Onkyo TX-SRS02 6.1 AV Receiver.

Manufacturer: Onkyo USA Corporation, 18 Park Way, Upper Saddle River, NJ 07458; 201/785-2600; www.onkyousa.com

Price: $300

Source: Manufacturer loan

Major Specifications:

* 75 watts per channel FTC(8 ohms, 20 Hz-20 kHz, <.08%THD)

* 2 Assignable component video inputs

* 4 sets composite and "S" video inputs

* 1 composite and "S" video output

* 4 assignable digital inputs (3 Optical, 1 Coaxial)

* 7 analog inputs including one 5.1 input

* 1 analog monitor output

* Dimensions (W x H x D): 17 1/8" x 5 7/8" x 14 13/16"

* Weight 22.5 pounds

The Onkyo TX SR502 under test here has recently been discontinued. It has been replaced in the lineup by the TX SR503-R, which is similar in all respects except for the addition of a seventh channel. The performance of the TX SR502 is so good that I want to make sure that our readers know about it, even though it is no longer a current model, and as I just mentioned, its successor looks to be cut from identical cloth, so I believe my comments below still have currency.

Above I list the analog, digital audio, and analog video inputs and outputs (I/Os) of this unit. Onkyo, like most AV receiver manufacturers, has a very comprehensive website, so if this unit does have enough I/Os, you are sure to find one that does. The I/Os look to be generous given the unit's cost. To keep a lid on cost, though, Onkyo does not include automatic speaker setup or automatic room equalization (I will have more to say on the utility of these features in a future issue). I also note the video assignment system will not up- or down-convert video signals in the three different formats it supports. On the audio side, the unit has no phono preamp.

Let's start with usability, a key feature for AV receivers. The Onkyo has nicely equipped their front panel with buttons for selecting inputs and these are repeated on the remote. For some reason, though, the display for the selected input is limited to three characters (e.g., "Tape" thus becomes "Tap.") Bass and treble are separately controlled through the front panel or remote. Only the left and right channels get tone controls. Because the tone filters are digitally controlled analog filters, they still work when the receiver is thrown into analog bypass mode. This is a pleasant surprise.

The universal remote was designed for small hands and great eyesight--the remote is chock full of tiny buttons with small writing on either the side or top of the buttons. What labels apply depends on the mode being used. In addition to the receiver, the remote can supports up to eight different items on your equipment rack.

Using a single button on the remote, you can rotate through the five modes that synthesize 5 channels from 2 (Dolby PL II movie, music, and game; Neo 6 music and movie). To get at the control modes for PL II or Neo 6 music synthesis modes (center width, etc.) requires five button presses or manipulating a jog control on the remote. It takes two to get out. The receiver stays in the control modes once there; with no time out. This permits one to listen for a while, and then make adjustments as needed. Be forewarned, novices--pushing the wrong sequence button can trap you in perma-control from which it may appear there is no exit. Turning the unit off is the easiest way out when all hope seems lost.

A button on the remote engages the Dolby level-adjustment noise signals. Two pushbuttons on the remote adjust speaker level. Whichever speaker the noise emerges from is the one targeted by the level adjust. You can let the noise signal move through each of the 6.1 speaker locations (this unit adds a channel for center back) or you can use a fourth push button to freeze the noise at one speaker. Given that the unit does not do have automatic speaker level adjustment, Onkyo's smooth implementation of the level setup function prevents the loss of hair while setting the speaker levels. Unfortunately, level adjustments are limited to 1dB steps and level adjustments for the 5.1 bypass mode are separately entered.

DSP modes are accessed through a separate pair of pushbuttons on the remote. Direct stereo mode has its own pushbutton.

The tuner's performance is typical of an AV receiver, i.e., local channels only. Only a pair of buttons lets you scan up and down all the presets. Most current stereo receivers on the market still supply individual presets

The integration level of the analog preamp section of the TX-SR502 is amazing; it's almost all on one Rohm semiconductor chip, the BD3817KS. The BD3817KS subsumes all solid-state input selection, tape output assignment with active buffering, stereo analog bypass, and bypass for the 5.1 analog inputs (SACD and DVD-A). In normal 5.1 operation, the chip switches in the signals from the seven internal DACs (remember, this unit is 6.1). The chip supports two levels of analog gain control (digitally selected) that in turn drive the power amp inputs directly. This chip also supports the analog bass and treble controls that come after the volume controls. By choosing the large scale of integration afforded by the BD3817KS, Onkyo can gain many advantages, not the least of which is cost reduction. I will have a more detailed discussion of the internals of this receiver in the next issue as well as a general article discussing the innards of an AV receiver.

