Pro-Ject Pre Box S2 Digital


(Sean) #787

That’ll work just fine. You can just use the USB output port (5V/2.4A) and a USB type to micro USB cable like this:

You can also achieve the same thing using one of the many USB powerbanks available (like below):

To get the isolation from mains power though (like during critical listening) you don’t want to be charging (connected to AC mains power) at the same time as listening. So just run off the battery with the charger unplugged.


(Geoff Mirelowitz) #788

@Sean2016 Thanks so much!


(Sean) #789

Not a problem. I would lean to the Mophie though, over the one you linked - they’ve been making battery banks for a long while. I think Apple Stores sell Mophie, so I assume Apple are happy with them too. Just for feel good factor - I don’t have any facts as to why one brand is better than another.


(Magnus) #790

I heard that power banks has switched circuits inside to get correct voltage, so its not a linear power.


(Sean) #791

They sure do.

But it may be a choice of the lesser of the evils… powerbank switching regulators (which by the way, is followed by ultra low noise linear regulators inside the DAC unit itself…) vs linear PSU’s with mains power coupled leakage current loops and mains coupled RF…

The powerbank has the advantage of being de-coupled from mains RF and AC leakage current loops… but only if you unplug it’s charger from the wall of course during listening, otherwise the powerbank is mains power coupled and you defeat this potential advantage entirely.

Best to trust your ears in the end, of course.


(Geoff Mirelowitz) #792

Thanks for the advice. I have to say I’ve been pleased with he quality and value offered by the MassDrop products (two different headphones) I’ve purchased. Your advice is likely a safer choice. I’m still thinking it over.


(Magnus) #793

I experimented a little, and tried batteries as power, one 6v 12ah for the Pro-Ject DAC, and 4*1.2 rechargeable AA batteries for my transport (Allo USBridge). And I have to say I am very impressed by the result, far better than the old iFi iPower 5v I was using. The step-up in sound quality was very noticeable.

They batteries last more than one day, so charging them at night. And the lead battery is sealed AGM so safe to use indoor (or so I hope) :slight_smile: The battery is not as big as it looks on the picture, its about the size of a thick pocket book.

The only problem: I am unsure how the DAC will handle 1 - 1.5V over spec in the long run. Have to wait and see I guess.

Here is a picture:


(Sean) #794

Does it come with charging adapter? And what cables do you use to get it from the battery leads down to microUSB for the DAC? Can you share some photos. I was interested in this same Panasonic for something else.

I’d measure it’s Vdc output if you can - in case it’s output is greater than 6Vdc. Just to be safe.


(Magnus) #795

No cables came with it, I bought a 5.5x2.5 mm DC connector with cable, and a DC adapter -> micro USB, and then the 4.8mm clips that fits the battery connectors. Also bought a charger.

VC output is about 6.5v when charged, but the DAC seems to handle it. If you buy one, it would be interesting to hear a comparison with a good LPS (I only used iFi iPower 5v before and the battery sounds much better than those).


(Sean) #796

USB power specification allows up to 5.25Vdc.

Are you sure the DAC isn’t switching to USB bus power because your SLA battery is over the limit?

If you unplug the USB cable, does the SLA battery still power the DAC?


(Magnus) #797

Yes, I use the UpTone A>B connectors which have a “cut power” switch which I turn off (it needs to be on when detecting the DAC, but then its ok to turn it off). So the DAC only gets power from one source.

This battery business for the DAC and Allo USBridge started as a little experiment cause I was bored, but the sound improvement is big enough that I will keep using it even with a little extra work to charge batteries at night.


(Sean) #798

I’ve discussed PSU’s with a couple famous DAC designers. Their benchmark is always to compare their DAC’s PSU section design/performance when connected to AC mains power, with performance powered by a car battery.

SLA’s have lower output impedance than any linear PSU on the market. In addition to being mains power de-coupled of course.

No surprise it’s the best SQ you’ve had :slight_smile: But I am just as surprised as you that the DAC’s power input can handle over 6Vdc…

Which model charger did you get? Does the battery itself have any electronics to indicate low power (it needs charging)? Or is it just a basic SLA in that regard?


(Magnus) #799

No indicator on the battery, but the DAC shuts down at around 4.5V so thats a good indication :slight_smile: but I have a multi-meter so can measure the DC on the battery (right now i have played it for 1.5 days and its at 5.1V so going to charge it tonight).


(Sean) #800

Cool! I’ll pick one up when I get a chance.


(Magnus) #801

Loaded the battery when I slept, it has 6.7V fully loaded, but the DAC seems to work fine (and sounds very good). The only thing I notice is that the DAC gets a little warmer than usual, I guess some internal voltage regulators has to work harder.


(Martin Webster) #802

Stick an LDO between the battery and the DAC; these operate with minimal input to output differentials, so 6V to 5V is achievable. A few quid could save your DAC in the long run.

Something along the lines of this …

https://www.analog.com/en/products/lt3045.html


(Magnus) #803

That might be a good solution, but I think I will run it as it is for now since it seems to work. The DAC gets warm but not hot (a good temperature for warming your hands). And I have been thinking of upgrading, and if it breaks I can explain to my wife that I have no choice but to upgrade since its broken :slight_smile:


(Dick Vliek) #804

What does she do to achieve the same ?


(Martin Webster) #805

Yes, let’s hope @Magnus doesn’t get upgraded when the wife finds out! :rofl:


(Magnus) #806

She says: “Im going out, taking your credit card with me.”
And I reply timidly: Ok