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Cartridge loading explained

the thin end of the wedge

Postby bouquet » 14 Aug 2006 12:36

BenC,

The quality of the resistor does have effect on the sound.
I use carbon composite , preferably Allen Bradley , but Philips will do allmost as good. Metal film sounds too harsch in my opinion.
It's depending on personal taste.
When tuning your cartridge loading you have to consider component quality in the entiry chain as well.

regards

Ron
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Postby carlosfm » 14 Aug 2006 18:46

It is also important to match resistor values between channels.
Even if using 1% tolerance resistors, measure them and pick two of the exact same value (one for each channel).
This means buying at least 10 resistors of each value you need, and then hand-selecting two that measure the same.
Matching components between channels always pays off: better soudstage.
This is not done on mass market gear, produced by the thousands, but as you are doing it yourself, then take a little time to make things the way they should always be done.

We're talking high-end here. :mrgreen:

I (always) love matched resistors and caps. :-({|=
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Postby BenC » 15 Aug 2006 05:49

Hi Ron!

Am using metal film (Tantalum) resistors right now. Allen Bradleys are hard to source nowadays. Will try some Rikens or kiwame carbon films and see which one I prefer most!

Hi Carlos!

Yes, indeed matched resistors is the way to go! But first have to experiment with different kinds (carbon comp, carbon film or metal film) of resistor (as advised by Ron) then go for the matched ones after I've decided on what kind of resistor I'll use.

Thank you guys and thank you Vinyl Engine for this forum.

All the best!
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GAS ON the FIRE

Postby gleichnerr » 17 Aug 2006 16:48

To further "complicate" this thread, let me interject one additional item:

When playing with the loading, you may need to consider what type of amp input you are dealing with:

Correct me if I am wrong, but many older integrated amplifiers had phono inputs that incorporated RIAA equalization into their designed frequence response. I know that many records were pre-emphasized in the production process, in order to accound for the physics of "the avergage Joe's" cartridge (moving mass - increasing difficulty to maintain accurate tracking with increasing frequency), vs. the electrical characteristics of the "generator", where output is naturally higher as movement/speed increases while cutting flux lines.

If this is in fact the case, you may actually want a non-linear, or at least, not "flat" calculated frequency response curve from your test program. It would probably look flat when plotted on a logarithmic (spelling?) graph, so that when equalized internally, the net result would be a flat frequency response.

I know that the spec. sheet for my NAD 7225's phono input states:
Input Impedance: 47k Ohms resistance / 100 picoFarads capacitance
RIAA Response Accuracy: +/- 0.5 dB, 20-20kHz

Or, does this mean that the frequency response should be this flat, assuming that the source material (vinyl) utilizes "standardized" RIAA equalization/pre-emphasis?

If you use a separate phono pre, then you would want a flat response from the output of the phono pre, going into your line-level inputs.

Those who are most familiar with these factors -- please enlighten us further.

Once I get good answers, I am ready to start playing with my cables and maybe some capacitors.


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Postby Guest » 17 Aug 2006 17:27

Hi,

The output of the phono stage should be flat.

To do this its electrical response should follow the RIAA curve.

(edit : The RIAA curve accounts for the fact that MM and MC output
is determined by tip velocity, unlike ceramics where output is due to
tip displacement. The width of the groove at various frequencies is
kept ~ constant ( for a given level ) consequently the output of an
MM or MC rises considerably across the frequency range, the RIAA
curve in a phono stage is the inverse of this output characteristic.)

The pre-emphasis and pre-distortion put onto certain records increases
as the tracked radius decreases, to follow the distortion and tracing loss
characterictics of a typical 0.7 thou spherical stylus.

Certain records only used pre-emphasis, zero at the run in
groove and 2 to 3 dB treble boost by the run out groove.

There is nothing the phono amplifier can do to correct this. To correct
it it would have to be done in the turntable and involve a tranducer
that knows the position of the tonearm, a crude method is a variable
resistor connected to the vertical axis pivot.

So the phono stage has to follow the RIAA curve, which is not flat.
Consequently phono stage response is given in terms of deviation.

With a perfect test record and cartridge the phono stage output is flat.

:)/sreten.
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Re: GAS ON the FIRE

Postby carlosfm » 17 Aug 2006 22:38

gleichnerr wrote:I know that the spec. sheet for my NAD 7225's phono input states:
Input Impedance: 47k Ohms resistance / 100 picoFarads capacitance
RIAA Response Accuracy: +/- 0.5 dB, 20-20kHz


Hi Ron Gleichner,

These specs are given as the result of one of the two following methods:

1. The software simmulation of the phono stage circuit, which is most of the times the first stage of the development process. Here you can tune the component values until you have an exact RIAA curve.

2. Using a reverse RIAA circuit before the phono pre, feeding it line level signals through a signal generator or a soundcard and measuring the output of the phono pre. Frequency response must be flat.

Neither of these methods have into account the cartridge, and it's electrical parameters.
The final production units may not fulfill the specs in what regards to RIAA accuracy, as in mass production they don't match components, and in the very rare cases that they do, it's on horribly expensive gear.

