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+5vDC fan for cooling, how best to electrically isolate

IWC Doppel

IWC Doppel

pfm Member
I have been modifying the power supply on the analogue board on a naim AV2 using the transformer from an XPS and this will result in a lift of pre reg DC supply to the board LM317 and LM337 regulators. So I will move from a pre reg DC supply from +-20V to +-24V when the post reg supply is +- 15V. I have ordered some copper pads to add the the back of the existing heat sinks to help, which I will nylon bolt to the heat sinks. But want to keep the unit cool, so want to add a small fan to help the temperature rising too high internally

I can pick up a 4.3V DC supply near where I will mount the 5V fan (used to supply the only lightly used digital board). Other than say a 0.1uf cap to GND on the +ve side of the fan any better ways to isolate any electrical noise, which may be no issue at all but I don't want to realise it sounds worse when the fan is running ?
 
I suspect that the acoustic noise will be more of an issue than the electrical. But one way to test this and find out how much this fans runs assuming that it is operated from a temperature sensor is to run it temporarily from a separate remote power supply which could be a wall wart.

If you find that it only runs rarely you could set up a power supply which uses batteries?
 
How much power does the AV2 actually use though? It's only a preamp with some extra simple processing. An extra 4V at a low current will probably give naff-all increase in heat production. The existing heat sinks might be fine, have you actually checked temperatures before you start adding fans and copper pads etc?
 
The LM317's with the stock 20V in are around 50 degrees when in stand by, difficult to measure in situ with signal through. Perhaps just adding the 20x20x1.5mm copper pad will be enough, I could also double up and effectively have a 3mm copper pad.

I will be moving from a 5V delta to 9V delta

The AV2 does run quite warm compared to anything else in my set up part from the Lumagen which has a fan. Not sure what the 'ideal' temperature is for an LM ?
 
50C in standby? Do they actually have any kind of additional heatsink already, or did you mean the TO220 metal tab when you referred to a heatsink in your original post? And if the former, got any photos of it?
 
Is this it?

Anyone modified a naim AV2 for multichannel analogue ?

I have spent some considerable time realising that AV processors are a compromise and as I am running 7.3.0 with no overhead channels and high quality amplification and definitely appreciate that replacing analogue out is an expensive compromise. I wondered if anyone had added additional power...
www.diyaudio.com www.diyaudio.com
 
Yes PFM needs me to have a seperate web portal or link but I don't unfortuntley have that, yes that's the picture the 220's have a heatsink already
 
IWC Doppel said:
The LM317's with the stock 20V in are around 50 degrees when in stand by, difficult to measure in situ with signal through. Perhaps just adding the 20x20x1.5mm copper pad will be enough, I could also double up and effectively have a 3mm copper pad.

I will be moving from a 5V delta to 9V delta

The AV2 does run quite warm compared to anything else in my set up part from the Lumagen which has a fan. Not sure what the 'ideal' temperature is for an LM ?
Click to expand...
if you increase delta V from 5 to 9V it's almost twice as much power to dissipate so definitely need bigger heatsink , I assume you measured 50C at the heatsink ?
what is the current draw from LM317?
 
^ that.

The abs limit you can get reliability from the T0220 package without added heatsink is about 1w dissipation.

Even quite-small add-on finned types will give 10degC/W, which is a huge advantage. Add the internal circulating fan after that is a .... quite-small bonus. Local heatsinks first, every time.

Adding an internal fan? - yes, I've a couple of suggestion how to make that 'quiet' in a couple of senses: but it would not be my first recourse.

[@IWC Doppel - I've a good Fluke IR thermometer, just 'around the corner' from you - happy to come over to play : ) ]
 
Martin, thanks.

Slawekt, yes I pointed an old Fluke 62 mini at the back of the LM's. I can also add a finned aluminium heat sink as well if I'm careful I can rivet it to the copper pad before bolting it to the LM's. I am not sure of the current draw as excluding the over voltage heat dissipation the OPA604's 32 of them and I think these are 5 mA each so perhaps not loads of board consumption, may be a 1/2 w on top ?

I have had a great idea (I think !) , as the AV2 now has a captive lead joining it to the XPS power supply I was thinking I could wire another captive lead to a 3cm 5V fan that I can squeeze in near the back inside the AV2 where I removed the unused digital board. I can then use a 5V USB charger lead cut and soldered to the fan and power it from my laptop that resides near the back to run the subs mini DSP and update the Lumagen software. So no worries about the power in the AV2 to drive the fan it will have it's own discrete power supply !

