Phono stage w/automatic Load-Impedanance.
I have simulated it using J_carrs model and indeed considering the simple ideal model a MC cartridge can in theory resonate with cabling capacitance in the Mhz range. However in spice, you are feeding a signal from a generator that has no problem creating a 0.2mv (or whatever) signal at the resonant frequency in order to excite it. I want to know is how a physical cartridge is generating its full rated output at these high frequencies in order to cause these issues. dave |
Dave, The cartridge is not physically generating at these frequencies. It's an electrical resonance at a particular frequency which can cause overload or oscillation. This occurrence will also intermodulate and affect the mid/high frequency range with an overtone coloration. A common example of this occurring is with the DL-S1 MC going straight into a phono stage with extended bandwidth. The cart has very low output (0.15mV) due to the coreless design, but its impedance is 33 ohms. This low output requires extraordinary gain and makes the problem more likely to occur. To deal with this, a prominent poster on Asylum loads his DL-S1 below the impedance value of the cart (22 ohms I believe). Apparently his phono stage has enough gain to compensate and he's happy with results. Not all phono stages will be thus affected. If a design is more bandwidth limited, then this overload is less likely to occur. If phono preamp response rolls off at 100K, it probably is immune to resonance in the MHz range. I've read about tonearm cables for MC's with very high capacitance. More capacitance will lower the frequency of electrical resonance and might be a bad idea. A phono cart generates output with magnets and coils. The internal cart resistance reflects the size of the coils. Some coreless designs have stronger magnets inside the cart and lower impedance/inductance. The AT 50ANV and ART7 are such designs. Output is still extremely low, but so is inductance. Regards, |
^^ The cartridge itself provides the excitation and it does not have to do so at its rated output by any means (that is the nature of resonance- it does not take a lot of excitation to get it going). Harmonics of signals on the LP or noise in the LP surface is all it takes. I think many people don't realize that one of the reasons the LP sounds better than digital is that it has a lot more bandwidth. We run an LP mastering operation; we can record a 30KHz tone on a lacquer and play it back on a modest stereo (Technics SL1200, Grado Gold and H/K 430 receiver from the 1970s) with no worries at all. Cartridge manufacturers only show 20-20KHz response on their spec sheets but the cartridge always goes much higher than that. There is also noise that appears in the grooves of many LPs that is ultrasonic, caused by the pressing process itself. So its pretty well guaranteed that the resonant peak is going to contain some energy. |
Bpoletti wrote: There's ONLY one parameter that counts. Bpoletti wrote: Czarivey - I'm with you. No SUT, just a silent high-gain mc input stage. Bpoletti, just look at the contradiction. First, the OP proposes a new phonostage in the market with a lot of enthusiasm but instead of a thumbs up, all you have to say is "I dont care about the design and all that, the only thing matters is the sound". And then when he tells you that it sounds good, your reaction is "hey, I dont care how it sounds because it has an SUT"!! You dont even stop there, then you write: Chakster - Are you in any way associated with the company or designer that produces this unit? Seriously ? Thats the first thing that occurs? Just because the OP is talking about phonostage which is not a Herron VTPH, you have all kinds of problems. Then you even write this: How can a cartridge be autoloaded when the manufacturer specifies a particular load to voice a cartridge? (Sounds like more audio hooey and snake oil to me.) Extremely well respected phonostages like the 47 Labs phonocube have been designed on this concept but probably the Herron VTPH does not fall into this category so it is snake oil ? I am sorry that I am derailing the thread and bringing this out but this has been a prolonged observation that for you everything starts and stops at a Herron VTPH. It is okay as long as you do not treat other member's opinion about their phonostages with a condescending attitude (illustrated here). |
hey The cartridge is not physically generating at these frequencies. Agreed.... It's an electrical resonance at a particular frequency which can cause overload or oscillation. doesn't this contradict your first statement? In order to excite a resonance you need an electrical signal at the frequency in question. I can see a cart generating signals up to say 100Khz but the resonances in question are a decade above that which is why I asked for the source of the excitation signal. dave |
