Been messing about with this Musical Fidelity tube buffer, and while the verdict's still out on whether it's gonna be life-changing (definitely hear the effects on some things, but not others), what I have noticed is that the cables are more of a factor. I said in another post that the bass slackened when using the buffered RR2150 with my turntable, but then, when I used the Audience interconnects I had laying around while my CD player is being repaired (I was using some leftover Outlaw PCAs), the bass tightened up instantly. It surprised me, because earlier I'd said that the Audience interconnects hadn't overwhelmed me when I first introduced them into my system months ago. I keep wondering if that can be attributed to break-in…

Tubes are higher output impedance devices than anything solid state. This higher impedance can interact with cables which have varying amounts of capacitance and inductance. The difference is usually in the higher frequencies, but there could be something happening in the bass because of interaction with that cable.

It's all kinda mysterious (and fascinating) to me, Altec. I've read that the MF X10-D is a unity gain buffer with much lower output impedance, though if I understand you correctly, "low" for a tube device would still outpace something solid state.

It's very difficult for tubes to have as low an output impedance as solid state unless an output transformer is used - and even then, solid state is lower.

The tube buffer is undoubtedly a cathode follower output which is "low" impedance in the tube world, but relatively high in the solid state world.

Thanx for the info, but that brings up another question: I keep reading that upgrading the unit with an outboard 12VAC power supply or something really improves its sonic capabilities. Might your above comment have something to do with why that is? Just trying to clarify/understand stuff.

An "upgraded" power supply is utter nonsense. Think about it - does that mean that they are supplying an "inferior" supply as standard?

Any electronic device will only use the current it needs, a supply which can supply more than that is a waste of money (although one which a lot of unwary people fall into).

The power supply has nothing to do with the output or input impedances of a circuit.

Exactly…kinda what I had deduced. For what some of this equipment costs, the idea that anything on it might be substandard is a bit ludicrous, if not plain maddening. Thanx for the insight.

This cable discussion has me thinking it might be interesting to try different cables from my current Kimber PBJ's with my Yaqin buffer. From what Altec says the cables to change would be the output cables to the power amp; is that right - the 990 having a low-impedance output?

Got other stuff on my plate but I'll share my experience if I do any experimenting.

The cables coming from the output of the tube buffer would be the ones which might affect the most change. The ones going to the input of the tube buffer would not likely make any change since the output impedance of the 990 is probably quite low.

Hey psyprof1. I don't know what your cable budget is (mine's low, but I've splashed a bit in the past year), but a little bit ago I stumbled upon this site, www.usedcable.com , that discounts "high-end" cables and considers trade-ins. Haven't bought anything there yet, though. For what it's worth…

I said I'd share the experience if I did any experimenting - now there's something to report. Having just removed my old-but-trusty Adcom GFA535 (100w into 4 ohms) and re-installed my two nOrh L2 monoblocks (>350w, same impedance) I tried a half meter of Tara Labs Quantum 66 from the Yaqin buffer in place of Kimber PBJ. Sound: smooth and laid back; some loss of sibilance and presence on male voices on PBS Friday evening talking heads shows. Maybe it was the nOrh amps, which have been out of the system for over a year (don't get me started on why)? So I turned off the Outlaw, unmuted the Panasonic plasma, quickly swapped the Kimber PBJs back in, and turned on the Outlaw again. UNMISTAKABLE improvement in male voice quality, and the credits music suddenly had more space, plus the sense of power the nOrhs can give. So can cables make a difference? They sure did for me!

I think if you did an analysis with lab equipment you'd find that that the high end is being rolled off slightly due to the higher output impedance of the tube buffer interacting with the capacitance of the cable.

Nothing bad about that, but it's just something worth knowing.

Altec, I have no doubt you're right, but that leads to two other questions:
1. Are there any cable characteristics that do affect the audio signal from equipment with low output impedance (i.e., solid state), since capacitance apparently doesn't?
2. With tube equipment should one look for cable with the lowest capacitance to avoid high end rolloff?
Thanks as always for your knowledge.

The interaction of output impedance with cable capacitance is always there - it's just a matter of degree. Solid state has less, but it still has some, especially if the cable is long enough.

Cables can also have inductance, which will also restrict high frequencies. Inductance is typically pretty low however with most cables. Ironically (or not) the high end boutique cables tend to have higher amounts of inductance and capacitance - this is why they tend to "color" the sound to a noticable degree. Again, nothing wrong with that, but the same effect can be had with standard cable and judicious use of resistors and capacitors.

With tube gear, the thing to do is keep the cables as short as possible. If the tube preamp is a cathode follower (like the tube buffer probably is) the output impedance is higher than solid state, but not extremely so. If the signal is taken off the anode, the output impedance is going to be very high, and an extremely short cable must be used.

I use plain RG-59U cable for all my interconnects. It's capacitance is reasonably low and it's bandwidth is guaranteed to be very good (it is, after all, made for 6 Megahertz video signals). The equipment I design makes use of BNC connectors for all analog inputs and outputs because this connector is extremely reliable, with high bandwidth capability. Good quality RCA connectors from companies like Canare are great for connecting to typical consumer gear. They can be had in 75 ohm impedance for use with digital S/PDIF signals.