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Old 30th September 2006, 01:56 AM   #211
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Default Zetex is fine but

The IRFD110/9110 looks to be an good substitute, but I wouldnt be concerned if using Zetex
ZVP RDson= 8 ohm (VP=4 ohm) max
ZVN RDson= 4 ohm (VN= 2.5 ohm) max

If it works, make holes for the IRFD and a pattern on back for the SOT-223.

Another solution would be to place those Zetex on component side and mount(eg. solder) them to a standing position. If this is a simpler or easier solution, make it. Then there is also an option to pre-mount the Zetex to a small Al-strip (epoxy) and then solder all four transistors in a standing position on the board including some support for the Al-strip.

I have done it in SMPS´s so I know it works.

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Old 30th September 2006, 02:01 AM   #212
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The straight line thing is ok but why not keep it as the original. Those small fined sinks are cheap even new only a couple of dollars each.

Quote:
Then there is also an option to pre-mount the Zetex to a small Al-strip (epoxy) and then solder all four transistors in a standing position on the board including some support for the Al-strip.
I did this years ago on a project and it works fine. I would have no problem doing this.

Mark
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Old 30th September 2006, 08:08 AM   #213
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Old 30th September 2006, 12:48 PM   #214
PWatts is offline PWatts  South Africa
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OK here's the progress made so far:

1) Routed ground and power. Important grounds routed separately one their own line back to the star point.
2) Routed predrivers and their resistors and Miller caps
3) Added support for the Zetex SOT-223 MOSFETs at the bottom side (this was damn difficult). The board now supports three different packages for the FET's. Added vias and a large copper pour for proper heatsinking of them. They can be seen as the grey blocks.
4) Extended bypass caps for 5, 7.5 and 10mm pitch.
5) Added large electrolytics at the bottom since there was space anyway.
6) Enhanced silkscreen, added Reference Designators.
7) Fixed a MAJOR routing mistake

I tried going as symmetrical as possible as Al did, but here and there I had to shift a few things for better routing. Besides, rather symmetrical routing than symmetrical component placement.

The white line is where the driver stage can begin in order to allow enough space for a heatsink for the predrivers. The driver board will have the five transistors, the four emitter resistors, one resistor and trimpot for the bias, the 100nF CE bypass cap and the four power supply bypass caps.

One issue may be with the reference designators. I added them last, and it's quite difficult to know what belongs to what. I suggest that I add a second set of them INSIDE the footprint to aid during soldering.

Unfortunately this current design will be very difficult to adapt for a separate driver board since there is no space for the terminals. Those who would like to do so would have to hardwire it. Because the heatsink will be so large, it may also not be feasible to make the boards breakable in order to strengthen them. I guess this particular aspect would need to be discussed first.

The routed part of the board as it is measures 105 x 92mm (4.1" x 3.6")

What still needs to be done is:

1) Further improve silkscreen; make the Reference Designators easier identifiable
2) Route driver stage according to heatsink used
3) Ensure holes are large enough
4) Support for trianglular trimpot pinouts
5) Add mounting holes

Any other suggestions/comments?
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Old 30th September 2006, 04:48 PM   #215
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Quote:
Originally posted by PWatts

Any other suggestions/comments?

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Old 30th September 2006, 06:11 PM   #216
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Looking good! Could you post it as a PDF please, the bitmap is a bit difficult to read.
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Old 30th September 2006, 06:16 PM   #217
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Default PWatts,

The progress is not far from a finished board, and it looks very good so far

Here are some tips due to only practical matters (based on a very low resolution picture of the board and you have my apology if I have missed this):

1) make all donut pads as large as they can be due to nearby routes. This will raise the quality of the board, especially when member with limited knowledge to soldering works are going to solder the components.

2) the pads/footprints for the TO-220 transistors could also larger (rectangular pads ?). Those transistors will produce a lot of heat and this will weaken the solder pads mounting/glue to board when aging.

3) Now, if you route the last part of the board: the driver (and thermal tracking) transistors
be sure to have at least 1-2 mm space to the rest of the board. This is for to make cutting away the driver-stage easy for those who wants to do so. You can add some donut pads for the wire connection on each side of this cutting-line if this is practical. You could even make or print some reference markings on the up or the down side of board for to make cutting easier.

4) Dont know why you mention the reference designator dont you use same as in the original schematics?

Excellent job so far Pierre

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Old 30th September 2006, 10:02 PM   #218
PWatts is offline PWatts  South Africa
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OK, I will post a PDF next time, the 100kB maximum limit makes it difficult to post a proper bitmap. For the time being, here's the last bitmap, the next post will be PDF.

