Datasheet says 11.5 A (typ), 7 A (min). It's in the spec table, hence, tested in production.
Thank you.
Perhaps for opamps of that era, that's true. The LME49710 will have vanishingly low THD both in inverting and non-inverting configurations. By vanishingly low, I mean even the pros have to resort to special tricks (lowering the loop gain) in order to measure it at all (see the LME49710 data sheet for more details).
I did consider inverting vs non-inverting configurations and ended up using the non-inverting as it allowed me to build the board with one less op-amp (lower board area, lower cost, etc) and still get stellar performance.
Yep. With precision circuits, the layout is the circuit. The schematic is just along for the ride...
Um, no. It's min. 7 A at an ambient temperature of 25 ºC. 11.5 A typical. This means that if you grab a random part in the tube, you're pretty likely to get one that can deliver 11.5 A. But National/TI won't throw a part away as a test failure unless it falls below 7 A. I've attached an excerpt from the data sheet table for your convenience.
~Tom
Attachments
That is the part of the specification I was referring to, when I said:
The minimum value for the maximum current when Tj=25°C is 7A
That is the peak value for a low limit device when passing an AC signal.
Yes it can be much higher and usually will be as specified by the typical value of 11A. Again that is a peak value for Tj @ 25°C
The minimum value for the maximum current when Tj=25°C is 7A
That is the peak value for a low limit device when passing an AC signal.
Yes it can be much higher and usually will be as specified by the typical value of 11A. Again that is a peak value for Tj @ 25°C
It's mainly a measurement bandwidth thing; see Audio Precision's remarks for a recap. Since Modulus-86 THD+N is measured with an 80kHz bandwidth I don't think the high frequency 18k+20k or 19k+20kHz IMD tests would provide any new information---I'm not aware of any distortion mechanisms 19k+20k IMD would pick up which wouldn't also appear in the 19-20k portion of a THD sweep's harmonics. One could argue that maybe the amp develops horrible fifth order distortion at 20kHz which it lacks at 16kHz and hence a high frequency IMD check is needed to get around the lack of a 100kHz measurement bandwidth. If this is actually the case I will be flabbergasted until next Tuesday.
It is IMD as opposed to IMD+N. So there is potentially some harmonic information in this test which could be masked by the noise floor in a THD+N sweep. However, THD+N versus level provides pretty much the same information. One could also just run plain THD like HOLMImpulse does.
The more common 60Hz+7kHz 4:1 SMPTE standard test is perhaps a bit more useful. The low frequency portion of a THD+N sweep should capture thermal tracking error in feedback resistors. But SMPTE IMD may help with diagnosis and, as a steady state measurement, might capture longer term thermal behaviour which a THD sweep could miss. I wouldn't expect the Modulus-86 to have any limitations in this regard and I've not been able to measure any drift in nonlinearity, thermal or otherwise, even in the surface mount amps I've built which have higher C/W than through hole.
Since THD is a special case of n-tone IMD where all n tones happen to have the same frequency one could argue SMPTE IMD is more a useful additional check than high frequency tone pairs. The reasoning here would be that since the SMPTE tones are much farther apart in frequency the test is more different from THD than high frequency IMD. However, I've never seen any SMPTE or high frequency IMD data which didn't track with THD+N. And this isn't for want of looking or similar discussion on other DIY Audio threads---at the most it may sometimes look at first glance like THD and IMD don't track due to differences in measurement conditions.
It remains, though, some folks just like to have the additional data point provided by IMD. Makes 'em feel better and have more confidence in the amp.
I'm all about measurements. No worries there. I was just curious what someone would be able to deduce from an IMD/SMPTE measurement, that's all. Regardless of motive, it would be interesting to look at the IMD.
On my todo list are: IMD/SMPTE, noise floor, frequency response, and clipping behavior. In addition, I need to revisit the THD+N vs power as I think I had a setup issue when I performed that measurement. Specifically, I was using a thermal pad (SilPad 400), rather than the thermal compound, thinking that the SilPad should be good enough and much less messy than the thermal goop. As a result, the SPiKe protection engages prematurely and the max output power is a good 10 W too low. I need to go back and retake those measurements along with THD+N vs frequency at higher output power. I would also like to measure the output spectrum near full power so see if I'm actually measuring THD or just the noise floor. The lack of a plateau in the THD+N vs power curve indicates that I'm really looking at the SNR rather than the THD.
Stay tuned...
~Tom
On my todo list are: IMD/SMPTE, noise floor, frequency response, and clipping behavior. In addition, I need to revisit the THD+N vs power as I think I had a setup issue when I performed that measurement. Specifically, I was using a thermal pad (SilPad 400), rather than the thermal compound, thinking that the SilPad should be good enough and much less messy than the thermal goop. As a result, the SPiKe protection engages prematurely and the max output power is a good 10 W too low. I need to go back and retake those measurements along with THD+N vs frequency at higher output power. I would also like to measure the output spectrum near full power so see if I'm actually measuring THD or just the noise floor. The lack of a plateau in the THD+N vs power curve indicates that I'm really looking at the SNR rather than the THD.
