marshall tsl 602 - dull sound

[spunicz]

hey there,
some of you guys seem to know marshalls pretty good.. so i think there might be a chance to get a few hints on this:
i got a marshall jcm2000 tsl 602 combo used from 2003 which sounds unnaturally dull.. especially in overdriven channels.. just like a turned down tone pot on the guitar..
i've played the tsl 60 head on a 1960cab with vintage30s and i just loved the sound.. it was so damn amazing but way to expansive to buy it in the store, so i got the combo.. i even replaced the stock speakers and bought vintage30s.. no change on the actual problem..
i've also replaced all the tubes.. no big change but just bit more gain.. but still damn dull..
turning presence and treble all the way up sure makes it fuzzier but lets one still recognize the dull essence.
and i'm sure it's not supposed to sound like that.

what else could it be besides sloppy soldering?

[oc disorder]

Can you try another one in a store to make sure the dull sound is peculiar
to your one ?

[spunicz]

i did play another one and as i said i am sure it is unusual.

the sound is just not shiny or organic at all. absolutley boring.
it sounds like somewhere in the early preamp a part of the signal gets lost.

[oc disorder]

It seems like no one else is tackling this at the moment so some basic checks.
Does the clean channel seem ok? If you crank it has it got some bite?
The reason I ask this is there is a problem that occurs with these ..the power to the filaments or heaters (the bits that glow in the valve) is DC for the first 3 little pre-amp valves and the bridge rectifier that converts the supply to DC
sometimes heats up and wrecks the solder joints.
But usually they stop working altogether.
See if the first 3 little valves are lighting up ok sometimes that is hard to tell
as the filaments can be concealed..
This site details one persons experience with a similar model

http://www.historiclespauls.com/music/index.php?option=com_content&task=view&id=22&Itemid=48

Titled "Fixing the infamous bridge rectifier / heater wire problem"
Although its not the same amp the basic idea is the same.
Yours may not have ths problem but should eliminate the possibility.

[spunicz]

well now, i had no particular problem with the clean channel.. but for me it's allways harder to tell if somethings wrong with the amp when listening to the clean channel... i could have lived with it.. also i didn't pay so much attention to the clean channel when i first played the other tsl.. so i guess i really can't tell.

the first of the valves seemed to be glowing not as bright as the others.. and so did the v1 of the replacement valve set.. now is that actually unusual?

i will follow the instructions for the rectifier bridge repair..
but i just hope there's something more i could do as it's open.. i just have a bad feeling about assambling and diassambling the amp so often.

i'm really thankful for your help so far

[Tubis]

Well, alot of stuff. One gets tired just looking at the schem

[oc disorder]

the first of the valves seemed to be glowing not as bright as the others.. and so did the v1 of the replacement valve set.. now is that actually unusual?

Well I would have thought as the first 3 valves share the DC heater supply
that the first 3 would have looked dull if the bridge rectifier area is faulty.
However disregarding that assumption for a moment with the chassis out
and only the mains switch on (ie in standby mode) have a look at the first 2 valves "brightness" (obviously with the shield removed on the 1'st).
Now swap 'em over and see if the first valve looks dull in the second position.
If it does then there must be a bad connection somewhere along the supply chain.
The reason I was asking about the clean channel is if thats ok the problem
is more likely in the switching circuit or the associated componentry rather than in the fillament supply or the first valve.
If you look at the diagram Tubis supplied you can see the input jack is permanently connected via R77 to pin 2 of valve one.
So no matter which channel is switched in, signal will always go through the first half of V1.
So if you think the clean channel is fine we have to check other areas.
Quote from the handbook

2. Clean Gain
This controls the preamp level of the clean channel,
at lower settings the sound will be very clean and
at higher settings the sound will start to ?Crunch?
up in a traditional blues sort of way. In between,
around midway, depending on what type of guitar
you are using, you will find some great semi-
clean/semi-crunch tones, just like those great
vintage amps that had minimal features, but great
tone.

If the sound is a bit whimpy there could be a problem in the more dangerous area the high voltage or HT supply (high tension).
Do you have access to a multimeter soldering iron etc ?

[spunicz]

ok.. resolderd every joint on main, crunch and master pcb so far... and there might be a little more gain now but nothing really stunning.

flipping the first 2 valves results in the v1 in position 2 glowing as little as in the first position and v2 in first glowing as much as before as well.

yeah and i think the clean channel is allright...

i do have a multimeter.. what should i measure?

