I had the same problem with Bryston amp ... So it would seem that the problem is most likely unrelated to the amp, and that it is related to something else that is occurring during that hour. Does the same thing happen whether or not the CD player is spinning a CD during that hour? Does the same thing happen whether you are listening to vinyl or to CDs (I see in your system description that you have a turntable in your rig)? Does the same thing happen if you are not playing music during that hour, so that the speaker drivers are not being warmed up/loosened up during that time? Regards, -- Al |
What about my third question? If, after the system has been unused for a period of time that is typical of your listening habits, you turn the amp on, play no music for the first hour, and then start to play music, what does it sound like?
Regards,
-- Al |
Ron, because he said in the original post that the same thing occurred with a different amp.
Best regards,
-- Al |
Did the Synchrony Twos exhibit the same symptoms as the Ones? Could PSB being 4ohm possibly be the reason? As Mapman asked earlier, what models were the Bryston amps? Regards, -- Al |
Have you tried different speakers, as Kijanki thought you might have? And if so, did the same phenomenon occur with them?
I'm still suspicious of the possibility that the performance of your speakers is changing after they have been playing music for the hour.
Regards,
-- Al |
Peter (Csontos), your point is an interesting one. But in this case, given that we now know that the problem has been observed with two different speakers (having similarly low impedances; here is the plot for the Synchrony One), and given that the specs on all three of the amplifiers are not suggestive of strong performance into low impedances (the M6i has no 4 ohm spec; the B135 has no 4 ohm spec in the manual, although there is one at the website; and none of the three amps are rated to double power into 4 ohms), I'm now thinking that the problem is simply that none of these amps can hack it with these speakers. And that raising the bias, if it is practicable to do so, would risk damage. Not sure what else to suggest at this point. Regards, -- Al |
In addition to the experiments that Ralph (Atmasphere) suggested, if readily practicable it may be worthwhile to try running the amp with its top cover removed, which would lower its internal temperatures. You would suggest I get 8ohm speakers? If you are happy with the sound of the speakers during the first hour, and if the conclusion is reached that either the speakers or the amplifier has to be changed, it would probably make the most sense to either change the amplifier, or to purchase a separate power amplifier and drive it from the M6i's pre-outs. Regards, -- Al |
FWIW, I'd just like to emphasize that the impedance curve I linked to earlier shows that the speaker's impedance is in the vicinity of 2.7 ohms at several frequencies in the deep bass and the mid-range, and is less than 4 ohms throughout most of those regions.
Also, I would not attach much significance to amplifier current capability specs, as they usually do not indicate how long the specified current can be sustained for, and my impression is that in many cases that amount of time may be measured in milliseconds.
Regards,
-- Al |
My MF amp should be adequate @ 200wpc or no My strong suspicion, consistent with points that were made earlier by Foster_9, Mapman, and others, is "no." As I previously indicated, the three amplifiers you have tried either do not have a 4 ohm rating, or have a 4 ohm rating that is not particularly good relative to their 8 ohm rating. That would certainly cast doubt on their ability to handle 2.7 to 4 ohm impedances, which occur in parts of the frequency range that typically require lots of energy. Regards, -- Al |
04-11-13: Fishing716
After enjoying the system sounding great for 2 hrs the bass dried up. I waited 1 hr.tried again but no improvement. Turned off amp for 1hr.returned & the presentation was still awful. I also observed when I change source on the amp it seems to create a break in the circut & the bass leaves soon after. I've sometime observed after turning a record around/changing channels on a cable box or changing imput buttons on the amp may upset the delicate balance.
04-11-13: Fishing716
Disregard previous post: Makes no sense!@ But there is no pattern when system sounds optimal: Could be am or pm
04-12-13: Fishing716
Sometimes I switch speaker cables from L/R to R/L
And lower bass returns for an hour or less.
