Portable Stereo HiFi development

The MDF has now been cut by Stalite Signs of Exeter, to produce the Box Construction Jig.  There are one or two problems, basically mistakes I have made and need correcting before I proceed.

But that aside, our outside wall has some cracks in the lime plaster (the house is over 220 years old) and the damp has destroyed some of the plaster inside our house.  So before I can carry on with the Portable Stereo construction, I need to do some exterior and interior decorating as it will only get worse.  And now I have discovered it, it will get worse fast and much quicker than I expect, Sod’s Law and the fact it’s winter and all that . . .

I hate decorating.

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Why do you need Lasting Power of Attorney?

There comes a time for all of us when the people who are closest and dearest to us, reach an age where they are not physically and/or mentally as capable as they used to be.  This usually happens late in life but can also happen earlier.  Especially with older people, I cannot help but feel certain institutions are circling above waiting to swoop down and grab any morsel they can get their beaks onto, so protecting our loved ones best interests can potentially, turn into a fight.

My wife’s parents.  A very good friend of ours, who has recently been through the same landscape, advised obtaining a Lasting Power of Attorney straight away, both for finance and also health.  I searched the Internet for reasons why I might want to do that but all returns were from institutions that made money from instigating a PoA and though it all sounded good, they clearly are biased as there is a large financial return for them.

So my wife asked my friend for some idea of why PoAs are a good idea.  His answer was so good I thought it worth sharing here so that others may benefit.  You will find my wife’s email below, together with his response.

There is a point I would like to make.  I had difficulty convincing my wife to talk to her parents about it as she did not want to come across as money or power grabbing.  It turned out that her mother was only too ready, willing and happy to proceed.  But her mother was reticent to talk to her husband due to concerns he would not like the idea.  It turned out that my wife’s father was also only too ready, willing and happy to proceed.  A lot of dangerous time had been unnecessarily wasted through trying not to hurt anybody’s feelings but nobody’s feelings were hurt at all.

  • Do not waste time worry about feelings as this is far too important.

A second point here.  Having convinced her mother and father to go ahead, her mother downloaded all the documents from the government web site, both finance and health ones and then asked her neighbour to be a witness to the signatures.  Their neighbour has known them for nearly two decades now and was in a good position to do this.  Unfortunately the neighbour then convinced the mother to not bother with the health one as it would save £82 for each of them and wasn’t really necessary as “your doctor has your best interests at heart and the health one is a waste of money”.

  • Do not let someone with no knowledge and only a single experience talk you out of this.

I’ve just entered my 60’s and though I consider myself far away from needing any kind of Power of Attorney, I will donate this to my wife as soon as possible now I know more about it:  you may not need anyone else to drive your car but if you put someone on the insurance, they are legally able to drive you to a hospital when you break a leg and they don’t get access to your car when your leg is good.

Government Web Site for Power of Attorney:


A lasting power of attorney (LPA) is a legal document that lets you (the ‘donor’) appoint one or more people (known as ‘attorneys’) to help you make decisions or to make decisions on your behalf.

This gives you more control over what happens to you if you have an accident or an illness and can’t make your own decisions (you ‘lack mental capacity’).”

Here is something that may or may not be relevant, a BBC 28 minute video on;

Communication and Dementia
Michael Rosen explores how to communicate with people with dementia. Alison Wray offers advice, such as to respond to the feeling behind the words rather than the words themselves.


That’s the end of my rant, here’s the good stuff.

Hi *,
Sorry to bother you but could you please give me some advice?

My mum has decided not to go for the health part of the power of attorney paperwork. Could you outline for me the reasons that you’ve come across why this might be a bad decision on her part?

Both my mum and dad are more than happy for the financial power-of-attorney paperwork but I don’t know why they wouldn’t want to have the health POA.


