Multi-channel power amp build thread

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I've posted this on avforums already, but thought I'd also post a summary here and gather people's thoughts...

Since changing my stereo and home cinema layout, I'm now using a Marantz AV8801 pre-amp / processor to replace my ageing Sony STR-DA7100ES. I had pretty much decided to go down the Hypex UcD route as I love the sound they produced, and it struck me that there aren't any commercial solutions really made up for this. I know you can get single and maybe dual channel enclosures, but no one seems to make a multichannel enclosure housing amps, power supplies, etc.

So I set off on a design mission to come up with a chassis housing several channels, potentially up to 9, but now I've scaled it down to 7 - in a normal 19" / 445mm cabinet, 3RU high.

I had made some preliminary designs and had some enclosures built by protocase, a prototype manufacturing company based in Canada who allow you to design enclosures with their software and have immediate online quotes for fabrication costs. My initial design with them housed up to three UcD 400 modules and a single SMPS1200 power supply, all in a small clam-shell design. It works very well.

Design in software:
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After assembly:
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In place: 3ch UcD400 + 2ch UcD400 + 2ch Ncore
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The only problem with that design was that it gets rather warm to the touch as the chassis is used as the heatsink with the modules fixed directly to the case.

So if I were to expand this to a full size chassis, it's clear that I'd have to work on the cooling side as the chassis alone won't be enough to dissipate the heat of up to 9 400W UcD modules.

After speaking to various extruded aluminium and heatsink manufacturers and listening to their recommendations in terms of maximising efficiency and performance with just passive cooling (I don't want to add fans if at all possible), they've quoted me for some very nice black anodised aluminium heatsinks and sent me free of charge a couple of samples cut to different lengths: one at 40mm (if ever I wanted to make a single channel 1RU chassis) and one at 80mm for the normal multichannel setup.

I did some testing with them and they work very well - after driving a module quite hard for half an hour, the tip of the heatsink is around 45 degrees C, tip of the blue heatsink on the UcD module around 47-48. So it does a good job dissipating the heat.

This is of the smaller one where temps were a tad higher, just hovering around 50 degrees C.
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So back to the case design, I know if I can squeeze the modules and heatsinks in with sufficient ventilation around them, it looks like we're on :)

After playing around with various configurations, some more crazy, some more sane, I've ended up with this:

The heatsinks are fixed to the modules with some aluminium L-brackets
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The base of the L-bracket will fix to the chassis, so some heat will transfer to the chassis.

Putting them all together on the base of the enclosure, with power supplies fitted:
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Having an odd number leaves a space in the corner which will be used to place a PCB I've put together which controls the power state. I spent some time researching how to control the power of the amps as Hypex haven't really included that, and annoyingly, their "disable" is active high which seems a bit illogical to me (their SMPS can be turned into active low by an undocumented link - I had asked them!). I posted a thread on here and you helpfully directed me to ESP amongst other things, but I thought to myself: surely, it can't be that hard designing a basic logic circuit and sticking it on a PCB? :)

Designing the circuit would also allow me to include 12V triggers so the amp can be powered on by my processor, as well as including an obvious power button on the front. Might as well also throw in a 12V trigger output, so after some researching and playing around with the breadboard, I came up with this:

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With some help from you guys, I transferred the design to a PCB. At first, I tried very hard to get it on a single layer, but I think it's impossible with the VDD and VSS of the ICs. Maybe I could have redesigned it without ICs, but as it was working, I really didn't want to go back to the drawing board. As it turns out, the long thread on PCBway here convinced me to give them a go, and after some niggling issues (you can read about it in the other thread), I ended up with my PCBs :)

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With some components fitted:
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Which, for now, leaves me with the external case design. I'll admit I got a bit carried away with the design and rendering and making it look pretty. But the modelling really is an invaluable tool when it comes to checking things will fit, connections are ergonomically placed, etc. Also, getting a custom case made up isn't cheap, so getting it wrong repeatedly is rather expensive.

I did consider using Protocase again, but it turns out the cost for a larger case with all the holes was prohibitively expensive. And there are the extra costs with shipping and customs (I was stung when importing the earlier designs). So after speaking to some local fabricators, they've quoted me happy and have been very helpful in identifying the materials I can use. It turns out they make the enclosures for several broadcast manufacturers so their experience is second to none in these scenarios :)

Here's what I have for now (going for the minimalist approach):
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There's a chance this will end up as a small commercial product as I've had a lot of enquiries from those in the home AV / cinema domains. I've ensured I stick to all the safety standards as it would have to be CE approved if it ends up being a commercial product. Ironically, the toughest thing so far is trying to locate an IEC C17 socket - although several manufacturers make them, no one seems to sell them, only the C13 variant with earth pin. But as the design is fully double-insulated...

Anyway, enough ramblings. Let me know what you think, ideas, suggestions on improving it.

