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Adjustable capacitance for non MC carts

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Igorevich View Drop Down
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    Posted: 12 Aug 2020 at 10:52am
I'm sorry, if this question has been answered already. In this case please point me to that answer, I couldn't find it.

Why do the GSP phono stages not offer adjustable input capacitance? For example, my Era Gold V seems to be fixed at 100pf. Audio Technica carts are quite famous for requiring just slightly more than 100pf overall, tonearm cables plus phono cables plus phono stage input. On the other hand, Ortofon wants much more AFAIK. 

I'm using Grado carts which are insensitive to such things. Still I wonder, why the choice of fixed input capacitance?
Igor
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RichW Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2020 at 11:37am
Hi Igor,

The top of the range Accession MM does have 4 adjustable input capacitance settings.Smile

As 100pF input cap is fine for the majority of MM cartridges the extra cost of incorporating
adjustable settings for the lower range models was probably not in keeping with the value of the products.

Majestic/Enigma, Accession MM & MC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Igorevich Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2020 at 11:57am
I see, the price point at which this feature is delivered is much higher than that of other phono stages though!

Anyhow, I'm very pleased with my systems sound right now. Just being curios.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2020 at 1:48pm
Just listen, if it sounds good to you, enjoy it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2020 at 4:55pm
I remember my physics teacher teaching the class about the audible range of frequencies. I'd have been 12. He had a full range speaker and an amplified signal generator. He swept the frequency very slowly from the lowest to the highest frequencies, announcing the number of hertz in base-10 steps. As soon as we heard the lowest frequency, we each had to put our hands up. Then as the highest frequencies were reached, and we couldn't hear anymore, we each put our hands down. We also had to write-down our start and stop frequencies. My upper frequency was about 22kHz. One kid went much higher. It was realised he was suffering from tinnitus because he could still hear whatever he was hearing after the equipment was switched off.

Many years later, only a few years ago, probably aged 60, I tested myself again using our test equipment. I wasn't surprised that my upper-frequency hearing had dropped to 13kHz.

The point is, though, you have to listen very carefully, and there can be no noise in the background, because where the limit is reached, the sound is hushed, and then, it's gone. Maybe I could make out an octave lower with other sounds present, but that would then be 6.5kHz.

According to Fletcher and Munson, we hear best between 200Hz and 6kHz, and there seems to be some resonance at 13kHz. I'm not a bad match then! I'd need about 10 dB bass and treble boost at normal listening levels to hear everything "flat," but that wouldn't be real.

Our 10kHz hearing is about 5dB down, but would we hear a 1dB difference so high? If you don't think so, then stop worrying about adjustable capacitance. If you believe you can detect a 1dB difference at 10kHz, then it would have to be a slow-playing harpist or pianist tinkling the highest notes. The difference in amplitude at 10kHz between a 350mH and 650mH MM cartridge, loaded with 100pF of wiring and 100pF of phono stage input capacitance, is 1.2dB.

Circuit speed (slew-rate and transient intermodulation distortion), and high-frequency stability reveal a damn sight more.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Igorevich Quote  Post ReplyReply Direct Link To This Post Posted: 17 Aug 2020 at 3:01pm
I assumed capacitance is an important value for MM carts, because of the frequency response graphs I saw (of some Shure and Audio Technica carts). Different values were "dragging" the curve in different directions, not just attenuating one particular frequency. 

If the effect is as small as suggested (1.2 dB at 10kHz) I don't expect to hear it much. It definitely won't matter in this case.

Edit: I've looked at the "variable phono input loading" thread. The issue of slew rates being different on input vs output never occurred to me. Thanks for that in-depth explanation!


Edited by Igorevich - 17 Aug 2020 at 3:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 17 Aug 2020 at 9:05pm
Measurement, as well as simulations, show that capacitance makes a difference to the high-frequency cartridge response. I could never deny that.

The problem I have in coming to terms with its audibility is that it is at the limits of, and beyond my hearing capabilities. At the limits, how can I be confident that I hear something slightly different from another? I don't think anybody can do if the truth were known.

But if you limit high frequencies a little more by, say changing 100pF preamp loading for 220pF, a difference can sometimes be heard. I suggest that the difference is of the sort mentioned in Matti Otala's studies of overshoot, which is about the slewing capabilities of the circuit.

His research took place 48 years ago, and perhaps it was overlooked by a mostly non-technical press?

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