John and Christophe,
I understand why you want to have a very wide bandwidth preamplifier and amplifier stage, but why would you want to allow through such high frequency noise? Even if you determine the 3db down point at let's say 24Khz wouldn't the upper frequency filter be lower than the upper limit of the cartridge output? Isn't the RIAA curve much lower than even the 24khz range on a vinyl album? I know I may be being lame here, but it just seems that this would be equivalent to allowing high frequency RF through a circuit for no practical acoustical gain?
I understand why you want to have a very wide bandwidth preamplifier and amplifier stage, but why would you want to allow through such high frequency noise? Even if you determine the 3db down point at let's say 24Khz wouldn't the upper frequency filter be lower than the upper limit of the cartridge output? Isn't the RIAA curve much lower than even the 24khz range on a vinyl album? I know I may be being lame here, but it just seems that this would be equivalent to allowing high frequency RF through a circuit for no practical acoustical gain?
Much, if not all, of it is comprised of the resonances that MCs are prone to, exacerbated by the mistracking to which John alluded. Look at some square wave responses of popular models- the ringing is extremely high in amplitude. You're losing nothing by getting rid of it early, unless you've got a record made using mikes, preamps, recorders, and cutters with 100kHz+ response. I don't think there's many of them...
The very best cartridges I've heard were MMs with extremely low tip mass and well-controlled resonances, as well as low DCR and inductance.
Thanks Sy,
That is what I was thinking. Leaving noise in for no apparent gain in sound quality and the problems that this could cause driving such high frequency noise seemed like a perfect reason to filter out the excess high frequencies which I assume are not related to the original pressing of the album but are mechanical in nature and not correlated to the music. Unless you really do want to listen to the sound of dust and scratches!
That is what I was thinking. Leaving noise in for no apparent gain in sound quality and the problems that this could cause driving such high frequency noise seemed like a perfect reason to filter out the excess high frequencies which I assume are not related to the original pressing of the album but are mechanical in nature and not correlated to the music. Unless you really do want to listen to the sound of dust and scratches!
Toole's bit of early work on subjective evaluation of cartridges showed a null result at best for the MC cartridges that the panelists were dead certain they preferred to MM. All vestige of preference went away and even reversed towards MM when some flattening EQ was applied. Of course the panelists were appalled and blamed the electronics.
I hope I can persuade him to publish these data again. They appeared in a series of articles in a quasi-popular Canadian audio magazine many years ago. FT is now so down on LP and beyond that two-channel that it's a bit of an uphill task. He recently gave me a few feet of his last LPs which he was retaining just out of sentiment, having long ago gotten rid of playback equipment. I was most grateful: test records, direct-to-disks, spoken word, a lot of nice stuff and with very few exceptions little-played and well cared for.
I hope I can persuade him to publish these data again. They appeared in a series of articles in a quasi-popular Canadian audio magazine many years ago. FT is now so down on LP and beyond that two-channel that it's a bit of an uphill task. He recently gave me a few feet of his last LPs which he was retaining just out of sentiment, having long ago gotten rid of playback equipment. I was most grateful: test records, direct-to-disks, spoken word, a lot of nice stuff and with very few exceptions little-played and well cared for.
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After the earlier discussion and disagreement about whether to cut all the response of a digital source above 16Khz, though I did not agree with that, why would you want to allow through any frequencies from 40 to 200Khz from a moving coil pickup just seems to be more than pushing the envelope here! Are we trying to call bats or what? Wouldn't this just take your super wide bandwidth devices and make an untenable situation? Seems like it would take all the slew rate you could throw at it and eat it all up. This surely must make the feedback network work overtime to keep the distortion down.
Partly true. The severe overshoot and ringing is usually from the cartridge, the ripply stuff on top is from the cutter-head. You can demonstrate this by comparing the same record at 33 and 45- the cartridge resonance doesn't change frequency, the cutter-head ringing does.
Audio used to show square wave traces in their reviews- very useful for gauging how well controlled the cartridge's resonances were. Likewise, if you read Stereophile's review of the Technics EPC100C Mk4 (rated A), the reviewer describes how it was selected by a very smart fellow just from looking at photos of square waves published in (I think) HFNRR.
Audio used to show square wave traces in their reviews- very useful for gauging how well controlled the cartridge's resonances were. Likewise, if you read Stereophile's review of the Technics EPC100C Mk4 (rated A), the reviewer describes how it was selected by a very smart fellow just from looking at photos of square waves published in (I think) HFNRR.
Kindhornman, the idea to try to set fast amps, is not to reproduce signals higher than the ear bandwidth, it is to allow the amp to reproduce the bandwidth well.
It looks stupid, but my horn decrease after 16Khz, however i can listen the difference between an amp of 200V/µs and the same, once modified to current feedback up to 1000V/µs. The result is not more treble, on the contrary. The first thing you notice is the improvements of the basses, drier, more detailed. It seem even you lose some treble, but when you listen more carefully, they are just more fluent, less harsh, more natural.
The only measurable change in the amp bandwidth is between 1 to 8 Mhz.
It looks stupid, but my horn decrease after 16Khz, however i can listen the difference between an amp of 200V/µs and the same, once modified to current feedback up to 1000V/µs. The result is not more treble, on the contrary. The first thing you notice is the improvements of the basses, drier, more detailed. It seem even you lose some treble, but when you listen more carefully, they are just more fluent, less harsh, more natural.
The only measurable change in the amp bandwidth is between 1 to 8 Mhz.
