I had a Phono Cube back in the day. The best solid state phonos I ever owned. Foolishly sold it for an over hyped Tom Evan’s stuff.
That is how it was all explained to me. Low impedance went with lower gain model.
Dynavector used to make a current based head amp that had a switch that would allow you to use higher impedance carts.
https://www.dynavector.com/products/amp/e_pha100.html |
I know nothing about the Phono Cube, but what Chak says is interesting. In voltage world, 75db gain ought to be more than enough for even the MC2000. I can't imagine what cartridge needs 90db.
pcosta, What you say about the 75db vs the 90db versions of the Phono Cube is interesting and surprising to me, because one would think that MC cartridges with higher internal impedances would be those with higher voltage output, because higher impedance is associated with more turns of wire in the coil, which usually means higher output. But since I know nothing about the Phono Cube, I'll take your word for it.
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From what I know about these Phono Cubes is the 75db version is for low impedance cartridges like the Miyabi's and the higher gain version is for higher impedance carts like Benz. |
BTW @lewm did you notice that a 90dB version has been made for extremely low output carts (standard version is 75dB).
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"The Miyabi Standard has an output voltage of 0.2mV and an internal impedance of 2.0 ohms, while the Miyabi/47 has 0.3mV output voltage and an internal impedance of 2.0 ohms". Pretty much as nearly all my favorite MC cartridges, they are all low impedance 2-3 Ohm and low output 0.15 - 0.25 (but not extremely low as the Ortofon MC2000 @lewm ). The 47 Labs 4712 Phono cube has been made at the time when Miyabi 47 (designed by Takeda for 47 Labs) was in production and distribution in the USA by Sakura Systems. Anyway, the difference between Pani and me in this thread is that i bought my current drive phono stage especially for my old Miyabi collection. So i don’t care about other cartridges capabilities with Phono Cube or vice versa. But i'm pretty sure that all similar low output and low impedance carts can be used with 47 Labs Phono Cube. |
I've done a bit of studying on "current-driven" phono since you started this thread, Pani. Do you or does Chakster know what is the input resistance/impedance of the Miyabi cartridge that makes it such a good candidate for current drive? Cartridge output is also a factor. According to one recommended criterion, the Ortofon MC2000 for example is not a great candidate for current drive despite its very low internal resistance of 2 ohms. This is due to its very very low output of .05mV. So, you'd want a cartridge with at least 0.2mV output and less than 10 ohms internal resistance. (There is a minimal recommended ratio between these two parameters, but I cannot recall the value.) These rules can be broken, but the result might not be optimal. The manufacturers like to say that the input resistance of their current drive phono is 0, but that cannot be true, I think, because in that case the signal would go directly to ground, thus "muting" the output. The input resistance must be at least a few ohms above ground. If I am wrong, I am interested to be corrected. Also,from what I can tell, current driven phono stages simply use (typically) a solid state gain device which can thrive with a very low input resistance as the first stage of amplification. The output from that stage is then fed to a conventional RIAA circuit for filtering and further gain if needed. It's not magic. In fact, it's kind of an alternative to using a SUT or a conventional outboard active gain stage in lieu of a SUT, except for that exceeding low input resistance which therefore sees the cartridge as a current producing device.
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Waiting for your opinion @chakster |
Well, i’m in, hope it’s not too late :) As the owner of two different Miyabi cartridges (MCA and Standard) i just bought 47 Labs 4712 Phonocube with Humpty. Pani told me he never tried his ex 47 Labs phono cube with Miyabi cartridge. This is exactly what i’m gonna try! Fascinated by Nelson Pass current source power amp (First Watt F2J) in my system i am up for "current injection" phono stage with ZERO load impedance finally. Hope i am not alone ... MORE ABOUT PHONOCUBE:
Input impedance 0 ohm
Most of currently available phono equalizers are designed to amplify the voltage that appears at both ends of a resistor when a current generated by the cartridge is carried to the ground through this resistor. Our Phonocube has a unique and original circuitry ( with input impedance of 0 ohm), which enables all of the current generated by the cartridge to flow directly into the amplifying circuit.
Unique equalizing circuit with advantages of both NF and CR types.
