DIY Amp build

mattkhan

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having just completed my 2019 projects (better late than never), time to move onto the 2020 lockdown build :)

recently arrived

3 x Hypex UcD180HG HxR
1 x Hypex SMPS400A180

2 x Hypex UcD400HG HxR
1 x Hypex SMPS1200A400

5 x Neutrik XLR chassis connectors
5 x Neutrik speakon chassis connectors
1 x powercon connector

next up, an amp case (if modushop in italy is still open for business, might be optimistic but they say they are still going so....)
 
Lockdown will prolly be over by the time you get the kit!
 
Hi Matt,
Very interested to see these come together & what they end up costing you?
 
about €1k for the amps & power supplies, £90 for the connectors, case is ~ €140 (inc getting them to drill the back panel as that bit sounds like quite a pain). No doubt there will be sundries along the way that add a few quid here or there.

reasons to DIY are 3 fold

- I need 3 channels with limited power & all commercial hypex amps these days are based the mp models (which are generally 2 channel units)
- I need the case to fit in 2U
- QC from most of those vendors seems a bit ropey

the 2U requirement led me to the older UCD series, performance still looks good enough to me though & even 20W fed into a CD will be enough to deafen me

1585475890041.png

20W is ~110dB so more realistic max levels for me are in the region of -8 hence a peak of about 1.5W and average of 0.015W

0.01% is -80dB btw


I intend to mod the UCD180s to reduce gain from the default 26dB down to 13dB which should improve performance some more. It means going from requiring ~0.6V to ~2.8V to deliver 20W which also makes it easier to put a hard limit on the volume (i.e. protect ears!)

I'll probably do the same to the UCD400, they'd require ~7.7V to reach 300W which is coincidentally exactly the peak output from my audio interface (+20dBu)

The 400s will be used for surrounds btw

I might subsequently build another 3 channel amp for my mids (or a 6 channel amp and sell the current one) but until then I will use the 6 channels of my cinepro for the mids and woofers.
 
Very nice Matt & extremely satisfying when you get great results from something you have made & fine tuned to your specific requirements :thumbsup:
P.S. Still very grateful for the heads up on the Faital pro drivers, I absolutely love the sound of my bass cabinets.
 
Can i say i envy your technical expertise? :)
Good luck for this project, i will follow it with great interest ...
 
Found the resistor required for the gain mod, is a truly tiny smd resistor so removing that should be fun. Need to find some random circuit board to practice on first.
 
I think I've worked out how to lay it out and wire it, comments welcome (particularly from anyone with actual mains electricity experience)

2U case - Slim Line 02/350 2U 4mm NERO

internal layout

1586079466448.png


2 UCD400 on the left attached to one of these https://uk.farnell.com/fischer-elektronik/sk-85-75-sa/heat-sink-75mm-1-2-c-w/dp/4621852

3 UCD180 on the right attached to one of these https://uk.farnell.com/fischer-elektronik/sk-47-75-sa/heat-sink-75mm-0-45-1-05-c-w/dp/4621888

amps mounted on the chassis base via some standoffs https://uk.farnell.com/ettinger/05-34-407/standoff-round-female-nylon-7mm/dp/2691449 (base is only 1mm steel so seems a bit thin to actually tap a thread into)

respective power supplies placed behind them

https://www.neutrik.com/en/product/nc3fd-lx-bag and https://www.neutrik.com/en/product/nlt4mp-bag used for chassis connectors, aligned directly behind the respective amps

powercon connector on the far right hand side - https://www.neutrik.com/en/product/nac3mpa-1

DPST switch on the front to provide a user accessible power switch, this needs to handle a chunky inrush current so I think https://uk.farnell.com/marquardt/1932-3112-02/switch-dpst-ip65-black-i-o/dp/1839503 will do the job
 
need to sketch out the wiring but I think it is basically

- powercon ground to chassis using some locking washer
- powercon live to inline fuse (not sure what rating this needs to be, need to work that out) placed v near the powercon then onto switch
- powercon neutral to switch
- switch out to some terminal block then split onto each smps
- smps to amps
- amps to chassis connectors

I think this is all that is required to make it safe to use

tightly twisted wires for all signal/ground pairs (so powercon to switch, switch to smps, xlr to amp, amp to speakers), try to keep high level and low level signals apart (though that looks pretty tricky in reality with this many channels in a small case) & insulate all the things so no bare connectors/wires are visible anywhere

one thing I'm not sure of is how to determine the loop area within this wiring scheme which I gather I need to minimise, something to look at later
 
