I am currently researching and designing electrical audio equipment, example devices:

  • Tube and solid state guitar amplifiers
  • Guitar effects pedals
  • Mixing / filtering units
  • Synthesizers

Some of these devices will be mains powered and some low voltage.

For context I am in the UK and hold a Masters' degree in Electrical and Electronic Engineering.

I have had friends, relatives etc approach me to ask if they can buy some of my products.

At present I do not plan to make a business out of this but it could be a possible future consideration.

The price I would be selling the equipment at would not warrant £1000's of test certification, as I do not have the money for this I would prefer not to sell if test houses are the only option.

My primary concerns are safety and liability.

What safety standards do I need to comply with and can I self certify?

Can I remove / reduce liability by selling as a kit product / prototype?

I notice people online selling amplifier kits, presumably they are not liable for incorrect wiring / use.

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    \$\begingroup\$ If you can use a mains adapter from a reputable manufacturer then someone else has taken care of the mains voltage safety requirements. I assume that won't work for the amplifiers. \$\endgroup\$ – Andrew Morton Jun 28 '19 at 12:35
  • \$\begingroup\$ I did think about that for SELV products, but it would still be nice to be in control of the PSU design especially for noise reduction on the pedals \$\endgroup\$ – LazyMoggy Jun 28 '19 at 12:41
  • \$\begingroup\$ Do read my answer in electronics.stackexchange.com/questions/429146/… \$\endgroup\$ – Huisman Jun 28 '19 at 14:26

For compliance to EU requirements and to carry the 'CE' marking you can self-certify without using a testing agency, and to do so you need to create a declaration of conformity, which authorities can request at any time, and maintain a technical file which documents your evaluation of the design and manufacturing process' ability to maintain compliance - so that'd include some quality plan to periodically check production capabilities, and individual item testing if justified. It's up to you to determine all the requirements that are relevant to your particular application.

I'd follow suggestions to use an off-the-shelf power supply that someone else has assumed the responsibility and liability risk for, and maybe just add in some further conditioning and filtering if you're using if for a low noise application. One big reason for this is that demonstrating EMC compliance might be expensive in itself, and an off-the-shelf PSU will likely have the input suppression sorted for compliance.

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  • \$\begingroup\$ In terms of 'production capabilities' these will be one off or small batches made by me in a garage. I assume that with the self certification I would be liable if an accident occurred where I had missed / overlooked a safety element. The off the self supply idea is also not possible for the amplifier designs, they will need their own supplies. I suppose what I'm looking for is a way of selling these products as 'use at your own risk' to absolve me of liability \$\endgroup\$ – LazyMoggy Jun 28 '19 at 14:07
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    \$\begingroup\$ "you can self-certify without using a testing agency" is in most cases true, but for some devices you have to use a notified body. In fact, the official text (How to obtain CE marking? point 3) starts with saying: "For some products, special conformity assessment bodies ('Notified Bodies') must verify that your product meets the specific technical requirements." and then makes the exception: "This is not obligatory for all products." \$\endgroup\$ – Huisman Jun 28 '19 at 14:19
  • \$\begingroup\$ @Huisman Good point, that is most commonly necessary for medical and machinery, but probably not for this kind of equipment. \$\endgroup\$ – Phil G Jun 28 '19 at 15:26

You also have to obey the speed limit and will be held liable when you cause an accident. The same applies for selling products... But if you want to strictly obey the law, read the European site (well, maybe soon not applicable to UK...) regarding CE marking and seek contact with a testing house and don't rely on (most) amateuristic advises you find on this site. I'm neither an expert, but found and proved using the European site that most advise is only half the truth or partially completely wrong (like this EEVBlog video.

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    \$\begingroup\$ I was involved in product certification in the UK before and during EU harmonization. I'm glad I won't be there if Brexit does go through....I doubt the politicians are aware of the enormity of the change it will have on products for the UK market. \$\endgroup\$ – Phil G Jun 28 '19 at 15:29

Rather than close this for duplication, read my recent answer and search me & FCC.

If you use an AC/DC class 2 supply and test it with an AM radio for spurious emissions or better methods of self-certification and document the results., you are doing some due diligence. Then do some sample testing for HIPOT, and test to failure, with a current limited 25kV from a very long carbon wire pair from your car engine (1M) using mica HV rated caps as a voltage divider with 1M series and NE2 bulb. Or cross your fingers and write to OEM for DVT report on same.

OK as long as the PS you choose won’t cause leakage currents when the breakdown voltage is exceeded and arcs a 1 cent capacitor (or designer oversight ) to kill someone from some undocumented distributor on EBay.

Lack of surge protection recommended for safety is always a risk.

I suggest use with a “surge-protected Common Mode Choke line filter” . I suggest that document all sales and ads with this caveat for best practise, so guitarists won’t get the “wrong” buzz when they plug into their AC powered AMPS in Florida with 100k lightning strikes in one region per year. Then their loved ones can’t sue you successfully for a wrongful death.

Expect the worst thing that could happen then offer a solution.

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