What Does 'Isolated Output PS' Mean?

[Agung Kurniawan]

Hi everyone..
I have a little question here. I was look for some PS that come from well-known brand. Maybe for the example, it's Voodoo Lab pedal power 2+ wich one I have seen it's used by some great guitarist.
They said on their page that this PS have 'Isolated' every output. So my question is:
1. What does 'Isolated' output mean?
2. Is that any special wiring to do that?
3. Is That any way to make my own 'Isolated' output?
Thanks...

[EBK]

Hi everyone..
I have a little question here. I was look for some PS that come from well-known brand. Maybe for the example, it's Voodoo Lab pedal power 2+ wich one I have seen it's used by some great guitarist.
They said on their page that this PS have 'Isolated' every output. So my question is:
1. What does 'Isolated' output mean?
2. Is that any special wiring to do that?
3. Is That any way to make my own 'Isolated' output?
Thanks...

Isolated (when used properly*) means that each output has its own secondary winding on the power transformer.  That means individual pedals do not interact through noise dumped on the power rails.  (Probably a somewhat simplified or inaccurate characterization, but it is how I think of them).
Yes, you could technically wind your own transformer or buy a transformer that has appropriate secondary windings and make your own supply.  I think R.G. may have had instructions on his site for winding your own transformer at one time before deciding it was safer to not encourage risk-ignoring types to do so.  Voodoo Labs is a great brand name for isolated power supplies, by the way.  If you are looking to buy one instead of making it yourself, I would suggest you use their product prices as a ballpark for what you should expect to pay.  In other words, never buy a 5-output "isolated" power supply for $50.  Hope this helps.

*Just because a product claims to have isolated outputs doesn't necessarily mean it is true.  Often, in bargain power supplies, each "isolated" output will share a common ground.  That is not isolated.

[EBK]

Just wanted to add that "technically", a multi-outlet power strip with a bunch of individual wall warts is also an isolated power supply.... 

[Agung Kurniawan]

Isolated (when used properly*) means that each output has its own secondary winding on the power transformer.  That means individual pedals do not interact through noise dumped on the power rails. 

So then if I have 1A CT transformer with 3 secondary winding, I may build 3 output isolated ps,right?
of corse each power line has it's own diode bridge, filter cap, and regulator.
because the point of isolated ps is to have individualy power line and ground for each output

[Rob Strand]

because the point of isolated ps is to have individualy power line and ground for each output

Using the word "ground" for DC outputs isn't good.  Maybe use +V and 0V.
An isolated power supply does not connect the DC outputs to the mains ground or the chassis.

The mains ground should be still be connected to the enclosure and transformer.
Sometimes special rules (country specific laws) apply to the transformer leakage for isolated outputs.  Things like "wall warts" generally pass these requirements and many pass without
a connection to mains ground.

[antonis]

So then if I have 1A CT transformer with 3 secondary winding, I may build 3 output isolated ps,right?

If CT is refered to secondary windings (meaning that you have 3 windings in series with a common wire for each pair of them) then the answer is NO...

You need absolutely "isolated" windings so the GNDs of the individual rectifiers shouldn't have any common spot between them..

[EBK]

So then if I have 1A CT transformer with 3 secondary winding, I may build 3 output isolated ps,right?

If CT is refered to secondary windings (meaning that you have 3 windings in series with a common wire for each pair of them) then the answer is NO...

You need absolutely "isolated" windings so the GNDs of the individual rectifiers shouldn't have any common spot between them..

If you had 3 windings in series with taps between each, it wouldn't be "center tap", right? ("third tap"?).  I imagine the transformer in question had a single primary and a single, center-tapped secondary, making 5 wires in all.  Still, I agree you can't make a multi-isolated-output supply from that (unless you could split the coils at the tap...).

[Mark Hammer]

The need for isolation has become more important as an ever increasing number of pedals become digital.  Many players have found that pedals that were absolutely dead quiet, turned into gigantic hiss machines when they brought home a 2nd digital pedal from the store and plugged it into a shared power supply. 

When there's only one digital pedal being powered, all the clock spikes it produces that are riding on the power line are so high up you can't hear them.  If several digital pedals, sharing a common power source, generate clock spikes that are reeeeaaalllly close, but not absolutely identical (e.g., 3mhz and 2.9999mhz) they can generate sum and differences, much like a ring modulator.  You obviously won't hear their sum, but the differences can easily be in the audio range.  And given how many different clock rates can exist in a single pedal (various divisions of a master clock), the possibilities for generating many  different differences are substantial.

