Anything wrong with this DC Fan Supply?

[tictac]

I've seen this circuit drawn both with and without a floating ground; this drawing is my "as built" inserted into a Standel type amp.

The PSU works but there is noticeable noise coming thru the speaker when the fan is plugged in. (the fan is for cooling the power tubes)

Even when I move the fan as far as possible from the power tubes the noise persists. When I use an AC power fan there is no problem with noise.

Thing is I don't have an auxiliary AC plug on the back of the amp but I do have a DC plug for the PSU so I'd really like to use the DC fan but it's just too noisy as is.

FYI I'm running a 12VDC fan with 5VDC from the supply. I have this arrangement on another amp of mine with no problems.

Maybe it's the power tubes (1625's: a 12V version of an 807) since they were used as radio transmitters during WW2 perhaps they pickup RF noise easily.

I always thought DC would be quieter than AC but maybe it's the way I'm implementing the fan hence the request for another set of eyes

Thanks,

TT

[tubeswell]

Could be transients from the rectifier diode switching (going back into the PT winding and into the other windings). Maybe try UF diodes (or parallel .01uF snubber caps).

[tictac]

Hadn't thought of that; I'm using a 1 piece bridge but I'll have to try the UF diodes and snubbers.... Thanks for the idea

TT

[sluckey]

Noisy fans are very common. Try another one.

If I was gonna run a 12V fan at reduced voltage I would simply use a dropping resistor in series with the fan and get rid of all the regulator circuitry. There's no reason for voltage regulation since the load is mostly constant.

[Stevem]

If to start with you get a tad bigger 220 volt fan you can run on the 120 vac and it will be noiseless, cool the tubes enough and save you from that whole mess of a D.C. Power supply!

220 volt fans on 120 run at half speed and last forever!

[tictac]

Really great suggestions from everyone... thanks so much

I've got a dozen or more of these little boxer fans and computer cooling fans; a few 120V AC, a 24VDC, some 12VDC, so I'm trying to use up what I've got but I really like the simpler is better approach everyone seems to be advising....

I went the regulated supply route because I've got the parts to do it. I may try to add a 2-wire AC outlet and be done with the DC route. I've got a 120V AC fan that runs real quiet, like a "whisper" fan...

but I really like the 24oV fan idea too; I'll keep my eye out for one....

TT

[shane]

I often use an encapsulated bridge rectifier, but I put a fast recovery diode (usually a uf4007) between it and the first smoothing cap or in your case between it and the voltage regulator.

[JMFahey]

Sorry but there´s a couple problems with your schematic.:
1) please actually ground the artificial center tap, replace the .02uF cap with a wire link.
No need to keep filaments floating if anyway the fan supply and load can be left floating themselves.

2) since regulator is not referenced to ground, it won´t help reduce supply noise.
*The Fan* will receive smooth DC between its terminals, but said DC may ripple relative to Ground, so you gain nothing.

3) given that, you may reduce the rough 15/16V DC you get rectifying 12.6V filaments to 12VDC or 5VDC or whatever is needed by your fan by using a plain resistor, value as needed as to get proper fan voltage; filter chain will then be CRC (first capacitor > dropping/filtering resistor >second capacitor > Fan) which will not introduce noise by itself.

4) I *suspect* that rather than actual Hum, you may have a "whirr" sound caused by Fan internal active switching coupling magnetically into some sensitive point.
I have had that problem many times if fan is not real far from reverb tank pickups, go figure.
If so, you´ll have to reorient parts until you reduce it.