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

[tudeloo]

statements like cheap caps go boom is somewhat misleading because a popped capacitor can happen in any device with capacitors and the result is they basically stop performing their function, one down isn't going to be a major concern apart from the noise made when it happens.

This is just false. If a component fails you dont know if you get a "just not working" component (open circ), a short or due to some unlucky incident more damage to other parts of the circuit creating more shorts.

Regarding fuses a carefully chosen double insulated power supply that isn't overpowered for the rest of the design is the safety factor.

It is ONE safety factor. That alone wont get you a med cert. But I wont go into small currents and problems with them: there is no such thing as perfect isolation. Manufacturers suggest using fuses with transformers, because they can - and will - fail due to many reasons.

At this point, the way you are trying to come in and say a bunch of safety issues suggesting to buy an expensive device with a med cert without knowing what was behind this type of design with a track record of over a decade of people building this type of device successfully while people who use estim also find numerous undesirable qualities of many estim devices on the market as well makes me think you are affiliated with an estim manufacturer and working to defend them.

For what it is worth: i am not. However, since safety is a real issue, I will make suggestions that are appropriate for people who did not study computer engineering.

For all the excited amateurs out there, here is my sole reason for caution:
if the design is not properly isolated - like this one here is to some degree, but it is not medically safe (wouldnt be allowed to be used on humans by european or US standards in medical facilities) - you can by just touching a wrong part with your left hand provoke current to flow over your hand, arm, chest to your privates. If that current just comes close to something of 40-50mA (your typical USB port uses about 1000mA) your heart has a real risk of stopping or working incorrectly (pumping irregularly).
Why is it an issue here? Because you reduced your bodies impedance greatly: lupe, maybe even inserted something in your urethra/anally. Another problem is component and device failure without failsafes in place. Those might not pose the risk of death, but electrical burns can also be very very bad and destroy tissue. Just know, there is a real risk if you dont know what you are doing.

Stay safe!

[lolol2]

if the design is not properly isolated - like this one here is to some degree, but it is not medically safe (wouldnt be allowed to be used on humans by european or US standards in medical facilities) - you can by just touching a wrong part with your left hand provoke current to flow over your hand, arm, chest to your privates. If that current just comes close to something of 40-50mA (your typical USB port uses about 1000mA) your heart has a real risk of stopping or working incorrectly (pumping irregularly).

Thanks for making this clear, now I'm understanding about what scenario you are talking.
I have just added a basic health warning at the top of my first post.
Noticed that I kind of forgot something like that, when you post about estim over years you start to forget to inform about warnings more and more.

Not sure if there is any estim audio device which is based on an amp and has any medical certification?
I guess all the commercial estim devices are based on some TENS base?

[mantrid]

As I wrote earlier, protection against dangerous potentials is ensured by the transformer. There can't be any current from amplifier through body to Earth (potential of PC chassis, heater, ...).

Dangerous potentials can only occur in case of a malfunction (otherwise touching a connector and touching Earth at the same time would be dangerous too). But malfunctions can occur. And it's not just the amplifier, It's also the PC which is connected to the amplifier. I would consider everything before amplifier output as unsafe.

That's why safety has to be ensured by the output circuit.

[tudeloo]

As I wrote earlier, protection against dangerous potentials is ensured by the transformer.

Consider electrode placement, tho. What about nipple clamps and chest pads? You still see them in every darn shop. Those will be output circuit protected against faulty currents regarding earth. But we both know current will flow. Will it reach lower tissue? Probably not in most cases. But what if it does? What if by some chance the path over the heart (maybe because the potential shift in your heart muscle was JUST RIGHT at that moment) will lead to that deeper current flow ...

Just be safe, keep it below the waist and isolated

Also to say it clearly: I think you all are doing a good thing trying to bring open source hardware into this field and also considering isolation etc. Better than just hooking up to an audio amp. So, dont get me wrong, keep up the good work! We can always improve upon good things :)

[JakofClubs]

Tudeloo,

I'm using a medical grade isolation transformer for my stimming laptop and 12v power supply, that I got off EBay for $70 shipped. Like this one linked below. I realise that mains power isn't the only safety concern, but it's a big step in the right direction. I didn't get this just for stimming, but I had it for my electronics hobby, so why not use it?

https://www.ebay.com/itm/Toroid-Medical ... 3843870273

[Caius1]

I'm looking into building my own box so I've been reading stuff on this forum.

