We want measurements!
The reported distortion spec is .01% either harmonic or IM at 3V out (balanced). Actually, single ended is closer to 1V out for the same spec. because some of the residual second harmonic is not cancelled, unless you use both outputs together. This is where I set my test equipment when measuring them. It is nothing special in low distortion, except for the lack of higher order distortion components. Such as 7th, 9th. There may be a little 5th at voltages over 3V, but it will be very low, below 100dB.
My JC-80 preamplifier will measure significantly better, but then it is designed with the similar components and has negative feedback. I have no way to post any measurements.
Now why am I so non-concerned about having a set of extensive measurements?
Well, with a class A circuit, running open loop, I know that I can predict the amount of distortion at any level within clipping, if I know the distortion at one output and the order of its harmonic components.
My JC-80 preamplifier will measure significantly better, but then it is designed with the similar components and has negative feedback. I have no way to post any measurements.
Now why am I so non-concerned about having a set of extensive measurements?
Well, with a class A circuit, running open loop, I know that I can predict the amount of distortion at any level within clipping, if I know the distortion at one output and the order of its harmonic components.
Dear Mr Curl:
Thank you very much! It does take a lot to get you started but I see now that it's been worth the trouble. Measurements come to those who wait.
Now, let us proceed in the same spirit of cooperation and goodwill, shall we?
In view of the recent objections to your internal wiring approach, I'd like to know whether you tested channel crosstalk and with what results. Also, did you spot any difference in measurements for different phase switcher positions?
Regards,
Milan
Thank you very much! It does take a lot to get you started but I see now that it's been worth the trouble. Measurements come to those who wait.
Now, let us proceed in the same spirit of cooperation and goodwill, shall we?
In view of the recent objections to your internal wiring approach, I'd like to know whether you tested channel crosstalk and with what results. Also, did you spot any difference in measurements for different phase switcher positions?
Regards,
Milan
Dear Mr Curl,
Please excuse my forgetfullness but I do have a couple more questions, which I hope haven't been answered earlier.
I find it quite curious that the BT control pots are on the left side of the front panel and source switcher on the right. Is there any technical reason for such an unorthodox implementation? Also, how come the rear panel has the RCA connectors for the right channel on top of the left channel (and not the other way round)? In short, why is your preamp upside down?
Regards,
Milan
Please excuse my forgetfullness but I do have a couple more questions, which I hope haven't been answered earlier.
I find it quite curious that the BT control pots are on the left side of the front panel and source switcher on the right. Is there any technical reason for such an unorthodox implementation? Also, how come the rear panel has the RCA connectors for the right channel on top of the left channel (and not the other way round)? In short, why is your preamp upside down?
Regards,
Milan
You guys have one of preeminent three?, four? high-end solid state designers of last twenty five years willing to field questions and you ask for crosstalk measurements or why the right inputs are above the left? Wacky. How about:
- How much effort do you expend optimizing circuit and layout for considerations above the audio band? At RF frequencies? Power line RF rejection?
- At what point in a design do you consider the measurements 'good enough' to serve as a jumping off point for development by ear?
- What's the balance of design effort between achieving a low numerical THD and reducing higher harmonic components? How much 2nd harmonic is too much?
- The balance of effort between power supply and audio circuit design?
- Are there topologies you find yield consistent quality results or is all "horses for courses"?
Try to weasel the real dirt! Mr. Curl can spout meter reading all day and it won't provide a single nugget of design gold relevant to bettering our projects.
- How much effort do you expend optimizing circuit and layout for considerations above the audio band? At RF frequencies? Power line RF rejection?
- At what point in a design do you consider the measurements 'good enough' to serve as a jumping off point for development by ear?
- What's the balance of design effort between achieving a low numerical THD and reducing higher harmonic components? How much 2nd harmonic is too much?
- The balance of effort between power supply and audio circuit design?
- Are there topologies you find yield consistent quality results or is all "horses for courses"?
Try to weasel the real dirt! Mr. Curl can spout meter reading all day and it won't provide a single nugget of design gold relevant to bettering our projects.
rdf said:
I'm sorry to disappoint you but I prefer sticking to the point of this thread, which is the Blowtorch design and not "Ask Jeeves". Anyways, I believe many of the questions you are asking have already been covered in these 100+ pages.
I'm sorry if you are under the impression that I am trying to weasel dirt from John. I'm just asking questions which truly interest me for my own selfish reasons. Others will have to ask their own questions and dig their own gold, including you.
Regards,
Milan
P.S. My system is only 28300W ERP but covers millions.
moamps said:
There are quite a few British designs that are made that way. Here's just one example:
An externally hosted image should be here but it was not working when we last tested it.
It is probably not that much a matter of convenience, but daring to be different
Then again, the Brits do a lot of things on the wrong side.
Somehow I am not convinced that John was daring to be different.
It's logical that input connectors on the rear panel are on the same side as the input selector on the front panel (that is, in parallel), which is what John did (if he was the one who did it), so I expected an explanation from him more along these lines.
Regards,
Milan
Somehow I am not convinced that John was daring to be different.
It's logical that input connectors on the rear panel are on the same side as the input selector on the front panel (that is, in parallel), which is what John did (if he was the one who did it), so I expected an explanation from him more along these lines.
Regards,
Milan
moamps said:
I agree, not "Ask Jeeves". "Ask John". For me it's odd that fundamental questions of design goals were at best alluded to in off-hand one liners which were never followed up. And yes, I did just scan 1000+ posts.
Ton's of great information on implementation specific to solid state but so little on the larger targets and goals in the design process of the Blowtorch. A few tantalizing tidbits regarding feedback vs. none, a word or two about the relative impact of 2nd and 3rd harmonic distortion components, somewhere a post about the difference between designing for low distortion in a signal generator vs. good audible performance, and one very, very interesting and not a little short-tempered rejoinder about not designing for 'a sound'. Plus of course the hundreds of shots from the usual cast of skeptical curmudgeons making for an incredibly high signal-to-noise ratio. So far almost exclusively means with no ends. You're also correct that everyone pursues their own answers, which in my case are best summed up by this post by Mr. Curl: http://www.diyaudio.com/forums/showthread.php?postid=903774#post903774. Speaking only for myself, I'm way more curious about "the 'reality' of making a good sounding circuit" than knob orientation (upside down model for Australian export?).
Hi, Rdf
Moamps point was not about illogical placement of commands, but rather their actual placement that makes some air wires travel longer this way, with chances of picking radio frequencies far easier...
John explained that the air surround on separate wires was far better that braided cables in the Blowtorch case... Agree, but only if the whole case acts like a REAL Faraday cage, or air wires would love acting like antennas... So, it's perhaps the reason for this massive case.
Love too Rolv-Karsten "vacuum case" idea... Somewhat hard to build, but interesting idea though
Jbaudiophile
Moamps point was not about illogical placement of commands, but rather their actual placement that makes some air wires travel longer this way, with chances of picking radio frequencies far easier...
John explained that the air surround on separate wires was far better that braided cables in the Blowtorch case... Agree, but only if the whole case acts like a REAL Faraday cage, or air wires would love acting like antennas... So, it's perhaps the reason for this massive case.
Love too Rolv-Karsten "vacuum case" idea... Somewhat hard to build, but interesting idea though
Jbaudiophile
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