A classic power amplifier from the 80's. What a beauty! - Page 1
Forum section: electronics / projects

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 02:14:38 pm
content: My father gave this classic power amplifier, which was sitting idle in his house for, um, probably 25 years? But look at this design, the elegance. They really don't make them like this anymore

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 02:16:54 pm
content: It's the Universum System HIFI 7500 SL. Universum is a brand of the famous German retail chain called "QUELLE". So far, I have just powered it on and was glad that it was uneventfulNext step, I need DIN to RCA converter cables to drive this thing. And the specialty speaker jacks at the outputs will have to go and replaced with proper screw type terminals.BTW: Are those speaker terminals still being used? I don't even know what they are called, so no idea what to google for

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 02:19:50 pm
content: It's amazing how smooth the bass/treble and balance pots are after so many years! I love how the bass/treble pots have intenten positions at the numbers in the scale, You can quickly adjust to the number and you will feel it "clicking" in there. Ooooh I love itAnd the volume knob is also clicky, moving in very small discrete steps.

author: Gyro
author_rank: Super Contributor
timestamp: March 19, 2018, 02:21:24 pm
content: They are also DIN connectors - DIN Speaker sockets.https://duckduckgo.com/?q=DIN+speaker+socket&iar=images&iax=images&ia=images

author: madires
author_rank: Super Contributor
timestamp: March 19, 2018, 02:23:57 pm
content: Yep, and you can still buy them.https://en.wikipedia.org/wiki/DIN_connector#Loudspeaker_connector

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 02:27:01 pm
content: Oh, cool. Then I will definitely try to get them. Would hate to cannibalize this beauty just because I can't get speaker jacks

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 02:31:15 pm
content: And those input select buttons, so precise and so light to press after all these years, just like the trigger of a well oiled Glock 9mmHuge respect to the engineers that built this!

author: Benta
author_rank: Super Contributor
timestamp: March 19, 2018, 04:29:05 pm
content: You do realize that Universum was the lowest end brand in those days? If you want to talk about beauty, there are amplifiers from those days with a much finer pedigree.

author: nctnico
author_rank: Super Contributor
timestamp: March 19, 2018, 05:14:07 pm
content: Quote from: Benta on March 19, 2018, 04:29:05 pmI agree. There is a big fat warning on the rear saying not to use a load less than 4 Ohm. This makes me wonder whether the amplifiers are short circuit proof.BTW I'm still using a JVC amplifier from the late 80's every day. The only thing that needed replacing was the relay which connects the outputs.

author: Gyro
author_rank: Super Contributor
timestamp: March 19, 2018, 05:30:08 pm
content: QuoteProbably not. Few consumer amps in the '80s were short circuit protected. Not something to put to the test, regardless. I have a JVC JR-S100 Receiver in the garage still, It sounds really nice.

author: taydin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 07:55:51 pm
content: Quote from: Benta on March 19, 2018, 04:29:05 pmI know there were much better amps in those days. But comparing this to the shit I'm seeing nowadays, there are many things to be liked about this model.Once I have the cables in, I'll measure the specs of this. I'm not expecting greatness, but I'm sure it won't be crap, either

author: oldway
author_rank: Super Contributor
timestamp: March 19, 2018, 09:19:19 pm
content: Using one STK-3042 more 2 x STK- 0050 II as power amplifiers.....Not that great at all.....but if you like it, enjoy it.....

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: March 19, 2018, 09:41:17 pm
content: Quote from: taydin on March 19, 2018, 02:14:38 pmOh, I'm sorry. This must not be made anymore then:or this?What about this?The amplifier has now been integrated and is everywhere. But that just means there are more of them. They didn't suddenly stop making good, "elegant" amplifiers. It's just that they also now make amplifiers for a much lower-end market too.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 19, 2018, 10:51:33 pm
content: Yeah, but where is the FM tuner? This one has a tuner with 1200 watts into 4ohms (just tacked on the back..)All this wood-trimed goodness (46kg and 175V/uSec performance) celebrates her 40th anniversary this year.http://www.hifi-forum.de/viewthread-84-17073.html

author: taydin
author_rank: Frequent Contributor
timestamp: March 20, 2018, 02:21:18 am
content: Quote from: Cliff Matthews on March 19, 2018, 10:51:33 pmThat looks wonderful!!! Must be a pleasure to useThe universum 7500 SL also had a receiver unit, but my father said he threw it out after nobody was able to fix it. Here is an idea about how the whole set looked like when everything was working:

