Worrying noise....

here is an updated pic of where I think you should try first, if you have decent resistors lying around just change them if not unsolder one end and check them, but do it in circuit first in case one is way out.
check they have the same colour bands on them first (4 near the output) and 2 near the pre should also be a pair, change for 1% types.
I suspect one of them may have been overheated during maufacture, or cracked.

twist that wiring up too *blue dots* probably wont make much difference but should be twisted.

 

Cheers...........I'll take a look

 

Yes, thats what mine looked like before I set too. I'll have another look tonight, but I spent hours on it last night, with no success. Its so annoying that its been fine for 18 months and then bingo.

Im pretty sure it on the pre side of things as I cant find anything at all on the power amp, Ive measured everything numerous times. arse.

thanks for the help guys

 

spotted this ....

http://www.audioasylum.com/forums/amp/messages/96136.html

sounds familiar !

 

this was the answer...........


Is there any signicant amount of DC in the left channel signal? If yes, check input coupling capacitor (if the amp has one) and see that the tube sockets are making good contact. I just worked on a circuit where I was seeing DC on one of the grids and I couldn't figure out where that was coming from until it dawned on me to clean the sockets and resolder the connections. No significant DC after that.

Otherwise, I'd check left channel ground connections on the amplifier, particularly at the input jack and volume control, if it has one.

 

sounds about right, i'd just resolder the lot as it sounds like there may be manufacturing problems, dry joints etc.

this probably all that is wrong with both of your amps.

good luck

ps changing them resistors and twisting the wires is still good practice.

also you may want to think about valve rectification in the future, shouldn't be too hard to do and will open the sound right up.

 

Yes my initial thoughs were of DC present, I couldnt find anything worrying but I changed the output caps for Hovlands & Wilmslow Audio anyway.

After many many more hours I was still at a loss. However, the last few times Ive switched the cdp (through a Monica 2 dac) off first and left it 5 mins and Ive not had the slightest noise (touch wood).

Its now time to start checking the dac (if I can be bothered).

 

did either of you have any luck sorting out your amps?

just out of interest, what do they sound like when they are working well?

 

I've been tied up with other things..........

but the rustling is greatly deminished and if I leave the amps on the balance comes back to centre...........????

 

how long do you have to leave them on?

 

An hour or so maybe two.......[but I normally give the 20mins warm up anyway]

 

have you removed the input caps?

a good idea anyway and could be your problem but I doubt it.
anyway have a look at this it may help to get a better sound even if it doesn't fix the problem.
http://www.hifi-forum.de/viewthread-111-558.html

 

Guys, all this talk about pops. If you have a capacitively coupled preamp you will ALWAYS get pops if your power amp is not powered off FIRST. The reverse applies at power up. Turn the amp on LAST. This is because, believe it or not, the cap doesn't block DC until it is charged! This phenomenon has affected audio systems since the dawn of time. Sometimes these pops can be sufficient to damage loudspeakers.

Also, my 2p worth on removing the input caps on the Dynavox: DON'T DO IT. There is a DC offset at the grid of the 6F2 or whatever you have in there which is small at low volumes, but rises to several hundred millivolts when you turn up the volume. The volume pot doesn't like this and gets quite scratchy. I also find the amp gets excessively bright and the balance goes out a bit. The caps that are in from the factory are junk and cause everything to sound like it is coated in a layer of fuzz. Replace them with decent polyprops such as Solen FC's and the improvement is immediately audible (even to my wife). Also, the correct value is 0.22uF and you should use 250V or more to allow for the driver valves ever failing and passing that failure back to your source....

 

Ive always done the amp on last/off first but I find I need to turn the cdp of first to avoid those thuds through the speaker. I note your recommendation on the input caps but both Pete (Zanash) and myself use these as power amps (after a slight mod to the input side of things) with a seperate pre. My pre is cap coupled so I dont see the need (though I welcome advice to the contary).