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Sony TA-EX66 - STK-4162MK2 vs. TDA7294
Sony TA-EX66 - STK-4162MK2 vs. TDA7294
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Old 20th February 2020, 08:11 PM   #1
Injection is offline Injection
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Default Sony TA-EX66 - STK-4162MK2 vs. TDA7294

Hi!

Years and years ago I've built a stereo amplifier with 2 x TDA7294 and two 26-0-26 V 100VA toroid transformers but it's collecting dust because I've never built a housing for it.

Today I've ran into an ad in my local city where a man was selling a faulty Sony TA-EX66. The housing looked nice and in mint condition and the price was pretty cheap (18 $) so I was thinking about using it's housing to finish my 7294 amplifier.

After I brought it home, I noticed that the amp is not completely dead. There's just no sound on the output. I don't have my tools here currently to open it and find the issue, but I'm 90% sure that the STK-4162MK2 amplifier IC is burned.

If this is the case, my idea was to remove the STK and the power transformer (which is probably around 120 VA and not enough for 2 x 7294) and try to squeeze my 7294 AMP and toroids inside if there will be enough room, but keep everything else (tone controls, motorized volume potentiometer, input selector, speaker relay etc.). At last, I could add a Bluetooth 5.0 module inside to get a nice amplifier for parties.

But, after I did some reading, it turns out that STK might have a little better sound quality after all and now I'm not sure if I should just replace it and return it to stock condition or put 7294 inside. 7294 will definitely be twice as powerful. This amp is declared to 2x60W 6 ohm, but according to the datasheet and the power transformer, I would say that it's 30W max per channel. 7294 could output up to 60W of clean sound.

If STK is better option, where to buy the original Sanyo one? Ebay is probably full of Chinese clones. They also seem very expensive. One (probably fake) piece on eBay is more than I paid for the whole AMP

Sorry if it's the wrong place for the topic or if the topic doesn't make sense, I would just like to hear your opinion before I start butchering the Sony.

PS. Not related to amps, but maybe someone knows where could I find the original remote for it?
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Old 21st February 2020, 02:43 PM   #2
maxhifi is offline maxhifi  Canada
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The 7293 and 7294 have been used in some very good sounding Linn amps. I'm not sure that the boards you have would provide comparable performance to Linn, but I do believe that you aren't limited by the chip. STK modules can sound pretty good too dependent on implementation and which module it is. Finding genuine ones is a challenge, though.

In your situation I would probably just repair the Sony. And $18 for an STK module is not exactly big dollars, you wouldn't expect a new engine for a $500 car to cost $500, would you?
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Old 21st February 2020, 02:58 PM   #3
Injection is offline Injection
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Quote:
In your situation I would probably just repair the Sony. And $18 for an STK module is not exactly big dollars, you wouldn't expect a new engine for a $500 car to cost $500, would you?
I see your point but those on eBay are probably clones. It doesn't even say "genuine" or "Sanyo" anywhere. And it's not 18$, the cheapest one with shipping from China is 27$. So I wonder how much would the original cost then.

I bought this broken amplifier with purpose to serve as a housing for my 7294. But I started getting doubts when I read somewhere that STK sounds better. I've used this 7294 previously a lot and I was very satisfied. I'm not an audiophile, I'm mostly listening to electronic music and good, deep and strong bass is the most important to me. But I guess that this depends a lot on the preamp section as well. The 7294 without preamp sounds "too flat" for me.

I've been looking through the web these days to find a trustful store to get an original STK but without success. So I guess my first step will be to try to connect the preamp output from Sony to my 7294 and see if I'm satisfied with the sound. If it will lack bass or something, then I will probably throw everything out and put some custom preamp as well.

I was also considering an option to build some more quality solid state amplifier which would fit to the Sony's power supply (something up to 30-40 W per channel).
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Old 21st February 2020, 03:54 PM   #4
maxhifi is offline maxhifi  Canada
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I sometimes buy though eBay, and have not had any failures, there are US and Europe based sellers as well.

I would not expect an STK module to generally sound better than a monolithic IC, it is all down to implementation, and in this regard I trust Sony over a generic Chinese board.