author: taydin
author_rank: Frequent Contributor
timestamp: March 20, 2018, 02:32:59 am
content: Quote from: TheUnnamedNewbie on March 19, 2018, 09:41:17 pmAt some point it will be a subjective matter whether one design is more elegant than the other. I do own the Marantz PM6005, but the 7500 SL looks and feels much more appealing to meIt's partly because it has sentimental value (gift from my father), but you really have to try the buttons, the volume and bass/treble knob on this thing to appreciate what I'm talking about, they are amazing

author: oldway
author_rank: Super Contributor
timestamp: March 20, 2018, 10:51:00 am
content: Each one has its conception of beauty and technical perfection.Here's mine.

author: newbrain
author_rank: Super Contributor
timestamp: March 20, 2018, 05:06:31 pm
content: When in Italy, I use daily my Luxman L2.After exactly 40 years, I still think it looks amazing.Here in Sweden I have a Pioneer compact. I keep it well hidden.Ps: not my L2, picture fromthis site

author: taydin
author_rank: Frequent Contributor
timestamp: March 20, 2018, 07:45:01 pm
content: Quote from: oldway on March 20, 2018, 10:51:00 amYep, that's rightThose analog VU Meters alone are so much more pleasant compared to the LED band rubbish going on these days. It's almost hypnotic watching those scales dance to your favorite beat

author: PChi
author_rank: Frequent Contributor
timestamp: March 20, 2018, 08:42:00 pm
content: The beauty is that they are all still working decades later. How many of the current compact music systems will be working after a similar time period?

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: March 20, 2018, 09:02:33 pm
content: Just today I could reunite a friend with a Marantz 1072 he bought from the small ads for little money. Technically it was in bad shape, had blown fuses, a couple of fried transistors and burnt resistors and needed new caps.Someone tried to "fix" it before as it looked like, because there was a wire soldered on the back of the main PCB that did not belong there. That someone wired the +35 VDC rail to the -35 VDC rail - bloody genius!The service manual with very nice and detailed schematics that are available on the net made it a really fun project for me. I learned quite a bit on that repair and my friend is now a very happy owner of a superb 1980s amplifier. He already had the matching tape deck and I found a TT4000 that might be up for grabs as wellNever really looked into Marantz until now, but I really like the sound of that amp. I have a Sony TA-E86B / TA-N86B in the "record room" and a small Akai amp in the living room. The TA-N86B is a pain in the butt though. The dual output symmetric -whatever- switching power supply in that thing is making trouble on a regular basis :/

author: labjr
author_rank: Frequent Contributor
timestamp: March 20, 2018, 09:34:18 pm
content: I think you have to go back a couple more decades to find the real classics. I've been restoring this early 60's vacuum tube FM stereo receiver. Made in Long Island NY. Only about 35watts/channel but sounds heavenly.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 20, 2018, 09:52:59 pm
content: Nice! In case you can't find a replacement for the el-cap on the left, there's a guy up here in Canukistan selling vintage parts.http://www.justradios.com/capacitors.html

author: labjr
author_rank: Frequent Contributor
timestamp: March 20, 2018, 11:32:46 pm
content: Quote from: Cliff Matthews on March 20, 2018, 09:52:59 pmThanks! I've been putting off finishing this project for some time because the power supply needs quite a bit of work. I'm not sure how I want to attack it. I don't like some of the aftermarket PCBs people are using. I want to preserve the original circuit and appearance as much as possible. There's actually 2-3 more cans on top of the chassis. Blown resistors in the power supply etc., among other problems. There's a guy in Wichita, Kansas who makes multi-section caps to order, in original size and configuration. I may go with him.I've located all missing parts except the vent screen on the top, rear of the cabinet. I could buy a reproduction, but would rather an original.

author: raptor1956
author_rank: Frequent Contributor
timestamp: March 21, 2018, 01:18:48 am
content: What appeals to us is about as subjective as it gets and getting two people to agree on what makes a beautiful bit of kit is fraught with impossibilities. You are likely to get agreement on what makes a pretty girl more easily than who's amp is more aesthetic. Apple has done a good job in convincing a large percentage of customers that they have the secret to make a turd palatable -- even an unpolished turd, but even there not everyone agrees. And, that's before your get into the Audiofool area...Brian

author: BrianHG
author_rank: Super Contributor
timestamp: March 21, 2018, 03:33:59 am
content: Quote from: Cliff Matthews on March 19, 2018, 10:51:33 pmNow that's a beast!

