Pioneer A-717, a Retrospective

lorne

Sonic Lizard
I started this thread in response to an inquiry on another thread — Echo Wars' celebrated “DC Offset and You”. 440hz was trying to dial in the offset in his A-777 and wondering if it was the same as an A-717 illustrated on a web page noted below. He also wanted to know what I thought of mine.

Inquiries regarding this model have been raised before. The response has been serious, but rather sparse. So I thought that I would review what has been said in the past, as well as call on members to throw in any fresh input they deem relevant. Hopefully someone might even come up with a — dare I say it — a schematic.

Currently, Nishi-san’s marvellous site contains the only reference to the A-717 on the net AFAIK — albeit in Japanese:

http://www.niji.or.jp/home/k-nisi/a-717.htm

In a nutshell: the A-717 was a 100 watt/8 0hms, 19.6 kilo variable bias adjusting Class-A or non-switching integrated amp. It appeared in 1987 and was produced through 1989. I have no idea about it’s export history.

It used various materials and hexagonal shaped forms throughout its construction in an attempt to control resonance and vibration. The transformers received special attention and were potted using pitch in iron cases. Relays were used in conjunction with careful layout in order to create the shortest signal paths.

The amp appeared a year after Sony layed the F-333ESX on the market and ran off with laurels for having presented a ton of build quality for a very modest price. This stimulated responses from other makers, and soon Pioneer and others were trying to unseat Sony from its throne atop the affordable, high class integrated amp. It seems that the big guys were struggling in a battle for public prestige when the Japanese economy and society was having the party of its life. In other words, Sony and Pioneer could afford their little war, and a lot of people could afford decent audio.

The A-717 had siblings:

The A-90 (1987) was far more expensive. It had a little more power and enlarged on the whole theme in order to weigh in at 29+ kilos. It was aimed at the AV crowd and came with a serious, on-board DAC.

The A-838 was a stripped down A-90 with no DAC. It too was more expensive than the 717, but at only half the price of the A-90, Nishi says that it was a notable bargain.

Here are some things that members have said in the past:

:arrow: griz780 bought one during his navy travels and liked it very much. He says it introduced him to high-end.

:arrow: Leestereo said he has an A-757 (1989) which he thinks is identical to the A-717.

:arrow: Bolly reports the Bluebook as saying it has ‘hybrid coil transformers’ (I don’t know what they are).

:arrow: PMik was more than impressed with the ‘Direct’ function. He said that overall the 717 is a very transparent amp, and it is hard to find a weakness except for the RIAA circuit. PMik points out that the successors to the silver-face series (of revered memory) are the black models that include the A-717, 757, 777, 818, 858, A-90 and 91.

:arrow: Now my 2-bits about the amp itself. It intrigues me — the whole unit as a concept and product. I like the sound, but I am wondering if this is one machine that could really benefit from fresh caps. For awhile I was alternating between my Sansui Au-alpha707Extra and the 717 until the Pioneer’s phono section packed it in. I intend to rebuild all the boards some time in the future. How can you leave an amp with a honeycombed, copper-plated chassis and iron-cased transformers in the closet?

Is 440hz’s A-777 the same machine? It looks to be, but I just don’t know. I hope that somebody out there has the definitive answer to that question. I hope that others have some things to contribute in regards to this and other older, black face Pioneer integs. If anyone can come up with ... say ... a scanned schematic? ... well I’ll be pulling the bubble packed lump out of the closet and writing a parts order. :banana: :smoke:

Cheers all — Lorne
 
Great stuff Lorne, I have schematics for the A-717 (I PM'd you about it). How about some pics of your A-717? especially inside? that would be great. I will put the pics I posted in the other thread here and hope I see a few more similar pioneers posted here.



 
Fantastic 440hz! No time now, but I'll put up pics of the 717 when I get time to unpack it and pull the hood. — Lorne
 
I Goofed ....

I once said that I thought the Pioneer A-717 and the A-777 were the same. Apologies! It turns out that I could not have been more wrong. I don't know what I could have been thinking.

Still, there is definitely a family resemblance. Just how far it extends I can't say, but I hope that the following pics illustrate the essential differences sufficiently, despite my rather poor camera/lighting technique. Pics in sequence are as follows: main board (one channel only) looking down from the top and from the right side; main board amidships looking down from the front bezel; filter and cast transformers from the left side; front exterior; back exterior.

Not shown is the bottom plate which is copper plated and has a roughly centrally located foot — apparently at the point of the center of gravity. Also not shown is the hood which is ventilated by hexagonal cut outs. Just how much this fussing with ergonomics or synergy has to do with sound — if anything!— I'll leave to people who like to debate such stuff. I am rather inclined to think that it had more to do with getting people to look at the machine. It got ME looking anyway, and it appeals to me.