04-12-13: Atmasphere
The only clue we have is that doing something with the speaker cables sometimes has an effect. Letting the system cool off does not. Not sure that we can say that conclusively at this point, Ralph, although the checks you suggested of the connections are certainly in order. I believe it was only one experiment that indicated that letting the system cool off did not result in recovery, and the report about swapping the speaker cables included the word "sometimes." I would be hesitant to conclude at this point that those results would be consistently repeatable over many trials. Presumably the amp was turned off when the speaker cables were switched, and perhaps the recovery was actually the result of it being allowed to cool off. Or perhaps it resulted from something else that occurred during that time. Also, I would repeat my suggesting of trying, as an experiment, running the amp with its top cover removed, if that is practicable. Concerning candidates for possible replacement of the integrated amplifier, while I'm not particularly familiar with the integrateds that are out there these days, my feeling is that finding one that can deliver 100 or 200 watts or more, provide good sound quality, be able to handle 2.7 to 4 ohm impedances gracefully, and cost in the vicinity of the $3K or so price of the M6i, is likely to be a tall order. Personally, I would go with a separate power amplifier, driven from the pre-out terminals of the M6i. Regards, -- Al |
Currently just listened 2 complete LP's without losing the bass using just the right speaker connected. I don't know why that is. Connecting just one speaker will certainly make life easier for the amplifier, and reduce the internal temperatures that it will reach, compared to playing music into two speakers at a similar volume setting. Regards -- Al |
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 |
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 |
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 |
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 |
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 |
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 |
Here's an additional thought for the OP to consider:
In my experience as an electrical engineer, when a baffling problem occurs that defies diagnosis by the usual methods, including substitution of relevant hardware, it often turns out that TWO problems are present at the same time, both of which happen to produce similar symptoms.
Not sure what this might mean in this particular situation, but it's something to keep in mind.
Regards,
-- Al |
Mapman, why do you persist in pointing to the amp(s) as suspect when the phenomenon only occurs after a period of time? If they are not up to the task, don't you think that would be evident from the get-go? No, not at all. And I agree with Mapman. If the ability of the amps to handle 2.7 to 4 ohm loads (at frequencies where most musical energy is concentrated) is marginal, it seems very conceivable that symptoms would not manifest themselves until internal temperatures have had time to rise, and more or less stabilize, following a cold start. The one factor that seems to rule out the amps as being the culprits, of course, is that three different ones have been tried. However, all of them are integrated amps having specs that are not suggestive of robustness in dealing with very low impedances. Yes, it seems improbable that three different amps would cause similar symptoms, but whatever the cause(s) of this problem may turn out to be, it seems clear at this point that they are improbable. "“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” -- Sherlock Holmes Regards, -- Al |
In order to use a power amp that means purchase of a preamp as well,correct? No, not necessarily. As I suggested previously, you could borrow or purchase a separate power amp, and drive it from the pre-out jacks that are provided on your M6i. You would then be using only the preamp section of the M6i, together with the separate power amp. Regards, -- Al |
04-17-13: Bifwynne
Al and Ralph -- take a look at the graphs at the URL above. I'd like to read your thoughts about whether a solid state amp, or any amp for that matter, would get indigestion from those impedances. Hi Bruce, Thanks for providing that additional data. Earlier in the thread I had linked to JA's measurements, which provide better resolution than the Soundstage graphs. Also, for some reason the worst case numbers you quoted from HT Lab differ from JA's, with his numbers being more severe. In any event, IF the problem is amplifier-related I agree that the Zeros would be a reasonable solution, used with their 2:1 impedance ratio. Higher ratios would reduce the maximum amount of power that could be delivered to the speakers to significantly less than the amp's 200W/8 ohm rating. That said, there are certainly a great many separate power amplifiers that can be expected to provide good results with these speakers, especially given that phase angles are very benign aside from the dip that occurs around 27 Hz. Although, of course, a suitable high quality separate power amplifier would most likely cost much more than a set of Zeros. Best regards, -- Al |
+1 to Mapman's comment just above (as well as his other comments).