I once rebuilt a Yamaha receiver with a bad output stage in a similar way to what you propose with an LM3886 data sheet circuit, and I was unhappy with the result. It sounded flat and lifeless, it ended up in the trash eventually.
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Old 21st February 2020, 06:01 PM   #5
maxhifi is offline maxhifi  Canada
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This one appears to not be fake:
STK4162II "Original" SANYO Stereo Amplifier 18P SIP IC 1 Pc | eBay
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Old 21st February 2020, 10:12 PM   #6
aparatusonitus is offline aparatusonitus  Croatia
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You do not have to limit yourself to the originally installed amplifier module...you can also use any of the following - STK4172II, STK4182II as well as STK4192II without any modifications. An even better option would be if you can find Sanyo amps that are in the same or similar casing, with the same pinout but with a fully complementary output (STK41x2 have quasi-complementary output).

For example Original Authentic STK4192II amplifier IC | eBay
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Old 22nd February 2020, 03:23 PM   #7
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Interesting, STK4192II seems to be more powerful but it's much cheaper than 4162 although the above linked 4162 is expensive due to shipping because it's in USA and I'm in Europe.

STK4192II would be a good replacement since it has clean 50W of power, but I would probably need a stronger power supply. Its recommended voltage is +-35V, my toroids are 26V AC, which would be around 36V DC, so maybe I could put them inside instead of factory transformer.

Do you know if STK with fully complementary output and same pinout exists and if yes, which is the model?
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Old 23rd February 2020, 06:51 AM   #8
aparatusonitus is offline aparatusonitus  Croatia
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Quote:
Originally Posted by Injection View Post
STK4192II would be a good replacement since it has clean 50W of power, but I would probably need a stronger power supply. Its recommended voltage is +-35V, my toroids are 26V AC, which would be around 36V DC, so maybe I could put them inside instead of factory transformer.
Don't change anything about the power supply ... I'm sure the transformer is under-sized (intentionally) as well as the heatsink for the STK module, so B+/B- sage under under heavy loads and thus protect the STK module (from overheating / overcurrent / puff) in a primitive way.

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Originally Posted by Injection View Post
Do you know if STK with fully complementary output and same pinout exists and if yes, which is the model?
Searched with in my archive and online but found nothing that would fit (which somehow surprised me ... I was convinced that something with a fully complementary output existed)
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Old 23rd February 2020, 11:14 AM   #9
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Tek sad vidim lokaciju Split

Quote:
Originally Posted by aparatusonitus View Post
Don't change anything about the power supply ... I'm sure the transformer is under-sized (intentionally) as well as the heatsink for the STK module, so B+/B- sage under under heavy loads and thus protect the STK module (from overheating / overcurrent / puff) in a primitive way.
If the power consumption on the casing is correct (125W), the transformer is not that much undersized. The amplifier is 35+35 W (this 60W as stated from Sony is actually the maximum for this STK on maximum power supply and with 10% THD).

I don't have my tools here currently so I can't do much but I borrowed my friend's multimeter yesterday; the transformer is OK. It has 10-0-10 AC and 26-0-26 AC outputs, and after the bridge rectifier and electrolytes, it has +-35V DC.

The AMP has uPC1237HA protection and a relay, but I can't hear that relay when turning on the AMP. So either the protection has failed, or STK has failed and there's DC or something on the output which triggers the protection to not connect the speakers. I will have to dismantle the board and measure. Also, I can see that somebody has already tried to do some repairs. There are a few resistors, where the board is burned underneath but the resistors look like new, probably changed already. Also the board is broken where the phones output jack is.

If I still decide to put more powerful amplifier and power supply inside, will I have to modify the protection circuit?
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Old 23rd February 2020, 03:12 PM   #10
aparatusonitus is offline aparatusonitus  Croatia
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Tek sad vidim lokaciju Split


Check with DVM for DC offset at the output of both channels (pins 10 and 13 of STK4162II), if this is correct, check all voltages on the uPC1237HA pins as well as STK4162II, also check the values of the changed resistors according to the service manual.

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If I still decide to put more powerful amplifier and power supply inside, will I have to modify the protection circuit?
You won't get much with this (except better regulation of power lines -> a slightly better definition of LF), since the amplifier is likely to be handicapped elsewhere (e.g. pcb and how the input/output currents and signals/grounds are controlled).


It will not be necessary to modify protection circuit as +B/-B will remain almost unchanged as 2*26VAC toroid will give 26 * 2sqrt2 - 2 * diodes drop ~ 35.6VDC unloaded.
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