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View Full Version : Can anyone help me understand this ?



Marc B
16-10-2009, 18:07
I bought a Dussun V8i amp and the balance seems to change every so often.

One day it sounds bright with no bass , then slowly the sound starts to become harsh in the mids and then the bass becomes extreme, then it returns back to being bright with no bass again.

It's as if I have some parametric EQ with a 5db boost and I'm slowly sweeping the frequency.

The really confusing thing is that each time it changes the perceived boost amount lowers.

When I first plugged the amp in 2 weeks ago it was overly bright with a huge bass. After a few days the brightness tamed and the bass recessed but with a midrange hardness.
2 days ago the amp changed again to a balanced sound but then proceeded to go bass heavy and now I'm back to what sounds like a upper bass/low mid suckout as I don't have any drive in the sound. Deep bass is full but drum hits, acoustic bass and vocals sound thin and hollow.

This amp isn't brand new , it was bought used but has been in storage for 2 years.

I'm hoping it somethin to do with the 16 large capacitors reforming or something but I've never heard anything like this before in an amp.

Any ideas if this is a normal thing or something is bust ?

If it's a problem , any ideas where to start?
The amp is a large 250 watt per channel, solid state, (allegedly class A) dual mono amp with seperate pre amp section. I've tried different pre-amps with the same sound, so the changes are affecting both power amp sections at once.

cheers

Marc

ps.. I'm not bonkers or imagining it :)

Rare Bird
16-10-2009, 18:54
Do you have a different pair of speakers to try as it has a very sensitive speaker protection circuit that kicks in

Marc B
16-10-2009, 18:59
No sorry , I only have the Dali H400s.

Wouldn't the protection just cut the sound from the amp rather than change its balance ?

I'd like to add though , that the last change came about shortly after I changed the IC from the DAC.. don't know if its related or coincidence.

Rare Bird
16-10-2009, 19:07
I read this somewhere a couple weeks ago, i can't remember, i do rember that it had a sensitive protection device that kicks in thats all..I suppose it would alter the sound slightly..are the speaker cables all ok! Anythings worth a try..I know they are chinese amps but suppose to be highly regarded, they are certainly very well constructed inside.

Marc B
16-10-2009, 19:09
cables are fine , I was using them with a Primare amp until I got this amp 2 weeks ago.

Speaker cables I've tried are VDH CS122 (the stuff that's wired internally) and QED Revelation. Both sound pretty much the same.

When the amp is balanced it's amazing and probably the best I've heard. so I'm quite gutted that it comes and goes in cycles.

Rare Bird
16-10-2009, 19:21
Marc read these remarks

http://www.nysound.com/exec/servlet/CategoryServlet?action=productdetail&itemID=kos-2010-01001

Marc B
16-10-2009, 19:32
hmmm

Not sure if it's the same problem but it makes you wonder.

Rare Bird
16-10-2009, 19:36
Indeed it does, sorry for taking you down the wrong road early on but it was something i remembered i read...

Marc B
16-10-2009, 19:42
I'm just waiting on a guy to arrive and buy my CD player... then I'll get my tin opener out on the amp and search for NEC thingies

leo
16-10-2009, 20:17
Bias drift? especially if solid state

leo
16-10-2009, 20:25
BTW also some classA SS amps are not that well designed for reliability , I've known some have things like capacitors too near say heatsinks which greatly reduces their life, some of the caps are not even rated for high temps, they go dry,leaky and noisy , this can have undesirable effects on performance especially if the caps are used in critical places.
When the amp rises in temp is when things start to go bad

This is not to say your amp is poorly designed of course (I don't know the Dussun V8i )

Marc B
16-10-2009, 20:33
I did check for obvious leaking of caps when I first got the amp and I realised something was odd.

In the time I've made the thread today, the amp has now gained a large top end spike. An uncomfortable brightness sting that sits pretty much at the top of my hearing threashold, but the bass has evened out a bit and warmth has sort of returned to the bottom end.

The cycle is now taking hours instead of days... grrr

Maybe in a few days it'll sound like a phaser effect

leo
16-10-2009, 21:15
Not so much leaking as can be seen but electrically

Harshness/brightness can be caused from instability , ears are good at detecting it

Anyway I'd be tempted to take it for a full check up tbh, sounds like it needs to be put on the test gear

Marc B
16-10-2009, 21:22
Yeah I was thinking the same.

I don't suppose you know any repair place in or around Lancashire as this weighs about 40kg?

by the way , it sounds great now but tomorrow I'm expecting to be back at square one.

Rare Bird
16-10-2009, 22:02
Marc i've a feeling your never gonna be happy with this amp even if you eradicated the problem, i'm guessing it's always gonna be in the back of your mind something could re occur...A simular amp would be one of the Esoteric range of amps..Probably the best Jap amps out at the mo.

http://www.esoteric.jp/products/esoteric/a80/indexe.html

Marc B
16-10-2009, 23:41
I'm sure I have a spare $20,000 fell down the back of the couch , let me just check :)

Rare Bird
16-10-2009, 23:55
:lolsign:

Sorry didnt realise the price..

Themis
17-10-2009, 05:35
I'm sure I have a spare $20,000 fell down the back of the couch , let me just check :)
:lol::lol:

Marc B
17-10-2009, 22:30
hmmm fixed ??

A swap of speaker cables and different cables between the Pre/power sections and it's spot on :)

how odd