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Pioneer CS-701a - Bass cuts at lower volume

Rob_Feature

Rob_Feature

Rob Feature
Love this pair of speakers but one cabinet's woofer has recently started cutting out at low volume. If I turn up the volume, it stabilizes. I've swapped speakers ensuring it isn't anything earlier in the chain.

I popped off the back and the crossover (SNP-035) has 4 can caps. Does it sound like that's the most likely culprit? Should I order a couple of each and replace them in both speakers? (the caps look original).

Sound like a good plan...any other things to check first? Thanks in advance!

PS: I can't read the voltage on the smallest cap, which is 1.5uf, because it's turned in a way to make it hard to see without removal, Anyone know what voltage I should get for a replacement (dont wanna remove it until I have the replacements in hand)?
 
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Somebody will correct me if I'm wrong, but I think that Pioneer used first order filters on their woofers whenever they used a filter at all. If this is true with your crossover, too, there are no capacitors on the woofer leg of the network - only an inductor. And inductors rarely, rarely go bad.

If I'm right on this, you still probably need a recap, but it's not going to affect your woofer at all.

Can one of you electrical techs confirm or deny this?

GeeDeeEmm
 
Most likely, there's a break/crack in one of the flex-leads between the woofer cone and woofer terminals (otherwise known as "bad lead wire").

This is usually fixable, but will require the right kind of flexible wire and some soldering.

Regards,
Gordon.
 
Rob_Feature said:
Love this pair of speakers but one cabinet's woofer has recently started cutting out at low volume. If I turn up the volume, it stabilizes. I've swapped speakers ensuring it isn't anything earlier in the chain.

I popped off the back and the crossover (SNP-035) has 4 can caps. Does it sound like that's the most likely culprit? Should I order a couple of each and replace them in both speakers? (the caps look original).
Click to expand...

Rob, the woofers in your 701's have a 1st order low pass filter, which means a coil in series with the woofer and a cap in parallel. That cap would NOT cause the volume drop at low voltages/volume.

Gordon might be right about the woofer leads. Another possibility, Rob, is a cold solder joint somewhere in that 1st order filter. Re-solder the connections at both ends of that coil. Next re-solder the connections to the woofer.

Often times a cold solder joint will work when we have plenty of voltage, but will fail when the voltage is cut back.

Good luck!
Jerry
 
Awesome stuff here everyone! I'll open 'er back up again and see what I see and at the very least will pop a little solder on the ends of those connections and see what happens. Thanks!
 
I LIKE MUSIC said:
Crossovers, 1st order and second order.

View attachment 922945
Click to expand...

Thank's for posting the schematics. If Pioneer followed SOP and used a first order filter on the woofer, there are no caps in the woofer leg. Changing the caps won't affect the woofer output. So, at least at this point, we know what won't help! Now we need to find out what will help.

Time to start tracing through the system.

I recently traced down a problem with one of my Small Advents to a cold solder joint where the voice coil leads attach to the speaker terminals. In that case, the woofer would simply stop working after a little play. Methodically traced the problem to the cold solder joint, but that brings up the question: why now?

That speaker has been working perfectly since 1975 with the same solder joint. Why does it take 42 years for the cold joint to cause problems? You just never know.

GeeDeeEmm
 
OK...only 4+ months later and I finally got to this....and...BAM. You guys were right on!! Thanks to everyone here but especially Gordon who nailed it: the lead to the cone was slightly frayed...I (carefully!) heated the connection between cone and the lead touched a little solder to tighten it up and it seems like that fixed everything.

Thanks again all, I absolutely adore the sound of these speakers...now I can enjoy that sound uninterrupted at all volumes :)
 
Nice speakers! I'm glad you got them sorted out. I'm not sure of the A vs Non-A differences either. Those are one of my favorites from that era Pioneer lineup.
 
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