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Best way of powering 12V DC chassis fans?
Best way of powering 12V DC chassis fans?
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Old 15th October 2019, 02:17 AM   #1
Deke609 is offline Deke609  Canada
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Best way of powering 12V DC chassis fans?
Default Best way of powering 12V DC chassis fans?

Hi all - I'm hoping for some suggestions about how best to power 2 X 140mm chassis fans for cooling the filament shunt regulator boards in my 300B preamp. I can't post a schematic for intellectual property rights reasons, but the schematic is irrelevant to my question. Suffice it to say that the shunt reg circuit is designed with very tight tolerances for putting out 10V DC @ 1.2A (only 5V of which is dropped across the filaments - the 300Bs are filament biased). And I am using EML 300Bs which draw 1.3A - and this is putting some heat stress on the regulators. I've looked into increasing the size of the heatsink, but there is only one bigger that will fit, and its datasheet suggests that it would offer only marginal improvement in heat dissipation.

... So I'm going to experiment with forced air. My question is how best to power them? I'm worried that their motors might inject noise into the amp via the power supply. I don't know if they would or could in fact do so (I'm still very much a noob), and would appreciate any insight that you all might have on this more fundamental issue as well.

The options I see are:

(1) battery power - completely disconnected from the amp's power supplies (HV and fil), and quiet in any event. Downside: will require frequent recharging of batteries; and seems a bit inelegant.

(2) Seperate 12V DC supply connected to the mains wall outlet - diy or ready-made.

(3) internal 12V DC supply (trafo, recitifer and smoothing circuit) that taps the mains supply coming into the amp that also supplies the HV and filament transformers (I'm installing dedicated filament transformers to get a bit more raw voltage from the secondaries - the voltage form the existing heater windings is a bit low).

(4) power them from the new 12.6VAC filament supplies (rectified and smoothed to 13.5VDC for feeding the shunt regulators) - by way of a dropping resistors.

In case it is relevant, I'll add that the HV has a CLCLC filter, the Fil supply will have a CLC filter, and both the 300B B+ and the filament DC are shunt regulated. So there's a lot to isolate the signal wiring from any noise at the beginning of the power supplies. But I am a bit paranoid about noise

I should also add that I recognize that vibration transmitted to the chassis could be an issue and plan to damp that by mounting the fans on the open underside of the enclosure via a trampoline-type suspension - basically on rubber bands.

Any thoughts, insights, suggestions?

many thanks in advance,

Derek

Last edited by Deke609; 15th October 2019 at 02:18 AM. Reason: forgot question mark
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Old 15th October 2019, 02:24 AM   #2
rayma is offline rayma  United States
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Can you post a drawing of the heat sink with dimensions?
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Old 15th October 2019, 02:33 AM   #3
Deke609 is offline Deke609  Canada
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Best way of powering 12V DC chassis fans?
Hi Rayma - I believe it is the FA-T220-51E (the 2.0" tall one). Profile and dimensions are identical. Datasheet attached. As best as I can see, going to the largest (2.5") doesn't offer much more benefit.
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File Type: pdf sink_f_r-1265536 (1).pdf (412.3 KB, 13 views)
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Old 15th October 2019, 02:36 AM   #4
rayma is offline rayma  United States
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Will there be one heat sink or two? How many regulator ICs or other power devices?
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Old 15th October 2019, 02:38 AM   #5
Deke609 is offline Deke609  Canada
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Best way of powering 12V DC chassis fans?
1 regulator with 1 heatsink per filament - the regulator is the LM1085
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Old 15th October 2019, 02:41 AM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by Deke609 View Post
1 regulator with 1 heatsink per filament - the regulator is the LM1085
Ok, you've already spread out the dissipation as much as possible.
Are there preregulators before the shunt regulators?
Can you post a general block diagram of the filament supply?
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Old 15th October 2019, 02:42 AM   #7
Deke609 is offline Deke609  Canada
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Best way of powering 12V DC chassis fans?
Apologies - I missed the question about other power supplies. The C4S/shunt reg boards for B+, 1 per channel, also have 2 heatsinks each (I believe they are the same as the ones used on the LM1085s).

So there are 6 existing heatsinks in total.
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Old 15th October 2019, 02:44 AM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by Deke609 View Post
Apologies - I missed the question about other power supplies. The C4S/shunt reg boards for B+, 1 per channel, also have 2 heatsinks each (I believe they are the same as the ones used on the LM1085s). So there are 6 existing heatsinks in total.
Can you post a general block diagram?

Last edited by rayma; 15th October 2019 at 02:47 AM.
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Old 15th October 2019, 02:51 AM   #9
Deke609 is offline Deke609  Canada
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Best way of powering 12V DC chassis fans?
Quote:
Originally Posted by rayma View Post
Are there preregulators before the shunt regulators?
I don't know what a preregulator is - can you explain?

But I should emphasize that I want to do the forced air experiment. I like tinkering and want to see if it can be made to work - even if additional heatsinking is possible. If it doesn't work, it can easily be removed. So this is where my focus is at the moment.

cheers and thanks, Derek
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Old 15th October 2019, 03:03 AM   #10
rayma is offline rayma  United States
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Quote:
Originally Posted by Deke609 View Post
I don't know what a preregulator is - can you explain?

But I should emphasize that I want to do the forced air experiment. I like tinkering and want to see if it can be made to work - even if additional heatsinking is possible. If it doesn't work, it can easily be removed. So this is where my focus is at the moment.
Sure, how will the air flow if the sinks are installed on a pcb, are the boards vertical?
If so, are the sinks mounted so their wide dimension will be vertical also?
Do you have an infrared temperature gun?

A preregulator fixes the input voltage to a regulator, so the regulator dissipation can be minimized,
without having to take into account line voltage variation.

Last edited by rayma; 15th October 2019 at 03:07 AM.
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