DIY Power Supply - recomended Voltage for common pedals

[MoruyaGuitarist]

Hi All,
This may have come up before and if so you are welcome to send me a link to a previous discussion 

What are your thoughts on voltage to use for common pedals such as Boss, Tc Electronic, Joyo etc ?
I'm building a power supply including Lithium cells that will also run for several hours when it is unplugged.

Thoughts on maximum safe voltage as in don't blow it up, is running slightly higher voltage useful ?
i have measured 9.6 volts with a new battery under load in a normal manufacturer pedal. You can also buy these 9 to 18 volt converters for pedals.

One thing I do know as I have done some mods on Boss pedals is that quite a few use some 16 volt capacitors in their circuits though most seem to be 50 volt caps. Now I've never stress tested caps before but I'm pretty sure 18 volts into a 16 volt cap will make it pop 
I don't know much about the Boss MIJ pedals except they were "designed" to run on 12 volts. I highly doubt their circuits would be different, at a guess they may use a Series diode for protection copping a .6 volt drop vs a parallel diode ?

I also have some pedals such as a TC electronic Dark Matter and Digitech Valve Distortion that have internal charge pumps and run at 18 volts or more from a 9 volt supply. Obviously you wouldn't want to use one of those 9 to 18 volt convertors on one of those pedals........

I will build an adjustable control, my current guess is run a regulated & filtered output at 9.6volts to 10 volts. I suspect running "normal" pedals at 12 volts would still be fairly safe in terms of circuits containing 16 volt caps, not sure IC's have that much limit on them, Op-Amps can often run over 30 volts and pedals generally don't run enough current where power/heat becomes an issue.

Cheers,
Wal

[DIY Bass]

I'm going to say "it depends".  I had an old ibanez analog delay that needed 2 9v batteries or an 18V power supply.  Most modern pedals are designed to run off 9v, and modern power supplies are usually regulated pretty tightly to 9V.  Some pedals will work fine at higher voltages, others will be damaged.  You can be pretty sure that if you feed it whatever is specified on the pedal or in the manual, then you will be safe.  If you want to feed it higher then you will pretty much need to evaluate each circuit on a case by case basis.

[composition4]

"You can please some of the pedals all of the time, you can please all of the pedals some of the time, but you can't please all of the pedals all of the time".

I'd build it for 9.6V like a new disposable alkaline and be done with it, you could spend forever deliberating over a few millivolts which will in reality make no difference. Or 9.0V. Not worth making it adjustable over such a small voltage range.

[Rob Strand]

I've run the old ACA adaptor Boss pedals on 9.2V to 9.5V at the DC jack and they do work fine.   I'm much happier about running them from 10V to 11V.   Some of the pedals have quite a large drop from the DC jack to the circuit. You have to remember these pedals were often ran from batteries so they need to work down to the 7V to 8V battery voltage region.


Here's some user perspective results from some old ACA adaptor Boss pedals
based on the LED.

Tip: there's no need to open the pedal to measure the internal supply voltage.
Place the DMM meter + lead on the DC jack + and the DMM - lead on the
chassis/audio ground.

LEDs are dim by todays standards to it's easy to misinterpret where normal is.

The LED is interpreted loosely as (internal voltage/battery voltage):
10V battery new, 9V battery OK, 8V battery low but still OK, 7V battery clearly low, 6V LED barely lights, 5V LED off

The drop from the ACA adaptor socket to the circuit isn't consistent across pedals.
That means the external voltage varies quite a bit for the given LED indication.

LED = Battery a little low but OK, external voltage at least 9.2V to 10.2V 
LED = Battery OK, external voltage at least 9.5V to 13.0V
"At least" means some pedals need the upper voltage to interpret the LED as indicated.
So yes, some pedals have DIM LEDs and a high drop so they need 13V before the LED looks bright

[MoruyaGuitarist]

Thanks Rob,
so it's not just me that think 9volts might be too low 
I didn't know that about the brightness of the diode light but now when I look it does actually say "check" on the Boss pedals.

Curious about the drop between the power jack and the circuit as you said with some pedals. A pedal I recently modded was a Boss NS2 and these use a parallel diode for protection, so there is no .6 volt drop. I have seen the series protection diode's in schematics which is the more obvious design choice in electronics.

In those cases, say for an average pedal (not digital) with a brand new fresh battery you would get around the 9.5ish volts (depends on the current draw). Now compare this to a "tightly regulated power supply" at 9.0v, when you take off the diode drop it means you would get 8.4 volts at the circuit.

9.5 volts vs 8.4 volts is more then just a few millivolts difference.....   

[Rob Strand]

I didn't know that about the brightness of the diode light but now when I look it does actually say "check" on the Boss pedals.

I believe that name is historical.   From memory, some of the *very* early Boss pedals the LED only came on when battery was flat.   Then later they realized a LED was better off used for effect/bypass and let the LED dim when the battery goes flat.   The didn't change the labels.  There's a story like that anyway, even if I'm off a bit on the details.

You can find old schematics with the old LED schemes on the web but they are hard to come by.

Curious about the drop between the power jack and the circuit as you said with some pedals. A pedal I recently modded was a Boss NS2 and these use a parallel diode for protection, so there is no .6 volt drop. I have seen the series protection diode's in schematics which is the more obvious design choice in electronics.

