My new Pass ONO and the use of MuMetal

[harryeng]

Hi group,

I want to share my latest project; pimping my Pass Aleph ONO.

After finishing my Aleph 5, I wanted to upgrade my phono pre-amp. Because of the fantastic sonic results of the Aleph 5, I wanted to choose between Pearl and the Pass ONO. Because I use a MC element, I chose to go with an Aleph ONO.

I was not able to buy the PCB’s, but was able to get fully populated boards. Making my own boards will of course be the next step!

I just finished my first PCB’s, soft start for my Aleph 5 and did not think I was up to designing the ONO PCB’s from scratch, so I started looking for some PCB’s. I was not able to buy the PCB’s, but was able to get fully populated boards. Making my own boards will of course be the next step!

Ending up with populated boards gave me time to optimize the other parts; cabling and casing. I started out with the PCB’s and the trafo’s mounted on a wooden board, and started out from there. Physical restrictions and WAF factor prevented me from using the more normal 2 case solution, so I had to look for another solution. The solution was using three boxes inside a standard casing, and especially the use of mumetal.

The amplifier boards are located inside a box of copper, all 6 mm except the front and the back. I left these 3 mm because of finances, and because I thought with all the holes in these boards 6 mm would be overdone.

The power supply was first done with 8mm thick walls, using two aluminium plates and a copper plate sandwiched between. I found out that 50 Hz wave forms were still coming through, that is why I also used a mumetal box around the transformers.
After that I also introduced a mumetal sheet between the amplifier part and the power supply. Not that I could still measure 50 Hz waveforms, but I was unsure that my method of measuring (coil for measuring magnetic fields, and a oscilloscope to see the field) was exact enough.

All in all I ended up with a 20,5KG heavy box. When you look at the specs from the real XONO you see that the combination of two boxes is also around this weight!

[harryeng]

This is a picture from the inside, with the separate boxes closed.

After I finished the phono pre, I took it with me to when I got the oil changed in my turntable, I was able to compare it with a Jadis DPMC tube phono pre on a very expensive installation with Metronome Technologie equipment. I am very happy to report that the ONO was much more fluent, and a much better stage.

Good work Mr. Pass!!

[harryeng]

I found out that mumetal works great, but needs a lot of space. Mumetal saturates when mounted too close to the transformer. Further more two smaller transformers are easier to shield than one large transformer.


Mumetal changes the form of the field. What I measured is that mumetal does not completely contain the field, but also generates a field close around the mumetal. This means you get the best results as you magnetically isolate the mumetal from the box you put it in. Professionals use layers of mumetal with RVS holders between. I used bitumen to isolate the transformer inside the mumetal, and to isolate the mumetal box from the aluminium box.

Mumetal does not work anymore when you make the folds too sharp! I simply made a wooden box with rounded corners, and used a piece of wood and a hammer to fit the mumetal around. Then I opened up the box again and exchanged the wood for the trafo’s which I mounted in the middle of the box, isolated from the mumetal with bitumen.

One other item: The mumetal does not give through warmth as good as aluminium!


Greetings, Harry

[steenoe]

Good work Mr. Pass!!

Good work, Harry!! We have to digest your writings, to make further comments That is one nice phonopreamp Great work!

Steen

[steenoe]

Come to think of it, do you hear any noise, humm, buzz, hiss or anything like that?? I made several Phonostages, the only one thats totally silent is the Pearl

Steen

[audiotux]

very nice work Harry ,
thanx for the discription with mu-metal

Jürgen

[harryeng]

Hi Steen,

Absolutely no buzz, hiss, humm or anything. Just music


I chose the Aleph over the Pearl because my cartridge has only 0.24 mV signal. Mr. Pass tells in his Pearl article that the pearl wass a slightly more noisier, and a little less gain. He tested with cartridges that have twice the output of mine.

(And of course the ONO looks sleeker, and has a blue LED)

Greetings, Harry

[steenoe]

Absolutely no buzz, hiss, humm or anything. Just music

Thats just great, Harry! I made several phonostages and they all suffered from some noise Except the Pearl! It is in fact a Pearl The SK/SJ devices from Japan are not to be beaten, are they? What cartridge are you using? I am just using a cheap Denon, at this point. I am considering a Grado though, I used to have a Signature 6, before my son accidentally broke the needle arm

Steen

[harryeng]

Hi Steen,

I am using a Zyx RS30, which is a great combination with my unipivot arm from ClearAudience.

I tried the Grado series too, but the Zyx was much better in handling old scratched records. That makes the great combination with the ONO. I have a lot of people coming by now, with both a new Aleph 5 and Pass ONO, because real Class A systems are still rare in Holland. Most people cannot believe the "silences" the system can produce. They keep checking, because they expect small hisses, ticking etc.

Greetings, Harry

[jleaman]

totally good work. .. Look's Really nice for sure. How does she sound ? Did all that copper sheilding help ?

Congrat's.

J'