surface noise and cartridge/ phono pre questions

Doug is correct- the design of the phono section can influence ticks and pops and this has nothing to do with bandwidth.

I can take it a step further- if the phono section uses loop feedback for the RIAA curve, it will enhance ticks and pops. If the EQ is done by passive means and otherwise the phono section has no loop feedback, that will also have the least ticks and pops.

Kevvwill, I have to admit I was quite surprised when I heard how dramatic this phenomena can be.

Turns out that it has to do with the propagation delay (the length of time it takes the signal to propagate from input to output, something that all audio circuits have) and how that interacts with feedback.

If there is a small tick at the input, it moves through the circuit with the rest of the signal, and at the output is fed back to the input, out of phase with the original. Problem is that by this time the tick, which is very short duration, has dropped in amplitude (signal level) and the 'fed back' signal may well be most of what remains. That then moves through the circuit again and the process repeats, with each iteration the tick loosing some amplitude and changing its phase. The effect is a ringing phenomena which lengthens the time duration although frequency is not affected.

Now if you have no feedback, the tick moves through the circuit without ringing. What you find out through comparison is that a lot of ticks are so small that they are not really noticed, but can be distorted by this ringing process to become quite audible.

IOW, cleaning is important but is not the whole story.

Kevvwill, all I can say is that you have to try it to know. Its true that a tick or pop is part of the LP experience, but it is also true that electronics can ring at high frequencies due to stability issues in the design. This will exacerbate the tick or pop event to be both louder and longer in duration than the actual event on the LP surface.

I had this demonstrated in spades some years ago. A friend of mine bought a Mobile Fidelity UHQR pressing and he was quite excited to hear it. He brought it to my house to play (I think he paid $250 for this thing so he was concerned that it not be worn, and trusted my rig more than his own).

The LP played fine. But the next day he called me up- at his house it was loaded with ticks and pops! We had the same 'table, arm and cartridge. The difference was in our preamps. He was using a semiconductor based preamp that used active equalization in its feedback loop. My preamp was zero feedback with passive EQ. In addition, my preamp was vacuum tube, but on paper anyway had 2 more octaves of bandwidth compared to the solid state unit.

He brought his preamp over and we compared- sure enough, the solid state preamp had a presentation loaded with ticks and pops, while my preamp hardly had any. Since then I have seen this demonstrated over and over. And I can tell you that it has more to do with feedback (active EQ) than it does with tubes or transistors.

The bottom line is that the electronics make a difference in this area, IME as much or more than cleaning the LP.

Jonathon, I'm guessing that you've not heard one of our preamps in probably 15 years! Time to hear one again :)

I agree that its possible to use feedback without surface noise issues, but- its a lot harder to do. In addition, I have found that universally the use of feedback will cause the circuit to take on a hardness or brightness that is not part of the original signal. Of course there can be a lot of variables in any design; I am stating this out of working with many circuits over a period of decades- there are always circuits out there that are exceptional.

With regards to feedback I have yet to hear one that really does it right (no excess 'surface' noise, no compression of dynamics, no brightness), although IMO this is a subject for another thread.

Jcarr, I think you may find this article by Nelson Pass to be interesting:

https://passlabs.com/articles/audio-distortion-and-feedback

It seems to re-enforce some of your comments above. Norman Crowhurst wrote about some of this as well, although I'm don't have a link handy, I suspect I could find the article on Pete Millet's website given enough time :)

Essentially though, the issue as I see it is that as you add feedback, the problem/solution is in the way the 5th 7th and 9th harmonics are handled, but you also have concerns with intermodulation at the feedback node. This can result in a harmonic and *inharmonic* noise floor, with harmonics up to the 81st (although the circuit may lack the bandwidth for that).

The concern I have has to do with human hearing rules. The 5th, 7th and 9th are measured by the ear brain system to determine how loud the sound actually is; so if they are altered even in very tiny amounts the sound will be artificially louder and brighter than it really is.

There is also the issue of detail- due to the ear's masking rule, louder sounds can block the presence of quieter sounds. If the louder sounds are distortion then you will have less detail. It turns out that the one exception to the masking rule is the ability to hear into a noise floor composed of hiss; the ear can hear about 20 db into such a noise floor (something usually ignored by digital advocates). I suspect that this may be because analog hiss has a lot in common with wind noise, something with which our ear/brain system is very familiar. But if the noise floor is composed of harmonic and inharmonic noise, the detail below it will be lost as the ear cannot hear into that kind of noise floor.

If you want a link to Crowhurst's comments regarding this feedback phenomena, I can find it but may not be able to take the time until after CES.

Have a good show!

Panu21, it *can* be, but can also be a setup problem with the arm and cartridge. If the cartridge is not loaded properly, and is not set up correctly, it is conceivable that the additional RF energy that shows up at the end of the LP could bother some preamps.

However, it is far more likely to be an arm/cartridge setup issue.