[dlaloum]

The Ortofon phase article remains interesting....

It is not clear that phase is in fact the key... what is clear in that article is that the golden eared panel preferred an undamped setup, and the the optimum balance was achieved using light damping to bring the voicing back to a more neutral response while keeping things as lightly damped as possible.

Pragmatically speaking it seems to me that very light damping is in fact the key to optimum sound - and achieving neutrality should be attempted outside the cartridge ... (electrically/electronically/digitally)

Avoiding a resonance under 20k is also important as it has other impacts on tracking ability, harmonic and intermodulation distortion - but phase may not be the key factor - IF the resonance is above 20kHz.

If the resonance is down around 12kHz (like many basic pfanstiehl styli) then you have a major phase shift in a frequency range where there is a lot of critical musical material and where the ear is sensitive....

Using a circuit like Scotty's will effectively lower the inductance, making a high inductance MM/MI design behave much like an MC.... this absolutely implies giving up on cartridge loading as a method of achieving neutral response, and I would be hesitant to recommend it for any but the best cantilevers.

But it might be an ideal setup when mated with very high quality digital EQ....

[neobop]

I agree, except for one little detail.  The listening panel only preferred the imaging of the undamped MC.  He said it was so bright it was unlistenable.  I think they settled on +3dB @ 20K and imaging wasn't as spectacular.

Which brings up an interesting point about the Lyra carts.  With that high end response why don't they make your ears bleed? 
If you remember the curve the rise stopped abruptly at +7dB @ 20K and didn't continue to +18dB @ 27K like undamped MC200.  That's about the only explanation I can come up with other than test variations.



I was thinking of trying this X-induct, but I doubt if I have two appropriate candidates.  The Signet MR is out of spec and I'm not sure if I want to mess with it.  The Virtuoso and 95 are probably identical, but I don't have the right stylus any more.

The 440 has a tapered/ML.  Doesn't that resonate below 20K ?

neo

[*Scotty*]

neo, for what its worth I have been using been using an AT 440ML with this set up for about 18 years and have very happy with the sound.
You do have to be sure to dial in the VTA to the correct angle. With the recently purchased AT 150MLX stylus I am going to have to figure the VTA out all over again. Unfortunately while I can easily adjust the VTA on my arm I cannot do it on the fly.
Scotty

[*Scotty*]

Anecdotally, all of the Sheffield Labs, Crystal Clear, RR, and Sweet Thunder direct to disc records sound wonderful as do the Denon and Telarc records. The Mobile Fidelity Half Speed Master recordings are a mixed bag.
Scotty

[dlaloum]

yes the MLa resonates around 16kHz hence my running it at 32k....

[neobop]

neo, for what its worth I have been using been using an AT 440ML with this set up for about 18 years and have very happy with the sound.
You do have to be sure to dial in the VTA to the correct angle. With the recently purchased AT 150MLX stylus I am going to have to figure the VTA out all over again. Unfortunately while I can easily adjust the VTA on my arm I cannot do it on the fly.
Scotty

18 years - then I guess you haven't  tried your x-induct with other carts? 
Like David, I used to load the 440 at 32K, that is until I got an ATN152ML (beryllium)  Then back to 47K   I wonder if you'll have to change the value of those 5K resistors.
Speaking of which, it still looks to me as if they are the load, but no.  One 5K resistor is in series with the cart.  That adds to the cart DC of 790 = 5,790 ohms.
Then you have an identical load in parallel.  That changes the cart resistance to about 2800 ohms.  That number looks close to the impedance of 3.2K.  Is that coincidental?  I wonder what new impedance is.  Reactance should be much lower, approaching zero or is parallel inductance 1/2, like resistance? 

