Always check safety RCD RCBO type devices . I touched something in our workshop. I didn't feel a thing yet it tripped at 30mA. That I took to be unlikely. It happened so seems it was real. If you feel confident measure earthing especially for tight connections. Your bathroom and plumbing has important arrangements for this. Gas supply also. My own house is a PME system with additional earth rod. A nice arrangement. The rod holds down earth voltage.and is not fitted to all installations. An audiophile earthing that was there already.
The Variac I use is in a metal case. It's as unsafe as standard mains.
On reflection all DIY Audio projects are potentially dangerous as the better solutions need bespoke power supplies. Standard mains devices like toasters are slightly more dangerous. Life is dangerous.
The Variac I use is in a metal case. It's as unsafe as standard mains.
On reflection all DIY Audio projects are potentially dangerous as the better solutions need bespoke power supplies. Standard mains devices like toasters are slightly more dangerous. Life is dangerous.
Guys, I accept that many of us probably do have RCDs fitted to our mains supplies. Before they were introduced, ELCBs had also been mandatory for new installations here since the 1970s. Fully approved types are indeed reliable, fast protection and mandated for use on the power grids of many countries. It's good that many of us have that last line of defence in our fixed wiring because the safety devices you plug in before the DUT may not be a fully certified type or even considered safe without having properly bonded connections.
For the professionals and experienced hobbyists among us, don't forget that many fans of this very simple JLH amplifier will be newbies or otherwise struggling with electronics, electrical and general DIY matters. Not everyone will be aware of mains supply issues as they exist in their particular countries so before we click and pay, it's worth knowing the issues with variacs and isolation transformers at the workbench and especially what goes on inside them. Here's a video from the US that raises a problem or two with at least some "isolation" transformers too. YouTube
Rod Elliott covers mains safety issues in their various classifications and practices for audio DIYers. If possible, read and think carefully about it. The last thing we want anyone to assume is that because they are still alive, they must be doing everything right. Well, no. You can be at mains potential yourself without realizing it until by chance, you also touch a grounded conductor, chassis etc. It's only a matter of time and circumstance, then Wham!
For the professionals and experienced hobbyists among us, don't forget that many fans of this very simple JLH amplifier will be newbies or otherwise struggling with electronics, electrical and general DIY matters. Not everyone will be aware of mains supply issues as they exist in their particular countries so before we click and pay, it's worth knowing the issues with variacs and isolation transformers at the workbench and especially what goes on inside them. Here's a video from the US that raises a problem or two with at least some "isolation" transformers too. YouTube
Rod Elliott covers mains safety issues in their various classifications and practices for audio DIYers. If possible, read and think carefully about it. The last thing we want anyone to assume is that because they are still alive, they must be doing everything right. Well, no. You can be at mains potential yourself without realizing it until by chance, you also touch a grounded conductor, chassis etc. It's only a matter of time and circumstance, then Wham!
I had the weekend to think about this. My work is connected with electrical safety. I really enjoy studying international safety standards. The standard often required is called CB. This can be converted to mostly any counties standard. JIS being Japan. In many ways these tests are importation barriers. None the less a universal safety standard is exactly that. Canada adopted every good Idea from the world. Japan whilst having excellent intrinsic safety couldn't envision a nuclear power station getting into trouble. Apparently inability to take action due to Japanese managerial respect and disaplin meant engineers didn't act quickly enough. Putting the diesel generators higher up would have saved billions of dollars if only that. It's amazing in the country that invented the word tsunami that it's power station wasn't tsunami proof.
Fire risk due to loose screws is the hidden killer. This will kill thousands. Although I am an electrical engineer I am not allowed to check my electrical installation at home. This requires a yearly updated certificate. I think you can imagine what I do. My 1962 house has two RCDs. The earth is on a busbar which can be visually inspected. My installation is old school which I love. British standards are the best in the world as copper is saved and EU type installation is allowed. In my oppion a UK ring main for the hi fi is the best. That's a 32 amp supply on 54 amp cable. That's a basic standard that can be improved. JlH is happy with less exacting mains installation.
Fire risk due to loose screws is the hidden killer. This will kill thousands. Although I am an electrical engineer I am not allowed to check my electrical installation at home. This requires a yearly updated certificate. I think you can imagine what I do. My 1962 house has two RCDs. The earth is on a busbar which can be visually inspected. My installation is old school which I love. British standards are the best in the world as copper is saved and EU type installation is allowed. In my oppion a UK ring main for the hi fi is the best. That's a 32 amp supply on 54 amp cable. That's a basic standard that can be improved. JlH is happy with less exacting mains installation.
