That confuses me as well. An ideal current source should have infinite output impedance.
Tom, are those THD20k figures at well below 10ppm??I grovel at your feet in awe.
What's the bandwidth on the AP?
I like it too. The measurement bandwidth is 60 kHz for the THD+N vs Frequency plots. As the supersonic harmonics are, well, supersonic, hence not audible, one could argue that the measurement bandwidth could be reduced to 20 kHz and the THD+N plot stop at 10 kHz. I chose 60 kHz to drive the +N part down so the THD would actually resolve with reasonable accuracy (pushing the limits of the instrument here) in the audio band. 80 kHz bandwidth is commonly used. The difference in the 20 kHz THD+N at 60 kHz BW vs 80 kHz BW was negligible, so I chose 60 kHz.
PS Talking about Zo instead of DF might be easier for Soong to understand ... but then again, it might not
Well, he doesn't seem to want either and is unable to articulate what he wants. I'm at a loss here. I think I'll just move on.
Wow. You just can't make everybody happy...
I was slightly surprised to see the "high" THD+N at 2 Ω load. Then again, 2 Ω is awfully close to a short circuit and I'm not aware of any amp that matches the performance I'm measuring here, never mind beats the performance.
~Tom
Good point. Yeah, I can take a few measurements at various supply voltages. Right now, I need to focus on getting the documentation wrapped up and my website updated, however. I'll get there...
Crosstalk on one channel? That's sorta like the sound of one hand clapping, isn't it?
I'll measure crosstalk once I have a stereo amp implemented in an enclosure.
You take measurements? Cool! Where can I see them? I've looked at your website/blog but didn't find any measurements there...
I'm also curious how you manage to test your amplifiers at >100 W output power without blowing out your ears or speakers (in particular tweeters). Would you care to elaborate?
If you move the speaker cone with your hand, you can measure the induced voltage at the speaker terminals. That would be the "back EMF". I believe the theory is that the amp will drive the speaker cone forward and as the amplifier's output decreases, the speaker cone will move back due to the force of the speaker suspension. This generates a current in the voice coil that the amplifier has to sink. This would also create a small error voltage across the output impedance of the amp, which is why we want an amp with a low output impedance (voltage source). That's the idea anyway. How big (or real) this issue is, I haven't quantified.
Hence, my "or real" disclaimer above...
I find it entirely plausible that the back EMF "issue" was invented to sell speakers with multiple input terminals and more speaker cable. As with many "issues" in HiFi, there's usually a grain of truth somewhere that makes the "issue" seem real. I would be very interested in hearing from someone with a better understanding (theoretical background, not personal opinion) on this issue.Regardless, my recommendation is still to use an amp with a low output impedance.
Speaker drivers are incredibly inefficient. 1 W of acoustic power is a rather large amount of power, so that's probably a good thing.
~Tom
I am not complaining......Wow. You just can't make everybody happy...
...............
That was me voicing my interpretation of what I saw in the plots.
But maybe you need the paper showing the evidence that I am happy, before you believe me.
Both amplifiers are dead quiet, actually. The 1/f noise in the Parallel-86 is slightly higher. Still -120 dBV (20 Hz), -137 dBV floor is very, very quiet for a power amp.
-120 dBV is 1 uV.
-137 dBV is 141 nV.
I haven't had a chance to listen to the PAR86 in detail. It should sound exactly like the Modulus-86, but offer more output power.
~Tom
-120 dBV is 1 uV.
-137 dBV is 141 nV.
I haven't had a chance to listen to the PAR86 in detail. It should sound exactly like the Modulus-86, but offer more output power.
~Tom
@Ben123. When you first look at the plots Tom has put up it may look slightly disappointing, but then you realise that, with std 86dB/W type speakers the second harmonic (which is highest in all the plots) is well below most accepted levels of audibility. The noise floor is way below that so even with hyper efficient horns you should be able to put your ear right up to the driver and pick up nothing.
Yes, the only thing that matters is that you can't hear the bad stuff. Noise in the quiet bits is easy to assess, but you can also hear the distortion occurring at a separate "event" from the recording content - this is something one can learn to do, and then it is quite amazing to hear how much muck is generated on most systems, a constant grunge that never goes away, no matter what's playing. This is actually the signature "sound" that makes it easy for nearly everyone to pick a hifi system, vs. the real thing, even if they don't know how they're doing it for themselves.
Very clean amplifiers like Tom's sorting out makes the job of getting the muck in systems below audibility so much easier ...
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Problem is you link to some fairly random sections of other threads with no coherent description of what you want or why. If you can Sim what you want then you ought to be able to build it yourself too. Right now it really sounds like one of you 'reviewers' is telling you something and you are chasing some rainbow.
Sorry if you cannot understand what those two links are talking about. Can't help there. I was quite obvious to me when they explained it.