Martin as I am not working at the moment give me a shout you're more than welcome to pop over and see how the set up is getting on. My coffee machine is working again now, I can even supply espresso's !
 
: )

I am a bit flat-out, but shall shout, soon :)

I do think a dab of L-C decoupling, which I can supply out of the bits- box - would shove powering a small fan internally beyond-contention in terms of acoustic & voltage noise.
 
IWC Doppel said:
Slawekt, yes I pointed an old Fluke 62 mini at the back of the LM's. I can also add a finned aluminium heat sink as well if I'm careful I can rivet it to the copper pad before bolting it to the LM's. I am not sure of the current draw as excluding the over voltage heat dissipation the OPA604's 32 of them and I think these are 5 mA each so perhaps not loads of board consumption, may be a 1/2 w on top ?
Click to expand...
LM317 has junction/ambient thermal resistance of 38 C/W with another 1/2W junction temp will increase by another 19C without accounting for a heat sink so most likely you should be fine with .
Powering fan from a separate supply would be my choice tbh
 
Great

I have ordered on of these on page 32, the lower speed version and I can throttle it back a little to keep it quiet only 9.8dbA it was £21.00 and I know they are well made as its the same range used in the Lumagen.

I'll feed it with a hard wired USB cable and plug it into a laptop that is wired to a different ring main than the audio kit to start with, if the laptop stops powering when shut down I'll move to a plug charger

 
From memory if I have a unit that is say 38 C/W and I add say a I add a 15w/C heat sink to what is already perhaps the same I will hopefully be no worse off with a few more volts to dump. I also might prefer it wired up to the lower voltage tap !
 
LM317 could operate up to 150C junction temperature but you need to take into account ambient temperature so 125C is a maximum , dissipating another 1/2W shouldn’t take you near 60C I’d say you can try running as it is and monitor temperature to start with just in case
 
slawekt said:
LM317 could operate up to 150C junction temperature but you need to take into account ambient temperature so 125C is a maximum , dissipating another 1/2W shouldn’t take you near 60C I’d say you can try running as it is and monitor temperature to start with just in case
Click to expand...

I hope to keep the temperature below 50 degrees if I can, nearer 40 ideally as the original heatsinks look like the have a bit of convection I think a fan will be a nice edition. My plug count is a bit excessive so running this from a PC is helpful
 
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150C junct temp would have a lifetime measured in minutes.

The LM3x7 series fold-back output power at far lower junction temps, and on over-current transients, for self-protection. It's all in teh datasheet. That's why they remain great, effective, jellybean regulators.

- with 15degC/W heatsink added, that dominates; with maybe 30degC ambient inside the case, a couple of watts dissipation will push up towards c 65degC on the device. I'd not want to go beyond that for all sorts of reliability reasons, but seems a reasonable passive solution for teh numbers available. HTH.
 
To the OP, you may have moved on from considering a fan however, in case it feeds into your thoughts, I experimented with some brushless dc 'computer' fans and found, to my horror, that they injected a lot of electrical noise (presumably) from the commutator back into the power supply. This was blatant on a scope, it took a LOT of capacitance to quieten those spikes and I decided to avoid using fans. The fan would have been powered from the valve heater circuit and I didn't try to see if this noise would have been audible in the circuit because it didn't seem worth the risk of introducing buzzing in an otherwise very silent amp build, so maybe it wouldn't have been audible, but anyway, my tuppence worth.
 
Thanks, I have a Sunon 5V 3cm fan ordered and I will fit and see what it does for the temperature then I have three wiring options, I will wire up with a captive USB charging cable, then I can not use, or power by a 5V charging plug a computer that is on a seperate ring main (controls my subs) or a 5V linear power supply with a 5V USB supply

Lots of options, I can see how it sounds relatively easily 👍

I might prefer it on the lower tap and have completely wasted my time as well !
 
Well a Saturday morning with Tony Blackburn and the drill and soldering iron. I ended up fitting 20mm copper pads (20x20x1.5) to the outside of the existing heat sinks to the LM's fed by the uplifted Pre-reg voltages and also fitted a 30mm 5V fan, drilled the case to direct airflow (Well they are not expensive any any more the AV2's !) and after adding a 100R resistor to reduce the airspeed to make silent it works very well. The temperature of the LM's are all under 48 degrees most nearer 40 or less after 3 hours, the stock arrangement did rise to low 50's and the case felt hot, now the case feels just warm and measures 6 degrees lower than before so obviously the airflow helps.

A quick listen says it works okay, so I'll have a proper listen today, I wonder why naim seem to have a higher delta for the DC in pre-reg, I assume it sounds better ?
 
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