[Tutorial] Building your own DIY E-Stim Stereo Device

[bobross235]

Session 1 / X

I finally decided to start building one myself. As I'm a complete beginner I'll share all my thoughts, learnings and mistakes here. Maybe it'll help someone and/or encourage another beginner to try it. I'm trying to understand everything to minimize errors.

I bought this soldering iron:
https://smile.amazon.de/gp/product/B000 ... =UTF8&th=1
This box of shrink tubing for insulation:
https://smile.amazon.de/gp/product/B003 ... UTF8&psc=1
And this solder:
https://smile.amazon.de/Flussmittel-Kol ... hdGY&psc=1

I already made some mistakes when ordering :)
I misunderstood
"2x Chinch Input (red) (black) (white) - 6.07€"
and ordered two red, two black, two white! Looking at the picture of course it would have made sense to only order two in total.

Connecting two parts
I don't have any fancy clamps to help me soldering so I basically use a three step approach I saw on youtube:
1. Heat up the iron and put solder on the first part (eg. cable)
2. Heat up the iron and put solder on the second part (eg. cinch input connector)
3. Hold both parts together, heat up with iron and hope they stay together
It's a bit tricky but I'm making slow progress.

I pretty much use a shrinking tube to insulate everything after soldering. Result of first piece


Connecting three parts
I counted 9 times where three cables need to be connected. Here's what I mean:

The best way I found to do this is by just buying two times 5 of these wago connection clamps for three cables:
https://www.amazon.de/gp/product/B017KQ ... UTF8&psc=1

How do switches work
Probably most of you are laughing by now :D
But I didn't completely understand how to connect the switch with the 6 pins so I had a closer look at the idea behind switches.
Looking at the smaller switch with 3 pins first. It's an "on-on" switch.

See the little numbers 1,2,3? The switch is either connecting 2 and 1 or its connecting 2 and 3.

It works the same for the switch with 6 pins. The middle row is connected to the side where the "switch is switched to". All three pins in the middle are either connected to all three pins on the left side or to all three pins on the right side.

Connecting the AMP board
Before it arrived I had NO idea how to connect the board.

I was positively surprised when I found out a cable is provided. It looks like this:

It has this small connector on both sides. So my idea was to cut the cable in the middle and solder the white/red cable to the two POTS and connect the black cable to WAGO clamp. I was a bit surprised that the black cable was not insulated within the gray tube. It only insulated up to the black shrink tubing, inside the gray insulation it's blank metal. But it's still long enough to connect it, so should be fine.

Here's the end of my first session and my first question to the experts: The pre-existing cables from the AMP board connector are WAY thinner than the 0,5mm cable I bought. Is this a problem?

[lolol2]

Looks/sounds good so far.

The pre-existing cables from the AMP board connector are WAY thinner than the 0,5mm cable I bought. Is this a problem?

No problem, on the input site of the amp is no heavy load, so thin wires are okay.
Mixing thin wires with thick wires is also okay, all calculations have to be based on the thinest part of the wire.
But in this usecase the thin wire is totally fine.

[Electro]

The areas that need thicker wires would be everything from the amp output until it goes into the transformer, that wire should be the thickness of the transformer wire themselves or larger, which is not particularly thick wire.

[bobross235]

Thanks a lot @Electro & @lolol2

Session 2 / X
(almost 4 hours today):

Finished everything left of the AMP board first. Tried to understand a bit more about the parts. ChatGPT was a big help.

