steve Posted July 10, 2005 Share Posted July 10, 2005 Well, I auditoned these little digital amps, listening to them steadily for about a week, and I must say, they were pretty impressive for such small components. First impression was wow, what a lot of bass..where'd that come from? The highs rolled off a little, but with Klipschorns, that wasn't necessarily a bad thing, as Khorns can give up some highs here and there, and still put out a quality sound. Anyway, I played numerous tunes, ones I was very, very familiar with, and I thought the sound was pretty good. However, like any new piece of equipment, it either sounds horrible out of the box, or you want it to sound better than what you have so you hear what you want to. The latter was such the case for me. After the first few nights, I was thinking the bass didn't sound "natural" anymore..it was there, alright, but it was more like it was enhanced..I guess the best analogy would be comparing an optical zoom on your camera to the digital zoom. Artificially enhanced. To my ears, the bass was being digitally enhanced, and it wasn't natural at all..it sounded like a bad subwoofer that wouldn't keep up. Also, the highs rolling off were more pronounced, now that I had relaxed and listened to the music, not the equipment. So after keeping track of the selections I had chosen (yes, I wrote them down, can't remember a thing) I swapped my 300B SET back in..and what a difference! And to think I've written there was no bass! The bass was so smooth, maybe that's why I haven't "noticed" it. So natural. And the highs?? They weren't rolled off at all, and I realized the little Moles definitely lost some of the detail..I listened to my original system for two nights, and realized I really didn't have any desire for digital..just give me tubes! I have to add this..the digital amps would do a good job for less discerning listeners (not any of us here) and would satisfy people who enjoy background music, and no equipment maintenance. They are small enough to hide anywhere..probably be a great match for Bose cubes!! But for my tastes, only tubes and KHorns are gonna float my boat. And finally, Jim Johns at Flying Mole Electronics has been a great guy to deal with..very helpful, and willing to work with you,,especially on auditions, and shipping. Seeing how I haven't lost anything but the shipping costs, it was well worth it. Makes me appreciate what I have..(well, another thread will be in the works later..I have just ordered a new tube preamp) Anyway..that's my take on the digital mono amps. Regards, Steve Quote Link to comment Share on other sites More sharing options...
TheSoundBroker Posted July 10, 2005 Share Posted July 10, 2005 We picked up this amp line and we've been nothing BUT impressed...especially for the $$ (750 for a pair of 100 watt monoblocks). The only thing in the Klipsch line they won't power to full potential is the RF-7 (they have some 300 watt monoblocks coming for those). They are great for the Reference line and do pretty well on the Heritage series...which ARE best with tubes, but not everybody has the $$ or patience for firebottles. Thing I've found about them is that they are very very sensitive to power line condition, which makes sense given the way they work. They also do have a wierd break in. They start good, get worse...then get MUCH better (too bad you couldn't have keep them for 2 weeks!). I've run them with Cornwalls, RB-75's, RF-7's, LaScalas, RB-15's, RB-35's and the THX Ultra 2 setup (KL-650's). We liked them so much on the RB-75's that we are going to be making a kit to convert RB-75's to an active monitor (ala the PMC Active monitors which use the same amp and are setting the pro world on FIRE!). They are not perfect, but for the $$ they are ridiculously good. Quote Link to comment Share on other sites More sharing options...
steve Posted July 10, 2005 Author Share Posted July 10, 2005 I think I may have talked to you about the Flying Mole amps..and that was the reason I tried them.(If not, sorry..mistaken identity) Anyway, like I stated I was impressed, and am not saying in any way shape or form that they were bad..I'm just saying that they weren't as good as tubes..we are really agreeing on things, as you said not everyone has the patience or dollars for tubes, and I said the same thing..although I said "less discerning listeners"..sorry, maybe a bad choice of words. I can only keep them for 2 weeks, and that's up in 4 days..so I don't think I'm gonna see a big difference. Were that the case, I'd bet the trial period would be 4 weeks..after all, if the manufacturer knows there's a "break in" period, they'd set the trial listening up for that amount of time. Or, extend it if they believed in their product, like Upscale Audio did with my AH! Njoe Tjoeb CD player.they said it would take a lot longer to break in, and told me to keep it longer than their original offer..and after an additional 2 weeks, they were right. Anyway, I just wanted to state my findings. They are unbelievable for their size. But call me old school or just old..I just like tubes and transformers..stuck in my ways..my humble opinion. No disrespect meant. Regards, Steve Quote Link to comment Share on other sites More sharing options...
