Bass leaves after amp warms up?

If the problem occurs in both speakers at same time when it occurs and does not with one, that would tend to indicate that amp/switch/control defect is less likely, but still possible. Definitely supports the amp is overworked due to load and getting too hot theory.

BTW testing with just one speaker in lieu of others to test with was a good call! Gotta remember that one.

Can you take the cover off and test as Al suggested?

If that helps, a good external + quiet cooling fan might help. Or if you have any fan that could be applied, just try that. ANything to help lower the internal temperature and see what happens.

BTW, if you can prove via testing that cooling the amp helps the sound quality, that would add leverage for you with your dealer and MF to get them to perhaps offer a trade or other solution to help you get better results with the PSBs. Especially since MF has told you what you have should be fine.

Agree...take the cover off, it's the only thing you haven't tried. Put your trust in Al and Mapman.

I don't think I'm good at taking the cover off.
I'll have a look at it

The fact that the system seems to work while running only one channel is a powerful clue.

The amps themselves are ruled out, as 3 amps have had the same behavior. Also ruled out is hearing and the speakers. The preamp and source/s are still under suspicion.

This has something to do with warmup, but I suspect not in the amp or the speaker. My suspicion right now is a defective power cord or wall outlet that heats up with enough current through it such that it eventually starves whatever amp is plugged into it. My suspicon leans this way because if it was a preamp it would not care if only one channel was running.

If the wall outlet, or either end of the power cord for the amp gets warm over time then I would think that this hypothesis is confirmed.

If the power cords and wall outlet seem OK, then the preamp and sources are under suspicion.

Ralph, note that all three of the "amps" that have been tried are integrated amplifiers. There is no preamp, although presumably there is a phono stage that is not listed in Fishing's system description. But the phono stage and turntable setup would appear to be ruled out as suspects, because the same problem occurs when the CD source is used.

Best regards,
-- Al

I use Musical Fidelity M1 vinl phono stage.
Listed uder my system

Using one speaker,the bass finally recessed after 100 minutes or 3 full LP's.
I'm wondering what to do now..

Generally I switch speaker cable
from one channel of the amp to the other or shut it down & try later/tomorrow.
Considering taking off cover to amp..
Electrician is coming tuesday to check for:
Line sag
Grounding
Phase
Tighten connections

I called cable company & request to borrow a pair of speaker cables:
Analysis Plus biwire also to arrive tuesday.
Thanks for everyone's participation,especially Al!
Welcome any other thoughts

So with one speaker, it took twice as long to show the problem? I'd say that is consistent with the amp running too hot theory. That would assume the amp still got too hot inside but took a fair amount longer to do so due to approximately half the heat being generated as prior, assuming bogh channels running similarly.

I'd really like to know what happens with cover off and/or better ventilation.

Yes but why is the amp running hot if they sell them by the thousands and no report of this problem?

"I'd really like to know what happens with cover off and/or better ventilation"

Guess it's in my best interest to take the cover off & try it.
I'll report back

"Yes but why is the amp running hot if they sell them by the thousands and no report of this problem?"

Each system is unique. You have different speakers than the next guy, diff cables, different power, etc.

There have been other threads where an amp was being pushed too hard and was running hot. One of the troubleshooting tools is to take the cover off.

The amp dosen't feel hot
Can it still be running hot?

If some or All output transistor without good contact to their heat-sink, the output transistor will run very hot. (The amp dosen't feel hot
Can it still be running hot?)

The amp doesn't feel hot
Can it still be running hot?

Without being familiar with the specific design, we probably can't rule out the possibility that some particular point or points within the unit are getting too hot, even though it seems cool on the outside.

The most meaningful places to touch on the outside are probably the heat sink fins that are at the sides of the amp.

Looking at some photos, it appears that the top cover is held on by 14 screws. If those are removed it will probably come right off.

Regards,
-- Al

I attempted to remove the 14 top screws but don't have the right tool..
Would you know what size allenwench to use or what size/type screws they are.

Don't know. Since it is a British manufacturer, they might be metric. If they require an Allen wrench, this writeup might be helpful, as it indicates which sizes are and are not interchangeable between millimeter and inch-based sizes.

Regards,
-- Al

Ant
Please don't listen to these guys and remove the top
cover to the amp you could get shocked.
wait for the electrician to show up
Best JohnnyR

Yes, I should have stated the cautions that the amplifier should be unplugged from the AC when the cover is being removed, and nothing internal to it should be touched whether it is plugged in or not.

