ARC is a good match.
30 responses Add your response
The specifications I’ve seen at arcdb.ws and audioresearch.com for numerous ARC line stages and preamps indicate in almost all cases a minimum recommended load impedance of 20K, although I’ve seen a few exceptions in which no recommendation is provided. The 20K recommendations, though, do not indicate whether that applies to the unbalanced outputs or the balanced outputs or both.
For example, see the specs shown here for the LS17SE.
For the XA30.5, Stereophile measured input impedances of 20K unbalanced and 29K balanced.
It depends on the specific designs, of course, and especially on how the preamp’s output impedance varies as a function of frequency. But since the majority of tube-based preamps and line stages have capacitively coupled outputs (including most and perhaps all ARC designs), and since the impedance presented by a capacitor increases as frequency decreases, the most common symptom would probably be some degree of rolloff of the deep bass. How audible that may be will of course depend on the deep bass extension of the speakers, the distortion performance of the speakers at those frequencies, and the effects of the room on those frequencies, as well as on the degree of the impedance mismatch.
Depending on the specific designs it’s also conceivable that the distortion performance of the preamp could be affected, and that frequency or phase anomalies could arise at various other points in the spectrum.
Regarding the matchup of an XA30.5 with ARC line stages and peamps, as Ralph and I said we don’t know if ARC’s 20K minimum load recommendation applies to the unbalanced outputs or the balanced outputs or both. But FWIW my own suspicion, not having directly relevant experience but taking into account posts I’ve seen here by you, Ralph, and many others having experience with ARC designs, is that the impedance issue would be sufficiently marginal that a reasonable case could be made both for and against.
D2girls, my only suggestion at this point concerns what NOT to buy. Given the high sensitivity of your speakers, the moderate gain of your power amp, and the fact that you are using a digital source, you should avoid line stages or preamps which provide very high gain.
Examples include most models from Conrad Johnson and Audible Illusions, which have line stage gains in the area of 25 to 30 db. Those would cause you to have to confine your use of their volume controls to undesirably low settings.
Good luck. Regards,
Indeed. And if your disc player also has a volume control you may not even need that passive pre/volume control (provided the DAC in the player is 32 bits internally). In my desktop system I use my computer as a source, into an ODAC usb dac with fixed level (2.1 Volt) output, and then an Emotiva Control Freak volume control, into a Quad 405-2. The Quad has a 0.5 Volt input sensitivity so I have added 16 dB inline attenuators to prevent accidentally blowing up my speakers, and to avoid the inevitable inaccuracies of using an analogue volume control at the low volume end of the range.
Why not just buy a Pass Pre-amp? They sound great and you don't have to worry about synergy issues. For best performance use the XLR connection between the Amp and Pre-Amp.
I use a pair of XA1005's paired with an XP20 driving a pair Focal 1008Be monitors with great results. We have very similar musical preferences.
Guf 1-11-2018A resistor-based passive preamp, or a light-dependent resistor based passive preamp such as the Tortuga models, is probably not a good choice for use with a power amp having relatively low input impedance. And I see that the descriptions of the Tortuga models for which a recommended load impedance is specified state as follows:
Works best with tube or solid state amps having input impedance of 20k ohms or higher.While the XA30.5 meets that requirement, it's usually best to provide a substantial margin relative to published specs.
A transformer-based passive preamp (i.e., a TVC) which provides balanced inputs and outputs may be worth considering, however.
We make two different tube preamps that have direct-coupled balanced outputs and can drive several Pass amps in parallel no worries.
My issue with TVCs is loading- which is a bit of a trick when a transformer is used as a volume control. The problem is that when a transformer is not loaded correctly, it can ring and/or the inter-winding capacitance acts as a coupling capacitor- causing ringing and non-linear frequency response.
If you have a fixed load like a power amp, and a fixed source like a CD player, its a bit of a trick to get the transformer to be loaded correctly at all volume control positions!
How would a mcintosh c2500 preamp fare paired with the xa30.5?
and by the way i purchased a xp10 preamp. its a great preamp and im very happy with it. just wondering if it would be worth the punt to try out a tube preamp though. the dealer i bought my speakers from suggested the c2500 with my pass amp, he said it would be 'proper hifi sound' :p
I took a look at the specs and also the schematic for the C2500, which is included in the service manual that can be found at hifiengine.com (registration is required), and I don’t see any technical problems that would arise using the C2500 in conjunction with your amp.
However I’m not sure that it would give you the tube sound you may be looking for with it. For one thing, its output stages are solid state. Also, it would presumably be desirable to use the balanced outputs of a preamp to drive the fully balanced Pass amp, and the C2500’s balanced outputs are driven with op amp integrated circuits, which leads me to wonder about their sonic quality. Finally, there are unusually large 47 uF (microFarad) capacitors in series with both the balanced and unbalanced outputs, and I would wonder about the sonic quality of such large capacitors.
In any event, enjoy the XP10! Regards,
P.S. to my previous post: I’ll mention also that the 47 uF capacitors I referred to, which are in series with the C2500’s outputs, are polarized electrolytics. From a sonic standpoint, all three factors (47 uF, polarization, electrolytic) are not optimal choices for a capacitor that is directly in the signal path, IMO. Personally I wouldn’t consider such a design, especially if it was to be used in conjunction with equipment of the caliber of a Pass amplifier.
I couldn’t find a schematic for the C2600, but based on the "block diagram" (to use an electrical engineering expression) shown on page 29 of the user manual, as well as on the specified output impedance, I would feel just about certain that the output stages are solid state, as they are in the C2500. And given that the C2600 was apparently the direct successor of the C2500, and also that the C2600’s block diagram is highly similar in most respects to the one for the C2500 (shown on page 28 at this link), I would think it to be a very good bet that the concerns I cited above for the C2500 apply equally to the C2600.