Best phono stage

bazelio

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I would like to construct a model that supports the theory. You and Ralph can continue to portray that as an attempt to grasp a simple concept if you must. I really don't care. Again, the audibility of tics and pops with information generated by the cartridge with respect to phono input stability is credible. Going on to then say if you hear a difference when loading down a cartridge that you are simply preventing a MHz oscillation from entering an unstable circuit is not credible with mere hand waving and appeal from authority.

Back to the model : Is the cartridge inductance a series element of the resonance or a shunt one? If in series with the required source of excitation (the coils), then Jcarr's model holds and we need an MC cart to excite a ~2 MHz resonance. If it's a shunt element from an external source then Jcarr's model does not hold and a new model is required. In that case, as per above, the best guess resonance is now at 30-50MHz. Can it still be excited? Possibly so, but then this same approach needs to be applied to every aspect of the circuit.
 
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ack

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Going on to then say if you hear a difference when loading down a cartridge that you are simply preventing a MHz oscillation from entering an unstable circuit is not credible with mere hand waving and appeal from authority.
No one said exactly that either. Toning down the peak resonance is one thing, but at the expense of shunting precious little current from the cartridge to ground is the other, and it's a major contributor to the eventual sound we hear. This is why the better phonos would enable one to load at 47K
 

ack

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That has been conveyed over time across multiple forum threads, yes. It spans Audiogon, WBF, and one other as I recall.
Here's also the Genesis phono https://www.genesisloudspeakers.com/products/phono/

The Design

The Genesis Phono-Preamp is designed from the base of the tone arm onwards, and a Genesis designed cable is supplied with a mini-DIN connector – the standard with most high-end tone arms. There isn’t a plethora of loadition options. The inductance of the coil of the cartridge interacts with the capacitance of the tonearm cable to create a reactive peak. This peak can be as high as 32dB, and is the usual reason given for all the loading options for a phono stage. However, when the graphs of this reactive peak are shown in the marketing literature of many phono stages, the frequency scale is often omitted. In computer simulations, we can easily see that this reactive peak is in the megahertz range – far outside our hearing. However, if this peak is present, it can easily cause problems for a phono-preamp. High loading (if used to tame this peak) also reduces dynamics and transparency.
 

bazelio

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Audiogon threads could have written, and probably did write that description. It's the Jcarr sim and adds nothing new to this discussion. Oh and by the way, I wonder how current injection phonos can possibly sound transparent and dynamic if "shunting precious current to ground" is such a disaster.
 

ack

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Oh and by the way, I wonder how current injection phonos can possibly sound transparent and dynamic if "shunting precious current to ground" is such a disaster.
"current injection phonos"?????

Here's from the CH Precision P-1 manual https://www.ch-precision.com/images/usermanuals/P1_user_manual_2v2.pdf

The P1 provides 3 inputs, two of which are in current mode, dedicated to MC cartridges. The third input is in voltage mode, accommodating both MM and MC cartridges as well as step-up transformers. The MC1 and MC2 current mode inputs require no impedance matching. However, the MM/MC voltage mode input is fitted with a variable resistor seen by the connected cartridge as a load for impedance matching. All the inputs have multiple gain settings.

1.1 Input stage

Three inputs are available on the P1. Two of them are in current mode, dedicated to MC cartridges. The third input is in voltage mode, accommodating both MM and MC cartridges as well as step-up transformers.MC1 and MC2 Current mode input: a current mode input reads the current generated by the cartridge (not its voltage). Current mode inputs are usually dedicated to MC cartridges. The current from the cartridge is amplified by a discrete transistor based trans-impedance amplifier. Using current mode inputs provide a superior signal to noise ratio compared to a conventional voltage input, better immunity and by essence no necessity to match impedance. The gain of the trans-impedance amplifier is intrinsically dependent on the cartridge internal resistance. The lower the cartridge internal resistance, the higher the gain. Multiple gain settings are available on each input to accommodate the variation of resistance among cartridges.
 

ack

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Yes!!!!! The point being, they attempt to load the cart with a dead short. You can't get much further from 47k.
Reference? They may not be as transparent and dynamic for all I care
 

bazelio

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Reference? They may not be as transparent and dynamic for all I care
Why don't you look closer at the ad print you were reading.

Technical Specifications
MC current-sensing input impedance
< 100mΩ, virtual ground Equivalent Input Noise (EIN)

The most lively and dynamic phono I've ever demoed in house was the VDH Grail, a current injection design like the P1. Anyhow, thanks for the conversation.
 
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ack

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Why don't you look closer at the ad print you were reading.