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Christophe,
I understand the reason for the bandwidth and the slew rate in the amplifiers, I was just curious why you would really want to leave all the noise from the cartridge going into the preamp in the first place if it doesn't add anything to the audio band we are listening to? That is why I made the reference to Rf and here the extended bandwidth that John showed was coming off the moving coil cartridge. It just seemed logical to cut this hash before you try to amplify a signal that isn't something I would think that an engineer would intentionally try to put down on a vinyl album.
I understand the reason for the bandwidth and the slew rate in the amplifiers, I was just curious why you would really want to leave all the noise from the cartridge going into the preamp in the first place if it doesn't add anything to the audio band we are listening to? That is why I made the reference to Rf and here the extended bandwidth that John showed was coming off the moving coil cartridge. It just seemed logical to cut this hash before you try to amplify a signal that isn't something I would think that an engineer would intentionally try to put down on a vinyl album.
Kindhornman, OF COURSE it would be better not to have a lot of extra ultrasonic garbage, but it is NOT EASY to remove it without effecting the in-band frequency response and phase. Now I realize that many here who are used to extreme high frequency cut-off due to listening to digital and even FM radio, but extended response can still sound better, IF the following equipment can process it and gently filter it, if necessary.
Let me give an example: Let's say you have a MC phono cartridge with a 10 ohm resistance. It would take about 0.5uF to load the cartridge to -3dB at about 30kHz, and -1dB at about 15kHz. See what I mean? It would take 2.5uF loading for a typical Ortofon cartridge.
It is better to handle the higher frequencies effectively, using high speed circuitry, then not go crazy to keep the ultrasonic bandwidth extended, by gently rolling off each following stage of gain. This gives best transient response.
For the record, the CBS test record that is used for square wave analysis has about a 40KHz ring on it, so IF you can't see the ringing, your cartridge is already rolled off internally. This is easy with MM cartridges. Also, the ORIGINAL test waveform is actually a TRIANGLE WAVE that is DIFFERENTIATED by the phono cartridge, you know dV/dT, to create a square wave. Differentiation will exaggerate the ringing, but it will mostly go away with RIAA EQ that is necessary before you can listen to a real audio signal.
Let me give an example: Let's say you have a MC phono cartridge with a 10 ohm resistance. It would take about 0.5uF to load the cartridge to -3dB at about 30kHz, and -1dB at about 15kHz. See what I mean? It would take 2.5uF loading for a typical Ortofon cartridge.
It is better to handle the higher frequencies effectively, using high speed circuitry, then not go crazy to keep the ultrasonic bandwidth extended, by gently rolling off each following stage of gain. This gives best transient response.
For the record, the CBS test record that is used for square wave analysis has about a 40KHz ring on it, so IF you can't see the ringing, your cartridge is already rolled off internally. This is easy with MM cartridges. Also, the ORIGINAL test waveform is actually a TRIANGLE WAVE that is DIFFERENTIATED by the phono cartridge, you know dV/dT, to create a square wave. Differentiation will exaggerate the ringing, but it will mostly go away with RIAA EQ that is necessary before you can listen to a real audio signal.
Try my square wave two speed trick- you'll be surprised. I'll try to dig up and post some scope photos to illustrate this point.
We use the term slew rate in audio pretty loosely, and I sometimes wonder if we're allowing enough daylight between it and in-band performance. After all, slew rate is a limiting condition, like full squared wave clipping, and doesn't have a *direct* correlation with small signal performance. The best we can say about it as a quality factor is that there's *usually* lower high frequency distortion in higher slew rate amplifiers. But:
An example of low slew rate amplifiers with potentially low high frequency distortion are valve-based designs. An example of high slew rate amplifiers with high high frequency distortion are type LF357.
Thanks,
Chris
An example of low slew rate amplifiers with potentially low high frequency distortion are valve-based designs. An example of high slew rate amplifiers with high high frequency distortion are type LF357.
Thanks,
Chris
There are different definitions of slew rate. The "Audio" one is for the input stage in saturation state, gived good numbers and ignores the recovery time. Another definition used where accuracy is an issue, is something like "3% distortion amplitude and frequency". The point is that at that amplitude and frequency the control of the output has degraded to an unacceptable level. This can easily be 10X slower than the marketing number.
Vacuum tubes may or may not have significant TIM. It takes a lot of feedback to force many amps into slew rate limiting. This is why the very idea that the CTC Blowtorch can have any slew rate limiting is absurd, because it doesn't have ANY loop feedback. Tubes are usually limited to 20dB, so they do not behave exactly like op amps.
It is IMPORTANT to note the difference between rise-time and slew-rate limiting. One rolls off higher order harmonics, and the other, slew-rate limiting, generates harmonics.
It is IMPORTANT to note the difference between rise-time and slew-rate limiting. One rolls off higher order harmonics, and the other, slew-rate limiting, generates harmonics.
For a traditional LTP input amp, the HF distortion comes up a long way before the slew rate is reached - as Demian points out. But is this also true for other architectures - thinking here about CFB and Barrie Gilbert's AFA? I'm just wondering out loud whether the marketing number's 'reality factor' is actually different between architectures - my gut is telling me yes, but I have no feel for by how much.
This is obvious and known. On the other hand, DIM30 or DIM100 do not say much about linearity, even HF linearity. CCIF IM and DIM are different kind of tests addressing different issues. DIM test is not any universal cure.
I assume you like Cabot's distortion methods comparison paper
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