I did use real numbers. It's trivial to show (as I did before) that with a 1mm displacement of the stylus at 2Hz, the output is a microvolt or three. Translate that to dBu- remember, a magnetic cartridge is a velocity sensor.
OK, what output do you measure from an MC at 2Hz with a warp? Or distortion from a 1:10 (or 1:12 in the case of the Jensen) stepup transformer at 2Hz/1uV input?
Seriously, this is simple first order analysis. If it's annoying to you because it forces John to deal with reality rather than handwaves, I can't help that.
SY -- You are missing the point, perhaps or there is this point ---- one microvolt it may be or more. Multiply that by 40-60-80+db phono gain at low freqs and you have a millivolt of output to the line stage (another X10). That low freq stuff is there all the time - unless the TT isnt rotating. Its background noise which is constant --- from warp, rumble and actual LP surface irregularities.... noise you would get from a "silent" groove. A constant 10mV of LF noise. use your own dB's but given the additional power amp gain and speaker sensitivity, it is a real live issue.
And, what does this have to do with MC transformers or balanced circuits? How do you handle those LF junk signals best? And, if not handled, what are the audible consequences down line - the whole system is affected in various ways with these sub-sonic signals.
Thx-RNMarsh
And, what does this have to do with MC transformers or balanced circuits? How do you handle those LF junk signals best? And, if not handled, what are the audible consequences down line - the whole system is affected in various ways with these sub-sonic signals.
Thx-RNMarsh
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Is this discussion about how much distortion of a 1/2 hz signal? Or is it about that signal causing distortion of the audible portion?
My amps generally strip dc out via the feedback loop LP.
jn
Its about distortion and where it comes from and how JC deals with it... or how others deal with it.
And, we start with the signal source itself.
Preventing emi/rfi and hum and IM generated by unwanted freqs is all part of the signal source issue.
[your servo in the pwer amp or LP filter is another issue all by itself and how low the 'dc' servo or Lp filter cutoff is vs unwanted freqs getting into the signal source]
Thx-RNMarsh
And, we start with the signal source itself.
Preventing emi/rfi and hum and IM generated by unwanted freqs is all part of the signal source issue.
[your servo in the pwer amp or LP filter is another issue all by itself and how low the 'dc' servo or Lp filter cutoff is vs unwanted freqs getting into the signal source]
Thx-RNMarsh
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John was just talking about distortion from the input transformer. That's a microvolt or two of signal at subsonics because of the velocity characteristic of the cartridge. If you're concerned about what else the preamp does, that's absolutely valid, but whether the first gain block is a pair of coils is irrelevant, it's what happens downstream that's the killer.
Indeed true- to generate that microvolt of subsonics, the cartridge has to be undergoing severe stress.
I got a copy from Old Colony. Jesse Klapholtz had them reprinted from a pristine copy he borrowed from Mark Gander. So you can get a newly printed version for less than the cost of a used book. Still contains an error or two, if you do get it let me know and I will look up the corrections.
I know. But the question is, how does an input transformer deal with 1uV of half hz signal? I wouldn't worry about distortion of the 1/2 hz signal at all, but moreso what happens if it causes the ac signal to ride up the BH curve sufficiently to cause distortion of real audio.
Extrapolation of distortion below 1-2hz by curve fitting is inherently unreasonable, as the 1000 percent distortion question raises. Reminds me of the ultraviolet catastrophe.
jn
I understood and still do -both JC and you. But i know where this is going.... you might also. hell the phono cartridge produces sooo much distortion at best,.... the rest is insult to injury anyway...
[toss the Edison's (?) LP concept and join the 21st century. But, thats just my opinion and not really important re phono preamps.]
Thx-RNMarsh
Couldn't agree more. The design problems are still interesting, though, once the clutter is cleared away.
AP did a nice job with uV signals low distortion and a Jensen transformer. Of course this was on the generator side but we still use it to measure uv sweeps on phono stages. Some of the transformers are pretty good but I still prefer not to use one but that is just my choice.
SY you made a very good point about cartridge output when you think of low level music playing VS rated output. While I DC couple I still prefer to use the RIAA HP filter it keeps out more than record warp.
SY you made a very good point about cartridge output when you think of low level music playing VS rated output. While I DC couple I still prefer to use the RIAA HP filter it keeps out more than record warp.
If you include the transformer in the feedback loop it can be very low distortion. A-P doesnt just plunck down a transformer in series the way we do in MC phono amps.
However, The TT/LP record's extraneous ouput to/from the cartridge.... what are the numbers and frequencies produced by IM and THD products and what are thier levels is relevent. The preamp has to handle them well without causing additional distortion from them [as does the whole system]. Balanced source input doesnt address this as well as it addresses common-mode signals.
Thx-RNMarsh
However, The TT/LP record's extraneous ouput to/from the cartridge.... what are the numbers and frequencies produced by IM and THD products and what are thier levels is relevent. The preamp has to handle them well without causing additional distortion from them [as does the whole system]. Balanced source input doesnt address this as well as it addresses common-mode signals.
Thx-RNMarsh
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It also doesn't cure cancer or increase gas mileage. That's not its purpose- its purpose is to reduce common mode noise. if you get some basically noise free gain out of it, even better.
The CMR rejection is fine -- do it with ss or transformers. But the other issues i bring up are harder to ielliminate from the LP/cart and to deal with without more unwanted side-effects. lets move on OK? JC deserves to be able tocomplete- fully- his explaination/totorial about his circuitry and why he went that ss route instead.... maybe it's total purpose will unfold.
Thx-RNMarsh
Thx-RNMarsh
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Absolutely. These are issues that are indeed best to eliminate at the LP/cartridge end of the chain.
What I'm hoping for in the technical exposition of phono stage design is technical accuracy and solid arguments about design choices- and when those choices are driven by market perceptions rather than engineering, an acknowledgement of that. I know, that's nutty-talk.
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