[neobop]

Think of the dummy cart as a parallel load.  You could put it right at the preamp input just like loading plugs.  In fact, loading plugs would be great for experimentation.  Solder 4 wires out of your plugs and hook them up to the dummy.  You can load it wherever it sounds best. 

I'm pretty sure it will sound way better without the 5K resistor.  Why don't you try it w/o the resistor in series with the cart (R2).  R3 becomes the sole load resistor and just vary that one.  I think all the stuff about preamp native resistance being >100K, is rendered moot by R3.  That's preamp load resistance.  Because it's in parallel with the cart and R2 it's confusing, but preamp load is shunt (parallel) resistance and capacitance.
neo

[orthobiz]

Wow! From such a humble beginning, this thread now has 781 posts! And I've only read two of them!!

Post away...

Paul

[*Scotty*]

The circuit topology as I have outlined it, with the parts values I have specified, functions in the manner I described, and provides a correction that results in a flatter high frequency response and a freedom from electrically induced phase shift.
Guaranteed.
Neo, as an experimental starting point I would implement the circuit as specified and acclimate to the sound the system has with the correction applied. Then one could short to ground the signal that would be passing through the cartridge body to ground by jumpering around around the cartridge body, thus removing the applied correction. The difference in sound between the two conditions should be easily heard. You could then remove the jumper which shorts the signal around the cartridge body restoring the corrected condition. The next step would be to try shorting the signal around the 5k ohm resistor that is on the side of the junction towards the phono cartridge. The volume will have to be adjusted before a meaningful comparison can be conducted but if the sound remains the same with and without the resistor in the circuit then it isn't necessary.
The resistors value was chosen to minimize value of the resistor in the legs of the circuit towards the phono stage which reduces the impact of the resistor on the sound. They could have been made 2.5kohm each but that would have cut the cartridge output voltage to 1.25mv which would have impacted the S/N ratio adversly. Occam's razor was applied when choosing to make the values of the resistors the same. If they are equal to one another the voltage stays the same in both legs, this may or may not matter. Both legs of the circuit need to have identical impedance behavior across the entire range that the circuit covered and it seemed logical to make both values the same to avoid the possibility of any variance between the source impedance and the load impedance.
 The ability easily change loading resistances makes putting this circuit into place much simpler. The combination of the cartridge body and 5kohm resistor can be substituted for the 47kohm loading resistor. Then all is that necessary is to put the other 5kohm resistor between the RCA jack and the input side of the 47kohm load resistor position.
If R2 and R3 in your rendering of the circuit are eliminated almost all of the cartridges generated signal will go to ground and there will not be enough signal present to use with the gain available from a MM phono stage.
Scotty

[neobop]

I'm not going to try this right now.  Maybe I'll get a Vista, but I think you're looking at the cart and dummy as a circuit and the preamp as separate.  It's part of the circuit.

"Both legs of the circuit need to have identical impedance behavior across the entire range that the circuit covered and it seemed logical to make both values the same to avoid the possibility of any variance between the source impedance and the load impedance."

The load impedance is usually much higher than the source impedance - it's supposed to be.   Look at the circuit as having 3 legs in parallel.  The first is the cart with a 5K resistor in series.  The second leg with the dummy is no different than the preamp load except for that 5K resistor R2 that's in parallel.

The preamp load resistance and capacitance is in parallel.  The only difference is you're adding inductance - also going to ground.  You could lose R2 and change R3 to 2.5K and have the same circuit without the voltage drop.  Adding 5Kohms to the resistance of the cart serves no useful purpose.  Change the value of the load resistor R3 to what sounds best.  The dummy cart is almost identical to the voltage source anyway, so what useful purpose does R2 serve?
neo

[*Scotty*]

The source impedance is the phono cartridge, it provides the signal therefore it is the source. The load impedance is defined by the cartridge body to ground.When the phono-stage input impedance is greater than 100k,the complete chain of components in the circuit including the phono cartridge on the tonearm is in parallel on a resistance basis with input restance, 100kohms or greater. The resistive sum of the components in parallel with the 100k changes very little from the that of components themselves which is why we want 100k or higher. The 500k resister in dialom's preamp allows him to change out load resistors without impacting their value due to parallel summing, it also allows him to change load resistors when the preamp in on without also unloading the input which a BAD THING. The load resistance is usually much higher but in this case we want the source impedance and load impedance to be the same and precisely track one another as frquency increases.
Scotty

[neobop]

Why don't you try removing both 5K resistors and selecting a resistance load for the preamp?  If the 2 carts are identical there's no need to make the impedance the same.  The impedance is already the same.   

