If you don´t want your LEDs to light up your room, depending on the LED, this kind of value makes the light output much more tolerable.
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Good testing scheme, but as you have noticed, it is not sufficient to find all problems.
That seemingly inconsistent kind of a response points at some active components that start to work as soon as they are powered, not beforehand. So, capacitors that are powered the wrong way round, ICs, power stabilizers etc, transistor bridges that are supposed to alternatingly conduct but instead conduct at the same time, etc. When you are measuring using a multi meter, none of these problems occur.
One way to avoid this is to use a regulated power supply and start with a voltage of 0 Volts and turn it slowly up to the value you want the circuit to be powered at while keeping an eye on the current. If the current quickly gets very (or too) high, this is an early sign that something is wrong. For my euro rack builds, I use 2 (in series), one for the positive and one for the negative voltage. I turn both up at the same time and check the current. If nothing odd happens, I set them to ±12 Volts and start further checks.
I use a power supply not unlike this one:
They are a good investment.
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Thanks Jos, I am considering investing in one - just doing a bit of research to figure out exactly what I need. I will take a look at the LW-K305D.
Thank you also to Fredrick, Dud, and Analog Output. I don’t know how I managed to reverse the power inputs for my op amps, but evidently that must have been the problem. I’m going to reply in the expression pedal thread since that’s where the discussion continued.
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Welcome to the club:
(I hope you didn’t use that picture as a guide 
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I put the image up for demonstration purposes. I have no experiences with the LW-K305D. Myself I have two similar power supplies of type MCH-K305D.
Note 1: One of these supplies will give you 1 output voltage. The + gnd and - socket may suggest that the output is +12 Volts against GND and -12 Volts against GND, but that is not the case. The output is 12 Volts between the + and - socket.
Note 2: if you do not want to invest in a power supply, you could also try an alternative to slowly turning up the voltage. That would be by limiting the current to a given maximum value by introducing a series resistor; it will get warm/hot, therefore it will need to have a higher wattage than the resistors you would normally use. Use e.g. a 100 Ohm resistor (1.5 Watt type) to limit the maximum current to 120 mA for a supply voltage of 12 Volts. Obviously you need to choose as a maximum current a value which is a bit higher than that which you expect the circuit to draw in normal operation.
Once you are convinced that there is not short, remove the series resistor and continue to test the circuit.
This one looks interesting, low cost and relatively large number of high ratings:
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Hmm, you make no mention of shipping costs, so I had a look:
$71.81 Shipping & Import Fees Deposit to Netherlands
and maybe duty costs (15 USD + a percentage of the estimated cost of the device) … That is a tad expensive!
Do compare this with aliexpress, the cost of the device may be 30USD plus about the same amount in shipping costs. So this can be much cheaper in the end. You may also find the free shipping variant that is about the same total amount. E.g. this one
There is a 3A and a 5A version for either 110 V or 220 V.
I bought a 30 Volts, 5A set in March for USD 50 so about 44 Euros including shipping, no duty costs. Prices do vary, though.
Just make sure it is usable for the mains voltage in your country.
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For me it’s free (Prime) shipping, delivery in a couple days.
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That’s “I’ve paid for shipping already,” not “free” 
I’d recommend checking local suppliers as well. They’re not necessarily that much more expensive if you factor in shipping/customs, and while I use a lot of cheap chinese crap in low-voltage builds, I tend to be a bit more careful with things plugged into 240 V mains. Especially if they’re cheap.
(If you’re not sure what I’m talking about, go watch some Big Clive videos )
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Hopefully I am not hijacking the thread with my question. In some forums that is a big no no. Did not want to start another one because in other forums that too is a big no no. LOL I been on too many forums.
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Ok My question
Many of you seen my thread on my big synth project. My idea was to compact my home-brew designs. The boards I have are 12inch (30.5cm) by 8inch (20cm) roughly. They are going to be put together in like a 12inch by 12inch or a 12inch by 24inch module. Needless to say the entire cabinet will need a heavy transformer. In America 15 amps at 120vac is the typical receptacle. In electrical math this means 150 amps 12vac secondary winding is possible. In real world application it is less due to loss of power in producing heat as a byproduct. Even so you would think you could still manage 100ampers from a donut shaped transformer with heavy winding for the amperes.
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When ever I search on google or bing I get at best a transformer or wall wart that puts out 2 amps. Where would I find a transformer capable of 20 or so ampers? I am willing to install mutliple transformers in my cabinet, but lets be real. A 2 amp 12vac secondary winding is not going to get very far for my idea. Any one got ideas?
I don’t know what you mean by “typical receptacle”, but in the UK you’d be close to blowing fuses with 15A, not to mention the heat dissipation. Okay, our voltage here is 240V but even so at 120VAC, 15A you’d be drawing 1800W, which is ludicrously high for modular synthesis. It’s twice the power draw of a really good microwave oven.
What are you going to be doing with audio frequency electric currents that will need that kind of power?
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You can get 12 V LED supplies up to at least 600 W. No idea if the output is clean enough for audio use, but you could perhaps address that by adjusting the output voltage (they often let you tweak that 10-20%) and running the switched output through LDO regulators to get cleaner analog rails (e.g the LM108x series mentioned here earlier).
But I’m going to echo @Bitnik here – what exactly are you doing that’ll use 100 A for the analog synth circuitry?
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I was in a tech class for electrical. The teacher got angry with me and my algebra. The guy did not know algebra because you don’t need it in electrical. However, all the receptacle or outlet boxes we assembled was 15 amps. Even the light switches; 2-way, 3-way, and even the nighmare 4-way switches can handle around 15amps. The breakers we had were 100amps for the service drop and 60 amp for both the 120 and 240 lines. National Electrical Code 2014 Page 70-72 Article 220 Branch circuit, feeder, and service calculations. Edit cant do the math right now. You get the point though.
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It should not be impossible to find something such as a transformer 7 or 8 amps primary winding and a 20 amp secondary winding. The big auditorium bass sub woofers have big donut shaped ones that draw about that much.
A typical synth module draws maybe about 40 mA, obviously that varies considerably but that’s a good rough average. 100 amps would then power about 2500 typical synth modules.
Even if I had 2500 synth modules and wanted to use them all at once I’d open a museum I wouldn’t do it with a single power supply.
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100amps is a very basic service drop for a household. I don’t have the time to do the correct math. Just trying to illustrate my point
I think the question here is not so much can you, as why would you need to. Synthesis isn’t something like power amplification where you need to draw a high current. It’s about running an audio frequency current through some transistors, diodes, and passive components to make an interesting sound.
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Never like to use my autism as an excuse, but it is something I fight with daily. Thanks for rephrasing these words for me. You might have a point. I did manage to find a power supply for an outdoor light system with 12vac with a little more than 8amps output capability. I suppose the better question on my end is, would this be enough for a start? I am building a computing system for MIDI and CV conversion as close to from scratch you can get without using bare logic gates. My mother gives me a hard time about how I can over think even the simplest project.
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Autism is in my family too, and I often get that uneasy feeling that my words are being misunderstood. Relax, you’re among friends here.
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It may not be well known here, but I have AS.
I think people are just concerned that you are working with dangerous levels of amperage (over 100 amps?) for something that probably doesn’t require it. Just split it up like @analogoutput said yo.
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To get an idea of what power typical synth modules need, you can go to https://www.modulargrid.net/modules/browser and click around a bit. Most modules there list their power requirements on the module page.
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