Is it safe to use a switching power supply instead of a linear unregulated?

[VintageCharlie]

Hello everyone,

i got my hands on a Classic Amplification CV-2 vibe and the builder strictly recommends a linear unregulated 300mA 18v neg tip power supply. These are impossible to find in europe. The only one that still is available that i am aware of is the electro harmonix one (it is positive tip though, but that can be easily changed), which despite claiming 18v in fact measures 24v.

I have a power supply that came with a FoxRox TZF II Flanger (analog) it is 18v neg tip 1000mA switching power supply. Works perfectly with the flanger and other analog pedals, no noise, etc. It's specs can be found here: https://www.acadaptorsrus.co.uk/replacement-18v-1a-ac-dc-adapter-for-model-sjshad180103-guitar-power-brick/

Is there any plausible way how this particular power supply might be unsafe for the vibe pedal? In my understanding, if the voltage is correct, enough current is provided and the polarity is correct, there is no other property that would pose a real issue, is this correct?

Thanks a lot for any input and kind regards,

VintageCharlie

[PRR]

> the builder strictly recommends a linear unregulated 300mA 18v neg tip power supply.

Quite strange. Maybe ask him?

> the electro harmonix one ..., which despite claiming 18v in fact measures 24v.

What about at 300mA? Get a 50 Ohm 10 Watt resistor and hang it on the output. That's 360mA so if it drops to or a bit under 18V it does what an un-regulated supply is expected to do.

[Rob Strand]

I have a power supply that came with a FoxRox TZF II Flanger (analog) it is 18v neg tip 1000mA switching power supply. Works perfectly with the flanger and other analog pedals, no noise, etc. It's specs can be found here: https://www.acadaptorsrus.co.uk/replacement-18v-1a-ac-dc-adapter-for-model-sjshad180103-guitar-power-brick/

I'm not sure if  that adaptor has any safety approval markings.  I can see CE but it might be the deceptive China-Export marking.  I'd be worried about using it unless they can supply documents showing otherwise.

(One tell tale sign was the exposed LED.   You normally cannot pass ESD testing with an exposed LED.  That's why you see light pipes going down to the LEDs on most power supplies these days.)

[Mark Hammer]

Some switching PS units and pedals don't get along very well.  I am not aware of any dedicated Vibe pedals, however, that are digital (except for maybe the TC Viscous Vibe).  So that sort of pedal should be fine with a switching supply.  No real risk of heterodyning that I would expect.

When someone says an "unregulated linear" supply, I'm not sure what they mean.  A wallwart that simply provides AC is clearly unregulated, since any regulation is normally intended as part of the rectification to turn AC into DC.  But then, an AC supply does not have either a tip or shaft that is positive, so the manufacturer appears to mean a DC, rather than AC, supply.  There IS such a thing as poorly or minimally regulated, in the world of budget wallwarts.  They still count as DC but would often be subject to introducing hum as a result of the poor regulation.

There are also pedals that have regulation on-board, but still stipulate a DC supply of a higher voltage.  For instance, many EHX pedals do so.  Since many regulators require an input voltage of at least 2 volts more than what they put out,  insisting on a 15-18V wallwart, for the operation of a pedal that down-regulates the higher voltage into a stable 12V, or 24V that gets smoothed out to 15V, makes perfect sense.  But the down-regulation does not benefit from, nor does it require "unregulated" DC.  Certainly having an already smoothed DC input helps in reducing any possibility of hum, but the on-board regulation is supposed to do the heavy lifting in that case.

My guess is that any old DC wallwart of suitable voltage, current, and plug orientation will be fine.  It could have some regulation, or have great regulation.  Gutshots of their other vibe pedal indicates they have on-board regulation, so I can't imagine the degree of wallwart regulation should make any difference.

[Rob Strand]

I found this site, which has similar *looking* power supplies.
They may be entirely different internally.

http://www.szrsun.com/html_products/1201500E-95.html

These are supposed to have approvals, which are indicated in the table.

Notice these ones don't have an LED.

I still don't see UL markings on the devices.  I only see CCC on some and CE on others.

[Max999]

It is safe but will prob defeat what the guy who build it wants you to have: less noise. This is all I can personally come up with about why he wants you to use unregulated linear.


The switching power supply will have a bit of noise ( even if you can't hear it), and the voltage regulation in a regulated PSU also adds a tiny bit of noise.

As a matter of fact, the unregulated one he specs is the most dangerous option.

[Rob Strand]

The only one that still is available that i am aware of is the electro harmonix one (it is positive tip though, but that can be easily changed), which despite claiming 18v in fact measures 24v.