Also, just to be sure, I assume that when you disconnect and reconnect the speaker cables you have the amplifier turned off while doing so.
Regards,
-- Al |
Hmmm, this is probably grasping at straws, but your mention earlier in the thread that you live "close to Brooklyn" prompts me to ask if you happen to live near JFK airport. A member recently mentioned in another thread that in the past he had sonic issues in his system that were caused by radar that was in use at a nearby airport. The problem went away when he moved to a different city.
Perhaps sensitivity to that or other kinds of interference will vary as a function of the warmup state of the equipment. Grasping at straws, as I say, but who knows?
Regards,
-- Al |
Does anyone know if all the amps in question are MOSFET outputs?? Ralph, I took a look at the schematics for the Bryston B60R and B135 integrated amps, which are available at the Bryston site, and they both use bipolar transistors in their output stages. A post earlier in this thread by Mcintech, dated 4-16-13, indicates that the Musical Fidelity M6i does as well. I couldn't find anything on the web indicating otherwise. Best regards, -- Al |
04-19-13: Fishing716
I have a portable cd recorder & plan to record when the bass is there & not-maybe hear the difference from the cd I make. The following was written before seeing Drubin's post just above, with which I agree: What would really be ideal, if you can arrange it, would be to mount a good quality microphone on a stand at the listening position, and record its output when the problem is and is not present (using a suitable microphone amplifier together with the CD recorder, if the recorder doesn't provide a mic input). You could then upload the two files to a web hosting or file sharing service, and we could analyze them with audio editing software some of us have (including me). One reason that may be more meaningful than an SPL measurement is that unless you use a CD or other recording that provides test tones, in conjunction with the SPL meter, the SPL measurements may not be able to distinguish between a reduction of bass frequencies, and a reduction of volume that may be perceived as a reduction of bass as a result of the Fletcher-Munson Effect. Regards, -- Al |
Anyone would like to hear the two versions please mention your email addresss I don't think that A'gon allows posting or communication of email addresses, and the onsite messaging system can't accommodate attachments. Can you upload it to a web hosting or file sharing service and provide a link? Regards, -- Al |
I listened to the two recordings on my main system, via both speakers and headphones, after transferring them to CD-R. I also performed various analyses of their waveforms using Sony Sound Forge 9, a professional caliber audio editing program.
By far the most notable difference was in the volume levels. Would I be correct in assuming that you created both recordings with the same setting of the volume control on the amp, and the same setting of the recorder's level control? And would I be correct in assuming that if the recorder provides AGC (automatic gain control) and/or peak limiter functions, that you disabled them?
Before doing any analysis, I cut out dead times at the beginning and end of each recording, because those dead times were slightly different between the two recordings, and that difference might have introduced a small bias in the waveform analyses, in one direction or the other.
With 0 db representing digital full scale (the maximum possible instantaneous volume), I found that the maximum instantaneous volume that was present on the "good" recording was 0.0 db, and the rms average value across the entire recording was about -18.6 db (the two channels being slightly different, but both very close to that number).
On the "bad" recording, the maximum instantaneous volume was about -1.9 db (slightly different between the two channels), with the rms average value across the entire recording being about -21.7 db (again, the two channels being slightly different).
I then produced a CD-R containing (1)the "good" recording, (2)the "bad" recording, and (3)the "good" recording with a 3 db level reduction. The volume difference between (1) and the others was, of course, completely obvious. My wife commented on it immediately from another room in the house. (2) and (3) had some subtle differences, but nothing that I would remotely characterize as missing bass, or even a fundamental change in the character of the bass. And the differences between (2) and (3) were small enough that I suspect they might have disappeared if I had done enough trials to more precisely optimize the 3 db level reduction.
