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Phono stage w/automatic Load-Impedanance.

Yes, automatic load impedance! The WLM PHONATA offers very high dynamics as a result of its very special design (see below)

A few years ago i purchased a slightly used demo unit from Australia. It was reasonable priced (mint- condition) WLM PHONATA reference MM/MC phono stage from respected WLM Acoustic brand (made in Europe). I use it since that day in my system.

a picture of the wlm phonata linked below:
http://audioaddiction.net.au/wp-content/uploads/2012/05/Phonata_3XL.jpg
http://audioaddiction.net.au/wp-content/uploads/2012/05/Phonata_4XL.jpg

When i bought mine demo it was newly released and totally different for previous WLM model (which was a smaller tube stage). The reference WLM Photana is not a tube stage. I'm not sure what's happened after, but probably it was not widely distributed, maybe they made first run and stop the production of this nice unit. They never updates their own website with info about this new unit. It's impossibe to find any reviews online and i assumed there are not so many users.

I wonder if anyone on AudioGon aware of this ice nproduct. I'm sure most of you familiar with amazing range of WLM speakers and different Tube Amps.

But do you know anything about WLM Photana Referense Phono Stage MM/MC ? It has some interesting features such as AUTOMATIC LOAD IMPEDANCE and 2 RIAA CURVES. It comprises pinnacle circuitry and design features that have never been realized before.

The PHONATA works with two-stage amplification:

• An inductive voltage amplification stage (for MC cartridges) using high
performance professional audio step-up transformers.

• A solid state current amplification stage, using specific MOS-FET transistors with tube-typical harmonic distortion characteristics.

The PHONATA offers utterly precise RIAA equalization:

• RIAA equalization is implemented across two amplification stages (within current amplification), providing a frequency expansion from 10Hz to 50kHz (Subsonic cut below 10Hz). Selected components (1% tolerance) are used.

• RIAA equalization can be selected from two positions with a switch at the back of the unit:

- Position “high” for records produced before 1965 or to improve the performance of somewhat “darker” sounding cartridges at higher frequencies. This position provides +3dB equalization as from 5kHz and +6dB as from 10kHz.

- Position “low” for all other records The PHONATA offers automatic adjustment of Load-Impedance:

• You don’t have to adjust the load-Impedance of your cartridge (plus the interconnect-cable between cartridge and Phono-Preamplifier). It goes automatically thanks to one ingenious piece of circuitry.

• You don’t have to adjust the source voltage of your cartridge as well.

• There are no micro-switches or any other mechanical contacts in the signal-path.

Technical Data:

MC-Input Impedance Range: < 100 Ohm to 50kOhm
MM-Input Capacity: 100pF
THD (Total Harmonic Distortion) @ 1kHz: 0.01%
SNR (Signal to Noise Ratio) MC: >72dB
SNR (Signal to Noise Ratio) MM: >85dB
Max. Input Voltage for MC-cartridges (theoretical value): 1200mV @ <1% THD
High Performance, Professional Type Step-Up Transformers.
chakster

Showing 4 responses by hdm

hdm
1,074 posts
 
A lot of back and forth going on here but I'm not sure it's related at all to what the OP posted on.

I've used the Aqvox happily for about 7 years now. I had a chance to audition it and there was clearly something pretty special going on (at least to me and relative to the phono stage I was using previously) in the fully balanced current mode.

I'm not really a technical guy, and because current mode phono preamps are relatively rare, there is not much discussion on them.

Manufacturers of them claim there are advantages in presenting this "short circuit" type of interface with the cartridge and perhaps the discussion should be more on the technical merits (or lack thereof) of this type of interface relative to loading the cartridge on a voltage input. I've never really seen that type of discussion before.

I won't be changing phono preamps any time soon but would still be open to hearing that kind of discussion. As I said earlier, there's been a generalization out there that current mode inputs do tend to work better with low impedance designs (at least from reviewers-not all but some, the TNT review on the Aqvox for example suggested a number of higher impedance moving coils also worked quite well with it).

As the impedance at the current input seems to be quite low in these designs I always wondered whether the supposed working better with low impedance MC's was more a result of most phono stages with fixed or even adjustable loading simply not having settings low enough to really maximize performance with very low impedance cartridges or if there is something more at work here technically?
hdm
1,074 posts
 
The Phonata operates in current mode with MC cartridges. Not anything really new here. I've been using an Aqvox for about 7 years now which operates similarly.

The loading is not fixed. From the Stereophile review on the Aqvox:

"MC cartridges may produce tiny voltages, but they output decent amounts of current from a source impedance that is both low and resistive. This is ideal for use with a current-mode input because such an input is nearly a short circuit. Different MC cartridges react differently to being plugged into a current-mode input, in part depending, of course, on the internal impedance, but the short-circuit loading means the cartridge is inherently damped and resistive loading becomes a nonissue."

The BMC (like the Aqvox, also designed by Carlos Candeias) is another current mode stage. From the Stereophile review on the BMC:

" Because the input uses current instead of an MC cartridge's ultralow voltage, the input impedance is very low, less than 3 ohms. There is no need, therefore to damp the cartridge's ultrasonic resonance with energy-destroying resistors in parallel with the input."

Some have suggested that current mode phono amplifiers tend to work better with very low impedance MC cartridges and there may be some truth in that.

I've used the Aqvox with a couple of cartridges, most recently a rebuilt Ortofon MC 20 Super with a 5 ohm internal impedance and there does seem to be particular synergy there. Aqvox themselves market a couple of cartridges that appear to be, for all intents and purposes, clones of the MC 20 Super (at least if appearance is any indicator) and do claim great synergy with the current mode input, but I'd expect almost any low impedance MC to work very well.
hdm
1,074 posts
 
Just a clarification. The Aqvox was NOT designed for the MC 20 Super. Aqvox only started marketing cartridges a number of years after they had introduced their phono preamp and it is only speculation on my part that their cartridges are based on the MC 20 Super.

I pointed out the use of the MC 20 Super only in light of its lower internal impedance (5 ohms) as many have suggested that current mode phono preamps tend to give their best with low impedance cartridges (say in the 1-10 ohm range).

In any event it is my experience that phono stages like this can offer up pretty good performance (there are also multiple positive reviews on the Aqvox and BMC, some of which probably delve more into the technical aspects of the current mode and the "non-need" for adjustable loading as a result of this design). I don't really miss or feel the need for adjustable loading under the circumstances.

Others with more technical knowledge than I can make the case for adjustable loading being necessary but the designers/manufacturers of current mode stages (as non-standard and as quirky as they are) obviously feel there are some legitimate technical reasons to take this track.

I was just putting the info out there to shed a bit more light on this as, for the most part, it seemed that most involved in this thread were not really aware of this type of design.
hdm
1,074 posts
 
Thanks Ralph. So in theory, at least, there are some technical advantages to this approach.

I'm only guessing that it has not become a bit more popular as a result of being "off the beaten path". That perhaps and the fact that the advantage is only realized in the MC domain.

My Aqvox, for example, tries to be a bit of a "jack of all trades" in that it offers typical voltage amplification, and both MM and MC compatability including adjustments for both capacitance and load, through its single ended inputs. While it's adequate I suppose through those inputs, that's about all I could say for it; I would not have purchased it based on its performance as a voltage amplifier.

In the current mode (fully balanced) its performance is very impressive though and I've been more than satisfied with it. But I think for many audiophiles using MC cartridges it is difficult to get their head wrapped around not being able to "load" the cartridge-I think this is perceived very negatively. Hence this type of phono preamp is probably a harder sell in the marketplace.
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