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Can I use SMPS to power bass guitar amp instead of HUGE transformer?
Can I use SMPS to power bass guitar amp instead of HUGE transformer?
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Old 26th July 2013, 09:06 AM   #11
brig001 is offline brig001  United Kingdom
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Sorry, I should have been more specific. I'm talking about the existng power supply smoothing capacitors. As you rightly say:
Quote:
Originally Posted by JonSnell Electronic View Post
The power supply doesn't need large capacitors as it stabilizes itself at a rate fast enough to cope will all requirements from a power amplifier.
So, the existing capacitors could/might have to be replaced with a much lower value.

Brian
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Old 26th July 2013, 09:18 AM   #12
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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The switch mode power supply will have its own tank capacitors and all that will be required is a couple of 100uF decoupling on the rails at the amplifier end.
If one uses large tank capacitors, the power supply may overshoot and give odd voltages.
Most guitar amplifiers use 4k7uF smoothing or 6k8 at most. Remove them and fit the lower value caps in their place. Don't forget they mainly use a +ve and -ve supply. So use a suitable twin output power supply!
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Old 26th July 2013, 10:24 PM   #13
Ian Finch is offline Ian Finch  Australia
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Have protagonists for DIY switchmode supplies checked forum rules, note 2?
This isn't the first time the issue has been raised and of course, it does not address current commercial design or practice which most us are well aware of, driven as it is by cost as much as weight.
Even if there is true isolation in the supply design, the distinction between commercial, sealed SMPS products and DIY builds or modifications requiring isolation transformers needs to be made - prefererably in the power supply forum, I should think.
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Old 26th July 2013, 10:31 PM   #14
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Ian Finch View Post
Have protagonists for DIY switchmode supplies checked forum rules, note 2?
This isn't the first time the issue has been raised and of course, it does not address current commercial design or practice which most us are well aware of, driven as it is by cost as much as weight.
Even if there is true isolation in the supply design, the distinction between commercial, sealed SMPS products and DIY builds or modifications requiring isolation transformers needs to be made - prefererably in the power supply forum, I should think.
I don't think the OP was considering making his own SMPS.

He should be ok with a professionally made company SMPS as it will be checked for safety and emissions.
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Old 26th July 2013, 11:02 PM   #15
brig001 is offline brig001  United Kingdom
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Quote:
Originally Posted by guitylerham View Post
Is it as simple as buying a sufficiently powerful module
The OP was definitely asking about COTS, so shouldn't conflict with forum rules.
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Old 27th July 2013, 12:14 AM   #16
Ian Finch is offline Ian Finch  Australia
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You may be correct there, Nigel. The problem, as a friend found last year with with his Ebay purchase of a couple of 24V Chinese supplies, was that were not fully isolated. An unmistakable shock from accidentally touching chassis earth to the 24V output says so.

Some supplies are not enclosed (e.g. Hypex) and rely largely on user measures for shielding and safety in their fitting, adjustment and use. See the VSSA thread for what I refer to. There is a big difference in the precautions taken by professionaly experienced manufacturers, engineers, technicians etc. to guesswork by DIY hobbyists and those just seeking to make matters easier for their hobby.

DIYs often assume commercial products to be safe but maybe not understanding the documentation or the nature of the products, can they really understand the risks among the many types available?
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Old 27th July 2013, 12:29 AM   #17
mcd99 is offline mcd99  United Kingdom
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Quote:
Originally Posted by Ian Finch View Post
Ebay purchase of a couple of 24V Chinese supplies, was that were not fully isolated.
This comes as no surprise at all. Some manufacturers just don't care.

Approval marks anyone?
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Old 27th July 2013, 06:15 AM   #18
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Quote:
Originally Posted by Ian Finch View Post
Have protagonists for DIY switchmode supplies checked forum rules, note 2?
This isn't the first time the issue has been raised and of course, it does not address current commercial design or practice which most us are well aware of, driven as it is by cost as much as weight.
Even if there is true isolation in the supply design, the distinction between commercial, sealed SMPS products and DIY builds or modifications requiring isolation transformers needs to be made - prefererably in the power supply forum, I should think.
I should not imagine anyone trying to make a smps without an isolation transformer unless copying a design from the Thorn/RBM days of the early Colour TV's. Sensible to point it out as one never knows.
They used a live chassis with an auto-transformer as a choke with a recovery diode and chopper transistor. Dead basic and the isolation was in the aerial socket but it worked!
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Old 27th July 2013, 03:42 PM   #19
mcd99 is offline mcd99  United Kingdom
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Quote:
Originally Posted by JonSnell Electronic View Post
They used a live chassis with an auto-transformer as a choke with a recovery diode and chopper transistor. Dead basic and the isolation was in the aerial socket but it worked!
Do you mean the socket in the wall or within the TV?
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Old 27th July 2013, 03:58 PM   #20
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Within the TV. The aerial socket used to be an isolator when the chassis all were live. ITT kb Hand wired colour tv's were nice to work on as were the Thorn EMI 2000 range.
Workshops didn't have isolating transformers either so the chassis went to Neutral. The newer Philips Monochrome tv's used a bridge rectifier at the front end and the chassis was always half live! That was the start of smps units in tv. Circa 1975
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