Even in my poor pic of the back panel it is evident that the 777's voltage selector is missing. This is not surprising as my machine is a domestic Japanese sub-variant of the 717 which is dedicated to the Japanese 100 VAC mains which run as either 50 or 60 Hz, depending on location.
 
From your pix, my 757 looks identical to your 717 except that the back panel on the 757 is not copper. The 717 was available in North America but had round knobs for the tone controls, speaker selector and the balance. IMHO, I find that this amp sounds more "tubey" (i.e., softer highs and under damped bass) than some of my other solid state stuff, very easy to listen to for long periods.
 
Different but related I would say. My A-777 doesnt have quite so much sheilding and the base and rear of the A-777 isn't copper plated. I notice your preamp section has more sheilding. Transformers and caps look the same though.

Your heatsinks look the same but your poweramps are on a single PCB and sit flat on the bottom, whereas the A-777 has 2 PCBs sitting vertical. The A-717 seems to have 2 seperate circuits on that one board though, with one a mirror image of the other.

But it is clear from the schematics that they are different, no IC's on the A-777, no manual bias adj. on the A-717. The front and back layout look the same. I am not clear on the jumpers on the A-777. they link ADPT in/out on both channels. Is this possibly a way of getting the preamp out signal and connecting to the poweramp input?

Would be great to hear how these two amps compare side by side. As far as the A-777 sounds, well I am using it my main system at the moment and have been for a little while. I really like the sound of this amp, I agree it is easy to listen to even at high levels and has plenty of power for my DIY floor standers.

I don't like the phonostage a great deal though. I have a feeling it is accurate and boring. There I said it ;) I can deal with listening to it but its missing a bit of the punch in the face I want with rock. I have other phonostages that give me a sound I enjoy more so I just use those instead.

CD replay is fine, I usually listen with the tone controls enabled at low volumes and they are automatically attenuated and have no effect at all by the time you reach room filling levels, you can defeat them altogether and bypass that bit of circuitry altogether (audiophile style) but I cannot hear a difference when someone else is pushing the button.

It wont be the last amp I own, think I may have already bought another since this, but it certainly is a very good piece of equipment. I think Pioneer did a great job, not sure how much it cost new (I believe its from around 1989) but it didn't set me back too much :)
 
Leestereo: Well, that is an interesting observation, and I'll be looking out for more details in regards to the comparison in the future. Please be aware that the speaker selector knob is not stock. It was missing at the resellers. It was marked as 'Junk,' which is a term used in Japan to mean 'sold as is'. The buyer is not permitted to ask for testing, or under-the-hood inspections. And there is no guarantee of anything. It's cash and carry, and you are on yer own. I think that the absence of the knob pulled about $50 off the asking price because collectors may lose interest. The knob I used for a replacement (far left) is a pretty close match, and it can be improved by the addition of some black paint on the gripped surfaces.

440 Hz and I believe that the 717 uses IC's to set the bias. I am unsure about what the scheme was for DC offset adjustment. Do you have any info on this is in regards to the 757?

You mentioned copper plating. Here is a shot of the underside that I missed in the last post:
 
Lorne: The 757 doesn't use copper plated chassis parts, IIRC the 717 that was available in North America didn't use them either. I thought that the knob on your 717 did look a little different, but I thought that it was due to the flash...

About the bias, the 757 uses Pioneer's Non-Switching type III IC (essentially their version of a sliding bias circuit, a concept that was initially developed by Nelson Pass for his Threshold Amps of the late 70s). The amp runs quite warm, so its biased somewhat hard and this may contribute to its particular smooth sound. The DC offset is controlled by a DC servo circuit (if you measure the DC offset at the output, it essentially remains constant regardless of whether the amp is cold or hot).
 
Leestereo: According to John Weeks' Silver Pioneer page <http://www.visi.com/~jweeks/stuff/pioneer/#x800> the SA-7800 and SA-8800 employed a non-switching technology. Could this be related to the 717 and 757 and perhaps others? I have a Japanese domestic version of the SA-8800. I am not sure how similar it was to the export models. It has been parked for some time and needs a refit. Apparently, the 7800 was the first of the non-switching designs. Weeks says the 8800 was an uprated version. Perhaps these amps are the ancestors of the later black series?? — Lorne
 
Kerozene: I am assuming that that you are talking about Nishi-san's archive web-site http://www.niji.or.jp/home/k-nisi/index.html. This is fantastic site for vintage fans interested in Japanese audio.