I have a couple of arms with VTA on-the-fly and I find myself using them all the time, but I don't think you'll have much of a change going from a 440 stylus to a 150.  Let us know how it works out.
neo

[*Scotty*]

Remember that original 47kohm resistor, the cartridge DCR would be added to that for the grand total resistive loading in a conventional circuit.
The mirror circuit total load has the cartridge DCR added to the 5k series resistor and the 5kohm resistor to ground plus the cartridge body DCR. The cartridge has all of that resistance to ground as the loading. Nothing is in parallel. You could lay the components out on a table and measure them with an ohmeter and get the approximately 11kohm value I referred to in my earlier post. Resistively speaking everything is daisy chained together with respect to ground.
Scotty.
Scotty

[neobop]

The cart is already going to ground with the green/blue wires.  In series with that inductance (above) you insert a 5K resistor.  The dummy cart and an additional 5K resistor is also going to ground in a parallel leg of the circuit.  The 2 - 5K resistors are not in series, they're in parallel.  The wire in between them labeled going to phono stage in your drawing, puts them in parallel.   At least that's how it looks to me.  The phono stage load resistance is > 100K.  The cart DCR (including dummy) is 395 ohms and the inductance is coils in parallel. 
What am I missing here?
neo

[Speedskater]

'neobop' your schematic looks like a reasonable representation of the circuit.  I don't understand the hand drawn sketch at all.

[neobop]

Hi Speedskater,
The sketch is of a duplicate cart body intended to cancel inductance of the cart in use. 

To combine the drawing and the green one above, first eliminate the preamp load on the right and substitute >100Kohm.

Then, on the drawing where it says  To T.T.  insert the drawing in the green circuit right after L1 the 650mH inductor.  Our values on the green, change to R1 = 790 ohm and L1 = 490mH.   They would be the same on the sketch, but they're not expressed. 

I'd make a drawing, but my scanner is down at the moment. 
neo

[*Scotty*]

I managed to confuse the situation yet again by mentioning trivialities like the cartridge DCR. Its value is immaterial to the functioning of the circuit. Something to think about though, is the cartridge DCR in a regular circuit in series with the 47k loading resistor or is it in parallel with the cartridges DCR? If it is in parallel, how far below the stated cartridge DCR will the sum of the two resistances be? Likewise how can the cartridge be properly loaded if the combined resistance is far below the target 47k ohms?
 The Inductance mirror circuit only shows the signal hot from the phono cartridge as it is assumed that the circuit is implemented internally inside the phono preamp. Cartridge signal ground is taken care at the input RCA jacks. I did not make clear where the circuit was to be implemented when I initially posted it. My bad.
Scotty

[dlaloum]

I believe this represents the complete circuit we are talking about?

[neobop]

Scotty,
The preamp load is in parallel to the cart.  When you make a loading plug you hook it up between the hot and ground, and it becomes a parallel load to the preamp resistance.   An old rule of thumb is the input impedance should be at least 10 x the source impedance.  It doesn't always work out that way, but if the input resistance is the same value as the cart you lose output voltage.  Like if you load a 30 ohm MC at 30 ohms you'll have less output.

You removed the load resistors from your preamp and the qualification is that it has to be >100K, so that's the preamp input resistance. Here's the x-induct circuit:



This is basically the same as David's, but adapted for your 440/x-induct.  The physical ground connection location doesn't matter as long as they go to ground.

neo

[*Scotty*]

Yes I removed the 47kohm loading resistors from the preamp and directly replaced them with the combination of the 5kohm in series with cartridge body to ground. The intrinsic input impedance of my phono-stage amplifying circuit is a great deal higher than that 100kohm minimum resistance so that this resistance doesn't impact the behavior of the circuit.
 Once again, due to the rising source impedance of the phono cartridge any high frequencies that the cartridge might produce beyond a certain point are lost at predictable rolloff rate. The inductance mirror to ground has a rising load impedance with respect to high frequencies therefore the high frequencies produced by the cartridge have no choice but to go on into the input of the phono preamp thus there is no roll off and there is no longer any phase shift due to phono-cartridge LCR related phenomena.

[dlaloum]

How do I go about measuring the intrinsic impedance of my phono stage? ....

