How to get my plexi clone sound like a orginal?

[Jana]

Super Bowl Sunday and we are sure taking the threads down a new avenue.

[cbass]

Its party time .You know the tomorrow is the most callin in sick day of the year

[Ukko75]

Oh I see.. what is missing in your amp's tone then?

I am sorry if I miss lead you. It is difficult to explain exactly what i mean. i do not know the right word for it.

Sound should be like a wall that is balanced. Mine sounds like some frequences (mostly high frequences) is coming out of the speakers and reaches your ears first and the bass is little loose.


I canged the loop resistor to 56k and NFB resistor to 100K and it helpped it a bit.

I will try another speaker cab to see what will that do.

[Littlewyan]

To be honest the Amp you've built can be very bright anyway.

Have you checked the layout of the original amp that you like? These amps varied a LOT when they were built. A photo of the inside of the original would help us help you

[Ukko75]

I might find the broblem. It was bad solderjoint.

There is alot variations of plexis circuit. I like it this way
coupling caps 0.022 after first stage
4,7n bright cap on volume pot
0,68yF V2 bypass cap
47k NFB resistor
0.68yF cap on the presence control
Filtering 40+40 40+40 32+32

Thanks all for help!

[Ukko75]

What is the meaning of output grid resistors? Early marshalls do not have those.
What happends if i leave them off?

[rp]

I'll toss in my 1 1/2 cents, are you testing this right off the bench? New amps sound 2D at first power up. You need to cook it for a while, loosen up the filter caps, play the shit out of it for a few days before judging the 3D-ness at least.

[talbany]

The devil is in the details!

First I've worked on and played close to 50 or so Marshall's (JTM45,1959,Plexi era,Jcm800,2203,Jubalee's)..Marshalls were my weapon of choice for a long time.. I also had a friend who was a Vintage dealer since the early 70's and repaired quite a few at VVT Amps.. The one consistency that ran through all those Marshalls were the inconsistent tone each one spat out..These at times were so inconstant that my favorite Marshall amp I ever heard was a JCM-800 late 80's 50w that had a great clean tone, which was kind of strange being that the 800's were designed more for preamp gain.Overall some of them sounded wonderful and others sounded ahh,Ok..Some of them sounded great clean while others sounded great dirty..The voltages varied over the years and I have heard both great sounding Marshalls coming from both higher and lower voltage versions (BTW.My Awesome sounding 800 had 480 on the plates)...Imo if you want to get the classic tones like the early Hendrix stick with the Black Flag JTM (exactly)and use the early Piher'Iskra' etc..as well as the Mustards..MC makes some similar to the early RS (w/100v tap) output transformers...Pick an era you like and gig up the voltages (metro amp forum) lists many of these voltages on there forum..Also a big part of the early Marshalls tone was had from those early ceramic treble caps that helped generate those 5th 7th (odd order harmonics) that helped give them that Marshall grind!..It won't sound the same with a silver mica or a new production cheap ceramic they make today..Mullard and Amperex valves can help in achieving that classic smooth breakup,although you might like how some of the newer production tubes go with your style of playing..

Good Luck!

Tony

[Reeltarded]

Totally agree with Tony except I like the lower voltage 800 better, but same as above.

[Smokebreak]

Great info Tony. Any idea where to source the old ceramic disks? I can't seem to find any.

[talbany]

Btw..The rule of thumb I use is?.. If your primary a clean player on the cliff of distortion play fairly loud and generally like punchy tone (think like Wind Cry's Mary/Little Wing,etc),and use pedals ,then I go with the higher voltages..Also if your into really heavy death metal stuff with plenty of crunch and tight bottom end..This style likes higher voltages too..
If your typical Classic Rock like Zep, AC/DC Van Halen and even stuff like early Cream/Blues Breakers etc.. I go with lower voltages..I like all those styles,so I stay in a constant state of confusion..

This is generally the rule I follow!

Those old RS caps are a bitch to find and when you do find them they are pretty inconsistent as to how they sound (they are cheap caps)..Could be a reason why some of the older Marshalls that used them were all over the place..As well as the voltages?..Who knows?.. If you run across any keep me in mind and I'll do the same!

If you set your treble control at noon...at least 1/2 of your tone comes from the treble cap?..Not to mention the bright cap!!
Tony

[Smokebreak]

Will do! My latest love affair has 420V plates and it's great, though I've got another with ~500V and i like it too.. Very imposing, that one.

[Ukko75]

Yes maybe i must play with it for a while.

I agree that treble caps do sound diffrent. I first put there silver micas but i like ceramic disc better. With micas the higer frequenses comes tight and sharp. With ceramic discs highs come moore ear frendly bit softer and mushier. Best would be something between, maybe i musta try to put 250p mica and 250p ceramic parallel and see what happends.

If anyone finds place to buy old caps i would be intrested them too.

[rp]

Some good Marshall info here.

When I see some old dusty junk on the street (so rare these days) I already go to look for any tubes, mustards, moldeds, speakers. I'm going to have to start diving for old crusty ceramics too now, to think of all the ones I missed. I'm in Europe too maybe I'll find the square ones! Good Lord, I need cure.

[ToneMerc]

Those old RS caps are a bitch to find and when you do find them they are pretty inconsistent as to how they sound (they are cheap caps)..Could be a reason why some of the older Marshalls that used them were all over the place..As well as the voltages?.

If you set your treble control at noon...at least 1/2 of your tone comes from the treble cap?..Not to mention the bright cap!!
Tony

I love old junk.

TM