I will call Caddock today. My calculations, basic as they are, say that this 15W caddock I have selected at 1/3 the price of the 60W will allow 6W dissipation with no problem with the heatsink, but I will call them to make sure. If not, then I will talk to the distributor about returning them and getting the 30W which absolutely has no problem handling 5-7W of dissipation and is still quite a bit cheaper than the 60W.
Do any of you know the exact amount of dissipation across this resistor? Remember we are dealing with AC not DC over the resistor and we are dealing with music not 100% power 100% of the time.
As it is right now my question to them will be "can it handle 5-7W" for a lifetime.
Dario, thats a beautiful BOM. I used to work in electronics manufacturing and our purchasing agent would be very jealous of how nice that looks and how detailed it is.
Uriah
Do any of you know the exact amount of dissipation across this resistor? Remember we are dealing with AC not DC over the resistor and we are dealing with music not 100% power 100% of the time.
As it is right now my question to them will be "can it handle 5-7W" for a lifetime.
Dario, thats a beautiful BOM. I used to work in electronics manufacturing and our purchasing agent would be very jealous of how nice that looks and how detailed it is.
Uriah
In the original thread some people reported good results also with TeddyRegs.
If the amplifier outputs 50 Watts into 8 Ohms, the current is 2.5 Amps. The power in the 0.5 Ohm resistor is 3.125 Watts. The heatsink thermal resistance is 12.7C/W and the resistor to case is 8.33C/W. Allowing for case to heatsink thermal resistance, the total is about 22C/W. Then 3.125 Watts causes a 69C rise in the resistor temperature, or an absolute temperature of 94C in a 25C ambient. This is acceptable both for the printed circuit board and for the resistor itself.
On a different subject, it appears to me that 50 volt diodes for D2 and D3 are not adequate. I think they should be at least 100 volts.
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
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
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With 50 Watts into 4 Ohms, the power in the resistor doubles. That is enough to overheat the resistor, but in actual usage the amplifier would never be run at continuous full output. It would be clippng most of the time and would sound awful even if the speakers could take that much continuous power. I don't think the resistor will get too hot with normal usage.
For the diode, to oversimplify things, assume a 44 VCT transformer feeding the pair of diodes connected as a full wave rectifier with no load. When the anode of D2 is at the peak of the 22V sine wave (31V), its cathode is also at nearly 31V. The anode of D3 is at the negative peak of the sine wave (-31V) so it sees a reverse voltage of 62V. The situation is far more complicated since the transformer is not ideal and it is loaded by the LM3886. The non-ideal items tend to reduce the diode reverse voltage somewhat and the diodes probably do not breakdown at 50.1 volts so there may not be any reported problems. Regardless, this operation is much too close to the diode rating and a higher voltage part is only a penny more. I plan to use higher voltage diodes in my build and would recommend that for everyone.
For the diode, to oversimplify things, assume a 44 VCT transformer feeding the pair of diodes connected as a full wave rectifier with no load. When the anode of D2 is at the peak of the 22V sine wave (31V), its cathode is also at nearly 31V. The anode of D3 is at the negative peak of the sine wave (-31V) so it sees a reverse voltage of 62V. The situation is far more complicated since the transformer is not ideal and it is loaded by the LM3886. The non-ideal items tend to reduce the diode reverse voltage somewhat and the diodes probably do not breakdown at 50.1 volts so there may not be any reported problems. Regardless, this operation is much too close to the diode rating and a higher voltage part is only a penny more. I plan to use higher voltage diodes in my build and would recommend that for everyone.
From reading Parts Connexion description of the Caddocks, increasing the dissipation and thus the wattage rating is as simple as how big is the heatsink attached to the Caddock. The heatsink linked by Parts Connnexion is actually a thin metal variant and the one you have chosen is beefier, thus will give a higher wattage rating.
Huntington [Mills] have 5-watt, 10-watt, and 12-watt power resistors, encased in alumina ceramic, which is, rudimentarily, the same material in firebrick, firebrick mortar and refractory materials, for example lining kilns and and castable fireclays for brick ovens etc. This is a far superior material than a basic cement resistor when it comes to heat resistance. You can also bet that alumina is present in space shuttle exterior tiles for heat resistance upon re-entry into the atmosphere.