Although NF type circuitry is known for its high S/N ratio, a rise in the high frequency is always inevitable. The unique equalizing circuit of Phonocube allows the same level of high S/N ratio while maintaining the smooth and accurate equalizing character of the CR type.
Extreme simplicity --- minimum circuitry
To preserve the freshness of the sound, we reduced the number of parts as much as possible, 25 per channel, and achieved the shortest signal pass length ever (44 m/m).
Rigid and compact chassis construction
The chassis of Phonocube is constructed from two aluminum tubular frames ( 40 x 80 m/m section ) and front and rear panels of 10 m/m thick machined aluminum. Each circuit of left and right channels is encased in a separate chassis to eliminate interference between them and to achieve ideal dual mono structure.
Compatibility:
Most of MC cartridges available in the current market are compatible with the standard version. For those cartridges with an extremely small output level and/or high internal impedance, we have the high-gain version. The standard version has 75dB and the high-gain version has 90dB of gain. Since it is a current amplification device with 0 ohm input impedance, output level is determined by the output amperage of the cartridge (output voltage divided by internal impedance). If you are not sure about which version suites better for your cartridge, please contact SAKURA SYSTEMS. Features:
- Unique equalizing circuitry that amplifies all the voltage the cartridge generates without loss.
- Complete dual mono structure with each channel in a separate chassis.
- Rigid and compact aluminum chassis to ensure a quick and smooth release of vibrations.
- World's smallest number of parts --------- 25 parts per channel
- World's shortest signal pass length -------------- 44 m/m
- Powerful voltage regulation with high capacity transformer - 170 VA cut-core transformer +- Individual coils
- To be upgraded into complete mono structure by adding another Model 4700.
Specifications: - Input impedance : 0
- Output impedance : 47
- Gain : 2 types to match the internal impedance of different cartridges
type A ( standard ) / type B ( high gain )
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I couldn’t think of the name when this thread was more current, but look @ the new Lyra Delos thread as the Delos should be a good match (and on budget).
Also, I've recently seen the 47 labs cartridge heavily discounted, if you wish to spend less.
DeKay
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why not a 47 labs cartridge?
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Pani, The only criteria for performing with your phonocube or some other current-driven phono stage are internal resistance/impedance and inductance. Ideally also you want a cartridge with very low voltage output. But since all these parameters go hand in hand, it’s easy. I would stick with LOMCs that have a published internal resistance of less than 10 ohms; the lower, the better. I read elsewhere that, yes, the Transfiguration LOMCs ought to work (but I don't know offhand how they measure). Note that HOMC cartridges are not a good bet, by the same tokens.
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I am thinking of the Transfiguration Phoenix S cartridge to with the phonocube. Has anyone heard the Transfiguration ? |
I'd welcome the input of others with conventional phono stages, like all of mine, but my experience with mono, derived by paralleling the two stereo channels, is the opposite of yours in terms of the effect on apparent hf reproduction. High frequency response always seems to improve, compared to playing the same (mono) LP in stereo. This is when I use the mono switch on my preamplifier, and therefore the cartridge remains the same stereo type used in stereo. Maybe there is some intrinsic difference for current vs voltage driven phono stages. I have never quite understood, anyway, the difference between current vs voltage drive in phono, because when you use a very low value load resistor, as is typical for LOMC cartridges, in effect you have enhanced the proportion by which the stage is driven with current. However, if there is zero load resistance with your current-drive phono stage, that condition usually cannot be achieved with conventional stages.
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Yes, I had a bit of trouble getting my head wrapped around it as well.
But there was a notable difference, namely that in parallel, the sound seemed to be rolled off in the highs, slightly muffled and slightly less open/detailed and dynamic than when wired in series. My gain settings, I was surprised, remained about the same; I actually reduced the gain very slightly when I wired in series, which surprised me.
Bear in mind that this is with a current mode stage and that results would vary significantly with a conventional voltage mode phono stage as voltage will double in series.
As there's no ability to adjust for loading with the Aqvox (and most current mode stages to the best of my knowledge), I can only conclude that halving the impedance (from an already low impedance) into the Aqvox was not a good thing. Doubling it probably put it back into the 6-10 ohm range, which is still quite low.
