Amp woes... Denon POA2400.

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mortron

Member
2011-08-20 6:02 am
Town
I have a Denon POA 2400 amp that has been loyal to me through thick and thin, even when I tried to trade her in and she sat in a shop for 6 months. Lately I have notice the output will occasionally drop and the amp sounds a bit anemic, if that makes sense. Now since it happens in what sounds to be both channels, is it safe to assume its a power supply issue? I am limited in my tools, and could only take a gander inside... is there a place go start?
 

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Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Have you downloaded a sevice manual to follow the basic checks?
Denon POA-2400 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
This model has some fairly complex bias and management circuits so it may not be practical to troubleshoot the logic circuits remotely. Nevertheless, it could still be a simpler matter related to ageing of caps, for example. If you are limited in tools like even a DMM, you need to think of service by a Denon service technician if you are not able to DIY.

Do any warning lights show?
 

unclejed613

Member
2006-12-28 12:19 am
if it's sounding "anemic", it's probably the DC correction caps. these will be on the inverting input of the diff amp, usually somewhere between 47uf and 470uf. if they are dried out, they will first affect the rolloff frequency of the amp, reducing the bass. as they get worse, they will reduce the overall gain of the amp.
 

mortron

Member
2011-08-20 6:02 am
Town
if it's sounding "anemic", it's probably the DC correction caps. these will be on the inverting input of the diff amp, usually somewhere between 47uf and 470uf. if they are dried out, they will first affect the rolloff frequency of the amp, reducing the bass. as they get worse, they will reduce the overall gain of the amp.

Used to live next door to a Jed... Wise man he was... Thought you may be him. This sounds most like my situation.

Problem is a tech wants $400 to recap :(
 

goodguys

Member
2011-02-23 3:51 pm
I have had this problem before and would advise a total recap, if one capacitor has dried up it stands to reason the rest are not too far behind..
I used nichicon kz's as replacements in signal pathways and panasonic's in psu. It took me half a day but i am very happy with the results, i also changed resistors for vishay's, for me if a job is worth doing it is worth doing well and only cost a few bucks more, personally i used slightly larger replacement components than the stock ones.

Best of luck with your project
 

mortron

Member
2011-08-20 6:02 am
Town
I have had this problem before and would advise a total recap, if one capacitor has dried up it stands to reason the rest are not too far behind..
I used nichicon kz's as replacements in signal pathways and panasonic's in psu. It took me half a day but i am very happy with the results, i also changed resistors for vishay's, for me if a job is worth doing it is worth doing well and only cost a few bucks more, personally i used slightly larger replacement components than the stock ones.

Best of luck with your project

My biggest concern is that I will change the sound of the amp by swapping resitors etc... caps I know need replacing but do the resistors really?
 

goodguys

Member
2011-02-23 3:51 pm
The best thing to do in that case is decide the kind of sound you want the amp to produce then use components which will deliver that.

For resistors here is my opin: Carbon comp :
1) kiwame ( lush sounding - the best ( to my opinion ! )
2) rihken ( taut and three dimensional but very expensive )
3) kamaya ( very good but 5 to 10% tolerance )
4) Ohmite little devil ( see kamaya )
5) morganite ( pleasant sound - tend to drift !! )

Metal :

1) roederstein ( tight 'n' fast - a little thin )
2) Holco ( very fast - "metallic treble )
 

goodguys

Member
2011-02-23 3:51 pm
Sorry, hit the wrong button and my post was cut short.

To continue: Google and find out from previous posts how different resistors and capacitors sound. You are right in that the sound may change if you shove any old resistor or capacitor in, but simply do some research and you can minimize or eliminate this. This may take a few days so it depends on how much time and patience you have

I think it would be a good idea to replace the old resistors as resistors last for about twenty years before they need changing so at least this is one less worry to think about.

For the bipolar caps i would recommend nichicon es

Personally i upped the psu caps by twenty percent so there is a little more juice for the components if they should need it..

Best of luck.:
 

unclejed613

Member
2006-12-28 12:19 am
i wouldn't recommend replacing all the resistors.... carbon comps are noisy anyway. carbon film and metal film are much quieter, and that's one of the reasons carbon comps aren't used much anymore. it's better to just replace the caps that need replacing. obviously the
dc correction caps need to be replaced, and if you can get your hands on an ESR meter, then i would replace any others that show signs of aging

for a description of why some people like carbon comp resistors (and why carbon comps are not always the best choice for amplifiers, unless you WANT increased distortion and noise) look here: http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm

keep in mind that article is about tube type guitar amps, and in guitar amps the distortion imparted by carbon comp resistors is somewhat desirable.

i don't know where gg got the idea that resistors have a limited lifespan.... unless he's thinking of carbon comps in a high temperature environment.... i've used equipment that's 40 years or more old, and the only high failure items in stuff that old are electrolytic caps. resistors (even carbon comps as long as they aren't overstressed) don't "age" like electrolytic caps do.
 
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Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
I think we are talking audiophile esoterics by playing with passive component types and their aleged audio distortion effects there. As unclejed points out, this is for guitar amp tweakers and those with deep pockets and plenty of time to kill experimenting to sort what may sound better (small chance) and what actually sounds worse (most likely). It's parts roullette with a lot of expectational bias, parroted opinions and no guarantees.

FWIW, all standard, phenolic bonded carbon comp. resistors drift with heat and time, particularly Stackpole Process types which were once cheap and ubiquitous. They were abandonded as soon as tougher and more consistent film types were developed in the 1960's. If there is any need for them, it's in high speed circuits that must have absolutely lowest inductance, like instruments and RF circuits. There may be sonic benefits in old audio designs that were built around these dinosaurs but if the circuits are designed with film resistors, they should be kept that way to maintain stability levels, IMO.
 
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