Regards,
-- Al

Wow . what a mystery ? Sounds like an April fools joke , no ?

I would not have plugged it in or touched inside.
Was unable to find a tool to try instead took shelf off above the amp for more ventalation

I gave more ventalation by removing the shelf above the amp..
The Bass still left after 1h 20 minutes.
I was listening to "Let it be" & that was my parting words after the sound changed.

Try the screws that are turned in crooked. Then call Dr. Phil.

If everything has been swapped out and the one constant still in the system is the speakers ? Then i would be willing to wager it is the speakers ! No ?

Bass returned after waiting 30 minutes.
After about 30 minutes of sounding good it disappated.
Surely something causes deep bass to come & go as it wishes.
I have(3)ideas to try this week:
Electrician is going to check connections
I am borrowing different speaker cables
May put up $1745(demo)& try ps audio p-3 power conditioner with return previlage.

Yes. If I'm not mistaken, the PS Audio P-3 connects one lead to the right temple and the other to the left. Be very careful in plugging in the ground:)

Should I ask where you plug in the ground?

I will preface my comments by saying I have not read everything said above, so I may be covering ground that has been rehashed to death. If the problem persists after certain components have been switched out, it lies with those that have not been switched out. If it happens with different sources, it is probably not the source components. If it happens with different sources, or when a source has been switched out, or with different components in the amplification chain, that really leaves the speakers to be suspect. If one overheats speakers the sound does change dramatically. If, for example the woofer voice coil gets too hot, resistance will shoot up and the speaker will sound lighter in bass. The crossover components can also heat up and this will affect the sound dramatically as well-component values will shift and change crossover points, filter characteristics, etc. and could lead to the loss of bass.

Such obvious change in sonic characteristics, if due to overheating of the speaker, constitutes pretty rough treatment of the speakers. Perhaps something designed to produce higher volume is needed for this particular application.

Does the dealer you bought from still sell the PSBs?

Maybe go there, talk to the dealer, and listen to your speakers there off a few different amps if possible. Maybe even take yours in and see what happens there off various amps if possible. Maybe even take the amp in to test out. See if same thing happens there.

Some of the recent posters have, understandably, not read through all of the 130+ posts in this thread. So here is a summary of some of the key facts that have been stated:

The same problem has been exhibited with two different models of PSB speakers (the Synchrony One and the Synchrony Two), both having impedances that are specified as 4 ohms nominal and 4 ohms minimum. JA of Stereophile measured the impedance of the Synchrony One that is presently being used as being between about 2.7 and 4 ohms throughout most of the bass and mid-range regions. The OP does not play the speakers at high volume levels.

The same problem has been exhibited with three different integrated amplifiers. There is reason to believe that driving low impedances is not a forte of any of those amplifiers.

The same problem has been exhibited with two different sources.

Connecting only one speaker to the amplifier considerably increases the amount of time between a cold start and the appearance of the problem.

When the bass disappears, it can sometimes be made to reappear by switching between sources, disconnecting and reconnecting the speaker cables, or other seemingly innocuous things. The integrity of all connections appears to be good.

My suggestion, at this point, in addition to the planned electrician visit, and attempting to borrow different speaker cables: Try to borrow a separate power amplifier that is known to be able to deal with very low impedances, and drive it from the pre-outs of the integrated amp.

Regards,
-- Al

I wonder if the problem could be better addressed if the OP had a SPL meter and a test disc so he could actually measure the SPL's at the listening seat. That way he would know if it was in his audio system or in his head. It would also help to know at which frequencies this loss of bass occurs and the actual amount of the loss.

Interesting, it is hard to account for all of the reported phenomena. It sound like the poster does not like the inherent sound of his system after all of the gear has properly warmed up. This would mean some kind of system tuning is in order-change in speaker and/or listener placement, room treatment, equipment change, whatever, and perhaps a change in listening habit--e.g., leaving the system on all the time so that it is warmed up from the get go.

Comparison with an amp well suited for the speakers, at least on paper, would seem to be the one thing to try with biggest upside. At a minimum, OP finds out if prime suspect, the amps ability to drive the speakers, is in fact an issue. At best, overall performance may well go up significantly and current problems would be but a memory.

I am hard pressed to imagine how power source would produce the pattern of sound deterioration over time described. Defective speaker wires might be a reasonable explanation. Replacing speaker wires with most anything else, even basic 12-14 gauge zip wire, should be enough to determine if current wires are defective in some way leading to deterioration of sound over time.

