[travisty]

Greetings,

I have just found and purchased a pair of copper Bent Audio Mu which have been "upgraded." Upgrades include silver RCAs (input and output) and connecting cables made with Audio Consulting silver wire (0.50mm (outer diam 0.56mm) 99.99% DCR: 0.085 Ohms/meter (0.5mm)) and cotton cable, lengthened to 40cm.

The gain has apparently been set at 1:5 for the previous owner's phono stage. The seller said that it could be set to 1:10 or 1:20 but there is no toggle apparent unless I am missing something (and no sticker on the bottom suggesting that there was an original setting). I do not know when they were originally purchased.

I use a variety of MCs, most of them in the 0.3mV to 0.5mV region, some occasionally lower. The phono stages I use are:
1) Hagerman Trumpet (44dB but specs here: http://www.hagtech.com/trumpet.html)
2) stage inside a Pioneer C-Z1 preamp (only spec I can find says phono input at 2.5mV)
3) ZYX Artisan (specs somewhere but not sure where, 35dB gain in MM section).

My questions are:

• How much more reflected impedance is created by the wires at 1:5, 1:10, 1:20 by the longer connecting cables?

Is this just simply (@1:5) 5^2 x 0.085 x 0.4 minus original connecting cable impedance?

• Is there a way to calculate the effect on the resistor loading?
• How do I configure for 1:10 or 1:20? Is the longer cable going to cause a problem at 1:10 or 1:20?
• If I have no space constraints (I can probably stick the cans just behind the phono stage), should I shorten those cables again?
• Is there a PDF copy of the manual available?
• Is there a guide somewhere on using/calcuating the resistors?
• Is there a way to know when it was made?

Thanks much.

[Robin Hood]

What are the recommended ways to burn-in (and not burn up) a pair of copper Bent Audio Mu that are set to 1:20? 

1. Use the Granite Audio MC Phono Burn-In & RIAA Test CD?
2. Connect the output leads of the Mu to a tuner playing white noise?
3. Play 500 or more LPs?
4. Other???

[John Chapman]

Hello!

I hope it has been fun so far - certainly don't wait to burn-in before playing with them!

For burn-in you won't harm them unless you plug them into some kind of wild cable cooker or a wall socket. You can use a tuner (or sat TV output or anything like that) plugged into the output leads. Likely since they have been around that is not an issue - I'd just use'em.

I had a trumpet here for some time - wonderful phono stage.  Have not used the others but they will all be great fun I expect. 35db gain a bit lowish on the zyx so that will depend on your overall system gain as to how levels will work out.

Don't worry about the longer wires - 40cm is not all that long. Just plunk them behind the stage and plug it all together. Ground the cans to the stage and your table to the stage too.

Folks were really getting stressed about the math of loading so I just suggest putting them in with no load to start and then play with loading after you get a handle on sonics. There is no way to predict ideal loads just by calculating - you must play and listen to get there.  Let me know if you have the original load packs and I can suggest starting points.

e-mail me to get info on how to change ratio's, etc...

Many were built as kits so there is no sure way to know when it was made. Most factory ones had round blue stickers on the bottom showing the original ratio. Only some had switches - many were hardwired to set the gain. They all used the same basic transformers - only the very earliest ones were slightly different but 99% odds that yours can be wired for 1:10 or 1:20.  I only shipped a couple pre-built 1:5 units from here - very rare to only need that small gain boost - so it could be a higher ratio if that 1:5 was just a guess or more likely the prior owner re-wired for that ratio.

Thansk!

John

[travisty]

John,

Thanks much for the quick response. I think the 1:5 was done at the same time as the other mods were performed (by someone well-known and quite skilled it seems) as it was done to match a particular pre (and the person changed pres therefore sold his trannies).

I have the original resistor packs.

I will start by trying it at 1:5.

Also... you've got mail.

[zhxia]

Folks were really getting stressed about the math of loading so I just suggest putting them in with no load to start and then play pandora bracelet/pandora charm bracelet/pandora charms with loading after you get a handle on sonics. There is no way to predict ideal loads just by calculating - you must play and listen to get there.  Let me know if you have the original load packs and I can suggest starting points.

[John Chapman]

Hello!

Not sure what is up with the spam link kindly posted by our new friend zhxia. Guess there is a first for everything.....

Sent by mail to travisty but pasted here for more info.

Hello!

Glad that you found some. MU MK2 was not likely - I just can not seem to find time to wrap it up.......

1:5 with the pioneer 2.5mv sensitivity won't be too far off gain wise likely.

Pop the top and gently pull up the cap to get at wiring.

For 1:5 you will see wires 2&3 connected and 4&5 connected and 6&7 connected. 1 goes to the input hot and 8 to the input ground.

For 1:10 connect wires 2&3. Connect wires 6&7. Connect wires 1&4. connect wires 5&8. 1/5 go to input hot and 4/8 go to input ground.

For 1:20 connect wires 1&3&5&7. Connect wires 2&4&6&8. the 1/3/5/7 group goes to input hot and the 2/4/6/8/ group to input ground.

The old info was html online so no doc to send but good info is here:

http://www.stevens-billington.co.uk/page103.htm

If using 1:10 then the load pack paper slips show net load the cart sees (along with resistor value).

If using 1:20 then the cart sees 1/4 of those loads listed. At 1:20 often the natural loading (no extra resistor) is not too far off what many carts like to see.

No likely you will stay 1:5 - you'll need more gain at least for the zyx and likely for the Trumpet anyway.  Still for a quick play it should be fun.

Thansk!

John