leok Posted July 10, 2005 Share Posted July 10, 2005 Steve, Interesting review. My impressions of Tripath's version of pwm are very similar, including what seems to be a more extended high end with my 2A3 SET. The thing I can't figure out is what happens to the hf in pwm. One possibility is, if tweeter impedance goes high enough in that top octave then the pwm output filter will begin to cut into the hf. The math is in the data sheet .. I'll take a look and see if I can predict tweeter impedance that would begin to make a difference. More bass is pretty obvious with the Chorus-II, but surprisingly no so with the RF-7s .. another mystery. (not power folks. I never run anything close to clipping: Voltage or current). However, tube amps, esp the no-feedback designs, due to their high output impedance, do back off in the low impedance regions of a speaker's frequency response. PWM, on the other hand, has no trouble at all with impedance variatons (except at the top end where the output low pass filter begins to cut in), so the bass won't back off a bit if a speaker has a low impedance region in the bass. Thanks for posting the review. Leo Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted July 10, 2005 Share Posted July 10, 2005 I don't know what I may or may not be giving up with my QSC amp, but I just love it. Still have my sights set on a pair of VRD's though. Sorry the digital amp did not work out. Chris Quote Link to comment Share on other sites More sharing options...
leok Posted July 11, 2005 Share Posted July 11, 2005 Just did a rough check of the low pass cutoff freq in the P6D and it's just over 100KHz .. I don't think that's getting in the way. I have a tendency to take the Tripath sound pretty seriously because it is the sound of a math algorithm, not the sound of components. In this case I'm not sure what it's telling me. It is certainly impressive. Leo Quote Link to comment Share on other sites More sharing options...
JulieHeartKlipsch Posted July 11, 2005 Share Posted July 11, 2005 Steve wrote: "The highs rolled off a little, but with Klipschorns, that wasn't necessarily a bad thing, as Khorns can give up some highs here and there, and still put out a quality sound." What do you mean? Aren't Klipschorns highs the same as my Heresy highs? They sound perfect. I do not want to muffle them. Quote Link to comment Share on other sites More sharing options...
JulieHeartKlipsch Posted July 11, 2005 Share Posted July 11, 2005 Leok said: "I have a tendency to take the Tripath sound pretty seriously because it is the sound of a math algorithm, not the sound of components. In this case I'm not sure what it's telling me. It is certainly impressive." In six semesters of College Algebra I never heard "The sound of math algorithm". How can you tell "it is certainly impressive"? Quote Link to comment Share on other sites More sharing options...
Colin Posted July 11, 2005 Share Posted July 11, 2005 Like hearing for middle-age men, the middle-age Khorns roll-off at 16kHz. Studies show that while we can not hear differences above 20kHz, even at the loudest SPL volume, we can sense an added improvement in tone with loudspeakers that reach above 20Khz. It is actually the area about 5 to 8kHz that most non-audiophiles think of as the treble range. Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted July 11, 2005 Share Posted July 11, 2005 ---------------- On 7/11/2005 12:43:02 PM JulieHeartKlipsch wrote: Leok said: "I have a tendency to take the Tripath sound pretty seriously because it is the sound of a math algorithm, not the sound of components. In this case I'm not sure what it's telling me. It is certainly impressive." In six semesters of College Algebra I never heard "The sound of math algorithm". How can you tell "it is certainly impressive"? ---------------- You needed to go on to appllied calculus and differential equations. Quote Link to comment Share on other sites More sharing options...
Parrot Posted July 11, 2005 Share Posted July 11, 2005 ---------------- On 7/11/2005 12:43:02 PM JulieHeartKlipsch wrote: In six semesters of College Algebra I never heard "The sound of math algorithm". How can you tell "it is certainly impressive"? ---------------- LOL! I never heard a math algorithm either. But since most of my mathematics instructors were foreign TAs with bad English, maybe I missed it. Leo lists a lot of components so I'm not sure what he meant. Maybe he's talking about particular parts. Quote Link to comment Share on other sites More sharing options...
leok Posted July 11, 2005 Share Posted July 11, 2005 Part of the Tripath approach is to use a very high switching frequency (actually it's a frequency range), so that the quality of the components has minimal impact. I think Tripath achieved this. I use some very high quality inductors and caps in the output filter and can (as have others who auditioned early prototypes) hear the difference. But the basic smooth impact of the amp remains the same .. low level detail and 3-d image quality improve with better components. The way the pwd algorithm completely ignors speaker impedance variations, except for the top end, is intellectually fun for me. I can ask: what does this speaker sound like with an amp that has a 0 Ohm output impedance? and I believe that pwm amps provide a degree of answer. The top octave is a mystery. My SET is not more intense in the high end, there is simply more there .. more like a real acoustic performance. I can't figure out why my P6D and other pwm implementations don't have that top end. My engineering side tells me it's the SET that's wrong. Some acoustic experiences side with that engineering approach and say there is just too much high end with the SET. If so, is it the recordings that are closely miked? RCA Living Stereo and Mercury Living Presence don't have the intense high end with the SET. As I said, the top end is a mystery. But for me, this kind of mystery is fun. Leo Quote Link to comment Share on other sites More sharing options...