ChatGPT: Describe in easy terms, what a "..." is doing:

Potentiometer:
A potentiometer is a type of resistor that has a variable resistance. It consists of a resistive element with two fixed endpoints and a third adjustable endpoint called the wiper. The position of the wiper determines the resistance between the two fixed endpoints, allowing the resistance to be varied continuously over a range of values. Potentiometers are commonly used as adjustable voltage dividers, for adjusting the volume or brightness in electronic devices, and for calibrating sensors.
Amplifier board:
An amplifier board, or amp board, is a circuit board that contains the components and circuitry necessary to amplify a small electrical signal. Amplification is the process of increasing the strength or size of a signal, and amplifier boards are used in a variety of electronic devices to boost signals to a level that can be used by speakers, headphones, or other devices.
The basic components of an amp board include one or more amplifiers, power supply components, and input and output connectors. The amplifier takes an input signal and amplifies it using a power supply, typically a voltage or current source, to produce a larger output signal. The input and output connectors allow the amp board to be connected to other devices in a system, such as a microphone or speakers.
Amp boards can be found in a wide range of electronic devices, including audio systems, home theaters, musical instruments, and other types of electronic equipment. They are an essential component in many devices that require amplification of signals to produce sound or other types of output.
Transformer:
A transformer in electronics is a device that transfers electrical energy from one circuit to another through electromagnetic induction. It consists of a primary winding, a secondary winding, and a core made of ferromagnetic material. The transformer is used to change the voltage and current levels in electrical circuits, and to provide electrical isolation between circuits.

Power Supply
I ordered the Leicke power supply first but as feared the one I got didn't have a "phase II" symbol. I found this one with very similar specs:
https://www.amazon.de/dp/B0BF9T6X64?psc ... ct_details
Would be great if the experts could have a quick look.
It has the double square sign on the back. It also provides a connector to two single cables so I don't need the additional power connector I initially ordered. The combination of the sign on the back and the fact the provided connector only allows two cables lets me hope its phase II.
I also tried to understand what phase II means and why it's important and to my understanding it's a safety feature, "similar" like a ground wire is a safety feature. It's additional protection in case of electrical faults. It's an additional layer of protection in form of double insulation.

That's the small connector provided with the power supply:



I continued following the schematics and finished almost all soldering.

Triphase mode
I tried to understand the triphase switch, hoping this is correct:
Switch off -> black cables are not connected:
The current flows from red to black1 and from yellow to black2.

Switch on -> black cables are connected:
Triphase mode. The current flows from both red and yellow to ONE black port. Just one black ports needs to be connected to the triphase cable and it doesn't matter which one.

Case
The case from the list wasn't available anymore. I bought this one which is a bit bigger. Did you just use wood drills to drill the holes?
https://www.amazon.de/dp/B07NVK538F?ref ... tails&th=1

Next steps
Still waiting for the 3,9 OHM resistors to be delivered. This will be the last step of building the unit.
I have an old plain digital multimeter to start testing. Hopefully that's sufficient?
My strategy for testing would be quite simple:
1. Test if there's no current flowing between red&black and yellow&black with no sound input
2. Test if there's currrent flowing with sound input and post the numbers here to hear your feedback.
I'll also post some more pictures of the whole unit next time.

Thanks again for your great support!

[SunnyDay]

Thanks everybody in the thread for sharing all this useful information.

I just wanted to add a note to recommend using correctly graded component for powering your device, to prevent safety hazard .

That means making sure the power socket part itself, and the wires from power socket to the power switch and then to the amplifier board have proper specifications. (The switch itself normally has limits well above requirement.)

In this post (the legendary post from lolol2 which is the reason why I'm here), the power supply is 12V/10A or 24V/5A, but power socket part in the list is only rated to 60 VA which is twice below power supply requirement of 120 VA (12V x 10A or 24V x 5A = 120 VA).
Also wires in parts list are 0.5mm2 (or 20 AWG) which is normally rated 1.5 A only (see note below). I wouldn't use it to connect the power socket to the switch or amplifier. The 12V x 10A power supply that I own uses 16 AWG wire (according to the thin printing on the cable) to transmit power to the power jack, so in this case that seems the way to go.

