As I wrote nearly the same in my post, I guess it is safe to assume that we agree?!
Not sure if "political" is the right descriptor, but surely you'll find an equivalent amount of "belief posts" (of the opposite kind) over at ASR as well. As said before, pretending to be an objectivist is much easier than to behave (mainly) as such.
"Incomplete" measurements is nearly always correct but is something very different than "mean nothing due to lack of specification" which was the phrase amirmaj used and which is an incorrect description.
Neither of those statements make sense to me, unless it's operating out of spec.
Before you jump to too many conclusions, JC is looking into the issue. At some point when he's ready he will post about his findings. Maybe he will also explain a little more about the working relationship he has with companies such as Parasound and ifi. John does not call all the shots, nor does he supervise manufacturing.
Last edited:
It is not reasonable to use this condition exclusively, as it doesn't reflect "normal" use of a preamplifier in a home stereophonic music reproduction system.
It should be obvious if you look at typical specifications for gain of power amplifiers, typical sensitivity specs of loudspeakers and the usual reproduction level at home.
This is complete nonsense. Is a cd player "normal"? Redbook CD is 2V out single ended (unbalanced) thus 4V out balanced. All the "normal" stuff I have at home in a "normal" "home stereophonic music reproduction system" is connected to my preamp using balanced outs and xlr cables and is putting out 4v into my preamp. My dac output is (at least) 4V balanced, my cd player output is 4V balanced, my minidsp same. Stop this nonsense, 2V single ended and 4V balanced is standard, Sony/Philips "redbook" specs for the cd medium, issued 1980, specified a "full scale" output for cd players of 2 volts. That would be for unbalanced outputs, and would correspond to 4 volts balanced, as tested in the review.
Pavel,
I though you had tried a diamond circuit? I have some also I tried and they were surprisingly low in distortion for the basic circuit. If I find the measurements I can post them. What did you get?
And yes a modern opamp like the semi-new TI/Burr Brown ones do much better on THD. But the issue always is did your measurements correlate to hearing. My preference has always been to measure IMD, as to me it correlates better then THD and is easier to measure.
ES
OK everybody, not all the tests are in, but yes, this preamp does not like 4V in, and 4V out at 20KHz, or even 10KHz. Why? I am still working on it, but it would appear initially that it is excessive non-linear capacitance, apparently coming from using the complementary differential input stage, rather than a simpler differential n channel only input stage, or better yet, lower input capacitance jets, that might have less Gm, but would lower this distortion, so the trade-off would be slightly more overall distortion (less feedback overall from the lower Gm of the input devices) and if I had to do it over again, I might select the 2sk247-j109 jet combination for both the input stage as well as the input cascade stage as it is already.
Now how important is this? Well it is an engineering embarrassment that was not caught by me, John Atkinson, or the engineers in Taiwan. What a bunch of 'dumb turkeys' we must be!
Oh well, we can't all be 'perfect'.
Now how important is this from an ACTUAL listening situation. Except for having the JC-2 in Bypass mode, not so very much. All Parasound power amps have a gain of 28.2 to match the Holman standard of 1V in = 100W out into 8 ohms, so 2V in is 400W into 8 ohms, and the amplifiers will soon clip with more input. 4V in? No way! Maybe somewhere there is a power amp that is still linear at 4V in, but certainly not one of mine, or anybody else that I can think of (for home use) so don't use this preamp to power a stadium at a rock concert. We have other circuits for that. They may be similar, but they will be driven by lower drive impedances which negates the problem. The higher input impedances of the home use preamps are usually higher (50K or more) to not load down an occasional tube FM tuner or some such. Pro equipment is usually limited to 10K in my former experience. Any exceptions, Ed?
Now how important is this? Well it is an engineering embarrassment that was not caught by me, John Atkinson, or the engineers in Taiwan. What a bunch of 'dumb turkeys' we must be!
Oh well, we can't all be 'perfect'.
Now how important is this from an ACTUAL listening situation. Except for having the JC-2 in Bypass mode, not so very much. All Parasound power amps have a gain of 28.2 to match the Holman standard of 1V in = 100W out into 8 ohms, so 2V in is 400W into 8 ohms, and the amplifiers will soon clip with more input. 4V in? No way! Maybe somewhere there is a power amp that is still linear at 4V in, but certainly not one of mine, or anybody else that I can think of (for home use) so don't use this preamp to power a stadium at a rock concert. We have other circuits for that. They may be similar, but they will be driven by lower drive impedances which negates the problem. The higher input impedances of the home use preamps are usually higher (50K or more) to not load down an occasional tube FM tuner or some such. Pro equipment is usually limited to 10K in my former experience. Any exceptions, Ed?
Ya but she makes me take them out to the driveway if I want to turn them up.
I have two out of six bedrooms taken up by speakers and drivers, and none of what you see in the driveway pic are kept in those rooms. I don't refer to it as a dedication but an addiction.
My name is Cal and I'm a Speakerholic.
Attachments
What is the input resistance on each side in this test? Typically the N and P FET's have very different input C so maybe there should be more seconds than thirds if this is the case?
That's what I suspected. I do have power amps where 4V in is full power out, but I configured them that way (with evil pro audio input chips). Not a good match for an AHB2 in low gain mode but I doubt anyone would try that!
Turntables.I used to keep speakers in the kitchen, but that's due to a shortage of bedrooms
I must have an exremely tolerant other half, 1 in the lounge, 2 in the front room (3rd bedroom) and 1 in our bedroom
The ladder is for when he "sneaks" those big grey jobs up onto the deck. Unbeknownst to wife, 4 of the boards in the railing are removable, and align nicely with the vertical ports!
Wouldnt want to effect that reflex tuning with a board blocking the port, now would we
The bedroom turntable was veto'd so I just have 2 in the lounge and 4 in the shedTurntables.
I must have an exremely tolerant other half, 1 in the lounge, 2 in the front room (3rd bedroom) and 1 in our bedroom
I dare not ask why Cal has what looks like a pair of stadium Subs in his garage.
