current input phono stages (MC) with switchable EQ curves

Original review here:

https://www.ultraaudio.com/index.ph...iews/517-zanden-audio-systems-120-phono-stage

We're not 'allowed' to have tone controls on our amplifiers, but it's quite ok to play about with wrong EQ curves on RIAA pressings instead

 

My understanding is that while RIAA was ‘supposed’ to be universally adopted by the 1970s, there are thousands of recordings by Decca, Columbia, DG, and others which pre-date that era using the labels’ proprietary curves. It’s not just vintage recordings, but a lot of classical and jazz from my youth. Also, while the labels were supposed to have adopted RIAA, there is some evidence that they didn’t, or didn’t by the time they said they would.

It’s not like this sort of skulduggery is unheard of in the music industry, or in business more generally, is it?

I’ve now read the Fremer piece, and I have heard the arguments before and I don’t think they are particularly well-founded.

 

I’m working on the assumption, BTW, that nobody knows of a current sensing phono stage with different EQ curves beside the one in the OP. Which is a shame .

 

I certainly haven't and whilst I've genuinely been looking and reading about phonostages I haven't came across any that are both current sensing and with variable EQ.
There seems to be a growing number of phonostages that include variable EQ settings but I don't think I'd have any use for them, I more interested in variable gain settings, impedance, etc.

 

I think my post (16) is pretty clear. But since we are here. To do what Gold Note are suggesting in their design, there are basically 3 ways they can implement this in their phono stage. To offer 72 different EQ's would require a significant number of switches to switch in and out the different resistors and capacitors needed to provide all the EQs, and these will need to be in the signal path, no getting around that. In the analogue domain as they are quoting this can only be achieved 2 ways, using relays or solid state switches:

1. Using relays for the switching would require a large number of relays all of which will have their contacts in the signal path. The main disadvantage is the large number of relays required which are large in physical size plus the number of contacts needed, plus their contact resistance, all be it lower than using solid state switches, plus all the tracks on the PCB required would make the signal path very complex and this would impact on the audio performance. To do this commercially would require the relays to be soldered directly to the circuit board. Relays are not massively reliable unless you use the expensive telecoms versions, which are expensive. The only other option is to use DIL sockets so the relays can be plugged in/out so servicing can be much easier. When relays have to be used this is the option I adopt.

2. Using solid state switches. This means that each switch which is basically a transistor will be in the signal path. The advantage of this method is that each switch is small and can be switched by a microprocessor. The massive downside is that you now have a large number of solid state junctions in the signal path and these will be of a much higher resistance than using relays. However there will still be a complex amount of tracks on the PCB which the signal will have to travel through for this implementation.

There is a third way using digital to A to D the analogue signal, then perform the EQ in the digital domain, then D to A the signal to the output electronics. I am ruling this one out as Gold Note indicate they do not use this approach.

As I said in my previous post, to have any noisy microprocessor plus a noisy screen spraying RF noise inside a phono stage is a complete No No in my book, as the last thing you should do is to introduce any noisy digital electronics into a small case which includes a very sensitive circuit like a phono stage which has to deal with such small voltages as low as 0.1mV. Personally unless you have a large number of mono records which indicate what EQ was used I really don't see the point of offering different EQ's for stereo records. See Nagraboy's post 18 with reference to Michael Fremer's Analogue Planet EQ article.

 

It would be interesting to actually measure the Gold Note performance then, because the criticism of their implementation is based purely on theory and assumption; I hate talk of measurement but in this case I reckon it would back up the reviews of their product(s).

 

If you want variable EQ there are other good options available which don't use digital in their implementation like Zanden and EMT.

 

Which doesn't address what I said. I'm suggesting the Gold Note performance needs to be measured to either dispel or concur with your assumptions. The theoretical noise you suggest it should suffer with doesn't seem to be reported by owners - including myself.

 

The noise will be at UHF or what ever the clock frequency of the microprocessor is running at, plus harmonics, so I doubt you will find that measured in any audio review. Anyway, you don't need a review or any measurements to tell you that you shouldn't put a high frequency generator in the same case as a sensitive circuit like a phono stage.

 

Can the Original Poster clarify what they are trying to achieve and what they want to play? I'm with GT Audio on this keep a phono stage simple and low noise.

 

Inaudible then. Immeasurable in the audio range. Ok.

 

RMD Audio Design PH2 Reference Phono Amplifier

https://www.monoandstereo.com/2020/01/rmd-audio-design-ph2-phono-preamplifier.html

https://www.google.com/url?sa=t&rct...o-amplifier/&usg=AOvVaw1evIOviQRrM9bpLLKEMjUX

 

No! The high frequency noise will be superimposed on to the audio circuit and possibly any ground plane to a degree, this will modulate with the audio signal changing the signal, you could call it distortion and it will be audible. It will also increase the high frequency noise within the circuit. It is definitely not something you want.

 

Sweep that UHF noise under the carpet...
Out of sight, out of mind.

 

But you said, "The noise will be at UHF or what ever the clock frequency of the microprocessor is running at, plus harmonics, so I doubt you will find that measured in any audio review. " So will it be audible and measurable in the audio range or not?

 

Fixt.

 

Out of sight...

 

It will certainly be audible if you could switch the digital circuits off with the analogue circuit still playing.

 

Feel free to take my phono stage and produce a spread spectrum which shows the interference attributable to a >300MHz noise spike at very low amplitude.

If the harmonics of a 300Mhz spike are still audible when they disperse and attenuate into the audio spectrum them I'd imagine the microprocessor is using a cement mixer for processing.

 

Steve, I think current/transimpedance phono stages are already a niche product, finding one with variable EQ sounds like find a needle in a haystack made of chicken teeth.

Probably something you'd need to have made bespoke for your needs I'd have thought.