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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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19th Sep 2019, 12:36 pm | #1 |
Nonode
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
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STK Audio Output Modules
A lot of audio equipment has/had modules from this range fitted to provide the output to loudspeakers.
A simple question: Apart from people inadvertently shorting the loudspeaker leads, how reliable are they? |
19th Sep 2019, 1:01 pm | #2 |
Heptode
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 734
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Re: STK Audio Output Modules
Hi,
I have had one fail in some equipment that has the speaker in the case case as the circuit boards. a replacement got the equipment working again... I think I have read elsewhere ? that the decoupling caps can fail, causing the main ic to fail...
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19th Sep 2019, 1:07 pm | #3 |
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
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Re: STK Audio Output Modules
In simple terms they are about as reliable as a conventional circuit of similar power, although of course it is more of a nuisance if they fail as they can be expensive or difficult to buy. As well as short circuits, damage can occur if failed soldering causes the legs to become disconnected in use, I always run the iron over these when overhauling an amplifier with one fitted. Dried up heatsink compound behind them is another source of failure, it pays to check this at overhaul too.
A problem that I have encountered with them recently is drift in the internal resistors which causes the bias current to fall to zero. The amplifier still works like this but the distortion performance is worse than it should be, the chances are that almost no-one would notice but it still isn't right. Even replacements are not guaranteed to be 100% in this respect, especially as you don't know where they come from these days. In a particular struggle that I had with a nice looking Technics amplifier it proved difficult to source a replacement for a hybrid chip which worked but displayed this fault, swapping over the other one from the other channel proved that the ancillary components were not at fault. In the end several had to be bought and tried before I found one that was satisfactory, there is nothing you can do externally to the device to adjust the bias in some designs. |
19th Sep 2019, 3:33 pm | #4 |
Heptode
Join Date: Jan 2008
Location: Sheffield, South Yorkshire, UK.
Posts: 652
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Re: STK Audio Output Modules
I have replaced quite a few, mostly in Marantz amplifiers. Failure modes have been no output, distorted output and a "whistling" noise on one output. I have also come across faked replacement parts.
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19th Sep 2019, 5:30 pm | #5 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: STK Audio Output Modules
I used to have to support a number of industrial vibration-testers that each used a pair of these modules in a bridge [input fed to inverting input of one amp, non-inverting input of other amp, transducer wired between the 2 outputs].
The modules failed every 3 or 4 years so I always had them in stock! [when one failed it took the other out, since the 'load' was DC-coupled]. Admittedly this was with the unit sometimes run for 6 months at full power. I wonder what happened to my stock of spare modules? |
19th Sep 2019, 5:41 pm | #6 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
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Re: STK Audio Output Modules
My akai AM-U04 audio amplifier uses them. One day, fed up with my Leak tuner's dry joint, I gave the case a tap to bring the programme back and it caused a loud 'pop' in the speakers, and the amp went into protect. One of the STK modules had gone short.
I hear on the grapevine that most of these new STK modules are probably fake.
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20th Sep 2019, 2:45 am | #7 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
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Re: STK Audio Output Modules
Quote:
The large projection type color sets, that use three CRT's use this type of device in the convergence circuits. Totally trouble-prone. I'm glad I quit repairing when I did! Dave, USradcoll1 |
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20th Sep 2019, 3:37 am | #8 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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Re: STK Audio Output Modules
When they first appeared about 1970 or so, there wasnt anything else available. Since that time I have learned to spurn them at every chance. HORRIBLE things. At the same time there were Sinclair modules available. They were better and could be repaired.
Thick film hybrids still have a place I guess, but not in my workshop. Joe |
20th Sep 2019, 6:29 am | #9 |
Dekatron
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Location: Sleaford, Lincs. UK.
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Re: STK Audio Output Modules
I can't really understand why manufacturers used them in their amps, from a component count POV they only really replace 5 transistors or thereabouts per channel so it must have been for cost. If you look at early amps compared to the later ones which used these modules, you get the feeling the manufacturers heart wasn't in it anymore. Later amps were made with thinner steel/aki, plastic knobs and smaller less well made transformers; there's nothing in them.
I think hifi making got more competitive, bean counters ruled the roost and STK modules were the fashion too. I have several of these STK modules including stereo versions, some made by reputable makers like Sanken, but have never really thought it worth while to experiment with them but might do after these have featured in a few threads recently to see how they perform in relation to a conventional amp. Andy
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20th Sep 2019, 9:11 am | #10 | |
Octode
Join Date: Oct 2003
Location: Newbury, Berkshire, UK.
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Re: STK Audio Output Modules
Quote:
Although from a repair POV I don't like these module, it may be that the internal transistors are a better thermal and electrical match than the discrete alternatives.
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20th Sep 2019, 11:04 am | #11 |
Nonode
Join Date: Jun 2009
Location: Herefordshire, UK.