[oc disorder]

Sounds like you havn't got the bridge rectifier problem and if you have resoldered it you shouldn't have it in the future.
Well as luck would have it I got a TSL 60 with a minor fault last week
so I took a few snaps and as they say in the cooking shows here's something I prepared earlier.
This can be dangerous because of the high voltages and if you set your multimeter to the wrong setting you can fry it as well.
Set your multimeter to the highest setting for DC probably 1000v dc
and connect the negative (black) lead to the chassis.
If you are inexperienced doing this have a friend around just in case
to pull the plug if something goes wrong (ie to avoid death!)
These are typical voltages there may be some slight difference.
With the chassis upside down and the knobs facing you you should be able to put the positive probe on the bit of metal in the slots of the 12ax7 pre-amp valve sockets. I havn't put all the grid voltages there cause most of them should be almost negligible.
I also put the voltages around the dropping resisters in yellow which can be read in the same way .(neg probe on chassis positive probe on resistor ends).
See if your voltages are similar ..good luck on your mission and don't self destruct !
You can leave the 2 EL34's out for this testing otherwise you have to have a speaker connected.The pre-amp valves have to be plugged in.

[spunicz]

noooooow
finally got to measure the voltages!

the high voltages, which are the anode voltages i suppose, almost all of them were like described.. a few were around 10volts higher.

BUT the heater voltages, which read 3.5v in your post.. they were allways around 3.0v to 3.18v.. now what?
this actually fits into what i suspected.. the tubes aren't saturated, right?

the only parts that are betwean the heater and the rectifier (or parallel) are these huge capacitors.. could be something wrong with them? other suggestions?


thanx

[oc disorder]

I was wondering if you were still in the land of the living... spose a "vale" thread would be in bad taste....however I feel I'm running out of ideas..
The variations in voltage measurements I think are still in the ball park
for instance here in Aust we're running on a 240volt mains supply
The heater supply for a valve is supposed to be 6.3 volts so in an ideal situation (rare) should get half of that (3.15v per leg) of the heater supply.
So in actual fact your measurements there are closer to what it should be
than mine were.However interesting they were lower yet the HT readings were higher. Normally with the 20% tolerance I would have thought it would be more random rather than what was found.Maybe meter differences..
I did use my cheaper one for the measurements.
Those big capacitors in the heater supply should not affect the sound.
At worst should only increase the background hum if faulty.
What brand pre-amp valves did you substitute ?
I'm starting to think the amp is not faulty.. still think you should go on a mission to compare it with another.
I'm working on the assumption the clean ch is ok but the other channels are
dull. If all the tone controls work ok I would think it was a coupling cap between stages that was only common to the over drive channels.
Really need 2 side by side to compare the difference.
A young salesman called in that used to sell them (when they were fab)
and made a comment along the lines of they were crap but as you have heard one that sounded great to you this is typical of salesmen's comments.
They are now selling the new 4 ? channel AVM ? can't remember the catch phrase... (model).I would get some different brand valves and experiment
putting them in different places. For instance a Sovtek one say 12ax7lps
a Electro-Harmonix one (I find these brighter) and some cheapo chinese
some of them crack up (distort) in a desirable way.
It would be eaiser to do this with the chassis out for quick swapping to compare. Hopefully someone else may come in here with some other suggestions as I no longer have the TSL here.

[Tubis]

Time for a sound clip

[spunicz]

some article gave me the idea of filter caps that could produce odd harmonics with certain notes.. and this i could relate to... coz i had a strange chorus like sound when playing a d4.. the frequency is close to 300 which can be devided by 50 (50hz german voltage frequency) so it could be the filter caps not managing to filter out the 50hz hum.

now after replacing the elctrolyt capacitors c35 and c29 with epcos which have the same capacity of 330uF but a higher temperature tolerance (105°C) and are rated 450V, the lack of attack is gone and the dull sound got much better.
just to let you know for anyone with similar problems (which i think are VERY likely)

[psemrad]

Hi,
the best way to bright drive channel = remove capacitor C84 (470pF) or make it switchable (off - clasic Marshall drive, on - suitable for ultra gain).

PS

[jakob1989]

Hi I have the exact same problem you have with your amp. My treble and presence have to be all the way up for the amp to sound near normal. would replacing the electrolyt capacitors be a quick fix?