[gundam91]

Hi John,

I couldn't wait any longer, and luck happened to struck as I was browsing the trading post. I've now got a pair of the MU in my hands. 

Just want to check in with you to make sure I am connecting the MU correctly, as I can still hear some low level hums when the music is not playing.

This is how I have it hooked up: tonearm wire inputting into the MU, and MU into ARC PH3 SE (phonostage). I had changed the cartridge loading on the PH3 back to 47k Ohm.

The ground wires from the two tonearm cables are connected to one "Y" connector. Originally, I just connect the wire to one of the MU "can". but the hum was really loud. Then I tried bypassing the MU, and connecting the ground wire directly to the PH3, and that drastically reduced the hum. Can't hear it when music is playing. But can definitely hear it from 3 ft away while no music is playing.

Should I have broken up the ground wires, and hook up each cable separtely to the two MU cans? Or should I make some ground wires and connect the MU cans to the PH3?

Tried different loadings on the MU cans, but that doesn't affect the lelve of hum.

FrankC

[John Chapman]

Hello!

Hum always seems to come down to grounding. Location / Shielding can have some affect but it seems once the grounding is happy that the system then much more robust and less sensitive to such things.

As I read your post you still do not have the MU can's grounded. I usually start the ground hook-up with the phono stage used as the phono system ground point. Leave the tonearm / table ground(s) connected at the phono stage like they are now. Then ground each MU can to the phono stage. This is most often quiet - let me know how it works out and we can play from there. It's not uncommon when the level knob is up well beyond normal listening levels to get a bit of noise on a phono front end but I have never met a system yet that could not be really quiet at listening level settings.

Thansk!

John

[gundam91]

Thanks John. Took a while for me to put together a grounding wire. Tested out last night and it seem to be working. Thanks!

[kdl]

Hi John,

I have my MU (picked up at Agon about 3 weeks ago) up and running for almost 2 weeks with Shelter 501MK2. Played with load impedance from your set, at 10:1, I found 15Kohm (113 load) is about right. When it gets to 100ohm, top starts sounding soft a bit.

I ordered quite a few brands of resistors around 15Kohm to try out. Holco, Vishay, Shinkoh, etc.

I would like to know:

1. Is the rated watt of resistors matter? 0.25, 0.5 or 1.0? I tried to keep low, but sometimes not available.
2. How can I break-in resistors?
3. From what I read, is it safe to connect the primary (RCA) to a CD player output (2V output), and just put a resistor in (unplug from phono input)? At 1:10, it will have 20V at the secondary, with a 15Kohm in place, it will generate some heat but not too much (< 0.03W). The question is really whether TX103 can handle 2V input (vs. 0.4mv from cartridge).

Thanks,

Ken

[John Chapman]

Hello!

1- Rating on resistor is not important and it can be small 0.125 is fine too. The power dissipated across that resistor is so tiny it puts no energy into the resistor.

2- You could hook them across a player's output or leave it in place if you are running the player into the unit as you suggest in your question 3.

3- That will be fine. The power is not an issue and the tx103 can handle that voltage fine. Also due to loading affects and the fact the average signal will be under the 2V rating of that player the average level accross it will be much less with a music signal playing.

Have fun!

John

[kdl]

Hi John,

Thanks for your quick reply.

What I am planning to do is to run pink noise in repeat mode from CD player, feed to MU primary (RCA) input, and on the MU secondary, only connect 15Kohm resistors to break them in (unplug MU from preamp phono though).

I found that in 20:1, Shelter 501MK2 didn't sound good (kind of flat out compared with 10:1). It has DC impedance of 12ohm. Just don't know exactly how it plays out since suggested impedance for 20:1 is up to 5ohm (good fit for Koetsu), and 10:1 for higher (but not as high of Denon 103's 40ohm). I am a bit confused, I saw people claim prefer Shelter 901 (14ohm) on 20:1 to 10:1, but my listening test showed the opposite and my findings are in line with what tx103 suggests.

Thanks,

Ken

[John Chapman]

Hello!

Your break-in plans will be fine.

ALWAYS load to listening rather than what the math would predict. I'm quite a fan of math but in this case of loading it is really hard to predict from the numbers what will work best. Just go with what sounds good! I removed the loading math stuff from my page for just that reason - I could sense some folks spending more time stressing about the number rather than just playing with the loads and getting a good handle on how they affect sonics.

Thansk!

John

[gundam91]

Hi John,

Another quick question. I have tried the MU with no resistors, and it sounded too bright. I then simply pick a set of resistors with value in the middle of the stack (113 ohm load) and found it to flatten the upper frequency too much. So now, which direction do I go? Do I tried something with higher load #, i.e. 298 ohm, or do I go with something with lower load #, i.e. 70 ohm?

[kdl]

Hi Frank,

If your MU is setup for 26db (20x) gain and you are using Shelter 901, it's probably not the right setting for MU to work with 901. If you can, try to use 20db (10x) setting of MU, and tap a 15K ohm high quality resistor, it will definitely sound right.

Or, if you are interested in getting rid of it, please let me know.

Happy Listening,

Ken

[gundam91]

Hi Ken,

Thanks for the info. You don't happened to have one of the prototypes with taggle switch to change step-up ratios? I have the older version with a pre-set ratio. I bought it used. So anyway to check to see what step-up ratio it is (for us that are technically challanged)?

