I don't mean to belittle lead free soldering, BUT I suspect that the REASON that techs suddenly do a better soldering job, is that MORE attention is paid to it.
Let me give an example from 80 years ago. At a major American company, a time-motion study was conducted. No matter how much light, or lack of it, etc, etc, the employees just produced faster and faster. It drove everybody nuts, until it was realized that the employees were being paid attention to by management, etc, and performed to please.
Unfortunately, lead free soldering MIGHT give real problems over time, and only TIME will tell for each and every changeover.
Let me give an example from 80 years ago. At a major American company, a time-motion study was conducted. No matter how much light, or lack of it, etc, etc, the employees just produced faster and faster. It drove everybody nuts, until it was realized that the employees were being paid attention to by management, etc, and performed to please.
Unfortunately, lead free soldering MIGHT give real problems over time, and only TIME will tell for each and every changeover.
Re: sorry for OT
I don't know where your info comes from but there are almost certainly many reasons for the military exemption. The two most highly rated are industry inertia (most kit is designed years before putting into service) and an acceptance that by comparison to domestic and commercial the volume is tiny.
I am aware of more than one industry funded "study" in the USA that have attempted to rubbish the RoHS directive and spread FUD about lead free, but they are not accepted in Eurpore. The far east IS building lead free to enable it to sell into Europe. The main "study" I came accross was a scare about "whiskers" growing on solder joints but that hasn't seemed to come true so far...
The original article is at http://www.sigcon.com/Pubs/news/10_01.htm
Curious about the dates here because the article about the power station shutdown is dated 4th July 2005. We weren't under the directive until 1st July 2006 so how/why was the board made with lead free solder anyway?
I don't know where your info comes from but there are almost certainly many reasons for the military exemption. The two most highly rated are industry inertia (most kit is designed years before putting into service) and an acceptance that by comparison to domestic and commercial the volume is tiny.
I am aware of more than one industry funded "study" in the USA that have attempted to rubbish the RoHS directive and spread FUD about lead free, but they are not accepted in Eurpore. The far east IS building lead free to enable it to sell into Europe. The main "study" I came accross was a scare about "whiskers" growing on solder joints but that hasn't seemed to come true so far...
The original article is at http://www.sigcon.com/Pubs/news/10_01.htm
Curious about the dates here because the article about the power station shutdown is dated 4th July 2005. We weren't under the directive until 1st July 2006 so how/why was the board made with lead free solder anyway?
john curl said:
Hi John,
You asked about how the JC-1 might be experiencing gm doubling, so I answered it.
It occurred to me that a coherent explanation of gm doubling and the influences on it might be helpful educationally to the other readers.
Or are you the only one licensed to educate on this thread?
As usual, your response is to evade and distract.
I was originally tempted to reply to your original post by asking you if your really knew anything about gm doubling, but I decided it would be better for all if I just played it straight and explained it in a very neutral way.
Regardless of your impolite response to it, I hope that at least a few others profited from the explanation. If you disagree with any part of the explanation, please chime in.
Bob
Bob Cordell said:
Where are these figures coming from and is anyone giving them any thought?
The JC-1 is a monoblock with +/-90V rails and 9 output pairs, right?
90*((9*2)*0.15)) = 243W idle dissipation (fn hot) Does this amp really run that hot?
I have a vague recollection that JC once claimed they were 0.33 or 0.39 ohms.
Cheers,
Glen
EDIT:
I just looked up the specs:
http://www.gspr.com/parasound/h_jc1.html
The amp has a "high / low" bias current switch for 10W class A / 8 ohms or 25W class A / 8 ohm.
It would make sense that the emitter resistors are 0.33 or 0.39 ohms for the 10W "low" bias setting for close to optimal bias, with significant over bias and gm doubling in the "high" bias mode.
Can't comment on the JC-1 but my 2 HCA-3500s (8 pairs per channel) run:
(8*2*90*0.15)/channel * 2 channels/amplifier * 2 amplifiers = 864W
0.15 ohm emitter resistors
I heat tacos on one, frijoles on the other.
(8*2*90*0.15)/channel * 2 channels/amplifier * 2 amplifiers = 864W
0.15 ohm emitter resistors
I heat tacos on one, frijoles on the other.
G.Kleinschmidt said:
Hi Glen,
The emitter resistors in the JC-1 are 0.15 ohm in either bias setting. The high/low bias switch just switches in a different Vbe multiplier.
