Cartridge options for current gain phonostages (47 Labs)

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.

 

"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.

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.

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?

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.