As I see it the 5K resistors have 2 functions.
1. cut output in half
2 degrade the sound

neo
 

[*Scotty*]

As I said in an earlier post, the 5k resistor in line with the cartridge may not be necessary, and the circuit should be intially built in the configuration that is known to function correctly before experimenting with untested variations  Within the audio band the cartridge to ground will have a low enough impedance that most of the phono cartridges signal will be shunted to ground as I pointed out in an earlier post.
Scotty

[*Scotty*]

It should be noted that the inductance mirror circuit is an AC circuit. It functions in the impedance domain and cannot be analyzed or understood applying simple DC circuit concepts. With impedance comes frequency dependent behavior of both components used in the circuit and the overall circuit itself.
 How the circuit operates is rendered slightly more difficult to understand because instead of a single component, we now have two components with the same impedance characteristics, the phono cartridge with an impedance characteristic that causes a HF rolloff and concomitant phase shift,and the cartridge body which, due to its position in the circuit, counteracts the first components HF and phase behavior.
Scotty

[neobop]

A couple of things to note.  All phono carts and power amps produce AC.  Preamp loads, resistance and capacitance are in parallel and go to ground.  I never loaded an inductor in series with the resistor so I don't really know.

The phase behavior of a low inductance cart is a shift at mechanical high frequency resonance regardless of electrical resonance.  That shift will only be higher in frequency if you use a boron cantilever. 

Loading a low inductance HO cart often requires more severe resistance loading.  All carts have a naturally rising high end.  Much of it is tamed by mechanical damping.  Such things as cantilever resonance and LCR interaction all figure in. 

Maybe David is trying this?  I imagine it will take some time to sort it out.
neo

[dlaloum]

I experimented with this concept a couple of years back before deciding that instead of trying to turn an MM into a MC, I should experiment with the EQ possibilities and their impacts (both phase and amplitude)....

Here is the Capacifier circuit:



This really is a "rif" on the same principle - set the capacifier R and C values to the same as Scotty's and you have Scotty's mod (some of them would be set to null value)

To go with this diagram I also have a spreadsheet that models the electrical behaviour - it can also be further tweaked by measuring the actual behaviour of a cartridge, cancelling the theoretical electrical behaviour from the measured to provide a "raw mechanical" (+ non linearities) baseline, that can then be used to model what will happen with various parameters.

These circuits do as advertised - you can (with the right values on the components) effectively get the same results you would have were your capacitance far lower - so it is a means to attach Audio Technica cartridges that work best at low C loading, to standard phono stages with loadings of 220pf (+interconnect of 100pf or more...)

This is very flexible - if you use a p-mount adapter in the circuit setup, you can quickly and easily switch cancelling cartridge bodies to experiment further with tweaking the voicing.

There is a long thread on this topic here:
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=19&t=33929

bye for now

David


P.S. please ignore component values on this diagram... I just threw it together to show the outline... values would obviously vary wildly based on what you are using it for and with which cartridges.... the two cartridges involved need not match. - For best results, as in all things audio, the two channels should be matched as closely as possible.... this is the trickiest part given variation in cartridge inductance between channels on many exemplars!

