MF x-dacv3 playing up

Hi folks,

Looking for some help off all you electronics experts out there

Recently I've been modding my x-dacv3 as per Zanash's excellent instructions. Yesterday I removed the two muting transitors but not the muting resistors and today I replaced the 4 power supply caps with panasonic FC caps, same value. I also replaced the 2 output resistors with vishays, again same value. Today I have noticed a slight popping/crackling noise occassionally when no source is playing. After one brief flurry of popping/crackling my arcam fmja32 turned itself off, presumably the dc offset protection kicked in turning the amp off. The popping/crackling is always at the same volume, regardless of the volume setting of the amp. WHen I totally remove the x-dac from the chain, including IC's the popping is not present. Do you think it has anything to do with the removal of the muting transistors? I have tried my own PSU and the wallwart, both with the same result. My amp has never turned itself off before. The noise presents itself in stereo,from both speakers.

ANy ideas???

 

All I can think of is to check the orientation of the PSU capcitors you replaced very carefully. If you have an electrolytic cap in the wrong way round it will break down, leading to high leakage currents - which could generate the pops and crackles. Check all the caps you changed with a multimeter (that all are in with the '-' side to at the lowest voltage) and check none of them feel hot...


If all is well here - well this maybe why the unit has muting protection!

 

Thanks Felix,

The caps are round the right way and none are running hot, all the same temp. I have unplugged the unit and left it for half an hour and then plugged it in to try again. That's been 20 mins without any noise. Maybe a static build up? The mains quality in my house is p** poor to start off with. I don't help matters by having all my hifi gear through a cheap 4-way extension lead. I thought the muting transistors were there for CDP's, so that when you skip a track or press a button you don't hear a slight popping noise? Surely no need for this in a dac or even a cdp to be honest.


Anyway, fingers crossed, so far so good. Just a bit concerned that the popping crackling could damage my speakers.

Have I missed anything or do you think mains and my poor mains setup could be to blame?

 

Well it was worth checking.

I missed this little detail - could well be mains-related noise then, the constant volume suggest there's another route in for the noise than the amps inputs. Do you have an inadvertant ground loops such as an earthed CD player and another connection to PC/freeview box /cable modem/ tuner with earthed aerial input..? In itself, such a loop may not be a major problem, but they can exagerrate the intrusiveness of mains interference - particularly if the different sources are plugged into different parts of the house mains circuit(s).

If the noise is only sporadic/infrequent I wouldn't worry too much while tracking-down the cause, it seems your amp is very effective in protecting itself.

 

Hi Felix,

Yes I do have SKY, CDP,DVD player all nearby, also RF aerial going into tv. The back of my tv cabinet is an pigsty of all sorts of cables. I will be buying a dedicated hifi rack soon which should help the problem as I will be moving to another mains socket. SO far thats almost an hour without noise. In truth it's only now and then but I had a bad spell earlier when it was every couple of mins. Since unplugging everything and tidying up some cables I've heard diddly squat. I think thats been the problemo. If it was a p** poor solder joint by myself or a dodgy component surely there would be constant interference right??

ANyway, cheer Felix :beer: