[TheChairGuy]

Tho ideally it's best to have the correct resistance in your phono stage itself, using phono 'plugs' give you flexibility to use lots of different cartridges.  But, I don't understand what load your cartridge sees 

For instance, my phono input to my MM stage (I have two separate rca jacks for MM and MC) is 47K ohms...and I use a 10K loading plug on the outside (attached to it)...does the cartridge 'see' 10K?  What of the internal 47K load? 10K being about best for the Grado hi-output units.

Also, my MC stage is now 10 ohms internally...if I use a 1K loading plug on the outside, does the cartridge see only 1K?  What happened to the 10 ohm load within?

Sales & Marketing major here, guys, so keep it 'light', please 

John / TCG / TheChairless and Clueless Guy 

[SMc Audio]

Hi John -

Your description of using resistive loading plugs (RCA plugs with different value resistors installed) implies that you have a pair of "Y" adapter cables (or something similar) plugged into your phono inputs, and you are connecting the phono cables on one side of the "Y" and the loading plugs on the other.  This will put the added load resistors in parallel with the fixed input load already installed in your preamp.  The formula for resistors in parallel is pretty simple: 1/Rt = 1/R1 + 1/R2.  That is, add the reciprocals of the resistor values in question, and then the reciprocal of that number is the total equivalent resistance.  So, in your case #1, we have 47,000 Ohms (47KOhm) in parallel with 10,000 Ohms (10KOhm).  Running these values through the above formula gives a total equivalent of 8245 Ohms - somewhat below the 10K load you had in mind, but not too far off.  A load resistor in the 13K range will get you closer to 10K equivalent if you wish to experiment.

Here are a few things to keep in mind:

1) When you add resistors in parallel, the result will always be lower than the smaller of the added values.

2) When dealing with a 47K input load (standard for most phono preamps), once your load value gets down around the 1000 Ohm range (1KOhm) the 47K load can pretty much be ignored.  47K in parallel with 1K gives 979 Ohms - pretty close to 1K.

3) Same thing when dealing with a 10 Ohm input load - 1K is so high in relation that it doesn't do much of anything.  The equivalent resistance is 9.9 Ohms.  You would have to use values closer to 10 Ohms (below 100 Ohms for sure) to have an appreciable effect.

4) Your method of using a "Y" adapter is very handy and is great for experimenting.  However, once you have settled on the best load for your cartridge it's a good idea to install the resistors inside the preamp and eliminate the "Y" cable.  Many preamps have someplace arranged for this, which certainly simplifies things, but worst case you only have to solder the resistors across the input jacks (from the center pin to the outer ring connection - usually ground).

5) This is high-end audio we're taking about, so don't forget that the type of resistor used will have its own impact on the sound - quite apart from the specific value.  Like everything else in audio, there is no agreement on which types are best, but the usual suspects are (in no particular order) Vishay bulk-metal-foil types (like the S102 series), Holco or PRP metal films, Mills wirewound, Caddock, and carbon types from Kiwame, Riken, etc.

6) Have fun!

Best regards,

Steve McCormack
SMc Audio

[TheChairGuy]

Brilliant Steve - thank you for your amazingly detailed reply 

I'm at a trade show now far from home, but need to digest all of this later tonite or tomorrow.

Again, thanks...

John

[SET Man]

Hey!

    Yeah, I had to open my pre, de-soldering, and soldering loading resistors 3 or 4 times before I found the value that I like. 

    Should have done the "Y" adapter or run wires with gator clips out at the first place, that would have made thing a lot easier! 


Take care,
Buddy

[TheChairGuy]

I thought I'd dig this one up from 9/2007 as it's the same topic...and it gives those who didn't see the first time an opportunity to see Steve / SMc Audio's thoughtful reply to my original question.

Thanks to member neobop (from another website I post at) and his solder skills, I'm the happy owner of 4 different value loading plugs to use with my much-loved Mitsubishi DA-C20 preamp.

I normally eschew any additional connections as they are poisonous to eeny-weeny phono signals, but in this case I must to test these wonderfully crafted Neutrik beauties out. 

He color coded each pair and I have 2K, 11.4K, 19.8K and 33.2K values to play with (in conjunction with my 50K input of the Mitsubishi)

I found a while back that while the best connection is no connection either with phono or line levels, when dealing with rca jacks and need a 'Y' adaptor...the solid metal bodied ones, insulated in teflon, are the least injurious to sonics.  They are easy to find and cheap to buy...mine are nicely machined Vampire Wire versions, but Monster Cable's look equally good and spec well.

The most injurious are any type of wire adaptors in my experience - not helpful at all to sonics.

I have just now inserted the 1 male to 2 female adaptor to my MM phono input....ran each side into one exposed female on either side and the 11.4K loading value in the other.  As simple as simple gets 

I am playing a rather abysmal recording of 'Amadeus' (soundtrack to movie) and my much loved Grado Gold w/shibata.  Run straight thru to my preamp I have always found the tandem to be near perfect.  But, always the glutton, I'm always of the belief that there is more perfect out there to discover (aren't most of us here at The Vinyl CIrcle similarly afflicted )

I'll update you as I go on how these loading plugs fare and if they are beneficial for the Grado (and other cartridges I have) or should we just respect Grado's recommended 47K loading?  Ditto for AT440ML/OCC and Ortofon X5-MC's 47K recommended setting. 

One of the more interesting pairing will be with my slightly too bright Stanton CS-100 in the MM stage...and the ill-suited Pickering XLZ-7500-s low output MM cartridge that needs MC-like gain (60db+), but atypical resistance loading (higher than the 10ohm MC section right now). 

Any higher value will reduce the severe treble scalping my current MC phono section gives it....it is otherwise a brilliant sounding cartridge.  So pure and wholesome.

One thing early on I can tell you I'm thrilled with is there is no extra hum or noise noted. I had bought a resistive loading, switchable box with several values on it from DB Systems hummed so badly it could've been a Billboard top tenner

Will update as time passes and bit and I can assess....

Thanks, John