IME an 150nF film cap can measure as much as 170nF, so unless all the components are measured and selected (throwing away most of them), or high precision components are used (expensive - like 1% precision caps) most specs are just academic, based on exact values, not necessarily present on the final units.
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cartridge loading explained

Postby Guest » 20 Aug 2006 21:05

Hi Carlosfm. At the beginging of this thread you explain what effects cable length have, the Incognito rewire upgrade installed a while back is 1.2 m in lenght, for my system i really only need it to be around 300mm long, are you saying that i would benifit by shortening them ? the wire within the incognito loom is 33 AWG Litz one piece from cart tag to phono, the pre-amp i use has an 80uV MC input RIAA equalisation is 500 Ohms,signal to noise ratio stated at -80db unweighted below full input and output impedence is less than 100Ohms it also has a loading input pair of phono`s i use a Goldring Eroica MC
Would there be any noticable improvement by shortening them ? i am not concerned about resale value and such,and apart from anything else they are untidy. your veiw would be appreciated.
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Re: cartridge loading explained

Postby Guest » 21 Aug 2006 11:15

JRC wrote:Hi Carlosfm. At the beginging of this thread you explain what effects cable length have, the Incognito rewire upgrade installed a while back is 1.2 m in lenght, for my system i really only need it to be around 300mm long, are you saying that i would benifit by shortening them ? the wire within the incognito loom is 33 AWG Litz one piece from cart tag to phono, the pre-amp i use has an 80uV MC input RIAA equalisation is 500 Ohms,signal to noise ratio stated at -80db unweighted below full input and output impedence is less than 100Ohms it also has a loading input pair of phono`s i use a Goldring Eroica MC
Would there be any noticable improvement by shortening them ? i am not concerned about resale value and such,and apart from anything else they are untidy. your veiw would be appreciated.


Hi,

For an MC there is pretty much no point in shortening the cables. If you
cannot resist I suggest you reduce it to 0.6m, leaving some flexibility.

:)/sreten.
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cartridge loading explained

Postby Guest » 21 Aug 2006 15:16

Hi streten, thanks for the advice 06m it will be then.
Although the incognito cable is very well shielded, at 1.2 m its hanging down behind my monster amp which must be generating quite a field, i know its matching preamp is sensative to this and i have had to move them apart to get rid of the hum.
I somehow got one cable "creased" near the phono yesterday and broke a wire,so had to shorten one channel, and want to make them equal, so while i have the iron switched on i may as well shorten them both.
Thanks for the advise, it is appreciated.
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Postby Guest » 21 Aug 2006 15:53

Hi,

I'd buy 4 extra phono plugs and knock up an "Incognito pre/power lead"
with the cable section you remove, could come-in useful at some point.

:)/sreten.
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cartridge loading explained

Postby Guest » 21 Aug 2006 17:03

:lol: Hi streten, already done, i had some silver Eichmanns left over from making pure silver I/T`s,and at this moment the left over phono cable is hooked up to my CD player while i tweek the T/T,they work well as CD I/C`s.
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Postby markse » 10 Feb 2007 23:56

Hi,
I just found this thread as I'm having some troubles with a decca cart and think it may be due to cartridge loading. I've been happy listening to a London Decca Blue cart in my system using some cheap phono terminated video leads but I decided it was time to optimise so I made some interconnects using some RG59 coax and bullet plugs. The difference was amazing....ly painfull! What was a fairly balanced sound now became unlistenable with very peaked and distorted sounding treble. I measured the capacitance of the two different leads - the old agreable cable was about 400pF but the new was around 90pF. So I ended up adding a 560pF polystyrene cap accross a bullet plug at the ends of the new cables and it was a bit better. I added these at the amp end but found that if they were at the cart end the sound was better still. But it's still not good.
So now I'm suspecting the resistive loading of the preamp. Its a Nytech CP211- does anyone know what the input impedence for this pre is? Is it safe to measure input impedence of a SS pre with a DMM with the power off?
I'm not quite sure how varying the input impedence of the pre could affect frequency response- surely it would just attenuate the signal across all frequencies? If not it must depend on the input parrallel capacitance of the pre? It would also have a different effect if placed at the cart or pre end of the cable. I understand that SME used to add caps inside the RCA plugs on their arm leads for different carts- this would make the cable directional- is this the root of the directional cable myth?
The inductance of my decca blue is apparently 130mH which is quite high- it has large coils.
Out of interest, here is a pic under the hood of a decca MKIII showing in-cart loading electronics which look like a 3.3nF cap and 4k7 resistor. That's very high loading for any cart but they had huge coils with very high inductance- 260mH!
Image
I'm not sure about that cap value- can anyone confirm? (it is a hunts cap marked .0033)
Makes me wonder why there is not more info in cart manuals about loading- perhaps this is the reason why deccas are so difficult and get a bad name- maybe they need special care with loading?
Mark

PS I'm not sure those bullet plugs are suitable for phono leads as they offer no shielding being plastic bodied. I'm getting more hum with these RG59/bullet leads - could be I need a foil shield but will try some metal body plugs too.
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Postby stpa » 17 Feb 2007 03:29

I may just tell you that 130 mH is not a high value for a MM cart. Many MM range roughly between 500-1300 mH. Anyway, the Decca London Blue is a moving iron cart, and it should be best compared with the Grado example, reported some messages above.

You should lower the impedance of your pre-amp, placing a paralleled resistor at the phono imput, as also suggest above. I guess that a 100K resistor or something around it may fix your setup with the 90pF cable. That is, if your pre-amp follows the "standard" impedance of 47K at the phono input.
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Postby Cobra2 » 10 Mar 2007 18:30

Would anybody please make a spread-sheet, or draw a curve for optimum match vs inductance?

Arne K
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How about Shure that needs between 400 pF and 500 pF ?

Postby thinker » 20 Jun 2007 01:20

The M44 series are 47K and 720mH

Any chance you would have one lying around to test ? :)


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