Pioneer non-switching designs (as they seem to be referred to) interest me as a DIY amateur. I place limitations on myself out of safety concerns and ... er ... ignorance. The possibility that I may take down a nice circuit is in there too. I try to arrange things so that I only deal with circuits that are not powered up. I am pretty feeble at diagnosis anyway. My approach is to change out parts and be as meticulous as I can. Then get my hands clear and power up. Usually things go well and the unit sings again. A circuit design that can automatically set bias, and so it seems DC offset into the bargain, (blast me if I am wrong) is good for me. For years I toiled under the hoods of my cars — setting breaker point gap and dwell. l worried about stuff like lubricating distributor cams, advance curves, worn rubbing blocks and so on. Then along came CDI. Phew — what a load off! And it was all due to electronics. Perhaps more adept members can tell us about a downside to auto-setting facilities in amps like some of the Pioneers. (There wasn't any in CDI!)

I would like to know how the silver face series compared to the next generation — the black series. To my way of thinking the black series units were participants in the last celebration of a golden age in mass produced, solid state audio. Notice that I said 'participants'. Numerous other makers were participating on an exciting, level field of competition and rivalry.

And here we are so many years later looking back on something produced by a technical sector that makes stupendous leaps in ever decreasing intervals of time. Cheers — Lorne
 
Kerozene wrote:
And, bty, those Pioneers are spectacular, I wish I had more money to feed this addiction...
Keep looking! My SA-8800 cost me less than a half tank of gas. And my A-717 cost me a wad less than a fill for an SUV. But I waited and looked. Don’t give the weasels and auction lizards on eBay the satisfaction. After you pay the price — whatever it is — any vintage will still need (or could use) a cap refit. In some cases old gear can use (or need) an update for many of the semiconductors.

Forums like this can act to excite markets, but they should also be useful for moderating them as well —in accordance with common sense! Kerozene: hold the line dude! I'm with ya!
 
Hi! :beatnik: im back after a long time offline ... :yes:
FYI. i have messured the idle current of my amp to be 400mA each channal..so no wonder it has a sweet treble. :sing:
My latest score a Stax SR-Lambda/SRD7/SB :bigok: comfirms that the potential of this amp is huge!, so i have planned to add a DACT Att. in the Pioneer :naughty:

Inside the Pioneer A-757 MKII :)



 
PMik: Nice pics. I see differences from my 717. Some questions:

* Is this stock? any new caps, mods, or semiconductor updates?

* Do you know how this mark II version differs from the original?

* Do you have any plans in regards to work you wanna do on it?

* What impresses you about it's sound or performance?
 
Hi lorne

So far i have only made very few, but audible noticeble mods.
the +-V and "null" leads from the main-caps to the PA board and the speaker output leads are changed from the original "door bell" wire to 2x 1.25# solid core wires (can be seen in the middle of the heatsinks at lower pic) the advantage was approx. 25-30% shorter leads :yes:
Parallel HQ caps are added for the un-reg. and reg psu's ;)
Changes are later going to be made to the PA board ...still "mint" condition
I have 4x 10.000µF/71V- el-caps in my stock, so i have made two pieces of metal to hold these caps below the PA board, if i wanted to ?
8x 10.000µF/71V- could be placed wo. compromising the airflow :naughty: ...but i have been lazy and not fitted the extra 40.000µF in yet...cuarse when its time to do that, i better make a complete mod.
I want to change the Toshiba output devices for fast Sanken's (2SA1215/2SC2921) to be able to do this, i will have to make the last stage hardwired :scratch2:
if im able to locate faster driver transistors... also these parts inc larger heatsinks will be upgraded in the same task.
The DACT Att. has to be fitted as well when the amp is in pieces.

About the sound ?
These amps has a lot guts! Cresendo! and ability to maintain a stabile, clear soundstage...acts like expencive amps :thmbsp:

The difference betwin the A-757 and the A-757 MKII is very minor.
first version of A-757 had different knobs for speaker/bass/treble/balance/phone selector controls
i prefere the round knobs used for the MKII

The A-757 MKII went into production in 1990
Im not sure about the stop "date" ..i believe it was in 92/93

The complete specs;

A-757 MKII

Continuous power output (both channels driven at 20Hz to 20KHz)**
T.H.D 0.003%, 8Ohm .......................... 95W + 95W*
T.H.D 0.005%, 4Ohm ....................... 140W + 140W*

DIN continuous power output (both channels driven)
1KHz, T.H.D. 1.0%, 8Ohm .................. 100W + 100W
1KHz, T.H.D. 1.0%, 4Ohm .................. 150W + 150W

Power bandwidth
0.05%, 8Ohm .................................. 5Hz to 70KHz*

Damping factor
(1KHz/20Hz to 20KHz), 8Ohm ...................... 200/70*

Dynamic power output (on EIA dynamic test signal)
4Ohm/2Ohm ........................................ 200W/300W***

Total harmonic distortion **
20Hz to 20KHz, 95W, 8Ohm ........................ 0.003%*
20Hz to 20KHz, 140W, 4Ohm ....................... 0.005%*
Inter-modulation distortion (at rated output) .. 0.003%*