So the current consensus is that a fuse is not a necessary safety feature but I also take it that a fuse wouldn't have any negative effects either. Negative as in having to rethink the wiring or specs too much.
I know a little about electronics and have interest in them so at least from a theoretical view: Where should you put the fuse if you wanted to add one to the build? Would it be correct to put it on the black (-) wire between the 12V DC power supply and the rest of the circuit? See the black S-shape in the picture below, it's the symbol for fuses, right?

Fuse placement in circuit?

fuse.png (45.13 KiB) Viewed 3997 times

Another thing about the fuse, how "big" should it be, I mean how many Amps (A)?
With all the parts in your shopping cart you can just add up their individual A requirements and get a fuse that's rated a little over the total?
If we go with the amplifier lolol2 originally listed being the only thing using power, you be good with as little as 0,25A fuse when the amplifier requires 0,2A? Something as little as this for example.

And couldn't you just use a circuit breaker in place of the switch to work as a fuse and power switch simultaneously?

EDIT
I also started to think more about the high pass filters.

So my recommendation:
Low cut-off frequency option: 100µF + 20 Ohm or 220µF + 10 Ohm
High cut-off frequency option: 100µF + 10 Ohm
In both cases, highest winding ratio that deliver sufficient power should be used.

I have 0 experience with the estim files/teases (only xp with basic Mystim device) so I don't really know if I should build a higher or lower cut-off. So I thought, why not go crazy and build them both? Usage would be like when there's a stim file with higher frequencies you connect the trodes to the high cut-off filter and vice versa and maybe flip a switch to change where the amp box feeds the output. Through which filter, I mean.
That would just mean more connector holes and somewhat increased cost but then you'd have the right cut-off filter for every situation. I think.

Another edit
I'm trying to work out a shopping list now, if I look at mantrid's list in the spoiler below, where's the 5,1 Ohm resistors supposed to go? I can't see it in the high pass filter diagram and it's only supposed to have 2 resistors, 10 Ohm for each channel in the filters.

Spoiler: show

I already posted Digikey part numbers for the output circuit in the past:

• Transformer: 237-1146-ND
• Capacitor: 493-17272-ND
• TVS-Diode: 1.5KE15CALFCT-ND (plenty alternatives, search for 1.5KE15CA)
• Resistor 10Ohm/2W: A138253CT-ND (plenty alternatives)
• Resistor 5.1Ohm/2W: A138346CT-ND (plenty alternatives)
  ...

Also this list would be super convenient for me because there's a Digikey webstore in my own country.

[TheHenchmen]

Great Thread, I essentially joined because of this.

I build my Estim as per the "seraah mk4b" setup from seraah dot net. It´s fundamentally similar, but has some design differences:

- It utilizes a 18W KEMO amplifier module for each channel, so 36W theoretical power
- the resistor is 5k Ohms at 10Watts ceramic resistor, not 1k with cooling. The resistor is placed at the output end of the transformers.

It uses the same transformers in the same configuration.

The following lessons have been learned thus far:
- KEMO Amp modules are quite bulky and take a lot of space due their fixed cable attachments
- The power requirement is a bit high, utilizing battery power in the first try killed the output in a short notice

The most frustrating part:
- The system doesn´t work properly with high frequency files (like tek files) or high-frequency sections in webteases (like tower). The tease says "now feel THAT!", my LEDs blink happily.... and I feel nothing.

[Electro]

Great Thread, I essentially joined because of this.

I build my Estim as per the "seraah mk4b" setup from seraah dot net. It´s fundamentally similar, but has some design differences:

- It utilizes a 18W KEMO amplifier module for each channel, so 36W theoretical power
- the resistor is 5k Ohms at 10Watts ceramic resistor, not 1k with cooling. The resistor is placed at the output end of the transformers.

It uses the same transformers in the same configuration.

The following lessons have been learned thus far:
- KEMO Amp modules are quite bulky and take a lot of space due their fixed cable attachments
- The power requirement is a bit high, utilizing battery power in the first try killed the output in a short notice

The most frustrating part:
- The system doesn´t work properly with high frequency files (like tek files) or high-frequency sections in webteases (like tower). The tease says "now feel THAT!", my LEDs blink happily.... and I feel nothing.

You should be able to feel it, I do with my StereoStim setup. I didn't see anything over 1000hz in Estim Tower.

