ritz@msb.com (Chris Mauritz) (04/17/91)
Someone was kind enough to send me a message saying that controlling the speed of an AC fan was not as simple as adding a pot. OK, how about I use a DC fan and siphon off power from the power supply for the amp? The power supply seems to be hefty. Would there be any danger that a small DC muffin fan would draw enough current to affect the amplifier in any negative way? Another question, I've opened the amp to see what kind of DC power comes out of the power supply. It says +17v, but my trusty little voltmeter says +20v. Would I need to get a 20v fan or can I use a 12v fan with some sort of resistance to chop the voltage. Any help would be greatly appreciated. As you can see, I'm a bit confused. :-) Cheers, Chris -- ------------------------------------+--------------------------------------- Chris Mauritz |People are strange ritz@msb.com |when you're a stranger. Copyright (C) 1991 |The Doors-
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (04/17/91)
In article <1991Apr17.022927.7094@msb.com> ritz@msb.com (Chris Mauritz) writes: >Someone was kind enough to send me a message saying that controlling >the speed of an AC fan was not as simple as adding a pot. OK, >how about I use a DC fan and siphon off power from the power supply >for the amp? The power supply seems to be hefty. Would there >be any danger that a small DC muffin fan would draw enough current >to affect the amplifier in any negative way? The fan will put noise on the rails of the supply. Use a seperate supply for the fan if you can. Power amp supplies have to deliver a large amount of power very quickly in order to track transients, but they also have to have very low noise to avoid affecting quiet passages. Power supply design is the real secret to good sounding amps, and if it works well, don't touch it. --scott
jon@inqmind.bison.mb.ca (Jon Chesnut) (04/18/91)
ritz@msb.com (Chris Mauritz) writes: > Someone was kind enough to send me a message saying that controlling > the speed of an AC fan was not as simple as adding a pot. OK, > how about I use a DC fan and siphon off power from the power supply > for the amp? The power supply seems to be hefty. Would there > be any danger that a small DC muffin fan would draw enough current > to affect the amplifier in any negative way? > Before you go any further, I'm concerned (slightly) about adding a fan. Solid State amps run better warm..... why did you want to add the fan in the first place? Rather than adding a DC fan, why not attach a thermostat to the heat sink. YAMAHA standard says 50 degrees celcius (sorry, I'm lousy in Imperial measures!) Is the ideal, so their thermostats are set for cut IN at 60 degrees, and OUT at 45 degrees. If this is a ROCK 'N ROLL type amp, such a circuit would be great, and much simpler to do, and probably better for the amp than tapping off it's supply. If it's a home amp, the cut-ins and cut-outs would probably get annoying... AARGGHH.... I can't find a farenheit conversion table around ANYWHERE! Later, Jon Chesnut
gt0869a@prism.gatech.EDU (WATERS,CLYDE GORDON) (04/18/91)
In article <1991Apr17.022927.7094@msb.com> ritz@msb.com (Chris Mauritz) writes: >Someone was kind enough to send me a message saying that controlling >the speed of an AC fan was not as simple as adding a pot. OK, >how about I use a DC fan and siphon off power from the power supply This should work, but I see 2 potential problems: 1. The voltages in the supply are really high(generally 60v or so) for motors. You would have to build a voltage divider, usually to below 35v, and then use suitable regulators to get down to 12v or so, for most motors. There are regulators around which should easily handle enough current- I can't see this carrying more than 500ma.(try 7812 or 7912- positive or negative 12v) 2. A motor hooked up this way has the potential to backfeed brush noise to the supply and the amp. Use fairly large filter caps in the motor circuit bypassed with small caps (big: typically 3000u, small; typically 1u or so.)One of each is a good starting point.Although this should take care of noise, further methods may have to be employed in some cases (see filtering in many EE text or handbooks) Hope this helps. Gordon. -- WATERS,CLYDE GORDON-Georgia Institute of Technology Atlanta Ga 30332 ******<LANGUAGE IS A VIRUS! - Laurie Anderson-Home of the Brave>******* uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt0869a Internet: gt0869a@prism.gatech.edu
hbg6@citek.mcdphx.mot.com (04/22/91)
>ritz@msb.com (Chris Mauritz) writes: > >> Someone was kind enough to send me a message saying that controlling >> the speed of an AC fan was not as simple as adding a pot. OK, >> how about I use a DC fan and siphon off power from the power supply >> for the amp? The power supply seems to be hefty. Would there >> be any danger that a small DC muffin fan would draw enough current >> to affect the amplifier in any negative way? >> All of the DC muffin fans I have used contain a bunch of digital control and analog drive circuitry ( tiny SMT parts under the cap at the non-moving end of the motor ). This stuff drives a brushless DC motor and probably would not take kindely to much less than their rated voltage. I'll see if there is one in our scrap pile to 'smoke' test. John ..................................................................... John Schuch - Motorola Inc., Computer Systems Division (602)438-3008 All opinions expressed are mine and not Motorolas, their loss. .....................................................................
hbg6@citek.mcdphx.mot.com (04/26/91)
In article <12462@qisoff.phx.mcd.mot.com> I wrote: >>ritz@msb.com (Chris Mauritz) writes: >> >>> the speed of an AC fan was not as simple as adding a pot. OK, >>> how about I use a DC fan and siphon off power from the power supply > >All of the DC muffin fans I have used contain a bunch of digital control >and analog drive circuitry ( tiny SMT parts under the cap at the non-moving >end of the motor ). This stuff drives a brushless DC motor and probably >would not take kindely to much less than their rated voltage. I'll see if >there is one in our scrap pile to 'smoke' test. > I found a fan around here rated for 6 -> 15 volts DC. There IS quite a range of fan speed based on voltage. It starts to spin at around 4 volts, moves a lot of air at 15volts, makes an interesting hovercraft or gyroscope demonstration at about 48Vdc, and gets mad and won't play anymore at around 65Vdc. :-) John