SUT and JFETs

[WESTLOWER]

A question to SUT or not to SUT or JFET or not to JFET?
pros and cons and has anyone done the comparisons?

Let battle commence!

[IslandPink]

Some food for thought here, see link. Low bass and bass timing were much better with the jFet option but in the end I couldn't quite get it to sound correct to my ears on female vocals.
This is with 103R which being highish impedance does have some trouble with the primary inductance of typical step-ups.
http://www.audio-talk.co.uk/phpBB3/viewtopic.php?f=11&t=3957&hilit=jfet

[Yomanze]

Subjectively there is a 'calmness' and 'natural openness' associated with transformers vs. using other components. This doesn't mean a lack of dynamics. ;)

[mayebaza]

IMHO generalising isn't that helpful it depends on many variables, sound preferences, existing equipment etc. But I have found jFets produce great rhythm and timing at the expense of inner detail. The outcome of using various SUTs can be very fickle.

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[WESTLOWER]

It's very interesting. Good link mark.

[RothwellAudio]

...to SUT or not to SUT or JFET or not to JFET?
Why only SUTs and JFETs? Why not BJTs and op-amps?
Step-up transformers give the lowest noise in terms of hiss but can suffer from hum if you're not careful. The frequency response etc. is generally poor compared to active circuits but still pretty respectable. In practice the sound can be delightful.
I'm not sure why JFETs are so popular for DIY LOMC headamps - maybe because it's easy to get a JFET circuit to work. However, JFETs are not ideal for low noise. Bipolar Junction Transistors (ie, the "ordinary" ones) are a better option for getting low noise. A good active circuit can have very low hiss, but not quite as low as a SUT. However, hum pickup should be less of an issue with an active circuit. The frequency response, distortion etc. can get a lot closer to text book perfect and the sound can be quite "hi-fi" in as much as it's detailed and impressive but can also be hard fatiguing.
Op-amps never used to be a serious option for LOMCs because the signal-to-noise ratio would be so poor, but some of the more modern op-amps are now good enough.

All of the above is subject to good execution of whichever circuit type is chosen. Badly routed wiring alone can ruin a circuit's performance.

[Arkless Electronics]

Why only SUTs and JFETs? Why not BJTs and op-amps?
Step-up transformers give the lowest noise in terms of hiss but can suffer from hum if you're not careful. The frequency response etc. is generally poor compared to active circuits but still pretty respectable. In practice the sound can be delightful.
I'm not sure why JFETs are so popular for DIY LOMC headamps - maybe because it's easy to get a JFET circuit to work. However, JFETs are not ideal for low noise. Bipolar Junction Transistors (ie, the "ordinary" ones) are a better option for getting low noise. A good active circuit can have very low hiss, but not quite as low as a SUT. However, hum pickup should be less of an issue with an active circuit. The frequency response, distortion etc. can get a lot closer to text book perfect and the sound can be quite "hi-fi" in as much as it's detailed and impressive but can also be hard fatiguing.
Op-amps never used to be a serious option for LOMCs because the signal-to-noise ratio would be so poor, but some of the more modern op-amps are now good enough.

All of the above is subject to good execution of whichever circuit type is chosen. Badly routed wiring alone can ruin a circuit's performance.

And then there's valves as well... very awkward to get quiet enough valves though but I have built such a thing and used it myself for a few years. It sounded fantastic!

There are reasons other than low noise for choosing a particular type of active device of course and JFET's are my usual weapon of choice. I would not generally use BJT's in a head amp myself as most simple circuits are not adequate IMO and to remove the issues requires much more complicated circuitry. I'm not going to expand on that for commercial reasons...

I disagree that head amps sound "hi fi". They are certainly the most accurate means of stepping up the low output from a MC cart. The signal levels involved are so low that everything becomes critical, from component choice to (more important) power supply design, layout etc

[RothwellAudio]

I disagree that head amps sound "hi fi". They are certainly the most accurate means of stepping up the low output from a MC cart.
Yes, I'm certainly not suggesting that all active circuits sound clinical or hard and fatiguing, just that if an active circuit is sub-optimal it's more likely to sound hard than soft. A sub-optimal SUT is more likely to sound soft than hard. Yes, that's a generalization, not a strict rule. Personally, I'd be happy to live with either a good SUT or a good active headamp.

[Arkless Electronics]

Yes, I'm certainly not suggesting that all active circuits sound clinical or hard and fatiguing, just that if an active circuit is sub-optimal it's more likely to sound hard than soft. A sub-optimal SUT is more likely to sound soft than hard. Yes, that's a generalization, not a strict rule. Personally, I'd be happy to live with either a good SUT or a good active headamp.

Agreed :)