Pioneer A400 faint distortion on right channel

Growers · 16th April 2004, 11:49 AM

Hi everyone,

I have recently purchased a 2nd hand A400 on ebay and unfortunately there is a slight but audible distortion on the right hand channel when signal is present. The distortion sounds like a partially blown speaker (I spent an hour or so checking my speakers over before realising it was coming from the amp!) – a sort of signal dependant mechanical buzzing. It is most apparent with a low level mid-range signal such as an a bass guitar note and is present using all inputs and also on the right headphone output.

Does anyone have any suggestions as to what may be causing the distortion?

Also, I did a search on this forum and found a thread regarding A400 schematics. Would anyone be kind enough to email me the schematics?

Thanks,
Duncan

SVI2004A · 16th April 2004, 12:17 PM

possible o/c transistor - tried cheching output transistor(s)

subwo1 · 16th April 2004, 12:21 PM

Two things I would check for are bad transistors and dried up electrolytics.

K-amps · 16th April 2004, 08:49 PM

Also no bias can be audible as crackling. Check bias too.

lucpes · 16th April 2004, 11:41 PM

Had some similar problems and the culprit was a blown diode

but in your case it could be almost anything. Take a digital VOM and compare against the 'good channel', whilst shut down first and then when fired up, taking G R E A T care not to slip connectors, but first read:

http://sound.westhost.com/articles.htm

check these first: http://sound.westhost.com/troubleshooting.htm

http://margo.student.utwente.nl/el/audio/amphelp.htm

Growers · 18th April 2004, 11:55 AM

Thanks for your replies. Since my initial post I've had a closer inspection of the PCB and noticed some evidence of electrolyte leakage which could have come from one of two caps which I will try replacing.

Without schematics (and with little familiarity of amp design) I find it quite difficult to do fault diagnostics on a good channel vs faulty channel basis.

Thanks again.

lucpes · 18th April 2004, 03:20 PM

Replacing all the low value electrolytics you find on both L/R PCBs isn't a bad idea at all + it's cheap.

mudan · 30th April 2004, 11:14 AM

Hi all,

I've replaced the old PSU smoothing Elna black/gold caps with Panasonic TSUP as I couldn't source any better of the same spec.

I'm soon about to replace the coupling caps with Audyn MKP QS , hoping this will make a worthwhile improvement. I'm also replacing some of the larger Elna/Nichicons for the L/R channels with Black Gates.

Any recommendations for mods to the A400, including my choice of the Audyn MKP QS would be appreciated.

Thanks,

Dav

16th April 2004, 11:49 AM	#1
Growers diyAudio Member Join Date: Apr 2004 Location: Wilts	Pioneer A400 faint distortion on right channel Hi everyone, I have recently purchased a 2nd hand A400 on ebay and unfortunately there is a slight but audible distortion on the right hand channel when signal is present. The distortion sounds like a partially blown speaker (I spent an hour or so checking my speakers over before realising it was coming from the amp!) – a sort of signal dependant mechanical buzzing. It is most apparent with a low level mid-range signal such as an a bass guitar note and is present using all inputs and also on the right headphone output. Does anyone have any suggestions as to what may be causing the distortion? Also, I did a search on this forum and found a thread regarding A400 schematics. Would anyone be kind enough to email me the schematics? Thanks, Duncan

16th April 2004, 12:17 PM	#2
SVI2004A diyAudio Member Join Date: Mar 2004 Location: Albany Western Australia	possible o/c transistor - tried cheching output transistor(s) __________________ .:Ride the Lightning...Feel the Thunder:. - Technics Triple Thunder www.welcome.to/Technics oh yes ppl plz send me them dead (or Alive) STK or SVI ICs

16th April 2004, 12:21 PM	#3
subwo1 diyAudio Member Join Date: Jan 2002 Location: North American Continent	Two things I would check for are bad transistors and dried up electrolytics. __________________ USMPS http://groups.yahoo.com/group/switchmode/

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16th April 2004, 08:49 PM	#4
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Also no bias can be audible as crackling. Check bias too.

16th April 2004, 11:41 PM	#5
lucpes diyAudio Member Join Date: Dec 2003 Location: Iasi	Had some similar problems and the culprit was a blown diode but in your case it could be almost anything. Take a digital VOM and compare against the 'good channel', whilst shut down first and then when fired up, taking G R E A T care not to slip connectors, but first read: http://sound.westhost.com/articles.htm check these first: http://sound.westhost.com/troubleshooting.htm http://margo.student.utwente.nl/el/audio/amphelp.htm

18th April 2004, 11:55 AM	#6
Growers diyAudio Member Join Date: Apr 2004 Location: Wilts	Thanks for your replies. Since my initial post I've had a closer inspection of the PCB and noticed some evidence of electrolyte leakage which could have come from one of two caps which I will try replacing. Without schematics (and with little familiarity of amp design) I find it quite difficult to do fault diagnostics on a good channel vs faulty channel basis. Thanks again.

18th April 2004, 03:20 PM	#7
lucpes diyAudio Member Join Date: Dec 2003 Location: Iasi	Replacing all the low value electrolytics you find on both L/R PCBs isn't a bad idea at all + it's cheap.

30th April 2004, 11:14 AM	#8
mudan diyAudio Member Join Date: Apr 2004 Location: Midlands	Hi all, I've replaced the old PSU smoothing Elna black/gold caps with Panasonic TSUP as I couldn't source any better of the same spec. I'm soon about to replace the coupling caps with Audyn MKP QS , hoping this will make a worthwhile improvement. I'm also replacing some of the larger Elna/Nichicons for the L/R channels with Black Gates. Any recommendations for mods to the A400, including my choice of the Audyn MKP QS would be appreciated. Thanks, Dav

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