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Re: STK Audio Output Modules
For what it is worth:
I've used several of the Sony/JVC/Sharp/etc 'Micro-systems' recently. All are post 2000 era. The output power seems to vary from 5 to 20W, and all have small loudspeakers - and STK modules. The price they seem to available for (about £5) at Car Boots reflects how the general consumer has moved on to other things, usually forgetting to provide the remote controls for the Micros in the selling process! Now, I have driven better quality loudspeakers with them and quite frankly the amps and their tuners seem fine to my ears. My concern in raising this topic explicitly, having read elsewhere on the forum comments about STKs, was just how much I was risking those better loudspeakers. Last edited by SteveCG; 20th Sep 2019 at 11:17 am. Reason: typo |
20th Sep 2019, 11:05 am | #12 |
Moderator
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Re: STK Audio Output Modules
I just avoid the damned things.
They perform no better than a normal discrete amp, but they do seem to blow up more often. Methinks the accountants were at work. Fewer components to purchase, store, load = more profit! David
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20th Sep 2019, 11:23 am | #13 |
Nonode
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
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Re: STK Audio Output Modules
I suppose that all the 'Home Cinema' 5.1 stuff, again available for not much at Car Boots, is stuffed full of these STKs as well as other bespoke ICs, now unavailable and physically unreplaceable anyway given the circuit board's construction.
So it is buy cheap, don't risk valuable loudspeakers, and throw away if it goes bang... |
20th Sep 2019, 12:02 pm | #14 |
Heptode
Join Date: Apr 2003
Location: Ayr, Ayrshire, UK.
Posts: 630
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Re: STK Audio Output Modules
Given the number of these I've replaced over the years, I'd make sure that any amplifier you've got that uses these has a quick-blow fuse on the output.. if you value your loudspeakers that is !
Andy
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20th Sep 2019, 12:10 pm | #15 |
Heptode
Join Date: Mar 2011
Location: Dorset, UK.
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Re: STK Audio Output Modules
Yes, quite agree.
The worst case was Sharp Optonica SM-7100 hybrid microcircuit power amplifier type S-603W. Quite a popular amplifier but approximately 30% of the modules failed during warranty period! Fortunately speaker protection was fitted, not the case with many other cheaper models. Like Sanken STK series, when fitting a replacement you must thoroughly clean away the old thermal grease and clean surface of the new IC. Apply a thin layer of thermal grease then ensure when attaching heatsink not to apply excessive torque. Original parts had a copious amount of heatsink compound with screws that must have been tightened by a proverbial sumo wrestler. After replacing hybrid, the amplifier was soak tested at half power into dummy loads for two or three days. FWIW would advise fitting some form of DC offset protection if using expensive speakers. Rich
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20th Sep 2019, 4:57 pm | #16 |
Pentode
Join Date: Oct 2016
Location: Near Coventry, West Midlands, UK.
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Re: STK Audio Output Modules
I too have replaced lot's of these over year's,and include them in my "usual suspects" list!
However,Bang&Olufsen have employed them in their design's since the mid 'eighties,particularly in the active loudspeakers,where one "stereo chip" is used to provide separate bass and treble amplifiers.They seem to have been really reliable in these instances,and I wonder if the peripheral design can be credited for this. I wonder too if the failures are more common among amplifiers where 'speakers are swapped,and the connections are suspect,something that can't happen in the integrated active speakers? Nick |
20th Sep 2019, 5:32 pm | #17 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,175
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Re: STK Audio Output Modules
The usual manufacturer of those was/is Sanyo, not Sanken. Sanken does make hybrids though, usually STR but possibly some STK types as well.
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20th Sep 2019, 8:49 pm | #18 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,792
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Re: STK Audio Output Modules
Perhaps I'm the only one to like these?
About 25 years ago, I used to play around with quality, late 1970s music centres and entry-level amps/receivers, and I would breathe a sigh of relief when I spotted an STK461 or similar. After checking a few peripheral Rs and Cs, the supply lines and the speakers/connections, I could be confident that a replacement (about a tenner from JJ Components or Dalbanis and 10 mins to fit) would restore normal operation without any drama. Compare that to faffing around with a cascade failure of unobtainable discrete devices. But nowadays, it seems that reliable replacements are hard to come by, so I suppose the situation's changed. N. |
20th Sep 2019, 9:23 pm | #19 | |
Moderator
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Re: STK Audio Output Modules
Quote:
I was nervous of a part without alternate manufacturers. Now they are no longer available as needed. Discrete amps still leave you opportunities in most cases (Well, not the Sony power J-FETs, and the Hitachi MOSFETs are getting rare) David
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20th Sep 2019, 10:03 pm | #20 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
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Re: STK Audio Output Modules
Point taken, but I suppose it seemed much easier to buy just one, easily-sourced device, rather than track down a dozen which always seemed to have to come from several different suppliers.
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