Product: Thule 250 preamp & power amp
Manufacturer: Thule - Denmark
Approx. price: $ 1.400 PR250B, $ 1.400 PA250 B
Reviewer: Dejan Veselinovic

The Thule 250 preamp & amp combo

This Danish company is, if anything, then dedicated to its own concepts. Only its entry level products use classic technology - from their mid priced units upwards, they use fully balanced topology.
Its crucial virtue is that it completely isolates the ground from the signal, thus also preventing any return effects, which improves the signal-to- noise ratio and consequently, the overall dynamics as well. The downside is the price - this is necessarily more complex to execute, and hence must cost more.
This model is a very versatile beast - it has full Dolby Digital and DTS decoding, courtesy of Motorola, but it can also be used for straight audio. It even has a command button labeled "Pure Audio", while its natural complement, power amplifier PA250 B, also has a command button labeled "2ch/5ch".

Anyway, the preamp and the amp were tested as a system for several reasons.
First, I believe, and practice seems to confirm this, that pre and main amp combinations somehow sound best when used as a natural pair, from the same manufacturer. Of course it's possible to mix-and-match it as you like, but chances are you won't be very lucky, though there are exceptions to this rule.
The second is the fact that both units are topologically balanced - this is to say that the entire signal path is in full balanced configuration, from input to output, which is not too often seen.
Much more commonly, one will find XLR socket, but inside, there's an electronic adapter which downconverts this to a standard line signal. Thus, to obtain a true perspective of what this combo can do one needs to be very sure that everything is in full balanced mode. And lastly, I believe most customers will opt for the combo anyway.

I completely disregarded the home theater capabilities on this occasion and evaluated these units on basis of their straight stereo audio capabilities. Perhaps this is not entirely fair, since Thule has straight audio pre and main amps, such as PR100/PA100 (standard line) and PR150 B/PA150 B (standard and XLR, inside fully balanced), for considerably less money, but I figured this was their top of the line stuff, so it had to sound good however one used it, and after all, they did allow for straight audio, didn't they?

Electronics - casing

Inside view of the Thule 250 power amp

The casing is typically Thule - sheet metal, thick front aluminium fascias, with a slight slope, all of it beautifully machined to very high standards. And of course, heavy, really heavy, which is good, since weight tends to decrease vibration.
The preamp uses a multitude of integrated circuits, with no less than 13 regulated power supply lines (all using LM317/337 regulators, properly bypassed and protected).
The video lines are especially impressive - their bandwidth is all of 80 MHz, way over what is actually needed, but in return, with little loss, if at all detectable.
The audio lines use what must be Thule's standard equipment, Burr-Brown's OPA 2134 FET input op amps. Now, these are far removed from the usual cheap and nasty ICs, and are in fact intended for audio use. They are relatively fast (20V/us), and FET inputs guarantee high input impedance, thus enabling excellent signal transfer characteristics.
Also, the fact that they are dual op amp chips makes them very suitable indeed for balanced configurations, since both halves will share the same die, and will thus be in theoretically perfect balance no matter what happens. The actual balance may not be quite perfect, but it's the next best thing.

No mechanical pots here - it's all done using National Semiconductor's LM1792 ladder network controls, and with no less than four of them. Using their laser trimmed resistor networks, the resulting precision is way better than anything possible using even the most exalted mechanical pots, such as those from Alps and Noble.
Also, there's no wear and tear, so their long term stability and precision are virtually constant, again something no classic pot could ever manage, no matter what.
The controls are thus electrical, and given to the remote control, with the notable exception of the volume, which may also be adjusted using the centrally mounted knob. Selection of source is via high quality, sealed, gold plated contact relays, while solid state devices provide the necessary logic. Very high tech indeed.

The RCA Cinch connectors are all gold plated (yes, even those intended for video), and the XLR connectors are high quality types. No wiring inside, thank you, it's all directly soldered with ribbon cable used only where absolutely necessary or most logical.

The power amp is a heavy beast - what else could it be, with two low loss toroidal power trasnformers, each rated at 550 VA? The centrally mounted heatsink is easily the most impressive one I've ever seen, and I've seen some good ones - however, its a solitary unit, which is chock-full of power transistors, all 18 of them, along its back.
Good as it may be, it won't take too much power for too long a time. Fortunately, in stereo mode, the amp provides 250 W per channel, which is a lot of power not many speakers can handle, and God alone knows what its impulse power will be, especially into low impedances.
This is likely to be very large indeed, given that there are two distinct blocks of filtering. The first uses new generation Philips T-Power capacitors, which are said to provide considerably better filtering than classic units - these offer 2x10.000 uF per channel, each toroid feeding one half in stereo mode.
Then, on the actual circuit boards, there are two additional 10.000 uF capacitors by Nichicon, providing local smoothing. Altogether 80.000 uF of filtering.
All high power lines use preferred screw down, heavy duty binding posts, as do the speaker output lines. Input connectors are gold plated.
SMD technology has been used throughout in both units, with additional classic component soldering only where unavoidable; this bodes well for reliability and long term stability, but also for the sound, since signal tracks are greatly reduced in length, thus decreasing possibilities of picking up stray interference, or stray capacitance.

