i know this topic has been covered quite comprehensively, but.

would something like this work well as an effect power supply?

http://za.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7212200

ripple voltage is 80mV peak to peak for 9V.

Chaars

makepeace wrote: i know this topic has been covered quite comprehensively, but.

would something like this work well as an effect power supply?

http://za.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7212200

ripple voltage is 80mV peak to peak for 9V.

Chaars

Those will work fine, I have a Meanwell too. BUT, these switched mode supplies are noisy as all hell. You're much better off either buying ($$$) or building your own linear regulated supply. Not only do they put noise into the front of the amp via the effects, they also put noise back into the power grid so your amp will be noisy even with your cable plugged straight into the amp and the switched mode thing plugged into the same multi-adapter.

Thanks ez. Shoooooo... This power supply story is confusing the hell out of me.. Ok, so you have switched mode, linear and normal (rectified and smoothed by caps etc). How do you determine which will be the quietest? I've just had a look at RS's linear supplies. One has 1.2V ripple! Surely that's not conducive to noise free operation?

I'm looking for 2 9v supplies each to power positive ground and negative ground pedals. Preferably rated at around 2A, below R200, and can be acquired from RS.

http://www.mantech.co.za/ProductInfo.aspx?Item=99M3185

I have that but the 2a version, earthed so its quiet, 2 amps so plenty power for all my pedals.

thanks for all the replies.

i actually considered building my own, but got over it once i saw the price of transformers and when there are cheaper and easier alternatives there's no point, and don't really have the inclination to build a SM.

i've pulled the trigger on one of these, will see how it goes when it arrives. going to put it through my fuzz and if it comes out unsoiled i'll be chuffed ?

just want to confirm, it IS all about ripple right? i mean when it comes to determining whether you'll have quiet power, or are there other factors? reason i ask is because on a previous thread i didn't really get a straight answer wrt this.

makepeace wrote: thanks for all the replies.

i actually considered building my own, but got over it once i saw the price of transformers and when there are cheaper and easier alternatives there's no point, and don't really have the inclination to build a SM.

i've pulled the trigger on one of these, will see how it goes when it arrives. going to put it through my fuzz and if it comes out unsoiled i'll be chuffed ?

just want to confirm, it IS all about ripple right? i mean when it comes to determining whether you'll have quiet power, or are there other factors? reason i ask is because on a previous thread i didn't really get a straight answer wrt this.

Not only ripple. If the ripple is nice and sinusoidal, you'll have monotonically decreasing harmonics (i.e. the ripple will have its fundamental frequency at 60Hz. The harmonics falling at 120, 180, 240 etc) in the frequency spectrum. That's fine then. The signal to noise ratio will then be of the order of ripple voltage / output voltage say 80mV / 9V. I think the Boss 9V supply is spec'd for ripple less than 100mV (IIRC).


However, with switched mode supplies, they switch on and off say 100 000 times per second, in order to regulate the voltage to the specified value. This fundamental switching frequency is far outside the audible range BUT it has very significant sub-harmonics (F0/2, F0/3, F0/4, ... F0->0 etc) in the audio range which you will hear (you will hear it when the supply comes and you use it ? ). The high-order harmonics is obviously because the actual voltage / time graph will show that the voltage almost a step from on to off and as such it is highly non-sinusoidal and hence will have significant high order harmonics).

Another effect is that because it abruptly switches the current on and off, you have the back EMF (Electro-Motive Force) which goes either way (into the supply and back into the mains) which manifests as further noise in your effects as well as your amp (unless you have these somehow isolated). Linear supplies do not have this effect.

I have one of these supplies. They work OK, they're MUCH better than the cheapie wall warts but they are noisy on both my amps. Like I said, if I plug my guitar straight into my amp (the new one, with its old school unregulated power supply, much like yours) and I plug the Meanwell into the same multi-adapter it hums like a swarm of bees. The moment I pull it out the noise stops.

I have to add, If you use a squeaky clean amp this may not be an issue. If you run your amp cranked like I do, then every little bit of noisy is amplified multiple times and the result is a bee's nest.

ezietsman wrote: They work OK, they're MUCH better than the cheapie wall warts but they are noisy on both my amps. Like I said, if I plug my guitar straight into my amp (the new one, with its old school unregulated power supply, much like yours) and I plug the Meanwell into the same multi-adapter it hums like a swarm of bees. The moment I pull it out the noise stops.

I dont get any humming whatsover, either with the Bassman or with the Classic 30, strange

Have you ever measured how much current your pedals are actually drawing with an ammeter? I suspect that you could power a room-full of overdrives with a 2A power supply! I have nine pedals on my board, including a reverb containing a Belton brick and a Boss DD-5, both of which are relatively heavy current draws. My total draw for the nine pedals is only about 180mA and I power them all off a Boss 200mA power supply with no problem.
You won't necessarily get any better performance out of a 2A power supply than a 200mA power supply if you are only drawing 150mA. Regulated power supplies are generally designed to have less than 10% ripple at full load current. The ripple, of course, decreases when you have less than full load. You can reduce ripple by adding more capacitance in the smoothing circuit.
I actually made a 9V regulated power supply from a spare 12V unregulated supply by adding additional capacitance and installing a single chip 9V regulator with a heatsink on the outside of the housing.
Hope this sheds a bit of light on the subject.