Nigel, you illustrate the point I was making about DIY builders quite well. EEs probably read thousands of pages of regulations, rules and guidelines for every kind of situation imaginable in the electrical and electronics industries, worldwide. You would expect no less from highly trained and well informed professionals.
That's fine but the vast majority of DIYs don't have any kind of engineering background at all. Perhaps they are musicians, clerks or chefs instead. In my experience, it's necessary to ask folk what they know before suggesting they wire up anything but it's impractical here, I think. We can do little more than ensure that we don't contravene the forum's own rules with our posts and trust that anyone else who wants to try our ideas will already understand the issues.
That's fine but the vast majority of DIYs don't have any kind of engineering background at all. Perhaps they are musicians, clerks or chefs instead. In my experience, it's necessary to ask folk what they know before suggesting they wire up anything but it's impractical here, I think. We can do little more than ensure that we don't contravene the forum's own rules with our posts and trust that anyone else who wants to try our ideas will already understand the issues.
I think the best thing is to always say best use switch mode power supplies unless fully aware of all safety requirements of linear power supplies. In the uk since 1996 what the public can do is limited. Strangely many devices that have critical requirements for safety are still DIY jobs.
I met a group of Australian engineers in my work. I was struck by how unusually careful they were over perceived risk. This surprised me a little. Could it be Australia has a culture of legal punishment for the slightest transgression. I remember being told Australia requires tyre treads twice that of the UK. Unusual as we are in my perception permanently wet and never see the sun. As some joker said in Australia some tyres are illegal when new. I remember asking a Brit couple about precautions in the Outback. They laughed and said you mean the back garden. I then realized that they weren't joking.
If anyone needs the CB standard the BSI is still alive and well. They seem very helpful and still issue the Kite mark. My company use NEMCO. I am told TuV have many regional offices which is helpful.
I met a group of Australian engineers in my work. I was struck by how unusually careful they were over perceived risk. This surprised me a little. Could it be Australia has a culture of legal punishment for the slightest transgression. I remember being told Australia requires tyre treads twice that of the UK. Unusual as we are in my perception permanently wet and never see the sun. As some joker said in Australia some tyres are illegal when new. I remember asking a Brit couple about precautions in the Outback. They laughed and said you mean the back garden. I then realized that they weren't joking.
If anyone needs the CB standard the BSI is still alive and well. They seem very helpful and still issue the Kite mark. My company use NEMCO. I am told TuV have many regional offices which is helpful.
I just checked the Building Regulations. I was very surprised how much is still DIY in the UK. Sockets can have up to three 2.5mm^2 into a socket if replacing an existing fitment. This is not easy to get right. One can not fit this as a new installation unless qualified. However if the almost identical fused spur you are. I find this unbelievable in safety terms. I could write a book as large as the Bible about this so restricting myself to the best illustration. I remember questioning earthing plastic fitments. It's for DIY people to transfer wires to metal fittings. It seemed so reasonable when told except should DIY be allowed.
I have two Variacs. The 10 amp one from India came with an old 15 amp British round pin plug. I didn't like the cable so changed it. Apart from that it is very safe. It has a metal case.I had to replace the voltage meter as it was jammed.
BTW. Any power supply over 50 volts is considered unsafe. That could be questioned when AC as 35 vac is circa 50 volts peak or 100 volts peak to peak. 100 watt amplifiers unless bridge type are double safe voltages. DIY Audio had a 1000 design for novice builders. That must have been a no no.
In the UK we have had connectors for gas cookers. I find that unbelievable. I had to connect one .
I have two Variacs. The 10 amp one from India came with an old 15 amp British round pin plug. I didn't like the cable so changed it. Apart from that it is very safe. It has a metal case.I had to replace the voltage meter as it was jammed.
BTW. Any power supply over 50 volts is considered unsafe. That could be questioned when AC as 35 vac is circa 50 volts peak or 100 volts peak to peak. 100 watt amplifiers unless bridge type are double safe voltages. DIY Audio had a 1000 design for novice builders. That must have been a no no.
In the UK we have had connectors for gas cookers. I find that unbelievable. I had to connect one .
