Dunlop PSU squeaking like a beast

[project_c]

I have a Tri-logic Bass Preamp II which is lovely, but changing batteries is hell, so I bought an 18V Dunlop PSU (recommended for this pedal), and the thing makes a squeaking sound which sounds like tinnitus. The sound actually comes out of the PSU, and it is also audible in recordings, which essentially renders it a 100% useless waste of money. It happens wherever it's plugged in, whether it's the socket next to my amp, my computer, my kitchen, my neighbours toilet etc. I can post a clip if anyone really wants.

This one is already a replacement for another one which was doing the same thing, so either I'm really unlucky, or I'm doing something wrong, or these things are just plain sh!t. Anyone have any good suggestions before I throw it out of the window in a fit of violent festive rage? thanks!

[flyfisher]

You don't mention the PSU part number but a quick search makes me guess it's a switch-mode PSU. These sorts of PSUs adjust their switching frequency depending on the current being drawn. In some circumstances, with some designs, if a high current is drawn from them, the switching frequency can drop down into the audible range as a squeaking/screaming sound.

Which makes some sort of sense.

But I also checked the preamp datasheet and the stated current draw is 4.3mA, which is tiny, so it makes sense to offer battery operation as well as an external PSU.

But that makes nonsense of my first paragraph!

Unless, perhaps, the PSU has a [u]minimum[/u] load requirement, which is more often the case with large switch-mode PSUs.

As a general rule, I don't like switch-mode PSUs for audio applications, especially cheap ones where the cost cutting is often around the noise filtering components.

If it were me, I'd send it back and look for a 'linear' 18v PSU, the sort that uses a traditional mains transformer,

[project_c]

Thanks for the reply!

The official name (incl. part number) is Dunlop ECB004UK AC Adapter 18V. I am not familiar with the term 'switch-mode', but this thing cost £17, which isn't cheap for a PSU, and Dunlop, as far as I knew, were ok when it came to stuff like this. Can you recommend an alternative 'linear' 18V PSU?

[flyfisher]

That PSU looks like a switcher and is 150mA, which is pretty low capacity but plenty for that pre-amp, if the 4.3mA figure is correct.

Note that I can't be sure that switching noise is the actual problem, it's only a guess, but if you want to try another PSU then almost any 18vdc unit will do. I quickly found this linear one:
http://cpc.farnell.com/1/1/85096-ac-dc-linear-psu-18v-500ma-universl-s2071st-stontronics.html#similarProducts

It's way over what you need at 500mA but that's probably a good thing as it's an unregulated supply. But I couldn;t find a 'ripple' spec and being unregulated it might not be that good (ripple is the variation on the outpur voltage, which can affect the device it is powering, depending on the device itself. Sorry to be vague but sometimes these things just need to be tried out. Beware of the DC plug polarity though - this one seems to be centre-positive but your PSU seems to be centre-negative. It's easy to change this, but if you're not comfortable with wiring/soldering then search for a different unit.

Or, try another switcher PSU just in case you have a faulty unit. This maplin one has multiple connectors so shouldn't need any messing about with connectors: http://www.maplin.co.uk/p/maplin-20w-switched-mode-acdc-fixed-voltage-18v-worldwide-power-supply-l49bl


If that all sounds a bit daunting, then it might just be easier to take the pre-amp and PSU back to the place you bought them, if possible.

Incidentally, because the current draw of the pre-amp is so low, a Duracell type should last about 100 hours at a current of 5mA according to this datasheet, so it might take quite a while to recover the cost of a PSU.
http://www.farnell.com/datasheets/612543.pdf

[project_c]

Thanks again - this Dunlop unit is already the second one after I took the previous one back, and the whole soldering thing is just overkill, so I think I'll cut my losses and go the Maplin route.

[Matt P]

i'm using a 9v power spply with isolated outputs and a doubler lead to power my 18v MXR Blowtorch, seems to work great, it's a harley benton junior so was pretty cheap, and i have 3 outputs left over to power other pedals (i actually have another power supply as well which is the palmer version as i have stupid power needs for my board so need 10 outputs in total)

if you're in the north-east then you'd be welcome to try out my power supplies to see if the problem goes away.

i think my the harly benton psu was about 23 quid and the doubler lead about another 5.

there are some 9v to 18v adaptors available as well if you're already using a 9v psu for something else. (diago make one i think)

Matt

[project_c]

Thanks Matt, great suggestions, it just all seems like such a massive effort for powering one tiny pedal.. is the squeaky 18V PSU a known issue that everyone's been aware of all this time? I thought I just had a just a dud, but it seems like this is something a lot of them do, which makes me wonder how they're ever used in a studio..

