Cary Audio SLI-80 Signature Amplifier

Details: Written by: Grzegorz Makarewicz; Published: 04 July 2025; Hits: 24

Grzegorz 'gsmok' Makarewicz

Stereo tube amplifier from the American company Cary Audio Design. It is not only an amplifier from an American company, but unlike many products of this type, it is not manufactured in China, but in the United States of America. A real shock.

Back to the point, this is a fully tube device - it even has vacuum diodes and as for a product coming from outside China, I traditionally could not find any schematic diagram on the Internet that would allow for a detailed analysis of the applied system solutions without having to draw the diagram from nature. The process of reproducing the diagram itself is quite pleasant and interesting, but on condition that you do not have to hurry. In my case, unfortunately, I cannot always afford this luxury. Photo 1 shows a general view of the amplifier. The amplifier does not have a factory cover for the tubes. From an aesthetic point of view, this is very good, because the whole thing, together with the speaker transformers set at an angle, looks great. It is a bit of a shame that the mains and speaker transformer housings are not unified.

Photo 1.

The front panel of the amplifier is visible in Photo 2. It is quite elaborate compared to purist audiophile designs containing only a power switch and possibly a gain control knob.

Photo 2.

Here we have a few more elements. Their functions are clearly described, as can be seen in Photo 3 and Photo 4. Here we have the power switch, input switch (CD, AUX1 and AUX2), volume control (large knob in the middle)...

Photo 3.

... balance control, remote gain control sensor, headphone/speaker switch and headphone jack.

Photo 4.

Photo 5 and Photo 6 show construction details seen from the top of the amplifier.

Photo 5.

In Photo 6 you can see the large electrolytic capacitors working in the power supply filters, peeking out shyly from behind the speaker transformers. I think that the manufacturer did not treat them as decorative elements, but simply could not fit them inside the housing.

Photo 6.

And here is a set of tubes and a proudly displayed inscription with the amplifier type. Now we know why the manufacturer did not use a tube cover.

Photo 7.

Photo 8 shows the amplifier seen from the side. There are no elements related to the operation of the amplifier on the side walls. This is important. Many tube amplifiers have power switches mounted on the side and also near the rear wall of the housing. Operating them is both inconvenient and dangerous. In the case of tightly arranged elements of the listening system, you have to reach blindly with your hand and run the risk of touching hot tubes. In this case, there is no such danger.

Photo 8.

The amplifier's power stage can operate in both triode and ultralinear modes. The operating mode is switched independently for each channel using toggle switches (Fig. 9).

Photo 9.

Another view of the vacuum tube set, mains transformer and...

Photo 10.

...we move on to photos taken from the rear side of the amplifier (Photo 11 to Photo 19).

Photo 11.

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Photo 19 shows a set consisting of a potentiometer and a large Jack Mono socket that allows adjustment of the quiescent current of the power tubes. The amplifier does not have the so-called "autobias" and after each replacement of the tubes it is necessary to set the quiescent current value specified in the amplifier's operating instructions. The current meter should be connected using a Jack plug, and the current value should be adjusted using the available potentiometer shaft. After making the adjustment, the position of the shaft can be locked by gently tightening the nut visible in the photo.

An interesting fact that may surprise users of tube amplifiers that require setting the quiescent current is the fact that a milliammeter should be used for this purpose, not a voltmeter!!! Inserting a plug into the measuring socket causes the connection of the output tube cathodes to be opened and the element replacing this connection must be an ammeter, which, via a Jack plug, allows current to flow between the power tube cathodes and the amplifier's ground. This is a rather unusual approach, considering the fact that in the amplifier, very good test resistors with values of 10Ω/1% are mounted in the output tube cathodes. I think that they are not intended for the amplifier user, but rather for the service technician, because access to them is possible only after unscrewing the lower chassis cover.

As you can see in the photos, the amplifier is equipped with two control potentiometers, one for each channel. This means that the correct (equal) division of current between the tubes of each channel requires the use of tubes with selected parameters (two pairs of power tubes are needed).

Photo 19.

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The amplifier stands on four solid rubber feet.

Photo 23.

Here's the leg with the cap (whether it looks pretty is a matter of taste)...

Photo 24.

... and here is the foot without the cap. The embossed inscription leaves no doubt as to who manufactured the amplifier.

Photo 25.

It's time for the most interesting part of the photo report, the undressing session. The next two photos show the entire interior of the amplifier after unscrewing the bottom cover.

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And now the details. Look and admire.

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In Fig. 44, in the central part, you can see a circuit generating a negative bias voltage for the control grids of the output tubes. It consists of a half-wave rectifier and a CRC filter. The second filter capacitor (electrolytic with a value of 47μF/350V) is additionally bypassed by a polypropylene capacitor MKP (2μF/400V), while the resistor in the filter is a DALE used, for example, in electronic systems in military aircraft, not to mention audiophile systems. As you can see, the manufacturer did not skimp on the quality of the components.

Photo 44.