In this other post from a different author the power supply is 12V/5A, but the wires in part list are 26 AWG which are rated 0.361 A. On Amazon the product description says 3A, but that seems very very suspicious. I wouldn't use such a thin wire in any case to transmit that amount of power. I wouldn't even use it at all in the whole device to be fair.

Please note that there are many tables on the web about wire size and current limit, but some of them seem to mistake limits of jacketed wire with limits of crude in-air wire, which don't perform the same heat dissipation. The chart I use is this one, which also has good explanations.

My recommendation would be:

• use the same wire size as the power supply for the power part of the device. If in doubt 16 AWG (1.31 mm2) would be a safe value since it can withstand 10A
• then using the same wire for the rest of the device would be the safest bet, but it can be difficult because of wire stiffness. Using 18 AWG (0.8 mm2) seems to be a good compromise and 20 AWG (0.5 mm2) seems still acceptable but I wouldn't go thinner
• be sure that the power socket you add (if the amplifier board doesn't have one) can support the amount of power provided by the supply, refer to maker specs

Btw by making these comments I don't mean to nitpick and the work done in this thread is awesome, it's just that having to deal with a fire hazard in the middle of a stim session is never the most pleasant thing to do

[RacerXxX]

I can't find a speco t7010 transformer near me, shipments too high to reach Europe.
it would cost me around 70/80€ including shipping.
what can i find similar?

PS. I see some have the lowest outputs at 0.5w and 0.25w, while others have the lowest at 0.625w, would both be fine?

[bobhill]

In this other post from a different author the power supply is 12V/5A, but the wires in part list are 26 AWG which are rated 0.361 A. On Amazon the product description says 3A, but that seems very very suspicious. I wouldn't use such a thin wire in any case to transmit that amount of power. I wouldn't even use it at all in the whole device to be fair.

Please note that there are many tables on the web about wire size and current limit, but some of them seem to mistake limits of jacketed wire with limits of crude in-air wire, which don't perform the same heat dissipation. The chart I use is this one, which also has good explanations.

My recommendation would be:

• use the same wire size as the power supply for the power part of the device. If in doubt 16 AWG (1.31 mm2) would be a safe value since it can withstand 10A
• then using the same wire for the rest of the device would be the safest bet, but it can be difficult because of wire stiffness. Using 18 AWG (0.8 mm2) seems to be a good compromise and 20 AWG (0.5 mm2) seems still acceptable but I wouldn't go thinner
• be sure that the power socket you add (if the amplifier board doesn't have one) can support the amount of power provided by the supply, refer to maker specs

Btw by making these comments I don't mean to nitpick and the work done in this thread is awesome, it's just that having to deal with a fire hazard in the middle of a stim session is never the most pleasant thing to do

Hi - that was the part list that I posted. I used the 26 AWG wire as it was in another parts list, but I appreciate your suggestion and will go to 20 AWG in future builds. I looked at my power socket specs and can't tell if it has the same problems you mentioned.

It's rated as:

Rated Voltage: Max 12V
Rated Current: Max 3A
Rated electric load: DC 30V /2.0A

Do you have a power jack that you would recommend for utilization in these boxes?

Thanks - BH

[bobhill]

I'm intending to build a stim box, but I have questions. After researching I landed on this schematic:



cap: bipolar 330uf (according to mantrid, this results in a cutoff of around 110 Hz)

I have a basic question on this. Does it matter whether the cap goes on the negative line before the R22, or after?

[diglet]

About wire gauge, the only thing that makes thin wires dangerous is that melt faster. Thinner wires have more resistance, which equals more heat.

How much heat is too much? Suppose that our input voltage is 12V and our power resistor is 4 ohm. If the amplifier outputs a square wave with the maximum amplitude, the current over the wire is 3A. We can use online tables to figure out the temperature rise of a single insulated cable in free air. For a 24 AWG (0.5mm diameter, 0.2mm2) wire the temperature increase is less than 10 degrees. Out of curiosity I grabbed a tightly wrapped bundle (3M) of 24AWG solid wire and hooked it up to a bench PSU at 2A continuous, after about 20 minutes the bundle hit 8 degrees celsius over ambient. Not a problem.

