• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Intermittent Static on ARC REF 3 Preamp

maxzimum

Member
2005-02-11 12:48 pm
Hi,
I've recently started getting an intermittent scratchy sound (like static) through my left speaker. I've isolated the problem to my Audio Research Reference 3 preamp. I swicthed the 6H30P tubes (left with right) and the noise is still from the left channel only.
Any help would be appreciated.
Thanks.
 

maxzimum

Member
2005-02-11 12:48 pm
analog_sa said:
Maxzimum

Do you get this this both in balanced and SE mode? The sctratchy sound may indicate oxidated contacts of the tube sockets, bad connectors, bad solder joints. I'll be very surprised if it's something else. How good are you with a soldering iron?

I haven't tried in SE mode. Will try in a few hours and post back.

I have removed and reseated the the tubes, even replaced them but with no luck. Pretty good with a soldering iron.
I have Deoxit spray, should I try spraying the tube sockets?
 
The SE test won't tell much. Unless you are lucky.

Start with the Deoxit and inspect all solder joints on the tube board. Seems there are always a couple of relays along the signal path, no matter what input is in use and relays are, annoyingly, also suspects.

If these casual measures don't help you would probably need to get your hands dirty, disconnect the amplifier board from the volume control section and test it using an external volume control, like a variable output cd player. This is not so straightforward as it sounds and probably involves lifting one side of the grid stoppers and providing grid leak resistors.
 

Dragon2

Member
2005-05-15 6:59 pm
Canada
Hi Maxzimum

I am a repairman and i have repaired a Ref 3 some time ago.

First: do not put deoxit on tube socket!
At first, it will wok but after a while, it will isolate the contacts because of the heat.
The heat make a sort of gum...

This preamp is too young to clean the tubes sockets.


The problem sems likely to be the plates resistors: they have pretty high voltage on them and sometime they make noise. Look for red resistors.

It may be also a fet or a cap but it is unlikely and you will need to order the originals parts if it is the problem.

You will need a scope to fix this unit.
Be carafull: high voltage.

Good luck
 
Dragon2 said:
First: do not put deoxit on tube socket!
At first, it will wok but after a while, it will isolate the contacts because of the heat.
The heat make a sort of gum...

This preamp is too young to clean the tubes sockets.






You will need a scope to fix this unit.



Hmmm. Deoxit is rated for 200C. Not good enough? I also thought the preamp was too new but if it worked under high humidity conditions oxidation is not too strange. Or at least not stranger than expensive overrated resistors going noisy :)

Why would he need a scope? Scopes are quite useless with intermittent phenomena.
 

maxzimum

Member
2005-02-11 12:48 pm
Already sprayed deoxit before I read the posts above.

It seems to have made a difference. The noise still does come but not as frequently as before.

"The problem sems likely to be the plates resistors: they have pretty high voltage on them and sometime they make noise. Look for red resistors."

There are plenty of red resistors. About 20 per channel.
 
Something you could try carefully is to wriggle around the tube in the sockets when the unit is powered and see if this is audible. Also knock on various components, pull wires etc. I always try this with intermittent faults but you obviously have to be careful and use a low power power amp which won't blow your speakers or ears. And try not to get electrocuted.
 

maxzimum

Member
2005-02-11 12:48 pm
analog_sa said:
Something you could try carefully is to wriggle around the tube in the sockets when the unit is powered and see if this is audible. Also knock on various components, pull wires etc. I always try this with intermittent faults but you obviously have to be careful and use a low power power amp which won't blow your speakers or ears. And try not to get electrocuted.


analog_sa said:
And btw, many here will be thankful for close up pictures of the main and ps boards.

The problem has since re-occured and hence seems to be something else. I have wriggled the tubes, tapped on parts and cables, but no luck. I have asked the dealer (in another country) to now check with ARC and let me know how to sort this.

Will post some photos soon.
 

maxzimum

Member
2005-02-11 12:48 pm
Hi all,
Turned out to be the Red Resistors (PRP). Changed all of them on the signal board and all is well now.

Strange thing is I did a google image search for the REF3 and none of the images I came across had any Red Resistors. Did they use PRP's only for a short while?
 

Vsquared

Member
2014-09-07 8:09 pm
scratchy noise

Hi all,
Turned out to be the Red Resistors (PRP). Changed all of them on the signal board and all is well now.

Strange thing is I did a google image search for the REF3 and none of the images I came across had any Red Resistors. Did they use PRP's only for a short while?

Hi Maxzimum -

14 years later, and I have the same issue with a unit I'm trying to repair for a friend - left channel as well. not the tubes or cabling or sockets, etc. I suspected the FET, but I just read your post and it seems it was the resistors. This unit does not have any of the PRP red resistors - they are all conventional - look like Vishay resistors. I'm curious - which did you replace? All of the ones all around the 4 tubes and 2 FETs? or any ones in particular I should focus on?

thanks!