Need some suggestions for troubleshooting speaker distortion

[DKT88]

I have a pair of PSB Stratus Gold speakers that have a slightly audible breakup-type distortion (treble) at all volumes. It sounds like its coming from the tweeter. Its in one speaker only. I did the usual swapping components and channels to make sure it was the speaker and not something else in the system. I'm currently using other speakers in the system and it sounds fine.

Since the PSBs are so old I figured that it was probably bad capacitors in the crossover, so I replaced all the electrolytic caps in both crossovers. Still have the same problem (in the same speaker).

Now I'm thinking that it will take some measurements to pinpoint the problem. I hope its not the tweeter. I have an old scope, audio signal generator, and a multimeter. Can someone please suggest a troubleshooting scheme? If its the tweeter I'm not sure how to positively diagnose that. I live in Korea and the speakers are at my house in the US and I only have a few weeks over the holiday so a jump start on the process would be appreciated.

 

[DKT88]

I also have REW and a measurement microphone.

 

[restorer-john]

Nice speakers.

Be very, very careful with test tones and tweeters- they are very fragile and cannot take high power high level pure tones.

I would be removing the offending tweeter from the cabinet, testing it a low level and if it's the culprit, dismantle it. You should contact PSB to ascertain whether the dome tweeter used ferrofluid in the gap. Ferrofluid tends to dry out over the years and becomes a nasty, sticky residue that can cause exactly what you are describing.

When dismantled, you can easily inspect the gap, any dried out ferrofluid and/or and voice coil damage. You can carefully clean old ferrofluid with cut up business cards in the gap and cotton-tips/alcohol on the voice coil. Ferrofluid can be purchased in tiny syringes.

Obviously, if you have a cooked VC (voice coil) or delaminating windings, a new tweeter will need to be found. If the damage and gap fouling (touching) is really minor, you may be able to get away with careful repositioning with screw tightening/shifting or even slight manipulation of the voice coil shape itself.

Unscrew the four cabinet screws, disconnect/cut the wires and then place the tweeter back down on the bench. Unscrew the three (3) inner screws and carefully hold each one as you loosen it so they don't magnetically skate into the dome and destroy it. Then (carefully) slide a guitar pick or two between the front plate and the dome mount substrate on the opposite side to the lead-in wires. Then, maybe a couple of other places around the circumference. Just a few mm in- no further- you are just trying to break any sticky adhesive or attachment from many years of screw-down pressure, that's all. The plate should come off either with the dome or without. If it half comes off, help it.

If none of this makes sense to you, I can post some pictures of a typical tweeter tear-down if it helps.

 

[DKT88]

Nice speakers.

Be very, very careful with test tones and tweeters- they are very fragile and cannot take high power high level pure tones.

I would be removing the offending tweeter from the cabinet, testing it a low level and if it's the culprit, dismantle it. You should contact PSB to ascertain whether the dome tweeter used ferrofluid in the gap. Ferrofluid tends to dry out over the years and becomes a nasty, sticky residue that can cause exactly what you are describing.

When dismantled, you can easily inspect the gap, any dried out ferrofluid and/or and voice coil damage. You can carefully clean old ferrofluid with cut up business cards in the gap and cotton-tips/alcohol on the voice coil. Ferrofluid can be purchased in tiny syringes.

Obviously, if you have a cooked VC (voice coil) or delaminating windings, a new tweeter will need to be found. If the damage and gap fouling (touching) is really minor, you may be able to get away with careful repositioning with screw tightening/shifting or even slight manipulation of the voice coil shape itself.

Unscrew the four cabinet screws, disconnect/cut the wires and then place the tweeter back down on the bench. Unscrew the three (3) inner screws and carefully hold each one as you loosen it so they don't magnetically skate into the dome and destroy it. Then (carefully) slide a guitar pick or two between the front plate and the dome mount substrate on the opposite side to the lead-in wires. Then, maybe a couple of other places around the circumference. Just a few mm in- no further- you are just trying to break any sticky adhesive or attachement form years of screw-down pressure, that's all. The plate should come off either with the dome or without. If it half comes off, help it.

If none of this makes sense to you, I can post some pictures of a typical tweeter tear-down if it helps.

John, I understand what you are saying and appreciate the help. I was hoping you would reply! I'll give it a go and be careful not to do any harm to the tweeter.

 

[restorer-john]

John, I understand what you are saying and appreciate the help. I was hoping you would reply! I'll give it a go and be careful not to do any harm to the tweeter.

So to recap summarize:

Remove tweeter.
Very low level (fraction of a watt OK?) (say 3KHz and up- no LF) tone tests direct on tweeter terminals. (you could also check DCR and compare with the "good" tweeter, but I don't expect it will be different based on what you have described)
If the issue is clear and audible, proceed to dismantling the tweeter.

