RCVR: Pioneer QX-646 Quadraphonic Receiver


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Senior Member
Jan 11, 2010
Melbourne - Australia
If you have any more photo's or comments to make on this Quadraphonic unit please feel free to post them in this thread....:)

Pioneer QX-646 Quadraphonic Receiver (1974)

Average Sale Price: $100.00

Currently several are listed on the Web from $35 to $150.

This was Pioneer's "baby" of the new 1974 Pioneer Quad range which included the QX-747 and top of the line QX-949. Info is sketchy....the rumour is that this model was discontinued after a year or so. The unit cost $499.95 and produced a fairly low 10 Watts RMS into 4 channels and no amp bridging to increase the power into stereo. (Note for comparison...the equally priced (Stereo) Pioneer SX-838 from the same year had 50 Watts RMS...and the Quad competition at the price for power output...Harman Kardon HK800+ 22Wpc x 4/ Sylvania RQ-3747 25Wpc x 4). Decoders included CD4/RM & SQ, however latter-day Pioneer SQ decoders are notorious for being among the worst ever, so you may be better off with an outboard SQ in that case.

Nevertheless, if you can live with the low power, and have an outboard decoder, these units are considered to be very nice sounding along with the rest of the Pioneer "Backlit Blue" receivers from this era.

The earliest brochure I've seen is dated 9-73.

Pioneer QX-646 Quad Receiver1.jpg
Pioneer's Full Logic SQ decoders were the absolute worst - very slow attack/release times and VERY audible decoding artifacts which created audible volume changes as front or back sources changed dominance.
I sold this stuff back in the day and remembering seeing pre release photos of the then new Pioneer Quad line. Everyone said "these are going to fly out the door." When we got them in, we found that the decoders, especially SQ were no great shakes. Unfortunately, the displays on 747 and 949 weren't scopes. Sad, because the amps sounded good, the pieces looked awesome and they had decoding/demodulating for all 3 Quad formats. Evidently, the engineers had some killer concepts , but marketing was obsessed hitting a pricepoint. Something had to give, so the scope became a light display and the decoders were sub-par. Imagine a 949 with killer SQ & QS decoders and a real scope. Perhaps we'd be talking about the coveted, highly classic QX-949 as the holy grail of Quad.

I sold a lot of QX-747's and 949's, but never personally sold one of these. Before they were discontinued, we took them off our list of stocked items. This piece looks very sleek, but without the scope-like display on the 747 and 949, plus the low power, this piece was ruled out by most customers. If they came in asking for Pioneer, they wanted that cool display. We sold a huge quantity of 747's and 949's. Although I explained how the decoders were shamed by most others, people often wanted the simplicity of everything in one box and thought the display futuristic. 646 actually looked more like Pioneer's SX-828 stereo line which was '72-'73. The subsuquent stereo line, SX-838, etc. had small black rectangular buttons for selecting speaker pairs and some other functions. They didn't look like this Quad line or their stereo predecessors.

Thanks again Quad Linda for your retail insight....Yep...I figured/suspected that the 646's day's were numbered the moment someone saw the funky display's on the 747/949's...still, dunno why, I actually prefer the look of the 646 units...a nice sort of neat 70's modern, modeled (..as you mentioned) on the previous range of stereo Pioneers.
Just a real shame about the low power output and the lame SQ Decoding.
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yikes, $499.95 for this, and it is only rated at 10 watts,

I have the price of the QX-949 listed at $899.95 Cdn- pricey too, but seems like a better deal
People in the record business would call an item like this a stiff. A lousy seller. $500 was like maybe $1500-$2000 in today's money. For 10 watts, no display and crappy decoders. Oh, but wait a minute, there were plenty of decoders, especially SQ, that did a crappy job back then. Well, maybe not this crappy.

it's well built, looks cool and was the first to include all three. I wouldn't want my sister to own one. I don't have a sister, so she can buy what she wants. :mad:@:

The QX-8000 & it's replacement the QX-8000A were top of the line of the older Pioneer Quad range that the QX-949 (..range) replaced. They were top of that range before the QX-9900 came along. The QX-9900 was an elaborate and unique high end Quad model from the same era (..1972-ish) and a bit of an orphan looks-wise. It became the top model of that early 70's Quad line. I might have seen a catalog image somewhere that shows them (the QX-8000A or maybe 9900 & QX-949) together, but I can't find it.

The mystery behind the QX-9900, is that it resembles the top of the line Akai AS-980 from the same era so closely, (...and the rest of that Akai range of Quad units), that some speculate it's a OEM Akai reskinned as a Pioneer. I'm just as confused as you are about the origin/thinking behind that model's origins...but....speculating again...I suggest that the big-ass Akai caught Pioneer off guard and did a deal (..model/tech sharing agreement) to quickly create a top end model to compete. It certainly makes the QX-8000A look a bit old hat.

The QX-8000 is considered by some better sounding than the later top line QX-949 ...see post 7 of linked thread....
the mysterious SX-6000...calling Lt. Columbo... - AudioKarma.org Home Audio Stereo Discussion Forums

P.S. Like most here, I'm a enthusiast more than an expert, but from the info I've read over the years (..old mags) I know some of the dates at that site you mentioned are not accurate. I'm pretty sure that the QX-8000/8000A dates from earlier than '74....at least '72, possibly 71. The QX-646, 747, 949 were introduced in 1974.

UPDATE...did a bit more searching...Earliest date of manufacture based on serial no. build codes are as follows... QX-8000 (1971) / QX-8000A (1972) / QX-9900 (1972) / QX-646/747/949 (1973) ....most of these, according to serial no's, continued to 1976 (..so they would have been sold side by side). The QX-9900 serial's don't go past 1974. Most of the Pioneer Quad line was discontinued in '76.....with the updated in 1975, QX-747(A) & 949(A) receivers continuing to be built until 1979.
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QX-8000(A) was a great sounding receiver. Not-so-hot SQ decoding. The engineers seemed to be in control. QX-949(A) & 747(A) had the marketing folks driving the bus. We had a blowout of QX-4000As at $299 when they went discontinued. For $499, we sold the QX-4000A with a Garrard SL-55, Shure M44E and four house brand speakers.

I bought a QX646 a month ago in very nice condition for 45 dollar with shipping. It works well, it for 45 dollars I am satisfied. It will be used in the stereo mode mostly.
I heard one of these quite a bit, they must have been very conservatively rated at 10w, my buddy used it not for quad but stereo-to-surround and had speakers scattered all over the house, one even in an old upright console radio by the front entryway. It rocked!
Yeah...I know old thread. But this was the quad receiver I bought for my university pad. SQ/QS(RM) was mediocre but adequate, but CD-4 decoded better than my current outboard JVC decoder ( and I used a Grado FTR+1 cartridge in the day)... The pots finally degraded to the point that I sold it...but it was a GOOD receiver, and a great entrypoint to 4-channel for a 19-year old in 1976.....
I have one of these as well (another eBay bargain). My brother was using it for a couple of years (in stereo mode), he just replaced it with his Luxman. Low power but good for a bedroom system, I might just use it for a monitor system around my work bench. When I get the chance I might try it on CD4. Too bad the SQ/RM decoder is so bad, considering that Pioneer sponsored a lot of the quad KBFH shows you would think that they would of put a good (if not great) SQ decoder in these things! It's a nice looking unit though.

I think that bad decoders coupled low power and high price helped to kill quad more so than multiple systems did. Given how finicky CD4 can be I just wonder how many people bought one of these and had trouble with CD4 plus were unimpressed by the matrix decoder, so back to stereo!