleep.


One of the benefits of being a single guy with his own home on a 1/2 acre is I can pretty much crank it whenever I want.


----------



## dwagar (Mar 6, 2006)

JCM800's are so loud because they rate them clean. Wild Bill had a chart on here somewhere.
A 50 watt Marshall when cranked can deliver something like 90-100 watts.
Which is also why you should always overspec your speakers on these puppies.


----------



## bcmatt (Aug 25, 2007)

dwagar said:


> A 50 watt Marshall when cranked can deliver something like 90-100 watts.
> Which is also why you should always overspec your speakers on these puppies.


Is this true? So, should I actually have speakers to handle 100watts? Would make my 1x12 cabinet for travel situations useless because a Governor is only rated for 75 Watts RMS? Meh, I imagine I should probably still be safe unless it is always cranked. What do you think?


----------



## Emohawk (Feb 3, 2006)

It has to do with a bunch of factors. Orange claims to rate their amps clean also. Word is the TT actually drives 28-30 watts wide open.

It's also voicing. Marhsalls (and similarly voiced amps) tend to sound loud partly because the sweet spot in the mids is around where the human ear is most sensitive also. That's part of the reason people love to claim a Marshall will always "blow away" a Mesa DR (or any other "scoop" voiced amp). It's just the way we hear things, not necessarily an emperical measurement of actual power.

But, that also means in real-world terms the Marshall will be louder and will cut through a mix better, generally speaking. All I know is my 2204 absolutely CRUSHES my Traynor Custom Special 100 (very DR-esque), at least in perceived volume. But then again, the Marshall can't approach the rib-rattling bottom end the Traynor does. Different tools for different jobs.

As for over-specing speakers, it's hard to say. I think some companies have different ratings for tube & solid state amps (the solid state rating being higher). I had the 2204 hammering into a 1x12 Epi cab the other day (70w Eminence) & it didn't cook. I only had the master at 6 though. Any louder and I think a time vortex would open in my living room. That was still "louder" than my 100w Traynor.


----------



## dwagar (Mar 6, 2006)

Emohawk said:


> Any louder and I think a time vortex would open in my living room.


ROFL!!

I don't think many of us crank these to the pin.


----------



## Wild Bill (May 3, 2006)

*Eminence ratings*

Eminence rates their speakers "real world". That means lots of "fudge factor" compared to some of the "other guys" who make speakers.

When they call it 75 watts that means 75 watts of RMS, played as long as you want at full power!

Speakers burn out because the wire in the voice coil gets warm from passing current. During softer parts of the music or times of no music it cools off. If you run too much power and it gets hotter faster than it can cool then that is what leads to burnout.

If the amp says it's a 50 watt amp then spec in a 50 watt Eminence, or whatever power is involved.

You can trust them!:smile:

:food-smiley-004:


----------



## bcmatt (Aug 25, 2007)

Wild Bill said:


> If the amp says it's a 50 watt amp then spec in a 50 watt Eminence, or whatever power is involved.
> 
> You can trust them!:smile:


Ya, I feel completely safe now. And the Eminence Governor says it's rated at 75W RMS and 150W peak. Cool.


----------