author: BU508A
author_rank: Super Contributor
timestamp: March 21, 2018, 07:13:53 am
content: I do really like the Braun Atelier HiFi series.Here is a nice example in very good condition (no affiliation with the seller):https://www.ebay.com/itm/122999769862

author: taydin
author_rank: Frequent Contributor
timestamp: March 21, 2018, 12:06:12 pm
content: Quote from: oldway on March 20, 2018, 10:51:00 amThat looks like a jewel. I'm sure when friends come over, they directly ask questions about this instead of your latest 100" 3D 8K TV

author: Gyro
author_rank: Super Contributor
timestamp: March 21, 2018, 12:41:06 pm
content: Quote from: BU508A on March 21, 2018, 07:13:53 amThat looks like a stable setup!Probably best to avoid carpet.

author: oldway
author_rank: Super Contributor
timestamp: March 21, 2018, 01:38:01 pm
content: Quote from: taydin on March 21, 2018, 12:06:12 pmYes, it is a jewel, even more beautiful inside than outside, a true electronic masterpiece.My 2285B is completely original, only a capacitor has been changed, it looks like it comes just out of the factory.But we must remember that in 1974 (date of manufacture), it cost a real fortune.In this time, the Marantz advertisement said it was the "Roll Royce" of hi-fi devices.

author: Jester
author_rank: Frequent Contributor
timestamp: March 23, 2018, 09:39:56 pm
content: I have an old Marantz 1250 (125W per channel) still works like new. I might have to put some new caps in it one day. No pictures as I’m away in the sun for a bit. I don’t think I will ever sell it. Edit: added some canned photosWould like to get a good tube amp someday.

author: @rt
author_rank: Super Contributor
timestamp: March 24, 2018, 03:26:03 am
content: I have a Leak TL12 Plus, and will be waiting forever to get another one to make a stereo pair.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 24, 2018, 03:46:45 am
content: Quote from: Gyro on March 19, 2018, 02:21:24 pmThose looks like the same speaker connectors that are on my early 1980s Bang and Olufsen Beomaster 6000. You rarely see those connectors here in the US. I've priced the connectors but anytime that you mention B&O, the price goes through the roof!

author: @rt
author_rank: Super Contributor
timestamp: March 24, 2018, 08:20:25 am
content: Was that a joke? Well it was a joke, but was it intended as a joke?Quote from: TheUnnamedNewbie on March 19, 2018, 09:41:17 pm

author: Circlotron
author_rank: Super Contributor
timestamp: March 24, 2018, 08:53:20 am
content: You call that thing (in the OP) a classic?THIS is a classic!Perhaps not the last word in specs by today’s standards, but definitely a classic.

author: Bicurico
author_rank: Super Contributor
timestamp: March 24, 2018, 01:34:55 pm
content: Actually, the late 70ies, early 80ies were the prime time of "High Fidelity". Many brands produced fine stereo equipment, only few are still aroun dproducing them.If one wants to have a great bargain and far better sound quality than modern soundbars & similar, just grab a mid range amplifier from this period at under 100 Euro. Get a pair of speakers from the same period, but pay attention it is in good condition. Spend a little in a quality DAC and off you go!I have a Mitsubishi amplifier (amongst other), connected to a pair of PILOT speakers. All together cost me around 140 Euro. The sound is fantastic. I would have to spend >10x this amount on a modern equipment to get a similar sound quality.The BRAUN stereo pictures a few posts above is great. It brings me fond memories: I had a neighbour when I was a kid, who worked as an Engineer at Braun (back in Germany). He used to have this stereo at home, amongst other fine Braun equipment.But beware: these stereos are sold at quite a high price and the connectors are of the old DIN style, so you need to either replace them or build adapters.Also, everything belt-driven (K7 player, LP player, CD player) will probably require belt replacement.Regards,Vitor

author: madires
author_rank: Super Contributor
timestamp: March 24, 2018, 03:28:28 pm
content: Some rare amp and preamp (actually complete stereo system) developed end of the 80's:http://wegavision.pytalhost.com/Delec/delecAkzent/(scan of a German brochure). That company also manufactured the SonoFer speakers.During my last year in school I got myself an afternoon job at that company to check out an EE carrier path and did some simple stuff in the lab like building prototypes and doing basic measurements. I can claim that I helped with the preampLater on I did an internship in the production (was required by the university). Very nice people, great EEs and good experience.

