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'Plate Amplifier' Design

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audiomik View Drop Down
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    Posted: 11 July 2013 at 3:47pm
A new thread to discuss some of the issues associated with designing a 'Plate Amplifier' with an Analog Xover and other filters etc, specific to the Cab design.... to build into Cabinets.

Am not going into detail yet of the actual circuitry which might be suitable, but looking at how to provide Heatsink blocks of at least 1º C per Watt three times will be a good starting point.
This equates to a single sheet of 255 x 255mm 3mm Ali mounted vertically in free air with a centrally mounted heat source.
With only one side 'open' to airflow when mounted into a cab, then something more complex will be necessary.
Three sections would be appropriate, two for a Low frequency (Bass) Amplifier and one more for the HF (Treble) Amplifier which will be of lower Power output driving a Compression Driver. An additional fourth single section if it is a three way design but the same type.
250 Watt Bass and 150 Watt HF Power as a starting point perhaps which should 'cover' many cab designs, consider Bass being 'Mid' for a Mid-Top cab as well.
Power outputs may be increased by increasing the number of Heatsink 'blocks'

A fan cooled tunnel is possible, but convection cooling for Class AB Amplifier(s) would probably be more suitable should Power Output be within suitable limits.

So anyone have any ideas on the shape of cooling fins to optimise for both Vertical and Horizontal convection cooling - so as to have a self powered cab which can be mounted in each orientation?

Also, convection cooling is probably a good idea as should a self powered Cab be used for Hi-Fi or Studio Monitor applications, then not having fan noise would be an advantage.

This really needs to be able to be built using "stock" components or extrusions, without machining, so as to be Diy-able

Mik

PS: this is a follow-on for a suggestion of having an SP Amplifier in a previous thread

Edit: add dimensions to 'Ali sheet equivalent Heatsink

Edited by audiomik - 11 July 2013 at 3:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 6:59am
well, over a week since I posted this question, 100 views, and no suggestions

Doesn't anyone else on here still build Amplifiers for occasional 'specialist' applications?

Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nitz V1505 Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 7:53am
Vertical fins is a must on a plate amp without a fan. I suggest mounting the plate amp onto a square cutout/recessed panel on the speaker box. Attatch it using t nuts so you can rotate it to suit the speaker orientation.
LET THE BASS ROLL LIKE THUNDER
& THE TOPS LIKE LIGHTNING.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GEB Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 8:22am
I would personally recommend one like this for 'any-way' round orientation:




Edited by GEB - 21 July 2013 at 8:24am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 8:42am
Nitz V1505
thanks, take it that you are suggesting something like this:
Schaffner HEATSINK WA210B from RS

Firstly I think that the cost will be prohibitive given small numbers of builds and am looking to not have to do any modifications for orientation so as to have a much more 'universal' solution.

At present, a form of 'layered sandwich' using Ali spacer blocks and flat plates is a suggestion from elsewhere which might work in both orientations?
However it is quite a lot of metalwork, at least for a prototype, but the materials cost looks promising.

Something like 3/8" or 1/2" thick 2" x 4" blocks should be more than enough for the central spacers and possibly a mount for the Semiconductors using stock Tee section - depends on packaging.
This would give suitable spacing between 1/8" plates of say 8" square, which should then work in either horizontal or vertical orientation of the cabinet.
Would have to fabricate a sample or two so as to assess the thermal characteristics??

Anyway, I've set a parts budget for this at £125 to start with, including all of the electronics, so will have to see if this is realistic!

Mik    

Edited by audiomik - 21 July 2013 at 8:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 8:48am
Originally posted by GEB GEB wrote:

I would personally recommend one like this for 'any-way' round orientation:





Was my first thought!
what is the thermal characteristic and unit cost?

Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GEB Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 9:06am
Sorry Mik no idea yet, was just thinking of your orientation problem for starters.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote madboffin Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 10:49am
Commercial heatsinks are always extremely expensive, one of the major cost items in any piece of electronics that uses them.
For a self-build project I think DIY would be necessary, but then it has to be designed it to be easily made with no specialized metalworking tools.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Muckerbarnes1 Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 11:43am
That looks like a chip heatsink. i.e. 50mm square (ish). The idea of a 'fingers' heatsink is great for orientation, but to get one off the shelf for no money would be difficult. I've had large ones cast before, and it's an expensive pain.
 
A plate and large diameter spacer system could be easy to make. It could also be easily squashed.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 1:30pm
Re: "A plate and large diameter spacer system could be easy to make. It could also be easily squashed."

Perhaps additional support pillars at the corners and/or spaced along the edges of the plates could reduce damage?

Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Muckerbarnes1 Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2013 at 10:39pm
Pressed/folded could be a way to go. So there is a first flat plate with o/p devices mounted, and an arrangement of bent plates, like a Z shape, with crush support.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2013 at 7:02am
Originally posted by Muckerbarnes1 Muckerbarnes1 wrote:


Pressed/folded could be a way to go. So there is a first flat plate with o/p devices mounted, and an arrangement of bent plates, like a Z shape, with crush support.


Malc
probably something for some company or someone with a well equipped metalwork shop to do as perhaps part of a Kit, but for small numbers to be made by individuals with limited metalworking facilities then the 'plates -n- spacers' looks practical.

Have to visit our local Metal Stockist for a few bits and pieces today or tomorrow, so will have a rummage in their 'off-cuts bin' for some bits of Ali to try a few things out

Mik
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