Hi 🍁,

Not a problem, I’m always happy to spout forth my opinion on things!
Caveat – everything I say is my personal opinion & may or may not be factually correct, in fact it could all be complete drunken bunkum!  🙂
An outline requires brevity – sorry, not my forte so your will to live may wane under the weight of my reply!
Firstly – maybe your mum has the standard generational thinking of our elders…don’t cause a fuss, doctor / lawyer / vicar / person of “importance” & “standing” knows best & is always right, etc.
Nonsense of course because one has every right to question & “cause a fuss” as it’s one’s health after all & believe me, doctors are not always right & the NHS often makes arbitrary decisions based on finances or outmoded medical thinking, puts juniors in charge, etc, etc…………….hospital “nutritionists” & the Liverpool Pathway spring to mind as prime examples of how not to do it that I have personal experience of.
Secondly – your mum may not want to give such angst ridden responsibilities to her loved ones – that’s you by the way 🙂 – & would rather let the system do it’s thing & absolve you of any responsibility for what may happen to her in a worst case scenario.
Admirably intended but misguided! – nothing is worse than seeing decisions & actions being made for your loved one’s health that you know are wrong (either factually or simply against what you know to be their wishes) & being helpless to do anything about it.
If you are not PoA for health then medical practitioners will usually listen to your thoughts as a relative but DO NOT NEED TO ACT UPON THEM, THEY CAN OVERRIDE / IGNORE YOUR INPUT in a contentious circumstance.
If you are PoA for health then you are legally deemed to be that person in the event that they can no longer make decisions themself….the doctors have to speak to you as if you were that person!
Thirdly – fear!  Fear of having control of her life taken away from her & your mum is possibly also fearful of acknowledging the unpleasant possibility of being in such a position in the first place.
She can rest assured that a PoA is only applicable if & when her health / mental capacity deteriorated.
Also, any specific wishes that your mum has can be written in to the PoA so that you have to abide by them – all decisions you make have to be in your mum’s best interests & not in yours. The ability to put specifics into the PoA (such as blood transfusion, Do Not Resuscitate, organ donation) protect your mum against any eventuality that she may not wish for.
It is also a fact that just because you may be acting for her under the PoA in a certain situation, it is not a legal “given” that you can act in for your mum in each & every scenario.
Ie: she may not lose total control over her life. There is legal precedent that lack of capacity, once acknowledged, can not be assumed in every occasion – this might seem at odds with what I’ve said earlier but imagine not being given the basic human respect of not being asked first what you’d like to eat, wear, do next, etc – these are basic things but important to one’s dignity.
(Also, there are far more complex situations which would not apply to your mum but for which this legal precedent is very important).
Fourthly – your mum may have had poor legal advice. A prime example here – my late mum initially decided to only do the finance PoA because her solicitor told her that there was enough protection in the law anyway for her health!
After all, a medical professional has to act in their patient’s best interests. But why would there be a PoA for health at all then? What if one disagrees with their opinion of best interests / does not wish to go along with their proposed treatment?
I knew from previous experience that this is utter rubbish & when I rang my own solicitor for their input they simply could not believe that my mum’s solicitor had advised her that way!
My mum, my brother & my sister all agreed with her solicitor (see my first point about some people doffing their caps & blindly believing that those in authority somehow always know best) & I frankly had to give up arguing about it with them all.
Move on a year when my mum had been very ill & had also changed solicitor – to one who as it happened advised differently, she changed her mind & took out a PoA for health!
Move on another year or two when dementia took mum’s ability to think for herself on so many things & we were all very glad that she had PoA’s in  place.
Basically, a PoA (be it health or finance) is a way of making sure that what one wishes to happen is what happens – it protects the rights of the donor (in this case your mum) in the event that they can not speak for themself.
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Dual Amplifier CV1460 Incandescent Lamp to LED Conversion

How to convert an amplifier or receiver from incandescent lamps to LED lamps

I use a Dual CV 1460 amplifier for my office/workshop and not just because it sounds good; I like the looks too.

Mostly the reason I like the way it looks is because of the big, analogue VU meters it has on the front.  But they were lit with incandescent lamp bulbs and I had already replaced them once when they all went again.  So this time I have replaced them with LEDs which should last a lifetime.  In this post I will document how I replaced them including the calculations.

The original incandescent lamps were rated at 12V/110mA as can be seen on the Service Manual circuit diagram.  The current is irrelevant to us as that will now be dictated by the resistance of the new LEDs.

Figure 1. Circuit diagram from Service Manual.

Figure 1. Circuit diagram from Service Manual.

I bought the LEDs to replace incandescent lamps in a Harman Kardon HK 730 receiver and had a few left over.  I could see that I had written on the packet I kept them in “12V/1W”.

I do not like the lamps on my equipment to be bright as I find it intrusive so I put one of the LEDs across the output of a power supply and gradually turned the voltage up.  The LED lamp came on at around 7.0V (note there are several LEDs within each lamp hence the high value of 7V) and was at a brightness I liked at 8.0V so with 3 in series I would need 24V dc to power them.

The original lamps were powered by 35V ac and they were also in series giving a voltage of 35 / 3 = 11.66V across each – so a little under-rated which is a good way to increase their lifespan.

