Vintage Technics SA-GX 130: any good or better sell it ?

Dear all,



my father still has his 3rd receiver from 1986, a Technics SA-GX 130, the 'Stereo Synthesizer Receiver' version (40Wpc into 8 Ohms).



He's using them with his old stereo boxes, 4 Ohms 3-way (dome tweeter, midrange, 12" bass). Needless to say, the amp is underpowered but the goal isn't doing disco at home.



He's a hobby musician, has a piano and an nice small electric organ too. And a good hearing :) but he never payed THAT much attention to quality and detail like myself.







I'd like to know how this receiver performs sound-wise. Does anybody know these kind of amps ?



I'm thinking about just keeping his speaker boxes (closed boxes), update them with appropriate new drivers - possibly using an AMT tweeter too - and then have them driven by something new.



Maybe going active with Class D modules - Hypex nCore ? (I think they would run rings around this Technics amp)..



What do you think ? (About this Technics and either keeping them for the updated boxes or use new DIY amp modules?).
 

kct

Member
2006-12-24 2:45 am
KW, Ontario
Well, as far as specs goes, the Technics SA-GX 130 does not impress, too much distortion for my taste, but the unit looks nice.

I suggest leave the speakers as is and drive them with a Technics SE-A7 (rated 60W, 0.003% THD) or even a SE-A5 (rated 120W, 0.002% THD), SE-A100, these Technics amplifiers have a higher performance and are more true to the signal with extremely low distortion. You would be amazed that the old speakers sound suddenly very good.

That at least was my experience when driving an old set of speakers, I remembered were soso, with an SE-A7. I could not believe, they sounded very nice. To this day I had wrongly blamed the speakers for been poor, when in fact I always drove them with inferior amplifiers.

Someone else's experience, I can sign off on.
My New Little Friend Technics SE A7! | Audiokarma Home Audio Stereo Discussion Forums

I am not sure about your expectations, Class D is on the other end of the spectrum. Great for sub-woofers and envelope power supplies. To me well designed Class D does not sound as pleasant as a well designed Class AB.

just my 2 cent
 
The SA-GX130 isn't from 1986 but rather the early-mid '90s (1994, I think). It's a bread and butter stereo receiver with electronic source selection and a remote. Does exactly what you really need and nothing more. Not much inside, but nothing much to go wrong with 'em either. Pretty much the equivalent of a Toyota Corolla. Excitement factor: pretty much zero. I don't think these were too expensive.

Is there anything more known about the speakers except '4 Ohms 3-way (dome tweeter, midrange, 12" bass)'? Were these premanufactured or a published DIY design perhaps? Doesn't sound like he'd be the guy to come up with an entirely new design. What kind of drivers do they use, what does the crossover look like? Old drivers aren't necessarily bad (after replacing rotted foam surrounds if needed), but having (or measuring) their TSPs would be really handy. Speaker simulation has gotten so much easier in the last 25 years; likewise, options to measure them have become much more affordable. Unsurprisingly, the state of the art in speaker design has moved on to the poin where things like waveguides now are basically a standard feature. A redesign could take advantage of that, as well as tackle other possible issues.
I would want to at least simulate or even measure the speakers as-is, ideally both (and before/after replacing any old electrolytic caps in the crossover - EDIT: "dull and lifeless" could indicate some dead ones). As much as we enjoy nerding out over our electronics, it's the transducers that tend to be the bottleneck.
 

kct

Member
2006-12-24 2:45 am
KW, Ontario
I forgot to mention, be sure your input cable has low capacitance and is kept short. Too long of an input cable gives more capacitance and that can lead to dullness and takes the 'sparkle' out.

I agree with sgrossklass, generally the speaker is the weak link.

Find out what causes the dullness, source and/or input cable and/or amp and/or speakers and/or crossover.
 
Good points. In general I know speakers are always first (to check if old, etc), and amp + source just later on. I'm into the DIY business since couple of years, just didn't want to jump in right into the heaviest to-do at the very beginning. (Hoped for a bad amp answer which might have solved the issue, at least partially) :D



The Corolla simile is great :) but now it seems the tyres are the weak point.



I didn't want to go into detail with the speaker drivers because I think they are the weakest link. Box is ok, good strong mdf-like with good wall thickness, really strong and heavy. Damping inside not much, but there is adequate amount of cotton wool there.



