Thekong,
I was wondering that myself. I suspect autoloading is simply the use of SUT for MC gain which will cover a range of input (cart) impedance.
In the case of this WLM stage, the SUT seems poorly chosen for most high end MC's:
*MC-Input Impedance Range: < 100 Ohm to 50kOhm*
Is it surprising a 4 ohm (or whatever) ZYX sounds better through a ZYX head amp?
A SUT must be appropriate for both gain and impedance. For example, a Cinemag 1131 set for 1:20 (26dB) will have an effective input impedance of 118 ohms. Set for 1:40 (32dB) it's 29 ohms.
The notion of one size fits all MC input impedance is entirely phono stage dependent. With many solid state stages it will make a noticeable difference. In the case of the 1131 SUT set for 32dB, the effective impedance will be below the output impedance of some carts (DL-S1). This is usually considered undesirable unless you're suppressing RFI. On some more revealing IMO solid state stages, loading makes a noticeable difference, noise notwithstanding.
Tubes are inappropriate for a high gain stage. They're too noisy, so they employ either a SUT or a solid state high gain stage.
Regards, |
Free advertisement over?
This thread isn't about tubes or the viability thereof. The Phonata is solid state and the discussion is now about current vs. voltage amplification.
**The answer is that no manufacturer 'voices' a cartridge in the way you are suggesting! The load is there to sort out an unstable phono section, not the cartridge.**
This is BS. All phono stages where one might prefer a load other than wide open, is unstable? Suggested loads are usually a minimum value or for SUT impedance matching.
We've been through this before. In the absence of noise one might prefer to load down a MC because of preference. Damping a cantilever/generator might improve focus and detail, while wide open might increase stage and size.
The analogy to amplifier damping is a bad one. The goal is to make the speaker play accurately with a high damping factor. A phono cart is an electro mechanical transducer on the source end, but no electrical damping isn't necessarily better. Mechanical performance is the overwhelming determinant of cart performance, something that many EE's don't get. Loading, electrical damping can be a way to balance factors other than amplitude response and noise.
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Atmosphere,
You should have quit while you were behind. I've read Hagerman's article and I could point out some erroneous assumptions, but they pertain mostly to MM's. If you're interested you should read the VE thread, Cartridge Loading Explained.
But we're talking MC's here and one HOMC with a solid state phono stage, and I still fail to see where your comments pertain. I know about the tank circuit on the output. I'm also familiar with high frequency overload or oscillation and the possible need to load down the preamp shunt resistance.
Apparently you think this is the only reason to load down a cartridge. If so, you're wrong. I've already explained that wide open is not always better. Maybe it is in your preamp, I wouldn't know, but we're not talking about your preamp.
If you have something to say about current amplification on the front end, that might be helpful.
Regards, |
If you go to WLM Acoustics they only show the tube phono available in 3 different configurations with SUT for MC gain. Specs to be announced.
http://www.wlm-acoustics.com/
Fremer reviewed the BMC MCCI phono stage on 8/13. This uses current amplification on the MC front end. The unit looks remarkably similar to Chakster's link for the solid state Phonata.
http://www.stereophile.com/content/bmc-phono-mcci-phono-preamplifier
Results seem different from what Chakster said, especially concerning cart impedance, and it's unclear if these are the same.
A couple of guys who post on the MM/MI thread own Atma-Sphere MP1 preamp. They each have high end systems in the extreme and think highly of the MP1 phono section.
Our disagreement is mostly one of appropriateness and in no way is a reflection on the product.
http://www.atma-sphere.com/Products/#MP-1 |
**I am talking about the fact that if you hear tonality change with a LOMC seemingly due to loading, its on account of the behaviour of the preamp and not the signal from the cartridge.**
I know that's what you're talking about. I made it clear that tonality change is NOT what I was talking about. What don't you understand? |
Atmasphere, From this thread:
*In the absence of noise one might prefer to load down a MC because of preference. Damping a cantilever/generator might improve focus and detail, while wide open might increase stage and size.*
*A phono cart is an electro mechanical transducer on the source end, but no electrical damping isn't necessarily better. Mechanical performance is the overwhelming determinant of cart performance, something that many EE's don't get. Loading, electrical damping can be a way to balance factors other than amplitude response and noise.*
Why does Jonathan Carr recommend for Kleos: *Recommended load directly into MC phono input: 95.3ohm ~ 816ohm* ?
http://www.lyraconnoisseur.com/Products/Products_Analog/kleos/kleos3.html
If you say that's because of inferior phono preamps, I say it doesn't matter or it's an inappropriate response. It doesn't matter because this isn't about you, it's about the Phonata. It's an inappropriate response because your examples and consequences are misleading at best.
Do you really think Kleos will start tearing up grooves if loaded at 100 ohms rather than 47K ? That's what you imply. Is every cantilever optimally damped? A MC cantilever is usually damped just enough to suppress mechanical high frequency resonance to between +3 to +7dB @ 20KHz. Of course usual isn't always and there are exceptions, like no cantilever or short ones. This is way outside the scope of this thread, but no-load always being better is a wrong assumption IMO. It's not right for any preamp all the time, and certainly not all MC's.
Regards,
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*The above comment was from jcarr, which seems to agree with what Atmasphere is talking about.*
Even if you agree with JCarr and Atmasphere about Lyra, does this apply to all carts? What about those which are underdamped?
Once again, this thread is about Phonata and I don't recall a Lyra being mentioned other than JCarr being used as an authority. He uses some kind of double damping system. Is this common to all MC's?
Atmasphere,
You seem to horn in on multiple threads seeking a free advertisement. Aren't you supposed to identify yourself as a manufacturer? I noticed the Liberty Audio guy took some flack about this.
Beside theoretical objections to wide open ALWAYS being better, there are plenty of real-world examples of that being untrue even with the MP1 or Herron phono stage. Don't some people load other than 47K ? Don't you offer a loading modification? I've read about Herron users preferring other loads.
Now you're implying benefits with consequences based on generalizations which may or may not be true. Elitist minded scare tactics? You ought to have an ad saying, You're Cartridge Working Too Hard? Tearing Up The Grooves?
Regards, |
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, |
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.
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Bpoletti,
The contention seems to be that current gain, rather than voltage gain is inherently better for MC's. This does not seem to be the case with Chakster's low impedance carts.
The Stereophile quote probably just echos the mfg. blurb, and I suspect does not reflect the whole picture. Current gain can be controlled by the use of feedback or controlling circuitry, but current gain is dependent on source resistance. To say, "but the short-circuit loading means the cartridge is inherently damped and resistive loading becomes a nonissue." is misleading.
Apparently the phono stage was designed for the MC20 Super. Other than that, YMMV.
Regards, |
" 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, |