I constantly go though lots of information to line up the dots. Also aware that not everyone are interested in doing so. Most would like a 12 course meal and then...
I expect interested people would understand enough to ask specific questions about them.
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Mr. Soong,
I must agree with Bill on this. You have a lot of vague generalities but no specifics. I am not certain why you feel compelled to afflict Mr. Christiansen with your seemingly endless allegations that somehow his design is lacking but yet will not provide any clear and understandable explanation of how/why this is the case. I went to your blog, "Hear the real thing!" and also found it long-winded and lacking in actionable information. I suggest either saying something of substance or finding something else to do. Tom has been more than patient and I feel sorry for him.
I must agree with Bill on this. You have a lot of vague generalities but no specifics. I am not certain why you feel compelled to afflict Mr. Christiansen with your seemingly endless allegations that somehow his design is lacking but yet will not provide any clear and understandable explanation of how/why this is the case. I went to your blog, "Hear the real thing!" and also found it long-winded and lacking in actionable information. I suggest either saying something of substance or finding something else to do. Tom has been more than patient and I feel sorry for him.
BrianL,
Actually I would have not purchased his boards if I thought they were totally worthless. I see great potential in his design capabilities if he is open minded to look beyond just the amplifier. Designing audio equipment is much more involving than one can imagine if you are dedicated to achieve a different level of performance commonly available in the market which generally lack integrated considerations. As of now, it seems that he has no interest in considering integration considerations, so it makes not sense for further discussions technically.
My blog is not intended to provide technical information for free, mainly because most of the issues I consider important are controversial to many, and I have no intention to convince people whom are already satisfied with published information. However, it serves as a log of what happens in the journey. The technical logs are confined because some eventual lead to patents, and some just remain propiatary. You are welcome to question whatever I have posted in this forum, and I will try to answer in a way I feel I can openly do.
The issue about amplifier damping, I have posted relevant links to the kind of data I am looking for. Look forward to seeing it even if they are only sims.
The imput impedance curves, I have asked to see them even before purchasing the boards. Never got to see the data yet.
The above two are the data consider important. Sure, I could also do it when I get the amps up and running. No bid deal. I have done that with the MyRef and found some deficiencies you can also see what I tried and what had changed, especially damping. I think that was specific enough. I do not intent to consolidate the information for others because I have other things to do.
If I do not get any replies to my posts, it is highly unlikely I will post more.
Actually I would have not purchased his boards if I thought they were totally worthless. I see great potential in his design capabilities if he is open minded to look beyond just the amplifier. Designing audio equipment is much more involving than one can imagine if you are dedicated to achieve a different level of performance commonly available in the market which generally lack integrated considerations. As of now, it seems that he has no interest in considering integration considerations, so it makes not sense for further discussions technically.
My blog is not intended to provide technical information for free, mainly because most of the issues I consider important are controversial to many, and I have no intention to convince people whom are already satisfied with published information. However, it serves as a log of what happens in the journey. The technical logs are confined because some eventual lead to patents, and some just remain propiatary. You are welcome to question whatever I have posted in this forum, and I will try to answer in a way I feel I can openly do.
The issue about amplifier damping, I have posted relevant links to the kind of data I am looking for. Look forward to seeing it even if they are only sims.
The imput impedance curves, I have asked to see them even before purchasing the boards. Never got to see the data yet.
The above two are the data consider important. Sure, I could also do it when I get the amps up and running. No bid deal. I have done that with the MyRef and found some deficiencies you can also see what I tried and what had changed, especially damping. I think that was specific enough. I do not intent to consolidate the information for others because I have other things to do.
If I do not get any replies to my posts, it is highly unlikely I will post more.
I don't recall any request for an input impedance plot. I just searched all email on my server for the words "input impedance" and found several, but none from you. It is possible that I missed it, but I rather doubt that. In any event, if the input impedance wasn't up to your satisfaction or you weren't getting a satisfactory answer from me prior to the purchase, I'm a bit surprised you made the purchase anyway.
As a vendor, I will ship to whomever drops money into my Paypal account. I will do whatever I can to provide the customer with the information needed to make an informed purchasing decision. I want my customers to feel confident that they're spending their money wisely.
I deliver a quality product. My business model is to deliver well-designed, well-characterized, well-tested, well-documented, and well-supported precision audio circuits. I back up my designs with tons of documentation and share a lot of it. Vendors that follow this model are very few and far between.
~Tom
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See post #388.
My assessment was that even if it does not turn out acceptable for listening, I could still use it as part of a test and measurement setuo, that is why I got the boards.
I am sure you meant to say that you want to design an active speaker as a 'system', but what you have done is confused good objective design with flooby dust reviewer claptrap. You need to find a 'designer' who buys into your 'tuned by golden ears' philosophy. It worked for the Honda NSX but can't think of any examples of commercial products that have this as their USP.