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Chip Amps Amplifiers based on integrated circuits

Fix or Build Plate amp for Sub
Fix or Build Plate amp for Sub
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Old 7th June 2012, 01:38 PM   #1
bunglehaze is offline bunglehaze  United Kingdom
diyAudio Member
Join Date: Jun 2012
Location: Sheffield UK
Default Fix or Build Plate amp for Sub

Hi folks, I am hoping this is firstly in the correct section and secondly is something one of you can help with. I have been using a wharfedale PC8 subwoofer for over a decade, never really been happy with it and only recently decided to try and figure out why.

If I turn up the volume on the active amp it sounds awful, distorting here and there, farting occasionally and naturally my attention started with the driver. I have pushed and the voice coil feels smooth so hooked it up to my rotel amp alongside a set of B&W 602 speakers, with bass turned up it sounds loud, punchy and deep (admittedly not using a crossover) but most importantly it seems to be able to handle tons more juice than it does when attached the the wharfedale plate amp. I have in the meantime ordered a replacement driver and am now fairly convinced that when this arrives today I will get a similar, distorted sound out of it.

As a result I have moved toward the plate amp, there has always been a low volume buzz when it is powered up, regardless of if the unit is connected to my Marantz amp, this is not a feedback type hum, a definite buzzing and it seems to be originating around the power supply.

The issue I have is that I am new to using a multimeter, even more new to trying to diagnose the source of the issue but not averse to a bit of soldering or having a go at diagnosing if directed. For obvious reasons I would prefer to either repair the plate amp by replacing components or if need be (and possibly managing to upgrade) I could look at making something similar that uses the original plate for connectors.

So, if any of you are able to help advise in any way I would greatly appreciate it, I have looked over all the connections and components and cannot see visual evidence of damage so I could really use a little expert help in where to start pointing my multimeter to find the issue and get sorting it. I have attached some images that will probably be of no use to anyone but should show how simple the plate amp PCB appears to be.

Thanks in advance.

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Old 7th June 2012, 02:29 PM   #2
Tekko is offline Tekko
Join Date: Jan 2005
This could be the result of broken solder joints caused by vibration, so looks for solder joinds that looks suspect and redo them and see if that fixes the problem, if not, do every joint on the board(s).

If that doesent fix it, something is wrong in either the filter part or the poweramp part.

The farting does sound like its developed a instability somehow.

IF you have a scope, see where the signal gets distorted, if at the poweramp input, the frontend stuff is faulty, if the input to the poweramp is clean but the output to the speaker is distorted, theres an issue with the poweramp.
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Old 7th June 2012, 02:38 PM   #3
bunglehaze is offline bunglehaze  United Kingdom
diyAudio Member
Join Date: Jun 2012
Location: Sheffield UK
Thanks Tekko, I dont have a scope, nor would I know where to begin using one so I guess I may leave that section for now

I have just had the new driver turn up, fitted it and connected up it does exactly the same thing really so I guess my theory of it being the amp is correct. I will pop the PCB's out and get a soldering station put up to give your suggestion a whirl.

I think actually calling the noise farting is probably a little inaccurate, I just tried a bass heavy track (Fannypack - Hey Mami) and on low volumes there is more distortion than turned up high, quite farty on low, more vibey when high (not massively technically described, I know)

I am more annoyed as I have had it so long and never really set my system up to its potential as I always kept the volume quite low on the sub, it has never really offered much in the way of depth or power IMHO
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