Once I was repairing 9kW switch mode power supplies at work, it's basically an inverter stage from a small chiller. In the test I did not solder one resistor in the filter because I did not have this value, but within ten minutes my colleague called me and said that all the phones in the company went crazy, I knew immediately that it was my test that put so much interference in the power supply that disrupted the operation of the switchboard. This is pure proof that just a small mistake with switch mode power supplies can lead to problems, not to mention the loss of someone's life.
Popular laptop bricks are the worst possible power source, have any of you opened one? no wonder they are gluing.
The same industrial ones have the exact specifications, attestations, protections and the specified output noise. The price is at least like a toroid of the same power.
I don't think it makes sense to put an amplifier or anything else, and especially human life, at the mercy of some cheap electrolyte or diode in a brick.
Popular laptop bricks are the worst possible power source, have any of you opened one? no wonder they are gluing.
The same industrial ones have the exact specifications, attestations, protections and the specified output noise. The price is at least like a toroid of the same power.
I don't think it makes sense to put an amplifier or anything else, and especially human life, at the mercy of some cheap electrolyte or diode in a brick.
I think making linear supplies is a don't ask don't tell situation. We just assume somehow the nearby constructor just found one.
I was putting an FM aerial in the loft yesterday. I moved in middle September. The guy was an electrician. The wiring is very untidy. However I like it. So easy to add to. I saw similar in Cuba. Almost like these preserved rusty cars with shiny engines under the hood. I bet when a client he did a neater job. Superficially it looks dangerous what he did. Where it matters he did a proper job. Something I like is additional insulation tape on top of wires as they enter junction boxes. I have never seen this before. It looks super neat and protects. Then it spreads out to the next box like a pile of scrap cable.
I was putting an FM aerial in the loft yesterday. I moved in middle September. The guy was an electrician. The wiring is very untidy. However I like it. So easy to add to. I saw similar in Cuba. Almost like these preserved rusty cars with shiny engines under the hood. I bet when a client he did a neater job. Superficially it looks dangerous what he did. Where it matters he did a proper job. Something I like is additional insulation tape on top of wires as they enter junction boxes. I have never seen this before. It looks super neat and protects. Then it spreads out to the next box like a pile of scrap cable.
Frankly, I don't think it's wise to question our local power distribution regulations and practices here. It doesn't seem like a professional attitude to me but then, I'm not an engineer and this thread isn't about power distribution engineering standards or rules that might be quite different elsewhere.
The elephant in our rooms, I think, is the phenomenon of a global, internet driven marketplace. It's dramatically changed the sources, costs and quality of smaller items we purchase, by simply bypassing our retail supply chains, import regulations and consumer protections.
Yes, I've bought several of those cheap power bricks over some years now, both fixed and adjustable voltage. I haven't been injured in any way but, there have been some failures, even with low loads. At the same time, other units that were supplied with laptops and various gadgets have been soldiering on for many years. I put this down mainly to capacitor quality but there's no point to breaking them open in the hope of a fix because you can't easily restore the integrity of the welded case
The elephant in our rooms, I think, is the phenomenon of a global, internet driven marketplace. It's dramatically changed the sources, costs and quality of smaller items we purchase, by simply bypassing our retail supply chains, import regulations and consumer protections.
Yes, I've bought several of those cheap power bricks over some years now, both fixed and adjustable voltage. I haven't been injured in any way but, there have been some failures, even with low loads. At the same time, other units that were supplied with laptops and various gadgets have been soldiering on for many years. I put this down mainly to capacitor quality but there's no point to breaking them open in the hope of a fix because you can't easily restore the integrity of the welded case
Ian. You have opened up an interesting debate. This is my everyday life. My best advice would be clubs be formed to help. From the word go people should understand like paramedics we would know more than a novice. Like a Vet isn't a surgeon we guys are not the IEC. Even so we could say something is totally unsafe if it is. A skeleton Variacs would be. Myself and I think a chap called Alan could do.it here. Alan still teaches the army age 80 and has been a TV engineer. TVs in the past were exceptionally dangerous.
An institution like a club and known as "Men's shed" has sprung up in Oz and has now spread a lot further. It probably fits the bill but not without the problems of willing but untrained members. Men's shed - Wikipedia
Some members here seem to be engaged in restoring old hi-fi gear here but it's a long hard road and there are few mentors who have the patience to assist with every electronic fault situation that a repair technician would be expected to have learnt to solve formally and with years at the bench. There's no easy answer among ordinary participants but this forum is a great reference, if you look at the threads which cover problems in a vast number of popular products from the past.
