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intrique45

Allison 7 crossovers

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1416412620_allisonCD7.thumb.jpg.760e30fe0fe56e9eb2a1163c011d8132.jpg

 

 

Hello new member to this forum.  I would like to ask for some help.  I have a NAD 7140 receiver and two pairs of Allison 7 speakers.  One set is the CD-7 series used for the back channel (B) All owned since new.  I had no problems with these with the receiver but came upon a problem when i switched the CD7 to be the main speakers and the regular Allison 7 to the back speakers (B)  While playing a cd on my  Parasound cd player on moderate volume  the CD7  speakers started to distort and lose volume on both speakers  the back speakers were fine.  I checked all wiring and all ok.  I turned off the receiver and tried playing the cd and the receiver did the same thing after a a few minutes    Strange thing is I then changed the CD7 to the B side and the regular Allison & to the front (A)  Problem went away.   With this setup  I can play all day at high volume without any problems

Could it be the caps in the CD7 creating the problem?   The crossover in the CD7 is different. It has two coils and a small blue resister?       Any recommendations on replacement caps for both crossovers?

allison 7 non cd.jpg

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Highly unlikely the capacitors in the Allisons are causing your problems.

The resistors in the CD7s are internal, thermal overload protection for the drivers and I’ve heard of instances of them going bad. 
You could bypass them and be careful of overdrivng the speakers but leave the original caps alone

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Hi thanks for your input  My concern is that  there are no problems with the CD7 in the back channel    I guess the B channel may get less wattage then the A channel so they dont clip?

I just played two CD s for about an hour at moderate to loud volume and no problems with any speaker.  Thats why I lean toward s the CD7  Maybe the ferrofuid in the tweeters are dried up or the cap is dried up and when under a high wattage load it creates the clipping??

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2 hours ago, intrique45 said:

Hi thanks for your input  My concern is that  there are no problems with the CD7 in the back channel    I guess the B channel may get less wattage then the A channel so they dont clip?

I just played two CD s for about an hour at moderate to loud volume and no problems with any speaker.  Thats why I lean toward s the CD7  Maybe the ferrofuid in the tweeters are dried up or the cap is dried up and when under a high wattage load it creates the clipping??

"The NAD design principles recognize that the minimum impedance of most speakers is somewhat lower than their nominal ratings. It is not uncommon for the impedance of a "4-ohm" speaker to fall as low as 2.5 ohms at some frequencies. If two sets of such speakers are operated in parallel, an amplifier with limited current capability may produce distorted sound or even overheat and shut down under prolonged or high-level operation. To help deal with this problem, NAD provides a switch in the rear of the Model 7140 receiver to reduce the operating voltage on its output transistors when driving loads of 4 ohms or less (this is designated the "normal" setting). When the switch is set to its "8-ohm" position, the increased power-supply voltage enables the amplifier to deliver its maximum output to nominally 8-ohm speakers."

…..Interesting read regarding your receiver.

When  I first read your post, my suspicions were about the amplifier section of your receiver and how well or not it could handle the load of 2 pair of Allisons over a long period of time.

Nothing lasts forever, and my first suspicions are that your amplifier section is getting "tired" sorry to say. 

In 43 years of dealing with the Allison Loudspeaker, I've never seen the kind of trouble you are experiencing be attributable to a ferrofluid or cap condition.

Bill

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On 1/9/2020 at 6:30 PM, intrique45 said:

Maybe it was this? Wire touching the frame and shorting out?

20200109_174044.jpg

Have to be very careful when removing and reinstalling the woofers. Those nonconducting tabs that secure the leads can easily end up like yours if they bang the cabinet.

 

Bill

 

Edited by newandold
Clarify

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