[Caius1]

What kind of amperage is going through the system in these builds? More precisely I'm thinking about the required A rating for the triphase switch on the secondary/output side of the transformers.

Still following mantrid's guidelines, if you get for example the MA-180 amplifier that has input power 12VDC 5A, Digikey 237-1146-ND transformer, 10Ohm 2W resistor and 100µF capacitor, then is the current on both sides of the transformer 0,25A?
This value I got from mantrid's data sheet, which only has current on primary side, row 12. I'm also assuming that the primary side means the input side of transformer?

[Electro]

What kind of amperage is going through the system in these builds? More precisely I'm thinking about the required A rating for the triphase switch on the secondary/output side of the transformers.

Still following mantrid's guidelines, if you get for example the MA-180 amplifier that has input power 12VDC 5A, Digikey 237-1146-ND transformer, 10Ohm 2W resistor and 100µF capacitor, then is the current on both sides of the transformer 0,25A?
This value I got from mantrid's data sheet, which only has current on primary side, row 12. I'm also assuming that the primary side means the input side of transformer?

For the price of that Digikey transformer, you could get a better transformer that has a higher frequency range and more taps to adjust turns ratio if you want, the Speco T7010 is $15 on Amazon. ..but if you are going to be building his build, I wouldn't interchange parts, go all out with his if you are going that route.

For estim purposes, we are using these transformers backwards. The audio line transformers we use are normally used as step-down transformers where the power goes into the primary winding where there are more turns around the iron core(ohm side) and out the secondary winding where there are less turns. For estim we are putting power into the secondary winding and wiring electrodes to the primary side with more turns.

A tri-phase switch goes on the electrode side. Amperage is normally around 50mA to the electrodes, spikes probably around 100mA would be too much for a person to handle (I think). Normally this is a very small amount of current for a switch. There is going to be current on both sides of the transformer. 100ohms is a different value than most StereoStim builds, Mantrid's build doesn't match most StereoStim designs. Not to say it doesn't work because obviously Mantrid is satisfied with his setup, but it's different because most people also aren't using capacitors and HV blockers in their circuits which changes the values required for the other components.

[lolol2]

I build my Estim as per the "seraah mk4b" setup from seraah dot net. It´s fundamentally similar, but has some design differences:

- It utilizes a 18W KEMO amplifier module for each channel, so 36W theoretical power

My design is inspired or nearly 99% taken from the first version of the seraah estim box.
I also tried the one with the KEMO single channel amp blocks but had no luck with a good output.
It felt very spiky and unpleasant, even after I tripple checked everything, not sure if maybe one of the AMPs had a problem.

At the end after a few hours of try and error I switched back to the first design and still very happy with it.

[Caius1]

For estim purposes, we are using these transformers backwards. The audio line transformers we use are normally used as step-down transformers where the power goes into the primary winding where there are more turns around the iron core(ohm side) and out the secondary winding where there are less turns. For estim we are putting power into the secondary winding and wiring electrodes to the primary side with more turns.

Oooh! The transformer's used backwards! Now that's a thing I missed completely
And now some things make more sense.

For the price of that Digikey transformer, you could get a better transformer that has a higher frequency range and more taps to adjust turns ratio if you want, the Speco T7010 is $15 on Amazon. ..but if you are going to be building his build, I wouldn't interchange parts, go all out with his if you are going that route.

Yeah, the Speco type seems quite popular, and it's way cheaper, and adjustable. Would it be possible to combine these, the high pass safety features mantrid's proposing and the adjustability of the Speco transformer? I'm guessing that it wouldn't be very feasible or worth the effort, but I like safety features, but I also like not using a lot of money :DD
Obviously people haven't had many problems without the filters but why not go safe if you can?

[mantrid]

So the current consensus is that a fuse is not a necessary safety feature but I also take it that a fuse wouldn't have any negative effects either.

A fuse indeed isn't a bad idea, because it protects against malfunction of the transformer. Especially shortcuts in the primary coil can cause current increase.

The fuse must be on the primary side, i.e. between transformer and amplifier. The fuse current can be calculates with the spreadsheet you already found. It's the I_P value, i.e. about 1 A.

The TVS diode at the output of the amplifier is a better protection against malfunction of the amplifier or power supply because it reacts faster. But it does not protect against transformer failure.

The only problem of the fuse is that it reacts so slow. Unless you play with selfbondage you will be faster than the fuse.

