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Old 16th December 2011, 04:10 PM   #51
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Rudi_Ratlos View Post
@Sheldon: please have a look at this image:

RMI-FC100, a single stage audio power amplifier Post #2

This is, how it has to be done.
I've built two of the amps, and I'm familiar with the entire thread. Yes, to avoid strain on the leads it's best to mount the transistors to the heat sink, before placing the board and soldering. You don't even need access holes if you never intend to remove the board from the heat sink after assembly. But if you do want to remove it, replacing it will be easier if you make the access holes generous. I've offered the suggestion based on my personal experience with this amp. But your board, your choice. I have no dog in the hunt.

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Old 16th December 2011, 05:33 PM   #52
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Pooge, this is what I am thinking about:

Click the image to open in full size.

http://www.abload.de/img/topview_psugelwy.png

The size of the PCB has increased by 10 mm.

If somebody wants to use the on-board PSU: he has it and only needs a transformer to get a channel running.
If he does not like the on-board PSU, because he has a better on, he can cut the PCB at the indicated line.

To insert alternative types of fuses, ...: that is very easy to do.

Best regards - Rudi_Ratlos
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Old 16th December 2011, 07:16 PM   #53
pooge is offline pooge  United States
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Quote:
Originally Posted by Rudi_Ratlos View Post
Pooge, this is what I am thinking about:

Click the image to open in full size.

http://www.abload.de/img/topview_psugelwy.png

The size of the PCB has increased by 10 mm.

If somebody wants to use the on-board PSU: he has it and only needs a transformer to get a channel running.
If he does not like the on-board PSU, because he has a better on, he can cut the PCB at the indicated line.

To insert alternative types of fuses, ...: that is very easy to do.


Best regards - Rudi_Ratlos

Yes, it is easy to provide vias for different fuse holder lengths. Although different lengths can be obtained by everyone, Europe and USA tend to favor different lengths, and good ones of each type may not be readily available at the same parts suppliers used to buy other parts. So choices are good. Also, a choice of the soldered in fuses without a holder would be nice.

Regarding your latest board, if you break away the rectifier arrangement, the caps come with it. Not a good choice. Some, like me, would prefer a dual bridge, anyway, and have at least some main caps on board. These rectifiers should preferably have heat sinks, also.
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Old 16th December 2011, 08:39 PM   #54
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I too prefer to use two rectifiers, this is one of the reasons I avoided adding the rectifiers on the PCB, Rudi like to use one rectifier. Sometimes I think about providing a small PCB that only holds the rectifiers, but always turns out to be a silly idea and I forget about it.

Last edited by metal; 16th December 2011 at 08:43 PM.
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Old 16th December 2011, 09:16 PM   #55
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Here is a picture, how Mihai himself did it.

RMI-FC100, a single stage audio power amplifier Post #5

METAL: I read so many articles on using a single or 2 rectifiers, but I neither found a stringent PRO nor a CONS for either of the 2 solutions.

Best regards - Rudi_Ratlos
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Old 17th December 2011, 05:46 AM   #56
Luke is offline Luke  New Zealand
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Looking good Rudi. Just for the record, I would like to use dual rectifiers, but Im happy to use a couple of cheap bridges.

Pooge, I read somewhere that putting rail to rail caps across opamps slowed them down and should be avoided, wouldn't this apply to power amps?
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Old 17th December 2011, 11:00 AM   #57
pooge is offline pooge  United States
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Originally Posted by Rudi_Ratlos View Post
METAL: I read so many articles on using a single or 2 rectifiers, but I neither found a stringent PRO nor a CONS for either of the 2 solutions.

Best regards - Rudi_Ratlos
See post #38 here:
2 Rectifier bridges : Why ?

And post #148 here:
Bob Cordell Interview: Power Supplies

The bottom line is that the ground line is not contaminated with charging currents, and the transformers can be quieter.

That being said, it would be preferrable to have separate ground lines for each capacitor input to the board, and that they not be connected together on the board until the star ground. This would allow those who prefer dual bridges to connect them that way, and it would NOT inhibite single bridge users to do it their way. Further, if each rail line input had a "ground" return input placed close to it on the right side of the board, the rail and return lines for each polarity could be twisted together right up to the board. Single bridge users could still run a ground line from each cap back to the transformer center tap.

Last edited by pooge; 17th December 2011 at 11:29 AM.
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Old 17th December 2011, 11:11 AM   #58
pooge is offline pooge  United States
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Pooge, I read somewhere that putting rail to rail caps across opamps slowed them down and should be avoided, wouldn't this apply to power amps?
I have no idea why this would be true. I have never read such a thing, so I can't comment on it. However, one would not have to use the option if it is available.

With onboard caps, a rail-to-rail cap may not be as useful as when caps are off board. The idea is to minimize the size of charging current loops that can couple half wave charging currents into the circuitry. A rail-to-rail cap on board can minimize the size of this loop carrying half wave currents compared to lines going off board to off-board caps. This is why I suggested at least a provision for an axial cap to the left of the break line in case the cap provision was broken off.
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Old 17th December 2011, 11:39 AM   #59
pooge is offline pooge  United States
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If fact, it seems it would not hurt to have the rail and return traces for each cap placed on opposite sides of the board. The capacitance between these traces should not hurt, but help. This keeps the traces very close together to reduce radiation due to charging currents, and again allows connectors to be very close together for twisted pair lines up to the board. Place the star ground between the fuse ends, and run the ground return path from the star ground under each fuse back to each cap. This keeps each of these loops as small as possible.

Last edited by pooge; 17th December 2011 at 11:59 AM.
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Old 19th December 2011, 07:01 AM   #60
zdr is offline zdr  Belgium
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Rudi, be careful not to change footprint orientation of any bjts which are termally coupled in pairs. I think you rotated one bc. They should all face each other.
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