author: cvanc
author_rank: Frequent Contributor
timestamp: March 24, 2018, 04:07:16 pm
content: Can't resist posting this photo -- just finished a full rebuild of one of these.Enjoy your vintage stuff!

author: BU508A
author_rank: Super Contributor
timestamp: March 26, 2018, 06:47:12 am
content: WEGA!Yes, I can remember this company, got a TV (Wega color 3022) from them with an ultrasonic remote control.And they designed this beauty, which can be seen also in the New York Museum of Modern Arts:https://studio5555.de/wega-concept-51k-von-hartmut-esslinger/

author: KhronX
author_rank: Frequent Contributor
timestamp: March 26, 2018, 01:00:43 pm
content: Last year i revived and "re-lit" a Fisher RS-1022 for an acquaintance. Some STK-something-or-other on the inside and whatnot.http://khronscave.blogspot.com/2017/05/fisher-rs-1022-rehabilitation-and-bling.html

author: raptor1956
author_rank: Frequent Contributor
timestamp: March 27, 2018, 03:24:56 am
content: Most of the name brand consumer electronics makers have a line or two of pretty darn good audio gear but you will need to pay more than most people are willing to pay these days. No, not audiofool dollars but even a modest sum in the $500USD range is way more than the vast majority of people are will to spend on an amp/receiver. Sadly, most (not all) folks under 40 have been largely raised with lossy compression audio and much of it fairly low bit rate stuff so there is pretty much nothing you can do at the back end to make that shit sound good. Frankly, many of them just don't know any better and appear happy with the crap they're listening to -- and I'm not talking about the type of music here, just the dreadfully low quality of it from a recording standpoint. At the other end you still have the audiofools that need O2 free copper cables etc.Somewhere in the middle but leaning towards the audiofool group are the folks that insist tube amps are "better" and "vinyl" is superior and it doesn't seem to matter that most of the music recorded in the last 30 years has been recorded digitally, the vinyl crowd insist it captures sound more accurately than digital. So, music that's recorded, mixed and mastered digitally then cut into vinyl has somehow managed to add detail not present in the original digital recordings.Brian

author: tecman
author_rank: Frequent Contributor
timestamp: March 27, 2018, 01:22:18 pm
content: To me a true classic piece of HiFi equipment is the Marantz 10B tunerpaul

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: March 27, 2018, 04:55:53 pm
content: Tip; When fitting 2-pin DIN speaker plugs, always sleeve the live pin. otherwise if the wire comes off it will likely short the pins together and blow the amplifier. Since there is no cordgrip that is a distinct possibility if the lead gets tugged.Or, replace them with Speakon, XLR or some better class of connector.STK modules are capable of quite reasonable sound quality. Their main drawback is that they are very easily blown by output shorts. A whisker of wire across the terminals for a brief instant is all it takes. Which, is one reason that a proper connector is preferable to screw terminals.While Germany and Scandinavia produced some fine equipment, their insistence on using those awful DIN connectors was the main issue. One of the key problems with the DIN connector was having both inputs and outputs on the same plug caused a 'gender issue' between amplifiers and signal sources. Only the EU could devise such a horrible scheme, and its existence was one of the main reasons that Japanese gear dominated the market even in Europe. You could buy a mix of Sony, Technics or Yamaha gear and it would invariably work together. Buy Grundig and Blaupunkt or B&O, and you'd have one hell of a headache interconnecting them.

author: taydin
author_rank: Frequent Contributor
timestamp: March 27, 2018, 05:29:00 pm
content: Thank you for the great tips, I'll be sure to wire the speaker connectors like that!Just noticed that the headphone connector has a different pin layout. Whereas the inputs at the back of the unit have the pins around an arc, the headphone connector has the pins distributed evenly within. Kinda like the "5" side of a dice. I'm wondering why a special connector was devised for the headphones

author: BU508A
author_rank: Super Contributor
timestamp: March 27, 2018, 08:01:14 pm
content: Quote from: IanMacdonald on March 27, 2018, 04:55:53 pmI am very glad to see, that I'm not the only one who hates these connectors. I didn't never understand, why they were used in fineHifi equipement. When I had to assemble¹ cables with these DIN connectors I cursed many time the people which developed them.And the people who forced other to use them. *grrr*¹during my apprenticeship as a Radio- and TV technician

