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]

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.

An externally hosted image should be here but it was not working when we last tested it.

Andy

 

[anatech]

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

-Chris

 

[rgonzale]

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

 

[anatech]

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

-Chris