It is hard wired at 500kOhm to allow easy plug and play of resistive load plugs.... but I have no idea beyond that of its own intrinsic impedance...

[*Scotty*]

I would go ahead and use it with the 500kohm resistor in place. However if this is a grid resistor on a tube, the 2000 to 3000pf miller capacitance will be the problem that has no solution. If this is solid state phono stage based on an opamp then you could remove the 500kohm resistor. If it is a solid state non-negative feedback design then you would be better off leaving the 500kohm resistor in place.
Scotty

[neobop]

Why remove the 500K input resistor at all?  Seems to me it's high enough value, and David has the option of using shunt resistors to experiment with load.

How was the value of those 5K resistors chosen?  Are they needed?  Any resistor in series with the signal (R2) isn't going to help SQ.

You could look at the 2nd leg of the circuit as the load, replacing the removed load resistors.  It's parallel to the cart and preamp so it really is, only the resistance value is 2.5K because of the parallel 5K resistors.  Isn't parallel inductance calculated like parallel resistance?  I guess you could look at it as dropping the cart inductance in half, or having the preamp load as 2.5Kohm, 490mH, _pF ?   
The thing is, the circuit must be connected at the input and not somewhere further down the line. 

2.5K is like a LOMC load.  Scotty, have you tried it without R2 ?  I think you might have better results w/o it, and just change preamp input resistance to a value you like.  You might want to do it anyway with the 150 stylus.  I think it would be much better w/o R2.
neo

Edit: Now that I think about it Scotty, you've invented an LCR loading scheme for HO carts that reduces the dreaded inductance, but there's still capacitance to consider.  1/2 the inductance is admirable, but it's not a LOMC or a TK9, 10.  Maybe David can figure out how to apply it to different carts and preamps.

[*Scotty*]

We are dealing with the phono cartridge's impedance behavior. While with respect to the input of the phono stage the resistors and the cartridge body are indeed in parallel with respect to ground, the phono cartridge on the tonearm sees the resistors and the cartridge body's inductive value as being in series. This is what influences the phono cartridge's high frequency charateristics. We have a tracking change in high frequency impedance by the cartridge body that mirrors the effect that the phono cartridge's inductance has on high frequency response and counter acts the roll off that normally occurs. The 5k resistors shunt half the cartridges output to ground leaving about 2.5mv to work with which is a gives an acceptable 6dB lower output which won't kill the phono stages S/N ratio in most cases. The circuit would sound better without the 500k resistor, but without knowing the circuit design of the phono stage up stream you are better off leaving it in place.
 By essentially nullifying the inductive effects on the phono cartridges high frequency response via the mirror circuit, the capcitance of the connecting cables now has about the same effect as it would on a LOMC.
Remember, electrically the circuit has flat responese to 100k verified by testing with a signal generator.
The MM phono cartridge now behaves like a LOMC but with 2.5mv output. Its high frequency extension is now determined by the stylus mechanical characteristics such as moving mass and the mechanical resonant frequency. Altering resistive parts values will not improve the circuits high frequency 3dB down point or response curve flatness.
Scotty

[neobop]

This is a little complex.  Impedance is resistance with reactance figured in.  What happens to impedance if you reduce inductance?  It lessens.

Do those 5K resistors somehow make the circuit work, do you need to cut output?  Seems like you could eliminate those resistors (R2, R3) and just use load resistors, whatever you like and you'd have full output from the cart.  The dummy cart to ground would still give you parallel inductance and resistance for that matter.  This should also cut cart impedance dramatically.  I don't understand the need for R2, R3.  They seem like the SQ limiting factor.
neo

[*Scotty*]

Remember only the effects of inductance on high frequency extension are counter acted, the actual individual phono cartridge inductance and that of cartridge body remains intact, they interact with one another through the mechanism of their high frequency impedance characteristics which offset one another resulting in improved high frequency extension and zero electrical phase shift effects in the audio band.
Scotty