[*Scotty*]

David, I suspect that if the inductive values between the cartridges were within 5% all around you would achieve the desired results. The setup tested with the signal generator did not have a specially selected pair cartridges with perfect matching.
 The Grado family of cartridges is another good candidate for this circuit as the Prestige series has the same inductance and resistance throughout the entire series. One could buy a higher line model replacement stylus and purchase a pair of Grado Blacks for the matching cartridge bodies.
Scotty

[neobop]

You mentioned the Capacifier before, but I didn't check it out.  This is very similar to Scotty's circuit except no series resistor after the cart, but there is one on the dummy (R4), and an additional one R5 and a cap in parallel to the dummy but not R4.  I believe there's a downloadable calculator?

This is a 35 page thread on VE. It's designed to null input capacitance?  Could you cut to the chase and tell us what happens to inductance?  It seems to me without inductance the net amplitude response will be defined by mechanical performance.  In many cases without the inductance in the original design amplitude response could be less than ideal. 

I plan on reading the thread, but that's what I said before.  If someone can load their MM with specified capacitance is there any benefit from this Capacifier?
neo
 

[dlaloum]

If you can load your cartridge with any desired capacitance from (say) 50pf up, as well as opt for a reduced inductance (which may not be needed if the C is low enough) then the circuit is redundant.

The whole idea was to overcome the limitations imposed by most phono stages which start out with too high a capacitance.

The additional bits of the circuit allow tweaking/adjustment of the electrical resonance, and the rolloff slope and turnover frequency...

So it not only allows one to "expose" mechanical behaviour but also to  voice the system by choosing how much compensation / EQ to put into the system.

Ultimately I found it easier and simpler to use traditional loading combined with a fully flexible low Capacitance and high resistance phono stage (ie: I can set up for R from 500k down and C from 50pf up)

It really is just a fancier version of Scotty's circuit - courtesy of LuckyDog who developed it - I did a lot of testing of it, and  helped convince him to also publish the associated calculator.

If you take that calculator and "mess" with it, it can be a very useful tool in modeling cartridge behaviour, and as I mentioned, with additional work you can also incorporate the mechanical behaviour allowing you to more accurately predict what a cartridge optimum load might be.... (it hugely speeds up optimising a cartridge!)

bye for now

David

[neobop]

Thanks David.  Does inductance change or is it more complex than that?   Electrical resonance is an LCR circuit so resistance figures in.  Interesting stuff.

On another thread the Grace F-9 carts came up.  In VE library is an F9 manual.  These were 2.4K impedance, 3.5mV (similar to 150MLX). 
In the manual is a response graph taken at 100K load.  There's a gentle rise from around 8K and peaks at 30K.  It's up a few dB at 20K w/100K load.  This is a sweet cart.  Wish I bought one back in the day.
neo

[dlaloum]

Sorry - what do you mean by "does inductance change?" ?

[neobop]

This really is a "rif" on the same principle - set the capacifier R and C values to the same as Scotty's and you have Scotty's mod (some of them would be set to null value)

To go with this diagram I also have a spreadsheet that models the electrical behaviour - it can also be further tweaked by measuring the actual behaviour of a cartridge, cancelling the theoretical electrical behaviour from the measured to provide a "raw mechanical" (+ non linearities) baseline, that can then be used to model what will happen with various parameters.

These circuits do as advertised - you can (with the right values on the components) effectively get the same results you would have were your capacitance far lower - so it is a means to attach Audio Technica cartridges that work best at low C loading, to standard phono stages with loadings of 220pf (+interconnect of 100pf or more...)

This is very flexible - if you use a p-mount adapter in the circuit setup, you can quickly and easily switch cancelling cartridge bodies to experiment further with tweaking the voicing.

There is a long thread on this topic here:
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=19&t=33929

bye for now

David


P.S. please ignore component values on this diagram... I just threw it together to show the outline... values would obviously vary wildly based on what you are using it for and with which cartridges.... the two cartridges involved need not match. - For best results, as in all things audio, the two channels should be matched as closely as possible.... this is the trickiest part given variation in cartridge inductance between channels on many exemplars!

Sorry, I didn't read the thread.   "the two cartridges involved need not match"  Do you mean just channel to channel?  Those are two of the same cart?

Do you change the values of R5 and C3 to tweak?  What about R4 ? 

