Highcooley Posted February 9, 2014 Report Share Posted February 9, 2014 Connecting a 5V fan (ADDA, AD0405DB-G70, brushless) to J3 causes some audible noise on the 5V rail (I am not talking about the mechanical air flow noise). It is a 10mV pp ripple somewhere in the mid audio band around 0.5-2.5kHz. Did anybody have the same issue and does know an easy solution for that? I tried several condensators in parallel to the fan, but so far it didn't help (no change at all). Interestingly, I can barely hear it over the PA, but it's very annoying over the pre headphones directly at my mixer. Quote Link to comment Share on other sites More sharing options...
Hawkeye Posted February 9, 2014 Report Share Posted February 9, 2014 If you´re using 8580/6582 SIDs, a fan might not be necessary - also you can passively cool your SIDs with heatsinks. No problem on my side so far with that solution :) Many greets, Peter Quote Link to comment Share on other sites More sharing options...
Highcooley Posted February 9, 2014 Author Report Share Posted February 9, 2014 I do cool my 6581s with heatsinks. So I just unplug the fan and see what happens on the long run :-) Thanks for the hint! Cheers Andy Quote Link to comment Share on other sites More sharing options...
Hawkeye Posted February 9, 2014 Report Share Posted February 9, 2014 (edited) Ok, those 6581 (12V powered) SIDs will run hotter than the 8580/6582, maybe have an eye on the surface temperature of your heatsinks, if you remove the fan and the fan grill on the backside you can measure with an inexpensive infrared thermometer after half an hour of usage without disassembling the unit :-). Bye, Peter Edited February 9, 2014 by Hawkeye Quote Link to comment Share on other sites More sharing options...
Highcooley Posted February 10, 2014 Author Report Share Posted February 10, 2014 Hmm, I haven't measured the heatsinks yet (can't find my temperature probe at the moment :rolleyes:). However, the front panel gets noticeably warm, which worries me a bit. So, the fan would definitely not be a bad thing. I'm wondering what effort would be necessary to get rid of the voltage ripple. It's probably a combination of either multiple fast ceramic condensers or a clever RC. However, I didn't try to measure how much energy the fan draws in between two ripples. Maybe it helps if I correctly measure the ripple frequency and calculate the LP filter. So far I directly measured 5V to GND. The 5V supply is a big mess with four Pics attached to it anyways, which is clearly audible as a quiet hissing sound as well. My fan is a 3300rpm model. So the ripple should actually not be around 0.5-2.5kHz but rather in the 110 or 220 Hz area, depending on the amount of coils which drive the motor or the amount of steps for one revolution respectively. It should be four steps (i.e. four switching cycles) with a standard DC fan which makes 220 steps per second for 55 rps. If I remember correctly from my electronics class, the LP filter would be calculated as fc=1/(2*pi*R*C). This leads to about 15 uF with a 50 Ohm series resistor. However, the resistor would slow down the fan significantly to only around 2000rpm, which would in the end lead to a 23 uF condenser. Maybe I am a bit too academic and a simple 100 Ohm resistor in series to operate the fan at the 12V source would do. However, I don't know if the a ripple directly in the 12V source might affect the audio out even more, as it is the direct source power of the SIDs. Quote Link to comment Share on other sites More sharing options...
Altitude Posted February 10, 2014 Report Share Posted February 10, 2014 Electro and ceramic caps help. An on/off switch is the most useful imho. Quote Link to comment Share on other sites More sharing options...
Imp Posted February 10, 2014 Report Share Posted February 10, 2014 What i would try is using a separate 7805 + some caps for the fan. Although i remember someone mentioning that hose regulators have a bad ripple rejection, i think it should be better than a resistor. Quote Link to comment Share on other sites More sharing options...
Hawkeye Posted February 10, 2014 Report Share Posted February 10, 2014 (edited) Good suggestions! What also really helps to remove motor noise is a LC filter (inductivity, capacitance) - just wind a few turns of cable through a ferrite core, and attach a big electolyte (e.g. 2200uf) and a small ceramic (e.g. 100nf) capacitor. Here is a small howto: http://www.fpvuk.org/how-tos/lc-filters/ Only connect the fan after the LC-filter, i´d bet you see a massive improvement. Many greets, Peter Edited February 10, 2014 by Hawkeye Quote Link to comment Share on other sites More sharing options...
