MC Phono preamp gains
Here's the Rhea's spec: Gain settings (dB): 75, 68, 62, 56, 50, 44, 38, Off. Loading settings (ohms): 47k, 10k, 5k, 2.5k, 1k, 500, 250, 125, 75 So, virtually any combination is possible for all three inputs? Like, having all three as MMs, all three as MCs with different gains and loads, and mix of MMs and MCs? |
^^ only if the phono stage is unstable. Loading of LOMC cartridges is all about the phono section and makes no difference to the cartridge other than reducing its output. The problem is that some phono sections act out a bit when presented with ultrasonic or RF energy caused by the resonance of the cartridge inductance with the capacitance of the tone arm cable (which is why loading seems to help). If the phono section is stable with this energy, you will not hear any effects from LOMC cartridge loading. |
Well, which would be better. One phono preamp with three inputs or three separate phono preamps, if the price is the same. If you go for three preamps, would you go for the same model for all three or different ones? How about additional cables? How about space? If Rhea costs $4000, would a phono preamp at 1/3 of Rhea be as good as Rhea? Well, for me, it seems to be more complicated and less attractive if I go for three phono preamps. If I have three different phono preamps, I may end up using only one that I would like most, and then I need to change cables each time I try different turntables. There are two used Rheas for sale now ($2400 and $2900), and they are out of my reach, but I will seriously consider it for my next phono preamp. Many thanks for all replies. |
If and when you consider the Rhea, a point to keep in mind is that its highish and frequency-dependent output impedance would be non-optimal if the input impedance of your line-stage is less than around 30K balanced and perhaps 20K or so unbalanced. See the second paragraph here. Also, if unbalanced interconnections to the line stage are used, and if the length of those cables is particularly long (e.g. 15 or 20 feet or so), it would be best to choose cables having low capacitance per unit length (e.g., less than say 25 pf/foot). Regards, -- Al |
Ihcho, if you're looking for MM premps (and you need 3 of them or one with 3 imput) why no try 3 different things with your cartridges and keep the best. So many MM preamps available, if you will search audiogon for preamp thread you will see at least 5 decent options to buy and they are not expensive. |
Chakster, I ended up having two turntables. One turntable has two arms. I use one arm for mono, and the the two for stereos. Some of my LPs are not in pristine condition, but I still listen to them. So I use more expensive cartridges (Ortofon SPUs) for mint LPs and use less expensive cartridges (Denon, Audio Technica, ...) for non-mint LPs. I currently have two phono stages for three arms, so I need to change cables from time to time. I am thinking of selling them and buying one that has two/three inputs. Or, I can keep the other two and buy a decent phono that supports one input. I didn't know about Rhea, and it appears to work well with my setup. The only problem is, I don't have enough budge for it, and I need to sell the other two afford it. |
Almarg, Re your comments on the Rhea. I own a Janus, recently inherited from the estate of a friend. I was poking around in it, and it seems that the output from its phono section is a 6992 used as a plate-follower, rather than as a cathode follower, as one might otherwise have expected. This topology would indeed give it a rather high-ish output impedance, but in the Janus, the phono section only has to drive the built-in line stage. Does the Rhea output stage also consist of a plate-follower? Thanks. |
Lew, sorry to hear of the loss of your friend. My relevant knowledge of the Aesthetix products is limited to what can be inferred from JA's measurements and from info at the Aesthetix site. Both the Rhea and the Janus are specified as having output impedances of 1K single-ended and 600 ohms balanced. The recommended minimum load for the Janus is specified as 10K single-ended and 20K balanced. A load recommendation of 10K min is specified for the Rhea, with no indication of which output it pertains to. In view of JA's measurements of the Rhea, I suspect that all of those minimum load recommendations are aggressive rather than conservative. What is particularly noteworthy is that it can be inferred from JA's measurements that different topologies are likely to be used for the Rhea's single-ended and balanced outputs, and given the similarity between the specifications of the Rhea and the Janus I suspect that the same holds true for the Janus. For the Rhea's balanced outputs JA measured 110 and 156 ohms at 1 kHz and 20 kHz respectively, which is suggestive of a cathode follower, and 3846 ohms at 20 Hz, which is suggestive of a somewhat low value coupling capacitor connected between the cathode follower and the output. For the Rhea's single-ended outputs he measured 2K throughout most of the audio band, and 3.05K at 20 Hz. That would seem to be suggestive of the output signal being derived from a plate circuit, again with a somewhat low value coupling capacitor in series. As I say, the similarity of the specifications suggests that the main outputs of the Janus are probably similar in those respects. In which case the concern I mentioned earlier about cable capacitance, with respect to the Rhea's single-ended outputs (but not with respect to its balanced outputs, since the balanced output impedance is low at high frequencies, where cable capacitance may come into play), seems likely to be applicable to the Janus as well. And the concern about the minimum input impedance of the component that is being driven, with JA's measurements suggesting more stringent guidelines than are recommended in the specs, seems likely to be applicable to both outputs of both components. Best regards, -- Al |
Did not know about JA's measurement. Thanks. I have not poked around in the line stage section of the Janus, as mine works fine. On the other hand, I did something to the L channel of the phono stage that I cannot seem to fix, which is why I was trying to figure out its topology without a schematic, just by measuring voltages. However, you've given me some food for thought. I had intended to use the Janus to drive my Beveridge direct-drive amplifiers, which are mounted inside the speakers. The Bev amplifiers use a solid state input and driver stage, so there is a chance that the Janus with its high-ish output Z might have a problem driving them, although I do not know exactly what is the input Z of the Bev amplifiers. I will need to figure that out. Thank you for your remark about the loss of my friend. He was by far my closest "audio" buddy; we knew each other for more than 40 years, and I do miss him. |