The Caddock with heatsink should be the most optimal of all, with a skookum heatsink, as is the one you have chosen. Clipping a bit of material off to fit other components is a minor consequence to obtain piece of mind for that reistor's function.
The only intangible with Caddock I can think of is that they are current sensing resistors. Whether relevant or not to the function of My Ref C I have no idea.
PS: That photo of Obligatos and boards is pure audio porn...[insert Homer Simpson drool photo here].
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.
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 will wait til later today to jump or not jump on the new heatsink. I will let you guys file in and give your idea of go or no go.
SHIPPING
I took a package with one stereo kit down to the post office today. I added some parts to it to make it a little heavier to make up for the few parts that are still en route.
Shipping and single stereo kit, 2 channels to
Singapore 13.65
Australia 14.20
Canada 6.97 (but different regions of Canada cost more or less so this is a total guess)
UK 14.20
Germany 14.20
So we can see a trend here toward 14.20. I think charging all international 15.00 and usign any excess to go toward shipping supplies is fair and easy to send out a single email to everyone to go to the shop and buy 15.00 worth of shipping. I will have to make a new product on my shopping cart that is equivalent to 15.00 shipping so dont go to the site to purchase it yet. I will email everyone when I am ready, probably tonight.
Shipping to Canada I will put at 8.00 and that should cover everyone.
If you have 4 kits I will instruct in my email to purchase shipping twice. I will ship two different boxes. This will make VAT much less for you guys as the nice price I put on VAT will probably draw no taxes, but shipping 4 kits in one box would probably draw to much attention from import agents. Maybe not. But if you ordered 6 kits, I think one guy did, then the International Flat Rate Box at 43.45 but when compared to 3 shipments at 15 each and VAT it might be better to go with 3 shipments.
If you international guys want to chime in here go ahead.
Uriah
SHIPPING
I took a package with one stereo kit down to the post office today. I added some parts to it to make it a little heavier to make up for the few parts that are still en route.
Shipping and single stereo kit, 2 channels to
Singapore 13.65
Australia 14.20
Canada 6.97 (but different regions of Canada cost more or less so this is a total guess)
UK 14.20
Germany 14.20
So we can see a trend here toward 14.20. I think charging all international 15.00 and usign any excess to go toward shipping supplies is fair and easy to send out a single email to everyone to go to the shop and buy 15.00 worth of shipping. I will have to make a new product on my shopping cart that is equivalent to 15.00 shipping so dont go to the site to purchase it yet. I will email everyone when I am ready, probably tonight.
Shipping to Canada I will put at 8.00 and that should cover everyone.
If you have 4 kits I will instruct in my email to purchase shipping twice. I will ship two different boxes. This will make VAT much less for you guys as the nice price I put on VAT will probably draw no taxes, but shipping 4 kits in one box would probably draw to much attention from import agents. Maybe not. But if you ordered 6 kits, I think one guy did, then the International Flat Rate Box at 43.45 but when compared to 3 shipments at 15 each and VAT it might be better to go with 3 shipments.
If you international guys want to chime in here go ahead.
Uriah
Troy,
Mauro never mentioned using a Caddock resistor and they require heatsinks so a discussion of heat dissipation has to come into it. The Caddock resistor is a TO type package from TO-126 to TO-220 to TO-247. They will work without a sink but they are significantly derated without a sink. The sound of a Caddock is reported to be one of the very best out there and thats the goal. Finding out how much the resistor is derated from 15W in this situation is not about changing the value but about making sure we keep it equal to or above spec.
Uriah
Mauro never mentioned using a Caddock resistor and they require heatsinks so a discussion of heat dissipation has to come into it. The Caddock resistor is a TO type package from TO-126 to TO-220 to TO-247. They will work without a sink but they are significantly derated without a sink. The sound of a Caddock is reported to be one of the very best out there and thats the goal. Finding out how much the resistor is derated from 15W in this situation is not about changing the value but about making sure we keep it equal to or above spec.
