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Old 22nd November 2013, 04:35 PM   #1151
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I looked at the range at Conrad Heatsinks, and was thinking of their longer, lower M35-50
4" deep fins * 14" long * just 2" high.
It's 0.43 c/ watt

Now looking for a nice case to accommodate the two boards & heat-sinks
My arithmetic gives a minimum internal size of:
250 wide (the width of two PCBs & two heat-sinks) * 350 deep (the length of the heat-sinks) * just 55 high
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Old 22nd November 2013, 04:59 PM   #1152
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Fetzilla case options

At Chassis case item

With the boards mounted side to side, and a series of holes drilled over the heatsinks, these look good:

a) the 80 mm high PRAL-47328R
Rounded corners look good too my eyes
But unnecessarily wide heavy & expensive

b) the 1 unit 65 mm high PRAL-1
Finish either natural or champagne
Or the similar but a little smaller PRAL-1a

At Audio Catalog
The AL-421B
Supplied with a power switch, RCA sockets and an IEC socket
In black or "silver"
$90

And the "AL-Dark Knight"
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Old 22nd November 2013, 09:48 PM   #1153
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Or if the heatsinks are 300 mm long, and the layout is the normal one with heatsinks on the side, the absolute minimim internal space (with Conrad's fin depth of 48 mm) is 300 wide* 234.

The computer motherboard ATX form factor is 305 * 244, so a PC case may work

if the aim were to have a case of minimal size, this would just fit:
S 3207 Aluminum Amplifier Case Enclosure Amplifier BOX PSU Case | eBay

Do the heatsinks sit right up against the boards?
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Old 22nd November 2013, 09:56 PM   #1154
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Damn. Forgot the space for the transformer(s)

Better to get them, lay it out/ build it then get the case

Mike, what rating and model is your trannie?
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Old 22nd November 2013, 09:57 PM   #1155
AKSA is offline AKSA  Australia
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You are stressing the heatsink, within limits certainly, but it's working hard.

You MUST ensure that the fins can be exposed to the external of the case.

Otherwise, you can halve the size of the heatsink if you use forced air circulation, and leave it inside the case.

Thermal management is crucial on a Class A SS amp. Get it wrong and MTBF drops like a stone. It is related to the Arrhenius Theorem, which related to chemical reactions as well. Increase temperature 11C, and MTBF drops HALF.

Transformer PER CHANNEL should be at least 160VA.

Cheers,

Hugh
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Last edited by AKSA; 22nd November 2013 at 10:00 PM.
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Old 22nd November 2013, 10:06 PM   #1156
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Hi Hugh

Thanks for the correlation between heat and MTBF

Im intending to drill lots of holes above and below the heatsinks, and mount the case on feet at least 10 mm high, to facilitate convection

My understanding is that if I keep the C/ watt at 45 or lower, it should be ok

I just found pics of the inside of ajst2duk's case. So the heatsinks are joined to the PCB's * underneath? I'd been thinking of them mounted on the * sides . . .

Cheers

Last edited by otto88; 22nd November 2013 at 10:11 PM.
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Old 22nd November 2013, 10:20 PM   #1157
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Quote:
Originally Posted by otto88 View Post
Hi Hugh

Thanks for the correlation between heat and MTBF

Im intending to drill lots of holes above and below the heatsinks, and mount the case on feet at least 10 mm high, to facilitate convection

My understanding is that if I keep the C/ watt at 45 or lower, it should be ok

I just found pics of the inside of ajst2duk's case. So the heatsinks are joined to the PCB's * underneath? I'd been thinking of them mounted on the * sides . . .

Cheers
You might be referring to the "during construction" photo where I had the PCB topside for final wiring etc - the heatsinks are actually on their sides with vents above and below in the case allowing full convection airflow
Here is a photo of the PCB's + Heatsinks as mounted
AJ
Click the image to open in full size.
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Old 24th November 2013, 02:19 PM   #1158
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Thanks AJ

Is this the normal orientation of the boards to the heatsinks - underneath?
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Old 30th April 2014, 06:49 AM   #1159
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Yes, Otto, I sell the case in fact for my larger NAKSA amps. Each heatsink sits atop a long rectangular slot which permits air circulation from beneath the case - so it's held off the base with four 12mm rubber feet.

This is a very long delay - my apologies!

Hugh
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Old 1st July 2014, 03:24 PM   #1160
ro9397 is offline ro9397  United States
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FETZILLA availability?
Price for 2-ch?
Power into this load? Flat 16 Ohm above the bass range, 12 Ohm minimum, easy to moderate phase angle

Sensitivity 93 dB actual: I am driving the speaker now to any desired level with amp making 50W into this load (16 Ohm).

I appreciate members saving me the time required to read all threads. Please summarize general consensus, overall sound quality of FETZILLA compared to AKSA 80 and AKSA 100 considering my specific application (less than average power requirements).

In room bass cutoff is high 30 Hz range. (For first octave I employ four piece distributed sub system ala Gedds/Welti/LeJeune, 1kW active, crossed high 30s). The main amp has little to no first octave requirements.
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Last edited by ro9397; 1st July 2014 at 03:34 PM.
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