DIY modding/fixing of gear, what voltages are dangerous?

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markjazzbassist
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DIY modding/fixing of gear, what voltages are dangerous?

Post by markjazzbassist » Tue Feb 13, 2018 2:44 pm

Hello - I've recently gotten into doing some small DIY stuff, i built my own "Motown DI" with an UTC A-10 Transformer and a Bud Box. Was fun.

I've read many times over don't work on Tube Amps because they contain lethal voltages (unless you know how), so i'm here to ask what else is lethal? Like could i mod/repair a synthesizer (say a micromoog) without worrying about killing myself? Or am I limited to pedals and stuff with an under 120v power supply?

Please advise (my wife and kids thank you in advance :shock: )

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by Nick Sevilla » Tue Feb 13, 2018 4:03 pm

The only time you can encounter lethal voltages is with power amplifiers.

Like Marshall / Fender amplifiers which have tubes in them. I've worked on some with them on, to do their biasing. I just stay well away from the power transformer and power capacitors and am fine.

Most synths are all low voltage affairs.

The only places you do need to be careful on those is in the power supplies, which have regulators to step down the incoming 110 / 220 votlage to the various voltages used inside the machines.

Always unplug them before use, and if you find capacitors near the power cord inside, learn to drain their energy safely, just as a good practice.
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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by winky dinglehoffer » Tue Feb 13, 2018 6:25 pm

The only really nasty voltage in a synth is the 120V coming in from the wall--generally not lethal. but not any fun either. The Micromoog's power supply is on a separate PCB from the synth workings, so that's helpful. Just watch yourself when you're inside the synth while it's plugged in, and make sure you unplug it when you should unplug it.

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by vvv » Tue Feb 13, 2018 7:56 pm

Doing a little reading is good but a couple of tips I have is wear rubber soled (tennies is fine) shoes, and try to only have one hand in contact with the amp at a time.

And yes, learning how to discharge caps is good.

FWIW, changing tubes with the amp on is not.

I told a story elsewhere here the other day about taking a jolt inside an amp, and immediately, reflexively, reaching in to do it again. Be aware of that possibility - it's not uncommon and if you know about it, you can stop before you do it.
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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by markjazzbassist » Wed Feb 14, 2018 6:32 am

great stuff guys. yeah i'm not interesting in building tube amps, just fixing synths, pedals, mix consoles (small ones), etc.

thanks for the info!

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by Scodiddly » Wed Feb 14, 2018 1:37 pm

The usual definition of high vs. low voltage is 100 volts, though things can still be a bit nasty below 100v.

In a typical AC powered keyboard or other device you're going to find 120 volts AC in the power supply, then more like 10-30 volts DC in the bulk of the circuitry. In a power amp you'll see higher voltages - solid state depends on the wattage, but tube amps will routinely have 400+ volts AC and DC in various sections.

Circuit-bending people typically only work on battery-powered devices to avoid any chance of touching high voltage sources. With a wall-wart you'll probably see 15 or 20 volts max, which is pretty safe to work on.

Though even at low voltages (like in a car) it's still possible sometimes (like in a car) to pass enough current to start a fire or burn your fingers.

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by vvv » Thu Feb 15, 2018 10:21 pm

There's a old auto mechanic's cliche:

It ain't the volts, it's the amps what kill you.

YMMV
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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by kslight » Sat Feb 17, 2018 5:21 pm

Synths and pedals are usually pretty safe as long as common sense is exercised (don’t lick the power caps, disconnect the power source, discharge any big caps before changing). More likely to damage the device itself than hurt yourself, in most instances.

Micromoogs are cake, I redid one a few years ago and gave it to my business partner for his bday.

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by emrr » Wed Feb 21, 2018 5:51 am

vvv wrote:
Thu Feb 15, 2018 10:21 pm
There's a old auto mechanic's cliche:

It ain't the volts, it's the amps what kill you.

YMMV
Yep. You can touch 300V in a single channel preamp with very little current capacity (and small filter caps) and get a scary spark, but much less limited danger than touching that same 300V in a power amp with a lot of current capacity, or a really stiff high capacitance power supply. One may kill and the other may scare. Compared, as others said, to a 12V car battery being shorted by a ring on your finger, and cooking your finger like a sausage due to the huge current flow.
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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by markjazzbassist » Mon Feb 26, 2018 2:12 pm

this brings up another topic, what is a solid Digital Multimeter that won't break the bank. I'm fine with new or used, would love to be around $100 or so. Just working on 120v and less stuff like synths, drum machines, pedals, etc.

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by illuminations » Tue Feb 27, 2018 8:40 am

I've actually been curious about the same thing. I've built some pedal kits in the past, but haven't done much else circuitry of electronics.

I'm planning on replacing caps on some of the boards for my Tascam 388. I think most are straightforward, but one is the power supply board. The power supply board is a spare so it hasn't been plugged in for a while, if that changes things. Are there any step I should take? Would discharging be necessary?

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Re: DIY modding/fixing of gear, what voltages are dangerous?

Post by The Scum » Tue Feb 27, 2018 10:51 am

The Fluke 115 is a really good general purpose multimeter, just a bit over your budget. But it's a reliable meter, and when you outgrow what it can do, you'll be looking at real meters (The $400 Fluke 87).

Don't be confused by it's close cousins, the 114, 117, etc. They're aimed at HVAC installers and other specialized trades, with targeted features for them.

Craftsman used to have a couple of decent meters, but I haven't checked in with them since my local Sears got demoed.

The Amprobe (formerly Meterman) meters are pretty OK, but not so much less expensive than the Flukes that I'm really recommend them over Fluke.
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