A real one here:
Notice the shielded cable,, twisted heater wire, Shield around input socket, Coax used for tone pots, and intereconect points, large distance between sensitive components.

http://forum.metroamp.com/viewtopic.php?f=3&t=23078

Also From Roccoforte Amps own site; Click on optional extras ,,, note the $200 fee for DC heaters.   Trust me you need it.

BTW your signal without hi imp buffer will be roughly 7 times SMALLER assuming the TDA input Z is say 20/30k with a good chance of bass loss.
The preamp was built for looking into a Hi imp Not a low one.
Yes the tone still works but nowhere near as good as it should.
Just thought I would mention it and YES I did go to the trouble of simulating it before I opened my mouth.

No it's not a TW amp but the *idea* of 10k cathode R on V3 comes from TW,,
It forces half wave clipping which enhances the Power tubes as they go into compression but on it's own into a super clean SS poweramp,,, I doubt it's worth/usefulness. A preamp of triodes does not maketh the Tube sound,,
That comes from the power tubes.

Without power tubes being compressed via the big signal swing from the triodes (which I should add is comparitively clean cept for some half wave clipping) then it won't distort like an all valve amp.
My guess is a bit of half wave rattle which is way to big for the opamp/poweramp input and the power chip is just slamming into the rails which will be distorting and MAY?? sound ok I guess.
From my own experience I'd go with one Ax7 unless you have a tube power stage.

Your setup has a 300 volt supply and those triodes won't do much distorting on there own you need to use diodes if you want triodes to distort like a PP pentode output stage. Or consider the SiAB (Stack in a box) concept as it is more suited for running into SS.

Even if you fix the ground problems your board has to many tracks to close together.
If you want heater tracks pull them all down to one side of the PCB Away from everthing else.

To generalise; You can't take the front end from an All Valve Amp design and just plug it into a SSpower Amp and expect it to sound even remotely like a Roccaforte.
I respect your commitment to your idea but I'm just hinting that it might be the wrong way to do it,,,Just my say,, best of luck with it. Phil.

Hey rockertalon,
                      Sorry mate but if you don't know what *Mains Voltage* means then you probably should not be messing inside this thing untill you have read up on some electronic servicing books.

Good that you are interested but DO seek out the basics and Safety issues First before you go poking around inside it.
Phil.

Almost forgot! 
IF That tone stack is running directly to the TDA7294 then you need a high imp buffer stage otherwise you are wasting your tone stack, it will be hardly working. Phil.

Hi mensur,
              I assume you are reffering to the hum on that mp3?
From what the drawing shows it looks like you are useing AC voltage for heater supply. (from Trafo2, red and black wires)
Then Welcome to the wonderful world of Valve Amps and the manditory
*AC Heater hum*

That is one good reason why you don't build Valve circuits on PCBs unless you are useing *DC heater supply*

The only way you can improve AC it is to use dedicated twisted heater wiring.
Even with DC heaters it takes a lot of know how to avoid hiss and hum when useing valves.
I can't seem to find the schematic but looks as if it uses two massive gain stages with that silly Trainwreck 10k cathode trick on V3.
Works on Trainwrecks because the guy knew about the importance of layout design. Add another gain stage like your's and it's impossible to be able to turn the knobs up.

General rule of thumb I use ; Any more than the classic Valve count and you are going to need to rethink the heaters. (ie, DC)
Even the cloners of all valve trianWreck type Amps run into trouble.

Sorry but I very much doubt that this circuit will work for you.
Maybe have a read of my comments here,, saves me saying it twice.
http://www.ssguitar.com/index.php?topic=1151.0
Phil.

Hi rockertalon,
                    Bin!   
No not the trash bin,,,,,,, That's a recource treasure BIN :tu:
Lotsa wire,, Resistors,,,Caps,,, reverb tank,, probably an LDR inside the sweel pedal,,,, speaker cloth can be reused,,,, the list is endless.

If you are starting out with electronics you will eventually need a supply of bits and this is one very cheap way to aquire such things.
Have fun with it, Phil.

Sounds like it might be the amp design This seems to be a common issue with a lot of gear out now.

