Is this to power guitar effects by any chance? If your components are working properly, you might want to look into the possibility of a ground loop somewhere. For instance, if you have your amp plugged in one outlet, and your effects power supply in another one on the other side of the room, you're almost guaranteed to create a ground loop. Try plugging all the gear your plugging into into one outlet or power bar and see if the hum goes away. Alternately, try unplugging (from the wall) each piece of equipment one at a time to see if the hum goes away. If it does, you've found the problem.
Im working on a power supply for some musical bits. Unfortunately its producing a great deal of "hum" in the circuit. Is there any way to filter out residual AC in the DC line?
If youve got any humm in the dc output still then something is wrong as it sugests the regulator is dropping out. ie the input voltage is diping too loo for the regulator to compensate.
Whats also likely is that you have ground or signal loops that are picking up mains humm, particularly if you have a few bits of equipment conected together or long signal leads earthed at both ends etc ..
You didn't mention if your wall wart is a switcher or a linear supply. If it's relatively light, it's probably a switcher. Could be a lot of problems there. But if it feels like it's got some iron in it, it's probably a linear. That would narrow down your possibe problems.
Even if you're drawing an amp from the unregulated linear, you shouldn't have more than 2V peak-to-peak of AC. If it's much greater than that, you've probably got a bad 3500uF cap. Try replacing that first.
If you're still looking at problems with 2V p.p. of AC, your stuff may be very sensitive to ripple in the power supply (the 7809s will probably cut that by at least 60dB, which would give you less than 20mV ripple on the 9V output). If you're measuring more than 20mV of ripple at the output of a 7809, you might want to look at replacing them.
The noise on the power supply we've been talking about is 100Hz or 120Hz from the wall wart. If it's higher frequency stuff, the output cap might be bad, and you could try replacing that. If not, you might be getting crosstalk between power supplies. A 7809 is very good at cutting down 100/120 Hz ripple, but it's not very good at audio frequency. If that's an issue, you might want to try putting an isolating resistor on each input to the 7809 like this (view in fixed font or M$ Notepad):
One other question: Why do you have 4 7809s at the output? You could get away with just one and run parallel lines to each effect from the one ouptut. I wonder if you've got some goofy ground loop with all these regulators. FWIW I power 5 effects and a tuner with one wall wart connected to a single
7809 with about the same filtering you have here with no problems. Your plan should work. Also, have you tried the obvious culprits (bad cables, connectors, etc)? Have you tried plugging in one effect at a time to see if any single effect is the problem? Have you double checked your solder connections and wiring?
Weeeell... Ill try removing 3 of them. I didn't want to mess with a daisy chain.
When I plug in my Boss DS-1 (which should draw 5mA max) I get tons of hum and not much sound. Plugging in the echo box doesn't work at all. Both work fine from the boss wall wart.
This circuit shouldn't be giving me fits like this. I think its a rite of passage.
FWIW - the regulators share the ground line. I was hoping to spread out any heat load by having multiple regulators. Im a long shot from an EE - which is probably why Im having so many issues with this.
Well, if the input is above 12 volts DC and the load is only 5mA, the only thing I can think of is it may be oscillating. Use the DMM to measure AC voltage at the output. It should be very low at 5 to 10 mV. You could try a small capacitor on the output, maybe 1-10 uF. Maybe that will help.
A couple of things are screwy here. First, a daisy chain is when you use one effect to power the rest. A few of the Boss pedals (like the NS2 noise suppressor) have 2 DC power jacks - one for the incoming DC, and the other to connect to the next pedal. You have 4 separate regulators, so pulling one or any or all of them isn't going to hurt anything.
Another thing you should double check is polarity. Some pedals use a centre positive connection and others centre negative. If you have things connected the wrong way, look out! Do you have the positive DC connected to the positive pin on the plug?
Seeing your schematic, I might say forget those textbook examples for regulators, DON'T use them without an elco at the output since usually it's a no-go.
I only see .1uF at the output of the regulator. Regs are rather sensitive to input ripple and output current variations. Input caps' size looks OK to me. Try compensating by buffering the output with an elco of say 2200u instead of larger input cap, so that any possible fed-through ripple gets caught by the output cap. By "under buffered" I meant "not having enough of energy reservoir (capacity) at the output to handle voltage/current variations".
Above I assume your wall wart is capable of delivering enough current, but as a side assumption : As far as I seem to read, all 4 individual regs take appprox 400mA, thus
1.6A together Is your wall wart capable of handling this ? If not, input voltage will drop until a level where input ripple (lower level) drops below 12V , thus making it impossible of regulating using a
7809
For your info also this: It IS possible using a 78xx series regulator and boost it's output current by using a simple setup as follows (copy and paste "image" below with a fixed font, say courier, in notepad)
Explanation: For low currents the transistor is closed, reg takes it all If reg current increases to say 0.32A, voltage drop over 2R2 will rise enough to open the transistor (Vbe rises above say 0.7V), thus having the transistor take everything above 0.32A output current. Transistor type has to be capable of handling the output current, in your case I'd say BD138 or something similar. This setup uses a SINGLE reg and ONE transistor with few discretes instead of 4 regs and buffering
Each regulator requires 400mA just to function *at all*? I didn't know this. My wall wart only puts out 400mA. Where would I look up this information? (more specifically - where did you get it from?)
NOPE I didn't tell you regs need 400mA to function *at all* (wonder where you read this, jeses) Regs of this type work with output currents from 0 upto 1A, see datasheets
Each regulator requires 400mA just to function *at all*? I didn't know this. My wall wart only puts out 400mA. Where would I look up this information? (more specifically - where did you get it from?)
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