I am actually not using the 901 right now. I am trying out this inexpensive MC cart from a very small Asian outfit. The guy basically told me what John said to use my ear to make the call.

I had first listened without using any resistors, and it sounded bright to me. So I took out the packets of resistors that came with the MU with loading ranging from 10 ohm to 382 ohm, and just pick a middle value to start (113 ohm). I thought it cut off the top end too much. So the next one I used was 225 ohm. I think I was going the wrong direction, so I thought I double check with John.

[kdl]

Hi Frank,

I do have the version with toggle switch, bought used from Agon. I used 501MK2, high gain (20x) didn't sound right.

If you google 'Bent Audio MU', there is an article named "Step Up the Plate". Lots of info there to read. Basically, matching is the key.

If you know the DC impedence of the Asian MC you have, it will help to know whether something wrong on setting.

If you have some fixed output CD pink noise, you can hook it up to MU input, don't plug into MM, and put any resistor on and measure the voltage between the resistor, and voltage on the CD output. Then you will know the ratio of your MU. 10X or 20X.

In general, if MC DC impedence is higher than say 10ohm, 20x will not work sound properly. Worse, if DC ohm is like reguler Denon 103, 10x might be no good. I take is that, for Koetus, use 20x is good fit, for Shelter, 10x is better but need resistor to lower load impedence.

First figure out your MU gain setting by a multi-meter, and also check the DC ohm of your MC cartridge.

Good luck.

Ken

[gundam91]

Hi Ken,

Thanks for your help! Ha! Ha! I don't even know how to use a volt meter. That's how technically challanged I am. Can you answer a few questions?
1/ Which setting should I be using? There's "A", "V", "F", and the Omega symbol. I assme we use "V" and the setting would be for AC (vs. DC)? The dial has settings from 200m to 2 to 20, to 200. Which one?
2/ Where should I be pointing the red and black leads? Do I touch the red one to the red interconnect coming out of the CD player, and the black one to the black interconnect? I assume to the interior side of the "exterior" wall, not the rod in the center?
I placed the lead on the input of my headphone amp (where the interconnects from the CD player connect to the amp) and use the setting "V" and 200m and got a measurement of 0.1 playing music.

The spec on the MC cartridge:
- output voltage: 0.5mV
- Impedance R = 5 ohm, L = 5 ohm.

Assuming the step-up ratio is either 10x or 20x, how do I calculate which resistors to add?

Thanks,

FrankC

[John Chapman]

Hello!

Missed out on most this thread! Just back from a couple days away in Seattle.

Likely by now you have it mostly sorted out. Basically I started off with the idea of 'calculating' the 'correct' load to use but quickly found this was not of much use......The chances of it actually being the ideal load is rather slim so I have for some time just played with loading to get to the right spot. Time listening to tunes being much more enjoyable than time searching the web and running calcs....

I usually start with no load like you did and then try a load about in the middle - again just like you did. The higher the load is the closer it is to no load so I would have thought that as you go up the sound would have tended to get closer to the no load sound. 

Some MU's were built switched and some have a sticker on the bottom showing the ratio (1:10 or 1:20). Some were built as kits and some have been modded along the way so if you want to sort it out just call and I'll figure exactly what you have. It is of use to find a starting point but you'll still want to play with loading to get the sonics where you want them. Also don't neglect tweaking table settings as well - like VTA, etc - the loading will only skew the balance so far and if you push the load too far in an attempt to get the sound where it does not want to naturally end up it'll never sound right. The meter can tell the story of what ratio you have - but there are some meters that do not like to read the windings of any transformer. The inductive load freaks them out and they won't lock on to a steady reading....


Thansk!

John

[kdl]

Hi Frank,

John already answered how to tell 10x or 20x, looking for sticker on the bottom.

If you MC DC impedence is correct, I bet you have a 10x MU not the 20x, 5ohm should matched well with 20x without load resistors.

You can try load around 50ohm to see any change on sound, 113ohm still too high.

Good luck,

Ken

[gundam91]

Ken and John,

Thanks you both so much for your assistance!

I checked with other cartridges in my collection. One has 30 ohm. The shelter 901 recommends 5 to 20 ohms of impedance when using STU. And the Benz Woodbody M2 has an internal impedance of 24 (ohm?). Do you recommend sending the SUT back to John to configure it to 20x? John, can this be done?

Sorry, to clarify, I checked the bottom of both, and there were no stickers. But from how much gain I was getting, I think 10x gain is probably correct.

[kdl]

Hi Frank,

If you are sure about 10x setting, it will be fine with 901. Your other cartridges also a good fit for 10x.

What Asian cartridge do you use? Mind to tell?

Ken

[John Chapman]

Hello!

Pop the lid off one can and then call or e-mail if you want to confirm the ratio. Most the TX103's out there can be wired 1:10 or 1:20.  It is a bit hard to guess ratio's from listening alone - since loading and cart impedance's will also affect levels.

I can flip the ratio if you need to - although it is rather easy to do for anyone who solders so maybe we can spot a local diy type who can save ship costs.

The recommended loads are only a wild starting point - and I personally seldom find those really low loads (like the Shelter recommendation) tend to sound ideal.  Easy to try that load so why not but definitely try some loads up higher too!

Thansk!

John