I recently fixed/tweaked a Laney LC 30 and the high gain section was just unuseable. This was untouched from new ,,so the hiss and heater hum was how it left the factory.
There is a point where more gain just destroys the playability of the equipment.
Sadly while ever consumer demands more and more *Gain* this is what we have to expect.

The best I can offer is: Take a pic of the guts of the amp (concentrating on the input area and preamp sections) and maybe hunt down a schematic for the amp as well if you can ,,, even then no promises from me but other minds here maybe of more help.
Hope it pans out,, Phil.

Just adding,
Logic suggests that the the black wire would be the CT (center tap)  and highest voltage on the secondary would be between the two *Red Wires* but it could be the two Blues.

You can work out which ones by following the circuit traces from the input pins across to the Bridge rectifier and big filter caps.

You can also get some idea of what DC voltage the amp works on just by reading the working voltage written on the Main Electrolitic Caps. The caps will always be rated at a slightly higher voltage than the amp uses. ie, with a pair 50 volt caps the working voltage will be somewhere between 37VDC to 45VDC. So divide by 1.4 to get a rough idea of the AC that you would expect to read at the AC secondary terminals.
Lets say the secondary is a 56VAC CT (same as 28/0/28) ..
Then you would be seeing a voltage of 56VAC between the two red wires,,, or 28VAC between one of the Red and the Common Black wire.
Phil.

Sorry Zappacat,,, OC= open circuit.

The 5 wires you tested are Likely the *secondary windings only*.
There will be at least another TWO Wires,, often these exit from another side of the winding stack but not always.
Edit; adding just follow the *Mains cord* through to the transformer.

With my limited understaning I think the very low voltage reading on the secondary *Maybe* indicitive of a primary failure, So I'd check that out first via a resistive reading of the primary winding.

If you cant establish the primary wires inside the chassis then as I mentioned take the reading from the *Mains Lead* itself.
Put your meter on ohms,, connect to both AC plug pins (not the earth pin) Now switch the power switch to the *On* position.
You should get a stable low ohms reading.
Maybe around 50/100 ohms,, depends greatly on the VA rating.  Generally really big transformers have greater current ability and they tend to have a lower reading due to the heavier gauge windings.

If the reading is high ,, like 10k ohms or the reading fluctuates a lot then the primary is proly stuffed.
And while you have the power socket in your hand check the continuity of the *Earth Pin* while you're there. you should see 1 ohm or there abouts from Earth Pin to Amplifier Chassis.
Phil.

OK now I understand,,, Hum before we start hacking away at the electronics ,,, have you considered that it might be wise to go to a music shop and find another frontman and see if it has the very same issues?

Fender may still replace it if it is a circuit fault.  does happen!
Phil.

I assume you have the Transformer wires *OFF* the main board when you took those measurements?

Maybe Try doing a Resistive reading on both the Primary and the Secondaries.
(all power off of course and unplugged from wall sockets)
My guess is if the tranny is stuffed then the Primary will be open circuit and it would read a very high ohms or wavering around ( ie, not able to get a stable reading).

Also read the primary from the active pins on the wall plug,, you never know the cord? the fuse holder? the main power switch?  all possible candidates for OC in the primary.
Some modern Tr's come with a thermal link inside the winding another point of OC failure.

Others here will be more qualified to comment as it's only a hobby for me.
Hope it helps. Phil.

Try and establish that the speakers are indeed the issue before you start punching holes in an otherwise good box,, it's hard to fill the holes up if it does not work.

I know some jensens had poor bass response.
I also know a lot of Amps today rip off way to much bass,, so maybe do a little Research first.
Cheers, Phil

Hello Wuchi, In reference to "will it deliver tubish sound?"
Having done same or similar to what you propose,, the short answer is you're wasting your time.
The real secret to tubes is in the Power Stages where the signal is huge and passes through a transformer. (more to do with *Pentodes driving Transformers* than a Valve in general)  In my humble Opinion preamp distortion (however you derive it) is always a little harsh and somewhat lacking in richness and depth.
Heck even the preamp stages of an old Marshall stay quite *undistorted* ,,
it's the power section that delivers most of the magic.