I also used the software to do waveform analyses after applying brickwall (essentially instantaneous cutoff) 300 Hz high pass and low pass filters to the "good -3db" and the "bad" recordings. The high passed content of those signals showed almost no difference in instantaneous peak level (0.2 db, with the "bad" recording being lower), and zero difference in rms level. The low passed content of those signals showed slightly greater but still small differences, about 0.7 and 0.4 db lower on the bad recording in peak and rms levels respectively.
I would agree, btw, with DRubin's characterization of the sound quality of the recording. Parts of the treble region are boosted excessively.
The bottom line: All of the differences, if any, were slight, except for the difference in volume, which on an rms basis across the entire track was about 3 db.
Regards,
-- Al |
04-22-13: Atmasphere
Al, 0.7 db across a spectrum can be quite noticeable to the ear, whereas on a sine wave is undetectable. Thanks, Ralph. FWIW, though, note that the 0.7 db was between maximum instantaneous values, which might have occurred on as little as one sample out of the many millions of samples in the track. Averaged on an rms basis across the entire track, the difference was 0.4 db (comparing the sub-300 Hz content of the "good-3db" and "bad" waveforms). You might normalize the two tracks, invert the phase of one and play them simultaneously, then you could hear the 'missing' bass. Actually, prior to posting my report I spent a good deal of time trying to do exactly that. Inverting one 2-channel signal and summing it together with the other 2-channel signal whose volume had (at least approximately) been equalized. And alternatively, playing them both at the same time. Unfortunately, I couldn't get the software to accomplish that properly, after trying several alternative approaches using two different software programs. Not sure why. Also, "normalizing" is somewhat ambiguous in this case, because the differences between the "good" and "bad" waveforms are different depending on whether peak or rms values are considered. Best regards, -- Al |
What is the goal of what what you are discussing? The goal is to characterize the symptoms as precisely as possible, in technical terms. Hopefully that would help to identify or at least narrow down the possible cause(s). Can I ask when you listen to both versions if one sounds more satisfying than the other? Hard to say. Partly because neither sounded satisfying, due to the excessively hot treble, and to some extent also due to a general lack of transparency. I have no way of knowing, of course, the extent to which all of that may have been contributed to by the original recording, vs. your system's reproduction of it, vs. your recorder and microphone. Also, as I indicated, precise equalization of volume levels was problematical, which further increases the difficulty of making any judgments. Can you provide an answer to my question about whether or not your recorder applied AGC and/or peak limiting when your recordings were created? If you are not sure, let us know the make and model of the recorder. If an external microphone was used with it, let us know its make and model as well. Regards, -- Al |
I petitioned my dealer to lend me a dedicated 250 w amp from Musical Fidelity. Do you feel this will resolve the problem? Could be, but I'm by no means certain. I would expect it to be more capable of handling low impedances than the integrated amps you've used, but once again it unfortunately does not appear to have a 4 ohm power rating. I use Marantz Professional cd recorder CDR400 w/built in mic. Couldn't find any info on a Marantz CDR400, but I did find this on the CDR420. If it is the same as or similar to that model, it does provide both AGC (referred to in the writeup as ALC) and peak limiting. To obtain recordings that are as meaningful as possible for present purposes, both of those functions should be switched off, and the recording level set such that the maximum level that is reached during the track at any time (whether or not the problem is present) is several db (perhaps 6 db or so) below the 0 db reference point. All settings should then be left exactly the same for both recordings. Regards, -- Al |
My comments about the CDR420 also apply to the CD300. Looks like it has a front panel switch that selects between ALC, Manual, and Limiter. It should be set to manual, and the recording level set such that its volume meter never gets near the 0 db full scale reference point during any of the recordings. On the other hand, if you set the recording level too low, then noise levels will increase, relative to signal levels, which is why I suggested allowing a margin of perhaps 6 db or so, relative to the 0 db reference point.
Regards,
-- Al |
I have analyzed and listened to "good" and "bad" recordings which Fishing created of Dawn's "Candida," in similar fashion to what I previously reported doing with a recording of "Respect Yourself."
