leok Posted April 24, 2007 Share Posted April 24, 2007 Shawn, I just checked the TA2024 datasheet. If the output impedance was really 4 Ohms at 20 KHz, the output should be down by 3dB at that frequency. According to the datasheet, the output is down by only 1dB at 20KHz. I think there's more to this, and for some reason, the impedance measurements are misleading. Leo Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 24, 2007 Share Posted April 24, 2007 Leo, "What was the output power during impedance measurement?" Depends upon if it was loaded or unloaded. I tested at a few different levels all were a couple of watts basically into the loaded state. "PWM, due to output filtering, may be slew rate limited making it appear to have a higher (than actual) impedance at upper frequencies. " The output filtering is two inductors in series with the outputs. An inductors impedance rises with frequency.... therefor the output impedance of the amp rises with frequency too. "If the output impedance was really 4 Ohms at 20 KHz, the output should be down by 3dB at that frequency." It was down right around that much comparing loaded (8 ohm) to unloaded at 20kHz. "According to the datasheet, the output is down by only 1dB at 20KHz. " Is the datasheet showing output frequency into a load? What is the value of the output inductors? Datasheets do not always match measured reality. What does the output impedance of you amp measure? Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 24, 2007 Share Posted April 24, 2007 "It was down right around that much comparing loaded (8 ohm) to unloaded at 20kHz." Here is a couple of frequency response pictures of the Teac. This is a picture of the Teac fed broadband noise unloaded. Quote Link to comment Share on other sites More sharing options...
martyfreeman Posted April 24, 2007 Share Posted April 24, 2007 Also, you do know that the shootout preferred the Trends over the Winsome Mouse. The Winsome Mouse wasn't included in the shootout. People on Audiocircle favored the Mouse over the Trends, but YMMV. Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 24, 2007 Share Posted April 24, 2007 This is the frequency response of the amp loaded @ 8 ohms. Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted April 25, 2007 Author Share Posted April 25, 2007 Also, you do know that the shootout preferred the Trends over the Winsome Mouse. The Winsome Mouse wasn't included in the shootout. People on Audiocircle favored the Mouse over the Trends, but YMMV. Yup, you're right! - I just looked, I confused it with the 'Flying Mole" Quote Link to comment Share on other sites More sharing options...
pauln Posted April 25, 2007 Share Posted April 25, 2007 Could someone provide an interpretation of the freq-response graghs Quote Link to comment Share on other sites More sharing options...
leok Posted April 25, 2007 Share Posted April 25, 2007 Shawn, 2 Watts may be way too high. With 2 Watts acoustic program material, power to the tweeter is probably 0.2Watts. This may be part of what is confusing here. People are reporting that the high end sounds detailed and extended (and that's what I hear too) while measurements are claiming the high end is reduced by as much as 50% or more. Can you try the output impedance measurement at a fraction of a Watt? On the datasheet, the load used showing 1dB down at 20KHz was 4 Ohms. Power is 1 Watt. Value of the inductors is most likely 10uF. My experience with datasheets has been, when reality doesn't match the spec., the measurement conditions are different. For example: I don't believe the 0.03% distortion spec. is met with a capacitor on the input, which is why, in my application, I re-biased the circuit so my input is DC coupled. I think there is something going on with the amp's performance at top frequencies, but I doubt it is really cutting in half (or even a quarter) the power going to the tweeter, and we have yet to learn how to effectively measure what is going on. To paraphrase a certain statement: "If is sounds good and measures bad, you're measuring the wrong thing." OK, I just re-checked the datasheet: The frequency dependency you mention is shown (Frequency Response, P7). That is measured at 1W. I suspect the "output impedance" is lower at lower power. Also, the filter in this case appears to be tuned so that a tweeter with 6 Ohms impedance will produce a flat response to 20 KHz. So, even if the "output impedance" is high, this doesn't translate into rolled off highs, and may translate into exaggerated highs if tweeter impedance is over 6 Ohms. One might check the impedance of the tweeter in use and compare it with the Tripath Frequency Response chart. The filter in my amps is the one measured by tripath to produce this chart. I don't know what values were used in the various amps that use Tripath chips. Leo Quote Link to comment Share on other sites More sharing options...