Macrodynamics

Inside view of the Thule 250 preamp

Well, with 250W of power on tap, what could you expect but excellent dynamics? Bear in mind that there is no overall feedback here, which generally imparts an air of freedom from grain, stain and other transistor nasties. The bass is especially impressive, in its tremendous drive and vivaciousness.
It imparts authority, however, it lacks the absolute control I have heard elsewhere, albeit at an even greater price.
It's not out of control, mind you, it just seems a little looser than it could be. Yet, it's not often I hear my JBL speakers deliver such thundering bass lines when the music requires it.
This does not go at the expense of the mid range and the high range, though. Both are very clear, highly focused and with plenty of detail, but completely avoid being clinical. You hear into the mix, you can pick out individual instruments, but you never doubt the wholesomeness of the entire sound stage, nothing leads and nothing lags.

Changing the JBL Ti600 for my venerable AR94 speakers, which were recently refreshed by putting rubber surrounds where the nasty foam surround used to be before it evaporated on me, and by installing a new pack of Sprague bipolar capacitors in place of the originals (while the originals still work, it has been 16 years or so, high time for new ones), the tonal picture did change slightly. The ARs are a more difficult load to drive, and while not as terrible as some (notably electrostatics, Yamaha NS-1000 and AR3a), they do tax the amp more than the generally better behaved JBL units.
Also, they are some 3 dB less efficient, which means I need twice the power for the same sound pressure level.

I did say "changed" - not much, to be sure, but to a very fine degree, just at the threshold of being discernible (and taking into account the different tonal colour of the speakers themselves).
Things got just a little bit harder in the extreme high range, not bad, not obvious, just a little less refined. In fact, I expected that to happen, it usually does with amps which have less than excellent speaker control and are less than very wide bandwidth design, which a zero feedback amp rarely is.
In this respect, my experience has it that amps with little feedback (i.e. less than 20 dB, or 10:1, of overall feedback) fare best in this respect if internally backed with substantial power supplies. My Harman/Kardon 6550 (2x50W/8 ohms, 1994) is a good example, even if not the absolute best - 14 dB (5:1) of feedback is all it takes to keep his high range almost uniform from speaker to speaker.

Microdynamics

Upon normal level listening, I could not escape the feeling that I was dealing with a semi-tamed panther - it was always quick to respond, and always ready to pounce.
It's a feeling of almost cat-like power, subdued for the time being, but forever present, feeling almost limitless. Not quite the Krell class, but not too far removed either.
The most important thing is that there is no discernible change of the soundstage when listening at low power - it's practically exactly the same as when playing at window rattling levels, just less in sheer volume. This is no doubt a strong virtue, not easy to achieve and most comforting to know and have.

Very fine nuances are completely preserved, nothing is overlooked or left out, but not as a matter of tideness or engineering principle, rather as a matter of the music itself.
The duo seems to start the music, and then leave the room and leave you to your music. It just isn't there and the only thing that sets it apart from the very best is that it leaves the door open, not quite close it like the Very Big Boys.
I also must mention the noise of the system, which is notable for not being there at all. Do turn up the volume to the maximum and go place your ear right to the speaker - if you live in an uncommonly quiet neighbourhood, you just might be able to make out something that just might be noise, which just might emanate from this pair.
Then remember that you are hearing noise at 250W of power and thank the Lord it was just noise, not music, or you would have been a frescoe on the opposing wall, probably with your speaker superimposed upon you, thus achievening sublime audio fidelity and complete simbiosis with your system and environment. And for God's sake, don't forget to turn the volume down after that test, or you'll make your mother-in- law's dreams come true.

Overall sound quality

Load tolerance is good, but I have heard better even for less money. This is not to say it's poor or lacking, just not as good as some others. The change was hardly detectable on my systems, but with still more difficult speakers, that may become more readily noticed.
Possibly a still bigger power supply might improve matters, but I submit a more powerful output stage would be a better bet.
Bass lines are, I daresay, fairly typical of zero feedback designs. Somehow, they never manage to do in the bass what they do in the mid and high ranges. Their bass is generally powerful, but never quite as well controlled as with minimal feedback designs. It's not that the bass is out of control, or that it's flabby - no, it's very warm, very rounded, very meaty - perhaps too much so of all that.
Good bass needs some measure of stiffness, taughtiness to be believable - trust me, I used to bang, sorry, play the drums. And Thule's products, including this pair, don't quite live up to that expectation.
You'll love their bass lines at first hearing, even after some hours of listening; but what of next week, next month, or next year? I'm not so sure of that.
Yet, the overall sound is very seductive, I can't deny that, it's clear, well integrated and with bags of detail if the recording provides it.

This duo can play an orchestral piece as easily and with as much aplomb as it can rock'n'roll, or play mystic Irish music, or portray a Russian army choire, singing "Kalinka". But play Enigma or Vangelis, with plenty of electronic and natural bass lines on hand, and you get the feeling that something is not quite right, though nothing is obviously wrong.
Things might change if you have a pair of smaller enclosures at hand, which naturally roll off bass before larger, multiple bass driver enclosures do. Or your boxes may tend toward being on the brighter side, in which case this duo might also restore your tonal balance.

Conclusion

So, let's see - we have a highly versatile, very well made duo at a very substantial price. This duo has what it takes to be in their price class and be worth the money asked for them. Of the two, I would say the preamp is overpriced, while the amp has an unusually fair price for what it delivers.
My only real reservation are the bass lines, I seem to be on about Thule's bass lines all the time - but that's to be expected of a consistent manufacturer and a consistent reviewer.
Changing your speaker cable will affect some change there too - exactly how remains to be heard upon trial. Also, your speakers will do their part, as will your room.
If you want a versatile pre and power amp combo, with both eyes on the future, with high quality construction and workmanship, very high tech and with a truly good sound, then do give these units a test ride. But don't buy them before you do - check them (and me) out.

© Copyright 2000 Dejan Veselinovic - http://www.tnt-audio.com