Quad 405: bypassing speaker protection PCB?

[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

[poynton]

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.




Andy

[anatech]

Hi Ralph,
Fix the protection network. Repair by removal is not a good option.

-Chris

[rgonzale]

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

[anatech]

Hi Ralph,
Are you sure you can't repair the protection circuit?

-Chris