steve Posted July 12, 2005 Author Share Posted July 12, 2005 Leo although I excelled in math in school, I've forgotten what I learned! Well, at least in trig and pre calculus! Anyway, like you said before, the digital amps just didn't "fill" the area, like your digital experience. It was more "canned" than live. Not bad, again I'm not bad mouthing the digital box, I'm just saying tubes are more there..at least for me! So although I don't quite understand the alogarithm explanation, I do know what I like! Good thing some of you out there know what the math formulas mean! And to Julie,well, I meant sometimes the KHorn, like any horn speaker can go "over the top" with a recording that's too bright. But not that often. I'll take my KHorns over any speaker! Steve Quote Link to comment Share on other sites More sharing options...
Erukian Posted July 12, 2005 Share Posted July 12, 2005 Here's a cool quote i picked up from this article. --QUOTED-- In operation, digital amplifiers use the width and frequency of a digital pulse train-pulse-width modulation (PWM) to carry an audio signal. The pulses are generated by trip comparators, matching the voltage levels of an audio signal against those of a sawtooth reference to trigger the pulses. Thus, a high-amplitude, high-frequency signal is represented by a dense cluster of short-duration pulses; a lower-frequency, lower-amplitude signal will have longer pulses, farther apart. The audio signal is produced by pumping the digital pulse train into a pair of power MOSFETs, typically wired in a push-pull configuration. An additional inductor-capacitor filter (as well as the speaker coils themselves) adds "persistence" to the signal, effectively smoothing out the pulses. Transistors are not natural amplifiers; they are switching devices. To get a transistor to behave as an amplifier, as with conventional Class AB amplifiers, you have to apply a bias current, which forces the transistor to forever hang in a region between being completely on and completely off. That means the transistors of the Class AB amplifier will be sucking up current-and generating heat-even when there is no audio signal present. On top of that, audiophile equipment manufacturers have learned that many types of power transistors perform most linearly (and are claimed to sound the best) when they are "hot biased"-that is, when they are given almost, but not quite, enough bias current to snap them into an "on" state. This will make the power transistors extremely hot to the touch, and it is no wonder (or exaggeration) that these high-end Class A amplifiers will come with 30 pounds of aluminum heat sink. The digital amplifier, in contrast, uses power transistors much more efficiently. The pulse-width modulator switches them on or off and tries not to spend too much time (or power) in the in-between state. Consequently, the chain among PWM, driver stage and power transistor output in a Class D amplifier is significantly shorter than it is for multistage AB amplifiers. The problem is that the output of the audio amplifier must be carefully filtered to block the residue and harmonics of the digital pulse train. That puts the semiconductor supplier in the filter design business, and there is no guarantee that the customer the consumer electronics equipment maker will adhere to the reference design or follow the semiconductor maker's recommendations. Thus, if the end consumer is unhappy with the sound quality of a home theater system, he or she might well blame the semiconductor supplier, when in fact it might be the fault of an underdesigned filter. Tripath Technology Inc. (San Jose, Calif.) was one of the earliest companies to attack the filter problem head on. Using a variable-frequency sawtooth oscillator to spread the pulse about a 1-MHz region-a form of spread-spectrum technology the company called Class T-Tripath effectively reduced the complexity of the filter network required. For example, it found that the electrolytic capacitors used with switchers operating at 250 kHz could be replaced with smaller, lower-value capacitors when the switcher operates from 600 kHz to 1.5 MHz. ... Even Tripath is using a form of DSP-sigma-delta A/D conversion-on the front end of its audio amplifier modules. The sigma-delta converter reconstitutes a 44.1-kHz audio pulse stream as if it were being sampled at 12.5 MHz (or 256 times 44.1). This "oversampling" effectively flattens audio amplitudes into a 1-bit-plus-sign digital stream-easily manipulated by a digital amplifier. The oversampling also positions the quantization noise and harmonics way up in the frequency spectrum, where they can easily be lopped off by a capacitor filter. --END-OF-QUOTE--- Good stuff eh? Probably nothing you wouldnt find in tripath's documentation though. -Joe Quote Link to comment Share on other sites More sharing options...