Now if you would hook up a 24V PSU and drive your stim box at the maximum power (6A), the wire might heat up to 35 degrees over ambient. I don't think this is a problem even with a bundle of wire, but for the cautious among you: I would instead worry about the 2x144W of heat coming from the power resistors.

A power supply might have thick wires to minimize voltage drop and maximize efficiency, but this is of no concern for our use case.

I use 24AWG solid wire in my build. I used a tiny bit of 16AWG for the 12v input, total overkill, really should've used something else for that part.





I also did some basis power tests with my box (pics coming soon). With a random stimfile at max volume and a dummy load, one channel, I saw a power usage of around 6W at input. I think it will hurt when stimming at even half this power. I tried a random music file, one channel +36db gain and got 12W. The power resistor got quite warm at 60 degrees celsius, that might be concerning because I have a printed case. Will need to monitor the temperatures during actual use.

snip

I have a basic question on this. Does it matter whether the cap goes on the negative line before the R22, or after?

I don't think so. I actually made a mistake soldering my box and the cap is between R3.9 and R22, seems to work fine.

[bobhill]

About wire gauge, the only thing that makes thin wires dangerous is that melt faster. Thinner wires have more resistance, which equals more heat.

snip

I have a basic question on this. Does it matter whether the cap goes on the negative line before the R22, or after?

I don't think so. I actually made a mistake soldering my box and the cap is between R3.9 and R22, seems to work fine.

Thank you for the info on the wire, and for the answer to my question!

[diglet]

Here is my build, game case for scale. Final dimensions (mm, including connectors) 98 * 63 * 170


Full album here: https://imgur.com/a/eyqi4Jq

The green button is for triphase mode (connects the two black posts). The pots are for master volume, left, right.

The box needs some finishing touches. The components are a tight fit, the amplifier barely fits upside down on the lid. There may or may not be room for a fan...

I did not use "log" resistors on the pots. After testing I found that, with a master volume pot, the sensitivity is satisfactory.

[bobhill]

Full album here: https://imgur.com/a/eyqi4Jq

Wow - that is very well done. Mine looks like a box of spaghetti! Do you have any additional photos of the circuit board that you built? Bottom photos and component parts (including the basic connectors) would be very helpful! Thanks! BH

[diglet]

Full album here: https://imgur.com/a/eyqi4Jq

Wow - that is very well done. Mine looks like a box of spaghetti! Do you have any additional photos of the circuit board that you built? Bottom photos and component parts (including the basic connectors) would be very helpful! Thanks! BH

I had to open the box anyway to crimp all remaining solder connections and replace an over-torqued post, so here are some additional pictures:







The bottom right side of the board is just a mirror image of the bottom left side. You might notice some parts are wired in a different order than on the schematic on previous page, that's a soldering mistake, but it doesn't matter.

The potmeters are wired approximately as in this schematic: https://mega.nz/folder/wBsFVKaK#HQqojgl6Fps0QMBeVfg4Vg (my stimbox schematic 1a.pdf), I didn't add the additional resistor and capacitor shown in the schematic.


The white connectors are JST XH connectors. Most parts were sourced from aliexpress. binding post, push button, switch. I like these rocker style switches better than the antique toggle switch, but you need a square hole to mount them... I think they also make them round, with LED's builtin.

The electrical components are as described in my first post: viewtopic.php?p=339064#p339064

[bobhill]

I had to open the box anyway to crimp all remaining solder connections and replace an over-torqued post, so here are some additional pictures:

Thank you - this is very clearly depicted and displayed in the photos!! I appreciate this additional information! BH

[JakofClubs]

I had to open the box anyway to crimp all remaining solder connections and replace an over-torqued post, so here are some additional pictures:

Nice build and write-up!