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Supercharging a mass-market reciever..
Supercharging a mass-market reciever..
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Old 15th April 2004, 07:34 PM   #1
mjarve is offline mjarve  United States
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Lightbulb Supercharging a mass-market reciever..

I came across a Sony STR-DE945 home theater receiver for practically nothing, and I decided to start experimenting with it. The home theater performance was adequate, but it severely lacked in the music department. I took it upon myself to remedy that.

First I added a cooling fan (powered by its own power supply) to the large heatsink. The receiver would get overly hot at times, a sign of a weak power supply. Then I removed the original power cord and added an EMI filtered IEC plug to the back. I also added two more banks of capacitors to the main amp power supply (now has a total of 6x 10,000uFd/80volt capacitors). I also added heatsinks to various power regulators and other ICs that seemed to get inordinately hot. And as of yesterday, I added an LED to the volume knob powered by a 5-volt source within the amp. Everything I have done (accept for the addition of the LED) has added, I believe, to the musical performance of the amplifier.

Now for the fun part. I have two identical transformers from two other amps (identical to each other, not to the Sony, although they are only a few volts off). I am thinking of increasing the current available to the amplifier by creating two more power supply sections from these transformers and adding them in parallel to the current setup. In theory this should almost triple the available current without messing with the voltage (too badly), and therefore running the output transistors horribly out of spec. The additional two power supplies would be mounted in an external enclosure with a cable running between the receiver and the “supercharger”. This would also give me the ability to use the receiver without the additional power supplies when or if needed.

Now here is the question: While everything works in theory, will I end up with a small explosion for all my troubles? I am planning on converging the power after the rectifier circuit (each transformer will have its own rectifier and filter banks), more or less like running several batteries in parallel. So that would be three transformers and three rectifier circuits.

For those who think me mad for putting all this time and effort in to supercharging a Best Buy Tax Return Special Receiver™, I can only say I have the parts and the time.
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Old 15th April 2004, 09:28 PM   #2
markp is offline markp  United States
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Do not add different voltages in parallel, big bad.
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Old 15th April 2004, 09:41 PM   #3
sam9 is offline sam9  United States
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I would suggest a better path. If the receiver has "pre-outs", just connect an external amp or amps and use it as a tuner preamp. My experience with the amplifier section of Sony receivers has not been good - I think they are just trying to do too much with too little. Then you will have a reason to build one of the amp projects diuscussed on this forum.

If you you decide on the above course and still want to make internal mods, the first thing i would look for is the possability of simply disabling the amplifier section entirely so that there is no even a quiescent current. Of course, this may not be possible but at least it can be checked in to.

The next thing would be to locate the "pre-out" circuit and see if you can find the output coupling cap. Depending on the space avaiable, and he value of the cap it maybe be desirable and feasible to replace it with a higher value. I'm not keen on the idea of direct coupling in a case like this.
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Old 15th April 2004, 10:08 PM   #4
mjarve is offline mjarve  United States
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The other transformers are from a couple of Denon AVR-5800 receivers that had bad shipping damage, but the power supplies were still alright. They are very large toroid units rated for 1200VA each. It seems that it may not be a good idea at all to try to integrate them with the Sony after all… I do have a set of transistors I was going to use to upgrade an Onkyo A-7 integrated amp (2N6609 (x2, PNP) and 2N3773 (x2, NPN)). Using those transistors and those power transformers, what type of amp could I build?
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Old 15th April 2004, 10:27 PM   #5
annex666 is offline annex666  England
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mmm - any chance of some internal photos???
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Old 15th April 2004, 10:37 PM   #6
Brian Donaldson is offline Brian Donaldson  United States
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If you are only going a few volts over, paralleling all three should be no problem. The 2 highter voltage psus will unload the smaller integral unit and it's rectifiers will never conduct.(unless voltage sags enough). But I don't think it'll gain you much.
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Old 15th April 2004, 10:43 PM   #7
ChocoHolic is offline ChocoHolic  Germany
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Hi Mjarve!
I never was able to improve the musical behaviour by using
a bigger transformer. Larger capacitors in the supply sometimes
may help. But a larger transformer usually is only required if you go for
continuos high power and the small transformer may run hot.

Hot heat sinks do not indicate a weak power supply. Hot heat sinks
simply indicate that the heat sinks are relatively small, or the idle
current might be relatively high.
But a high idle current is typically good for low distorsions and high
musical performance.
In fact I recently modified my NAD Receiver and increased the idle current more than ten times of the original values and the musical result was quite exciting! ....OK, increasing the idle current requires that you check in detail for the temperature compensation of the idle current...

The original idle current was around 15mA and the heat sink was
remaining simply cold. But the sound was agressive and unprecise.
Now I run each amp with an idle current of 170mA at steady state
without sound signal. The heat sink is at 50°C...60°C at this condition.
The sound is by far (!!) more charming!!!!!
I was not expecting this enormous improvement, but slowly
I am understanding more and more the friends of class A amps.
In former times I definitely underestimated the influence of crossover distorsions!

I did not only change the idle current, but also the thermal compensation characteristic. Now the idle current decreases when the temperature increases, which helps to avoid overheating.

If you do not feel comfortable with such insight modifications, which
may definitely kill the amp if you make any mistake, then I would
propose to go for Sams proposal and use the pre-outs to drive
a power amp with adequate properties.

Good luck
Markus
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Old 15th April 2004, 11:36 PM   #8
mjarve is offline mjarve  United States
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Following are some pictures of the interior...
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File Type: jpg img_1702s.jpg (78.7 KB, 573 views)
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Old 15th April 2004, 11:38 PM   #9
mjarve is offline mjarve  United States
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and another...
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Old 15th April 2004, 11:39 PM   #10
mjarve is offline mjarve  United States
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and one more...
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