Figure 2. My drawing of the original lamp circuit.

Figure 2. My drawing of the original lamp circuit.

LEDs conduct (and therefore give off light) only when a positive voltage is applied to its anode.  This means an ac voltage would cause the LED’s light to flicker at around 50Hz (mains frequency) and that can be seen by the human eye especially when one’s eyes are moving.  So I didn’t want that and to get rid of it I decided to use a bridge rectifier giving full-wave rectification.  With full-wave rectification the ac waveform output from the bridge is approximately 1.414 times the input less a volt or two for the voltage drop across the two conducting diodes (the exact voltage depends on the diode and how much current is being drawn).  So off-load (no current being drawn) the output voltage from the bridge is 35Vac x 1.414 = 49.49Vdc (off load – remember the voltage will drop a little across the diodes when conducting, usually around 0.6V for silicon and around 0.3V for germanium but who uses them anymore).  I used an electrolytic capacitor to smooth any ripples on the voltage output, it doesn’t need to be exact, anything between 47µF and 470µF is fine so long as the rated voltage is well above what it has to cope with – I would have preferred to use a 100V cap but 63V is Ok.

Figure 3. My drawing of the new lamp circuit.

Figure 3. My drawing of the new lamp circuit.

In the same way that the original lamps had a third of the input voltage across them, the LEDs will also drop a third of the voltage giving them each about 16.5 volts – too much.  Some of the voltage has to be dropped across a resistor (RL) to get rid of the excess.


As said above, the LED lamps had “12V/1W” written on their packet.

Watt’s power law says: W = V x I

Therefore: I = W / V = 1 / 12 = 0.08333A = 83.333mA or to put another way 83.333×10-3A

NB:  Since all three LEDs and the resistor RL are all in series, the same quantity of current flows through each of them.

So we know that the new LED lamps should have a current through them of 83.33mA at 12V.  But since I would be using them at 8V, the current/wattage used by them would change.  Why is it important to know the current or wattage?  The voltage applied to the LEDs is too high so must be reduced.  This is done by using a potential divider network which is a fancy name for what you see in Figure 3 above; the output from the bridge rectifier (at 49.49V) is across the resistor RL and three LEDs all in series (the capacitor is only used to smooth the voltage peaks, it can be ignored in these calculations).  The voltage of 49.49 volts is divided across each LED and the resistor.  For the sake of ease, lets say the voltage is 100V.  If the LEDs were 200Ω each and RL 400Ω then there would be 2V dropped across each LED and 4V dropped across RL.  The voltages dropped would be the same if the resistances were 2000Ω and 4000Ω (respectively) but the current would drop to 1/10th.  This is why the current/wattage/volts rating of the LEDs is important; it tells us what their resistance is and from that we can work out the resistance of RL.

But we aren’t running the LEDs at 12V and being a semiconductor, their resistance will not be the same at 8V (it is notable that the resistance change is non-linear).  However, when I put one on the power supply, I had a multimeter measuring the current flow and saw that at 8V it was 3.5mA – or thereabouts but it was a good starting point to calculate the LEDs’ resistance.

RLED = V / I = 8 / 0.0035 = 2285.7Ω

RLEDTOTAL = 2285.7 x 3 = 6857.1 = approx. 6857Ω

We want 8V across each LED which totals 24V across all three.  That leaves 25.49V (49.49 – 24) across RL.  So RL has to drop 25.5V.  We can now use Ohms Law to work out the resistance of RL:

RL = V / I = 25.5 / 0.0035 = 7282.85Ω which is approx. 7K3Ω.

But as already stated, the resistance of semiconductors changes depending on the voltage applied and it changes in a non-linear fashion and there is also the tolerance of the resistor to take into account so . . .  having constructed the circuit and turning on the amplifier, the LEDs looked a little dull.  When I measured the voltage across the LEDs they were 7.82V, 7.8V and 7.77V – all too far away from 8V so I wanted to get the voltage up closer to my ideal of 8V.  This meant I needed to reduce the resistance of RL so it has less voltage dropped across it, leaving more to drop across the LEDs.

What if I used the next common value down at 6K8Ω? Using the formula to work out the potential divider network:


( 6857 / 6857 + 6800 ) x 49.49 = 24.848V across all three LEDs.

24.848 / 3 = 8.283V across each LED (on average) which is perfect.  They look great, just right to me (brightness-wise).


Close up of power conversion circuit.

Close up of power conversion circuit.

Distance view of the lamp PCB.

Distance view of the lamp PCB.