How is overall inductance affected?  I don't think either Scotty's or this circuit nulls inductance.  Looks to me as if inductance is diminished so electrical resonance can be manipulated. 
neo

[neobop]

I can't say I would blame anyone for not wanting to tackle a 35 page thread on one of these forums, especially when the conclusions could be summed up in a couple of paragraphs.  Our time is a precious gift, and it's not recoverable.

Parallel inductance is calculated exactly like parallel resistance.  We know that putting 2 identical resistors in parallel results in 1/2 the value of the original resistor, so while inductance isn't cancelled by the capacifier, it's significantly reduced.  We talk about electrical resonance and significance, but I suspect many of us are fuzzy about exactly how this works.  Here is Hagerman's calculator - just before the first graph.  Plug in some values and see what happens:
http://www.hagtech.com/loading.html

If someone has a 681 (900mH) w/200pF = 11.9KHz electrical resonance.
Reduce capacitance to 50pF  =  23.7KHz

Lets go the other direction.  Signet 10ML = 85mH  w/200pF = 38.6KHz,  w/600pF = 22.3KHz 

With most med/high inductance carts, electrical resonance is used to augment the mechanical response which is the primary determent of overall amplitude response.  That is movements of the cantilever including mechanical damping.  If you read the TNT article you saw how capacitance is used to move high frequency resonance to a frequency that compliments response.  The conclusion was, an M97 needs 250pF to avoid severe mid-treble droop.

A word of caution about Hagerman page.  Most of it is about electrical performance only and is near useless for loading purposes.  The calculator can help you figure out what's going on, but most will need amplitude response tools that few people have. 

I invite anyone with questions or observations about particular carts, or situations, to join in.  This thread has come a long way from its practical beginning of Clearaudio stylus replacement.  MM vs. MC is now up, so please divert us.
neo



 

 

[Hank]

Are you looking for different cart models?  Okay, how about AT 0C9ML/II?  I haven't bought a pre for it, but have the Collins PCB and a lot of the components.

[neobop]

Are you looking for different cart models?  Okay, how about AT 0C9ML/II?  I haven't bought a pre for it, but have the Collins PCB and a lot of the components.

Hi Hank,
Do you already have the OC9II ?  Collins is a DIY phono pre?  Head amp or phono stage?  The OC9II is generally considered a bargain.  It's a great tracker, has a healthy output of .4mV and a boron/ML.  I think DC is 12 ohms.  It's a highly detailed cart, but in some systems can sound forward, even bright. Others say it's just about perfect.  A long time ago I read that someone loaded it at 20 ohms.  I think usually that's around 100 ohms.

I've only heard it a couple of times and it sounded great, like a $1K cart.  This guy had it worked out with the right cables (cable capacitance doesn't matter with most LOMC), and broken in, but I don't remember what resistance he was using.  It might have been 80 ohms.
neo

[Hank]

Hi neobop.  December 2007 I bought a used Wilson Benesch Circle turntable.  It has an RB300 arm with Incognito re-wire mod and an Audio Technica OC9ML/II cartridge (supposedly only 100 hours on it).  For many reasons, including upgrading my electronics and acquiring a fantastic pair of Acoustat Model 3's, and procrastination (which I have down to a fine art), I have not mounted the cart and put the TT into service.  The Collins design is based on his article in Audio Express.  He sold the circular PCB and matched JFETS which I bought and then bought Vishay foil resistors and need to buy the caps, switches and pots.  Very versatile with switchable loading.  I'll finish it "some day".  I had not heard of the OC9ML/II, but found a review of it which makes me wonder why it's not extremely popular.
Sounds Like Review: 
"Sonically, I found the OC9 to be a pure delight. This is without doubt one of the cleanest- sounding phono cartridges I have ever had the pleasure of using and the OC9s significant achievement in this regard added greatly to my enjoyment of the music.

The truth is, you could easily spend twice the OC9s asking price and still not equal let alone surpass its level of musical involvement, accuracy, or purity.

In all, the Audio-Technica OC9 provides most of the performance characteristics of the best of the breed, but without the heroic price, and without having to worry whether the sample you buy is a good one."