The original Boss pedal had the diode and resistor in the ground.   They used a Boss ACA AC-Adaptor.   The idea behind the boss scheme is you can daisy chain the power and you don't get ground loops or hum from current pulses from the unregulated supply going through ground of the effects.   It actually works very well.

Ibanez and many other manufactures have the more common connection where the -ve on the DC Jack connects directly to ground.   People did have problems with hum on these pedals when using unregulated supplies. 

In the late 90's Boss changed all their pedals to the directly connected scheme and removed the series resistor and diode. Boss call the adaptor for those the PSA adaptor.  It's regulated 9V.  The pedals have stickers near the DC connector saying PSA or (later) ACA.   However, the change over period was gradual.  I'm pretty sure there were some PSA in the mid to late 80s. 

So the NS-2 is a PSA type DC input,

http://obrazki.elektroda.net/47_1279571553.jpg

In those cases, say for an average pedal (not digital) with a brand new fresh battery you would get around the 9.5ish volts (depends on the current draw). Now compare this to a "tightly regulated power supply" at 9.0v, when you take off the diode drop it means you would get 8.4 volts at the circuit.

9.5 volts vs 8.4 volts is more then just a few millivolts difference.....   

Yes it takes out quite a bit voltage.  It's not just the diode there's a series resistor.  That has more drop than the diode, maybe 1V to 3V.   The series resistor varies wildly from say 56 ohm to 470 ohm.  Boss tune the value to suit the current draw from the pedal.  So high current digital pedals will be low values and the old-school low current analog pedal have high values.

If you think about loss of headroom going from 7.5V to 9.5V is quite significant.  You lose at least 1V swing on each rail due to the opamp so 7.5V had 5.5Vp-p swing  whereas 9.5V has 7.5Vp-p swing;  1.36 times more, and it could be a little higher than that.

[DIY Bass]

9.5 volts vs 8.4 volts is more then just a few millivolts difference.....   

Well, if you are going to talk diode drops then it's more like 8.8v vs 8.4v.  Thing is that is a difference, but is it a difference that you would hear?  I think that in most cases you wouldn't actually hear any difference when in use.  On the other hand, the slightly higher voltage is unlikely to break much, so you may as well.

[Rob Strand]

I think that in most cases you wouldn't actually hear any difference when in use.

It depends on the pedal for sure.   A BF-2 Flanger only has 5.6V going to the BBD so that's more of a bottle neck than the supply.  I suppose you could argue the input should over 7.8V or so to prevent the regulator dropping out.   The OD-1 Overdrive has clipping diodes which limit the signal.   However pedals like the OC-2 Octave have a gain stage at the front end.  When used with bass it can overload pretty easily.   I modded mine ages ago because it used to bug me and after the mod I can run the OC-2 on a 9.2V to 9.5V supply without it clipping.   Out of guitar/bass/keyboard the guitar is probably the weakest signal and you can get away with low voltages more often.

[DIY Bass]

That is useful to know.  I am thinking about building an OC-2.  I have regrets about selling one.  The first pedal on my bass board is first in line precisely because it has a -10 dB active/passive switch on it and the rest of the board does play more nicely with my variety of basses if I can switch that input.

[Rob Strand]

That is useful to know.  I am thinking about building an OC-2. 

I'm pretty sure I changed the 2k7 to 3k9.   That makes the gain of the clean path *just* over unity.  Since we usually add octaves on top of that the signal gets louder anyway but that's after the mixer which reduces the level - so no clipping.


"Check" LED on Old Boss Pedals

Quote

    I didn't know that about the brightness of the diode light but now when I look it does actually say "check" on the Boss pedals.

I dug up this old DS-1 mod sheet.  This official Boss mod sheet changes the very early LED behaviour to the LED behaviour we see today.

You can see the dotted line and non-numbered wire for the original circuit.   Basically the LED has nothing to do with the Bypass/Effect switching.     The way it worked was you hold the footswitch down and the LED lights if the battery is good.   In other words holding the footswitch down "checks" the battery.   So that's where the historical "Check" label comes from.   In normal operation the LED flickers when going from Bypass to Effect or Effect to Bypass since you normally press the footswitch quickly.

[MoruyaGuitarist]

Update :-
Have converted my Boss NS2 pedal to happily run and tested it at 13volts, will possibly go up to 16volts, just 2 caps to change. The main power supply filter cap C1 - 100uF is rated at 16volts, so is overrated to handle only 9v for a safety margin. 12 volts is probably ok but swapped this out for a 220uF - 25 volt for an increased margin, didn't have a 100uF :-P
A bigger issue was C21 - 47uF which is the Bias voltage cap only rated at 6.3 volts, cutting it close. I swapped this out for a 16volt 47uF, giving a max of 32 volt total supply voltage, with a de-rating safety margin is now more then fine. I'm not an expert with AC electronics, the majority of AC signal coupling caps in the NS2 are rated at only 16 volts. I know the maximum signal voltage swing will be slightly less then the power supply due to .7volt Si junctions so maybe 15ish from a 16volt supply. In any case am happy and can safely run it at a much higher voltage then before. I've decided to run all my normal analogue pedals at 12-13 volts, and the digital pedals and voltage doubled ones at 9volts (Internal charge pumps, convert 9v to 18v).

At the moment my "prototype power supply" consists of a 1.3 AH 12volt lead acid battery, full charge = 12.8 volts. Being super lazy I will probably end up using it for a while, it is a fully isolated power supply for %10 of the cost of a store bought one.