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what's so special about Boss PSA psu's? Drum Machines & Samplers
Old 13th September 2018
Lives for gear

what's so special about Boss PSA psu's?

any other centre negative psu, and my tr-626 comes on with the
'play' LED half-lit. even with a Korg 9vDC 600mA centre negative,
which should be decent quality.

the only psu it likes is the Boss PSA (2nd gen regulated type).
it doesn't even like the unregulated Boss PSA, the one that's
better for old guitar pedals.

surely the Korg one would be regulated? (electribe metallic series)

so what's the magic with the regulated Boss? - apart from the great
design that lets you unscrew it and repair it when the cable goes.

or is there a problem with my 626? maybe having a bad cap or something
in the power input circuit? maybe got a wrong voltage? (it works fine)
thing is, i have, um, two of them, and they both do the same thing, so
am inclined to think it's a psu thing.
Old 13th September 2018
Lives for gear

I don't know the box but 9V DC is 9V DC.
Old 13th September 2018
Lives for gear

Are you sure the other supplies you’re trying out can provide the same amount of current as the Boss unit?
Old 13th September 2018
Lives for gear
syntonica's Avatar
The voltage must match and the amps must be the same or higher. Probably, your amperage is too low.

Too high of voltage will fry your unit, too low will not power it on (most likely).
Too low of an amperage and you'll get weird, unstable behavior.

Last edited by syntonica; 13th September 2018 at 08:20 PM.. Reason: Ugh... New keyboard has mind of its own...
Old 13th September 2018
Lives for gear
fanriffic's Avatar

Originally Posted by niklasni1 View Post
I don't know the box but 9V DC is 9V DC.
But that 9V DC is being supplied by a PSU which clearly has other variables involved. Roland products are notoriously picky with PSU's, my SH101 for example. 2 different PSU's rated the same, one causes an awful hum on the output, one silent. Would be interested to know why myself.
Old 13th September 2018
Lives for gear

What @syntonica said. I've most often see half-lit LEDs from too little voltage, but it's easy to understand it also happening with too little current.
Old 13th September 2018
Gear Maniac
adamstan's Avatar

My 626 works even with cheap switching-mode PSU for stompboxes from Thomann. There is some whine induced by it, but it works.
Old 13th September 2018
Lives for gear
Muser's Avatar
usually caps suffer over time or a combination of that and the punishment they get.
so the older something is the more suspect that is, and caps in PSU's or power stages will often get punished harder.
Old 14th September 2018
Lives for gear

adamstan, that whine... seems familiar. did i notice that? i'll have to
check. that would freak me out, personally.

ok, so have it in front of me. says:
pri 220v~50hz 8VA
SEK 9V(DC) 200mA
then there's a little symbol like a resistor, with line running through it,
and: T500mA T25/E

this is the official Boss PSA-220

now, official Korg centre-negative, for older electribes. it's 600mA,
so should be ample (9vDC also, of course)
Korg KA189

pri: 230v~50hz 60mA
sec: 9V(DC)600mA

it also has the little symbol, as well as double insulation symbol that
the other one has as well.

2nd one is included as an example. if i use a generic multi-voltage 300 or
500mA, i get this same behaviour. so i'm thinking that this Boss psu is the
only one the 626 likes. even the earlier unregulated, official boss psa,
-which is known for delivering 12v unless under load, and more suited
to their early pedals- produces this half-lit LED.

i have, however, never had any problems with psu with sh101, which
seems a fairly tolerant machine, indicating, if memory serves, 9-12v.
so i suppose it depends how they've been treated.

my question about a capacitor etc. would involve something internal to
the unit, as opposed to in the external psu. and of course i get no
issue running it on batteries. as i said, both of these 626s exhibit the
same behaviour.(and i do find it hard to believe people feed 12vDC to
a 9vDC unit)
Old 14th September 2018
Lives for gear
Muser's Avatar
it’s hard to know why the LED would be less bright on a PSU which you feel is working better at the same time. it may be that the LED has some role and functioning improperly and that aspect is a coincidence. or it might be that the unit uses most of the power and starves the LED when using the lower wattage Boss PSU.

whereas with the Korg, it might provide too much overall voltage and if unregulated, you don’t know how much voltage and current might be changing against each other as the circuit operates with that particular PSU.

Boss PSU 1
1.8 watt

Korg PSU 2
5.4 watt

I think those values of volts and amps should convert to the above watts. the korg might not be a good idea to use. I had to make myself an LED volt and amp readout box with a couple of polarity switches and a DC In and Out, because no one makes one. that way you can tend to see what volts and amps are being pulled from a PSU by a given device.

so it may well be partly due to regulation and total power usage. or something with the LED, or they are all like that. ultimately hard to say without being able to see clearer actual power usage values in the different conditions.
Old 14th September 2018
Lives for gear

put more simply re: LED states

normally LED is off when not running, and (flashes at tempo?) when running.

with the non-Boss PSU, when not running, LED is 'at half mast', sort of
half on. (this is what adamstan should be seeing if he's not using the Boss)
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