Bob
Bob Cordell said:
That sounds very odd to me. 10W into 8 ohms = 12.6V peak.
So, 1.575A peak.
For class A operation to 10W/8 ohms bias would have to be 0.78A, or ~87mA per device.
87mA * 0.15 ohms = 13mV.
That would be a significantly under biased condition, would you agree?
Cheers,
Glen
PH104 said:
OK, I was not aware that they ran this warm.
Have you tried the "last nights spicy taco" tweak?You never know, it might work. 😱
Cheers,
Glen
These are modifed 3500's. The stock amps had 0.22 ohm emitter resistors and an auto-bias control that dropped the output idle current when no signal was presented to the amp. The auto-bias thing is gone. I never measured the factory idle current.
The spicy taco tweak is especially defecatory when applied to the power transformers.
The spicy taco tweak is especially defecatory when applied to the power transformers.
john curl said:
Not sure what you are getting at here.
So does your amp run "optimal" bias on the low setting, or on the high setting?
If the emitter resistors are 0.15 ohms as everybody says, then it must be on the high setting.
Cheers,
Glen
Sorry, Glen, but we just could not afford an 18 pole 15A switch or set of relays. I had to compromise, AND the low current setting is just as optimum or better than the high current setting, because there is NO optimum number for biasing, just re/2 to re. Study first, challenge the professor, later. Bob almost had me by the 'short hairs', but you don't.
scott wurcer said:
Well, I understand what you are saying and I understand that Dr. Geddes (not Mr...) 😉 draws the conclusions that he does.
Not sure that THD at max power is ever "low" , but maybe right before max power it still might be... but whatever.
And actually, if there is low level distortion(s) (crossover distortions?) of a certain level, are they not present at the same absolute level regardless of the level of the signal? (less as a %)Yes you say, but they are masked by the louder signal. But... are they really masked in a very low distortion (other than that) system?
And, if masked by the louder level, and not heard, do we really need to get a big S/N ratio out of much of anything in a real world audio system - especially the power amp?? Why do we bother with sophisticated voltage regulation and care about PSRR then?
I doubt that Dr. Geddes work is dispositive of the issue in totality.
The key elements that his AES paper seems to point out is that the absolute level of distortion does not correlate to perceived distortion. He does talk about higher order distortion being "not masked" and therefore audible under certain conditions. The conditions under which this occurs that he outlines are complex (via the Volterra expansions) but that doesn't change those underlying premises. The spectrum of distortion is a factor here, andy_c, but as a complex function - the GedLee Metric. Call it what you will...
We can discuss and debate the applicability or the completeness of this work if you wish. I think that it is sufficient to note the basic "trend" of correlations that Dr. Geddes work points to, and how it differs from the classic view of distortion & perception being amplitude related directly.
I didn't read yet about his methodology for generating his audio "test files" but it sounds from your description scott, that there might be some issue with the way it was done?
As far as there being some threshold like the 0.01% (?) below which all distortions are inaudible, I doubt that... but the more important finding is perhaps that very very high levels of distortions can be completely inaudible under the right conditions! Now that is surprising!
Is everyone here onboard with that conclusion??
What's even more surprising is that Dr. Geddes appears to be "in" with both the "1st watt club" as well as the "soft clip" club as well! SE toobers anyone? (SY?)
_-_-bear
PS. Just wondering scott, or anyone else for that matter, why do you bother designing opamps, amps or whatever with ever lower levels of distortions, if you buy into the idea that below some modest absolute level of distortion(s) everything is inaudible? Where the heck is that threshold exactly??
PPS. I'm not trying to pick a fight, I really want to know why anyone would bother if they really think they can't hear it (ever).
john curl said:
I have no intention of getting anywhere near your "short hairs". Are you capable of answering straightforward questions without so much bull?
Assuming 0.15 ohm emitter resistors, with 90V rails the "low" setting seems far from "optimum" to me.
Cheers,
Glen
It is RIGHT ON! Do some calculations using Cordell's analysis. Do it! Then we can talk about it.
bear said:
No, the really surprising bit is that he doesn't actually believe in burning in the wires, unobtanium teflon on ancient French silver capacitors or orienting the resistors for best sound.
His amp of choice is 200$ Pioneer. And cheap Toshiba CD player as source.
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