Stay tuned...
~Tom
Shifting the heat away from the silicon is critical - in some preliminary playing around with LM chips I was amazed at how quickly the thermal protection cut in - at trivially low sound levels - when I applied some very sloppy heatsinking, just to see if it all worked ...
My opinion, I can't speak for ~Tom, is that even a not so perfect execution of his boards built into an amp will spec more than adequately.
My take on it is that building up dual mono or two chassis is likely to yield the best specs with the least effort, as the grounding is somewhat easier to deal with.
How it sounds is another question, since the LM3886 is already a rather low distortion device.
Not sure what you mean when you say "measured in standard environment like all commercial hi-end devices"?
..same frequency and same phase. Otherwise on average the test tone would be nulled out if random phase were allocated to each same-frequency tone.
As I understand it high end commercial audio is defined by removing specifications and adding zeros at the end of the price tag. So maybe make it $60,000 a board, delete all posts in this thread which contain any measurement data, and discuss how to dowse for matched op amps?
I think the only real answer to the "question" is ~35W at <0.0004 % THD+N. I'd be surprised if any of the data already published (which is hugely more than any commercial amp I've ever come across) shifted meaningfully---any thermal error which might be reduced by ~1.5dB from a lower C/W is already suppressed by 70-250dB of loop gain.Yes, that's the large number limit if tone phase and amplitude are uncorrelated. Such a measurement seems not very useful.
If you buy my boards and populate them according to the BOM, you will get performance that matches what I measure. That's my business model, basically.
~Tom
That's very true. But if you think about it, without a decent heat sink it doesn't take much power for the die to hit 150 ºC. At ±28 V, the 50 mA (typ) idle current means 2.8 W of power dissipation already. At 25 ºC ambient, this means the die hits 145 ºC without a heat sink (43 ºK/W thetaJA). That's just the idle dissipation. Once you start burning any power at all, you will hit the thermal protection. Physics is not always friendly...
Since I performed the measurements shown in Post #1, I've been looking at those thermal pads. The best one I've found that fits the LM3886 is a Bergquist K-10. Even that has a thermal resistance of over 2 ºK/W for a TO-220 size. Basically, I can't find anything that'll beat the performance of the isolated LM3886 package. A thin coat of Wakefield 126 thermal goop has a thermal resistance of about 0.05 ºK/W. That makes the total thetaJS 2.05 ºK/W.
~Tom
Actually yes it would be amazing if there were listening reviews and comparison tests, cause stellar specs do not always mean great sound reproduction(details, controlled transients, timing etc), control over sound, low frequencies etc. :/
In the studio recently we compared a Pass Labs amp with a Bryston amp(which we were using for some time now), one of the SST pro models. The pass labs didn't have stellar measurements, but the Brystons have amazing specs.
Guess what, my buddy kept the Pass Labs in his studio and gave me the Brystons to play around for a project
We were able to hear more details, more precision, more of the essence of a track using the Pass Labs...hard to explain using words.
Listening 1 - Stellar specs 0
I hope we hear some listening/comparison tests (made by pros) for the Modulus-86 using top quality speakers in a treated room.
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I think tomchr qualifies as a pro. He says it sounds great. Don't you trust his judgement? I don't. I think it probably sounds the same as any one of several competent amps.
It's not hard to explain at all. You like a bit of harmonic distortion. That would explain it, wouldn't it? Without resorting to any mysticism?
If, on the other hand, you are just hell-bent on undermining the work of another member, then you've come to the right place.
So one just adds some harmonic distortion to any crappy amp, and gets an amazing sounding amp right ? Your explanation is amazing
When people say it sounds great, it sounds great when compared to "what" ? That's the question.
I'm not undermining anybody, on the contrary (I was even genuinely interested in the product and contacted Tom personally) ... but just like some other members, i'd love to hear some comparisons done on top class speakers( I am not being condescending but KRKs are quite poor quality speakers ), in a properly treated control room and the listening done by professionals (mixing and mastering engineer, which involves tons of critical listening all year round).
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My mission here is this:
I would like to invite those who post to this thread to view their posts within the context of this mission.
If it isn't already obvious from Post #1, I am an objectivist. I rely on objective measurements for the characterization of an amplifier. Based on my personal experience as well as that of "trained ears", I do find that it's possible to correlate measurements and perceived sound quality. An amplifier with a nearly flat THD vs frequency curve will, generally, sound better than one where the THD varies drastically versus frequency (as is the case for the raw LM3886). Some people prefer a little second order harmonic distortion. They go for my Damn Good 300B. Others prefer as little distortion as possible. They can buy my Modulus-86. Either approach is valid.
I rely on measurements because they allow for objective comparison between amplifiers. They also provide figures of merit, which tell me how much I'm pushing the current state of the art.