Post any pics as you go here, if you aren't sure and I (and others) can help.

 

[DKT88]

So to recap summarize:

Remove tweeter.
Very low level (fraction of a watt OK?) (say 3KHz and up- no LF) tone tests direct on tweeter terminals. (you could also check DCR and compare with the "good" tweeter, but I don't expect it will be different based on what you have described)
If the issue is clear and audible, proceed to dismantling the tweeter.

Post any pics as you go here, if you aren't sure and I (and others) can help.

Ok I will document the process and post it here. I'll be back there (in the US) in a couple weeks. Thanks again John.

 

[DKT88]

So to recap summarize:

Remove tweeter.
Very low level (fraction of a watt OK?) (say 3KHz and up- no LF) tone tests direct on tweeter terminals. (you could also check DCR and compare with the "good" tweeter, but I don't expect it will be different based on what you have described)
If the issue is clear and audible, proceed to dismantling the tweeter.

Post any pics as you go here, if you aren't sure and I (and others) can help.

haha, I already recapped

 

[vavan]

I also have REW and a measurement microphone

so, does rew show any difference between two speakers?

 

[DKT88]

A Stereophile review of these PSBs from 1991 which is the vintage of my speakers says they use ferrofluid:

"A 24dB/octave, Linkwitz-Riley, mid-to-tweeter crossover feeds the signal above 2.2kHz to PSB's metal-domed, polyamide-suspension tweeter. Made by Vifa of Denmark specifically for PSB (the diaphragm is made in Germany), this tweeter uses an aluminum voice-coil former to improve cooling under stress. Ferrofluid is also used in the voice-coil gap. A proprietary face-plate incorporates an integral "phase-plug" to improve the coherence of the radiated signal from various points on the dome, and also slightly recesses the driver from the front baffle, which PSB says smooths the tweeter response in the low treble."

 

[Blumlein 88]

If it is a slightly cooked voice coil, what John described about recentering and tightening down can work. As a diagnostic, if you have a gentle touch, slightly moving the tweeter you can feel a sticking or rubbing spot quite often. But be very careful.

 

[DKT88]

so, does rew show any difference between two speakers?

so, does rew show any difference between two speakers?

Good question. I didn't try REW measurements yet. At the time I was recapping I didn't have REW.

 

[restorer-john]

And send PSB an email, asking them nicely about the speakers, tweeters, ferro-fluid etc. You may be surprised, they might provide you with some information, insight and help (and maybe send you an ancient tweeter they found in the warehouse...OK, that's unlikely).

Main thing is to not write them off as too old to bother with. In my experience, the saddest thing in loudspeakers is a wonderful pair being consigned to the scrap-heap because of one faulty driver that seems to be unobtanium.

 

[vavan]

I've had some distortion peak in one of prior lsim 705 and I used rew measurements to explain the problem and return those to dealer in the past

 

[DKT88]

And send PSB an email, asking them nicely about the speakers, tweeters, ferro-fluid etc. You may be surprised, they might provide you with some information, insight and help (and maybe send you an ancient tweeter they found in the warehouse...OK, that's unlikely).

Main thing is to not write them off as too old to bother with. In my experience, the saddest thing in loudspeakers is a wonderful pair being consigned to the scrap-heap because of one faulty driver that seems to be unobtanium.

Yes for sure. You are right, these speakers are not to be abandoned for a a tweeter issue. We (my brother and I) bought them used (demos) in the early 90's and we won't dump them for a tweeter problem. They are great speakers and need to be fixed!

 

[DKT88]

I've had some distortion peak in one of prior lsim 705 and I used rew measurements to explain the problem and return those to dealer in the past

I will use REW in the testing that John outlined.

 

[Blumlein 88]

If PSB can't help, you might contact Madisound next. At one time (I've not done this in quite a few years), they could rebuild or repair voice coils in most conventional speakers.

https://www.madisoundspeakerstore.com/ You could look under services or call them if PSB is unable to help.

 

[DKT88]

If PSB can't help, you might contact Madisound next. At one time (I've not done this in quite a few years), they could rebuild or repair voice coils in most conventional speakers.

https://www.madisoundspeakerstore.com/ You could look under services or call them if PSB is unable to help.

Ok good idea, I didn't know Madisound did repairs. I have to say, you guys in this forum are an inspiration.

 

[RayDunzl]

I have a pair of PSB Stratus Gold speakers that have a slightly audible breakup-type distortion (treble) at all volumes. It sounds like its coming from the tweeter.

This may be worth a try...

https://support.psbspeakers.com/hc/en-us/articles/115015956327-Purchase-replacement-parts

 

[DKT88]

This may be worth a try...

I sent PSB and email and asked if they have replacements or can rebuild the tweeters.

 

[bigx5murf]

Have you tried swapping the tweeters yet? Are the tweeters fluid cooled?