But the results might be very different with another current mode stage depending on how the input is configured. Or with a higher starting point for internal impedance and a lower starting point for current, wiring in parallel may well have given superior results in my situation, but series clearly sounds better to me here in terms of what I am working with.
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I can't get my mind around the idea of hooking up the two channels in series for mono output. I don't doubt that it works, but I am not sure I understand why. Also, if you wire in series, is it not the case that internal resistance/impedance doubles (as you already noted) but also the output current remains the same? (I am thinking of Kirchoff's Law.)
What is your impression of the effect on mono performance, if you've tried it both ways (series vs parallel) with the same stereo cartridge?
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Lew:
Yes, you are indeed correct on that. Sorry, a bit of a brain lapse there. Parallel would halve the impedance while doubling the current.
I’ve been experimenting recently with both parallel and series strapping to convert stereo cartridges for mono use, trying to keep the technicalities right in my head and got that backwards!
I did not wire the Denon in series for mono, but interestingly, wiring an MC 20 Super in series (which would double the impedance) as opposed to parallel resulted in better sound quality with my Aqvox, which kind of surprised me, but I believe the current input may be closer to 3 ohms on the Aqvox as opposed to the zero that 47 Labs is quoting on the Phonocube.
Ortofon Cadenza Black might be another one for consideration for the OP but I'd be inclined to try and get the output voltage closer to .2 or .25 on the high end with all that gain in the phonocube.
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"My Sonic Labs Eminent, the Air Tight PC series, and, especially, the super-low-inductance Haniwa HCTR01 work extremely well with current amplification type phono preamplifiers." I found this statement online in a review of another phono stage that works by current amplification. Sadly, these are all in the category of "expensive". Other cartridges with very low inductance and very low internal resistance also will tend to be expensive. LOMCs with the lowest voltage output also tend to be those with the lowest internal impedance/inductance, because very low output is synonymous, in the case of an MC, with having a very low number of turns of wire in the coils, which leads to low resistance and low output. The good thing, in your case, is that low output (in terms of voltage) is irrelevant; your phono stage can handle it. You only have to worry about cost.
PS: The reviewer in the article cited above also mentioned the Ortofon Quintet Black. I think that one is about $1000 or near to it. I once spoke to the Haniwa designer at a show; he was adamant about the virtues of current amplification and that is what drove his design. Ortofon MC2000 should work well too, if you can find a decent used one.
HDM, It seems to me that paralleling the two stereo channels of your Denon to produce mono would result in halving of its internal resistance/impedance, not doubling. |
I am not familiar with and have not had the phonocube but have run a current mode phonostage for about 10 years now, the Aqvox.
The Aqvox is a bit more versatile than the phonocube in that it has fully adjustable gain between approximately and 55-75 dB depending on the output of the cartridge. Both voltage and current will come into play in terms of the output with a stage like this.
I could be mistaken (and if I am, hopefully others will step in to correct me), but the phonocube appears to have very high gain (75 as standard and 90 for very high gain situations). Generally speaking, the Aqvox, which has a very similar low input impedance input and design which essentially presents a short to the cartridge, prefers a lower impedance cartridge to a higher impedance design, not the opposite.
I have only run a couple of cartridges with my Aqvox, modified Denon 103R's and Ortofon MC 20 Supers, with about .3 mV output and 14 ohms internal impedance and .2 mV output and 5 ohms internal impedance. Both worked well.
But I've also run a modified Denon, strapped by wiring it in parallel for mono, which doubles current and impedance. This worked ok but was definitely the worst combination as there was, I think, almost too much or too much gain when the impedance and current were doubled. And this was with gain on the Aqvox turned down to the minimum.
In light of the gain not being capable of being reduced on the phonocube, I would expect that it would actually prefer a lower output (in terms of voltage), probably in the .10 to .25 mV area, as well as a lower impedance (probably in the area of 2-5 ohms), which is what the Proteus is, in fact. So I am not sure if you have worded your question correctly?
I do not think you want a high voltage/high internal impedance design. The AT Art 7 has a slightly higher impedance than this at 12 but a quite low output of .12 mV, so I would bet that it would still be a pretty good match with the phonocube at a reasonable price. Maybe someone who as used that combination can chime in.
Otherwise, look for cartridges spec'd as above; there are probably a few out there that others can recommend.
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