Bucking Transformer for Little Dot mk ii

[mightymonoped]

Having recently acquired this excellent headphone amp/pre-amp (who's sound I am thoroughly enjoying), I am a little concerned that I should be doing something about the fact that it is 220v currently running on a 240v supply.
I have seen discussions on here about getting simple bucking transformers to manage the step down but it's all a little out of my comfort zone.
Can any of you more capable bods point me in the right direction as to where I can get hold of a suitable spec bucking transformer either bought or made for a reasonable price (don't have the readies for anything in three figures [emoji4])
Thanks!


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[Firebottle]

It sounds sensible that you are considering reducing the voltage. Do the valve heaters look particularly bright to you?

The power consumption is only about 30W so you only need a small bucking transformer, say a 12VA as a minimum size, I may have a suitable one here.
I'm guessing you want something built up and cased that you can just plug in?

[mightymonoped]

That sounds ideal if you can Alan? They don't look particularly bright (or feel particularly hot); I upgraded the Chinese valves to Mullard 8100 and Novosibrisk 6H6pi-N and it's about 20 hours into 'burn-in'. Now that I'm finally getting into the 'magic', I don't want to risk wasting it all for the sake of a step down in voltage. :) More than happy to cover any costs to yourself, just PM me with any details?
Tony

[RothwellAudio]

Are you sure you're running on a 240V supply? The UK mains voltage is nominally 230V but the tolerance allowed means it could be less than 220V. I'd measure it before messing about with step down transformers.

[mightymonoped]

No, I'm not sure of anything other than fear, doubt and uncertainty imbued by tales of Chinese kit not suitably localised. How would I go about measuring the supply I am on?
Tony

[struth]

My supply varies a bit but 247 is not uncommon. I got a power inspired regenerator which all my gear goes through. it outputs 230v steady. not the cheapest option but a good one. Ive used a bucking tx before and it does work. you would need a 24v tx most likely.. you will get one from RS

[mightymonoped]

Sounds like I need to check out what's actually happening on my supply before going any further then. I've just got hold of the means to do that so will have a look when I get home tonight. :-)

[RothwellAudio]

How would I go about measuring the supply I am on?
I would measure it by putting the two test probes from a volt meter into the socket holes on the end of an IEC mains cable. I would recommend you do the same if I wasn't afraid of all the cries of " arghhhhh.... you can't do that, you'll kill yourself.....etc etc".

[struth]

lol. should be safe as long as your fingers dont stray onto metal. if in doubt you can buy plug in meters now i believe

[mightymonoped]

I've borrowed an installation tester from a colleague in work (CNC Maintenance Engineer). That should do the trick for a numpty like me! :-)

[RothwellAudio]

Better safe than sorry.

[mightymonoped]

Well, it's looking like a pretty consistent 244-245 at the moment! Will check a few more times later.


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[Firebottle]

No surprise to me.

Looks like you'll be needing a transformer then.

[mightymonoped]

No surprise to me.

Looks like you'll be needing a transformer then.

Looks like the safest bet Alan. Grant suggested 24VA?


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[mightymonoped]

Measured it again this morning from the surge suppressor that the headphone amp is plugged into and the reading was a constant 242V.

[RothwellAudio]

That's about 11% over the specified voltage for the amp, but personally I still wouldn't want an external transformer if I could avoid it. I would measure the voltage across the capacitors in the amp to check they're ok first. Anything to avoid extra boxes - and expense :lol:

[Firebottle]

Sounds like the OP isn't confident about mooching around inside the amp, but I agree that doing measurements to confirm the overvoltage (or not) is the best course of action.
If the valve heaters are running at +11% then that's going to be around 7V, not something i'd like to do for any extended time.

I modified a Chinese preamp that was rated for 220V, when I measured the valve heater voltage is was well over 7V with UK mains, so I fitted a bucking transformer internally.

Having just looked at internal shots of the Little Dot there isn't any room to fit an extra transformer internally.

I've just read that someone fitted extra low value resistors to combat the excess heater voltage as shown on this photo:

https://cdn.head-fi.org/a/78065.jpg

[RothwellAudio]

I've just read that someone fitted extra low value resistors to combat the excess heater voltage as shown on this photo

Yes, I was going to mention the possibility of dropping the voltage with resistors but didn't want to get too technical for the OP.

[struth]

if those get hot they are going to damage the board. think a 230v regen would be best overall. a bit pricier but will help everything and its not going to encroach on any design.. only a 5% increase in voltage should be fine

[mightymonoped]

Thanks all for your input on this, there's no substitute for the experience of people who have dealt with stuff every day! :)

I'm generally ok with condensing what I need out of a ton of technical information but my background is software and I have little exposure to electronics other than swapping components and rebuilding computers.

I'm inclined to go with Grant's suggestion of a 230v regen on the basis that it will cover everything, including any future purchases. Any preferred suppliers or devices I should be considering?

I was looking at this site a little earlier https://airlinktransformers.com/category/conditioning-balanced-power-supply

[struth]

Good price and very good if you dont have a huge amp... they do a bigger one if needed.... Ive got an older one of these

http://www.powerinspired.com/store/ag500-ac-regenerator-500w-with-pwm-fan-control-p-1811.html?osCsid=65197f93f6ad8eeae4553650501a94b0

[RothwellAudio]

I'm inclined to go with Grant's suggestion of a 230v regen on the basis that it will cover everything, including any future purchases. Any preferred suppliers or devices I should be considering?

I was looking at this site a little earlier https://airlinktransformers.com/category/conditioning-balanced-power-supply

Those don't regenerate the supply and they put out the same voltage as you put in, therefore if the the mains voltage you have at present is too high for the amp you're using it will still be too high when you use the balanced conditioner.
A 230V regenerator will still put out a higher voltage than the 220V you're looking for.
The voltage dropper resistors which Firebottle mentioned will dissipate some heat but it won't be much and having the resistors standing off the board by 2 or 3 mm will be enough to prevent any possibility of scorching.