Newby 2550 build!

[Jaymz77]

Hi all.
New to the forum and embarking on what some may see as an optimistic build for a newby... A Marshall 2550.
I am actually an electrician so I'm not totally new at this, just new at building amps.
Basically I have an obsession with a particular tone that I've been chasing for years and its going to take a 2550 to get there.

I was wondering if anyone might be able to assist me with component selection.
The schematic I have gives MOST of the component values but doesn't give their wattages or indicate if the part is ceramic or metal film etc.

If someone has a parts list with this information it would be great. Or if someone would be willing to work with me to create a list.

Any assistance appreciated.

[sluckey]

Marshall 2550 has been on the forum sometime this year. Search this forum and see what turns up.

[Jaymz77]

I've found some bits and pieces but nothing yet that answers my questions.
It's really only a few values I need to know and which of the components are critical to tone and require higher quality parts.
Maybe I'll make a list of specifically which components
Cheers

[Willabe]

Maybe I'll make a list of specifically which components.

That'll work.

But the transformers, tubes and speaker(s) will make a much bigger difference in overall tone and feel/playability than the type of resistors and coupling caps.

Those 3 parts are the biggest money for an amp, unless you start to buy "special", ie, magic mojo parts.

Resistor types, carbon comp, carbon film, metal film will mostly affect the noise floor in an amp. There is a school of thought and some test data that says that CC resistors will distort at higher DCV's, like plate R's, that could add warmth in the amp's sounds.

Build the amp, get her up and running, then swap MF R's for CC R's for the preamp plate R's and see/hear what you think.

Same thing with the coupling caps.


              Brad          

    

[sluckey]

Post the schematic you have and ask questions about specific components. It's pretty easy to make a parts list from the schematic.

[Jaymz77]

That's probably a good way of attacking it.
I'll use my best judgement based on the advice I'm given and info found and modify from there if required.
I guess I'm just trying to make the circuit as authentic as possible to achieve my elusive tone.
Il create a list and post it incase anyone can see any obvious issues and go from there i guess.
It's really only a few values (from memory) and component type (mf, cc, cf) that I need.

Thanks heaps guys ill post the schem tonight.

[TIMBO]

Hey James, I built the 2550 early in the year, I did my own layout and added a reverb. I used mostly orange drops and metal film resistors and as Willable said, and I agree that the mojo mostly comes from the big three.

[DummyLoad]

http://ceriatone.com/images/layoutPic/marshallLayout/Ceriatone2550Chassis7.jpg

no brands in that layout link above, but wattage values are there. seems like a good plan to follow, at least a place to start. punch up the board on hoffman's board maker.

click link below to design the board and have it CNC made, just for you...

http://www.hoffmanamps.com/php/TurretBoard/TurretBoard.php

xicon or speer CF resistors;
ohmite or xicon wirewound resistors;
mallory 150 or vishay-spargue 715 coupling caps;
bourns or alpha pots, and if you can afford them, PEC pots even better;
F&T or JJ can filter caps, or MIEC axial caps;
good quality PT & OT.

--pete

[Jaymz77]

Thanks for the great responses guys.
The schematic I want to use is called the 2550x. I can't remember what site I got it from but it a pretty good looking schem. It just adds a lead gain pot that the original doesn't have.
I'll post it when I get home.
Thanks again guys.
I'm really getting excited about this! There is nothing better than the satisfaction of doing something yourself.
I consider myself a good tradesman and that excites me knowing the quality of work I am capable of. This should be a damn good amp when I'm finished.

[TIMBO]

That will be the ceriatone layout that DL posted. I don't think that you will go too wrong with that, I used it and having the extra pot keeps the volume even when switching between channels.

[Jaymz77]

Ok, im home now and not typing on a phone.
I have got the Ceriatone layout but i was going to use a different one, similar though.
Here is the schem i was going to use...
And the layout...
I got them from SDM??
Anyway, looking at them again, it seems to be mainly diodes that dont have a rating marked.
I guess may main issue is what quality of component to put where, which component have an effect on tone, which have an effect on noise etc...

Anyway, any input is very much appreciated, as are all responses so far.

[TIMBO]

YEP, The 2550x is what I used, sorry

[Jaymz77]

Are you happy with yours Timbo?

[DummyLoad]

relay specified in SDM documentation is obsolete and no longer available.

use G6A-234P-ST15-US-DC5 it's a 16 pin, so use a 16 wire-wrap socket instead.

--pete

[TIMBO]

Yeah, I like it a lot, but the clipping circuit is too much metal for me so I put in a bypass switch.The clean channel stays clean to about "8" on the dial and the lead channel picks up from there. Its more like a JCM800 with the switch in/out clipping circuit.

It was way too loud for me so I gave to a mate for his Rock/Rockabilly type stuff.

