EVP-X12P 300W Speaker Teardown

Here is a little teardown of a Wharfedale EVP-X12P 300W active speaker.

BACKSTORY: So I borrowed two Wharfedale EVP-X12P active speakers for DJing at a 21st party, and half-way through the set, as Skrillex was playing, I happened to blow one up (if I remove the theatrics, what I really mean is that one of the bass/mid cone speakers stopped working). It turned off, and I smelt that ‘burnt electronics’ smell. It turned back in about 10minutes, however was not producing any sound from the cone speaker. I managed to survive the rest of the set with just one.

On the premise I over-drove it, I was looking for visibly wrong things such as blown fuses or dried up/non-existant thermal compound. All components were through-hole, so that made things easier to investigate…

It has thermal PTC  resettable fuses, so these couldn’t of blown…

The four gruntiest looking power compontns are all in TO-3P packages and directly bolted onto the aluminium heatsink. Designators are Q18, Q20, Q21, Q23. Two are the Sanken 2SA1492 PNP transistors (product marking A1492 55 P), while the other two are Sanken 2SC3856 NPN transistors. They are complements to each other (mentioned in the respective datasheets).

I tested the base-emitter voltage drop of the transistors while they were in circuit. I got a reading of 43mV for all four transistors, which is not what you would expect if you were testing a transistor by itself (0.3-0.7V is usual). But since it was in circuit, other components could of been affecting this result.

Since I had two speakers, one working, and one not, the next thing to try was a differential diagnosis. I removed the electronics panel from the working speaker and connected both to the same audio signal. I made sure that the speakers had the same left and right channel signals, and that all the panel dials such as volume and bass were all set to the same amount. Unfortunately, when the speakers had main power and I connected a ground lead up to the earth on each of the speaker circuits, smoke started coming from the broken one! Unsure of why that happened…

I measured the signals on the 6-pin connector going from the input board to the main board as follows:

Pin 1: (unknown use) +1.4V
Pin 2: (unknown use) -1.68V
Pin 3: (unknown use, possibly ground) 0V
Pin 4: (unknown use, possibly ground) 0V
Pin 5: Audio Shield
Pin 6: Audio Signal

All of them had 70kHz, 200-300mV noise present (relative to earth).

I found a pad labelled ground on the output board! Hooray for nicely labelled test points!

After finding to difference between the broken and working circuits, I decided to remove the speakers from the enclosures.

This is where I finally found the problem, the LF speaker coil had completely blown!

And then I discovered why I was still reading 4Ω at the connector on the amplifier PCB, there was another PCB between the amp and the speaker to filter the sounds between the LF (low-frequency, aka bass-driver) and horn (HF, high-frequency) speaker.

Now knowing that I needed a new bass-driver, I got the guys at South Pacific Music, the New Zealand stockists for Wharfedale Pro speakers, to re-cone the bass-driver.


Power Transistors

[gview file=”http://blog.mbedded.ninja/wp-content/uploads/2012/07/2SC3856-Sanken-NPN-Transistor.pdf”]

[gview file=”http://blog.mbedded.ninja/wp-content/uploads/2012/07/2SA1492-Sanken-PNP-Transistor.pdf”]


Posted: July 9th, 2012 at 7:10 pm
Last Updated on: March 3rd, 2013 at 3:15 pm

  • Robin

    Hi Thanks for intresting artical.I have a pair of thease and as they have quite a lot of power I would like to piggy back another pair of speakers off them.The only problem is the speaker outlet apears to be signal only .Is there any reason this outlet could not be conected up to the out put from the amp.

  • Hi Robin,

    I don’t quite understand what you are asking when you say “Is there any reason this outlet could not be connected up to the output from the amp?”. Are you wanting to drive another speaker with the EVP-X12P speaker’s amp? And is the problem that the “output” on the EVP-X12P is signal level, rather than the amplified sound?

    Cheers, Geo

  • Robin

    Yes I would like to drive an extra speaker off each one of the pair and output is signal level only.The monitor version alows conection to another unpowerd speaker with amplified sound but the EVP-X12P does not.300 Watts is a lot to drive one 12″ and a tweeter .I do not have a great deal of electronics knowlage but I can see no reason for it to be signal only.

  • Here’s a quote from http://www.mixfoundation.co.nz/discontinued-products/wharfedalepro-evpx12p.html. “Speaker Out
    The EVP-X12PM and the EVP-X15PM also have the added benefit of a
    ‘Speaker Out’ output which allows the user to add on or to ‘daisy chain
    a passive EVP-X12M/15M into the system directly from the EVP-X15M.” Is yours a X12PM/X15PM?

  • Robin

    Hi mine are EVP-X12 Powerd speakers .They have a speaker out, male XLR but unlike the EVP-X12M it is signal only and I would like it to be amplified sound.Is there some reason that I am not awear of for this or could I conect them up as amplified sound with out a problem.

    • Hmmm…I’m not sure why there is a difference, considering they are both powered. Maybe there is extra headroom in the amplifiers with the “M”. Or maybe it’s an impedance issue. Amplifiers are designed to work with a certain speaker impedance. When you connect another in parallel, the impedance drops. This has an adverse effect on the sound, and reduces the efficiency of the amplifier. Maybe the “M” version amplifier has two isolated outputs, so that the impedance matching with it’s own speakers is not effected.

  • Robin

    Thanks for advice .If I find out more will post info.