I'll try make the pads as large as possible and nice and wide apart; I keep having to remind myself that I too messed up many expensive boards when I was starting off.

The reference designators are different since this is a different schematic than the KSA50. I used the designators as used in the Mk2 schematic we all have. What I referred to was that with the tightly packed components it's sometimes difficult to see which designator belongs to which footprint. A solution to help the soldering process is to place a second set of the same designators inside the footprint, i.e. they will be covered up when the part is soldered on. I would still advise to check the traces too see what is connected to what to make dead sure before soldering instead of just blindly following designators.

Right, here's the next iteration. The blue border is roughly the size of the original board, and the mounting holes on the corresponding positions. The pads at the sides are for the output, power and transistor base connections to the output stages on the block heatsinks. People will have to decide whether they want it or not, but personally I think it would be nice to have the board resemble the original closely (esp with the driver heatsink) but with all the refinements. It also makes it an attractive drop-in upgrade for current KSA100 owners, especially for Mk1 owners wanting a hassle-free upgrade to Mk2 with the possibility of easily reverting back to the old board.

The board cost will not be much higher, only 36cm2 and there are no extra holes etc. I will still add the screw terminal connectors for those who want to connect to more other output stages.

I made a few routing changes, refined the silkscreen, and placed two more resistors on the bottom side. This makes heatsink placement easier and allows a more compact layout. Although a single heatsink for the predrivers is possible, a smaller one for each pair may work easier. "foldback" types are usable since I placed the resistor between the two sets on the bottom side.

The driver stage needs to go as low down as possible to have as much are above available for the driver heatsink. How low it goes down ultimately depends on how much space would be needed for the predriver heatsink. 5mm? 10mm? Unfortunately the nature of this layout caused the driver stage to be higher up than on the original board, so we need as little clearance as possible between it and the predrivers to limit board space and increase heatsink area.

I regret having to say this, but those who want a removable driver stage will have to do so at own risk. I'll try making the amputation process as easy as possible, but we're already pushed for space so I cannot do a proper distanced layout just for the sake of it. I will add some proper sized pads, but a connector is out of the question - that all is of course unless people want to abandon the whole on-board sink idea and go for the KSA50 clone's approach, but I like the old-school idea.

I've checked, it will be possible to add the fourth hole for the LTP's, but it will not be in a straight row. The third pin would therefore need to be bent a bit, but that's all that won't disturb the whole layout.

Still needs to be done:

1) Get more exact measurements of the original board diameters and mounting hole placements (I just extrapolated from pictures)
2) Add the LTP holes and triangle trimpot pad
3) thicken the power ground traces (no use having thick power traces and the return path is thin!)
4) Mounting holes for driver heatsink, new component footprint for the horizontal TO220 drivers

Somebody would also need to double-check the board for faults. Preferably someone who has P-CAD 2004, but with concentration a graphic approach would also work. Even though I very rarely make a routing mistake, accidents do happen and I don't want a lot of angry board buyers if something goes up in smoke. I also routed directly instead of first drawing up the schematic and importing the netlist in order to save time. The issue with the Delta Audio trimpots are a good example of what I'd like to avoid - and that was an easy mistake to fix fortunately. I have to say I'm quite chuffed that at my progress tempo, I placed the first component 30 hours ago and it was by no means the only thing I did this weekend.

Mark: take a look at the board and see if you can work with the space for the heatsink and whether I should lengthen the board more. I'll then add the heatsink and mounting holes, and give you the exact locations of hole positions and width needed.

Zen Mod: I forgot to mention earlier, I got intrigued by the design not because it's advanced or novel or anything, but in fact because of the very reason that it's so old and unrefined, yet it remains one of (sonically) best amps to this day.
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Old 30th September 2006, 10:10 PM   #219
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Consider designing a single PCB layout optimized for a narrow monoblock using On-Semi output transistors soldered directly to this PCB.

The KSA 100 weighs over 100 pounds. I purchased the KMA 100 monoblocks both for ease of moving and the better electrical isolation.

I usually build a single PCB monoblock similar to the attached photo, but with the transformer mounted either vertically to the front plate for cooling and more efficient packing, or on the bottom of the chassis to raise the heatsink above the floor for better thermal air pumping. A single PCB allows the use of high Ft output transistors with less chance of oscillation than a separate driver PCB spaghetti wiring. It is much easier to find two modest VA transformers than one monster VA transformer.

There are large heatsinks like the KL271 profile with 0.3 C/watt thermal resistance that I've been using in my designs.
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Old 30th September 2006, 10:21 PM   #220
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Linesource,

good stuff.
(as are Mr Poon's designs)
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