[Jaymz77]

Awesome.
For me its about the "Frusciante Grime". I have had a few amps that come close but not close enough for my picky, RHCP fanatic ears.
I also like the metal side but i am less concerned about that because any amp will do that will a good pedal in front of it.
I also dont need that much power. I thought about using the preamp circuit in a lower powered amp but i dont know enough about amp building to be able to modify the circuit the right way to account for the differences in tone between 34's and 84's, or 6v6's.
It WOULD have been too much for a newby. So i decided to just sick with the stock circuit, bar the extra lead gain pot.

Where did you source your parts Tim?

Thanks for that Pete.
Any idea on the diode values?

[DummyLoad]

schematic says 1N4007 - that's the type. 1N4007 is 1000V devices no mater whom you choose. i like fairchild. on semi, or sgs thompson.

--pete

[Jaymz77]

Thanks Pete.
Obviously just my average schematic reading abilities.

[Jaymz77]

What sort of effect do diodes have on tone and noise?

[Jaymz77]

Also, does anyone know what the value and type of the large blue caps that mount in the chassis are?

[Jaymz77]

They look to me like the 50u 500v caps on the schem. Is that correct?
What type of cap should they be?
The only other thing I'm not sure of is what the red circular led looking things on the layout drawing are. They look like LEDs and that's why I'm confused. LEDs on a board?

[Willabe]

They look to me like the 50u 500v caps on the schem. Is that correct?
What type of cap should they be?

Yes, they are 2x50uf 500v electrolytic caps in a single can. A can cap can have 2, 3 or 4 caps in a single can. The only way to get a large uF value in a small size package is to make an electrolytic cap. A 50uF 500v film cap would be about the size of your fist and cost 3 to 4 times as much as an electrolytic cap for the same rating. Doug sells them in his on line store.

The only other thing I'm not sure of is what the red circular led looking things on the layout drawing are. They look like LEDs and that's why I'm confused. LEDs on a board?

Yes their LED's. Their used as clipping diodes to clip the signal for distortion. Look at the schematic, the LED symbol looks like a diode symbol but with a little arrow next to it. Some like the sound of them and some don't.

When you can't figure out what something is from the layout drawing always look at the schematic to see if that will tell you what it is.


                    Brad      

[Jaymz77]

Thanks heaps for the reply Brad. That would explain why there is more shown on the schem than on the layout drawing.
It's kind of a case of confirming what I think the component is. I am used to wiring up high rise buildings and suburbs, not components, so my schematic reading quite often needs someone to confirm it for me.
Sorry to be a pest.

But thanks to all you guys I think I have enough info to start making a list of parts. At that time I will probably post the list for comment and go from there.

Thanks again

[TIMBO]

Hey James, Doug has all the parts that you need at a great price when the aussie dollar is better or you can try a local guy, Mac at EVATCO. 

[Willabe]

That would explain why there is more shown on the schem than on the layout drawing.

Look again, most are diodes (listed as 1N4007) not LED's. In the "clipper" section, I see 3 diodes and 2 LED's. All LED's have different ratings just like diodes do. Schemo says, Vf 1.8 at 20mA. Vf is forward voltage. That's how much voltage it needs to turn on. LED's are +/- polarized.

A different Fv LED in the clipper circuit will turn on at a different voltage than whats listed and will act/sound different. That's why they list it's Vf value. Get as close as you can to that Vf value, mA doesn't matter if it's a little more. The 2 LED's are in anti-parallel, 1 clips the + side of the signal wave and the other clips the - side of the signal wave. They clip the top of signal when the voltage exceeds 1.8Fv at turn on to "square" off the signal wave form.  

I see 3 LED's total, 2 are on the turret board and the 3rd is in the front panel as an indicator for when the relay foot switch is activated. All the rest are 1N4007 diodes.

schematic says 1N4007 - that's the type. 1N4007 is 1000V devices no mater whom you choose. i like fairchild. on semi, or sgs thompson.

I know your excited about this build but you have to slow down a little. Look for the arrow for LED, NO arrow then it's a diode.

              Brad      

[Jaymz77]

Thanks again.
I was actually referring to the caps when I said "that explains why there is more on the schem..."
I couldn't work out at first why it only showed 3 of those big caps on the layout when I could clearly see more on the schem.
Thanks for some good info though.
And your right, I probably do need to slow down a bit...

[Willabe]

Ok, but I see 6x50uF 500v caps total on the schemo. So 2x50uF 500v in each cap can = 3 cap cans. Schemo and layout match up.


               Brad    

[Jaymz77]

Its been a while since ive posted but ive been busy busy busy...
Anyway, my Dad and i have come up with a parts list... it helps having an electrical engineer as a father.
I thought i would chuck the list up for critique from you guys with previous amp building experience.
A few notes, im not using pull pots, im using separate switches for that, i have a few extra caps on the list to give me some tuning options (type not value), and i have an extra gain pot for the clean channel compared to a 2550 (as per the schematic i downloaded).
The brands listed are just what has been recommended to me so far, feel free to recommend others.