meagain Posted April 25, 2007 Share Posted April 25, 2007 Could someone provide an interpretation of the freq-response graghs Good question! Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 25, 2007 Share Posted April 25, 2007 "Could someone provide an interpretation of the freq-response graghs" They show that the frequency response of the amplifier varies depending upon load. With no load connected the Teac has a rising top end. With an 8 ohm load it is basically flat. Per the stereophile measurements the Sonic Impact Super T acts differently then this. Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 25, 2007 Share Posted April 25, 2007 "People are reporting that the high end sounds detailed and extended (and that's what I hear too) while measurements are claiming the high end is reduced by as much as 50% or more. Can you try the output impedance measurement at a fraction of a Watt?" Look at my measurements. It is reduced by just over 3dB at 20kHz when fed an 8 ohm load. Also note that the reduction *makes the Teac flat* compared to no load. As far as what people are hearing.... I'm measuring a different amplifier then what you are talking about. Per the Stereophile article the Super-T has a boost on the top end with an 8 ohm load. Per Al's impedance measurements the type AA is at roughly 10 ohms at 20kHz (when a 16ohm resistor is connected to the crossover, probably will be different with a real tweeter attached) which would result in more boost up top with the Super-T. "Can you try the output impedance measurement at a fraction of a Watt?" I can try but the lower the power you do it at the more margin for error. Have you measured yours? "but I doubt it is really cutting in half (or even a quarter) the power going to the tweeter" That is an oversimplification. Even if the amp is down 3dB from flat at 20kHz it does not mean the tweeter overall is receiving half the power. It simply means the tweeter is receiving half the power *AT 20kHz* then if the amp were flat. Can you hear 20kHz? "and we have yet to learn how to effectively measure what is going on." FR is easy to measure. The harder part is when it varies based on load (as it does with the TriPath) and also in simply correlating FR to personal preference.... not everyone likes the same thing. Witness the possibility that the boosted top end 'sounds better' then flat. Though of course that could also be because the amps boosting the top end might be partially EQing for a rolloff in the crossover or tweeter. "That is measured at 1W. I suspect the "output impedance" is lower at lower power." I hope not. If it changed based on power level that means the amplifier/speaker interaction will change based on power level too. In other words the frequency response would change based on output power level. "Also, the filter in this case appears to be tuned so that a tweeter with 6 Ohms impedance will produce a flat response to 20 KHz." On the Teacs it looks like they chose 8 ohms for this. "So, even if the "output impedance" is high, this doesn't translate into rolled off highs, and may translate into exaggerated highs if tweeter impedance is over 6 Ohms." Possibly, or it could go the other way. The Super-T is hot up top at 8ohms and rolled off at 2 ohms. "One might check the impedance of the tweeter in use and compare it with the Tripath Frequency Response chart." That chart is only valid for those using that exact same filter design. And likely very few people really know the impedance of their tweeter/crossover over its entire range. Shawn Quote Link to comment Share on other sites More sharing options...
meagain Posted April 25, 2007 Share Posted April 25, 2007 And Pauln - When you pushed it to 98db or so..... did you hear any degradation at all? Any harshness, etc. etc? And if it started to sound cr*ppier than at lower volumes, are you able to describe how? The higher volumes this does is what I'm interested in. Wanting to know if it goes South, what db it goes South, and what happens to the bass/highs. Quote Link to comment Share on other sites More sharing options...
