Is it difficult to repair that amp or is it easy?
I do repair amps occasionally but failed with a jbl 6290 once, it was just a black hole left in it after a couple of hours at a club and i dont want to risk anything with this amp.
-Are there any special pitfalls on MPX amps to watch out for?
I do repair amps occasionally but failed with a jbl 6290 once, it was just a black hole left in it after a couple of hours at a club and i dont want to risk anything with this amp.
-Are there any special pitfalls on MPX amps to watch out for?
Second question..
Is it possible to lower the dampingfactor on this amp?
It is roughly 50 times higher than what is recommended for the speakers.
Is it possible to lower the dampingfactor on this amp?
It is roughly 50 times higher than what is recommended for the speakers.
The damping factor is also related to the Loudspeaker leads it not really any use measuring at the amp terminals. You should measure at the speaker terminals. This will then include the resistance of the leads the differrance can be quite enourmouse
regards Trev
regards Trev
You could also include a small value resistor maybe 0.2 ohms in the speaker leads.
If you wanted to get really into it try the resistor in the bottom leg of the feedback network and then connect the return leg of the speaker to that junction !
But i would advise caution.
regards Trev
If you wanted to get really into it try the resistor in the bottom leg of the feedback network and then connect the return leg of the speaker to that junction !
But i would advise caution.
regards Trev
Thanks,
I probably have more than 0.2 ohm in connector/lead resistance so it seems that i am probably looking in the wrong place here...
I probably have more than 0.2 ohm in connector/lead resistance so it seems that i am probably looking in the wrong place here...
Damping factor isn't anything to worry about, and certainly not if you're trying to find a fault.
What is the matter with the amp anyway?.
What is the matter with the amp anyway?.
One channel has burnt down and the other channel is making a clicksound about a couple of seconds apart.
-I havent looked at it so closely, just opened the lid and put it back.
But i remember there were some burned fuses and exploded powercapacitors there.
-Just wondering if i should send it directly to repair or if its worth to try it myself...
(The dampigfactor-sound is probably related to my bassbins so i have to rebuild them i think. I have several MPX amps both 600 and 300)
-I havent looked at it so closely, just opened the lid and put it back.
But i remember there were some burned fuses and exploded powercapacitors there.
-Just wondering if i should send it directly to repair or if its worth to try it myself...
(The dampigfactor-sound is probably related to my bassbins so i have to rebuild them i think. I have several MPX amps both 600 and 300)
Nigel Goodwin said:
If you have to ask?, I suggest you don't try it
Nono, im not good but i am not that bad 😀
-Just wonder if its a hard amp to fix or an easy one. If its a hard one then i wont even try but if its a normal/easy one then i do it myself unless i get too lazy.
electroaudio said:
I've just recovered a JBL 6290 (manual and schematic here). One channel works fine. When I power up the other, the relay clicks and it jumps straight back into standby / protection.
Having just taken the cover off, it's now clear why. One of the transistors for the second channel (Q16 - 2N6728) and 2 nearby resistors seem to have suffered a dreadful melt-down. When powered on, there is a brief spark visible at one of the resistors. The ceramic on the centre of the resistors simply isnt there and the 2 outermost leads of the transistor (collector and emitter?) have disappeared.
I have limited electronics experience but had nonetheless thought simpy of replacing the components in question and seeing what happens.
Any thoughts on the whole business would be appreciated.
--Seek
Having just taken the cover off, it's now clear why. One of the transistors for the second channel (Q16 - 2N6728) and 2 nearby resistors seem to have suffered a dreadful melt-down. When powered on, there is a brief spark visible at one of the resistors. The ceramic on the centre of the resistors simply isnt there and the 2 outermost leads of the transistor (collector and emitter?) have disappeared.
Start by measuring all the components around it, where the current that destroyed it could have come from, before replacing it.
Start by measuring all the components around it, where the current that destroyed it could have come from, before replacing it.
That amplifier seems to be a QSC class H design licensed by JBL. Repairing such an amplifier is definitely not for beginners as circuit topology is quite unusual.
referring to the QSC amps, there are some that have toridal output ransformers in them. Are these transformers of any use? They seem to be a little poorly rated in frequency response for a toridal output tranny. Very odd. They have 25-70,and 100 V output taps. Supposedly they have a 'direct' connection as well.
Apparently the direct connecton does not use the transformer. bummer. I'd buy it in a heartbeat, if so. It's on ebay, right now. $99.99. one channel non functional. 200wpc, CX6T.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7422384160&fromMakeTrack=true
Apparently the direct connecton does not use the transformer. bummer. I'd buy it in a heartbeat, if so. It's on ebay, right now. $99.99. one channel non functional. 200wpc, CX6T.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7422384160&fromMakeTrack=true
Hi Ken,
Sending wide bandwidth signals down a 70V line is not desired. Bass is best cut off. A transformer with greater specs is a waste in a distribution line system.
Think of a string of PA horns. Nice.
-Chris
Sending wide bandwidth signals down a 70V line is not desired. Bass is best cut off. A transformer with greater specs is a waste in a distribution line system.
Think of a string of PA horns. Nice.
-Chris
Yeah, I've installed isolated systems on boats before, for 1000 island tour companies. A string of 20 JBL speakers, inches from people's heads, so they can be blasted by the din of a recording that tells them where to look, accompanied by the brutal din of the motor/drive system--which the owners REFUSE to repair.
Instead, they spend repeated Thousands of $ for audio installs which don't work, instead of a single noise control install. That such stupidity should exist in this world. Their ignorance and the refusal to correct that ignorance, is their curse, which, of course,....they are incapable of seeing. Obviously so.
Hey, kinda reminds me of bar owners, cheap ***** that they are.
Instead, they spend repeated Thousands of $ for audio installs which don't work, instead of a single noise control install. That such stupidity should exist in this world. Their ignorance and the refusal to correct that ignorance, is their curse, which, of course,....they are incapable of seeing. Obviously so.
Hey, kinda reminds me of bar owners, cheap ***** that they are.
Hi Ken,
LOL!
I just got a call from a project in a BIG plant. Some electricians quoted on adding 7 250W paging amplifiers. Now they want to hook in and they don't know what a 70V distribution is. I told the contracting company that I'm not going to touch that one! I'm going to stand back and watch them blow it up.
1. Government site.
2. 2,500W installed at 80% load now.
3. Emergency service call $$$$ for us.
I hate to do this, but they figured they know more, and if we give them some advice and they mess things up (and they will), we are involved. They should never ever have quoted the job. The contracting company should have refused them on the basis of no prior experience.
I warned them a year ago (the contractor). This is going to be fun and sad at the same time.
-Chris
LOL!
Oh yeah! I don't miss that business at all.
I just got a call from a project in a BIG plant. Some electricians quoted on adding 7 250W paging amplifiers. Now they want to hook in and they don't know what a 70V distribution is. I told the contracting company that I'm not going to touch that one! I'm going to stand back and watch them blow it up.
1. Government site.
2. 2,500W installed at 80% load now.
3. Emergency service call $$$$ for us.
I hate to do this, but they figured they know more, and if we give them some advice and they mess things up (and they will), we are involved. They should never ever have quoted the job. The contracting company should have refused them on the basis of no prior experience.
I warned them a year ago (the contractor). This is going to be fun and sad at the same time.
-Chris
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