Pioneer CT-S640S: Middle class contender

Submitted on: 17 Jun 13

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Category: Analog recorders/players

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This small cassette deck is a smaller relative of the high class Pioneer decks like CT95 or CT-830. Of course, it isn’t that great: it’s mass of just a little over four kilograms tells the whole story. The box is made of thin sheet of steel and the front mask is plastic instead of aluminium. Pioneer CT-S640S is a light category fighter comparing it with only few years older CT-S620.


We are talking here about 1995., when electronics became cheap and mechanical parts were relatively expensive. This is why the company cut the cost where it counts. Pioneer CT-S640S uses relatively simple (and cheap) ALPS single capstan three motor mechanism, although only two of them are engaged in cassette tape operation. The third one just opens and closes the door. The main motors rotate the capstan and reels. There are also solenoids there and little, thin and resonant housing of all elements helps this deck being pretty loud while changing transport functions. But this is the common thing on some TEAC decks, Technics RS-B models and some cheap Yamahas, not to count others. The good point is that this transport is easy to maintain: only one roller and one belt, easy to change. And that’s all.

On the other side there are many interesting options: I feel that Pioneer put out all patents kept for cassette decks Judgment Day. Beside variable range peak meters, music search system and the rest, there are some pretty serious options. One of them is Dolby S system, the latest one. Pioneer CT-S640 also auto calibrates it’s recording system according to the tape in use. It adjusts bias, level and high and mid equalization. This system is known as Super Auto BLE (“Super” because it is newer than “just” BLE and BLE means Bias, Level, Equalization) but here it’s known as Super Auto BLE XD. This is because it uses standard Super Auto BLE functions but also attacks the tape with strong, real-life signals and watch for resulting distortion. Just to mention that Bang&Olufsen did this almost 15 years before…

Anyway, CT-S640 uses -10 and -6 dB signals instead of just -20 dB used by most common auto calibration systems. I don’t like one other thing: although I didn’t have enough time to record the frequency spectrum during this process, I think this deck uses three frequencies by recording them on right channel to adjust both left and right.

The last interesting thing here is so-called FLEX system. It is switchable and used just during playback process. FLEX means Frequency Level Expander and it adjusts level of high frequency material CT-S640S is reproducing by judging tape’s dynamic output so that optimum enhancement is provided. Integrated circuit responsible for this is located on the very end of signal path and carries PA0059 mark. Don’t try it… You won’t find many info about it on Internet. Anyway, FLEX is intended to improve bad recordings, slight azimuth incompatibilities etc.

The sound

I wasn’t very sure how CT-S640S will sound, just looking the way Pioneer saved the money while engineering it. The things became different very soon: this modestly made Pioneer deck obviously gives advance to it’s electronic parts hiding his cheap mechanical part. It is very detailed, with highest frequencies very slightly emphasized, but never irritating. Middle spectrum is warm and soft although crystal clean. Bass notes are also soft but they loos their edge and don’t go down to the bottom, trying to make oval shape and fill the empty space that would remain in the case the bass notes were less soft and round. On the other side, taking everything into account, Pioneer CT-S640S is very pleasure to listen to and has pretty good sound balance. Comparing it to some higher class Pioneers like CT-959 or CT-979 I felt there is some compression on the high frequency territory. This makes some less three dimensional space during listening and some loss of transparency, but overall sound quality is still good. Turning on the FLEX system on Pioneer’s own recordings doesn’t make any sense since they are very good match to it. Using it for other deck’s recordings may be a good idea if there is a lack of high frequency material. The result is subtle change – this is not auto azimuth system or graphical equalizer, but FLEX gave life to some old, muddy recordings making them much more listenable. On the other side, it will make You feel better, but not that good: some relatively small amount of artificial color is always present during FLEX use and this is the reason why it should not be used on high quality recordings. The conclusion is that FLEX is not a miracle, but is very useful in some cases.

Dolby S system had strict cassette decks specification standards in order to be implemented. After few years companies started to implement it in middle class decks, guess why. Pioneer CT-S640S didn’t look to me as a device I would put Dolby S into. But, I was wrong: listening tests proved that CT-S640S works very well using Dolby S, with come dynamics added and most of the noise gone away. It is a pity there are no many Dolby S decks around.


Pioneer’s cute little deck can prove much more that You would think judging by just holding it into Your arms. For a middle class deck it is almost a miracle, getting as much as possible. Options and sounds are both very good despite of obvious cost cut.

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