OK, .001 W is at least above typical DC offset. I am not buying a millionth of a watt for a second. We are talking a signal delivered to a speaker at that level, not the difference between signals or some ultra cold sensor output.
Brad, I had not heard that description of noise in a tube amp, and maybe it is the tube amps I have, but have not heard the effect either.
Brad, I had not heard that description of noise in a tube amp, and maybe it is the tube amps I have, but have not heard the effect either.
Even with the bit of detail the results stated are absurd on the face of it. 1 mW referred to an 8 ohm load is still quite a healthy voltage (about 89.4mV rms), yet the claim is made that the Halcro has 8.9% distortion at this output power. Based on the noise levels measured for the amplifier, this would be very easy to see on an oscilloscope, without any need for signal averaging!
Either there are some serious typos or something very strange is going on. I disbelieve those results.
Another thing that smacks of marketing: the expressions in the form of fractions: "1/1000" and so forth. Reminds me of the soap ads that touted "Ninety-nine and forty-four one-hundredths percent pure" (Gee! Isn't that pure enough for just about ANYONE???)
Either there are some serious typos or something very strange is going on. I disbelieve those results.
Another thing that smacks of marketing: the expressions in the form of fractions: "1/1000" and so forth. Reminds me of the soap ads that touted "Ninety-nine and forty-four one-hundredths percent pure" (Gee! Isn't that pure enough for just about ANYONE???)
I seem to recall it was in an interview of Keith Johnson in The Abso!ute Sound, many years ago, but I could be mistaken. I do recall he remarked about the large number of charge carriers involved in a tube versus silicon devices.
As to the microwatt claim: JA states that for the DM58 he saw 82.8dB signal-to-noise ratio at 2.83V rms out, "unweighted", which I've concluded over the years means in an 80kHz bandwidth. The A-weighted number given is 96.8dB below the same signal.
82.8dB below 2.83V is 205uV. A microwatt referred to 8 ohms is 2.83mV. Although signal averaging would be helpful here, with just a little lowpass filtering I'll bet one could still easily see 8.9% distortion in a 1kHz sinusoid on a 'scope. And his discussion implies that the distortion would be expected to be still worse, due to whatever curious phenomena are accounting for the extraordinary rise going to a milliwatt.
Piscine in the extreme.
Steve may respond . i sent him an email , so less be friendly , err. ahh, Best to warn T, Huh ...
I had a similar conversation with Mr Audio Note some 15 + yrs ago and he was of the same mindset , that first watt got all of his focus ...
If it's the B&K test equipment I remember, some of it used to be quite decent and very utilitarian, as if designed by working technicians, and as well affordable for the most part. I'm sorry to hear they went out of biz.
PS: In fact come to think of it, I still use a BK Precision 875A LCR meter, and it's been quite adequate. I preferred the model that had a zero adjust but I think I gave that up when the family biz went broke.
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If it's the B&K test equipment I remember, some of it used to be quite decent and very utilitarian, as if designed by working technicians, and as well affordable for the most part. I'm sorry to hear they went out of biz.
NO , it's B&K audio .... They made amplifiers , et al .......
Not Following you Brad, 2.83 V @ * is 1 watt ... No ..?
Yep ---what do you find discrepant? The claim is 8.9% distortion (excluding noise as I read him) at a milliwatt, unspecified (but presumably larger) at 1 uW, again excluding noise.
I had a similar conversation with Mr Audio Note some 15 + yrs ago and he was of the same mindset , that first watt got all of his focus ...
You have to take inflation into account.
1mW is -50dB wrt full output of a typical 100W amplifier. Not particularly low level - D/A converter chips are normally characterized at -60dB wrt FS.
Unless he's not telling us something vital, its hardly 'unprecdented' to measure THD at -60dB for DACs, so what makes it so for amps?
Conventional test equipment in the world of audio means AP, that has had this capability ever since the dual domain AP1 which is a couple of decades old now. The DAC manufacturers routinely use AP to show the distortion performance of their chips (with -60dBFS stimulus signal) down to -140dB or so.
That does sound like an astonishingly poor result. The Halcro is nominally 200W so 1mW is -53dB and the THD is around -74dB?
Stereophile shows the performance at 157W output, its noise-dominated at 0.0006%. Its jolly hard to believe therefore that the stated 0.007% @ 2W is correct as it would imply that the distortion harmonics rise as the stimulus goes down in level. Even relatively poor digital systems manage to keep them roughly the same under those conditions.What am I missing?
Strange goings on. I get their main page now, but last time I got an advertising redirect when I clicked on the link on the audiogone profile.
The link for details to Virtual dynamics is dead. Last update on Luminance was 2 years ago.
He measured the associated VOLTAGE dB with those power levels, not the actual POWER dB. Do you know of any THD measurement device that deals with POWER directly?
That makes for the 1mW/200W ratio -106dB, not -53dB...
Those "digital systems" don't have a class AB output stage that generates cross-over distortions at low levels:
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Amp tests are done into a resistive load. Thus knowing the voltage we can infer the power.
Only if you were asleep during EE class. Power ratios are always 10log, voltage ratios 20log.
Like I already said (even you prefer to ignore it) probably he didn't measured power, he measured voltage. What tool would you use to measure directly the THD for POWER?
So when he said 1mW he measured the associated voltage on a specific load. 11.19mV on 8 ohm. Didn't measure the current too.
Sure, not correct in verbiage... but offers an explanation of his results.
So when he said 1mW he measured the associated voltage on a specific load. 11.19mV on 8 ohm. Didn't measure the current too.
Sure, not correct in verbiage... but offers an explanation of his results.
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I doubt that it is class AB transitional distortion. Even Self (who defines his class B in a somewhat funny way) allows for some quiescent current at 0 volts out. And you don't need much. The objection (as you all know) to "rich" class AB is that the transconductance of the (typically) emitter followers transition to what is typically a lower value as the one device turns off completely at a certain signal voltage. No, I'm pretty sure John Halcro Candy had this under control, whether you like how his amps sound or not.
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