leok Posted July 12, 2005 Share Posted July 12, 2005 JulieHeartKlipsch, I was thinking about the "math" that one hears and reading the quote posted by Erukian. One sound" that can be considered is the noise of the digital amp. Why are they not as easily annoying as inexpensively implemented pulse code modulation cd players? Well, the noise signatures are very different. There is an article in the July 2005 Stereophile, P55, "Contingent Dither." Keith Howard proposes that the Gaussian shape (probability density function) of analog noise is much more tolerable than the constant or rectangular shape of pcm noise (see fig 6 on p 65). Actually, that entire article is about the "sound of math." Now take a look at the error introduced by the pwm amps. In pwm there's a string of little up and down ramps crossing back and forth across what the signal should really be, then it is filtered by a 2-pole RC filter .. all defineable by equations and not all that affected by component quality. I don't know the shape (or probability density function) of the final error (maybe you can derive it?), but I suspect it doesn't look like the constant pcm version. Delta modulation used by SACD is noisier in the top octave or two than pcm, but people seem to be more tolerant of it. More sound of math. Leo Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted July 12, 2005 Share Posted July 12, 2005 Leok, Here is another quote which may be of interest regarding the Tripath upper frequency: "The latter is at issue here. Amplifiers that have no correction for the output filter (e.g. tripath) have a frequency response which is mostly determined by the output filter. When a resistor of precisely the rated load impedance is attached, the frequency response will be flat. For higher load impedances, there will be a boost at the end of the pass band. Most loudspeakers are inductive at high frequencies and at 20kHz they easily exhibit an impedance several times the nominal value. So, for most loudspeakers an uncorrected amplifier will actually boost the high frequencies significantly (several dB's). One would expect such an HF boost to sound harsh. Not so. If the boost is a mild resonant peak, you can put on several dB's at 20kHz before a change in tonality is heard. Instead, the soundstage becomes deeper, sharper and more airy. Interestingly, if the boost is a shelf, you get none of this. The sound only gets aggressive. The boost produced by an underdamped LC filter is definitely of the former, nice sounding kind." Mark Quote Link to comment Share on other sites More sharing options...
leok Posted July 12, 2005 Share Posted July 12, 2005 Well, that's interesting. An underdamped lc filter is what I was thinking also, but I certainly didn't expect the phychoacoustic impact. With the filter tuned so high (I calculated about 100KHz (10uH, .22uF) would the peak be seen as low as 20KHz? In any event, I wouldn't expect a high frequency loss. The high end smoothness of these amps almost sounds more "analog" than tube amps. Is there any chance tweeters are inductive between 10 and 20 KHz? It would have to be substantial to have an affect: the inductor in my Tripath amp is 10uH. Thanks for the info. Leo Quote Link to comment Share on other sites More sharing options...
sunnysal Posted July 12, 2005 Share Posted July 12, 2005 I think the La Grange multiplier is the key to good treble sound...lol tony Quote Link to comment Share on other sites More sharing options...
TheSoundBroker Posted July 19, 2005 Share Posted July 19, 2005 ---------------- On 7/10/2005 1:22:17 AM steve wrote: I think I may have talked to you about the Flying Mole amps..and that was the reason I tried them.(If not, sorry..mistaken identity) Anyway, like I stated I was impressed, and am not saying in any way shape or form that they were bad..I'm just saying that they weren't as good as tubes..we are really agreeing on things, as you said not everyone has the patience or dollars for tubes, and I said the same thing..although I said "less discerning listeners"..sorry, maybe a bad choice of words. I can only keep them for 2 weeks, and that's up in 4 days..so I don't think I'm gonna see a big difference. Were that the case, I'd bet the trial period would be 4 weeks..after all, if the manufacturer knows there's a "break in" period, they'd set the trial listening up for that amount of time. Or, extend it if they believed in their product, like Upscale Audio did with my AH! Njoe Tjoeb CD player.they said it would take a lot longer to break in, and told me to keep it longer than their original offer..and after an additional 2 weeks, they were right. Anyway, I just wanted to state my findings. They are unbelievable for their size. But call me old school or just old..I just like tubes and transformers..stuck in my ways..my humble opinion. No disrespect meant. Regards, Steve ---------------- Definitely no disrespect taken. I do love tubes with Heritage and said so. But for the folks who can't or don't want to go with hot bottles, these are mighty good. Wierd thing about the top end. They do sound a bit mellow on the Klipsch speakers...not necessarily a bad thing. But on the PMC monitors, which are seriously extended and VERY neutral on top (and the rest), they are totally flat and extended. Must be something with the way the horns load the amps on the top end. We REALLY like them with the Reference series speakers, they just seem to click. Also, they sound wonderful on the THX Ultra 2's where they run neck and neck with the Bryston SST series amps...which are pretty formidable competitors. Can't wait to get my hands on the bigger monoblock versions due at the end of the year. One other finding on them...since they essentially convert AC to power, they are very sensitive to powerline quality. We put them on one of the Exact Power EP-1500 regenerators and GREAT GOOGLY MOOGLY! Man did those amps get happy! Not a cheap combo ($750 amps, $2K power regenerator) but WHOA! Quote Link to comment Share on other sites More sharing options...
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