2. analog
  3. 1432420024

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
hdm
1,067 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?
atmasphere's avatar
atmasphere
12,077 posts
 
Hdm, current gain designs often tend to work with a slightly different principle. In tubes, one means is called 'grounded grid' as the cathode of the tube is used as an input. With transistors, the emitter device of the semiconductor becomes the input. In any event the input impedance is quite a bit lower. This prevents any chance of resonance from the cartridge/cable circuit from occurring.

While LOMC cartridges don't make a lot of voltage, they do qualify as a low impedance source as they have no troubles whatsoever driving a 100-ohm load, unlike most preamps, which would have difficulty doing the same thing.

So its the inherent low impedance input that is why loading isn't an issue. Many preamps do have provisions for very low impedance loads, but if you are working in the voltage domain, bypassing the cartridge output with a very low impedance will simply serve to reduce the output of the cartridge.
hdm
1,067 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.
atmasphere's avatar
atmasphere
12,077 posts
 
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.

Yes, the importance of loading the cartridge and how that all works is one of the more prevalent myths about LOMC cartridges. Once you get what is really happening though, you see that being able to load the cartridge or not really isn't a problem- so long as the phono section has either a very low input impedance or is stable with ultrasonic noise or RFI at its input.

The advantage of balanced operation is that the interconnect between the arm and cartridge will not have any sonic artifact. This is really helpful as the cable is at the very source of the signal path- if it messes things up, there is little you can do about it downstream. So insuring that it works right is important and balanced operation can do that.
fleib
1,124 posts
 
" Intactaudio
Can someone please tell me how this resonance in the MHz range is being excited?"

The output of a cartridge has inductance as a property of that output. If you draw the circuit, the voltage of the cart has its self resistance and inductance in series with it (voltage).
The capacitance of the preamp + cables is in parallel with preamp input impedance (resistance), and they go to ground.

This creates a resonance tank circuit, the frequency of which depends on the value of component parts. Because a LO cart has low inductance (reflected in its impedance), the electrical resonance will be at a very high frequency.

It's commonly thought that capacitance doesn't matter with a MC. It does or might. Higher capacitance will lower the frequency of electrical resonance. This electrical resonance effectively gives the cart output (noise) at a frequency where there is no mechanical output.
You can calculate the frequency at the Hagerman link.

Amplifying current avoids this potential problem, with low input impedance. The BMC MCCI has MC input impedance of 3 ohms. The Aqvox 2Ci is 10 ohms.

Regards,
More to discover