author: NivagSwerdna
author_rank: Super Contributor
timestamp: March 27, 2018, 08:07:08 pm
content: It might not be much but...bought with my first post graduation pay packet. <3 and still working todayPSTotal harmonic distortion: 0.003%

author: cat87
author_rank: Regular Contributor
timestamp: March 31, 2018, 06:02:50 pm
content: I don't know if the age itself makes it a classic, but the series might do it...This is my Sony 700 ES series amp (full name is TA-F700 ES). It's among the best bipolar amps Sony made, before switching to Mosfets.My unit was made in '92 I think (might remember it wrong but way newer than anything mentioned here). I've had it for about 3 years and it's a beauty. The caps are still original and don't show any signs of leakage, so keeping my fingers crosed.All in all, a nice bit o kit.P.S.: Don't ask about the ladle... long story

author: taydin
author_rank: Frequent Contributor
timestamp: April 05, 2018, 08:01:51 pm
content: I opened up the unit, and I was shocked at what I saw ... I was expecting to see lots of dust, but this thing has such a weird, strong stink, It's gotta be rodent piss or some other kind of animal excrement.And in addition to that, it looks like somebody has removed a power transistor, and also it's heatsink, and then probably lost the damn heatsink, because the transistor is mounted to the chassis and wires are brought in to its original location

author: taydin
author_rank: Frequent Contributor
timestamp: April 05, 2018, 08:09:07 pm
content: But of course I wouldn't be deterred by this setbackSo, I took out all of the cards (had to cut lots of cables, but no worries, I took lots of pictures, too).Notice how all wires are attached to the PCB using wire wrappingThat brings memories ...

author: taydin
author_rank: Frequent Contributor
timestamp: April 05, 2018, 08:18:11 pm
content: After taking out all of the cards, I put them into my industrial ultrasonic cleaner (which I use in my metalworking shop). 5 minutes at 50 degrees celsius. Pictures are below. In summary, it wasn't bad, but the cards were still kind of greasy. Could be the result of the detergent I used. Or maybe the flux leftover on the bottom of the PCB as a result of the wave soldering is tougher than expected and the ultrasonic just wasn't able to cut through it all.I had to go over all of the PCB's with isopropyl alcohol.

author: KhronX
author_rank: Frequent Contributor
timestamp: April 07, 2018, 02:30:12 pm
content: A few weeks ago, my girlfriend got her mits on a freebie Yamaha AX-930 from the early 90s, "on my behalf"(ie. sent me a photo of it and asked if i wanted it)For once, the <ahem> "marketing wank" might be considered as being in the ballpark of honest advertisingSpecs & co:http://www.hifi-wiki.de/index.php/Yamaha_AX-930

author: taydin
author_rank: Frequent Contributor
timestamp: April 07, 2018, 04:06:05 pm
content: Wow that thing must have been running in an isolated environment with air filtering :O No dust and rat piss at all ...

author: KhronX
author_rank: Frequent Contributor
timestamp: April 07, 2018, 04:16:43 pm
content: Maybe not visible in the photo, but it did have a little bit of spider-web in the rear right corner, and a couple dead bug corpses under the front panel, but all in all, not bad for over a quarter century, indeed

author: taydin
author_rank: Frequent Contributor
timestamp: September 07, 2018, 11:18:59 am
content: Finally got around working on my classic amp. I borrowed a wire wrapping tool so that I can restore the amp in its original condition.And then I started assembling the PCB's to the frameAnd finally re-did all the wire wrapping

author: taydin
author_rank: Frequent Contributor
timestamp: September 07, 2018, 11:28:00 am
content: The unit was now in a state where I could power it up and apply a test signal. I did this and I was getting no output.I had already found the schematic of this unit. Checked the power rails, all were good. Started tracing the signal from input into the amp and found out that the pre-amp doesn't output anything. The pre-amp was not getting 24V power.I following the pre-amp power to the main power supply, and, not surprisingly, the BD135 that was removed and mounted to the chassis was a single transistor regulator, obtaining 24V from +40V. And it was bad. The schematic says that it is a 2SC1449 and the closest equivalent that was available here was BD377. So I replaced it with that and also inserted a small heat sink.Re-tested after installing new transistor, and I was getting output from the amp!

author: taydin
author_rank: Frequent Contributor
timestamp: September 07, 2018, 11:30:16 am
content: Testing the repaired unit with a spotify media player, which is another project I'm working on.I remember this amp having a great sound, and I was really pleased to hear it after this long. I love it