Technical Specifications
MC current-sensing input impedance
< 100mΩ, virtual ground Equivalent Input Noise (EIN)

The most lively and dynamic phono I've ever demoed in house was the VDH Grail, a current injection design like the P1. Anyhow, thanks for the conversation.
Again, it seems to me you are making assumptions. Yes, 100mΩ is low, but why do you assume it's shunting to ground? I bet it doesn't and opposite to a voltage-gain stage with a loading resistor.
 

Atmasphere

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They also sound different depending upon where and how you strike them. You've effectively used the simplest model to describe the resonance but you're relying on an as of yet undefined model to excite it. Sure there's theoretical possibility, but the theory chain is only as strong as its weakest link.
Even though they might sound different (different harmonics) the fundamental remains the same.

Because we are dealing with an electrical model though, the energy that puts the resonance into oscillation will not affect overtones (harmonics) regardless of how that energy is applied.

There's a lot of information about this on the web. I was a radio amateur when I was 14, Right out of high school I began servicing consumer electronics as I put myself through engineering school; that was 1974. So this stuff is probably too obvious to me. You are assuming that the cartridge needs the bandwidth- that is a mechanical issue! We are talking about an electrical issue that isn't related to the mechanics of the cartridge's operation.
 
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I wait my future phono preamplifier Accuphase C47....
 
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That's about it. I have had deep thoughts regarding the Boulder. I love my tube Allnic. It takes the right rolled rectifier tube to get the best out of it. My Pass XP-25 sits as backup..literally unplugged from the system.
What rectifier tube are you using on the Allnic?
 

analogsa

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Again, it seems to me you are making assumptions. Yes, 100mΩ is low, but why do you assume it's shunting to ground? I bet it doesn't and opposite to a voltage-gain stage with a loading resistor.

All current input stages work on the same principle: the input is a virtual ground. So, yes, the cartridge is effectively loaded with a dead short. Unless 100mohm is not a dead short in your view.

To me these phonos sound very dynamic, but perhaps unsurprisingly, a bit overdamped.
 
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Atmasphere

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All current input stages work on the same principle: the input is a virtual ground. So, yes, the cartridge is effectively loaded with a dead short. Unless 100mohm is not a dead short in your view.
There's a pretty big difference between ground and a virtual ground! As an example, if the opamp has a gain of 1000, which it will need if you have a low output moving coil, that gain is of course the ratio between the input and feedback resistors. Now in this type of circuit, the cartridge itself is the input resistor; so the gain will vary from cartridge to cartridge, but if you assume a 10 ohm impedance, the feedback is then 10,000 ohms. The input of the opamp is often fairly high impedance, especially if it has FET inputs. So the actual impedance the cartridge sees is considerably higher than a short; it can easily be over 1000 ohms even though its output is at virtual ground.
 

analogsa

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So the actual impedance the cartridge sees is considerably higher than a short; it can easily be over 1000 ohms even though its output is at virtual ground.
Sorry but this does not make sense to me, neither does your numerical example give any indication of this. How do you come up with the 1000ohms?

Nor does the presence or absence of fets make any difference. Provided there is a sufficient OLG the positive and negative inputs are always maintained at the same potential. If the positive input is grounded, so becomes the negative, nfb forces this and resistor values are of little importance within a very wide range. 10ohm and 10kohm are just perfect for an ideal virtual ground with a fet input opamp.

Of course this is an idealisation as in practice OLG falls with frequency. The virtual ground won't be so perfect at high frequencies and the 100mohms won't hold at 20kHz. This can be calculated or simulated once the amplification circuit is revealed.
 

Atmasphere

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Is this what we're talking about (V- ~= 0V)? And if so, why is the input Z of the phono spec'd at ~0 ohms?

That's close but the input is slightly different. The cartridge is R1 and the other end of it is at ground. So it is literally connected to the virtual ground of the opamp, which for a good opamp is 0 ohms. The only thing is, the cartridge isn't connected to ground or shorted out by this virtual ground. As you can see. This confusion is common- the idea that ground and virtual ground are the same thing and somehow act the same way. The word 'virtual' does not mean 'actual'! Here is a Wiki link on the topic:
https://en.wikipedia.org/wiki/Virtual_ground
 

bazelio

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In that case, the cart sees nearly a dead short across frequency. Well under 1 ohm at 20k, and maybe 5e-4 at 20 Hz. Note I chose this low noise opamp with 20k input Z, as you can see, but it could be anything.

 

analogsa

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Still waiting for Atmasphere to prove that a cartridge may be seeing a 1k load cause there is a "common confusion". Numbers please, not general Wikipedia articles. This is basic 101 electronics, not rocket science.
 
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