The stereo ADC, the seven DACs, and the digital data receiver for the optical and coax inputs are in a single chip (AKM AK4588VQ). Worst-case, full-scale THD (presented as an equivalent number of bits) is slightly disappointing at 13 bits, but are specified at a typical value of 15 bits. Dropping the signal level down 60 dB yields a little less than 16-bit performance worst-case with the typical spec two bits higher. The part is noise-limited at this signal level since the SNR numbers (A-weighted) are identical to the -60dB THD specs. The digital filter passband ripple is [+ or -] 0.02dB and the stop band attenuation is 54 dB. These numbers are typical of the 16-bit-class DACs we have been seeing and indicate a relatively short FIR digital filter. While these numbers are lukewarm on an absolute scale, they are very good for an AV receiver in this price range.

The ADC part of the chip has worst-case noise performance similar to the DAC. Provided the analog input signal level is not so low as to prevent more than about 12 bits from moving or too high to allow the DAC to clip any analog (analog tape, or external phono preamp) signal should pass transparently. Like all AV receivers I have tested, the unit has no way to adjust incoming signal level to the ADC.

The main transformer has four secondary windings to prevent the many different electronic functional blocks from talking to each other. A small additional transformer keeps the front panel alive so it can respond to issue startup commands when the remote tells it that it's time to wake up. The unit is also well populated with voltage regulators given its price.

The weight of any AV receiver tells you more than you would think. Transformers that can supply lots of current and voltage are heavy and power transistors need big heat sinks to get red of all heat generated in the process of sending that current to the speaker. At 22.5 pounds, this unit has a good-sized transformer and sizable extruded heat sinks. The competition may not tilt the scale as much at the $300 price of the Onkyo

The unit is specified (FTC standard) to produce 75 watts into 8 ohms at 0.08% from 20 Hz to 20 kHz in two-channel mode. The power amp is fully discrete and the number of circuit simplifications to keep the cost of each power amp channel down is surprisingly few. I believe this explains why the amplifier's distortion numbers come in under 0.1%. The primary filter caps are 10,000 [micro]Fd 65V. That's not a lot of capacitance to supply charge to six hungry channels at 20 Hz, and even the stereo 20 Hz distortion number here may be affected by the size of the primary filter caps (low frequency signals spend more time drawing current from an individual (+ or -) power supply terminal than higher-frequency signals). Still, the size of the primary caps in this unit is very good considering the price.

75 watts translates to a peak voltage swing of 31 volts into 8 ohms. Into 8 ohms we are probably not current-limited, but we have no 6-ohm power spec (no other FTC specs are given in the spec sheet). It takes at little less than 4 amps peak to get 75 watts out into 8 ohms.

Dynamic power specs (I think Onkyo used a 100-msec isolated tone burst composed of 1 kHz sine waves) are in the spec sheet on the website. These should not be in a US spec sheet, but the Onkyo website appears to cover all of the Americas. While dynamic power ratings are easily abused by sales people, which is why the FTC stopped use of them in the USA, they can give useful data if interpreted carefully. More on dynamic power in the next issue of T$S.

The dynamic voltage swing into 8 ohms in 39V, up from the steady state number of 31V. The dynamic voltage swing declines to 33V into 3 ohms. From this spec we can determine that at least with the quick dynamic bursts, the amplifier can source 11amps. The output devices are a single set of Toshiba 2sa1941 and 2sc5198 complementary bipolar pairs. The performance I have just outlined is consistent with the safe operating area curves (subject to additional factors of safety to insure a very reliable product) supplied by Toshiba. Nothing in this unit is under-designed, but neither is it overbuilt.

The specs give no FTC power rating below 8 ohms, which I assume means it will go into thermal shutdown on the worst-case preconditioning tests below 8 ohms. The unit is UL rated. As I understand the UL ratings, the unit should not overheat to dangerous levels even if the speakers attached present an impedance well below that recommended by the manufacturer.

In practice, the Onkyo will readily drive lower impedance loads until the internal current limiter (an advanced limiter with no analog foldback circuits) trips the relays and disconnects the speakers from the amplifiers. The protection circuit activates the relays when the transistors are pulling too much current over an excessively sustained period of time period, i.e., the safe operating area of the output transistors, as specified by Toshiba, is being exceeded. I replaced my reference amplifier with this unit during the speaker tests in this issue and felt no loss even at high levels in a big room.

To sum up, the Onkyo TX-SR502 gets you an amazing amount of high-performance electronics for its price. It has a good user interface, which means you can actually use all the features of this receiver in the multi-channel mode. As a bonus, the complete digital bypass makes it a fine choice as a low-cost stereo-only receiver, while you think about putting your toes in the multichannel waters, provided you do not need a phono stage or individual tuner presets.

--DAR