Phono stage capacitance - how critical ?

[WAPFU]

Greetings,
A rambling here, but hope someone can assist in my thoughts.
With the availability of varioius phono stages I see that the input capacitance varies from make to make. Some can change via dip switches or internal bridging etc, but how critical is it. A shure V!5 requires 47K ohm and 220pF how well does it go with 100pF.
My Project phonobox is stated as 47k ohm and 100pF, can the imput capacitance be increased by adding capacitance at the right place (if there is a right place) to make it OK, for little expense, or am I pie in the sky? and trying to make a silk purse out of a sows ear.

Kind regards
Bill

[michaelwnz]

It's more crucial with fixed coil cartridges like your Shure than with moving coils.

The amount you apply will affect the cartridge's performance, mainly at the top end and will also affect how well the phono circuit suppresses RF interference.

If it's not adjustable on your phono preamp you can add extra capacitance by soldering appropriate resistors across your input terminals.

Only do this if you are competent at electrical work !

This page may help

http://www.hagtech.com/loading.html

I would try your combination out first.

By adding the capacitance value of your arm wiring to your Pro-Ject's capacitance you will probably get close to the recommended 200pF without modifications.


cheers

[WAPFU]

thanks Michealwnz,
resistors or capacitors to be added?
Will check out the link
Kind regards
Bill

[michaelwnz]

Capacitors for capacitance !

My goof , sorry.

[blueintheface]

This page may help

http://www.hagtech.com/loading.html

I would try your combination out first.

By adding the capacitance value of your arm wiring to your Pro-Ject's capacitance you will probably get close to the recommended 200pF without modifications.


cheers

Yes well according to those graphs the best results with the moving magnet cartridges are from far lower capacitance values.

It seems the higher the load, the lower the bandwidth and the higher the resonance. The writer estimates 10pF would be optimal (that would be a line between the dark blue and the mauve) and indeed that would appear likely to produce a flat response. I'd settle for that or for the dark blue line . . . I can live with a dB or two down at 20K for a more natural response.

What was news to me was that higher capacitance values increase the resonance around the cut-off frequency (probably obvious if I'd thought about it more carefully) but I wonder to what extent any cartridge might be relying on this high frequency lift to produce a flat response . . .
?

Listen to your Shure with and without added capacitance. Adding more may not improve it.

[jvo]

Some MM- cartridges are sensitive for it and some are not. Of what I can remember Ortofons like to see a total of 400 pF, but Shures will not change their sonic results.

In some threads people point you at the fact that you first should measure the current total capacitance.

And some sources mention as a nomal interconnect value of 110 pF and an amp- input value of 100pF. That's why there was a CAP 210 - mod for Ortofon VMS 20 E MkII and its stablemates, which I guess adds a value of 210 pF, making a total value of appr. 400 pF.

The extra pF's will tame the high frequency resonance (at 19 kHz or higher still). But a worthwhile benefit is the output increase in the midrange region of approx. 2dB.
This gives a flatter response, because the traditional midrange- level decrease will be corrected a bit.

It is easy to experiment with it, by soldering a 220pF capacitor across the arm's signal leads in the turntable base.

[docjowe]

hi
please go to the gallery, under letter D.Then open the DB systems DBP-6; you will see a simple way for playing with capacitance without soldering inside your gear.
I do not know if the kit is still available, look for DB on the net.
I have built such a thing in the past and I can remember it was simple and effective.

[WAPFU]

Many Thanks to all.
Warm Regards
Bill

[blueintheface]

The extra pF's will tame the high frequency resonance (at 19 kHz or higher still). .

This is what I thought but not what the graphs are saying.

The graphs are saying the increased capacitance increases resonance around the (reduced) cut off frequency.

[jvo]

This is what surprised me too when I saw these graphs. The graphs in my ancient HFChoice booklets tell me that extra capacitors will lower the high frequency resonance.

The interesting site http://www.vandenhul.nl says:

38 Q: Do I need to connect some capacitors parallel to the M.M. or M.C. input of my amplifier ?

A: Fundamentally: No. With modern M.M. cartridges the frequency response is such that the average capacitive load of around 125 pF formed by the tone arm cable and the internal wiring together is just enough to straighten out the frequency response. With M.Ms. the load must be around 47 kOhm.

[JaS]

Docjowe has uploaded a scan from 1979 showing a couple of different types of phono equalisation kit that where available back then, not to mention turning up occasionally now on ebay.

The scan is in the 'various manuals' section.

Regards,
JaS

[WAPFU]

Greetings,

Help my dislexia.

SME give a capacitance value of around 200pF for there lead (thats what they quoted me), The project has an approx 100pF at the input. What do I have, 66pF or approx 300pF?.
So if the Shure requires 220pF where am I ?.

Brain dead over this, or should I just leave things alone?
Warm regards
Bill