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Old 5th January 2014, 02:43 AM   #11
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Default VSSA = most "bang for the buck"

Below is what I'm putting to my IPS board.
The VSSA "core" performs wonderful.
No more PSRR issue - and LOTS of power with the
EF3.


I will use ... this - http://www.nxp.com/documents/data_sheet/PBSS4140DPN.pdf

One little tiny dual BJT + the hawksford = killer amp.

Thanx !

OS
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Old 5th January 2014, 01:34 PM   #12
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Hm, just had a potential idea and I'm looking for some feedback.

The PMI / MrEvil capacitance multiplier power supply seems to be popular amongst VSSA builders, so why not partially integrate it in to the VSSA PCB?

The idea would be like this:

1) Have off board bulk supply so the large components like the main reservoir capacitors, rectifiers, are NOT on the PCB with the amplifier but the actual CM circuit is. In a way the CM output capacitor is already there.

2) This way each module has its own CM, improving performance with a shared bulk supply.

3) Rail shutdown on fault would be easy to incorporate into each module individually. Even a solid state relay on the output line as added defence against a fault could be included, though that may be redundant since I'm sure a speaker could absorb the contents of the 1000uF capacitors without much risk though it would make a thump.

Any thoughts?
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Old 5th January 2014, 06:43 PM   #13
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I like the idea.
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Old 5th January 2014, 07:57 PM   #14
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I think it is an excellent idea. I will go one further and suggest also adding Bigun's solid state relay speaker protection circuit on the same board also. The schematic is provided in this thread:

TGM8 - an amplifier based on Rod Elliot P3a
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Old 5th January 2014, 08:09 PM   #15
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Quote:
Originally Posted by Ranchu32 View Post
I think it is an excellent idea. I will go one further and suggest also adding Bigun's solid state relay speaker protection circuit on the same board also. The schematic is provided in this thread:

TGM8 - an amplifier based on Rod Elliot P3a
That is part of the motivation for the suggestion, adding a means to protect the speaker on-board.

Given the ability to basically 'hit the kill switch' on the PSU with rail shut down would we benefit from a solid state relay in the output line for the VSSA?

Also, in looking at what needs to be on-board I would be rapidly heading into surface mount devices to free up the required real estate. I don't have an issue with that, but for the moment I'm on a thread dedicated to through hole design.

Anyhow, I'm playing the schematics in sim and layout options as well. Time will tell how much integration makes sense.
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Old 5th January 2014, 08:20 PM   #16
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I would be very interested in a SMT version to keep the board size managable with all these extras. What about the stored charge in the caps - is that going to be an issue?
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Old 10th January 2014, 06:30 AM   #17
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Quote:
Originally Posted by jkuetemann View Post
Hm, just had a potential idea and I'm looking for some feedback.

Have off board bulk supply so the large components like the main reservoir capacitors, rectifiers, are NOT on the PCB with the amplifier but the actual CM circuit is. In a way the CM output capacitor is already there.

Any thoughts?
That is exactly what I suggested PMI in a "bucket list" discussion we had last year. The CM works better if it's close to it's load, and my both implementations for LC VSSA boards include a p2p CM without large storage caps that is placed very close to the modules (pass transistors mounted on the main heatsink and rectifier with filter caps mounted close to the toroid)

He was not sure if this idea will be largely appreciated, as there are people who want separate power supply for the front-end stage, or there are people who want to use SMPS... His point was that VSSA will loose the flexibility if he will be doing such integration and he thought that maybe a smaller PCB for CM (without the rectifier/storage part) would be better received by the builders.

Probably a VSSA with the CM on one PCB will be OK if you can easily remove the CM part in case you don't want it. And in case you want it anyway (like myself for example) you will solder short bridge wires from CM to VSSA (like excess terminals from resistors you will actually use in the build).

Of course, if one increases the rail caps on VSSA to 2x2200uF or even 3300uF + 2200uF you can simply forget about output CM capacitor and the whole CM part will be very small. Then, in case you don't want CM you will not mount the associated components and just put a bridge wire between D and S of the associated pass transistor.

The same I see the idea of an integrated loudspeaker protection: a part of the PCB that can be cut-out; or integrated but with possibility to easily bypass it.

The cut-out idea can be better because you have the option to do it without SMD.

I designed PCBs in the past, and I know very well it's very difficult to accommodate good design rules and flexibility of different options on the same plate. But it's not impossible

Well! These are my thoughts, hopefully you don't mind the too long post. A flexible solution will have more appeal among the builders.

Cheers!
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Old 10th January 2014, 12:03 PM   #18
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Quote:
Originally Posted by metallicus69 View Post
That is exactly what I suggested PMI in a "bucket list" discussion we had last year. The CM works better if it's close to it's load, and my both implementations for LC VSSA boards include a p2p CM without large storage caps that is placed very close to the modules (pass transistors mounted on the main heatsink and rectifier with filter caps mounted close to the toroid)

He was not sure if this idea will be largely appreciated, as there are people who want separate power supply for the front-end stage, or there are people who want to use SMPS... His point was that VSSA will loose the flexibility if he will be doing such integration and he thought that maybe a smaller PCB for CM (without the rectifier/storage part) would be better received by the builders.

Probably a VSSA with the CM on one PCB will be OK if you can easily remove the CM part in case you don't want it. And in case you want it anyway (like myself for example) you will solder short bridge wires from CM to VSSA (like excess terminals from resistors you will actually use in the build).

Of course, if one increases the rail caps on VSSA to 2x2200uF or even 3300uF + 2200uF you can simply forget about output CM capacitor and the whole CM part will be very small. Then, in case you don't want CM you will not mount the associated components and just put a bridge wire between D and S of the associated pass transistor.

The same I see the idea of an integrated loudspeaker protection: a part of the PCB that can be cut-out; or integrated but with possibility to easily bypass it.

The cut-out idea can be better because you have the option to do it without SMD.

I designed PCBs in the past, and I know very well it's very difficult to accommodate good design rules and flexibility of different options on the same plate. But it's not impossible

Well! These are my thoughts, hopefully you don't mind the too long post. A flexible solution will have more appeal among the builders.

Cheers!
Thanks for your thoughts, I appreciate some feedback on this. I'm looking at cooking up some different arrangements to see what might offer both flexibility and performance.
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Old 10th January 2014, 06:59 PM   #19
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Any boards left or wait for the next GB? I am in no hurry!
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Old 10th January 2014, 07:06 PM   #20
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PMI has apparently has had some personal business to attend to of late, so until we see his return I think everything is just in a holding pattern for the time being.

That said, I have some boards of my own design coming so perhaps following my QC build you may be interested in a pair of those. I ordered an initial run of 20 pieces but need to actually build at least a stereo set prior to officially offering the surplus. A photoview of what I have coming was posted a page or two back.
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