Tubed pre
- Thread starter nirodha
- Start date
As the Jazz is a tubed preamplifier this will raise another issue. If you do not choose the output transformer the output will probably be capacitor coupled. The value of this capacitor must be known in order to know if the Jazz is compatible or not with the Spectral. In this case the key parameter is output impedance at 20 Hz, not at 1000 Hz.
They claim 10K ohms input impedance, so not much else to say. I am sure the voltages that their preamps swing also help (80-100V peak with the 30SV).
I totally agree and thought I didn't get it at first. If you are taking about the link between your CD player and the pre-amp, the MIT cable should ideally be appropriate for the preamp input impedance. Th amp will not be effected. That said, my guess is that a cable designed for a 10K preamp input impedance is a bit low (50K or 100K is preferred since the preamp input is 75K), but I also don't think it will do any harm to the preamp. The worst that can happen is the sound may not be optimum. As far as I can tell, it won't hurt to at least try it and see what you think. That said, although I love MIT interconnects (and have to use them with my Spectral gear, I don't think you would be disappointed with a pair of Cardas Clear interconnects to connect the CD plater to the preamp at a fraction of the price of the MITs. It's a fabulous cable and what I use to connect my phono stage to my preamp. It is also Audio Research's "go to" recommended cable, which suggests they think its pretty darned good a well.
The way it's been discussed in various threads in the past (like the very informative "Cable conundrum" thread) is that this "impedance matching" thing relates to eliminating reflections in the cable, and is critical in some applications but perhaps not so much in others (and we don't need to debate the truthfulness of said cable reflections existing at all, here). For example, it's critical in the transport-to-DAC interface (quite critical, in my mind) to minimize reflections and jitter, and I would also say in the phono interface as well; this is one of the reasons I think the MA-X phono cable is untouchable by any other, because you can adjust the impedance on it to mirror the load setting on the phono preamp (I set both to 1K). Keep in mind the impedance setting is all about the load impedance (not the source) - hence "low" for Spectral amps - and as such, you can guess what I think about other network phono cables that are sold as "perfectly impedance-matched" when on the other hand the user is free to adjust load impedance on the phono preamp at will... In other situations, I would say it depends, although I personally would always use MIT cables anywhere I can for optimal performance (I just haven't heard anything better or seen a better engineered cable; YMMV etc), and I also believe in using cables from the same manufacturer.
This is the maximum peak to peak output volatge, not the operational voltage. I have found that typical Spectral amplifiers have sensitivity about 1.5 volts/nominal output . This means that maximum operational current will be around 150 microamps - much less than 1 mA.
This means that their output stages are designed with high headroom, both in voltage and current.
Not sure where the disconnect is... You keep talking RMS and I keep talking peak - the amp might be drawing tens of mA peak at 100V peak output from the preamp, if not more. Do the amps sound loud, even maxed out, at 1.5V RMS? Sure, I measure around 0.9V at 1kHz from the Berkeley if I recall correctly, and with unity gain in the preamp, it's pretty loud. But that's not the point. For example, we have posted in the past that the Berkeley just can't drive the amps correctly during complex dynamic swings, and it's easy to prove - see also this post http://www.whatsbestforum.com/showt...ates-Believers&p=219121&viewfull=1#post219121. Feel free to call them up and have them correct their manuals, if you feel like they are in error; but the whole issue is about optimal *performance* and amplifier stability.
And for what it's worth, here's the language from the DMA-400RS manual:
So basically, when I said 100-200mA earlier, it was based on this latest figure (180mA) and previous ones in older amps (100mA). So take it as you may. Finally, as marty pointed out, I believe the aforementioned language has changed again since then (in the 300RS, I think), to again REQUIRE a Spectral preamp, and be set up by dealer so he can attest to the system approach for warranty coverage.
And for what it's worth, here's the language from the DMA-400RS manual:
So basically, when I said 100-200mA earlier, it was based on this latest figure (180mA) and previous ones in older amps (100mA). So take it as you may. Finally, as marty pointed out, I believe the aforementioned language has changed again since then (in the 300RS, I think), to again REQUIRE a Spectral preamp, and be set up by dealer so he can attest to the system approach for warranty coverage.
Probably this requirement of high current is due to the need to drive the capacitance of the input at several tens of MHz. IMHO this requirement is exclusive for Spectral preamplifiers - as this thread consider using the Spectral amplifier with another brand of preamplifier this issue does not apply.
In the commonly defined audio bandwidth we can not consider 10 kohms as a low impedance - we have many designs with 600 ohms input impedance.
As always, knowledge of practice and user ears will have to help the decision.
What you are alluding to is that by simply removing the Spectral preamp from the picture, there is no issue properly driving their amps, contrary to the manual's language. People can draw their own conclusions, and I may be the only one who doesn't understand what you are talking about, but it shouldn't really matter at this point. And yes, 600ohms is even lower impedance, and I have seen even lower than that (Krell, DartZeel - 50ohms), but I also think this is just irrelevant to this discussion.
Good point about the Dartzeel and the Krells. The Dartzeel has three user selectable inputs - RCA, XLR and BNC 50 ohms. The 50 ohms input must be driven by a 50 ohm output - it is a closed system using 50 ohm cables, although some people use non-Dartzeel 50 ohm cables.
The Krell CAST system was current coupled, not voltage coupled. Theoretically it should have zero ohm input impedance!
As ACK has noted Spectral design the amplifiers to be driven by Spetdal preamps. I think individuals concluded that one parameter such as input impedence of the amp is easy to satisfy and all is good. Most if not all of us do not possess the knowledge of design in the Spectral amps so pairing an non spectral pre amp is outside the "system" design. I wish those who use other preamps good luck and continued good luck. I do use the Spectral preamp and I am very satisfied with Spectrals system design as it removes any guess work with what Spectral have presented as their approach to amplification.
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