Phono Stage Shootout

[Marco]

Hi Graham,

Before you go any further, you'll need to open a trade account. Therefore, please PM me so we can sort that out. No further posts on the forum until then. Cheers!

Marco.

[Bigman80]

🤔

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[Firebottle]

That's good to know because there are over 1000 satisfied Tron Seven owners around the world who are very happy with theirs... Also the Tron Seven has been in continuous production for 11 years...

BTW I have the serial number recorded on the Convergence you have modified so the 2 year warranty is now void.

Hi Graham,

I am only stating my personal opinion given that it was suggested that the Reference used feedback equalisation.
I'm more than happy that there are many satisfied Tron customers, more power to your elbow.

The lack of warranty is of no concern to me as I would expect something of the quality of the Tron to perform faultlessly for many many years.

[RothwellAudio]

if it's the same as the unit i took a butchers at it has two gain stages then a cathode follower from which series negative feedback, including the RIAA, is applied to the cathode of the input valve.

...that's very interesting to know about the Tron reference. I can state categorically I wouldn't like it, without even hearing it. In my experience negative feed back equalisation is never as good as passive

I know that since Jez made that post it has become clear that the Tron does not have the RIAA EQ in the feedback loop, but it still raises the question of the relative merits of active versus passive RIAA EQ.
For what it's worth, my view is although feedback reduces distortion it can only work properly if the feedback network itself is free from distortion. If there's a distortion generating component in the feedback loop (which a capacitor can be), the feedback cannot work in the textbook manner. I wish I could do a mathematical analysis of a feedback system with distortion within the feedback loop, but I'm afraid it's a bit beyond me.

[Bigman80]

I just wish I knew what all of that meant 😂😂

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[Arkless Electronics]

I know that since Jez made that post it has become clear that the Tron does not have the RIAA EQ in the feedback loop, but it still raises the question of the relative merits of active versus passive RIAA EQ.
For what it's worth, my view is although feedback reduces distortion it can only work properly if the feedback network itself is free from distortion. If there's a distortion generating component in the feedback loop (which a capacitor can be), the feedback cannot work in the textbook manner. I wish I could do a mathematical analysis of a feedback system with distortion within the feedback loop, but I'm afraid it's a bit beyond me.

Personally I don't have a problem with feedback RIAA as such. There have been many fine phono stages over the years that use feedback EQ and also many that use passive eq and I have had great results with both... or combinations of them. There are certain issues to bear in mind such as with series feedback the minimum gain is unity and so the top end does not keep rolling off with frequency indefinitely. Some units have even had an extra passive pole added after the actual RIAA eq to combat this and some have also claimed greater compliance with unofficial eq applied by Neumann lathes to records by playing with this extra pole... it is in dispute whether or not this Neumann lathes thing even exists though!

The main problem with passive eq is that it needs great headroom in the driving stage and this makes it generally an iffy proposition with solid state phono stages as they will usually have poor overload margin and may clip on clicks and ticks from the record. It's a trade off in noise against headroom ultimately and often a compromise can be found which will give good subjective results in a passive SS design, but, it will always be rather marginal on overload.... In a valve stage with likely 200V or so available this is usually not an issue.

[Firebottle]

Spot on Jez.

[RothwellAudio]

Yes, I agree with everything you say, but none of it addresses the issue of feedback components which produce distortion. Consider for a moment an amplifier with a flat frequency response (simply because it removes some complexity). A portion of the output is taken with a potential divider and fed back to the input. The potential divider is made up of two resistors, and the feedback reduces distortion etc. But what if the resistors are themselves non-linear? Imagine that the op-amp has zero distortion to start with but the signal which is fed back has been distorted by the two resistors. Would the op-amp still produce zero distortion?
Now consider what happens with capacitors in the feedback potential divider. Capacitors are much more likely to produce distortion than resistors are.

Maybe I'll make a more serious attempt to get to grips with the maths.

[Arkless Electronics]

Yes, I agree with everything you say, but none of it addresses the issue of feedback components which produce distortion. Consider for a moment an amplifier with a flat frequency response (simply because it removes some complexity). A portion of the output is taken with a potential divider and fed back to the input. The potential divider is made up of two resistors, and the feedback reduces distortion etc. But what if the resistors are themselves non-linear? Imagine that the op-amp has zero distortion to start with but the signal which is fed back has been distorted by the two resistors. Would the op-amp still produce zero distortion?
Now consider what happens with capacitors in the feedback potential divider. Capacitors are much more likely to produce distortion than resistors are.

Maybe I'll make a more serious attempt to get to grips with the maths.

The distortion produced by good quality resistors and by the types of capacitor dielectric used in eq stages would be so small as to be immeasurable though... also this would apply to every feed back amp and not only phono stages... then what of this distortion from all other resistors and capacitors in the signal path?

[RothwellAudio]

... also this would apply to every feed back amp and not only phono stages...

That's the point I'm trying to make, apparently without much success.