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Old 5th March 2014, 06:37 PM   #11
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Quote:
Originally Posted by SY View Post
Noise and CMR.
Care to elaborate on that? Currently using an SUT for my MC-cart in combination with a MM-pre. Pretty happy about it, but not afraid of trying to make a separate MC-head
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Old 5th March 2014, 06:51 PM   #12
SY is offline SY  United States
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Go over to the Articles section of diyAudio and look at "His Master's Noise." Lots of detail, and don't hesitate to pipe up in the comments thread. Loading the SUT secondary properly is very important and almost universally overlooked.
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Old 5th March 2014, 06:59 PM   #13
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Well yes, I got the loading part down, sound is perfect, everything is matched to the max. However, I never did a real side-by-side comparison between a SUT and a MC-head. Thanks for the info. I'll have a go at the article
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Old 5th March 2014, 07:23 PM   #14
andyr is offline andyr  Australia
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Quote:
Originally Posted by Wirehead.be View Post
... but not afraid of trying to make a separate MC-head
Why don't you do it, then! Threads like this are just a polarised slag-fest ... "SUTters" putting forward all sorts of justifications why a transformer is the only way to go ("noise and CMR" ) while adherents of a JFET-based head amp do the same.

So you really have to build one, to find out for yourself.

All I will say is:
1. the SLA-powered, JFET based head amp that I use is dead quiet. You cannot hear it above the intrinsic noise of a phono stage.
2. cart loading is easy; the head amp has a default 47K load res ... and a parallel pair of input RCAs, so you can plug in "loaded" RCA plugs into the 2nd pair.


Regards,

Andy
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Old 5th March 2014, 07:28 PM   #15
SY is offline SY  United States
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Quote:
Originally Posted by andyr View Post
a transformer is the only way to go ("noise and CMR"
I didn't use the word "only." But there are a lot of advantages to it, if done correctly. It's rarely done correctly.
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Old 6th March 2014, 05:17 AM   #16
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Nice article SY, enjoyed reading that. I'm no tube junkie though, but gave me some good insights.

Andyr, I do not think a FET-preamp is suited for cartridges/transformers that are loading your stage with a low impedance. Bipolar inputs should give you better noise performance. If you're running an MM with say, stock 47K input impedance (or higher (100k) for Quadrophonic carts), in that case, choose FET; you'll have better performance due to lower current noise (which is the dominant factor for noise there). With an MC and lower input impedance; you're looking at voltage noise as primary contributor, which is lower in bipolar inputs.

The ADA4898-2 seems like the ideal candidate for a MC-headamp.
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Old 6th March 2014, 06:26 AM   #17
andyr is offline andyr  Australia
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Quote:
Originally Posted by Wirehead.be View Post

Andyr, I do not think a FET-preamp is suited for cartridges/transformers that are loading your stage with a low impedance.
Mmmm, Wirehead, you're not making much sense, IMO. I'm talking about a "head amp" which boosts the signal from a LOMC cart so it can be fed into a MM phono stage. A transformer doesn't fit into the picture.

Quote:
Originally Posted by Wirehead.be View Post

I do not think a FET-preamp is suited for cartridges/transformers that are loading your stage with a low impedance.
When a LOMC plugs into a head amp, the cart loading takes place at the input of the head amp. The output impedance of the head amp will generally be very low - so it will easily "feed" the 47K Zin of a typical MM phono stage.

IOW, the head amp "loads" the phono stage.

Quote:
Originally Posted by Wirehead.be View Post

Andyr, I do not think a FET-preamp is suited for cartridges/transformers that are loading your stage with a low impedance. Bipolar inputs should give you better noise performance. If you're running an MM with say, stock 47K input impedance (or higher (100k) for Quadrophonic carts), in that case, choose FET; you'll have better performance due to lower current noise (which is the dominant factor for noise there). With an MC and lower input impedance; you're looking at voltage noise as primary contributor, which is lower in bipolar inputs.
That's your opinion, Wirehead ... I'll ask the designer of my head amp why he chose to use JFETs - I suspect he will say they are (despite their idiosyncrasies) ideal for small-signal components ... phono stages, microphone amps ... and head amps.

Regards,

Andy
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Old 6th March 2014, 09:19 AM   #18
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Quote:
Originally Posted by andyr View Post
Mmmm, Wirehead, you're not making much sense, IMO. I'm talking about a "head amp" which boosts the signal from a LOMC cart so it can be fed into a MM phono stage. A transformer doesn't fit into the picture.
Hi Andy, sorry if it's not that clear. Maybe this will explain it better. If using e.g. an op amp as head-amp; You'll be loading the MC-cart/Head-amp with a low impedance resistor (input side) - e.g. 100ohm. A bipolar input will get you better (lower) noise floor than a FET-input in this case.

Now for the case of the MM-phono stage that follows the head-amp; you can get away with a lower input impedance as well. The regular 47k input can be changed to a lower value. If that's the case, then bipolar inputs should have a lower noise floor (all depends on the implementation) compared to FET's.

That's what I was hinting on. If you can vary your input impedance, and you don't need high impedance, then you can reach lower a noisefloor with bipolar inputs. And with step-up transformers, or diy-head-amps, you can get away with that lower impedance quite easily.

Quote:
Originally Posted by andyr View Post
That's your opinion, Wirehead ... I'll ask the designer of my head amp why he chose to use JFETs - I suspect he will say they are (despite their idiosyncrasies) ideal for small-signal components ... phono stages, microphone amps ... and head amps.
Regards,
Andy
Fully agree, all comes down to preference and taste. But that should not be an excuse to question things

Edit: maybe we should make a separate topic about this
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Old 6th March 2014, 10:04 AM   #19
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To first order, the current noise is immaterial, at least for reasonable values of current noise. The input impedance is also immaterial, it will not affect the noise. Remember, whatever the input impedance, it is paralleled by the cartridge resistance.
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Old 6th March 2014, 08:15 PM   #20
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Hi,

Quote:
Originally Posted by SY View Post
I didn't use the word "only." But there are a lot of advantages to it, if done correctly. It's rarely done correctly.
Whilst I agree that there are advantages I also know that there are limitations. There always are.
From my admittedly limited experience with SUTs it takes a truly exceptional design to beat a well designed active circuit.
It's not as if xformers are noiseless either.
Granted, most commercially available active designs are far from perfect.
For some weird reason this area has been greatly neglected but I'm pretty sure it can be done.
Balanced or not balanced, hollow state or discrete. Stand alone stage or integrated.

It's not even so hard to do with a trioded penthode a la DA3, a EC8010 or even a more common 6DJ8 (when //ed).

And if you use a SUT, why not run it in balanced mode? After all a MC is a balanced source.

Ciao,
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