MC Cartridge Loading and Damping

little eddy · Post by **little eddy** » Mon Jun 22, 2009 10:37 pm

I have a new phono preamp with an ECC83 cascode first stage. I have a 1:10 step up for my MC25FL and the builder has initially fitted a 100k load resistor.

The MC25FL is said to have a resistance of 6R and requires a load of >20R. The 100k equates to a load of 1k0, significantly greater than Ortofon's stated minimum of 20. What would be a reasonable load because doing a bit of surfing and reading, I have seen a few implementations with and input R of 6k8 equating to a load of 68R. Has anyone any experience in terms of optimum loads for Ortofon MC cartridges and if so, does this make much of a difference? The load resistor also doubles as the grid leak resistor for the first stage - is 6k8 a bit low and if so, what might be the optimum to best satisfy the needs of the cartridge and input stage?

Looking one step further, MJ (and Sowter and Jensen for that matter), talk about a damping series resistor/cap in parallel to the load/grid resistor. MJ suggests 2k4 and for 6R cartridge a 1nF cap - has anyone any experience of this type of Zobel network?

MJ goes on to suggest damping cap type FKP2. Is this OK? He also suggests that the load resistors should be 'low noise' - what types of resistors would therefore be best suited for this application?

Mike H · Post by **Mike H** » Mon Jun 22, 2009 11:23 pm

So the impedance ratio is 1:100, so make the amp's input resistor 500k for 50k input? For example.

Or, just connect the secondary to the grid and put resistor of your choice across the primary. In either case you need to change / remove the 100k resistor in the amp.

Neal · Post by **Neal** » Tue Jun 23, 2009 8:54 am

I used a 25FL for a few years I found it was best loaded between 47R and 100R, I prefered the 47R, 68R is in the ball park.....1K is way too much it will sound over bright, thin and tireing IMO. I've never really worried about resistor types in this position and just use carbon but I suppose a good stable metal film is the better engineering choice.

I also tried the MJ Zobel idea on my WAD PhonoII:

This setup turned this:

...into this using a 1n5 cap and 5K adjustable pot:

TBH I prefered the sound *without* the zobel

little eddy · Post by **little eddy** » Wed Jun 24, 2009 11:16 pm

Neal,

Thanks for this. Will order some 4K4 rc65y, (and also parts for the Zobel as it's only a couple of quid to try).

Mike.

little eddy · Post by **little eddy** » Sat Jul 11, 2009 8:07 pm

Well my plans changed after I managed to acquire a pair of 5k0 Charcroft CE-S102C bulk foil resistors (as recommended in this position by MJ).

Things are now tighter and transparent but I'm unsure whether it was the value or the resistor type that fundamentally made the difference.

What is most interesting is that the overall improvement seems to be very dependant upon the recording. Some tracks/albums are jaw dropping especially in terms of an expansive soundstage so its so extremely disappointing when other favourite albums from the past fail to inspire.

Anyway no doubt you can give it the thumbs up (or not as the case may be) at Owston.

Andrew · Post by **Andrew** » Sat Jul 11, 2009 8:25 pm

Neal wrote:
...into this using a 1n5 cap and 5K adjustable pot:

TBH I prefered the sound *without* the zobel

Sorry Neal I missed this, dunno how....Anyway, I just need to make sure you are being completely serious about the zobel, you preferred it without?

I've been meaning to try this out and well....

-- Andrew

Neal · Post by **Neal** » Sun Jul 12, 2009 11:17 pm

Yep, without....

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MC Cartridge Loading and Damping

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