Subjective comparisons are often contradictory. One person may perceive the cone breakup of a tweeter as "harsh" (negative) where as another perceive it as "precise" (positive). Or one person's "muddy bass" (negative) is perceived as "warm and open" (positive) by another.
So that's where I'm coming from. I'm not interested in a peeing contest. I outgrew those a few decades ago and never found them that intellectually stimulating anyway. If you're into those or lengthy discussions on subjectivism vs objectivism, I'm sure there is a thread in the Lounge that you can contribute to.
BTW: I never said I auditioned the Modulus-86 on the KRK R6s. I used my Dali 3As for the listening test.
~Tom
- I like to push the envelope on the state of the art within DIY Audio by developing the best performing circuits I know how to design.
- I back up my designs with solid engineering and tons of objective measurements.
- I do my best to be as helpful as I can to the DIY community. This should be fairly obvious to anybody running a search for my forum posts.
- In the interest of openness, my amplifier designs and my credentials are available on my website for anyone to see.
- To support my design efforts, I sell circuit boards. It's a (barely) self-sustaining hobby.
I would like to invite those who post to this thread to view their posts within the context of this mission.
If it isn't already obvious from Post #1, I am an objectivist. I rely on objective measurements for the characterization of an amplifier. Based on my personal experience as well as that of "trained ears", I do find that it's possible to correlate measurements and perceived sound quality. An amplifier with a nearly flat THD vs frequency curve will, generally, sound better than one where the THD varies drastically versus frequency (as is the case for the raw LM3886). Some people prefer a little second order harmonic distortion. They go for my Damn Good 300B. Others prefer as little distortion as possible. They can buy my Modulus-86. Either approach is valid.
I rely on measurements because they allow for objective comparison between amplifiers. They also provide figures of merit, which tell me how much I'm pushing the current state of the art.
Subjective comparisons are often contradictory. One person may perceive the cone breakup of a tweeter as "harsh" (negative) where as another perceive it as "precise" (positive). Or one person's "muddy bass" (negative) is perceived as "warm and open" (positive) by another.
So that's where I'm coming from. I'm not interested in a peeing contest. I outgrew those a few decades ago and never found them that intellectually stimulating anyway. If you're into those or lengthy discussions on subjectivism vs objectivism, I'm sure there is a thread in the Lounge that you can contribute to.
BTW: I never said I auditioned the Modulus-86 on the KRK R6s. I used my Dali 3As for the listening test.
~Tom
That's why measurements are useful. To expand on what Tom's saying, if you spend enough time on DIY Audio even you'll find folks using opposite subjective terms to describe the same objective change made in controlled A/B testing. And the antonyms will both be describing positive perceptions, rather than one indicating a positive listener perception and the other a negative listener perception like you'd expect. Or sometimes the opposite words both indicate negative perception.
You'll likely find it helpful to refer to Harmon-Kardon's research in this area; Sean Olive has a three part set on his blog which is a good starting point. In particular, refer to the papers "Differences in Performance and Preference of Trained Versus Untrained Listeners in Loudspeaker Tests", and "Hearing is Believing vs. Believing is Hearing". The first you can get via a free download link in the references of that link, the second from the references here. To summarize the findings, they're that measurements, untrained listeners, and trained listeners all converge on what constitutes good sound. But that even trained listeners are easily swayed by other factors such as a commercial product's appearance.
That's easily achieved; solder up the boards you're looking at ordering and hire a good studio for an hour---this is DIY Audio, after all. Harman's findings should assist you in getting good data and controlling for variables.
What I would be most interested in hearing is from those who already have and are using LM3886 based amps, and who build this one up (in the same power levels, please) and relate their entirely subjective reactions.
What would be ideal is to compare the two versions in either the same chassis/power supply or identical ones.
As far as cost, I could if asked quote a price on just the assembly of this amp, assuming that all the chassis and parts were prepared - I think that it would be a bit rich for most folks, just because of the hours wrapped up in the raw labor. So, the cost of the boards while not the lowest I've seen here on DiyAudio, isn't all that high compared to the cost of the rest of the parts. Add in the time and cost for design and development...
Can't wait to see what people have to say, after some get built.
_-_-
Btw, I would take Harmon's findings with a grain of salt - valid to some extent, not all extents and situations.
What would be ideal is to compare the two versions in either the same chassis/power supply or identical ones.
As far as cost, I could if asked quote a price on just the assembly of this amp, assuming that all the chassis and parts were prepared - I think that it would be a bit rich for most folks, just because of the hours wrapped up in the raw labor. So, the cost of the boards while not the lowest I've seen here on DiyAudio, isn't all that high compared to the cost of the rest of the parts. Add in the time and cost for design and development...
Can't wait to see what people have to say, after some get built.
_-_-
Btw, I would take Harmon's findings with a grain of salt - valid to some extent, not all extents and situations.