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05-23-2020, 11:39 PM
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#1
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Human being with feelings
Join Date: Apr 2008
Location: Wales, UK
Posts: 757
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replacement power supplies for audio interfaces...
sorry, a bit OT this, but this is a knowledgeable and active forum, so...
My Scarlett 18i8 power supply is kaput. Looking round to buy replacements, I see that sometimes they may deviate slightly, or more than slightly, in terms of the amperage. the original is 0.5A, possible replacements are 0.4, 0.6, maybe 1.0. Does this matter at all, as long as the voltage matches - 12V?
I got an E in physics at A-level, so basically am crap when it comes to electronics...
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05-24-2020, 12:47 AM
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#2
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Human being with feelings
Join Date: Oct 2008
Location: West Wales
Posts: 766
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Shouldn't matter if it's over. (I got an E too but a pass is a pass:-) Not telling what I got in chemistry.
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05-24-2020, 12:56 AM
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#3
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Human being with feelings
Join Date: Aug 2007
Location: Norfolk UK
Posts: 1,351
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over is ok
they wouldn't let me take the exam...
__________________
Windows 10 Pro. Intel i7 3400ghz. 16GB Ram. Focusrite Scarlett 8i6. Reaper 64.
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05-24-2020, 01:11 AM
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#4
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Human being with feelings
Join Date: Mar 2008
Location: Oakland, CA
Posts: 10,478
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Are you sure it's the power supply, and not the Scarlett?
Did you test the voltage coming out of the power supply with a voltage meter?
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05-24-2020, 01:20 AM
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#5
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Human being with feelings
Join Date: Sep 2014
Posts: 2,643
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You would be better with the 1amp one than 500ma as it would be less likely to blow.
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05-24-2020, 02:51 AM
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#6
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Human being with feelings
Join Date: May 2011
Posts: 2,695
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I am so old I forgot what I got at school! But from what I remember a very qualified friend told me I think the principle is the device will attempt to draw what it needs so as long as the power supply can cope it should be OK.
PLEASE seek proper advice from a professional before relying on me though!
OT has anyone any idea why so many Soundcraft mixers for sale on ebay have no power supplies? Seems like that's the norm!
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05-24-2020, 03:50 AM
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#7
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Human being with feelings
Join Date: Feb 2017
Posts: 4,823
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Quote:
Originally Posted by martifingers
OT has anyone any idea why so many Soundcraft mixers for sale on ebay have no power supplies? Seems like that's the norm!
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i think maybe it's because they are quite specific to the make & expensive to replace - when the power supply goes people can't justify the expense of a new PSU and just try and sell the desk instead?
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05-24-2020, 03:57 AM
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#8
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Human being with feelings
Join Date: May 2011
Posts: 2,695
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I think that sounds right but then wouldn't you expect there to be an opportunity for 3rd party manufacturers? Or maybe there's patent issues. I speak as someone with 2 Spirit desks and one psu! The extra desk was so cheap I bought it as a spare!
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05-24-2020, 03:58 AM
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#9
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Human being with feelings
Join Date: Mar 2009
Posts: 514
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Hi,
as already stated here: 1A will stay the powersupply cooler as is not in the maximum demand. (The current that is running depends on the demands of the focusrite, not of the capability of the supply).
But something different may be of interest:
If possible try to get an old fashioned linear working supply with an ordinary transformer and a linear voltage regulation.
The modern digital supplies, expecially the cheaper ones, will generate steep signals on top of the voltage that will not harm the focusrite but will induce strange noise.
horst
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05-24-2020, 04:46 AM
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#10
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Human being with feelings
Join Date: Jan 2020
Posts: 680
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Several things to consider when replacing a power supply. Short answer long!
1 Current capacity. That should be a minimum of the original. There can be advantages to a slightly higher current models but see below. The higher current models might run cooler and be more likely to have longevity. They will often be bigger.
2 For contant voltage supplies, such as is typical for audio equipment (digital and analogue) the voltage (12v dc in this threads case) is crucial. Undervoltage means the supplied equipment might not work or performance is impaired. Typically some psu used to provide power in battery charging (and battery backup) might not work. Overvoltage and current drawn will be higher and safety margins reduced and maybe increases amp front end noise where the voltage is excessive. Tolerences often not in the manuals!
Power rails may be single sided such +15v or supply positive and negative rails such as +/-15v.
There is often a relationship between voltage output and actual current supplied (as opposed to specified). In a poorly regulated psu the output voltage can vary as the current drawn varies; as the current rises the voltage can often fall. The specified 12v on the psu may only be nominal. Similarly noise as ripple, particularly mains frequency and it's harmonics in linear supplies, or for switched mode supplies the higher switching artifacts can increase with power supplied. (Just noticed @siehorst's post!)
