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Old 4th December 2006, 06:03 PM   #1
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Default Quad 405: bypassing speaker protection PCB?

Hi, I have a Quad 405 series 1 amp which is producing clipping distortion on one channel at only about 3-5 watts output. The same channel clips even when I swap the left and right PCBs, and the power supply caps both read 49vDC. So I think the problem is in the little PCB mounted on the speaker posts, which I understand involves protection for the speakers in the event of a large DC output. Is it easy to simply bypass this PCB, assuming it isn't too foolhardy when using dynamic (non ESL) speakers?

Thanks a lot for any help!
Ralph
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Old 4th December 2006, 07:06 PM   #2
poynton is offline poynton  United Kingdom
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Default Re: Quad 405: bypassing speaker protection PCB?

Quote:
Originally posted by rgonzale
Hi, I have a Quad 405 series 1 amp which is producing clipping distortion on one channel at only about 3-5 watts output. The same channel clips even when I swap the left and right PCBs, and the power supply caps both read 49vDC. So I think the problem is in the little PCB mounted on the speaker posts, which I understand involves protection for the speakers in the event of a large DC output. Is it easy to simply bypass this PCB, assuming it isn't too foolhardy when using dynamic (non ESL) speakers?

Thanks a lot for any help!
Ralph
Hi.

You can simply remove the board from the output sockets.

Click the image to open in full size.


Andy
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Old 4th December 2006, 07:19 PM   #3
anatech is offline anatech  Canada
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Hi Ralph,
Fix the protection network. Repair by removal is not a good option.

-Chris
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Old 7th December 2006, 07:37 PM   #4
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Default Thanks!

Thank you so much Andy and Chris! I removed the protection board (I didn't realize it was simply a matter of desoldering it and reattaching the leads) and that fixed my clipping problem immediately. I've also taken Chris' advice and am ordering a replacement protection board from Quad.

Now maybe I'll get motivated and do some mods... reducing the opamp gain seems the most significant and easiest...

-Ralph
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Old 7th December 2006, 08:00 PM   #5
anatech is offline anatech  Canada
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Hi Ralph,
Are you sure you can't repair the protection circuit?

-Chris
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