The dropout in sound as described seems to fall in line with what one would encounter if one phase of the signal/incoming power feed were to drop out somewhere along the line. Preamp volume control or ac outlet problem possibly? However, I cannot reconcile the fact that it only seems to occur after warmup with my hypothesis.

Ant
When is the electrician coming over?
Best JohnnyR

The speaker cables were already replaced with the same model *audioquest comet biwire

The problem still persists:

I am auditioning different speaker cables tomorrow followed by Electrician to check connections.

I will report back

Thanks to everyone

Agree with Newbee on using an SPL meter and LF test tones to gather data.

I substituted Different high end speaker cables today.
What I heard was alot of bass but it wasn't the lower octive & punchy kind which I get from Audioquest.
Is it possible audioquest cables can in the first hour put out a more desirable bass like a subwoofer that is punchy but then "resort" to bass that is less deep or punchy?
Which is unsatisfying to me

Perhaps I need a subwoofer?

But this is perculular:
I put back Audioquest cables using just one speaker & was unable to get the "correct" bass from either side of the amp.
I then tried the other speaker cable from audioquest & the bass was powerful & deep again.
So I don't know what this means

Is it possible audioquest cables can in the first hour put out a more desirable bass like a subwoofer that is punchy but then "resort" to bass that is less deep or punchy?

No, IMO.

I put back Audioquest cables using just one speaker & was unable to get the "correct" bass from either side of the amp. I then tried the other speaker cable from audioquest & the bass was powerful & deep again. So I don't know what this means.

My guess is that something else was changing (perhaps as a result of cooling off somewhat) while you were changing cables. Although you'll want to determine if the different behaviors with the two different cables are repeatable, to cover the possibility that one of the two cables is defective in some manner.

Regards,
-- Al

Either or both cables work well at any given time:
There is no pattern

When the electrician comes also confirm continuity with his volt meter red to red and black to black at both speaker wire ends .....
Also when you hook the AQs back up make sure the bass goes to the low speaker posts and tweeter goes to the high posts .
This will make sure your speakers are in proper phase.
You can also disconnect both speaker wires at the amp take a double a battery red to batteries plus black to neg and run it on both speaker wires if both speakers woofers are moving in the same direction all is good.
JohnnyR

Things to try:

-measurements with sound pressure level meter and test tones
-confirm the year and results of your last hearing test and those of anyone else who hears the same thing (just because your S.O. hears the same doesn't mean anything. They might be an ex-rock musician with years of 110 dB experience, for all we know) I believe you, but with your musician background this should be confirmed before the thread reaches a few hundred posts.
-power down the whole house (including tenant)using breakers except for the outlet for audio. If there are other items on other outlets running off the same circuit unplug them. Plug just your amp directly into one wall outlet and just your CD player into the same wall outlet. Retest. If still bad, try moving your amp, speakers and CD player to another circuit and repeat.

The OP isn't willing to try much.

SPL meter? Nope. He's a professional musician, won't try the SPL meter. Taking the cover off the amp? Nope, no tool. Unwilling to go to the store to buy a set of allen keys. Besides, he isn't good at taking the cover off, he has the dexterity to be a musician but he can't turn a screw.

(Hardware stores will have both US and metric sizes by the way -- really easy investment.)

Likes swapping speaker cables though.

Refrain from responding Wilsynet
As your attitude speaks volumes

There's 148 posts to this thread and I haven't read them all but I know that's it's been brought up. I just don't know what your response was.

Why don't you at least try a power regenerator like a PS Audio unit to rule out any chance that it's a power problem from high usage? That way you know that your power to all of your components is consistent.

Chuck

I may have missed it among the 140+ responses, but did anyone suggest you run an extension cord from another part of the home to the amp? Perhaps the circuit breaker or the wiring/panel/outlet has a resistance and after an hour of high current from the power amp the thermal resistance is increasing, therefore limiting the bass notes. Notice that the phenomenon took longer with only one channel driven ( as the single channel driving a speaker will draw less current from the wall, but problem still occurred later, nonetheless). Adding a powered sub to the circuit will exacerbate it as another amp is being shared with the AC, no?

3 amps with exact same issue rules out the amps for sure, plus as I used to repair Musical Fidelity, I know the M6i runs very cool (if properly biased), and is Bipolar transistor powered. Removing the cover would be not help if the amps cover is cool to the touch. Plus, I know the M6i is fine with 4 ohms; all day long.

Hope this helps.

Steve