X-can V2 complete schematic

[Deleted]

Modding one of these amps for one of Mikes customers.

Since the V2 schematic that exists isn't accurate and I had my hands on one I decided to draw the real schematic and a complete one with the powersupply PCB.


Here you can download the much higher resolution pdf file:
www.mediafire.com/view/?c5c8re5i2unipes

I noticed the volpot is a linear type (which explains the gain questions).
I also noticed the PCB quality is rather poor (for my standard) and the SMALL transistors all had 'moved' while in the solderbath.

My recommendations (and Mikes) have been incorporated in the schematic.

[mrarroyo]

Thanks

[PinkFloyd]

Fantastic Frans, that is very much appreciated by a lot of X-CAN owners, thanks for taking the time to draw that out

The solder pads, traces and PCB are poor quality and you only have to sneeze in their general direction and they lift. The weak spots are the valve sockets and the transistors.... the heat of the transistors cause the traces to become loose / intermittent and more than one or two "tube rolls" may cause the valve sockets to part company with the pads (in places).....

Other weak points are the DC socket pads, the quad phono block, the headphone socket and the pot... all of which have a degree of movement on insertion / touch / usage. It's no secret that the MF boards (in the V2) are FAR from the best for the job.

A VERY common problem is broken / intermittent joints on the valve bases..... IMO, the "pin witness" (Canadian standards years ago) that MF soldered the parts in accordance with is flawed.....

It's fine for "servicing" in the field but does not make a reliable joint.... much better to make a mechanical join by bending the pin to the pad (contact) and then flooding in with solder to secure the join.... these through hole straight pin joins are fine if done properly, on a DECENT PCB with DECENT traces but pretty useless if incorporated on a wafer thin trace.....

Pretty much built in obsolescence.

I notice you've gone for 50V instead of 35V caps? That (in my experience of these amps) has never been a weak point.... 35V caps have lasted..... Plenty of years (20+)..... the weak point sonically is not the voltage but the capacitance..... These amps definitely sing a better song with more UF.

Did you have a listen to the amp Frans? Knowing you you'll say it sounded like an "amp" and "all amps sound the same".... seriously man, what did you think of it considering it's 20 years old and actually "MADE" in England?

That amp was £129 GBP when it was released back in the day.

Still going strong despite a few flaws and up there with most of them

[Deleted]

That is very nifty, great job Franz.
Taking all the abovementioned into account, would there be any mileage in having new uber quality boards made up?
Firstly loads of peeps have these things and secondly it may make rescuing fried units more viable.

[Deleted]

Taking all the abovementioned into account, would there be any mileage in having new uber quality boards made up?

Shhhhh!
Someone from MF may read this and make them available at PREMIUM prices. Clearly, they also appeared to be aware of some of the things Mike has done with them.

[Deleted]

Sept 11, 2012 23:41:08 GMT PinkFloyd said:

The solder pads, traces and PCB are poor quality and you only have to sneeze in their general direction and they lift. The weak spots are the valve sockets and the transistors.... the heat of the transistors cause the traces to become loose / intermittent and more than one or two "tube rolls" may cause the valve sockets to part company with the pads (in places).....

The amp I am modding appears to be in new state.
You can only see some very minor discoloration that is hardly noticeable.
The pads indeed come off when looking at them..
The only way to prevent that is: desolderwick them, bend the legs while heting them and pull off the parts when the pads cooled off.

Sept 11, 2012 23:41:08 GMT PinkFloyd said:

Other weak points are the DC socket pads, the quad phono block, the headphone socket and the pot... all of which have a degree of movement on insertion / touch / usage.

In this particular case all solderjoints were surprisingly good (checked with a special 3D inspection device) In my case ONLY the small resistors (one excluded) had 1 or more 'rings' in the solderjoint, indicating they had moved while cooling down.
In case of the PS board, this could spell trouble.

Sept 11, 2012 23:41:08 GMT PinkFloyd said:

I notice you've gone for 50V instead of 35V caps? That (in my experience of these amps) has never been a weak point.... 35V caps have lasted..... Plenty of years (20+)..... the weak point sonically is not the voltage but the capacitance..... These amps definitely sing a better song with more UF.

Those caps I put in were supplied by a certain guy in kit form.
Something with a colour and Floyd or something.
It appears 'over the top', the 50V rating as 35V will indeed do, BUT with 25V on it and the amp getting hot (eventhough 105oC) lifespan of the 50V version is longer.
Because they were supplied I used them.
The few parts I checked electrically were all O.K.

Sept 11, 2012 23:41:08 GMT PinkFloyd said:

Did you have a listen to the amp Frans? Knowing you you'll say it sounded like an "amp" and "all amps sound the same".... seriously man, what did you think of it considering it's 20 years old and actually "MADE" in England?

That amp was £129 GBP when it was released back in the day.

Still going strong despite a few flaws and up there with most of them

It's still disassembled and am going to take some measurements first.
When it's home again I will have a listen.. promissed.

[PinkFloyd]

That was the cheap "budget" kit Frans, comes supplied with 50V / 1000uF Panasonic NHG..... the standard kit comes with Panasonic 35V / 1500uF, MUSE in/out caps etc.

[Deleted]

Some measurements and findings of the amplifier with modifications as in the pdf.