Midranges are 2x 8Ohm Orion (Hungarian brand) MD-40 drivers, the blue membrane types were made by BASF back then. ORION MD40 ^^Węgierskie Głośniki Średniotonowe^^ - 7114979472 - oficjalne archiwum allegro


Tweeters are 1x 4Ohm Orion dome types, SQ isn't the best, people used to change diaphragm quite often (as an upgrade). https://img.index.hu/imgfrm/9/3/0/4/BIG_0005019304.jpg


Bass was originally 1x 4 Ohm paper membrane, old design, I burned the voice coil when I started to discover Prodigy when I was at around 16 or so.. :D They have been replaced and then again replaced last year, now a nominal 200W 12" woofer is there, some kind of unknown manufacturer (Chinese maybe), yellow kevlar membrane, not much magnet, of course no T/S at all, sensitivity probably below midrange and tweeter section..



So I think his boxes are AS-IS hopeless. He changed the original bad sounding crossover to a new one, recalculated some crossover points based on some forum suggestions but then that's it, he has now a simple 3-way 2nd order Butterworth with absolutely no adsitional resistors or whatsoever. All drivers have their corresponding LC components in front of them, no sensitivity-matching L-Pad, no impedance correction..



So I thought based on the dimensions of the boxes and the size of the drivers (to fit cutouts) I can ease his pain designing 2 boxes of the same arrangement (1 tweeter, 2 mids, 1 woofer) and do a big upgrade.



I could even imagine going active with a Class D module for bass and let the Technics drive mid+tweeter but that would just complicate things a bit. All-active would be no-go, way too much cabling and amp boxes etc, wife-factor is big..



So if you say - and I agree - boxes should be upgraded first, then I'll do accordingly. I might simulate these boxes in WinISD with new drivers, closed (as is now) and also experiment with a bass reflex design to a bit deeper with bass, the good old boxes can accomodate a well sized reflex tube on the back. (Maybe on the front too, then it comes to the front).



Cables are short, he has a same-aged Technics SL-PG100 player just below the amp, connection is good thick gold plated modern looking unknown type RCA, that might be okay I think.



But I'm going to make him a surprise for Xmas with a Raspberry Pi based Volumio network streamer and player (with I2S reclocker, double ES9038Q2M DAC, built-in HDD, ultra low noise PSU etc.) so new audiophile grade source is on the way as well.
 
So I thought based on the dimensions of the boxes and the size of the drivers (to fit cutouts) I can ease his pain designing 2 boxes of the same arrangement (1 tweeter, 2 mids, 1 woofer) and do a big upgrade.
Sounds like a plan. I would consider going for a nominal 8 ohms (or mixed) as well. Certainly easier on the amp.

Good luck finding an exact match for the two 38 mm domes though. Something 10 cm / 4" may fit (and maybe just one). Otherwise consider keeping them. I assumes domes are closed at the back... cones may appreciate getting a bit of volume of their own.

32 l, you say? Sounds reasonable enough for a BR with a decent 8" woofer.

I'm a bit worried about crossing over bang in the midrange. Looking at some 38 mm domes like the Scan-Speak D3806, they tend to be useful down to 1 kHz at best (and something like the Visaton M10 is no better), and I'm not sure about displacement down there. XO would have to be reasonably steep to avoid excessive lobing. One reason why people no longer do this outside of PA.

If you find a good tweeter, you generally want to cross that over at around 3 kHz.

Small 3-ways like this have pretty much gone the way of the dodo as in the days of waveguides, you can pretty much do an 8" / 1" 2-way with high-order XO at ~2.5 kHz and call it a day. (See e.g. Behringer B2031A, one of the best values there is. The passive B2031P proved a good target for crossover mods if you can find any used, have a thread bookmarked somewhere.)
I could even imagine going active with a Class D module for bass and let the Technics drive mid+tweeter but that would just complicate things a bit.
Or a lot. Not sure whether using something with an easily accessible volume control as a power amp in an active setup would be a good idea.
 
Excessive lobing ? What do you mean ? The movement of the bass driver having an effect on midrange membrane ? (Closed box).



I have some favourites, a Faital 4" midrange (or 2) would do the job easily. The main issue is rather closing the back chamber for midrange and tweeter, or find closed-back types from significantly better types.



I don't have any real choice yet, maybe it's easier to completely redesign the boxes as well, just sell these for chips and have nice aesthetically looking new boxes built by a carpenter (woodworker) in the same colour what my father likes. A somewhat bigger, but not all that big half-pyramid design would do, no parallel walls, big woofer at the bottom, reflex design, smaller upper chamber closed and that'it then. We could even make the new box 2 or 3 separate boxes, to align voice coils vertically. Midrange box would sit on woofer box, tweeter box on top of midrange box. Not a big deal from money side, at least it makes this little project not much more expensive.



Ah, too much thinking. I'm sticking to upgrading the existing boxes somehow. By closing the upper part of the chamber we'll loose some volume though. :(