Wow building amps now Mat, now that’s progress 😂
 
chassis arrived today, order to delivery in under a week so it's got here before the assorted connectors I've ordered to assemble the thing :suicide:
 
realised the chassis is steel top and bottom but anodised aluminum front/back/sides so need to think a bit more about how to safely/easily ground the entire thing
 
I thought making speakers had some boring bits, little did I realise that drilling and tapping holes many small holes in metal would trump them by some distance :suicide:

doesn't look like much but holes drilled in the base for the power supplies + a boat load of holes drilled and tapped in the heatsinks to attach it to both the chassis and the amps

1587323121114.png
 
Hi- Ideally the mains supply should be kept away from amplifier wiring, esp. inputs - you say there will be a high inrush, which can be bad for contacts, so you are beefing up the switch....
However, there may be an alternative:-
Introduce a low-power PSU ( about 12v at 1A - a tiny encased s-m psu will do).... a more modest panel-switch and relay, to switch on relays for the main supplies. Ideally after small delays - reducing the inrush and far less likely to blow fuses.
If there is any interruption to the supply, then the relays will drop out and the process must be repeated. Delays can be by RC if the power relay coils are 12v - or by using some logic - I'd suggest the delays should be about quarter-second, or longer.
Should you want to reduce the switch-on surges even more, then the individual relays could be Zero-volt types, so the amplifiers are powered from the mains zero-crossing - If there are three amplifiers you could have a front=panel LED =RGB, which will show "almost white" when all are on.
Ideally the mains input should be split 4-ways with 2 fuse ratings: 1A for the control PSU and whatever rating is appropriate for the amplifiers. A neat trick is to use a 6-way fuse-strip, so you can include a spare of each rating. As you know these should be ceramic fuses.
Should you want to make even more of the switch-on, then the amplifier outputs could be controlled by relays as well. A resistor is put in series with each load, until a second or so after the amplifiers have settled. Unless the amplifier is very highly rated, modest wirewound "power" resistors can be mounted on the chassis, with little or no heatsink, since the power is only being dissipated for a little more than a second or so. I guess the speakers should be receiving about 1/20 or 1/10 normal power briefly, until the relay shorts out the resistor - Also, the Mains / Speaker relays are kept separate - like opposite sides if the case. They'll be different types, but it's best to keep their wiring well apart....

Good Luck.
 
Powered up tonight, nothing blew up and I didn't kill myself so that's nice :)

Need to test noise levels next

The LEDs on these are absolutely blindingly bright btw, crazy
 
Ran a quick test with a spare cd connected, some hiss audible at about 1' but inaudible beyond that. CD tested is 5-6dB less sensitive than the ones I use so still might have to do gain mod.
 
Ordered another audio interface today (a motu ultralite avb) as naturally I need 13 channels out but only have 12 on the current interface :facepalm:

Hopefully arrive by the weekend so might be able to try it out then

I then need to get time to pull a speaker out of the LCR and measure it in the garden to get data for (active) crossover design.
 
I think I might build another amp, a SMPS3k400 powering 3 NC400s to drive the mids on the LCR. This would allow me to use my cinepro bridged to drive the woofers. This is most likely massive overkill but it seems a bit pointless building another 3 channel amp to replace the cinepro when the cinepro is more powerful. Only downside to the cinepro is it is massive (5U high) so takes up loads of space.
 
tested all the channels & found noise level was a bit variable, rewired taking much greater care with twisting and signals paths and that improved matters. I then discovered one was suffering from increased buzz compared to the others which turned out to be a slightly dodgy pin 1 soldering on the xlr input. Fixed this and now they all have similar noise levels.

I then tested driving some speaker and these really can go v loud, now thinking I have to do the gain mod *and* add an xlr attenuator on the input if I'm going to feed a 113dB sensitive CD from a +20dBu output otherwise the risk of deafening someone via fat finger error is just too much!
 
the thought has occurred to me that I'm spending time and money arriving at a unity gain solution, why do I even need an amp?
 
final layout of the interior which kept power away from signal cables as much as possible

hindsight says

* cut the signal cables a bit shorter
* use a separate speakon output per channel (actually I did plan for this but there was an error with the dxf file used for the back panel so I ended up with 3 connectors)

1588448733224.png
 

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