Battery power for ‘street’ amp.

[adrian_k]

I have a Boss Street II ‘busking’ amp. It runs on 8xAA batteries, so that’s 12V dc. It will also run on the supplied mains adapter which provides 9V dc (actually that’s the spec, I should check though).

I also have a Makita drill, and have noticed that I can use the battery with one of these to get 12V dc: Waitley ADP05 Power Source 2 USB... .

However I don’t want to plug that into the amp dc input which seems to be expecting 9V without some idea of what will happen, even though it works with 12V of AA battery power. I’ve tried checking to see whether the dc power input is connected directly to the battery terminals, the negative is but the positive isn’t. It’s tricky to check this though because afaik the positive (outer) is designed to disconnect the battery power when plugged in.

Any thoughts?

[ajay_m]

Playing it safe by wiring 4 X 3a diodes in series on the hot side will drop 2.8v and waste a little power but is simple and cheap, the diodes cost pennies on eBay and you can just make up an adaptor lead with a bit of heatshrink. Also gives you reverse polarity protection on the battery side for free!

[Wonks]

It’s also possible it works on 6v (probably 5v internally once regulated) with a 2 x 4 battery arrangement for more current capacity (probably then with some voltage increasing circuitry for the power amp circuit) Don’t assume it’s 12v just because of the eight batteries.

In that instance you’re already reducing 9v to 6v or 5v, so more than 9v could be pushing the regulator.

[adrian_k]

Ah - thanks.

@ajay_m Little electronics knowledge at this end, so having done a little reading, something like these?

https://www.ebay.co.uk/itm/281668779916 ... media=COPY

Just to check my limited understanding, you get a .7V drop in the forward direction for each silicon diode (hence your 2.8V series total).

Above diodes are rated 3A, battery and the power adapter are 2A, so should be ok? Does the voltage rating matter as it seems to refer to the max reverse voltage? Sorry for all the dumb questions…

@wonks - hi! Re the 6V possibility, when I checked the negative battery terminals connection to power socket centre pin would I have found two battery terminals that connected (I only found one)?

[Wonks]

If it uses the sort of arrangement shown above, then it could be 12v or 6v. It just depends how the two sets of battery terminals are connected.

[adrian_k]

If it uses the sort of arrangement shown above, then it could be 12v or 6v. It just depends how the two sets of battery terminals are connected.

Yep that’s the arrangement. When I checked the connection (with a multimeter) to the centre pin of the 9v input, only one of the negative battery terminals connects, so suggests no common negative terminal between subsets of batteries, and double checking just now that is the case. So unless I’m missing something they are all in series i.e. 12V. ?

Edit - managed to measure the voltage at the ‘9V’ input socket, with batteries in, with no plug in (so batteries not disconnected), and saw about 11V, so I think it’s safe to say that’s what’s being used.

Anyway, dropping the input voltage from the drill battery seems a cheap and safe way to go.

[Wonks]

Yes, looks like a 12v arrangement. But worth checking.

[tacitus]

I ran a phono preamp off an 18v strimmer battery, which worked but didn’t make it sound any better to my ears. I used a black and decker one off our, er, strimmer.

I then bought a 14.4v b&d battery to run a blutooth turntable outdoors. Both these used a B&D charging clip rewired with the required power connector.

In the end, I tried both items with both batteries, trouble free, though the 18v appliance might have died earlier with the lower voltage source.

I now need to find a 9v battery supply for my Roland interface. Trickier voltage, and the Roland psu voltage seems to be very accurate. So I could do the trick already mentioned or get the required voltage with a D-cell frame or two.

It’s not a major issue - I normally record in places with power, but some churches have the tea urn plugged in to the only socket …

[James Perrett]

It is always worth remembering that battery voltages are only nominal voltages. A 12V rechargeable lithium pack may well contain 3 cells in series which would range from 12.6V when fully charged down to 8.4V when fully discharged. An 8 cell 12V NimH pack would go from 12V when fully charged down to about 8V when discharged.

If the device is expecting to be used with a regulated power supply then you really need to use a regulator with an external battery pack to keep the output voltage constant. It looks like the device that the OP linked to incorporates a regulator so the diode trick would work in this case but beware of connecting batteries direct to a device that is expecting a constant voltage.

[ef37a]

Can I put a plea in here for some consideration if buskers are using amplification?