On 6/3 and 6/4 it might look like I was clarifying Atmosphere's response. My posts were delayed for 4 or 5 hours on those days. When I wrote them, there was nothing to clarify. They hadn't yet appeared. I'm not saying this to be contentious, but the explanation of resonance in the MHz range, came from J Carr, and seems plausible. This is somewhere on Raul's MM/MI thread, around p.200? Of course a cantilever can't wiggle fast enough to output in MHz and I think this is completely a function of the tank circuit and not a harmonic of 30K (or whatever) noise. Two separate, but related issues or two aspects of the same issue is moot. In a voltage amplifier front end, both the stability and bandwidth of the device come into play. Some think (Goldmund) a power amp needs bandwidth at least to 200K to make speakers play accurately. What about a preamp? Some might not share this opinion, but if wide bandwidth is a positive attribute of analog where's the cutoff point? Are some phono preamps flawed by having too much bandwidth? Maybe it's a bad cartridge design with a tiny output and relatively high inductance/impedance? Just a bad matchup? Are any of these current amplifiers considered top rated? Seems worth pursuing. |
Allen Wright wrote in his Preamp Cookbook that he could hear the difference when his RTP phono stage was "rolled off" at 750,000 Hz, vs when he fixed the problem allowing it to go much higher in frequency. Of course, that kind of subjective statement is impossible to dispute, but I am dubious that what he might have been hearing was due to bandwidth and not something else. On the other hand, he was smarter than I, in this area for sure. |
All good points. Nevertheless, he wrote in favor of very extended bandwidth. I will try to find the quote; perhaps I mis-remembered. He might have been referring either to the linestage section of the RTP or to one of his amplifier designs. Anyway, his point was that although the roll-off was occurring at frequencies impossibly high by any rational analysis as regards any effect on the audio bandwidth, there was in fact an audible (to him) "trickle down" effect, because the roll-off created distortions down in the audio range. |
I have found that is true as well. If for example if that 50KHz step was really employed (and if I understand correctly, meaning that it goes to flat response at 50Khz), the ear will interpret the resulting phase shift in the audio band as brightness. The old MFA Magus preamp used to do this and it also sounded bright. I found that by restoring the RIAA curve at 50KHz eliminated the brightness. |
Dear all, after quite some time of using different phono stages from cheap Grado PH-1, iPhono2, to the great JLTi and finally Gold Note PH-1 i have to say the old WLM Phonata is really good. For some reason the WLM bass is addictive and none of my phono stages can do the same. Input resistors for MM carts has been upgraded to 100k Ohm Vishay Naked Foil last year. It was a huge upgrade and some of my favorite vintage MM cartridges are really really good with this phono stage. Well, i decided to upgrade Capacitors in my WLM Phonata Reference. Last year i took some pics of the circuit and realized the original stock caps are all German made Audyn. Constant upgrade is rule number one. Time to replace these Intertechnik Audyn MKT (Axial Metalized Polyester-foil) capacitors. Intertechnik manufacture High End Audio capacitors in Germany since 1983. As you can see my caps are 6.8 C/µF (160v) and 1.0 C/µF (250v) with 5% tolerance, they are very cheap. Right now Audyn offers much better audiophile grade caps. In the biggest capasitors test review i found that Audyn Reference, True Copper, True Copper Max and True Silver received the best verdict! I just bought Audin Reference caps, 4 of them cost me 170 euro with shipping. I’m thinking to upgrade stock built-in SUTs on the motherboard too. Looking for the right one from Swedish Lundahl (they made then since 1958). Actually my stock SUTs claimed to be Lundahl too, but they does not looks like any Lundahl i can see on the official website now. Here is a picture of the motherboard with stock SUT and stock caps that i want to upgrade ASAP. But which step-up ratio to choose? |
Thanks @atmasphere Well, sadly the SUTs in my WLM are not Lundahl, i’ve noticed that, but today i got an email from Lundahl support to make sure. The SUTs are what’s WLM called professional step-up transformers. Actually the WLM Phonata model with Lundahl SUTs in 2009 catalog, but probably never was released! http://www.6moons.com/audioreviews/wlm8/retailprices.pdf Anyway, it’s the right signal for me to replace them with a proper Swedish Lundahl high quality SUTs. First recommendation by Lundahl support is this one (LL9226 / 1:10): http://www.lundahl.se/wp-content/uploads/datasheets/9226.pdf " LL9226 is an MC transformer based on (and pin compatible with) our classic LL9206, but with reduced copper resistance and level capability. The new design has resulted in an even better frequency response but still with enough no load impedance to maintain the LF bandwidth. The transformer is built up from two coils, each coil with one secondary winding surrounded by two primary windings. Advantages with this structure are excellent frequency response and high immunity to surrounding magnetic fields. All winding ends are available on the pins. Thus, the transformer can be used with a set of different turns ratios. The LL9226 core is our cobalt based uncut amorphous strip core. The transformer is housed in a mu metal can." I hope experienced users can review this to help me with a best choice |
