Down The Active Servo Subwoofer Restoration Rabbit Hole

[BGS.13]

Hello, I found this forum through one of the posts about someone that restored an old Yamaha YST-SW100 Active Servo Sub by replacing the two 7"inch woofers with 6.5" drivers and wanted to see If I could do the same to my sub that's the same model.

So Recently I acquired that same Subwoofer from a relative, only thing was it didn't have any woofers installed. So I did some research and found that the original woofers that came with the sub had a 10 ohm resistance. So finding a replacement with the same impedance was out, as finding odd impedance woofers is not that easy. so I looked online and found a post about someone who replaced the woofers with a 6.5" replacement that was 6 ohms. So I ordered my replacement pair that had the same impedance of 6 ohms 150w RMS that was pulled off an old Panasonic Sub on eBay.

Long story short . . . Woofers arrived, I installed it and now the sub has this odd oscillating pattern when I power it on even with no input is connected. I did some testing and found if I disconnected one woofer and use the Sub with only one connected it stops the oscillation and plays fine, did same test on both speaker leads and can confirm that both leads delivers audio signals coming from my mini 2.1ch amp rated for  2x50w and a 100w sub out.

The oscillation only happens when both leads are connected to speakers. I'm not sure if using only a single woofer on a dual speaker cabinet strains the amp inside the sub that's rated at 70w 5 ohms. Does anyone know what might be causing the oscillation? Side note, the oscillation isn't severe but it prevents the sub to play any sounds.

Edited April 17 by BGS.13

[The Rock Puppy]

Welcome to Stereonet.

Reckon you should hop over to the "Speakers, etc" section and ask there. Probably more chance of a response if you do. Or maybe try the "DIY" section.