There is a guy who rocks up in our town centre with a Vox cube and a mic. The cube is a very impressive little amp but I can hear him 100mtrs away. We sometimes get an old boy on an accordion and, rarely for me, a gal playing classical violin. Neither of these people stand a chance against 'Vox Man'!

I don't blame the guy for the vocal support. Singing all day he needs to care for his voice but he does not need to be SO bloody loud! I still drop a couple of quid in his case but I give more to the acoustic artists.

Dave.

[adrian_k]

Haha well I don’t use the amp for busking, but I will bear that in mind!

[ef37a]

Haha well I don’t use the amp for busking, but I will bear that in mind!

Look Adrian! You said "busking amp" FFS! Don't confuse this old, deaf one eyed, meds ridden bloke.

Dave.

[ajay_m]

Not Schottky diodes they have too low a voltage drop. Just regular silicon diodes are what you want. Well to be honest you could use Schottky diodes but you'd need about 7 in series instead of 4 that's all

[Folderol]

Not Schottky diodes they have too low a voltage drop. Just regular silicon diodes are what you want. Well to be honest you could use Schottky diodes but you'd need about 7 in series instead of 4 that's all

They are also considerably more expensive. Also, bear in mind that in order to drop voltage, diodes use energy... which they turn into heat so they don't want to be too enclosed. If you're dropping about 2V all told at about 1A, that's 2W of heat that has to go somewhere.

[adrian_k]

Haha well I don’t use the amp for busking, but I will bear that in mind!

Look Adrian! You said "busking amp" FFS! Don't confuse this old, deaf one eyed, meds ridden bloke.

Dave.

Fair point!

[shufflebeat]

Assuming they the internal voltage from the battery back is 12v - is there a problem with just fitting a second socket that connects directly to the battery pack +/- terminals?

Remove the batteries, by the way.

We used to run guitar and bass amps off motorcycle batteries with no problems.

[adrian_k]

Assuming they the internal voltage from the battery back is 12v - is there a problem with just fitting a second socket that connects directly to the battery pack +/- terminals?

Remove the batteries, by the way.

We used to run guitar and bass amps off motorcycle batteries with no problems.

Thanks yes I did think of that, but having proved that the installed battery voltage shows up at the dc power adapter input socket, I think that plugging 12V in there achieves the same thing.

[resistorman]

I'd use something like this:

https://smile.amazon.com/dp/B07JZ2GQJF/

[adrian_k]

That’s a snazzy thing….

[Jimmy B]

If you don't mind me asking, what is the rated output current of the supplied power supply (it should be printed on it)?
The reason that I ask, is that the Boss website quotes a current draw of 390mA. This is not in any way consistent with a claimed output power of 2x5 watts (more like 2x2.5 watts at most).
The accompayinng battery life figures suggest a current drain of 250 mA.
Perhaps the current draw is some sort of average music power usage?
Don't get me wrong, I have heard a number of buskers using this amp and have been surprised at how loud and clear it is.
Perhaps there is a different way of specifying portable amps?

[Wonks]

You need to know what 'watts' they are basing their claim on. You've got RMS, AES, music power and peak to chose from. I'd guess 'music power', given that playing back music is its job. So, yes, probably 5W music power compared to an 'RMS' 2.5W, though AES watts tend to give a bigger figure than the older RMS value (itself a vague and nebulous value without full clarification of the signal used).

[Jimmy B]

I did wonder about that. Since 1974 there has been a strict rule in the USA on how to define output power for consumer amplifiers, but I'm guessing that this rule may not apply to pro audio equipment?
https://www.ftc.gov/legal-library/brows ... ifier-rule

[Folderol]

I did wonder about that. Since 1974 there has been a strict rule in the USA on how to define output power for consumer amplifiers, but I'm guessing that this rule may not apply to pro audio equipment?
https://www.ftc.gov/legal-library/brows ... ifier-rule

Interesting. I didn't know about that. Looks well thought out. Not much wiggle room there

[Wonks]

Given that it's a nominal 9v input not 12v, if the 390mA is for that 9v input and not the batteries, than that equates to 3.5 watts. Allow 0.5w for the digital circuitry, that's 1.5W per channel for the amp. So that 5W+5W figure may well be peak watts.

Iin terms of SPL, it's a 5.2dB difference between 1.5W and 5W.

But that 390mA may also be an average current draw with dynamic music playing.

Just not enough information!

[Jimmy B]

Yes, it's also a moot point because in an integrated unit we don't know how efficient the loudspeakers are, and the evidence is that the whole product is extremely fiit for purpose. I was just curious, that's all.