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Head amp' PSU

V

Vinny

pfm Member
I am using a Japanese head amp' using an Airlink wall wart - the only small 240V-100V transformer that I can find, in fact 240/100V transformers are hen's teeth (yes, I know that there is a 600VA TGK one on EPay at the moment).
There is very modest hum coming from the head amp' and/or the psu - obvious when not playing music, but annoying just because I know that it is there.

Is there a simple way to determine where the hum is coming from - wall wart of amp'? Is there likely to be a way to fix it, simply and at least moderately inexpensively?
 
Thanks - why didn't I think of that? The simplest answer is generally the best!!!

In terms of what sounds like 50Hz hum, what supply would be least worst? High or low VA, torroidal or E-I?
 
I can't imagine a head amp running more than 25v internally, assuming solid state. You'll probably get away with 20va or less and a replacement rectifier board. What model is it?
 
Yamaha HA-1

It will be running at two-thirds of next to no VA for sure. Just interested in what transformer option should run quietest.
I have had the bottom off and the TX has just a code number on it - I'll have to desolder the leads and measure what the output is - ?-0-?, presumably common ground and two positive rails, one for each channel.
 
Vinny take a couple of pics of top and bottom of the innards of the head amp and post them here (or send to me - drop me a pm , and I will.) It'll help, the help.
 
It looks to be complicated to get apart beyond exposing one side of the boards by removing the bottom and one internal plate - I'll drop you a PM. Cheers
 
The innards:

yam1.jpg


yam2.jpg


yam3.jpg
 
@Vinny - That transformer has a single, centre-tapped secondary - top pic, the two red wires are the phases and the adjacent black wire the centre-tap return.

I'd power it up and use a DVM reading AC volts to measure the voltage between the two red wires where they are soldered to the pcb. Halve that, and thats the voltage you need - eg if you see 24vAC then a 12-0-12vAC transformer will work.

Nice discrete regulator that, current sources and what not. :)

Edit: the relays are marked 12v, so regulated voltage rails likely 12vDC
 
Many thanks @martin clark.

It was recommended by someone here and I took a punt.
It sounds pretty good - it basically replaced a McKinnie that died and although I obviously could not compare them side-by-side, I am confident that it runs the McKinnie close.

Is there any benefit to using either a torroidal or EI transformer?
 
the existing under the cover is going to be EI, so that's likely what will be easiest to fit. This is a very low-current device, and the internal supply well fitered and regulated - so trafo 'type' not a thing to get neurotic about imo.
 
That was a surprise - just shy of 27V.

Fit a 14-0-14?

Although a quick search and I am finding 12V, 15V and 18V - it is a LONG while since I bought a TX.
 
If the transformer is not heavily loaded compared to its VA rating then it will measure in circuit as a higher AC voltage, sometimes as much as 20%. I would suspect you have is a 12-0-12v that is just lightly loaded. For context last week I lightly loaded a nominally 24v, 26VA transformer with 40mA load and the AC voltage measured at 27.6v.

John
 
Thanks @john.luckins

The TX retaining bolts are recessed and I can't shift them as yet without fear of stripping the cross-slot heads - they may be Loctite'd or painted
 
Quiet has two different meanings here.

A toroid will have a lower external magnetic field, which you really care about for a head amp because of the low signal levels. It is also more likely to make a mechanical noise, as the efficient magnetic circuit takes the core closer to saturation, so you get a bigger magnetostrictive effect. Encapsulated ones are usuallly more or less silent.

EI has more external field, but less likely to make humming or buzzing noises. It is entirely possible that there is a tiny toroid under the can. If so, I would stick with a toroid, and assume Yamaha know what they are doing.
 
Thanks @PigletsDad - I have had a hunt through the spares/junk and found a 12-0-12 torroid, but will give it a whirl some distance from the actual amp. For one box (actually a box within a box, within a box, and more), it is actually very quiet for a head amp. But I know that the hum is there.............................

I can't shift the self-taps holding the existing TX anyway :)
 
Vinny said:
...I have had a hunt through the spares/junk and found a 12-0-12 torroid, but will give it a whirl some distance from the actual amp.
Click to expand...
If you do that, keep the three secondary wires / connection to the Yamaha twisted together at 2-3turns/inch or similar to minimise the area between them; it's a source of EMI, because of the peaky haversine currents flowing (even if likely small in this case) which could spoil things readily in a head amp.
 
Interesting!
Using a toroidal from the spares bin, about 2m from the head amp', the hum is horrendous. Earthing the amp' case to mains earth made no difference at all.
 
I had to mount my head amp transformer in a remote box, torroid or laminated in the case hummmmmmmmmm.

Pete
 
Just some observations -

The housing is a moderately complicated box within a box within a box. The bottom comes off, the complete circuit then slides out in a 5-sided tray (no top - that is formed by the bottom of the enclosure as a whole). The actual amplifier circuit is housed within a lidded box, inside/part of that tray.
The power supply is at the front of the box, presumably so that the signal path is minimised when connected to the back.
The cable supplying power to the power supply, runs from the back of the unit, along one side through a gap between boxes - what is the bottom of the first pic' above.
To supply power to the power supply with no cable running the length of the box, I'd need to knock a hole in the front of the box.
The original power lead looks to be very ordinary twin flex.
I could remove the whole power supply outside of the enclosure and just run DC in - not a vast job, but the hum is slight as is.
 
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