It's been a while since anyone has posted about CS-A31s, so I thought I'd add my story. Back in late July, 2026 I bought a Pioneer ER-420 and a pair of CS-A31. I did a cleaning and recap on the ER-420 and I've been listening to it through the CS-A31s. I got sound out of the ER-420 pretty early and listened to it sparingly until I finished the recap. Once the recap was done, I put it into daily use here in my office. At low volumes it was pretty good, but the opportunities to turn it up left me with pretty muddy sound. Overall happy, but somewhat "meh". I had been hoping for more out of this setup.
Today I recapped the speakers. They had the standard 14uF and 1.6uF caps in the crossover filter. When I pulled them, the right measured 3.215uF and 32.55uF while the left was 3.198uF and 40.79uF. So while it had drifted more than 100% out of spec, the tweeters were still matched pretty well while the squawkers were more than 25% unmatched.
I put in Audyn Cap Q4 15µF 400V and Dayton DMPC-1.5 1.5µF 250V from Parts Express for about $40. The two Audyn 15uF were within 5% of each other and the two Dayton 1.5uF were within less than 1%. Overall, a pretty easy job. The crossover filter sits on the floor of the speaker cabinet and is easy to get to. Each speaker took me about an hour each.
The end result is much, much clearer audio all the way across the volume spectrum. I'm getting some distortion at very high volumes, but that's probably the amp. I suspect some of those tubes are just "ok" as I didn't replace any of them. I paid $100 for the speakers plus the $40 to recap and I think it was worth it. They sound great and I appreciate listening to the vintage gear that's matched pretty well.
Today I recapped the speakers. They had the standard 14uF and 1.6uF caps in the crossover filter. When I pulled them, the right measured 3.215uF and 32.55uF while the left was 3.198uF and 40.79uF. So while it had drifted more than 100% out of spec, the tweeters were still matched pretty well while the squawkers were more than 25% unmatched.
I put in Audyn Cap Q4 15µF 400V and Dayton DMPC-1.5 1.5µF 250V from Parts Express for about $40. The two Audyn 15uF were within 5% of each other and the two Dayton 1.5uF were within less than 1%. Overall, a pretty easy job. The crossover filter sits on the floor of the speaker cabinet and is easy to get to. Each speaker took me about an hour each.
The end result is much, much clearer audio all the way across the volume spectrum. I'm getting some distortion at very high volumes, but that's probably the amp. I suspect some of those tubes are just "ok" as I didn't replace any of them. I paid $100 for the speakers plus the $40 to recap and I think it was worth it. They sound great and I appreciate listening to the vintage gear that's matched pretty well.
