John Curl's Blowtorch preamplifier part II

[Joachim Gerhard]

I have only the Lundahl in house. I look up what model.
What i had is a long discussion with Brian Sowter and he prefers MU-Metall core.
The Lundahl has a amorfous core . Ask Allen Wright. He prefers amorfous because of the sound. Sowter said that MU-Metall has lower distortion for this purpose though.

 

[Joachim Gerhard]

Thats the one i am using. I like it a lot. I was especially surprised about the treble extention.

 

[john curl]

I have both amorphous and MuMetal Lundahl transformers here. I think that MuMetal is more practical, because of record warp modulation.

 

[jlsem]

Lundahl makes any number of transformers with Mu-Metal cores, including the LL1681 and LL1933 which can be used as moving coil step-ups.

John

 

[john curl]

Yes, that is my current choice, but I am trying to be open minded about other choices.
The difference between Mu-Metal and Amorphous cores with regard to low frequency distortion, is striking. Mu-Metal is MUCH lower in distortion below 100Hz.

 

[Steve Eddy]

I have both amorphous and MuMetal Lundahl transformers here. I think that MuMetal is more practical, because of record warp modulation.

How do you mean?

se

 

[jacco vermeulen]

What the world needs is a balanced turntable
hookup that appears singled ended.................

Why not both.

 

[pooge]

Here's anothor option:

Stevens & Billington Limited Audio Transformers

 

[SY]

$2600 a pair? Holy ****! For that amount of money, I'd expect Stevens' and Billington's daughters to orally service me while I'm listening to records.

 

[pooge]

$2600 a pair? Holy ****! For that amount of money, I'd expect Stevens' and Billington's daughters to orally service me while I'm listening to records.

Look further down the page if you don't require those accessories.

 

[john curl]

I think that we could also save time and money by redesigning SY's phono preamp using a single 12AX7 and a generic input transformer. Should measure about the same.

 

[SY]

No, it won't. Not by a long shot.

 

[john curl]

Once again, let me explain the problem with balanced vs unbalanced. Most phono tone arms come with unbalanced wiring with RCA connectors. Unbalanced wiring is generally cheaper, more popular, and just as quiet in a normal domestic environment. For example, my Linn Arm that came with my Linn Sondek, has single ended wiring and RCA connectors.
What about balanced then?
Balanced operation, to be successful, requires balanced lines from the tone-arm to the preamp. This is because balanced operation works on common mode SUBTRACTION of the interfering external noise being picked up EQUALLY by both the + and - signals in the same cable. Nothing else will work as well, if at all.
So if you try to use a single ended cable into a balanced input, no matter how well designed, you will get noise pickup.

 

[john curl]

I think you overstate, what it takes to make a phono stage from YOUR perspective. It seems to me, that a slightly modified DYNA PAS-3 phono stage with an input transformer, will do the job nicely. Please prove me wrong, if you can.

 

[SY]

It seems to me, that a slightly modified DYNA PAS-3 phono stage with an input transformer, will do the job nicely. Please prove me wrong, if you can.

If you read the article I wrote, you will see why that's not the case. Mediocre distortion, poor RIAA conformance, slewing, high output impedance, lousy power supply rejection, sensitivity to output loading, and poor overload margins and recovery are inherent to that design. Time to get your head out of a 1979 mindset and join the 21st century!

 

[SY]

So if you try to use a single ended cable into a balanced input, no matter how well designed, you will get noise pickup.

"Doctor, it hurts every time I do this."
"Don't do that."

Replacing a tonearm to preamp interconnect is trivially easy. And cheap, if you don't go in for snake oil. I used shielded CAT 5, though mike cable would probably work just as well.

 

[Steve Eddy]

Once again, let me explain the problem with balanced vs unbalanced. Most phono tone arms come with unbalanced wiring with RCA connectors. Unbalanced wiring is generally cheaper, more popular, and just as quiet in a normal domestic environment. For example, my Linn Arm that came with my Linn Sondek, has single ended wiring and RCA connectors.
What about balanced then?
Balanced operation, to be successful, requires balanced lines from the tone-arm to the preamp. This is because balanced operation works on common mode SUBTRACTION of the interfering external noise being picked up EQUALLY by both the + and - signals in the same cable. Nothing else will work as well, if at all.
So if you try to use a single ended cable into a balanced input, no matter how well designed, you will get noise pickup.

Well, first, just because a cable is terminated with RCA connectors doesn't necessarily mean the cable isn't balanced, i.e. symmetrical. A simple twisted pair is "balanced" as far as that goes.

Second, one of the beauties of transformers is that they can give you excellent common-mode rejection even when fed from unbalanced sources.

Third, this can also be achieved electronically, as witnessed by Bill Whitlock's InGenius^TM balanced line receiver (see patent 5,568,561).

se

 

[john curl]

I'm too lazy, and besides, single ended works for me just fine.

 

[john curl]

Well, maybe somebody, somewhere, can take a 75 ohm cable, like a Radio Shack, and balance it effectively, but I would not recommend it.

 

[Onvinyl]

I had my tonearme rewired from the headshell plug in one go to the balanced phono plug. Even my unbalanced phono stages profitate. There is less hum and considerable better sound. Some snake oil involved, though.

I guess it's because you have two identical dedicates wires (+, -) and an additional shield rather than a shield that serves as a signal return at the same time.

Rüdiger