It's possible, from what I understand,  to design a pedal to block outgoing spikes.  But folks who make power supplies can't assume that every pedal you're powering has such "protection".  So, they have to anticipate the worst case scenario to avoid being blamed for your pedals sounding noisy.  And so,  the PS provides "isolated" outputs.

[Agung Kurniawan]

Ok everyone, thanks for your help.
Imma working with ground loop on my pedal chain.
When I using 3 pedal (Boss MT-2, Metal Monster, and Cyclon Delay) my gig is tottaly dead quite. When I add preamp infront, it's became worst.
I just figure out that maybe Boss MT-2 have ground loop inside it

[Agung Kurniawan]

I agree you can't make a multi-isolated-output supply from that (unless you could split the coils at the tap...).

What did you mean about split the coils at the tap?

[Rob Strand]

When I add preamp infront,

Adding gain can make things worse.
You should also check the the preamp by itself is fine.

I'm assuming the preamp is powered from the same power supply as the effects. (right?)

Imma working with ground loop on my pedal chain. 

Try putting a 10ohm resistor in the 0V rail between the power supply and *each* effect.
This should remove any ground loops.

If the power supply doesn't have enough power sometimes what happens is:
- you add an effect, it takes more current
- the power supply voltage on the unregulated DC drops
- the regulator no longer regulates and humm gets through the power
  This is more a problem with transistor base preamps but I have seen issues on other effects.
- You hear hum but it is the power supply not a ground loop

The way to check that is you have all the devices powered, plugged,  and active.
You connect the guitar to one of the effects at a time and take the output only that effect to the the amp.
You need a dummy 6.5 jack or cable to keep the others effects powered.
The idea is the power supply is supplying full power but you only listen/use one effect.
This still might not pick-up high gain situations.
The other way is to check the regulator is not dropping out with an oscilloscope.

[ElectricDruid]

They said on their page that this PS have 'Isolated' every output. So my question is:
1. What does 'Isolated' output mean?

Depends how strict they're being about the interpretation of "isolated". EBK has given you a strict definition, so let me give you a more common, less strict one: An isolated output has its own power regulation. So a multi-output supply would have a single secondary winding on the transformer, and a single rectifier, but multiple sets of voltage regulators and smoothing capacitors on the DC side. This is enough to block (isolate) noise on the 9V power rail, but the supplies share a common ground, although it will only be connected at the power supply (it's a star ground system - that helps).
I couldn't tell you which way different manufacturers build their famous multiple output power supplies. I can guess which way the cheap ones do it, but I wouldn't bet against some of the expensive ones doing the same thing and just charging more for it. High prices are unfortunately no guarantee of quality.

2. Is that any special wiring to do that?

As described above - take the standard 7809 regulator circuit and copy it lots of times.

3. Is That any way to make my own 'Isolated' output?

Yes, you can build one of those easily enough.

HTH,
Tom

[EBK]

They said on their page that this PS have 'Isolated' every output. So my question is:
1. What does 'Isolated' output mean?

Depends how strict they're being about the interpretation of "isolated". EBK has given you a strict definition, so let me give you a more common, less strict one: An isolated output has its own power regulation. So a multi-output supply would have a single secondary winding on the transformer, and a single rectifier, but multiple sets of voltage regulators and smoothing capacitors on the DC side. This is enough to block (isolate) noise on the 9V power rail, but the supplies share a common ground, although it will only be connected at the power supply (it's a star ground system - that helps).

This is a very important point.  While I would consider Tom's example definition to be of the dubious quotation-fingers (or air quotes) kind, it is apparently legitimate enough to avoid a claim of false marketing.  (Tom, I think you at least somewhat agree.  I'm definitely not intending this as an attack against you!)

I couldn't tell you which way different manufacturers build their famous multiple output power supplies. I can guess which way the cheap ones do it...

Luckily, if you happen to pick up one of these power supplies, you can measure continuity between the contacts of separate outputs as a quick check.

but I wouldn't bet against some of the expensive ones doing the same thing and just charging more for it. High prices are unfortunately no guarantee of quality.

So true.  Too-good-to-be-true pricing is a good indicator of junk, but junk can easily be passed off as quality merely by price association.  I realize in hindsight that I gave advice earlier that would play right into such a trap. 

[ElectricDruid]

Oh, don't worry, I totally agree - what I was describing is an "isolated" supply indeed!

T.