It appears that the recordings of "Candida" were done with reasonable level settings, and with ALC and peak limiting properly disabled. I found that the "good" recording was about 0.4 or 0.5 db lower in both peak and rms volumes than the "bad" recording. Essentially the same 0.4 or 0.5 db difference existed between the volumes the two recordings when frequencies above 300 Hz were filtered out, and also between the volumes of the two recordings when frequencies below 300 Hz were filtered out.
The sound quality was generally very poor in both recordings. I suspect that the major reason for that was the low quality of the recorder's built-in mic. The single built-in mic, of course, also resulted in the sound being monophonic. Nevertheless, I sensed a VERY slight loss of definition in the bass on the "bad" recording. Not looseness, not weakness, just an almost unnoticeable loss of definition. Presumably the difference would have been much more apparent if the recorder and its built-in mic had not been in the loop.
Fishing also provided yesterday a "good" and "bad" re-recording of "Respect Yourself." I did not listen to those, but my software revealed nothing more than about 0.2 or 0.3 db differences in volume, frequency content above 300 Hz, and frequency content below 300 Hz. As with "Candida," the "bad" recording was the (VERY slightly) louder of the two.
Finally, today he provided a second set of re-recordings of "Respect Yourself." However, the recording level on these apparently was set too high, and the waveforms were clipped in numerous places, so I didn't do anything further with them.
FWIW.
Regards,
-- Al
|
Could the line conditioner have been robbing dynamics even if no components were pluged into it? Seems extremely unlikely to me. Your AudioPrism Power Foundation Conditioner appears to simply provide a bunch of outlets and some passive noise filtering. With nothing plugged into it, unless it is defective it should be drawing negligible current, and have no effect on line voltage. If it were defective and drawing enough current to affect line voltage, it would be getting hot and/or its breaker would trip. Assuming that it was turned on when you made these observations, I suppose it is remotely conceivable that it could have some effect on noise conditions on the line, that might affect noise entering components plugged in elsewhere. I suppose it is also remotely conceivable that if it is located close to susceptible cables or components it might affect them to some small degree by radiating EMI or RFI to them. And if either of those effects were occurring, I suppose it would then be remotely conceivable that the sensitivity of your audio components to those effects might change during warmup. How remote is "remotely conceivable", IMO? If I were a betting man I would be happy to offer 1000:1 against those possibilities. Regards, -- Al |
Was certain Alaister said Red treble,black bass/Red treble & black bass...It turns out from top down the correct way is Red Treble/black treble & Red bass/black bass.. Could you clarify in detail what this means? After thinking about it for a couple of minutes, I have no idea. In any event, glad some progress appears to have been made. Regards, -- Al |
Fishing, I still find myself uncertain of the meaning of your description of the connections. I think you are saying (correct me if I'm wrong) that what you WERE doing was:
1)Connecting the "red treble" banana plug of the cable to the red binding post of the high frequency part of the speaker.
2)Connecting the "black treble" banana plug of the cable to the black binding post of the low frequency part of the speaker.
3)Connecting the "red bass" banana plug of the cable to the red binding post of the low frequency part of the speaker.
4)Connecting the "black bass" banana plug of the cable to the black binding post of the high frequency part of the speaker.
In other words, you were interchanging the connections of the two black banana plugs at the speaker end of the cable.
If that is correct, like Dan (Drubin) I don't see how that would cause the bass to be fine for an hour or so, and then mostly disappear. JJ offered a clever theory, but looking at the description and photos of the Comet at the AQ site I don't see anything suggesting that the gauge of the treble wiring is extremely thin, which it would have to be for a resistance rise due to heating to become significant.
Regards,
-- Al |
Actually, what he said he did with the interconnects was to reverse channels, not phase. He didn't say anything about also reversing channels with the speaker cables, so the right channel is apparently being reproduced by the left speaker, and vice versa.
Best regards,
-- Al |
