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Old 25th November 2003, 06:03 PM   #1
D3 is offline D3  England
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Question heat sinks

Hi out there.........this is my first posting....I am a Brit hi-fi nut who back in the 90's built amp o2.....Ben Duncans offering.....best investment I ever made....now I have been eyeing up the A75 for a while and I am going to give it a go!!!!

However, I am an architect not an electrician..........so I will need plenty of advice..........at a fairly basic level. I have gathered that one of the major issues with the A75 is heat sinking......now I am after a really professional finish..........can anybody advise me where I can get hold of suitable heatsinking.....hopefully in the uk.
Any PDF guides on A75 or other info would be most welcome......

Will the A75 suit a passive preamp.......

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Old 24th December 2003, 04:49 PM   #2
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Default Heatsinks

I got mine from Redpoint Thermalloy - see the Pass DIY web site.
Their new name (I think) is

Aavid Thermalloy
Cheney Manor,

Phone +44 (0) 1793 537861
Fax +44 (0) 1793 615396

I found they were rather less expensive than some of the others.

I got a 150mm lengths of EA150-1 which cost 26.58 + VAT each, black anodized. I got 3 (don't ask, its complicated) and the post and packaging was 15.

One of these (300mm by 150mm by 80mm) is just about enough for one monoblock channel of the A75s with no fan, I hate fans. 200mm would allow the full bias current at a guess but the 4U boxes limited me.

The old Redpoint catalogue I have is full of useful info on how to calculate heatsink size, including if you want to use a fan (yuk) how to do forced air cooling calculations.

Obvious notes
- with convection cooling, a pair of 1*C / Watt heatsinks next to each other does not equate to a 0.5 *C / Watt heatsink.

- when you do the sums, remember to add in the thermal resistance of your transistor package insulators, unless you use plastic package transistors. From memory I used SilPad 3000 but they are expensive and very soft = they damage easy, very easy with a TO220 package which has one screw rather than the (TO3 which has 2). Its very easy to get the corner of the transistor digging through them if things are not 100% straight. Think how you will mount your transistors and gate / emitter resistors and how you will assemble the amp first. The way I made mine looks easy but is in fact a bit of a pig.

S Goodwin
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Old 24th December 2003, 05:01 PM   #3
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Default Heatsinks

Just to clarify... I should have said my posting in the Gallary on Mr. Pass's DIY site.
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Old 24th December 2003, 05:16 PM   #4
Coulomb is offline Coulomb  England
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Why build an A75? Why not an Aelph-X for instance?


Former Brit.
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Old 24th December 2003, 05:32 PM   #5
moe29 is offline moe29  United States
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i'd reccomend reading everything on the PassDiy web site.

The Zen articles will get you up to speed on the Pass designs.

A Zen amp or an Aleph amp would be easier at this point to build
than an A75...
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Old 24th December 2003, 05:32 PM   #6
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Default passive preamp and heatsinks

Two more heatsink suppliers which I've just dug out the catalogues for are

IMI Marston Ltd. +44 (0) 1902 397777 in Wolverhampton and
ABL (Aluminium Components) Ltd. +44 (0) 0121 789 8686 in Birmingham

IMI do some very cool (if a bit expensive) heatsinks that lock togeather to make a box.

= =
= =
= =
= =

ABL do some MONSTER heatsinks. 100 Series High power heatsinks 84mm deep by 300/400/500/600/750mm long !! Length whatever you like I guess. Partcode 195AB/196AB.../199AB.

These catalogues are a bit old though... like 5 or 6 years...

Re passive pre-amps, I found my A75 sounded better driven ballenced with an active preamp.

If you go passive unballenced you may be OK but ballenced the input impedance of the A75 is a bit low.

My DIY preamp uses a pair of OP27 op-amps with a BUF634 for each channel. I think the BUF634 data sheet has an example of how to do this. I may try a OP627 at some stage.

Some opamps are a bit unstable when driving a cable due to the capacitance direct on the output. The use of the BUF634 makes the perfect cable driver.

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Old 24th December 2003, 05:34 PM   #7
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hey, another architect. welcome to the club. what is it about us architects...i think we're born dilettantes.

i second the aavid thermalloy route. although i haven't bought any heatsinks from them, i have used their online worksheet to help calculate heatsink profiles. it's really useful.

/andrew - not a brit, but i play one on tv.
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Old 24th December 2003, 05:34 PM   #8
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I am currently building my A 75, 2*100Watts the PCboards are ready, got 48 TO3 and 750 VA toroids ; facade and back plate ready ...

And waiting for the heatsinks that I expect for the 6 january 2004 {I had 10 weeks of delay!!!}

I have choosen ThermaFlo EH 1126 in 8" length
and will put 6 on each side of the "enclosure"
exactly they are the sides of the enclosure.

It will be a good prototype before the X

PS: I ordered Aleph-X Pcb's for next project...

Merry X-Mas

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Old 24th December 2003, 06:33 PM   #9
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Default Heatsinks et al

I would second reading all that is to be read on the Pass DIY site. Do not think the A75's are a quick build. Its a lot of work.

In theory you should be able to make an A75 with a soldering iron and a multimeter but I was glad of my scope, audio test set, multiple multimeters, temperature probe, dummy loudspeaker test load, you get the picture.

I can not comment on the ALEPH-X but the A75 is the best amplifier I have encounted to date. I think it is better than the French single ended design from LeLed magazine I made, I guess due to the extra power and grip on the speakers - this amp is very good, very very good.

Make sure you use anti-static protection - its FETs - and go for it.

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Old 29th December 2003, 07:19 AM   #10
D3 is offline D3  England
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Hi, thanks for the great replies........just had a good if not fattening Christmas!!

I have decided to go with the Aleph X there is alot of interest on the site and I think there should be very good support.

Your advice on the heatsinks is great!!!

As for being an architect, well I guess I hate comprimise, I am sick of compromising design........so here's my chance to go for it! I think some of the designs people have come up with are great!

I am fortunate my brother.... used to work for Heybrook Hi Fi in Plymouth, he was responsible for developing their P3 power amps. So, hopefully I might stand a good chance of getting through this! (P.S. If your interested he got to the finals in Robot Wars......with Hellbent......you'll find Hellbent on the web if your interested.)

Many thanks for the response.....have a happy new year
D3 Bolton Lancs.
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