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Old 9th October 2002, 06:08 PM   #1
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Location: Brazil
Default Receiver Mod

Some time ago my wife bought a Pioneer receiver, model VSX-511S.

We didn't use it for too long, because I found the sound a bit "bland" for my taste, though not necessarily bad.

So I ordered the service manual to see if something could be done with it, upgrading active & passive parts and whatever might be improved.

The good surprise was that the power amp was discrete, which at least allowed some deeper improvement there.

The bad one was there are at least two electronic switches I can't probably bypass.

The areas that I basically think can be treated are:

1) Preamp chips: mostly garden type. Sockets might allow me try different duals and see which sounds best.

2) Preamp power supply. The 7X12 used could be improved by at least 3X7 types or perhaps a Sulzer regulator. Using a Jung/Didden here should be a waste, as this supply will be powering all +12v/-12v stages.

3) Bypassing stages. Basically going straight from line preamp to power amp, using a switch. By doing this balance and eq stages are eliminated. The switch should be used when listening to music.

4) Power amp. This the major part of the mod, and the one area where I would like to have some opinions on now.

The original Pioneer circuit is attached. As you can see it's a pretty much standard class AB circuit, but I think the lack of personality mentioned above might come from it.

So during the last two or three years I have been trying to find a circuit I could replace it for and get a better sound. There are limitations for this project, as I intend to use the same pcb. Class too, as I can't fit a larger heatsink inside. But in spite of those limits, I think there is still ground to improve things.

The input pair is a dual monolithic transistor, which is good and not very usual for such a consumer product. Though the abundance of small caps around the input, as well as the zobel between the input collectors, suggest something might be happening there.

My first idea had been to do a "Douglas Self job" here, correcting all the distortion sources he names on his book. But many people, here included, seem to think it may not sound much better.

Another thing I would like to add is a regulator for the low current stages.

So what do you think?

As you may imagine, this mod type can be applied on many other receivers.

Later on we can return to the preamp stages.


Carlos
Attached Files
File Type: zip powamp_511.zip (65.2 KB, 100 views)
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Old 23rd November 2002, 01:04 PM   #2
halojoy is offline halojoy  Sweden
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Default How far have you come?

Quote:
Originally posted by carlmart
Some time ago my wife bought a Pioneer receiver, model VSX-511S.
The good surprise was that the power amp was discrete, which at least allowed some deeper improvement there.

The bad one was there are at least two electronic switches I can't probably bypass.

4) Power amp. This the major part of the mod, and the one area where I would like to have some opinions on now.

The original Pioneer circuit is attached. As you can see it's a pretty much standard class AB circuit, but I think the lack of personality mentioned above might come from it.

So during the last two or three years I have been trying to find a circuit I could replace it for and get a better sound. There are limitations for this project, as I intend to use the same pcb. Class too, as I can't fit a larger heatsink inside. But in spite of those limits, I think there is still ground to improve things.

The input pair is a dual monolithic transistor, which is good and not very usual for such a consumer product. Though the abundance of small caps around the input, as well as the zobel between the input collectors, suggest something might be happening there.

My first idea had been to do a "Douglas Self job" here, correcting all the distortion sources he names on his book. But many people, here included, seem to think it may not sound much better.

So what do you think?

Carlos
This is a challenge, use same board and same heatsink.
But of course improments can be made, even that may effect the sound for the better.
Transistors can be altered,
currents can be changed. Caps/resistors can be replaced and altered in values.

How far has this project come?
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Old 23rd November 2002, 01:23 PM   #3
halojoy is offline halojoy  Sweden
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Join Date: Nov 2002
Exclamation See the original ZIP for a better resolution

How high is the power supply voltage?
Can you change to a bigger more potent trafo?
I suppose you have already change that 4.7 elyt at the input.
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File Type: gif powamp_511s.gif (14.5 KB, 135 views)
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Old 23rd November 2002, 01:26 PM   #4
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Join Date: Mar 2001
Location: Brazil
Halojoy


Can you e-mail me?


Carlos
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