John Curl's Blowtorch preamplifier part II

[scott wurcer]

Originally Posted by Soundminded

An awful article. A prime example of why I not only don't subscribe to this magazine, I rarely read it even for free and never take anything it says seriously.

ftp://194.45.31.243//Parasound/Revie...rch%202011.pdf

I've been to the home of one of the folks mentioned in the article, the listening protocall was to say the least not rigorous. $26K on the word of two partying dentists? BTW did they mention if they loaded the cart the same for all cuts? If not....

[Steve Eddy]

Originally Posted by john curl

Direct measurement comparison between the mumetal and amorphous transformers: LL1931, and LL1933, show a VERY large difference in distortion at 10Hz.

That's probably because Per isn't using cut cores in the LL1931.

That means no air gaps, which means higher efficiency (more like a toroid which also doesn't have an air gap). That means that all else being equal, it will saturate sooner than a laminated core or a cut C core.

se

[john curl]

Moving coil input, simple ratio 5:1 optimum, 10:1 usable. Load, paralleled differential jfets giving an equivalent input noise from the fets alone of about 0.5nV/rt Hz. Need to extend to 0.2nV/rt Hz or so, with transformer, so DC resistance is important.

[Soundminded]

Originally Posted by scott wurcer

I've been to the home of one of the folks mentioned in the article, the listening protocall was to say the least not rigorous. $26K on the word of two partying dentists? BTW did they mention if they loaded the cart the same for all cuts? If not....

The protocol was a joke. The first thing the guy did wrong was to record them on a cd. Since those who swear vinyl is the ultimate recording and MC cartridges the only way to listen to them detest cds with a passion, as soon as any signal passes through that filter they'd consider it all but worthless. And that's just for starters. The article IMO was as worthless as the tests, merely a space filler to sell magazines. Now he had played recordings of dentist's drills, a sound they'd be familiar with.....

[SY]

Originally Posted by scott wurcer

BTW did they mention if they loaded the cart the same for all cuts? If not....

Did I overlook the part about level-matching?

[jacco vermeulen]

Originally Posted by pieter t

being a socialist I actually give them away for a small additional fee

Mr T,

in that case, may i suggest a last name change.

[pooge]

Originally Posted by john curl

Yes, Scott, presuming the transformer is IDEAL! However, there are differences between transformers, and I seek to find these differences. Then I can chose between them.
It is POINTLESS for me to put in a less than optimum transformer. I am willing to go as high as 200 Euros / transformer, in limited quantity, 100 or so. Pieter, can you work in this range?

Stevens & Billington Limited Audio Transformers

[Steve Eddy]

Originally Posted by pooge

Stevens & Billington Limited Audio Transformers

I thought they stopped selling transformers to DIYers and OEM's?

se

[john curl]

S & B transformers have too much self noise. 0.8nV/rt Hz. They may sound good, but they will not help in my application.

[SY]

Originally Posted by john curl

S & B transformers have too much self noise. 0.8nV/rt Hz. They may sound good, but they will not help in my application.

The spec is 0.8nV of noise, not 0.8nV/rt Hz. It doesn't appear to be a noise density spec, nor were they kind enough to specify bandwidth. I didn't see a DCR spec, but from the winding description, it's presumably close to the same as the other good MC step ups.

I think that for Pieter to design the transformer properly, you'll have to spec the input capacitance of the FETs in your circuit.