Higher current capacity does not necessarily mean better noise performance it is more down to quality design and design of the device being powered! Better a supply where the the design and components are not pushed to their limits to give good performance and reserve such as being impervious to mains power fluctuations. If the device being powered is designed to work with very clean power rails (i.e. it has limited filtering) then poor supplies (lots of noise/ripple on their rails) may not give a combination with good performance!
You pays your money and makes your choice....or something.
You can be quite lucky as far as performance goes but some parameters need to be matched!!
Next there is connector compatibility, style and size, and polarity of the terminals both physically and electrically.
Note: most of the above applies to 'constant voltage' supplies where within limits the current supplied is what is required by the load and the voltage stays 'stable'.
There are, but much less common in the type of equipment we usually consider, 'constant current' supplies -and hybrids of the two. For most purposes though that can be ignored, just be aware in case you ever come across one. The two are not interchangeable!
Also a bit like 4 wire speaker connections there are supplies that sense thd voltage at the load and adjust output accordingly. These usually (but not always) need the remote sensing wires connected to provide the correct voltage. Where they do need the sensing, failure to have it might lead to overvoltage supply or non at all. Again not common in most audio equipment but certainly a feature in computer motherboard power supplies -excepting external laptop supplies.
Last edited by Allybye; 05-24-2020 at 04:53 AM.
Reason: typos and a bit more clarification in places
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05-24-2020, 07:59 AM
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#11
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Human being with feelings
Join Date: Apr 2008
Location: Wales, UK
Posts: 757
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Thanks so much Allbye - I've just booked the week off work to read and understand your post!!
Oh and in answer to an earlier question, i know it's the power supply because the wire is clearly breaking up inside - I have to try and wiggle it into a position that stays on, and somehow hold it there, which is not easy...
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05-24-2020, 08:37 AM
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#12
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Human being with feelings
Join Date: Jul 2009
Posts: 7,570
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didn't see anyone mention this skimming through the thread but did you ask the company if you can buy a replacement?
that said if it's just some fraying wire you can shorten it by an inch and solder it in again, if you are able to open it without destroying.
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05-24-2020, 08:41 AM
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#13
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Human being with feelings
Join Date: Apr 2008
Location: Wales, UK
Posts: 757
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Quote:
Originally Posted by EpicSounds
didn't see anyone mention this skimming through the thread but did you ask the company if you can buy a replacement?
that said if it's just some fraying wire you can shorten it by an inch and solder it in again, if you are able to open it without destroying.
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I have actually just emailed Focusrite asking that. Might be safer bet - I just saw some 3rd party power supplies on Amazon and was thinking of taking that route initially...
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05-24-2020, 10:13 AM
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#14
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Human being with feelings
Join Date: Mar 2008
Location: Oakland, CA
Posts: 10,478
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Quote:
Originally Posted by Mudchild
Thanks so much Allbye - I've just booked the week off work to read and understand your post!!
Oh and in answer to an earlier question, i know it's the power supply because the wire is clearly breaking up inside - I have to try and wiggle it into a position that stays on, and somehow hold it there, which is not easy...
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If that's what it is, like the previous poster said, if possible I'd just cut the cord where it is fraying, strip both ends, and solder it back together. Make sure you don't mix up + and -, you might put colored tape on one of the two if the cable isn't clear - slice the cable open with a knife beforehand if necessary.
Or get a replacement direct from Focusrite, better than buying some Chinese knockoff unit off eBay.
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05-24-2020, 10:19 AM
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#15
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Human being with feelings
Join Date: Aug 2007
Location: Near Cambridge UK and Near Questembert, France
Posts: 22,754
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@Peter: (grin) Want to take a bet that the "official" ff power supplies are mide in China these days as well?
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Ici on parles Franglais
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05-24-2020, 11:06 AM
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#16
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Human being with feelings
Join Date: Jun 2011
Location: Belgium
Posts: 5,246
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Yep.
Besides, don't worry too much. Most nominal 12V powered interfaces take 10 to 16 V as input because someone might want to use it outside. A car battery is often a simple solution.
And since filtering is done after the internal switching power converters, don't look for an "analog" supply either. Bulkier, heavier, more expensive...
__________________
In a time of deceit telling the truth is a revolutionary act.
George Orwell
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05-24-2020, 11:08 AM
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#17
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Human being with feelings
Join Date: Jan 2020
Posts: 1,927
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Quote:
Originally Posted by ivansc
@Peter: (grin) Want to take a bet that the "official" ff power supplies are mide in China these days as well?
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Being made in China isn't a bad thing necessarily (speaking purely in terms of product quality). Most iPhones are assembled in China and they are pretty solid. Where you get into trouble is when some Chinese factories take it upon themselves to cut corners and make things that aren't to original spec to save money (or because they don't know the original spec). I'm talking about factories that have nothing to do with Focusrite but claim that the power supplies they produce are "compatible with" a given interface. So it's more of a management or quality-control issue than a locational one.