[Agung Kurniawan]

An isolated output has its own power regulation. So a multi-output supply would have a single secondary winding on the transformer, and a single rectifier, but multiple sets of voltage regulators and smoothing capacitors on the DC side. This is enough to block (isolate) noise on the 9V power rail, but the supplies share a common ground, although it will only be connected at the power supply (it's a star ground system - that helps).

did you mean something like this?

that was my 5th ps project, but I no longer use it again

[Agung Kurniawan]

Adding gain can make things worse.
You should also check the the preamp by itself is fine.

I'm assuming the preamp is powered from the same power supply as the effects. (right?)

nothing wrong with the preamp, its a TL072 inside. I set the gain close to 9 o'clock. it just add tottaly a little bit of hiss to my distortion, and that wasn't to anoying me.
yes, its powered by the same power supply

Try putting a 10ohm resistor in the 0V rail between the power supply and *each* effect.
This should remove any ground loops.

If the power supply doesn't have enough power sometimes what happens is:
- you add an effect, it takes more current
- the power supply voltage on the unregulated DC drops
- the regulator no longer regulates and humm gets through the power
  This is more a problem with transistor base preamps but I have seen issues on other effects.
- You hear hum but it is the power supply not a ground loop

The way to check that is you have all the devices powered, plugged,  and active.
You connect the guitar to one of the effects at a time and take the output only that effect to the the amp.
You need a dummy 6.5 jack or cable to keep the others effects powered.
The idea is the power supply is supplying full power but you only listen/use one effect.
This still might not pick-up high gain situations.
The other way is to check the regulator is not dropping out with an oscilloscope.

there is only one point that connect the 0V and my fx chain ground.
wich from my ps to my Boss MT-2. I just cut the other 0V to avoid ground loop. the noise is at low frequency. the noise is appear when I enggaging my distortion

more stompbox plug to my ps = more bigger noise level

Only 2 effect plug in = quite
preamp + Boss MT-2 + Metal Monster = quite but I can hear the low freq noise a little bit
preamp + Boss MT-2 + Metal Monster + Cyclon delay = the low freq noise becaming anoying
that 4 stompbox + Chrous = worse

[antonis]

did you mean something like this?

Probably yes, Tom meant something like this but, it still isn't fully isolated...

To make it clear, forget about primary transformer winding and focus on secondary windings..

You need one individual secondary for each supply which by any mean shouldn't share any common point..!!
(i.e. your multimeter should show open circuit between them..)

[EBK]

I agree you can't make a multi-isolated-output supply from that (unless you could split the coils at the tap...).

What did you mean about split the coils at the tap?

Merely an academic lark.  That falls into the "Kids, don't try this at home" category.  In theory, if you have access to where the center tap connects to the coils, you could physically cut the winding into two windings (turning 3 wires into 4), sort of like splitting a humbucker pickup into two single-coil pickups.  In all seriousness, please don't try this.  The most likely result would be a ruined transformer, and it simply isn't a practical idea for many reasons.

[Rob Strand]

there is only one point that connect the 0V and my fx chain ground.
wich from my ps to my Boss MT-2. I just cut the other 0V to avoid ground loop. the noise is at low frequency.

That should work OK too.

more stompbox plug to my ps = more bigger noise level

Only 2 effect plug in = quite
preamp + Boss MT-2 + Metal Monster = quite but I can hear the low freq noise a little bit
preamp + Boss MT-2 + Metal Monster + Cyclon delay = the low freq noise becaming anoying
that 4 stompbox + Chrous = worse

OK that is good information.  If your power supply is not dropping out, I'm not sure what is going on.

1) How close is the power supply transformer to the effects pedals?

Try:
- move the power supply box close to the effects and see if it gets worse
  and away to see if it gets better.
- also try many different orientations of the power supply box hold it in you hand
  and rotate it on all axes.

If you hear any changes in the humm then maybe you have to move the transformer
far from the effects and cables.

2) Is the power supply 0V connected to the mains ground?
If it is you need to disconnect the grounded 0V connection as this forms a ground loop (causing humm)
through your amplifier.

[anotherjim]

You're looking for multiple secondary winding type. More than 2 secondaries are not commonly held in stock.
Nothing stops you using two dual secondary types, simple feed both off the same AC supply.

2 primary windings is very common. Wired in series for 220v and parallel for 110v.
Look for the dots adjacent to the coil ends. These show relative phase of the windings. When the Dot end of one winding is going positive, so are the Dot ends of all the other windings.
You must have the phase information for these more complex arrangements or you could get a big bang or nothing at all.