Trying to figure out my SP/CS BENT MU TX-103 stepups

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miab

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Hi John
 I have a pair of the BENT tx-103 step-ups with a silver primary and copper secondary. I've never seen another pair like these. I always see either all copper or all silver.

 I've had these for a number of years and only recently put them to use. I don't have a manual for how/why to load them with the resistors. I was wondering if you could decipher for me the little labels that come with the resistors? An example of one label is '140 ohm load = 20K res'.  Another label says '10 ohm load = 1K ohms'. My cartridge has an internal resistance of 21.5 ohms. Which resistors do I use?

 Also I believe my set are wired for 1:10. Is it possible for me to change that to 1:20 by opening up the units? Is it a complicated affair. I havn't tried to open them up in case there is a jack in the box ready to throw parts all over the room.

Thnaks in advance
Joseph


John Chapman

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #1 on: 10 Nov 2010, 02:07 am »
Hello!

I had forgotten about those - an experiment that we did way back. They are indeed a one of a kind I think. Honestly I don't recall sonics really but in the end with silver and copper I found that for most folks it was a case of them being fans of silver or fans of copper - and often not liking the other. Because of that and because I felt we already confused folks enough with the choice of silver or copper I was reluctant to add yet another choice to the mix!

The loads are marked for the 1:10 ratio and they show the load the cart sees (ie "140 ohm load") and also the resistor value (20K in that case). If using 1:20 just divide that marked load by 4 to get the 1:20 ratio values. In the end the loading must be done to ear and not using a calculator... I kinda wish I had marked them simply 1 to 12 and let folks start in the middle and play from there - it is easy to get hung up on exactly what the numbers are and the math involved but really that time is best spent listening - more fun too!

For your cart I would start (as I always suggest) with no additional load. Keep in mind you always do have a load there - the phono stage input load is always present. Then once you get a handle on sonics  try the 140 ohm load you mention then simply go up and down from there.

It is possible to do a re-wire to change ratio's. You pop the lid and gently pull up. Most likely the leads are long enough to allow you to make the change but if not pop the bottom and push up on the transformer to pop out the whole package (lid and transformer together). 1:10 will have wires 2 and 3 tied together and also wires 6 and 7 tied together. Split these connections and tie 2 and 6 to the input RCA ground (where 4 and 8 will be now) and tie 3 and 7 to the input rca hot (where 1 and 5 are now). If you can solder it is not hard to do. I am happy to make the change here but the ship costs would add up a bit so if you can do it local that is the least expensive way to do it.

Thansk!

John

miab

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #2 on: 10 Nov 2010, 02:36 am »
Thank you John for the quick reply.

 Theoretically was there any advantages to doing differentmetals for primary and secondary windings?
 So you are saying that a (in this example) 20K resistor would load the cartridge 140ohms for a 1:10 ratio gain. Is there a certain specification in my phonostage that would give me a mathematical starting point for loading?
 When you say to pop the lid, do you undo the 4 larger Allen head keyed screws closer to the center or the 6 tiny allen head screws around the peripheral? Are the wires numbered like you describe them (2,3,4...)?

Thanks again
Joseph

John Chapman

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #3 on: 10 Nov 2010, 04:39 am »
Hello!


>>Theoretically was there any advantages to doing differentmetals for primary and secondary windings?

It was just a curiosity to see how it would sound - ie how much copper and silver sound would result. Wish I could recall but I expect they would be fine step-ups in any case.


>>> So you are saying that a (in this example) 20K resistor would load the cartridge 140ohms for a 1:10 ratio >>>gain.

Exactly.

>>> Is there a certain specification in my phonostage that would give me a mathematical starting point for loading?

The standard 47K ohm MM phono stage load gives 470 ohms to the cart at 1:10 and about 120 ohms to the cart at 1:20.


>>> When you say to pop the lid, do you undo the 4 larger Allen head keyed screws closer to the center or the >>>6 tiny allen head screws around the peripheral?

It is the 6 around the peripheral need to be removed. Likely a small torx bit.  The 4 large ones in the center press down on the transformer to clamp it in place.


>>>Are the wires numbered like you describe them (2,3,4...)?

Yes they have wire numbers on them.

Thansk!