Dear Chakster, maybe I should read more of this thread before writing this, but I am confused. If the phonata is a current type design, why would you even be using any SUT? An LOMC cartridge with low internal resistance should plug right into the MC inputs. I am sure I am missing some point you must’ve made back there in 2015. |
@lewm we’re talking about internal SUTs on the motherboard inside WLM phono stage. WLM Phonata has "Automatic Load Impedance for MC" as its unique feature or a simple marketing? I wish to know, the unit is long time out of production, company went out of business and returned re-branded with different owners, strange story. No tech support from WLM for old products. As our Fleib pointed out it can be just a "fixed impedance", other users pointed out it can be a "current type phono stage". I had no idea what is a "current type phono" back in 2015 when i started this thread, simply a lack of knowledge. It’s an old post as you can see, last year i have opened up this phono stage to replace 47k Ohm resistors for MM input (for a Vishay 100k Ohm). I’ve noticed the SUTs inside (you see one between the caps) does not looks like Lundahl SUTs, now i decided to upgrade the caps with higher grade Audyn Reference (ordered this week). I want to replace the internal SUTs with Lundahl LL9226 (here is the whole catalog). Last night i have re-read the whole thread again. Maybe it’s not a current type phono stage? --------------------------------------- FROM THE MANUAL: 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. • 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. |
There is another thread of much more recent origin around current-driven phono stages. But in any case, by definition, a current-driven phono stage with so-called automatic impedance loading would not require an SUT. As I think I wrote elsewhere, these stages try to offer zero input impedance to the cartridge, and they only work really well with very LOMC cartridges that have very low internal resistance, less than 10 ohms. (This is based on my own understanding of what I can find on the internet. I am not an EE; I only pretend to be one on Audiogon.) So, the first tube or transistor of the phono stage itself acts like an I/V converter to drive the downstream phono circuit with voltage output. It’s really not so complex. This circuit would work but less well with LOMCs that have internal resistances above 10 ohms, would not be recommended at all for HOMCs or MMs. But I guess the Phonata has separate dedicated MM inputs. I am curious to try one myself. Which is to say that I am curious to try a current-drive phono stage, not necessarily the Phonata. I've had my eye on the BMC MCCI. Conversely to my description, if the Phonata does incorporate an SUT in its LOMC circuitry, it probably is not a current-driven phono stage in the technical sense, although I suppose you could say correctly that a SUT converts current to voltage too. |
To summarize it from the manual: WLM is An inductive VOLTAGE AMPLIFICATION (SUTs) + A solid state CURRENT AMPLIFICATION stage (MOS-FET) There is a separate MM phono stage inside and i’m happy about the quality of it with 100k Vishay load resistors. My upgrade now is all about separate MC part of Phonata, so i think i will replace SUTs and i will also replace stock 47k Ohm resistors in MC path with better qulity 47k Vishay. I wish i could just measure step-up ratio of the stock SUTs to replace them with similar, but better quality SUTs from Lundahl catalog. Actually recommended by Lundahl SUT (as safe alternative) is very small LL9226: http://www.lundahl.se/wp-content/uploads/datasheets/9226.pdf Turns ratio and possible use at different termination alternatives for this SUT: A Turns ratio: 1:5 Copper Resistance: 20Ω / 260Ω Suggested use for best frequency response: MC cartridge < 100Ω C Turns ratio: 1:10, Copper Resistance: 5Ω / 260Ω Suggested use for best frequency response: MC cartridge < 50Ω E Turns ratio: 1:20, Copper Resistance: 1Ω / 260Ω Suggested use for best frequency response: MC cartridge < 25Ω ------------------------------------------------ Actually most of my MC cartridges have a fairly low impedance such as 2Ω, 3Ω , 5Ω, 8Ω ... only one of my MC has 20Ω impedance. So maybe i need another SUT from their catalog with step-up ratio ? |
@chakster since you live in Russia why not try and get hold of a SA Labs SUT. I bought one then 3 more since it was that much better than my Kondo SFz SUT (and at a 1/4 of the price). http://en.salaboratory.com/step-up-transformator.html |
