120mm tall? I would not use that chassis unless you has 16 ohm speakers and don't like class A bias.
Consider this one QUEENWAY WA68 all aluminum pure stage power amplifier case Chassis 430mm*150mm*412mm 430*150*412mm-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
I use it for a F5 turbo on +/-32V at around 1.5A bias.
Edit: noticed you're in Europe, so Zen Mod's suggested Italian case might be cheaper including shipping.
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Hi! So, this means about 100W dissipation. How hot is the heatsink at normal room ambient temp?
Temperature is about 32 degrees over ambient. I designed my own PCB to spread out the transistors a bit, but the placement is still a bit too much in the middle.
As in Taiwan the summer is rather hot, I might need to lower the bias a bit in the spring.
I have to say cases from China have very nice panels fit and finish, let's say not worse than the widely popular European option. Now if the shipping costs and duties are too different then that may be a different story
This is an adult enough size I believe for F5 aluminum class A amplifier chassis /home audio amplifier case (size 330*150*326MM)-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
I actually used one similar to neptune's link for F6, but 80mm tall. It was a bit too small, but workable
Think there are at least 2 ways of selecting a case:
1) Single project you will keep unmodified for a long time. Buy the smallest case that still works. This will be the most cost effective.
The F5 will work in a case with 300 x 85 mm heat sinks as absolute minimum. It will run hot (around 55-60 C) but works. If too hot for your taste, you can reduce the bias a bit, maybe to 1A. Sound will be great. Or go a little larger.
A potential issue with any small case is the electronics being close to the transformer, resulting in (more) hum/buzz. This gives an amp which has very good performance when you remove one input, but might buzz when both channels inputs are connected. Worst case, with high efficiency speakers this buzz might be audible at the listing position.
If the standard solutions of reducing buzz don't work well enough you might need to get a smaller transformer (or a bigger case...)
2) Want to try different class-A designs in the future? Then buying a small case is not a great idea as you probably end up buying multiple cases (don't ask me how i know...). If you like to tweak, buy the biggest case you can afford. In a large case, less chance for buzz problem. You might even go for dual mono config, eliminating the buzz problem altogether.
1) Single project you will keep unmodified for a long time. Buy the smallest case that still works. This will be the most cost effective.
The F5 will work in a case with 300 x 85 mm heat sinks as absolute minimum. It will run hot (around 55-60 C) but works. If too hot for your taste, you can reduce the bias a bit, maybe to 1A. Sound will be great. Or go a little larger.
A potential issue with any small case is the electronics being close to the transformer, resulting in (more) hum/buzz. This gives an amp which has very good performance when you remove one input, but might buzz when both channels inputs are connected. Worst case, with high efficiency speakers this buzz might be audible at the listing position.
If the standard solutions of reducing buzz don't work well enough you might need to get a smaller transformer (or a bigger case...)
2) Want to try different class-A designs in the future? Then buying a small case is not a great idea as you probably end up buying multiple cases (don't ask me how i know...). If you like to tweak, buy the biggest case you can afford. In a large case, less chance for buzz problem. You might even go for dual mono config, eliminating the buzz problem altogether.
Hi all! Thank you for the replies. It would be a lot easier if the Chinese manufacturers would share the thermal resistance for the heatsinks, but they don't even have an idea about what it is, not to mention the actual value itself. Based on my calculations and approximations, a heatsink that is 150mm long, 50mm tall (with a 5mm base), and 350mm wide is sufficient for a 100W if it has about 25 fins. This is almost exactly the same value, as shanghai2004 mentioned, so my calculations are not as incorrect as i have thought. But i like safety, and i want to reuse the case for more projects in the future (maybe a Pioneer A-51 DIY rebuild, even it does not need a big heatsink), so i think i will end up with a slighly bigger one.
I wish they'd display the sizes in inches. Also want to know if they're anodized. They're using more an more powder coated finishes these days, and it's hard to tell from photos.
I think you have overlooked how the Rth s-a is specified.
Let's start with a 0.75C/W heatsink that has been specified for a DeltaT of 75Cdegrees.
If you input 100W spread evenly across the whole backplate the temperature of that backplate rises to 100W*0.75C/W = 75Cdegrees above ambient.
If during this test the ambient temperature (Ta) is 25degreesC, then you now know that the backplate sits at 25+75 = 100degreesC.
The temperature of the devices transferring the heat to the backplate must be hotter.
Lets now input 20W from 2devices located near the middle of the backplate.
Using the standard formula: DeltaT = Rth s-a * Watts * De-rating Factor,
then you will find that the the predicted DeltaT is not 0.75*20 <> 15Cdegrees.
DeltaT will be much higher.
You must take account of the De-rating Factor. I will assume it is 1.5 for this example.
DeltaT = ~0.75 * 20 * 1.5 = ~22.5Cdegrees.
For a rise of only 22.5C my first guess at DF=1.5 is a bit low. I'll try 1.6 to see the next iteration of the prediction.
DeltaT = ~0.75*20*1.6 = ~24Cdegrees. (these DF tables are in the manufacturers' datasheet, but they take some finding.)
Now we use that prediction to arrive at a summer season heatsink temperature
Ta =32degreesC, DeltaT = ~24Cdegrees. Therefore Ts= ~56degreesC
The two devices have an Rth c-s value of 0.5C/W and each dissipates 10W.
therefore Tc = 0.5C/W*10W + Ts = 5 + 56 = 61degreesC.
Now you look up the device datasheet and determine the temperature SOA de-rating of the device because it is operating above 25degreesC.
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Zfoil
The latest v3 pcb has zfoil holes for R3, R4 10ohm resistors. But BOM says they needs to be rated 1w. But zfoils are 0.4w rated. Do you think it is works?
And i have 5k foil trimmer resistor also rated 250mw, as far as i read from AndrewT post they are rated 500mw Do you think they are work?
Best Regards...
E.OZDEN
The latest v3 pcb has zfoil holes for R3, R4 10ohm resistors. But BOM says they needs to be rated 1w. But zfoils are 0.4w rated. Do you think it is works?
And i have 5k foil trimmer resistor also rated 250mw, as far as i read from AndrewT post they are rated 500mw Do you think they are work?
Best Regards...
E.OZDEN