100k ohm input loading

[Kmmm]

Hi
I'm new on this board and a newbe in the DIY-field as well....
I do have a question that might be silly: I would really like to change my input loading to 100k.
Could any one advice me to what kind of resistors would be the best, where to get hold of them and exactly how to solder them in to my seduction? I will probably have to change it back to 47k using MC cartridges, so what would be best: replace or ad resistors? also; do they have to be matched? To what tolerance?
I hope someone can help me with this :-)

Best regards
K

[Grainger49]

I am not following, why do you want to change the input resistors?

The input loading resistors, 47.5k, are mounted on the input RCA jacks to the ground plane.  If you have the C4S that board is on top of the input RCA jacks and the resistors.  If you do not have the C4S you can get to them easily.  If you are using a high output MC cartridge you need to load it at 47k or 47.5K.  If you have a low output MC cartridge the Seduction doesn't have enough gain to use it, you need a step up device first.  That step up device will want to be loaded at 47k ohms.

The Seduction is suggested for cartridges of 2.5mV or greater.  Any MC cartridge with that high an output will need the stock resistors at the input.

If you just want to try it get some solder wick and remove the resistors.  Replace with a metal film, like the stock resistors.  The stock resistors are probably 5% (maybe 1"), they do not have to be matched, any wattage is fine, they do not get hot.  You can order from Parts Express, Mouser, Angela Instruments, maybe even Radio Shack (RS) will have the value you are looking for.  Most RS resistors are metal film.

[dobbykins]

Just as a note - both of the cartridges I use with my Seduction benefited from loading adjustments.  I briefly installed trimpots for easy adjustment, and ended up with 8k for my DL-160 and 32k for my AT440MLa.

Also, while skeptical of the sonic impact of these resistors, I ordered a pair of 8k TX2352 from Texas Components for about $7 each, and I was very pleasantly surprised that there was a noticeable improvement in resolution.

[Kmmm]

Thank you for your fast reply :-)
The reason for changing my input resistors is to check if there really is some truth in what so many people claim regarding loading of MM cartridges. Some claim 75k - 100k is an ideal range for most cartridges, while dobbykins here, ended up with 8K and 32K for his two cartridges. I belive there are few MM cartridges that sound optimal at 47k.
But that is another discussion for another fora :-) I would just like to test my MM Cartridges at 100k and see if there is any improvement. Yes - I have got the C4S so I will then remove the 47k's and replace them.

dobbykins: Did you order the TX2352 directly from Texas components?

Thanks!

[Grainger49]

That could tailor it to your taste.  Cartridge manufacturers most often say 47k.

I think the C4S, that you say you have, will be in the way of changing the resistors.  It sits on top of the ground plane that the input RCA jacks are mounted into.  That was my warning.

[dobbykins]

I did order directly through Texas Components - they don't have a minimum order and are extremely polite and helpful.  I got in touch with them through their website, but for simplicity, you could just email Arbie Lopez at [email protected]   He contacted me once I sent an email through their site and assisted me through the rest of my order.

I would suggest you do as I did, before you buy expensive resistors, and install trimpots (100k, in your case) in place of the 47k resistors.  They won't sound optimal, of course, but this should let you quickly dial in your favorite loading value.  Then you can replace them with quality resistors.

As Grainger points out, the C4S board is above the input RCA jacks, but with the plate flipped over, it's not too hard to access the resistors.

I also wanted to note that with MM cartridges, I wouldn't expect you to end up with anything nearly as low as 8k - that value was for my DL-160, a high output MC.

[Kmmm]

Thanks'

Yes it might be a good idea to use trim pots first. What kind did you try?
Are you able to adjust the trim pots "on the fly" when the music is playing?
That way it would be quite easy to find the best load for me.
Or would this in any way be a risk? (don't want to break any thing...)

[dobbykins]

Well, with the trimpots mounted where the resistors are, it may be unsafe or inadvisable to do too much poking around while playing.  

A simple way to go about this is to get some rca y-adapters, such as these: http://www.partsconnexion.com/BB-67500-086.html which are on sale from partsconnexion.  If you remove the resistors completely, then run the trimpot from one of the male center pins to the outer part of the rca y, you can plug in the phono leads to the open female end of the y (with the second male end plugged into the seduction) and then very easily adjust the loading.  I don't think there's any reason to not do this on the fly, but perhaps someone else can chime in.

Just make sure you have the trimpot connected correctly so that when you measure resistance between the female center and outside, you see that resistance.  I don't know the effect of having a completely unloaded or shorted cartridge, but neither sounds like a great idea.

Once I have some time, my intention is to take this a step further and just make a little box that plugs into the y-connector, which has a stereo pot in it, for easy adjustment of both channels at once.

As far as the type of trimpot, I just grabbed the cheapest ones from the local electronics store which covered the range I was interested in.  As I wasn't going to leave them in long enough to do anything but find which setting was the best, I didn't think I needed to worry about their quality.

I hope all of this is clear!  Let me know if I've confused you, and I can put together a couple self-explanatory little pictures.

[dobbykins]

I began to worry that my words didn't paint as clear a picture as I had hoped, so here you go:

(http://i1140.photobucket.com/albums/n561/dobbykins/loading.jpg)

This assumes you have already removed the 47k5 resistors between the input and ground plane.

[Grainger49]

   .  .  .   A simple way to go about this is to get some rca y-adapters  .  .  .   If you remove the resistors completely, then run the trimpot from one of the male center pins to the outer part of the rca y, you can plug in the phono leads to the open female end of the y (with the second male end plugged into the seduction) and then very easily adjust the loading.

I think that is an excellent idea.  He can clip only one lead of the load resistors that are there and move them away so they won't touch the clipped lead.

There is a higher chance for noise but you can zero in on the best sound faster this way. 

Great idea!

[Kmmm]

Thank you so much!

This was a great help! I will go a head get some Y-adaptors. I guess i could also use some resistors that I have got all ready but it would be great to have a trimpot...
The only thing I found a bit unclear is "Just make sure you have the trimpot connected correctly so that when you measure resistance between the female center and outside, you see that resistance."
It might be really simple but i'm not sure i got that part... could I just disconnect the pot and measure the leads?

[Grainger49]

Pots usually have 3 lugs, connections.  The full resistance is between two of them, no matter where the pot is set.  Those are the ends of the pot. 

The third is the wiper which moves and changes resistance to the other two as it moves.  So set it midway, you will find two lugs that are the pot value or within 10% of the nameplate value.  The third one, to either of the other two, will be maybe half to the other two connections (if the pot is linear, that is preferable, and audio taper trim pots are really hard to find).

Since you want to use the pot for a variable resistor you attach one of the "Ends" and the wiper leaving the other end unattached. 

[Kmmm]

Ah- ha! Now I get it!
Thanks' :-)