@sksos1 Well, thanks, but i think you missed the point, i have an external SUTs and headamps, but this topic is about WLM phono stage with internal SUTs, they are small and mounted on the motherboard inside my phono stage. I don’t need another external sut. Also i trust SUTs manufacturers like swedish Lundahl more than to a local DIYers. Lundahl made SUTs since 1958. All i need is to solder two better SUTs directly to the motherboard of my existing phono stage. |
@lewm You are right, i thought it was a current-driven because of the "Automatic Load Impedance" feture advertized by the manufacturer, and because of the comments in the beginning of my post (from 2015). But never too late to learn. As we noticed now the real current-driven phono stage works best with cartridge with very low impedance. But based on a comment from one of the WLM owner (from 2015): "The Phonata works very well between 25 - 100 ohm cartridges". And base on info from the manual: " MC-Input Impedance Range: < 100 Ohm to 50kOhm". This is definitely opposite to the current-driven phono stages. In the beginning of this thread two people made two different comments: @hdm 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. @larryi It may be the case that "automatic" really means "fixed." There are some manufacturers that don’t think that any sort of precise setting of loading is important and so they go with a reasonable fixed value, typically somewhere around 125-150 ohms (e.g., Linn). So i think Larry was right. The question is which SUTs step-up ratio i have to choose now when i will replace WLMs internal SUTs if my cartridges are all low impedance (under 8 Ω estimate ) and low output (under 0.25 estimate) ? |
I want to make sure we are talking about the same thing. Cartridges have a fixed DC resistance (DCR) if you measure the resistance between hot and ground connectors for each channel using a simple ohmmeter. Cartridges also have an output impedance, which would be the DCR + any changes in impedance with frequency of the audio signal. However, we are typically not told much about the frequency-dependent resistance, except usually we get a figure for "inductance", which is very low for most LOMCs. Anyway, I usually would go by the internal resistance (DCR) in order to choose a load resistance on the phono stage side or in thinking about an SUT. Rule of thumb says you want the ratio of the output impedance (in this case, the DCR) to the input impedance to be at least 1:10 or thereabouts. Also, in choosing an SUT, we need a certain minimum turns ratio to guarantee that the signal at the secondaries of the SUT will be sufficient to drive the downstream phono circuit. The turns ratio then has to interact with the load resistor at the phono circuit input, usually 47K ohms. As you know, the impedance "seen" by the cartridge will be equal to the phono load (e.g., 47K ohms) divided by the square of the turns ratio. So, if the turns ratio is 1:10, affording a voltage gain of 10, then the impedance/resistance seen by the cartridge would be 470 ohms (47K divided by 10^2 or 100). Any typical LOMC can drive the 470 ohm load, because any typical LOMC has a DCR <47 ohms, which exceeds the desired 1:10 ratio of output to input impedance. If your LOMC cartridge makes at least 0.3mV, the net signal voltage after the SUT would be 3 mV, enough to drive most MM phono circuits with at least 40db of gain. (This also depends upon the input sensitivity of downstream components and the efficiency of your speakers.) I have two very different phono stages, but both have sufficient inherent gain for any LOMC that I can imagine. I now find that I prefer to listen to most LOMCs with "wide open" loading, setting the load R at 47K. That cannot be done with an SUT, because of the obligatory effect on impedance, in relation to the square of the turns ratio, that is a property of any SUT. |
@lewm Yeah, i know you like Ralph prefer 47k for LOMC I can do that too with my Gold Note PH-10 or with JLTi phono stages, but this is another story. I have separate vintaage Luxman toroidal silver SUT for carts with 3 Ω (DC Resistance) or less. But for that god damn WLM Phonata i have to choose an appropriate Lundahl SUTs to replace stock SUTs on PCB. I have no idea about parameters of the stock SUTs i have in it. That "Automatic impedance" confusing me. I’ve checked the article here and there to understand. I know that 1:10 is safe, but my cartridges are lower in output than 0.3mV: 0.050 mV (Ortofon MC2000) / DC resistance 3Ω 0.15mV (FR PMC-3) / DC resistance 8.6Ω 0.2 (Klipsch MCZ Ruby) / DC resistance 2Ω 0.24mV (FR-7fz) / DC resistance 5Ω Which step-up ratio of the SUT would you choose for example for your Ortofon MC2000 ? 1:32 or more ? I’ve checked K&K Audio for which Lundahl SUTs installed in their kit. There are two kits (basic and premium). Basic with LL9226 http://www.lundahl.se/wp-content/uploads/datasheets/9226.pdf Premium with LL1931 http://www.lundahl.se/wp-content/uploads/datasheets/1931.pdf Maybe i have to choose one of these SUTs from Lundahl to soldeg them in my WLM instead of the cheap stock SUTs i got there now. |
