P3a Heatsink Thoughts

[audioferret]

Please help me with selecting a Heatsink for a P3a.

Loudspeaker Supported:
Mass Loaded Quarter Wave Transmission Line (Custom)
Active 3-Way Crossover (Project 9)
2 P3a Amps (low and Mid)
1 P3b Amp for high

Drivers:
Low MLTL - Vifa MG18WK09-04 Driver (Madisound)
Sensitivity 90.5, 4ohm impedence

Mid - Sealed Enclosure on top
Vifa MG10MD09-08 Midrange
Sensitivity 88.5, 4 Ohm

High - Hi Vi RT1L Circular Ribbon
Sensitivity 88, 4Ohm

Amp Components:
Standard P3a Setup from ESP website
150 VA, 30/30 Torroidal Transformer (713.302 from toroid.com)

The Heatsink I am considering is the E1162 from thermaflo.com
http://www.thermaflo.com/

There are 14 fins, each 1.5" high.
The HS is 4.56" wide and I am targeting about 4" in length.
On the ESP HS calculator that gives me about 1.0315C/Watt.

Does anyone see any flaws with this arrangement?
- I am not so much concerned about cost, but more about sound quality. I am having trouble determing what size heat sink I will need as this will be used in a three-way MLQTL. By the design, each driver should need a bare minimum of power.

[paulb]

National has a calculator available. A search on this site should find it if you can't find it yourself at www.national.com .

[Greg Erskine]

hi audioferret,

I have a standard P3A (one stereo pcb) into 4 ohm speakers and I use one 0.37C/watt heatsink. The HS only gets sightly warm with the recommended bias after many hours of normal playing.

BTW: For 4 ohm speakers I think Rod recommends a max of 35vDC (i.e 25-0-25 toriod).

Hope that helps.
Regards

[audioferret]

Dude,

Where did you get your heatsink? When you say "one" is that one for each board, or one for both boards? How is that laid out in your chassis? I would like to use the heat sinks for the R+L side walls, but I can be flexible.

[Greg Erskine]

ferret,

The HS is the last one, here:

http://www.conradheatsinks.com/products/single_f.html

This pic should answer your other questions.

[AKSA]

Conrad's the go...... very good heatsinks.

Nicely made, Greg, neat job!

Cheers,

Hugh

[AndrewT]

Hi,
at 1Cdeg/W and 150VA both your heatsink and transformer are on the small side.
On 50Vdc rails P3 can produce about 200W into 4 ohms and if you want good bass your supply should allow operation into 2 to 2.5R without sagging excessively. This requires a transformer between 300VA and 500VA per mono channel 500VA to 800VA for stereo or 2 channel.
On 37Vdc your power ratings are reduced by about half but if you go towards the lower end then the regulation of your transformer increases and gives a poor PSU with again sagging voltage.

Your heatsink for domestic ClassAB should be able to dissipate about a quarter your maximum output or for party/PA use about 60% of maximum output. so you are in the range 25W/50W domestic and 60W/120W PA.
At these levels of dissipation your heatsink/s are going to run at least 25 Cdeg above ambient when listening to loud music on 4 ohm speakers with 37Vdc PSU rails and even worse for the other options.

[Greg Erskine]

Thanks Hugh,

I actually bought the PSU, heatsink and Toshiba output devices from someone around the Melbourne area. I finished building this one a bit after my AKSA so there may be some similarities in layout.

ferret,

As Andrew pointed out you may need to think about your transformers, those toriods I used are 25-0-25 160 VA.

Regards

[audioferret]

That helps so much, thank you!

This site rocks, you guys rock...

Rock on!