Uriah
One thing with postal service to Canada is the magical cut-off point where Canada Border Service Agency decides to assess duties and taxes. It seems that $40 and higher is the magic moment where the package either proceeds straight through unmolested by duties, taxes and delays [if under $40], or is shunted off to a mountainous pile of parcels where staff at CBSA then apply duties, taxes...and additional week delay.
A declared price amount of $39 or so would speed the package right on through unmolested by border piranahs.
At least that has been my experience with Canada Post and Canada Border Services Agency.
Currently, I'm personally still at 4 boards and no kits only because of transition to spring, summer, fall employment and there is a delay waiting for other trades on this project so... I'm still awaiting a definative moment for work start-up. I just can't pull the trigger on a pair of kits until that employment is more definitive and secure.
A declared price amount of $39 or so would speed the package right on through unmolested by border piranahs.
At least that has been my experience with Canada Post and Canada Border Services Agency.
Currently, I'm personally still at 4 boards and no kits only because of transition to spring, summer, fall employment and there is a delay waiting for other trades on this project so... I'm still awaiting a definative moment for work start-up. I just can't pull the trigger on a pair of kits until that employment is more definitive and secure.
I'm sure that's true, but the printed circuit board is probably rated for 105C and solder joints can deteriorate if the resistor leads are very hot. I still don't see a problem with the resistor temperature under normal use - driving a speaker at sane levels. Running a bench test into a 4 Ohm load resistor at full power for hours on end may be another matter.
I think I will go with the larger heatsink then. Here is what Caddock told me when I emailed them a few minutes ago.
Uriah:
I mentioned that the MP915, like all Caddock models are conservatively rated for different qualities of mounting.
I cannot tell you how conservatively rated the parts are, but your temperature measurement in-situ at worst case power would tell you.
I recommend mounting the parts on your heat sink, applying worst case power for 15 minutes and measuring the leads at the point where they exit the resistor (the “fat” part of the lead, as this is a direct copper connection to the resistor element.
The maximum element temperature is 150C, so for a good design, I would think that a lead temperature of +120C or below would be a conservative design.
We look forward to being of service to you.
Sincerely,
Dave Anderson
Senior Applications Engineer
Commercial/Industrial Applications
dave.anderson@caddock.com
Tel.: +1-541-496-0700
Fax: +1-541-496-0408
Caddock Electronics, Inc.
High Performance Film Resistors
Caddock - High Performance Film Resistors
Uriah:
I mentioned that the MP915, like all Caddock models are conservatively rated for different qualities of mounting.
I cannot tell you how conservatively rated the parts are, but your temperature measurement in-situ at worst case power would tell you.
I recommend mounting the parts on your heat sink, applying worst case power for 15 minutes and measuring the leads at the point where they exit the resistor (the “fat” part of the lead, as this is a direct copper connection to the resistor element.
The maximum element temperature is 150C, so for a good design, I would think that a lead temperature of +120C or below would be a conservative design.
We look forward to being of service to you.
Sincerely,
Dave Anderson
Senior Applications Engineer
Commercial/Industrial Applications
dave.anderson@caddock.com
Tel.: +1-541-496-0700
Fax: +1-541-496-0408
Caddock Electronics, Inc.
High Performance Film Resistors
Caddock - High Performance Film Resistors
Regarding postage
Uriah,
I've 4 kits and various spare boards:
4 MYREFC KITs
6 Single PCB for MyREFC
5 DCB1 BOARDS
3 LDRs and Mounting Board
It seems that I'll need 2 shipping, is it possible to ship the two packets to different addresses?
I'm not buying only for me but also for other two guys.
Uriah,
I've 4 kits and various spare boards:
4 MYREFC KITs
6 Single PCB for MyREFC
5 DCB1 BOARDS
3 LDRs and Mounting Board
It seems that I'll need 2 shipping, is it possible to ship the two packets to different addresses?
I'm not buying only for me but also for other two guys.
Thanks Uriah
When I'd considered the R3 swap a simple high quality crossover resistor was in my mind, not Caddocks.
To me seem reasonable a 15W/30W resistor with a small heatsink but I'm not an expert.
When I'd considered the R3 swap a simple high quality crossover resistor was in my mind, not Caddocks.
To me seem reasonable a 15W/30W resistor with a small heatsink but I'm not an expert.
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