I'll post updates as and when they come along :)
 
Oh drat! Just noticed an error in testing the PCBs, I'd grounded the input to the optocoupler for the trigger out to the wrong ground (Gnd instead of VSS). So currently, opto is always on, always driving the 12V trigger out regardless of wheter the power state is on or off.
I'll try increasing R9 to see if it can drag the voltage low enough. Otherwise, it'll give me a reason for a v1.1 board where I will also increase the track seperation on the mains voltage side.
 
Hi, I think what you've done here looks very nice so far but I have one worry based in the pictures of your power control board that you have included above.

If you actualy want to get this thing properly ce marked it will need to comply with quite a few bits and pieces of legislation, one of which will be the low voltage directive for mains powered equipment. In here you will find that you need to observe fairly strict creepage and clearance spacings within the product which it looks like you have failed to do do on the power control board.

As a very rough guide (this is just off the top of my head and will need checking with the proper standard requirements) you need 4mm between your mains voltage traces (live to neutral, live to any low voltage sections, including your "ground" connection on the PCB).

This means that you will need to remove the ground pour around your mains traces, increace the spacing between the live and neutral traces and probably swap out you connectors for something which allows you to maintain the clearance values where they pins are inserted into the pcb.

Apologies if there are any nonsensical words in this reply but I've been having a bit of trouble typing this much on my phone.

Andrew.
 
Hi Andrew.

Thanks for your input - it is worth the effort on a phone

I'm aware of the directives, CE self-certification, etc.

As it stands, I'll need to make a second version of the board anyway following my stupid mistake on the trigger out...

I've been reading up about creep, etc, and the new PCB version will have more track seperation and a bigger gap for any copper pour. I'll post back when I've finished it and would welcome any suggestions.

Thanks again for your input :cheers:
 
Interesting. I wonder why it's discontinued? No sales? Too expensive? I don't fully understand their connections either: they say it's an amp, but provide firewire/usb (?) and a digital input when they say all signals are sent from the HTPC. Is the HTPC inside the chassis?

I've decided for simplicity to stick to just an analogue power amp, it's not worth me coming up with any integrated DACs.
 
New PCB design. This time, I've fully tested it!

Interestingly, the relay wasn't working properly on the first version which I thought was strange: being 400 ohm, it draws around 35mA and the optocoupler I was using was rated to be able to sink around 100mA, but just didn't work. I guess the relay's coil's inductance was causing problems?

New design is now with enhancement mode FETs acting as switches and it all works fine. The 12V trigger out can sink around 100mA providing I give it a beefy resistor: I made some tests shorting out the 12V to ground, and the 330 ohm 1/4W resistor I that was handy got rather warm rather quickly :D

Never under-estimate the vailidy of breadboarding a prototype! As it stands, I have a nice collection of geeky beer mats ;)

Also removed the pours from the AC side, and increased the seperation between tracks. It's around 2.5mm at minimum now.

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No, it's alive and fully working :)

It's progressed a bit since all the theory and renders above, I have some fully built enclosures now which retain the modular approach. My current one used in house is actually a hybrid setup with UcD and Ncore amplifiers providing 7 channels for my home cinema setup.

The control board has also seen further revisions improving on the design. I've also done another package more for single-channel / mono-block setups for a purer HiFi approach. They're based on Ncore500 units. It's a similar setup to what Boggit has done although he went commercial before me :)

I moved away from ZenitPCB and have redesigned the PCBs using KiCad as it has a far greater following.

I see you're in Caversham, just up the road from me. If you're interested, I'd be happy to come round so you can have a listen. I'm always keen to see how it sounds in a different setup :)
 
No, it's alive and fully working :)

It's progressed a bit since all the theory and renders above, I have some fully built enclosures now which retain the modular approach. My current one used in house is actually a hybrid setup with UcD and Ncore amplifiers providing 7 channels for my home cinema setup.

The control board has also seen further revisions improving on the design. I've also done another package more for single-channel / mono-block setups for a purer HiFi approach. They're based on Ncore500 units. It's a similar setup to what Boggit has done although he went commercial before me :)

I moved away from ZenitPCB and have redesigned the PCBs using KiCad as it has a far greater following.

I see you're in Caversham, just up the road from me. If you're interested, I'd be happy to come round so you can have a listen. I'm always keen to see how it sounds in a different setup :)

I found this thread whilst researching the building of a multi channel power amp. I don't have a 'proper' home cinema set up in Caversham; I'm in the process of buying a larger house where I'd like to get back to having 6/7 full range speakers. If we can sort something for next month before the house sale/purchase completes and I move to Manchester, you can try an amp in my 2 channel system if that would be of any use to you?
 
I found this thread whilst researching the building of a multi channel power amp. I don't have a 'proper' home cinema set up in Caversham; I'm in the process of buying a larger house where I'd like to get back to having 6/7 full range speakers. If we can sort something for next month before the house sale/purchase completes and I move to Manchester, you can try an amp in my 2 channel system if that would be of any use to you?
Sure Alex, why not? :) Do you have a pre/processor? Drop me a PM when convenient and we'll sort something out :)
 
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