This is quite normal.

I once took some statistics of unregulated power supplies.  Here's the results

Vnom is the DC voltage on the label
                                                    % of Vnom under stated conditions
Open Circuit Voltage:          min  111%      average 127%           max 146%
Voltage at rated current:      min  76%        average 90%            max 100%

On average, manufacturers allow the voltage to dip to 90% at maximum current.  Presumably in order to take the edge off the unloaded voltage.  One might expect 141% for unloaded voltage if we design for 100% but on average we get approx 90% of 141% =  127%  which is what I actually measured!  It's like wall-warts are design to be 10% down.

If we apply that to Vnom = 18V,
Open Circuit Voltage:          min  111%      average 127%           max 146%
                                          = 20.0V           = 22.9V                   = 26.3V

So 25V is certainly in the expected range.

The web site says:

Our Classic Vibe CV-2TM and Vibe-Baby CV-2TM our pedals are tested during the build process and the post-build tuning process with a standard 18v/300mA linear un-regulated power pack (wall-wart) as this is our recommended power method.

So we can only assume the unit is designed to handle the elevated voltages.   When the effect is present it will load the supply and the voltage will drop from the open circuit voltage.
The psu current spec is indicated as well  but without the power draw of the unit we can't guess what the voltage will be when loaded by the effect pedal.

If you use an 18V regulated supply the pedal may or may not work 100% correctly.  You would have to ask the manufacturer.

[Mark Hammer]

But wouldn't you think that the impact of degree of regulation would depend on what the actual gap is between the external supply, and what the on-board regulation aims for?  For instance, if the on-board circuitry takes a nominal 15VDC external supply, and regulates it down to 12V internally, that could be problematic for the reasons you note, but an 18VDC external supply could still vary and hit the target nicely.

[Rob Strand]

But wouldn't you think that the impact of degree of regulation would depend on what the actual gap is between the external supply, and what the on-board regulation aims for?

Exactly!  We don't know what's inside so we can't guess.  Only the manufacturer knows.

For an unregulated 18V supply, even though the *average* voltage under load might be 23V but there's ripple on the supply so the dips of the ripple will be low.  Maybe say 1V.     So the minimum voltage might be 23-1V = 22V.  (Or for the lowest case in my table maybe 20-1 = 19V).   The thing is it's always more than the 18V you get from a regulated 18V supply.

If the device has an 18V regulator then it probably won't work with the regulated supply.  However if it has a 15V regulator it probably will work.

When I read the website the site specifically mentioned stuff about the original not using a regulated supply and it implied that was the reason they used an unregulated supply.   My guess is it probably has no regulator.  So the circuit probably expects around 22V.   If you use 18V from an unregulated supply then the voltage is down by a substantial fraction.   The output of the oscillator will be low, that won't drive the lamps (or LEDs) as hard and then the depth of the effect will be weaker.

[Mark Hammer]

So, if I read you correctly, more a question of optimal performance than one of safety.

I have a couple of Boss BF-1 flangers.  They only use an external DC supply.  The chassis says 9VDC, but the service manual says 12VDC.  It "works" without any problem, using a 9V supply, but the sweep is actually wider and more impressive with a 12V supply.

[Rob Strand]

So, if I read you correctly, more a question of optimal performance than one of safety.

Safety has more to do with the design of the plug-pack.  The OP was concerned about blowing up the units since the unit says 18V and he measured 25V

I have a couple of Boss BF-1 flangers.  They only use an external DC supply.  The chassis says 9VDC, but the service manual says 12VDC.  It "works" without any problem, using a 9V supply, but the sweep is actually wider and more impressive with a 12V supply.

I believe 12V is the measured voltage and 9V is the nominal rating of the plug-pack.  The old Boss adaptors were 9V unregulated however the measured voltage as about 12V.   That's where the difference comes from.
The circuit has an on-board regulator which will produces about 10.3V on-board (possibly less if the plug-pack voltage drops).  If you connected a 9V *regulated* supply you probably get about 8.3V   How the circuit responds to 10.3V and 8.3V depends on the specifics of the circuit.  Like if the performance shifted only 10% then you might not tell but if it shifted 20% then you might.

I don't think there's any doubt the Classic Amplification CV-2 will work with 18V or 25V.  The question is whether the performance will change enough to notice.   Like some people collect golden units of particular effects which have very subtle differences in performance where as other people use different supply voltage without ever considering it could have an effect.   Like anything, when you start looking details everything is a big confusing mess and you wonder why anything works at all!