Bottlehead MC Step-Up Update?

[nullspace]

Hey Bottlehead Guys,

Any update on the status of the MC step-up transformers you all have been listening to? I'd be interested to hear about listening impressions and when you might expect to have them available. Thanks very much.

Regards,
John

[Doc B.]

They still sound great. Our initial attempt at shielding in a single mu metal can was only partially effective and so we need to work out multiple shields. I have been super busy lately with a few other products that were ahead of it in the queue and I hope to get back to that one after the first of the year.

[nullspace]

Thanks Doc. I'll be keeping an eye out.

Regards,
John

[Paully]

Anything new to report on this?  No worries, I am a ways from being able to buy anything significant anyway!  But you know your loyal fans, what have you done for me lately?

Paul

[Doc B.]

I am waiting to hear from Mike at MagneQuest about some shield cans I hope to use for the initial run. He's been fighting snow storms and hasn't been able to get at his storage. Hopefully I'll hear from him soon.

[Paully]

Cool beans, thanks.  So just how many irons do you have in the fire?  Don't tell me, I don't want to know.  But it sounds like you are in striking distance on at least 3 or 4 projects.  Awesome.  I do love Bottlehead.

Paul

[Grainger49]

Concerning this from PJ:

 .  .  .   For step-up transformers like these, there are optimum source and load resistances for the transformer. Resistances far from the optimum will result in problems with the high frequency response. These resistances include the winding resistance of the coils, which are not always trivial for MC step up transformers. There are six variables in addition to the turns ratio that determine the transformer's response -the source resistance (12 ohms for the cartridge selected), the primary winding resistance, the leakage inductance referred to the primary, the self-capacitance (mostly of the secondary but including the preamp input capacitance)) referred to the primary, the secondary winding resistance, and the load resistance. In most cases, none of these can be safely assumed to be out of the picture.

Unfortunately, it is rare to see these requirements and winding resistances spelled out in the sales literature for such transformers. I would be cautious about exactly how the loading is applied, if you are going to deviate from the transformer's design intent. That design intent should be specified as the design source and load resistances, plus a range of acceptable load capacitances.

I wanted to post this earlier, but I didn't and still don't have a good answer beyond the above cautionary note.

For me and others who are considering a move up in cartridges will the Bottlehead SUT will accept a wide range of LOMC cartridges?  I guess I'm asking if the prototype that is in hand does.

The fact that the Bottlehead transformer is coming from MagneQuest is a very high recommendation.  We all think Bottlehead is top notch equipment, that is obvious.  And I have no way to audition a more expensive cartridge when I decide I am flush enough to do it.  

Help!

[Grainger49]

Doc,

Your last update in this thread was March 2.  Any news?

[Frank Mena]

From Bent Audio ..... it looks like it going to be a while.....

Cheers FM


Re: Any update on MU step-up replacement?

[Grainger49]

Frank,

Just to be certain, this is a response by "John" about the Bottlehead SUT, right?  I'm not sure who John is.  But I guess we can draw from this post that the MQ transformer is presenting problems.

[Frank Mena]

Hi Grainger.

"John"  in my copied  post above is John Chapman the owner of Bent Audio.   It was my understanding that he and Mike Lefevre of Magnequest were working together to produce a new MC Step-Up which Doc had mentioned as the new Bottlehead Step-Up.  I can't speak for Doc and Co. but I think this is the one and the same MC Step-Up that Doc has referred to in the past as the new Bottlehead Step-Up?. Doc  please correct me if I am wrong (which I have known to be on more than one occasion).

Cheers
Frank M

[Doc B.]

Yes guys, it's all the same transformer. Mike doesn't want to get involved in getting the transformers shielded, he feels that is beyond his manufacturing scope. I guess the same goes for John, he gave me the info about shield cans and the like that he had pursued, which were somewhat spendy. I have done some prototyping work with a couple of approaches. While the results have been about as good as the shielding on 4722s I am hoping to get it a little better.

The bottom line is we need to determine what form of shielding works best so we can determine a price and then see if the price will be acceptable. As usual we have several different projects going in parallel, at various paces. Right now I need to concentrate on getting Stereomour delivered, and then I should be able to try to get a final solution to the step up shielding question.

I really appreciate everyone's patience, I know it gets kind of frustrating when we talk and talk about some of these things and they never seem to happen. They are moving along, but the more people involved in a given project the more time it seems to take to get it wrapped up. We do have some interest by a couple of clients for a high end finished phono preamp and that could be a good stimulant to get the step ups rolled out.

[Paul Birkeland]

John is John Chapman of Bent Audio.

He initially expressed interest in the transformer, and helped with the development, but had too much on his plate to bring them to market. John was excited to hear that Doc was interested in the SUT's and bringing them to market, and that is what is referred to in that message.

[Grainger49]

Thanks to all for the clarification.  I didn't know of a John on the Bottlehead crew.  I got it now.

Looking at that auction site I see some single 4722 transformers for $250 each and a pair for $400.  And a MC SUT setup for $1000. 

Can any of the Bottlehead crew help me with an answer to reply #6 of this thread?

[Paul Joppa]

Reply #6 would be post #7, right? The one by Grainger?

The question there was whether the stepup would work with a wide range of cartridges, in light of my analysis that says in theory, no stepup will work with a wide range of cartridges.

The theoretical problem is high frequency resonances, which may be overdamped or underdamped if the source and load impedances are not close enough to optimal. To answer the question of what are suitable ranges of impedance, one would need detailed measurements of the transformer parameters. As far as I know, these measurements have not yet been done by anyone - Mike LaFevre, John Chapman, or Bottlehead. Chapman has done some frequency response measurements showing exceptional performance, but I don't have copies of them or details of how the measurements were done - especially, what source and load impedances were used. I will do that analysis if I can get a sample to measure, but it will take a while even then.

In practice, if the resonances are high enough in frequency, the damping may not have much effect within the audio band, and so may not be audible. Based on my memory of Chapman's measurements, that is at least somewhat the case here - IIRC the first resonance is around 100kHz, but don't quote me.

Also in practice, the theoretical model does not always predict subjective performance, presumably due to other variables that may have been neglected or are actually unknown.

The only way to know reliably the frequency response and distortion as a function of source resistance, load resistance, load capacitance, and signal level is to measure the response over a wide variety of those parameters. The only way to reliably know how it will sound with a wide variety of cartridges is to listen to a wide variety of cartridges through the transformer, with a wide variety of music and on a high-resolution audio system. Nobody has undertaken either of these extensive and time-consuming studies yet, and I don't expect it to happen until we see a sales potential of thousands.

So we may have some theoretical guidance eventually, but a reliable and detailed answer won't happen anytime soon.