700B WOPL Screech !

mattoe

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#1
Hey Guys,

I need some direction .... My WOPL 700B has just recently developed a scary loud screeching from the one channel just as I turn it on...
I will turn the amp on without any input signal , one channel VU will freak out and then the protect relay connects and then .... Screech pop bang ! Scary nasty....
If I let it settle..... about 3-5 seconds it plays fine again..... Help ???

Mattoe. :pale:
 

jbeckva

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#2
Hey Guys,

I need some direction .... My WOPL 700B has just recently developed a scary loud screeching from the one channel just as I turn it on...
I will turn the amp on without any input signal , one channel VU will freak out and then the protect relay connects and then .... Screech pop bang ! Scary nasty....
If I let it settle..... about 3-5 seconds it plays fine again..... Help ???

Mattoe. :pale:
What if the pre's powered up first? I always go preamp then amp, and the same in reverse when powering down. How about with the level controls all the way down (if they are connected) - what happens then?

(obviously.. pull the positive leads on the speaks while doing all this, if your condition persists.. )
 

mattoe

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#3
The Pre being on or off has no affect .... "Thought".... During the original build I somehow forgot R 41L .... (Dum dum award) this resulted in 90 ish volts to the Left op amp..arg... and the protect relay active because of 90v at the output of the left channel... I installed R41L and all was well (maybe)..... I have sometimes get sense that the left lacks some depth and base punch compared to the right. Would you swap op amps side to side and see if this screech follows ? with R41L out what damage was likely ???

Mattoe... :sad3:
 

jbeckva

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#4
The Pre being on or off has no affect .... "Thought".... During the original build I somehow forgot R 41L .... (Dum dum award) this resulted in 90 ish volts to the Left op amp..arg... and the protect relay active because of 90v at the output of the left channel... I installed R41L and all was well (maybe)..... I have sometimes get sense that the left lacks some depth and base punch compared to the right. Would you swap op amps side to side and see if this screech follows ? with R41L out what damage was likely ???

Mattoe... :sad3:
It's an easy quick check, sure.
 

mattoe

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#5
Screech ..... ???

An update to the screech....

I removed the 700 from my system the other day and it sits proudly on the bench with some cheap speakers to sacrifice if the screech gets out of control.... I checked the bias and found the offending channel ( L ) was at 3.43v and the right at 3.60v ... I have reset the left to match the right at 3.60.... no screech yet ...... Could that differential in bias have been the problem ???

Something else I noticed....

1) If I turn the 700 off before shutting down the pre (signal input) the meters still "play" for several seconds then fade to a stop... Normal ?

2) If I turn the 700 off and then back on, the meters (both) tend to "slam" to the right one time before the protect relay connects the outputs .... Normal ?


Mattoe
 

laatsch55

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#6
3.43 volts is a while lot more than 360 MILLIVOLTS.....a differential will not cause a screech. Cold solder joint on a cap??
 

laatsch55

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#7
1.
If you don't have the DC protect --yes.

2
Doesn't sound right. Should be an on delay with the DC protect.
 

jbeckva

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#8
Doesn't sound right. Should be an on delay with the DC protect.
Won't the meters still deflect upon powerup tho, if they are connected to the outputs prior to the DCP? I see that every now and then, especially if the amp has been off for a bit (initial inrush of current for caps until stabilized?)
 

mattoe

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#10
Screech !

Thanks for jumping in guys.....

I dare not put the paradigm studio 100's back on the 700 until I get this figured out.... Your help is most appreciated....

The Screech /bang pop was scary loud from the left on power up as the left meter went crazy....

The power on "bounce" of the meters happens in unison and doesn't appear to cause or result in anything bad.... Dunno.....
Should this be addressed... What's the cause.... ??

That being said.... The 700 hasn't had a freakout in about a week ... Maybe 30 power up and downs....

Any ideas ???


Mattoe
 

orange

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#11
Some amps and integrateds will bounce like that but that there should be a relay that keeps the outputs off until all is up and ready. My Sanyo Plus Series A35 does this, the only problem I have is that it pops when the timer is used to shut it down (not when the power button is used).
 

stuwee

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#12
Some amps and integrateds will bounce like that but that there should be a relay that keeps the outputs off until all is up and ready. My Sanyo Plus Series A35 does this, the only problem I have is that it pops when the timer is used to shut it down (not when the power button is used).
That is not normal either, My A35 doesn't burp/fart ever.

Matteo, I hope these guys can help you with this problem!
 
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