Crown D-75 Balanced Input Static/Noise

[Siegfried Meier]

Hey guys,

I have 3 of these amps that I use in the studio and 2 of them seem to have a strange issue.  The unbalanced 1/4" work fine, but the XLR balanced ins seem to have static and noise on one side, very loud.  One one amp it's the left, and the other it's the right side.  Is there an opamp or something that might have blown in these amps?  Would it make sense that they work fine with the unbalanced ins?

Thanks!
Sig

 

[Samuel Groner]

What do you mean by "static and noise"? Can you describe the sound in more detail (hum, broadband random noise, ...)?

Any mechanical contact (connectors, switches) is a first suspect.

Samuel

 

[Siegfried Meier]

More like white noise, at a pretty loud volume.

I've checked the physical external connections and nothing.  I'll have to open up and see if anything is weird inside...

 

[Samuel Groner]

On page 20, the service manual (http://rdn.harmanpro.com/product_documents/documents/3603_1438110698/Copy_of_D75_Service_Manual__original.PDF) suggests that there's an additional opamp in the balanced path, so you might check this one first.

Samuel

 

[Siegfried Meier]

Ahhhh perfect - let me check it out, thanks Samuel!!

 

[moamps]

My bet goes to dirty/worn normalling  contacts on the 6.3 input jacks.
I had one D75 in the past with this fault. 

 

[Siegfried Meier]

6.3?  What exactly are you referring to here?

 

[moamps]

6.3?  What exactly are you referring to here?

Sorry, 6.3mm  is 1/4 of 1" 

 

[Siegfried Meier]

Ahhhhh so you're saying you think the contacts of the unbalanced 1/4" jack are the issue?

Would it make any sense that I don't get any noise from the 1/4" jack then, and that it only happens when I use XLR?

 

[PRR]

On XLR, signal goes through the "switch contact" on the 1/4" jack. On 1/4" plug the switch contact is open, not carrying signal. The contact is made by self spring tension, which may have fallen-off since the amp was made; it is also semi-exposed to all the smoke and beer-mist in the room.

Clean the jack and see. It is more likely and a LOT less trouble than finding and fixing electronic (cap, chip) trouble.

 

[Siegfried Meier]

Alright, will do!!

 

[Siegfried Meier]

PS - does anyone know why the power LED on these things flashes the way they do?  I've seen it happen on other Crown amps, but all 3 of these amps do it as well.  Just drops in and out.  Is it faulty?  Or is that just the way they do it?

 

[Brian Roth]

Some of the older Crowns used a neon power indicator...not a LED.  Neons get old and start flickering before going totally dead.

bri

 

[Siegfried Meier]

Ohhhh I see!  Worth fixing at all?  Or just leave it?

 

[musika]

Are you talking about the power indicator light (white for power on) or the red IOC indicator(s) which is a separate circuit that compares input to output as I understand it?  I have a D150A with the IOC's which are red and the power light (white) had been burnt for some time now.

 

[Siegfried Meier]

Power indicator, which is indeed a neon bulb.  IOC LED's are perfect, no probs with those.

 

[Philip Parker]

Hey ya'll id like to revive this thread as I have the sam exact issue.  My XLR input (on right channel) had static and noise first,  the 1/4 inch input seemed fine,  now fast forward 6 months both inputs are noisy and the noise is now constant without signal. Someone mentioned to me about balanced biasing pots on this thing once. Curious if you guys have every experienced this problem.

Philip

 

[PRR]

Clean the jack and see.