[Musky]

[quote name='project_c' timestamp='1387395335' post='2311574']
Thanks Matt, great suggestions, it just all seems like such a massive effort for powering one tiny pedal.. is the squeaky 18V PSU a known issue that everyone's been aware of all this time? I thought I just had a just a dud, but it seems like this is something a lot of them do, which makes me wonder how they're ever used in a studio..
[/quote]
I seem to remember Dave Hall commenting that switch mode supplies could make a high frequency noise if they were powered up before plugging into a pedal, although as I remember it he was talking about electrical noise rather than mechanical.

Edit: Finally found the post I was talking about. http://basschat.co.uk/topic/7552-feedback-issues-on-vt-1-purist/page__p__80353#entry80353

Edited December 18, 2013 by Musky

[flyfisher]

That's a similar situation to some switch-mode PSUs needing a minimum load.

If the OP fancies playing around with things, it might be worth trying to increase the load on the PSU because the pre-amp is only drawing a tiny current - less than 5mA.

I would add a resistor across the PSU 18v terminals to draw extra current. It's a 150mA PSU so something around 50mA would seem reasonable. A 360 ohm resistor will draw 50mA and dissipate 0.9W, so something close to that will do.

Just checked Maplin and their nearest suitable resistor seems like this one:
http://www.maplin.co.uk/p/wirewound-10-watt-470-ohm-resistor-h470r

470 ohms will draw about 38mA at 18 volts and dissipate about 0.7W, so a 10 watt resistor should not get too hot.
Worth a go for 84p if there is a Maplin store nearby.

[project_c]

Actually in the meantime I've been doing a bit of research into all this, turns out Dunlop - for some BIZARRE reason - make two types of 18V PSU's, one that is useless and whines like a castrated pig on amphetamines, and one that is regulated and seems to be the answer to my problems.

The difference in the product names is almost impossible to notice, unless you're some kind of magical wizard, which I am not: ECB-04, as opposed to ECB004.

This is the regulated one: [url="http://www.musiciansfriend.com/accessories/dunlop-ecb-04-barrel-18v-adapter"]http://www.musiciansfriend.com/accessories/dunlop-ecb-04-barrel-18v-adapter[/url]

..and this is the whiney one: [url="http://www.sweetwater.com/store/detail/ECB004/"]http://www.sweetwater.com/store/detail/ECB004/[/url]

So I'm going to order the regulated one and see if it fixes this problem, in the meantime hopefully someone will see this thread and learn from the error of my naive ways and save themselves £17.99.

[flyfisher]

That ECB-04 unit looks like it's a US-only version. This website shows it having a fixed US-style mains connection.
http://www.americanmusical.com/Item--i-DUN-ECB04

This type of unit will require 110v mains supply and would not work in the UK without using a step-down transformer. it's a great shame, because it looks like a linear regulated PSU and would almost certainly do the job, but such devices have fixed mains voltages.

This is an advantage of switched-mode PSUs - they can operate on any mains supply around the world.

[project_c]

yeah, I realised that, there's also a UK version which I ended up ordering from GAK, let's hope it works..
[url="http://www.gak.co.uk/en/dunlop-ecb-04uk-18v-dc-regulated-power-supply/35999?gclid=CPu6sMaXvLsCFUbKtAod8VcAQg"]http://www.gak.co.uk/en/dunlop-ecb-04uk-18v-dc-regulated-power-supply/35999?gclid=CPu6sMaXvLsCFUbKtAod8VcAQg[/url]

[project_c]

Here is an update: I ordered the aforementioned item from GAK, and they sent me the wrong thing - i.e. the same PSU as the one I already have. They also sent it a day later than promised, which means I sat about waiting for a delivery yesterday for no good reason.

That's the last time I order anything from those weed-stinking red-eyed ketamine-sniffing ironic-jumper-wearing Brighton wastemen.