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Old 24th April 2010, 05:44 PM   #491
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Guys,

I am embarassed to admit that I made a mistake on my BOM. The Caddock I used is not MP2060, but MP930, which is rated for 30 watts and a lot cheaper. It is in a TO-220 package. That has proven to be completely reliable after months of continuous use. Lesson learned: check records, and don't rely on memory.

The resistor presently selected for the kit is somewhat smaller, with less surface area for dissipation and heatsink contact, in a TO-126 package. I hope all these calculations and suppositions are correct and the smaller resistor is adequate.

The heatsink issue is troubling. I chose that particular sink because it is compact and had a decent rating. The alternative chosen by Uriah APPEARS to be more efficient but is actually slightly smaller. I am not an expert on heatsinks, but I think the rating appears a bit optimistic. How can it be so much more efficient, yet smaller? Perhaps it is more massive, with thicker material. I'm not sure how the TO-126 package will fit into it. I guess you can always use a heatsink for a larger package with a smaller resistor, but not the other way around, so it should be okay if a little sloppy.

Peace,
Tom E
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Old 24th April 2010, 07:12 PM   #492
40 watt is offline 40 watt  Canada
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T0-126 package could be the MP915 with a 15W rating [again...depending on heatsink]. Perfectly adequate. The slightly smaller body of the resistor and corresponding heatsink even give more compactness, which seems to be desireable on these boards as well.

Great price and for a group buy on a 100 or so is certainly an excellent choice. I think Uriah did VERY well on the selection that also kept the total kit price damb reasonable, especially considering the Obbligatos.

My first chip amp LM4780 has Caddocks MK132 and upright soldier mounted Rikkens. Sounds awesome! Making a physically big resistor fight a tight space is something I learned right out of the gate...

Mounting Note: Mount on a smooth, clean, and flat heat sink surface with a thermal interface material, such as thermal grease. The entire exposed ceramic portion must be in thermal contact with the heat sink. When screw mounting, use a compression washer which provides a mounting force of 150 to 300 pounds (665 to
1330 N). This will provide sufficient pressure on the package over time and through large temperature varia-
tions to maintain the maximum power dissipation capability. Mounting torque to avoid package damage is 8
in-lbs. (0.90 N-m). If a spring clip is used, a clip force of 8 to 30 pounds (35 to 130 N) is recommended to be
applied to the center of the package. The clip should be round or smooth in the contact area to avoid concen-
trating the load on a small point of the plastic body of the package. Another mounting option is to use a
pressure bar method which can achieve a greater mounting force with a greater contact area.
For additional applications information regarding mounting and pulse handling see the Caddock
Applications Notes at caddock.com or contact Applications Engineering

Last edited by 40 watt; 24th April 2010 at 07:37 PM.
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Old 24th April 2010, 07:44 PM   #493
40 watt is offline 40 watt  Canada
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Case Temperature (Tc) + [Thermal Resistance (RθJC) x power applied (Watts)] ≤ TMAX considering the full operating temperature range of the application.
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Old 25th April 2010, 02:32 AM   #494
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Bill_P talking about 1N4001 diodes led me to think about them particularly about the recovery characteristics of such diodes.

We spent money on MUR820 diodes for their ultra fast/soft recovery (less HF pollution) but in the same power lines we use 1N4001 standard diodes...

Uriah, do you think is possible to swap the two 1N4001 with other diodes?

If so SBYV27-100 are very good candidates (I've used them a lot of times with good results), relatively cheap and with higher specs than 1N4001.

The Mouser code is 625-SBYV27-100-E3/4
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Old 25th April 2010, 02:56 AM   #495
Bill_P is offline Bill_P  United States
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SBYV27-100 is good electrically but it is larger than the 1N4001 so it would need to be checked for proper fit in the board. If 1N4001 is supplied, I plan to substitute UF4002 since I have them on hand.
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Old 25th April 2010, 07:01 AM   #496
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Guys, how about fuses? Don't see that in the BOM, I can see there are several preferences, like stereo, dual mono, one fuse per mono, 120/240v main, etc

Last edited by pengboon; 25th April 2010 at 07:02 AM. Reason: Posted in the other thread, but thought this thread is more relavent.
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Old 25th April 2010, 12:12 PM   #497
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Quote:
Originally Posted by ClaveFremen View Post
Bill_P talking about 1N4001 diodes led me to think about them particularly about the recovery characteristics of such diodes.

We spent money on MUR820 diodes for their ultra fast/soft recovery (less HF pollution) but in the same power lines we use 1N4001 standard diodes...

Uriah, do you think is possible to swap the two 1N4001 with other diodes?

If so SBYV27-100 are very good candidates (I've used them a lot of times with good results), relatively cheap and with higher specs than 1N4001.

The Mouser code is 625-SBYV27-100-E3/4
Uriah,
You could check if we might be able to fit a pair of MUR820 where the 1N4001 are. Although I don't think it will make any difference, because they are no supplying anything in the siignal path. What are your thoughts, guys?
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Old 25th April 2010, 12:40 PM   #498
Reality first!
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Quote:
Originally Posted by regiregi22 View Post
Uriah,
You could check if we might be able to fit a pair of MUR820 where the 1N4001 are. Although I don't think it will make any difference, because they are no supplying anything in the siignal path.
MUR820s costs are twice...

Sure the rectified voltage is not used in the signal path but they are fed (and pollute) by the same AC1 and AC2 lines.

The HF noise injected in power lines then passes to the amp PSU...

Quote:
Originally Posted by Bill_P View Post
SBYV27-100 is good electrically but it is larger than the 1N4001 so it would need to be checked for proper fit in the board.
SBYV27-100 are a perfect fit:
Attached Images
File Type: jpg SBYV27-100.JPG (75.5 KB, 216 views)
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Old 25th April 2010, 12:53 PM   #499
Reality first!
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Quote:
Originally Posted by pengboon View Post
Guys, how about fuses? Don't see that in the BOM, I can see there are several preferences, like stereo, dual mono, one fuse per mono, 120/240v main, etc
I've used one 3.15A slow-blo fuse for this configuration:

  • 2x 120VA R-core transformers
  • 2x MyRef Boards
  • One case with one VDE socket
  • 230V mains
But this could change if you go for two cases (a complete dual mono config) or bigger transformers or different mains.
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Old 25th April 2010, 01:11 PM   #500
Bill_P is offline Bill_P  United States
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I can imagine Uriah cringing every time someone talks about changing parts. I am not expecting him to make changes at this late point in the group buy. The problems I pointed out are for the benefit of those buying their own parts. If you want to change D2 and D3 there are lots of options. The MUR820 is extreme overkill, is expensive, and the leads would have to be formed to fit the hole spacing on the board. Here are some 100 piece prices from Mouser.

1N4001 $0.038 each
1N4002 $0.038 each
UF4002 $0.099 each
MUR120 $0.152 each
SBYV27-100 $0.35 each
MUR820 $0.56 each

Regarding fuses, those are not on the PC board and would not be supplied in the group buy. In my present chip amp there are two 200VA toroids, each fed by a 2A slow blow fuse (120 VAC line).
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