Deang Posted April 25, 2007 Share Posted April 25, 2007 It's 10 watts Lisa, and they do what all low power amps do when you push them -- they run out of headroom and the sound starts to compress and then sounds like a bandsaw ripping through your skull. It's common sense -- if you like to listen at live levels you don't buy a 10 wpc amplifier. It's a very good and involving sound up to about 95dB in my small room. It gets loud enough for me. On the FR front, another variable to factor in is that most run these without preamps, so there is no buffering for the VC. Quote Link to comment Share on other sites More sharing options...
leok Posted April 25, 2007 Share Posted April 25, 2007 Shawn, Essentially, I agree with all or most of your comments. I do think the impact on what people hear is more benign (thus my comments about this issue being hyped) than simple numbers indicate. In that the upper frequency response is flat for some nominal tweeter impedance means that the deviation for a particular tweeter is only a function of that tweeter's impedance deviation from the amp's target nominal. People may simply not know this. Also, the pwm immunity to impedance swings at mid and low frequencies is beneficial with many of the older Klipsch 3-ways which have a significant impedance peak in the midrange, making them sound thinner with designs less tolerant of impedance swings in that area. PWM also handles the often encountered impedance dips in the bass region. For those who are concerned, the pwm output filters can be tuned to maximize flatness in the upper region. For most, this is probably not an issue, and not a source of such objectionable types of distortion that are perceived as, say, harshness. And, in the end, remember: this is a $130 stereo amplifier we're talking about. Leo Quote Link to comment Share on other sites More sharing options...
sfogg Posted April 25, 2007 Share Posted April 25, 2007 "It's common sense -- if you like to listen at live levels you don't buy a 10 wpc amplifier. It's a very good and involving sound up to about 95dB in my small room. It gets loud enough for me." Right, room size, listener distance and of course speaker efficiency will all factor into how loud an amp is going to play before distortion. What one plays for music will also factor in as well. The modded channels on my Teacs are good for 9w cleanly then start clipping after that. I can hit 105dB per speaker (peak level... average is in the 80s depend upon what I'm playing) at the listening position cleanly/easily with that power level. But I'm biamping so that is a different ballgame....the 9w are only running from 500hz and up and are on a driver rated at 111dB/w/m. The woofers have the full power of the Teac available to them... around 33w before clipping... and they have it easy too as they are only run above 80hz. Below 80hz I have 1250w. Shawn Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted April 25, 2007 Author Share Posted April 25, 2007 Cut-throat - - have you listened to yours yet? Is Pauln the only one with this in the system now? (Sorry, if I missed a post when scanning through here). I still have not received mine yet. They delayed shipping due to some problems with some LEDs. I am thinking I'll it next week. Quote Link to comment Share on other sites More sharing options...
kaiser SET say Posted April 25, 2007 Share Posted April 25, 2007 Cut, from your post reply to Seti on page two of this thread you said a lot of people are runnings pairs bi-amp, if these are not bridgeable why have two? How are they configuring to run that bi-amp setup? Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted April 25, 2007 Author Share Posted April 25, 2007 Cut, from your post reply to Seti on page two of this thread you said a lot of people are runnings pairs bi-amp, if these are not bridgeable why have two? How are they configuring to run that bi-amp setup? They Are Bi-ampable, just not Bridgeable. They have each amp powering different drivers on each speaker. Not each amp powering separate speakers. Personally, I am not a big fan of Bi-amping. Quote Link to comment Share on other sites More sharing options...
kaiser SET say Posted April 25, 2007 Share Posted April 25, 2007 I like it when it's done right it can sound great so you have described just how I was planning to run rights out to right speaker and left outs to left. I would think this means each speaker gets the full power potential from each amp versus one amp pushing both out of stereo and all drivers? Guess I'll need dual binding post installed on my LaScalla's for this unless I want to tie them straight down at them x-overs no? THX Quote Link to comment Share on other sites More sharing options...
pete almquist Posted April 26, 2007 Share Posted April 26, 2007 hi all, my question too. would love to have a walkthru on how to bi-amp these to the klipschorns. thanks very muchly...! pete Quote Link to comment Share on other sites More sharing options...
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