Cheers!

[Jaymz77]

Has anyone got any comments to make about my list?

[TIMBO]

Hey James, that all looks good. The next step is sourcing those part and doing a chassis and circuit board layout.

[Jaymz77]

Im just going to use the layout i posted earlier.
I have been sourcing parts and i can pretty much get most of it from the Hoffman store.
The transformers have been the only issue. I can get heaps of different ones but i thought i might just use genuine Marshall ones.
I just had a huge argument with the Marshall parts distributor in Melbourne who tried to sell me a 1.2H choke when every piece of info available on the net (that i have seen) says the Jubilee used a 3.5H choke. I even sent them a pic of an original Jubilee choke under test and measuring 3.84H.
So im basically just getting to the bottom of that and finalising where im going to get them from.

[Jaymz77]

Well, after a few months i am happy to say i have a working amp that sounds FANTASTIC!!!
I'm really happy with it.
Bar a small issue... Hopefully someone can help.
I built the 2550x, with the extra gain pot for the clean channel, and whats happening is that when i crank the clean gain right up, after a few minutes of playing the sound goes really grainy and yuck and the volume drops to roughly half of what it should be.
I tried re biasing but the problem is much the same.
Amp seems to work fine until you crank the clean gain.
Any ideas?

[TIMBO]

Hi James , Good to see you got it up and running. Sounds like you may a bit of a dry joint somewhere and when things start to warm up it goes funky on you.

When the issue starts (while the amp is on) try moving/ tapping on the solded joints with a plastic or wooden stick (chopstick ) to see if it is a cold joint.

[Jaymz77]

I did a bit of that last night but not every solder joint.
Ill try some more.
thanks Timbo

[Jaymz77]

Well Timbo you must have been right.
All i did tonight was poke around and redo a few solder joints... and the problem seems to be gone.
Well, it didn't present itself in 5-10 mins of light playing when previously it would, so fingers crossed.

Aside from a few teething issues the build has been relatively straight forward for me being a sparky.
What i wasn't prepared for is how great the amp sounds. I mean seriously good. I have never played a real Jube so i have nothing to compare it to but recordings, and some of the verbal descriptions of them that i have read seem at odds with what I'm hearing, but who really cares when you get instant wood the first time you hear it. Its not often you get that from even bought amps.
I have a 62 reissue start with SD SSL1's in it and now the 2550x, John Frusciante himself would wet his pants.
I took it round to show my guitar teacher, who is a reasonably reputable guitarist in Sydney, and he was blown away. Might have an order coming my way.

All in all i am over the moon with the amp, it is exactly what i was after.
Thank you to everyone who contributed info and assistance, especially Timbo, it is VERY much appreciated.
Ill post some pis when i can.
Cheers

[tubenit]

All in all i am over the moon with the amp, it is exactly what i was after.
Thank you to everyone who contributed info and assistance, especially Timbo, it is VERY much appreciated.

All VERY cool!  Thanks for sharing your success!  It's an amazingly helpful & friendly forum.

With respect, Tubenit

[Jaymz77]

I spoke too soon.
The problem is still there. Perhaps it didn't show itself last night due to it being late and me only playing lightly.

The amp is fine, until i crank the clean gain with the clipping off, then after a minute or 2 the sound goes very fuzzy and drops in volume.
This is driving me nuts.
I have been through and checked solder joints and cannot see any visible issues.

SOMEONE PLEASE HELP

[TIMBO]

Hey James,Does the drop in volume happen with the lead gain is switched on.

[Jaymz77]

No. Just clean gain. Weird

[TIMBO]

If you follow the signal path from V1 pin 1 it goes through a .033 cap then splits for the clean and lead volume so the only real change is that clean pot is put in the path when the relay is switched between the two pots, so look around that part of the circuit.

Or even look around the other half of the relay and follow the signal path of the clean circuit.

The rhythm switch is also part of the clean circuit is that working OK

Fine strands of wire are can be hard to see, so if you have compressed air on hand give it a gentle blow out or just turn it upside down and a bit of a shake and see what happens.

It could also be a bit of blocking distorting, but that is a bit over my head.

[Jaymz77]

Rhythm clip switch works fine.
In fact the whole thing works fine UNTILL you crank the clean gain.
Its such a weird issue.

The other night i was demo-ing it and accidentally unplugged the cabinet with it on.
It then developed this hum. I powered down and let it sit for half an hour. when i powered up again it was fine.
The next night this problem presented itself. But as i said, its only when the clean gain is cranked.

Whats blocking distortion?