Some members here seem to be engaged in restoring old hi-fi gear here but it's a long hard road and there are few mentors who have the patience to assist with every electronic fault situation that a repair technician would be expected to have learnt to solve formally and with years at the bench. There's no easy answer among ordinary participants but this forum is a great reference, if you look at the threads which cover problems in a vast number of popular products from the past.
The kit circuit test lacks any bandwidth limiting on the input which would limit the rise time of the circuit to the limits JLH designed this for.
In the case of the 1969 version there was an active filter built into a section of his modular pre-amplifier design. In the 1996 design there was a passive low pass input filter 4k7 plus 330pF.
The slope of the latter filter is 6db/Octave equal to a slope of 45 degrees on a graph plotting gain against frequency and time - the latter two having an inverse relationship with one another.
Generally speaking people understand the need for input filters to limit frequency response but there is none in evidence in the test subject amplifier in the Youtube presentation.
Sources like phono and CD do not generate frequency signals at high frequency large enough to impact on the input low pass filter. However if a signal generator put a 1MHz frequency at a sufficiently high level it would be realized that this spelt trouble.
With nfb the same rules of 6dB/Octave and 45 degress of slope also apply so people may be inclined to think aha I can reduce a 1MHz out of phase return signal on the output line by incorporating a lead capacitor.
The difficulty here is that unlike a passive filter which diverts the unwanted frequencies to earth with a lead capacitor this provides a short cut to the inverting input since capacitor impedance reduces with increasing frequency.
You might have your low pass effect however in the time domain it does not react instantaneously as a brief out of phase signal at high frequency can do.
You have to think about time and frequency as being inversely proportional to each other. It is reasonable to use a 15kHz square wave - then look at the rise time on the plot and work out f=1/t.
Those are the same boards as I played around with a bit earlier (and I guess many others, same as in the 'sublimed JLH' thread), and referred to as the 'white boards'. I used 15003 output transistors, and did not see the problems in the video. However, I think they sounded a bit 'dull'.
That could be down to what you are using ahead of the input. Ideally you need to keep the source feed impedance low. With say a 50k volume control there will be some series resistance affecting impedance that varies with settings.
This will be highest at low volume settings the human ear varies in sensitivity - look up "Fletcher-Munson Curve" for more information on this.
You can perceive frequency differently at different volume levels and the result is not a linear progression. That makes it hard to give a definitive judgment on whether or not a sound is dull or not.
To continue, if shielded cable is used between the control and the amplifier input, you have a low pass filter effect due to interaction of the series resistance in the control and connecting cable capacitance.
There is also diffusion capacitance between the emitter and base of a transistor.
Use is made of this fact to reduce frequency response in output stages by putting stopper resistors in series with the driver transistor bases. These might range in hundreds of Ohms
The effect has to be scaled down for small signal transistors but the impact cannot be ruled out entirely since the series resistance in a volume control could be in the range of thousands or tens of thousands of Ohms.
In my case I'm using a sound card to feed the amp, and only digital volume control. I think the output impedance of the sound card is around 100 ohms.
Theoretically this is not optimal since the whole digital bit depth is not used (24bit), but the gain is not so high on the JLH so the volume does not have to be turned down extremely low. I have used the same source for listening to all the amplifiers I made, and most of the distortion testing of the amps has also been done using the same sound card.
Doing loopback tests on the sound card at those levels, the results are way better than the amplifier itself.
Theoretically this is not optimal since the whole digital bit depth is not used (24bit), but the gain is not so high on the JLH so the volume does not have to be turned down extremely low. I have used the same source for listening to all the amplifiers I made, and most of the distortion testing of the amps has also been done using the same sound card.
Doing loopback tests on the sound card at those levels, the results are way better than the amplifier itself.
very interesting !!
I hope that solidarity between humans will be restored after the damn virus ends
Very well saiid Huggy.
Looking at bandwidth limiting. For some people restricting the input bandwidth of an amplifier is a symbol of poor design. They often seem to be selling high slew rates. I suspect the use of a JFET input could help.
Feedback compensation has the virtue of tons of current. Many don't like the idea. They seldom say why..
The VAS is very reliable using base collector compensation. However current is sacrificed.
Any thoughts?
Looking at bandwidth limiting. For some people restricting the input bandwidth of an amplifier is a symbol of poor design. They often seem to be selling high slew rates. I suspect the use of a JFET input could help.
Feedback compensation has the virtue of tons of current. Many don't like the idea. They seldom say why..
The VAS is very reliable using base collector compensation. However current is sacrificed.
Any thoughts?