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kitjv
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Impressed with Tubes!

For the first time, I auditioned a pair of Paradigm Reference Studio 100s run through a Rogue Perseus tube preamp & a Rotel RB1080 S/S power amp. Prior to that, I have never auditioned a tube preamp. Wow! What a difference! A richer, more integrated sound with the Rogue Perseus compared to S/S alternatives. Now that I am hooked on tubes, a few quick questions:

(1) Would there be a significant difference if I went with a tube power amp as well?

(2) Compared to the Rogue Perseus, has anyone had any experience with the Rogue Metis preamp?

(3) In addition to the Rogue Perseus, are there any other tube preamps that are recommended?

Thank you!!

KBK
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Re: Impressed with Tubes!

Tubes work well as preamps, you may not like them so much as an amplifier. Then again, you may!

The differences in speakers is the key point that can make or break the idea and use of the given tube amplifier. Preamps are more immune to the variances in the input impedance of the given amplifier. Tubes are 'load sensitive', meaning whatever they have to send a signal to, can impact the overall sonics that result. More so than Solid state, which is considered to be less susceptible to this as an 'issue'.

This is far more true in amplification. When attempting to put together a system with a tube amp, the tube amp and speaker have to be addressed as a 'pair', and tested. After a while, you'll get the hang of what works together and what does not. In the meantime, be careful of overall blanket recommendations of tube amps, and test the pair (amp/speaker) together, or, at least, try to get someone's opinion on the exact pair in question.

dcstep
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Re: Impressed with Tubes!

I agree with KBK, tubes are almost universally successful on the front-end of the chain. I've got a tube phono preamp and a tube headphone amp. My power is a SS Conrad Johnson CA200 control amplifier. The speakers that I prefer seem to work best with SS.

Generally, tubes are economical in the front end of the chain. they last long and good design is relatively easy. SS can sound VERY good also, but you generally have to spend more money to get equivalent resolution.

If you want to go all tubes, then you'll have to select your speakers in concert to make sure that you have a good match. Speaker matching can be an issue with SS also, but your range of logical choices is much wider.

Dave

bifcake
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Re: Impressed with Tubes!

I agree with that. Your amplifier choice is dictated by your speakers. Some speakers do well with some types of tube amplifiers and not others. Other speakers don't do well with tubes at all. It gets pretty tricky when you start talking tubes for amplification. The result is not always what you would expect. For the most part, it's safer to go with a tube pre-amp.

Jan Vigne
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Re: Impressed with Tubes!

As long as you're dealing with a contemporary push-pull tube based power amplifier (and not a SET), your choices in speakers will be quite open. You want to look for a mostly resistive load rather than a highly reactive load when shopping for speakers to mate with a tubed power amplifier. Find the most consistent impedance curve (the higher the better as a general rule) and the most benign electrical phase angle. If you read a speaker review which indicates the speaker load will draw high amounts of current from the amplifier, that's not a speaker you would normally pair with a tube based power amplifier. Hopefully any dealer can direct you towards appropriate technical matches for the amplifiers they represent. If not, try this; http://www.symphonysound.com/articles/tubefriendly.html

Read the measurements and comments JA provides for the various power amplifiers under review. The article should make more sense in combination with the explanations JA provides.

Tube based power amplifiers typically run much hotter in room than a solid state device, so make certain this won't be a problem in the summer. They also require regular maintenance that you don't have to perform on transistor amplifiers. Choose between fixed bias or auto bias for the least amount of concern about whether the tubes are running at the right bias point. Checking and setting bias is not a problem but not all tubed power amplifiers require such maintenance. The PrimaLuna gear relies on an auto bias setting that makes life easy for the owner. (Tubed pre amplifiers do not require constant monitoring of bias, this applies only to tubed power amplifiers.)

IMO tubes are often better suited to power amplifiers than pre amplifiers, most especially so if you run low output phono cartridges. However, what you might prefer will be something you should determine with your dealer rather than by what another person likes or dislikes. Personally, I've run tubed pre amplifiers and power amplifiers for several decades and can't imagine going back to solid state in either area. But my speakers have always been "tube friendly" and my phono cartridges have remained high output types.

If you like very high SPL's, you'll probably have to find higher sensitivity speakers or settle for solid state or a hybrid unit with tube input/driver and transistor outputs. While tubes tend to sound "more powerful" than equivalent transistors, you'll have hard time finding a 200-300 watt tubed power amplifier in a reasonable price range. Switching to a 96dB or higher speaker (check the Omega line of speakers and the other manufacturers who build with the Fostex drivers), however, will get lots of volume from even a modest tubed power amplifier.

Your term "richer" isn't all that descriptive and leads me to wonder what you actually heard. Various brands and models of tubes can alter the sound of a tube based pre amp or power amplifier. It's typically considered an advantage by most tube users. But "richer" makes me wonder if you're not hearing a tube or a whole pre amp with a bit of a bump in the midbass or possibly an interconnect that wasn't swapped out when the pre amps where changed.

Since tubes have an inherently higher output impedance than transistors, ask about the output impedance of any pre amp, tubed or solid state, and be careful of any spec higher than about 500 Ohms. This would be very important if you intend to run long interconnects between the pre amp and power amplifier. If your plans are to keep cable runs short, you might want to listen through a passive "pre amp" before dishing out cash for an active device. A CD only system might be even more appealing without any active gain devices in the signal path.

Ask whether any pre amplifier inverts phase.

In addition to the Stereophile Recommended Components listings you can find excellent tube based pre amps by doing a bit of research on the internet. There are quite a few tube based manufacturers who sell strictly through the web. Check Bottlehead and ignore the graphics. If you'll read a bit, you will also find references to several manufacturers who don't spend much money on advertising but have been around for years and sell by reputation rather than ad space. Audible Illusions comes to mind but there are others that fall into the same category.

Jan Vigne
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Re: Impressed with Tubes!

Also, if you prefer the "sound of tubes", you might try to find a power amplifier with MOSFET outputs. Give this an audition. MOSFET's are generally considered to have many of the benefits of tubes and transistors with not as many drawbacks as either. Quite a bit of the Unison Research Unico line will be hybrids with tubes in the pre amp and FET's in the outputs.

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