All that can be achieved with triode preamps is a bigger signal along with a bit of half wave clipping which will in most cases deliver some improvement but not enough to make it a *Winner*.
Mixing tubes with SS is always a tricky one but If you just can't help yourself and you just have to build a Valve stage then you will be hard pressed to find a better circuit than the *Messa VTwin pedal*. (you will need to find a 200VHT PSU though) Running valves way below there standard DC OP is just wasting a valve.
I only needed to build the clean section of the Vtwin as I found the crunch ch a waste of time and my SS units did a better job of preamp crunch anyway.

You mention Fet circuits and then ask if they would benifit from a valve stage.
Understand the in-escapable truth about Audio circuitry; (Valve or SS) The bigger the supply voltage then the bigger the signal that can pass through.

So a Fet working from 30VDC has no chance of competing with a triode working from a 200VDC supply. From my experience even if you use a valve with at least 90VDC HT you will have no need for a Fet.
We could get all complicated and mention *Current gain verses Voltage gain* but the dynamic way that a High Voltage, High Impedance triode type circuits work is sonically different. That does not mean SS is crap,, just means the whole design/ game plan has to be approached in a different manner. Now mix the two together and wow that can get you in a lot of strife.

To generalse it; Transistors are Low Voltage, Low impedance, High Current devices,, Whereas Valves are High impedance, High Voltage, Low current devices. That helped me get my head around the reason they are so different.

Just shoving a triode into a SS circuit does not costitute a Valve tone,,, sadly a lot of crap on the market tries to sell that school of thinking. Even more sad that so many believe it.

Re Vtwin schematic,
R24 270k around u1b is Wrong,, try a more civilised 27k instead.
You may not need that part but if you are driving the Powerchip direct from the Vtwin then you may need it.
You may wish to get ideas from my *Passive tone circuit* listed under *schematics and layouts* on this site.
It's just the tone section of the Vtwin without the Valves in front. (of course I opted for the Hiwatt tone design)
Don't forget *C2* 50nF 400volt,, as it decouples the HT from the lower voltage rated tone components.
You can use any OD circuit in front of it as it's still fairly clean but you may wish to add the second crunch Ch instead.
But Again I stress this still won't sound totally convincing through a SS powerchip.
I would want to hunt down a really good Distortion unit to add in front.

Re Stereo guitar, A lot of messing about for little gain. In my view it would have to be at the very least Twice as good as mono,,, sadly it's not.

Re Speakers,
More focus on circuit design is going to reap far greater rewards than swapping speakers around all the time. Even the implimentation of simple things such as a graphic EQ before the power stage is a lot easier to work with than swapping speakers.

I strongly suggest you bread board anything you conjur up and test it first before commiting to building it as there is nothing worse than building something only to find it ends up in the parts bin. BTDT

I have spent over 20 years trying to come up with circuits that really work for guitar sound/tone ,,sadly most of them have been complete disasters.  I have built a lot of DUD circuits that come under the catorgory of;
"seemed like a grand idea at the time".
So be warned it is not as simple as just soldering a few resistors to a board and putting it in a pretty box with a shinny coat of paint.
Hope it helps,, Phil.

I reinterate what J M Fahey asks,,, that is important for us to solve your problem.

Generally I've found some of these modern amps have horedous Hiss which might be the white noise effect you speak of.
I assume from your comments you purchased this amp sight unseen so is it brand new or S/hand?
If it's a new purchase ,,,take it back before you mess around inside it.
Phil.

Try in the area of *C139*
Don't forget Q101 (the FET)
Check you have all the DC voltages at the pins shown in the schematic.
Some of those comp circuits require a cap to charge which governs the speed of response,,, at a guess C139 might have something to do with time.
sorry can't be more helpfull,,, Teemu where are you?  He will be of more help:)
Cheers Phil.

From what I can gather,, I take it the original problem (which did not involve the compressor part) was solved?
And Now the compressor is acting up? 

I'm not familiar with this Amp though I have a fair idea how it works.
As far as the compressor issue,,, I would be looking at a dud cap,, leaky Electro maybe.

No schemo so that's all I can offer.
Phil.