Close up of power conversion circuit.

Close up of power conversion circuit.

The LEDs stood off from the substrate by about 5mm.

The LEDs stood off from the substrate by about 5mm.

I soldered wire to the LED's two connectors.

I soldered wire to the LED’s two connectors.

Bird's eye view of power converter and LED.

Bird’s eye view of power converter and LED.

CV 1460 amplifier using LEDs, in situ.

CV 1460 amplifier using LEDs, in situ.

Posted in Circuit Tests, Power Amplifier, Power Supplies, renovation, Testing, Vintage HiFi Renovation | Tagged , , , | Leave a comment

Woodwork drawing in for production

The drawing for the Box Construction Jig is with Stalite Signs of Exeter.  I have accepted their quote and they have sent the drawing to their production department.  When cut I will have woodwork for the jig but also one pair of Main 1A speakers together with their accompanying Subwoofer Stands and an Amplifier 1A.  I already have woodwork for the Portable HiFi.

Stalite cut all sorts of materials for sign makers but are also open to cutting for any other type of project.  They have been helpful and communicative – there is nothing worse than a company ignoring your emails.  With luck, this should be a good, ongoing relationship.

Box Construction Jig plans for Stalite Ltd.

Posted in Amp Cabinet, cabinet, Ghetto Blaster / Portable Music Player, Loudspeakers, Power Amplifier | Tagged , , , | Leave a comment

Slight Redesign of 10W High End Amplifier

Having found what appears to be a good company to cut my MDF for cabinet making, I now need to redraw my cutting information to suit their needs.  They need the files as PDF (Portable Document Forma).

But they also use a full size sheet (2440mm x 1220mm) which means a lot more space available and I am trying to squeeze as much as I can onto the sheet.  The main reason for having the next sheet of MDF cut is to get the woodwork for my Box Construction Jig but there is also space for my Headphone Amp woodwork, a set of the ‘middle’ speakers (which I call ‘Main 1A’) housing the full-range drivers (Monacor MSH-115), the smallest amp I will produce (approximately 10W per channel RMS, full bandwidth – the ‘Integrated Amp 1A’) and hopefully a set of stands for the Main 1A speakers.

I had drawn the amp using 6mm MDF so I have had to redraw the cabinet work in 12mm as that is what I am using for everything else.  That way I don’t waste any MDF and only have to stock one thickness reducing stock cost and storage.

Here is a drawing of the amp in 12mm:

Hi End Integrated Amplifier design.

Hi End Integrated Amplifier design.

And the unfinished drawing of the sheet to cut (it doesn’t yet contain the amp or stand information):

MDF Cutting Information.

MDF Cutting Information.

Once the Box Construction Jig woodwork is here, I can start construction of Frank’s Portable HiFi.

Posted in Amp Cabinet, cabinet, Construction, Design, Ghetto Blaster / Portable Music Player, Headphone Amp, Loudspeakers, Power Amplifier | Tagged , , , , | Leave a comment

How to Effectively Solder Joints

A friend of mine asked me about soldering and I thought the conversation may be useful to others.  Here is is.

My friends email:
Finally I have soldered all the connections to my new digital speedo on the bike!

Soldering takes me forever ‘cos I am crap at it BUT I think soldering iron is shyte & maybe the solder too!

I can never seem to find a higher power iron than the usual DIY shop type soldering irons & don’t know if solder is solder is solder or if some is better than others!

Any advice?


My response:

“The Two Governing Factors of Soldering.

Regardless of what is being soldered or how large the joint is; the most important two points to concentrate on when soldering are cleanliness and temperature.

1. Cleanliness
Solder these days is all pretty much the same. That said, you need to use stuff that has flux built into the solder itself to ensure the metals to join are clean. There is a new EU directive that says we should all be using lead-free solder. For my Liquiphonics solder, not only is it lead free but it also has a certain amount of silver in it. Soldering with it is not fun as it feels a bit like dried up toothpaste and has problems flowing. It skins over quickly and needs lots of flux which means you have to work fast with it and get the job done first time. But I doubt you are using this kind of solder and the older, lead type is not a problem by comparison.

So you will probably have solder which contains flux. But the flux can only do so much so you need to make sure both metal parts to be joined are perfectly clean. Do not rely on the fact that a piece of wire is free from oxidation just because it is inside insulation sleeving – it may have been cut at that point a while ago and moisture could have crept up the sleeving and corroded the wire. Clean any wire that looks dirty or corroded, using fine sandpaper, a pair of pliers or the side of a match box etc. Only if you can see bright metal is it clean enough to join and even then, the flux will be needed.