If Focusrite is on top of managing their contracted production like they should be, it wouldn't matter whether the power supplies they subcontract the production of are made in China, the US, or on the Moon.
Having said all that, I have no idea whether Focusrite makes their own, subcontracts them, or what. I'm talking more in general terms for these companies that have a lot of their stuff made in Asia, Mexico, etc.
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05-24-2020, 12:35 PM
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#18
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Human being with feelings
Join Date: Mar 2011
Location: On my arse in Glasgow, Scotland
Posts: 2,033
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Folks - please don't splice power cables using solder, it's neither safe nor reliable for this purpose. Use 'chocolate block' - the little double-ended screwhole stuff which is rated for these currents, and if you don't have a box to seal the join in, use insulating tape, putting a loop in the cable so there's no strain on the block.
A big lump in your power cable but at least it's safe.
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05-24-2020, 01:00 PM
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#19
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Human being with feelings
Join Date: Jul 2009
Posts: 7,570
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how is solder unsafe inside the enclosure? He said the wire was breaking at the power supply. I'm imagining that means not in the middle of the cable but around the strain relief, on the low voltage DC side.
But if the box doesn't come apart, and they're not comfortable with doing the repair then definitely stop there.
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05-25-2020, 03:29 AM
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#20
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Human being with feelings
Join Date: Jan 2020
Posts: 680
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Quote:
Originally Posted by Mudchild
Thanks so much Allbye - I've just booked the week off work to read and understand your post!!
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You are very wecome, it will pass the time in lockdown -unless you are busy chasing Boris's interlopers back over the border!
Trying to not confuse (!) but often getting fuller details is better. You can study at your leisure or ignore.
Cyrano makes a good point about voltage - where the load is designed to take that wide variation.
However not all equipment has internal switching convertors!!
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05-25-2020, 06:28 AM
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#21
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Human being with feelings
Join Date: Jan 2020
Posts: 680
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......I guess my emoticon does not work...... :-(
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05-25-2020, 06:59 AM
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#22
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Human being with feelings
Join Date: Jun 2011
Location: Belgium
Posts: 5,246
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Quote:
Originally Posted by Allybye
Cyrano makes a good point about voltage - where the load is designed to take that wide variation.
However not all equipment has internal switching convertors!!
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Every USB/FW audio interface I've ever seen is the same on that point. "Raw" DC goes in and is transformed in the +/-12V and 5 V DC needed. Unless the PSU is completely inside, like MOTU and some RME's.
If you take a simple mic or phono preamp, without ADDA, you'll probably find other recipes too. Including the "all discrete", no switching, to please the audiophiles.
Why is that switching PSU inside?
The hardest part in designing an audio interface is keeping digital and analog from interfering with each other. They need a separate DC supply and a separate ground on the board. Hence separate converters for each part of the circuit.
To keep the outside wall-wart simple, it's all done by tiny converters inside the box.
__________________
In a time of deceit telling the truth is a revolutionary act.
George Orwell
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05-25-2020, 10:52 AM
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#23
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Human being with feelings
Join Date: Oct 2011
Location: UK
Posts: 523
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Quote:
Originally Posted by Mudchild
Thanks so much Allbye - I've just booked the week off work to read and understand your post!!
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Had to laugh at this reply
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05-25-2020, 02:02 PM
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#24
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Human being with feelings
Join Date: Jan 2020
Posts: 680
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Completely agree with you Cyrano with the caveat that not all equipment and not all probably in use by readers (consider those with vintage stuff for example) will conform to that analogue/digital mix.
Although not external power supplies I have a mic preamp that has two linear PSUs one for +/- rails and one for phantom power.
Just trying to cover most bases!! (I grin too at recent posts including mine!!)
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05-25-2020, 11:19 PM
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#25
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Human being with feelings
Join Date: Mar 2008
Location: Oakland, CA
Posts: 10,478
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Quote:
Originally Posted by valy
Being made in China isn't a bad thing necessarily (speaking purely in terms of product quality). Most iPhones are assembled in China and they are pretty solid. Where you get into trouble is when some Chinese factories take it upon themselves to cut corners and make things that aren't to original spec to save money (or because they don't know the original spec). I'm talking about factories that have nothing to do with Focusrite but claim that the power supplies they produce are "compatible with" a given interface. So it's more of a management or quality-control issue than a locational one.
If Focusrite is on top of managing their contracted production like they should be, it wouldn't matter whether the power supplies they subcontract the production of are made in China, the US, or on the Moon.
Having said all that, I have no idea whether Focusrite makes their own, subcontracts them, or what. I'm talking more in general terms for these companies that have a lot of their stuff made in Asia, Mexico, etc.
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Exactly.
Lots of stuff is being manufactured in China, and the build quality varies from total shite cheap knockoffs, to high quality OEM certified.
You can't just lump it all togehter.
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