jonjin

Bent Audio Mu Step-Up Transformer

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Okay, this is part DIY, part Review and part Technical Section...

I've been happy with my Bent Audio Mu for a long time now. Comparing it to other trannies including a Peerless and Partridge makes me keep coming back to this. It has quite an even character. The Peerless might be a TAD (pun intended) warmer...

Anyway, the Bent Audio is basically a Steven & Billington 103 transformer, 80% nickel core, clock-wise and counter-clock wise winding bla bla bla... it's housed in a 1cm thick Mu metal housing with Mu engraved on the front, makes it quite heavy and relatively big for a SUT. Due to differences in opinion, unfortunately, S&B have stopped supplying OEM SUTs and therefore the Mu is no longer available.

I've been using the 1:10 step-up ratio. Today, I rewired it to 1:20. This presents a 100ohm-ish load to my cartridge - Ortofon SPU GM-e which has an impedance of 2ohm and output of 200microV. The manufacturer advises a loading of >10ohm. Previous to this, I was using a parallel resistor to load the SPU at 10ohm.

With the new configuration (1:20), the obvious difference is more gain. It might be my imagination, but there is a bit more coherence. The overall tonality is slightly brighter but that is not surprising as I was previously loading it lower. It is currently more faithful and realistic though as I have a feeling I've been previously listening on the warmer shade tonally.

It's interesting how the setting on the SUT makes a difference and shows how important it is to match the technical side to get a good subjective listening result!

Peace, Happy New Year & Enjoy-the-Music! :testy1:

JJ

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Posted (edited)
On 15/04/2019 at 17:39, charlieedgar said:

Hi, if you are still on the site can you please tell me how to rewire the SUT's to 1:20 please.

Thank you!

S&B stopped making these a long time back. Their website doesn't show it any longer, but it's available on webarchive:

http://web.archive.org/web/20070714132804/http://www.stevens-billington.co.uk/page103.htm

The wiring diagrams for the different possible gain settings are shown, and the chart for the gain/load settings.

Edited by rabski

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Hello Rabski. Are you familiar with the TX 103 break in process recommended by Thorsten Loesch?  I found this on the internet but I don't understand it, its from diyAudio;

Break-In Instructions from Thorsten Loesch

This worked very well for me, so I recommend it highly. This is what Loesch wrote, with a little editing:

"(The TX-103)... will require a substantial period of "forced burn in" to give it's best, simply because the magnetic core is huge and will not see much magnetisation with normal MC signals. Please consider connecting a CD-Player to the secondary (Output) of the TX-103 and then terminate the input with a low resistance resistor (quality uncritical), I'd say 27 Ohm when connected for 14db gain, 6.8 Ohm when connected for 20db gain and 2.2 Ohm when connected for 26db gain. Leave with a highly dynamic, wide bandwidth signal CD to play for a week or two. I would use music, but I'd expect pink noise to work well too."

Personal Note- While on a week's trip, I connected the signal (a tuner on a 24 hour "grundge" station) to the primary (Input) instead, and had great results. The rest of the circuit followed Loesch's instructions.

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Posted (edited)

Hi.

I know a lot of Thorsten's stuff, but haven't come across this. It does make some sense, especially if yours has been unused for a time. I can't really explain it better than Thorsten does. Basically, take the output of a CD player (which is not connected to anything else) and connect it to the output terminals of the 103. Depending on what ratio you have it wired for, connect a resistor across the input terminals of the 103 with the values as above. Play a CD on repeat for a good few hours. Obviously, don't connect anything else to the 103 (or connect it to anything else) at the same time.

Frankly, I'd not bother though. It will still work absolutely fine 'as is'.

Edited by rabski

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