Both wires should be ‘tinned’ before soldering. This is where the iron heats up the wire, solder is introduced and it flows all over the wire end covering it in a thin layer of solder (tin). You make sure both parts are tinned and only then should they be soldered together. Many wires come tinned already but if they look dull, they may need a quick scrape/sand first.

If the joint is dirty or corroded, the time to solder increases and that is not good as talked about in 2.

2. Temperature
You need to use an iron that is capable of producing enough heat energy to quickly heat up the two metal parts. But that is fixed and generally speaking, cannot be varied unless you use an iron with temperature control. I use Wellar soldering irons and change the tip in order to increase the temperature of the joint. The only reason I might change from a number 7 tip (e.g. for soldering components on PCBs) to a number 8 tip is if the joint involves thicker wire as the more metal there is, the more heat energy is needed from the iron. If the joint has too much metal for the iron it acts like a heatsink and will wick the heat away from the joint; the joint will take a long time to heat up. So not only will it start to corrode and get dirty as you try to heat it because the flux has all been burnt off, but the heat will travel along the metal and damage other parts.

Soldering iron temperature aside, the way to control the joint temperature is through time; how long you keep the iron on the joint. If the iron is not hot enough, the heat will have time to travel along the metal (e.g. wire) and start to damage something that is not meant to have so much heat (e.g. insulating sleeving, PCB copper track or an electronic component). What you need to make a good joint is a quick soldering action.

Most important – to ensure the metal parts to be soldered heat up quickly, add a small amount of solder to the tip of your iron just before you solder the joint – ‘wet’ the tip. This point does not matter so much when you are soldering lots of quick joints on say a PCB because the joints are made so fast the iron’s tip always has a small amount of solder on it and if anything, the excess needs to be wiped off when it builds up too much. Of course, the first joint in that example would need the tip wetted first. Wetting the tip increases the contact area between the iron and the parts to be soldered. With poor contact, the joint takes too long to solder, burning off the flux and that makes the joint difficult to solder.

Wet the soldering iron's tip.

Wet the soldering iron’s tip.

If you have two different size metal parts to solder, put the iron’s wetted tip on the larger part first and then solder the joint. If you put it on the smaller part first, the bigger part will not get hot enough fast enough so smaller parts are damaged, the flux burns off, the joint is difficult to solder.

Ensure the parts to be soldered are fixed in position as you cannot make a quick joint if bits keep moving around – have everything ‘ready to go’ for the jointing to work well.

To summarise:

  • Make sure all parts to be soldered are clean and fixed in place,
  • wet the tip of your iron,
  • immediately apply the tip to the joint to heat it,
  • press the solder lead up to the wires of the joint, keep tapping it on the joint, when the solder starts to melt, push it into the joint so that if flows all over, around and into any gaps,
  • if the smoke from the flux stops but the joint is not made, push more solder in to add more flux – if that goes on for long, you may have to remove some solder,
  • when all the joint is properly wet with no gaps, immediately take the iron away and allow the joint to cool.

Never move a joint while it is cooling as the solder may still be liquid or semi-solid. You can see it go solid, don’t move yourself or anything else – just freeze – until the solder is definitely solid. If the joint moves before the solder has solidified – redo it.
Never blow on a joint to cool it quicker; you will introduce stress into the joint with larger and smaller crystals and that could be a future dry joint. Just let the joint do its thing and cool as fast as it wants to.

When soldering multi-stranded wires, always twist the fine individual wires of the multi core wire together before soldering. If you don’t, the individual wire strands splay apart with the applied heat, as they expand. They will push their way through the insulation, the insulation will melt into the joint, the joint is then dirty with burnt plastic, that needs more heat to clean it off with – it’s a difficult joint to make and the insulation will not go right up to the joint leaving exposed wires.

I might put a video of soldering on my blog some day,


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MDF Cabinets Cutting

Having found a potential MDF cutter, I had to redo the drawings again! This will be the third time I’ve redrawn them. This time it is because the potential cutting company does not use DXF files and I need to provide the drawings in PDF form with all dimensions shown.

The two sheet drawings are now done and today I will check them over before sending for a quote. The two sheets will provide the MDF for both the Box Construction Jig and the Headphone Amp cabinet.

Once I have the Box Construction Jig, I can start building my first order for the Portable HiFi. And of course put my Head Amp into a box which should help me to stop tripping over the cables on my way to bed.

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