Frequency range with 32 Ohm resistive load:
-0.5dB = 8Hz to 70kHz
-3dB = 2Hz to 180kHz

Squarewave reproduction of 1kHz and 10kHz is excellent with no overshoot.
Even 100kHz is impressive (measured under 120 Ohm RESISTIVE load condition)

Output power:
This is a tricky one as these measurements are taken with the stock M.F. wallwart.
The walwart itself seems to be under-dimensioned and I suspect the great little Pinky will show considerably better measurements/performance because of this.

Open output voltage @ 1kHz (so no load): 14.7V_R.M.S.
Output voltage @ 1kHz with both channels driven with 300 Ohm resistive load: 12.5 V_R.M.S. = 0.5W/channel
Output voltage @ 1kHz with both channels driven with 120 Ohm resistive load: 9 V_R.M.S. = 0.7W/channel
Output voltage @ 1kHz with both channels driven with 32 Ohm resistive load: 4.0 V_R.M.S. = 0.5W/channel

The calculated 1.3W @ 32 Ohm is not reached because the internal resistance of the power supply is MUCH higher than the desired value.
Partially this MAY be done to protect the non-cooled output devices from overheating.
Overheating is only likely when very inefficient low impedance headphones are constantly driven to loud levels b.t.w. or on a test bench pushing max power in dummy loads.
Since this is an amp to provide music signals the powers mentioned above are the worst case.
In reality the output power into 32 Ohm may easily reach peak values of 1W with MUSIC signals though.
This also means that with low impedance headphones the sonic performance should be much less than with higher impedance headphones..
Why ? Simply because of the PSRR (power supply rejection ratio) of this amplifier design is not amongst the best designs.
Meaning variations on the power supply voltage also find their way (substantially attenuated though) into the signal.
This will consist of 50Hz (single phase rectifier) sawtooth modulated by audio content and show itself in the form of distortion figures that may reach audible levels.
As the little pinky (because of the used transformer) will have a much more stable power supply voltage the distortion will be less (could not check, lack of time).

Under continuous 1kHz sine-wave the power supply voltage before the 'regulators' (they are actually capacitance multipliers, not regulators) the voltage drops from 29V to 22V.
The ‘regulated’ voltage drops from 25V to 17V showing the high impedance of the power supply circuit.

If it were my design/amp I would have replaced the top board with a completely different one containing real regulators.

[Deleted]

Sept 12, 2012 9:27:50 GMT PinkFloyd said:

That was the cheap "budget" kit Frans, comes supplied with 50V / 1000uF Panasonic NHG..... the standard kit comes with Panasonic 35V / 1500uF, MUSE in/out caps etc.

I think when fed with a little Pinky the 50V isn't a bad idea.
Reckon the voltages on before the regulator will be very close to 35V.
What voltage (AC) do you measure under load with a Pinky ?

Have you thought about selling log type volpots for these amps ?
a lin type is not very recommended for amps.

Did you ever notice the red LED on the front panel to be 'flickering' when viewed at from the corner of your eye ?
Feeding it from the rectified heater voltage cures this.
It bugs me, but reckon other people have not noticed this.

I listened to it (extensively) and rate it as good as my other amps.
NOTHING wrong with this amp even at higher levels so the sonic effects of the measurements taken earlier might be 'masked' by the loudness of the music (high SPL) with low Ohmic HP's.

[PinkFloyd]

Have you thought about selling log type volpots for these amps

The volpots I use ARE 50K log (mini ALPS) Frans, they do make a nice difference.... I have been using them for yonks

You're right, it IS a nice amp

[Crispy]

Sept 12, 2012 0:02:48 GMT @cjarchez said:

That is very nifty, great job Franz.
Taking all the abovementioned into account, would there be any mileage in having new uber quality boards made up?
Firstly loads of peeps have these things and secondly it may make rescuing fried units more viable.

X2 even though I haven't got a clue how to read schematics

Frans,
I would certainly be interested in uber quality replacement boards - especially one of your modded PSU boards with real regulators
My boards are like everybody else's - pads and tracks lifted just by looking at them.

[Deleted]

I'll think about it....
the PSU board would involve using other transformers as well which means little pinkies also wouldn't work anymore.
Also the output devices would be needing small heatsinks mounted as well.

IF the sonic quality would improve is another matter.
Nobody has complained, yet, about the high internal resistance of the v2 power supply.
Food for thought.

Those with experimentative minds, good ears and a +/- 24V (0.5A or above) power supplies can contact me for some experimental voodoo.

[mrarroyo]

I recall doing a mod to allow more "juice" to reach the amp. It involved replacing the power supply transistors.

[PinkFloyd]

Frans, the pots I use in the V1 / V2 are the Mini ALPS (that's what I call them) they are 50K log. You can also use the 10K log mini ALPS.... here's a photo of them, nice pots, I once cracked one open with a hammer and they are very well made in typical ALPS fashion

[Will]

Sept 12, 2012 0:02:48 GMT @cjarchez said:

That is very nifty, great job Franz.
Taking all the abovementioned into account, would there be any mileage in having new uber quality boards made up?
Firstly loads of peeps have these things and secondly it may make rescuing fried units more viable.

Oh, I'd totally buy one of these if they were made.

Wouldn't a quality pcb, with Mike's mods built in from the start be the ultimate Rock Grotto Head-amp? Of course it would.

[mrarroyo]

"Wouldn't a quality pcb, with Mike's mods built in from the start be the ultimate Rock Grotto Head-amp? Of course it would."

YEAH!

[Deleted]

Go, Mikey, go

Gimme a M,
Gimme an I..........