Input sensitivity/impedance
PHONO (MM) ...................................... 2.5mV/50KOhm
PHONO (MC) ....................................... 0.2mV/100Ohm
CD, TUNER, LINE, TAPE ......................... 150mV/50KOhm

PHONO overload level
1KHz, T.H.D. 0.008% (MM/MC) ................... 200mV/19mV

Output level/impedance
TAPE REC, ADAPTOR OUTPUT ................. 150mV/2.2KOhm

Frequency response
PHONO (MM) 20Hz to 20KHz .............................. +-0.2dB
PHONO (MC) 20Hz to 20KHz .............................. +-0.3dB
CD, TUNER, LINE, TAPE (1Hz to 150KHz) .......... +0dB/-3dB

Tone control (volume control set at -40dB position)
BASS .................................................. .........+-8dB (100Hz)
TREBLE .................................................. ......+-8dB (10KHz)
Loudness contour (volume control set at -40dB position)
........................................ +5dB (100Hz)/+3dB(10KHz)
Filter (SUBSONIC) ...................................... 17Hz (12dB/oct.)

Signal-to-Noise ratio (IHF short circuit, A network)
PHONO (MM, 5mV input/MC 0.5mV input) ................ 98dB/77dB*
CD, TUNER, LINE, TAPE .............................................. 110dB*
Signal-to-Noise ratio (DIN, continuous power/50mW)
PHONO (MM, 5mV input/MC 0.5mV input) ................ 74dB/65dB*
CD, TUNER, LINE, TAPE ........................................ 92dB/68dB*

Power Supply/Miscellaneous****
Power requirements .......................... a.c. 220 Volts ~, 50/60 Hz
Power consumption .................................................. .... 820 W
Dimensions ............................ 420 (W) x 435 (D) x x 162 (H) mm
Weight (without package) ................................. 19.5 kg (43 lbs)

* Measured with the DIRECT switch set to ON.
** Measured by Audio Spectrum Analyzer.

My comments
*** Approx. 17Amps peak in 2Ohm
**** 110 Volt setting is present in my sample
 
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PMik: It sounds like you know what you are doing. My plans are much more modest because, frankly, I don't think I know enough to be modding — not without guidance anyway. OK, if I see some cruddy wire in a lead that is obviously 4 inches too long I can do something about it ... (duh).

My immediate plan is to change out all the caps using Panasonic/Matsushita FC and Chemicon LXY and LXZ caps. If they were originally Silmics as in my AU-al717Extra and my big Denon, I'd copy with Silmac-II's for archivy's sake. I have not decided on the big PSU caps yet. Any suggestions? They are 22,000 uF-x2. I plan to keep the pair as a pair, as opposed to creating a bank, so 22,000 per it is.

I may have some questions:

I want to change the Toshiba output devices for fast Sanken's (2SA1215/2SC2921) to be able to do this, i will have to make the last stage hardwired if im able to locate faster driver transistors... also these parts inc larger heatsinks will be upgraded in the same task.

* Sanken's (2SA1215/2SC2921) — a differential pair — form factor MT-200. Is the reason for having to hardwire these mod substitutes because of the form factor change? ... assuming it is a change?

* Unless my unit (A-717) is a variant piece, the ORIGINALS are Toshiba (2SA1265N/2SC3182N) in SC-65 form factor. What are the originals in your 757-II?

About the sound ?
These amps has a lot guts! Crescendo! and ability to maintain a stabile, clear soundstage...acts like expensive amps

Ahh ... thanks! This does press me on. There ARE bona fide impressions regarding components. They ARE subjective and dependant on a plethora of factors. But, on the whole, when indicated by serious enthiusiasts, they DO say something more or less about more or less.

Past experience has really pushed me to thinking that fresh caps make a vast difference in vintage or veteran machines.The potential I have heard from the 717 clearly comes up to your description. In it's current form, something always has intrigued me about the 717 when compared alongside the aformentioned Sansui. The Pioneer has the WHAM! Now if I can get it to do cello as well as the Les Paul then .... Maybe a no-go, but what the hell. Therein lies the fun — and the quest besides.
 
i have messured the idle current of my amp to be 400mA each channal..

just wondered how you are checking this? I have adjusted the bias to give me 10mV each channel on my A-777. I measured at the emmiter resistors on each channel, and adjusted the trim pots. Echowars told me this would give me about 45mA current flow (in the DC offset thread). I have no idea what the manual says it should be set at though as I cannot find a manual for my amp?

I was wondering if I should try increasing it, It think it used to run hotter.

Unfortunately I have no trim pots for DC offset on the A-777, and I measure between 50 and 60mV. I am thinking of installing some matched input transistors to get this down and recapping the amp in the deal.
 
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