John




marknoir

Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #4 on: 11 Jan 2012, 06:47 pm »
Hi John
 I have a pair of the BENT tx-103 step-ups with a silver primary and copper secondary. I've never seen another pair like these. I always see either all copper or all silver.

 I've had these for a number of years and only recently put them to use. I don't have a manual for how/why to load them with the resistors. I was wondering if you could decipher for me the little labels that come with the resistors? An example of one label is '140 ohm load = 20K res'.  Another label says '10 ohm load = 1K ohms'. My cartridge has an internal resistance of 21.5 ohms. Which resistors do I use?

 Also I believe my set are wired for 1:10. Is it possible for me to change that to 1:20 by opening up the units? Is it a complicated affair. I havn't tried to open them up in case there is a jack in the box ready to throw parts all over the room.

Thnaks in advance
Joseph

Hello all

I have a question: how did you find out that your windings are different? Generally speaking, how do you tell on TX103s which version they are?

Thx

John Chapman

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #5 on: 11 Jan 2012, 09:30 pm »
Hello!

The tx103 transformers themselves have a handful of primary wires and it is the connection of these wires that determines the step up ratio. There were a few very early tx103's that had just 2 primary windings (for 2 ratios) but almost all of them had 4 primary windings that could be connected for 1:5 (all primaries in series) or 1:10 (a combo of series / parallel) and finally the 1:20 ratio (all primaries in parallel).

The MU step-ups would often have the ratio written on a sticker on the bottom. Because it is not that hard to rewire and change the ratio at least some have been swapped by customers. Also some were built as kits. It is good to check inside to confirm the ratio. Units that were switched (toggle on top)  were typically 1:10 / 1:20 ratio.

For silver or copper many silvers will have a sticker on the bottom of the can marked 'S'. Again to confirm pop the top. If it is copper the leads will have teflon insulation (black / white / orange in color) and if it is silver the leadouts will be enamel coated silver - kind of a brass color typically.

Sorry for all that confusion in the answer. It was the down side of having the option of changing ratios.....

Thansk!

John

gundam91

Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #6 on: 12 Feb 2014, 09:40 pm »
Hi John,

I've read some posts where users have indicated that they were getting some improvements with different resistors. Since they are fairly cheap, I thought I buy a few to try. I've narrowed down to a few values (with the included resistors) that I like.

Here are a few questions about the resistors:
1/ Just to confrim, the value of the resistor itself is noted on the second part of the piece of paper inside the plastic bag.
2/ On Parts Connexion website, there are 1/2watt, 1watt, 2watt resistors. Which type should I use?
3/ When attaching the resistors to the Mu, should I leave the wires (of the resistor) straight, or should I wound the wires around the posts?

Regards,
FrankC

John Chapman

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #7 on: 12 Feb 2014, 10:11 pm »
Hello!

I hope it has been fun playing with loads.

1- Long time back when I made those papers but yes - I think the resistor value was on there. It will be in the range of 1K to 200K.

2- Any wattage is just fine - if you have a choice go with the smaller wattage. This is the power they can dissipate and that for this application it is almost immeasurably small!

3- Any way is fine. I'd tend to leave leads straight - maybe trim them so they don't stick out too far just for neatness.

Thansk!

John

Nick B

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #8 on: 13 Feb 2014, 07:49 pm »
Hello!

I hope it has been fun playing with loads.

1- Long time back when I made those papers but yes - I think the resistor value was on there. It will be in the range of 1K to 200K.

2- Any wattage is just fine - if you have a choice go with the smaller wattage. This is the power they can dissipate and that for this application it is almost immeasurably small!

3- Any way is fine. I'd tend to leave leads straight - maybe trim them so they don't stick out too far just for neatness.

Thansk!

John

Is the Optiload on your website still in the works or is it an abandoned project?
Thanks,
Nick

John Chapman

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Re: Trying to figure out my SP/CS BENT MU TX-103 stepups
« Reply #9 on: 13 Feb 2014, 09:40 pm »
Hello!

Like many things it is in slow motion - still moving forward but day to day work seems to impede progress! I have a handful of the loading only units out in the field and also some OEM's are using the switching pcb and the loading pcb in some product development.

Thansk!

John