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Old 23rd April 2010, 09:42 PM   #481
udailey is offline udailey  United States
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Ordered the taller sinks. 6.4W/C should do the trick very well and not leave room for doubt. Of course Avnet didnt get back to me and I had to track them down. By the time I did they were out of the 307 they had in stock this morning.. Had to go to Digikey. If you can believe it Digikey was second least expensive after Avnet. Of course Avnet is enforcing their restocking fee even though if I had been able to order the sinks I wanted this morning from them they would not have charged me, so if they had actually gotten in contact with me in a timely manner I would not have got the fee.... come on people!
Anyway, it sure is a nice day out!!
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Old 23rd April 2010, 11:49 PM   #482
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Uriah, can you post the part number for R3 and his heatsink so I can update the BOM for extra boards?

Thanks
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Old 24th April 2010, 12:21 AM   #483
udailey is offline udailey  United States
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MP915-0.5-1%
504222B00000G
Uriah
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Old 24th April 2010, 12:43 AM   #484
Bill_P is offline Bill_P  United States
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The more I look into the 24V supply for the speaker protection, the more problems I find. Besides too much voltage on the diodes, the value of R14 is too high at 470 Ohms. The attached files are from a LTspice simulation and they show only about 15 volts on the 24V rail. The relay needs at least 18 volts to guarantee switching. In the graph the green curve is the diode voltage, showing 58 volts reverse voltage. The blue curve is the LM3886 V+, about 28 volts from a 22V transformer, and the red curve is the 24V supply, running around 15V. When I build the amplifier, I will measure this circuit carefully to see what needs adjusted to bring it into specification.
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File Type: pdf schem.pdf (12.9 KB, 33 views)
File Type: pdf Output.pdf (17.4 KB, 26 views)
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Old 24th April 2010, 12:48 AM   #485
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Default Updated BOM for extra boards

Now includes the right Caddock and heatsink, some minor revisions.
Attached Files
File Type: zip MyRef BOM.zip (61.8 KB, 33 views)
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Old 24th April 2010, 06:19 AM   #486
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Default Just kidding (or not?)

  • Bigger caps (except C3 and C8)
  • SMD Speaker Protection
  • SMD LM318 and compensation network
  • Regulated LM318 PSU via LM78xx/LM79xx
  • ...
Obviously untested.
Attached Images
File Type: png MyRefC Mod.png (119.3 KB, 235 views)
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Old 24th April 2010, 01:48 PM   #487
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Quote:
Originally Posted by udailey View Post
Dang, just deleted my post... anyway.
Bill, what about a 4Ohm load?
The same diodes have been used for quite a while now. How do you calculate your concern?
Spoke to Caddock about a half an hour ago. The engineer agrees with you. Fine with no problems at 5W but 7W would be a problem. We are cutting the bottom fin off of that heatsink so I am guessing about 15W/C and 15C/W is what he and I talked about. This allows for the LM318 to be under it. You only have to cut the left side of the sink. Right can stay as is. So I think that 15C/W would be a good estimation. However.. We could be safe and return those sinks and use this one
Digi-Key - HS104-2-ND (Manufacturer - 504222B00000G)
6.4C/W natural convection. Its pretty close to the same price so it would basically cost me shipping back to them and shipping again to me, but not any kind of deal breaker.
It is almost exactly twice as efficient with the same footprint.
Of course this only comes into play when dumping 100% of the power into your speakers, which would melt my speakers but I suppose some of us might actually play it at full volume for a while.
Uriah
If it does fit with no problems, I will give it a go. Not that having it hot is a major concern, but for my tastes 94C seems a bit on the high side, don't know about what long term effects could it produce...
So, if cost is not very high and waiting time neither is, I would try to return them.


BTW, Why don't you go with heatsinks taller than that? We are allowd to use HS with more height that them. We could aim to source heatsinks as tall as 4 or 5cm. We have the space
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Last edited by regiregi22; 24th April 2010 at 01:53 PM.
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Old 24th April 2010, 01:58 PM   #488
udailey is offline udailey  United States
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Regi,
the Sink is actually pretty efficient at 6.4C/W so I am not concerned any more. It falls well within specs.
Dario,
Man we should all work the heck out of this board this summer. Could be a lot of fun.
Uriah
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Old 24th April 2010, 02:07 PM   #489
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Quote:
Originally Posted by udailey View Post
Man we should all work the heck out of this board this summer. Could be a lot of fun.
Yes could be funny, this was just an excercise since I've never designed or modified nothing with Eagle.

In an ideal world I would like to make also a FET based PSU for the LM318 and larger use of SMD...

Something like that:
Attached Images
File Type: jpg PS FET.JPG (38.9 KB, 224 views)
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Last edited by ClaveFremen; 24th April 2010 at 02:10 PM.
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Old 24th April 2010, 02:45 PM   #490
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Quote:
Originally Posted by troystg View Post
Not to start anything but...

Mauro did an expert job with the original design and parts specification (values and tolerances). Why is there any discussion of "will this dissipate enough"?

I guess I lost sync when the conversation went from changing "brands" of the parts to changing "values" of those parts.
I don't think Uriah is changing any value. The fact is that Caddock resistor's maximum power will be defined by the size of the heatsink attached to it. It is not like the usual 0.25W, 1W or 2W resistors, which are factory defined maximum power. So if Mauro said 7W output res., we might try to achieve that with a Caddock, so we must find the optimal heatsink size.

Appart from that, the higher the rated power for a resistor, the colder it will work, that meaning a longer life for the component.


BTW, anyone knows what are the differences between "current sense resistors" and plain resistors? If there is any...

Uriah, Thos obbligatos and pcb boards are very nice
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