Highcooley Posted February 11, 2014 Author Report Share Posted February 11, 2014 Thanks guys for all your suggestions! Yea, LC would be my first choice anyways... if I find some ferrite core or another inductivity laying around, which I think is currently not the case in my lab :-) Maybe I can scrap soome filter parts out of an old radio or something. Quote Link to comment Share on other sites More sharing options...
Janis1279 Posted February 16, 2014 Report Share Posted February 16, 2014 Hi, There are a lot of inductors ( coils ) you can find on an old computer motherbord. Regards, Janis Quote Link to comment Share on other sites More sharing options...
Highcooley Posted March 9, 2014 Author Report Share Posted March 9, 2014 Hey guys Time run fast during the last couple of days and I didn't have any time to work on this problem. So, I would like to give you guys a quick followup on my quest to silence my 5V fan on the power rail. First, I wanted to try to solve it as easy as possible, by applying a soft ferrite bead to the fan's leads. However, as the leads where already cut to length, I would have had to cut and extend them again. So in the end, building a propper LC filter didn't take much more time to solder together. I followed Janis' tip with the computer motherboards (thank you for pointing me in the right direction!) and knocked together a quick and dirty two-stage LC filter out of computer junk and four cm of veroboard: As I don't have an LC meter in my lab, there was no reason to try to do the math for a proper filter anyway. But from right to left, a large coil (with a little amount of windings) around a ferrite ring and a 3300uF cap from the cpu's power mains (which both where obviously put there to solve a similar problem) should suppress low frequencies in the first filter stage. The second stage consists of a small coil with a lot more windings from the reciever stage of a cordless mouse (again, with no selfspeaking information printed on it, but hey, it's from a HF stage) and a 100nF ceramics cap for higher frequencies (spikes). Of course, this filter is not capable of fully cutting the noise as it is not specifically tuned to a certain frequency. Additionally, people from R/C forums reported, that it is pretty hard to fully cut noise caused by brushless motors. Thy have to deal with similar problems in their quadcopters and their solution higher up from LC filters is to implement $40.- DC/DC converters to get rid of such problems. However, my filter now does the job to suppress the fan noise to a level where it neatly blends in to the basic noise floor of the synth, caused by leaking ADSR gates of the SIDs and the HF noise probably caused by the PICs. I hope this solution might help others with similar noise problems. Please feel free to comment and share your experience with other solutions (e.g. soft ferrite beeds). Thank you! Quote Link to comment Share on other sites More sharing options...
Magus517707 Posted March 18, 2014 Report Share Posted March 18, 2014 I had finished my MB-6582 the other day and when I went to play around with it I noticed an obnoxious buzzing on all audio out. At first I thought I screwed something up. Then I realized I had not noticed this buzzing before I plugged the fan in. Praise the forum search function. Just got done soldering and implementing the same solution and it helps a ton. Quote Link to comment Share on other sites More sharing options...
Hawkeye Posted March 18, 2014 Report Share Posted March 18, 2014 Hehe, cool to see all these LC filters in action :) I really use them all the time when FPV flying (other hobby) and they are great :) Magus, I don´t see it in the picture, maybe it is there, if you add a small ceramic capacitor (e.g. 100nf) to the big elko, they work even a bit better. Many greets, Peter Quote Link to comment Share on other sites More sharing options...
Magus517707 Posted March 18, 2014 Report Share Posted March 18, 2014 Good to know. I guess I'll open my box today and modify the circuit. Thanks Peter! Quote Link to comment Share on other sites More sharing options...
Highcooley Posted March 20, 2014 Author Report Share Posted March 20, 2014 Good to know. I guess I'll open my box today and modify the circuit. Thanks Peter! Nice filter, Magus! Yep, definitely add a small ceramics cap...it helps a second ton :turned: Quote Link to comment Share on other sites More sharing options...
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