PS Below is a table I drew up. It works like this. For a regulated output at the voltage in column A, you need a transformer with a seconday ac voltage shown in column B. To give 10% max ripple for the output currents shown at the top row of the other columns, you need a smoothing capacitor in uF shown at the intersection of the voltage and current. So, for example, for a 9V 200mA regulated power supply you would need a minimum 1343uF, so you would use the next available value up, say 1500uF. The assumptions are based on a 10% allowance for mains voltage drop and the use of a standard 78XX series regulator chip. Hope this is not too confusing

Smoothing capacitor calculations in uF Smoothing capacitor calculations in uF
Current mA
Reg O/P V Sec V rms 20 60 100 200 300 400 500
5.0 7.4 191 574 957 1915 2872 3830 4787
6.0 8.2 173 519 865 1731 2596 3462 4327
9.0 10.5 134 403 672 1343 2015 2687 3358
12.0 12.9 110 329 549 1098 1646 2195 2744
15.0 15.2 93 278 464 928 1392 1856 2320
18.0 17.6 80 241 402 804 1205 1607 2009

Thanks for the info Jonny B

So, say I've got one of those crappy white selectable output ac-dc power supplies rated at 12VA. I've measured the winding of the transformer for the 12V dc output and its 16V AC. What will I have to do to get a nice clean 9V supply out of it? Rectifier, regulator some resistors and a big cap? at the moment its got 4 diodes, 2 resistors and a 2800uF cap, and its noisy as ell.

MP, I think you might find this site useful for powewr supply theoryhttp://www.kpsec.freeuk.com/powersup.htm

The four diodes that you have will form a full-wave rectifier bridge. The 2800uF capacitor will provide smoothing. I'm not sure what the function of the resistors in the circuit is. They could be for current limiting to protect the rectifier and transformer in case of overload or short circuit. Essentially what you have is an unregulated dc power supply made up of a transformer (220V ac primary to 16V?ac secondary, a full wave bridge rectifier and a smoothing capacitor. Incidentally the rated secondary voltage of a transformer is normally measured at full load rated current, not on open circuit. As you load the transformer the output voltage falls.

Adding a regulator to the circuit will provide regulation but I doubt that it will get rid of the noise in the circuit. The noise may be a result of poor transformer design or manufacture or it could be the result of earth loops. So the straight answer to your question is probably no! :'(

I've got one number for you Makepeace: 7809 ?

?

Checked it eout already, got everything I need here from parts from other stuffs.

Cheers

7809 is the right number! It's a 9V three terminal positive voltage regulator that can handle up to 1A and can run up to 125 degrees C. Beware though, it has a thermal resistance between junction and ambient of 65 degrees C per Watt and a thermal resistance between junction and case of 5 degrees C per Watt. What this means is that if you intend to draw any reasonable current from the power supply the regulator will need a good heatsink, otherwise the chip will overheat and blow up.
You can work out how many Watts you need to dissipate in the heatsink by measuring the voltage drop across the regulator and the current through it and multiplying them together. Say 5 volts drop and 100mA current draw will give you 500mW or 1/2 watt. At 65 degrees C per Watt, with no heatsink, the chip would rise by 65*1/2= 32.5 degrees above ambient. If you were drawing 500mA at 5 volts drop across the regulator, the power to dissipate would be 2.5W and without a heatsink, the chip would rise to 65*2.5 = 162.5 degrees C and would fail.
Any heatsink will have a thermal resistance rating. Let's say, for example, 35 degrees C per Watt. Add this to the thermal resistance between junction and case of the regulator of 5 degrees C per Watt, and you have the total thermal resistance of the regulator and heatsink, say 40 degrees C per Watt. Now with the heatsink fitted (using thermal paste) and 1/2 Watt to dissipate as in the first example, the temp will rise only 20 degrees C above ambient.
I hope I haven't over complicated this. Bottom line is "use a heatsink". ?
If you want more theory, it's herehttp://en.wikipedia.org/wiki/Thermal_resistance_in_electronics

Sweet thanks for the info ?, i think i might use a heatsink ?.

I've discovered all i have at home is 5V regulators, so going to order some 9V's from RS. While I'm at it, i think i'll order some transformers. What about toroidal? RS has a good selection of V's with dual secondaries. Are the advantages there worth it or a waste?

hokay.

so needless to say, the RS smps was lank noisy, a different noisy to the linear power supplies though. a higher pitched modulated hum. :-\. its fine for low gain pedals such as delays, phasers, etc. but with gain pedals like my fuzz, rangemaster and sho its very noisy..

anyway, i've started prototyping a linear supply.

what i have currently is a 2x 18V secondary toroidal transformer rated at 15VA (lots yes), into a bridge rectifier with 1x 100uF and 2x 2.2mF caps across the dc output. I then have my 9V regulator and another 100uF across that output.

what i get is great, 8.something V with absolutely no noise. however, everything (except the regulator) is getting really hot! i can't touch the transformer once its been on for more than 2 mins, and the caps are also getting really hot.

is this just the nature of things? or is something likely to be wrong? when its not plugged into a pedal it still gets just as hot.

cheers

Well, with an 18V transformer your regulator is having to turn a lot more voltage into heat than it's letting through. 18V is double what you need already and once you rectify and smooth the DC it's something like 24V DC (IIRC), so the regulator is having to drain about 15V. So in other words, you need to use a much lower voltage transformer.

Cool I get that, but then surely my regulator would be getting really hot as opposed to my transformer?

Any ideas?