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2 X QSC RMX2450 for £200?

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ceharden View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2017 at 10:41pm
Originally posted by charlysays charlysays wrote:

 
Are they difficult to replace or hard to get hold of then? They work great now. I went mad with the IPA contact cleaner. Only one was a bit crackly and caused that channel to have 100MV dc offset. but all felt quite stiff. There's no resistance at all when turning them now, they feel pretty loose.
 
If the problem recurs I'll think about refurbing them, cheers for that.
 
How do you tell if the caps have gone bad? I guess they can dry up but still look fine and can bulge and leak. Can't see any bulging or leaks. 

The pots are actually meant to be quite stiff, they have a fairly viscous grease on the shaft which makes the operation smooth but with some resistance (so they're harder to adjust by accident etc).  If they're now really loose then it just means you've washed all the grease out with the contact cleaner.  I try to be very sparing with contact cleaner for that reason.  I've also found that just squirting it in doesn't really do a good job.

You can get hold of replacements quite easily but I was finding that the ones I was removing weren't worn out, just needed careful dismantling and cleaning.  I used to have some RMX's myself and looked after some installs that had them so it was useful to get at least one extra round of usage from them.  They probably fail quicker in an install in the corrosive environment you tend to get and because they never get moved.

Caps are a tricky one.  Bulging can be a sign, especially if it's at the bottom so you find they're no longer sitting flat and vertical.  Doming of the top of the cap can be a red herring if it's just the plastic insulation and not the metal can. If you can push it back down with your finger that's not a sign of wear-out.  The other sign might be an increase in mains hum on the channel or possibly less power/earlier clipping.  If they seem to be working fine then nothing to worry about.  Electrolytic caps don't like high temperatures so plenty of airflow in and around the rack (applies to all amplifiers) is always good.


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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2017 at 10:55pm
The RMX2450s I have open up are a bit of a bitch because the pot is on the main pcb (the EP2500 has a daughter board) TBH I would simply short the wiper to the signal which converts the pot to an on-off switch/Mute, no one in their right mind would use a pot on a an amp other than full open..

If you do crack them open 3in1 oil is the weapon of choice for clean, not contact cleaner as it cleans and lubes and stays put for more than 90 seconds...



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Post Options Post Options   Thanks (0) Thanks(0)   Quote charlysays Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2017 at 11:37am
Originally posted by ceharden ceharden wrote:

Originally posted by charlysays charlysays wrote:

 
Are they difficult to replace or hard to get hold of then? They work great now. I went mad with the IPA contact cleaner. Only one was a bit crackly and caused that channel to have 100MV dc offset. but all felt quite stiff. There's no resistance at all when turning them now, they feel pretty loose.
 
If the problem recurs I'll think about refurbing them, cheers for that.
 
How do you tell if the caps have gone bad? I guess they can dry up but still look fine and can bulge and leak. Can't see any bulging or leaks. 

The pots are actually meant to be quite stiff, they have a fairly viscous grease on the shaft which makes the operation smooth but with some resistance (so they're harder to adjust by accident etc).  If they're now really loose then it just means you've washed all the grease out with the contact cleaner.  I try to be very sparing with contact cleaner for that reason.  I've also found that just squirting it in doesn't really do a good job.

You can get hold of replacements quite easily but I was finding that the ones I was removing weren't worn out, just needed careful dismantling and cleaning.  I used to have some RMX's myself and looked after some installs that had them so it was useful to get at least one extra round of usage from them.  They probably fail quicker in an install in the corrosive environment you tend to get and because they never get moved.

Caps are a tricky one.  Bulging can be a sign, especially if it's at the bottom so you find they're no longer sitting flat and vertical.  Doming of the top of the cap can be a red herring if it's just the plastic insulation and not the metal can. If you can push it back down with your finger that's not a sign of wear-out.  The other sign might be an increase in mains hum on the channel or possibly less power/earlier clipping.  If they seem to be working fine then nothing to worry about.  Electrolytic caps don't like high temperatures so plenty of airflow in and around the rack (applies to all amplifiers) is always good.


 
They've actually stiffened up again now- I guess some contact cleaner got into the grease and made is less sticky but not the contact cleaner has evaporated they feel smooth again. Good news is that the DC offset on the crackly channel has stayed down and the amps are working perfectly so I guess enough cleaner got onto the track to get it working properly this time.
 
Looks like I got a great deal on them, may still sell them but I do like to have belt and braces approach with backups for most stuff apart from speakers. I have two ultradrives etc.
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charlysays View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote charlysays Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2017 at 11:39am
Originally posted by shagnasty shagnasty wrote:

The RMX2450s I have open up are a bit of a bitch because the pot is on the main pcb (the EP2500 has a daughter board) TBH I would simply short the wiper to the signal which converts the pot to an on-off switch/Mute, no one in their right mind would use a pot on a an amp other than full open..

If you do crack them open 3in1 oil is the weapon of choice for clean, not contact cleaner as it cleans and lubes and stays put for more than 90 seconds...



 
Haha, I used to use the pot to control output! Now I used the gain on the ultradrives output band but in some cases particularly my tops running of my PQM 13 it's still too loud even after turning the bands down by 15db, so I back the pot on the amp off a bit then.
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