An even better protection is a TVS diode at the transformer output, i.e. parallel to the electrodes. But value depends on electrodes. You have to measure the voltage between electrodes using a sinusoidal signal calibrated to a comfortable level and then choose a bidirectional TVS diode (the ones ending wit "CA") with a breakdown voltage that is at twice as large.

Such a diode also protects against hot spots which occur if the conductivity becomes to bad. (Output is current controlled. If the contact surface becomes smaller current density and voltage increases.)

I
EDIT
I also started to think more about the high pass filters.

So my recommendation:
Low cut-off frequency option: 100µF + 20 Ohm or 220µF + 10 Ohm
High cut-off frequency option: 100µF + 10 Ohm
In both cases, highest winding ratio that deliver sufficient power should be used.

I have 0 experience with the estim files/teases (only xp with basic Mystim device) so I don't really know if I should build a higher or lower cut-off. So I thought, why not go crazy and build them both?

You will only feel a difference with files that play with different frequencies. Then the low cut-off option is the better choice.

The problem is that many estim creators use low frequencies signals for pain. And that's IMHO a bad idea.

I'm trying to work out a shopping list now, if I look at mantrid's list in the spoiler below, where's the 5,1 Ohm resistors supposed to go?

It is intended as an alternative for the 10 Ohm resistor. You only need one resistor per channel. In my setup I have one channel with a lower series resistor.

But see below.

What kind of amperage is going through the system in these builds? More precisely I'm thinking about the required A rating for the triphase switch on the secondary/output side of the transformers.

Still following mantrid's guidelines, if you get for example the MA-180 amplifier that has input power 12VDC 5A, Digikey 237-1146-ND transformer, 10Ohm 2W resistor and 100µF capacitor, then is the current on both sides of the transformer 0,25A?
This value I got from mantrid's data sheet, which only has current on primary side, row 12. I'm also assuming that the primary side means the input side of transformer?

I do not recommend the red transformer anymore because I noticed clipping. I described that in the post with the spreadsheet you already found. The clipping is also the reason why I was less sensitive to certain volume effects others considered as harsh.

Use the black 1:22.4 transformer instead. On the end of the post you find a new shopping list with components for 4 channels. Only issue is that the power rating of the resistors could be larger. With the dummy load they became quite hot, but not too hot because max. operational temperature is 175°C or so.

Power and current calculation are in the spread sheet. With 1A per channel for power supply you are on the save side. The current at the electrodes is just a few mA. Almost all power is transformed into heat in order to make the signal current controlled.

In our case primary side is the transformer side with the low turn number.

For the price of that Digikey transformer, you could get a better transformer that has a higher frequency range and more taps to adjust turns ratio if you want, the Speco T7010 is $15 on Amazon.

I cannot find a datasheet for it. But with a proper datasheet and the spreadsheet (there is a manual for it) you can easily taylor values of all components.

I just prefer the smaller transformers from digikey because I can easily make modules from it and isolate them with shrink tubings. Together with boxed amplifiers this avoids complicated housings.

[hosenguy]

My main stim box is built with 18 watt Kemo amps. I built it a bunch of years ago, don't remember how many. It has served me very well. It is from a design taken from the SmartStim site.

I have built several other designs and tested all of them and compared them.

The build with the Kemo amps was plagued with problems when first completed as it wanted to provide an unwanted high frequency ringing after any signal peak. That made the signal seem muted and covered much detail of the signal and drained the battery quickly. I tracked the problem with an oscilloscope and ended up fixing the trouble by adding proper signal separation utilizing correct wire routing along with parts placement, adding filters to limit the input signal frequency at the input to each amp, and adding bypass caps on the power immediately next to the modules.
The Kemos are very nice package amplifiers and have a very wide frequency response.

I have not had this issue with any other box I have build with any other amp module. Of course I learned to be serious about cleanliness with the build layout and wire routing since that first box!

[TheHenchmen]

The build with the Kemo amps was plagued with problems when first completed as it wanted to provide an unwanted high frequency ringing after any signal peak. That made the signal seem muted and covered much detail of the signal and drained the battery quickly. I tracked the problem with an oscilloscope and ended up fixing the trouble by adding proper signal separation utilizing correct wire routing along with parts placement, adding filters to limit the input signal frequency at the input to each amp, and adding bypass caps on the power immediately next to the modules.

Interesting.
Please provide a sketch of these adaptions.

As you build with kemo amps, I need to ask again:
Is the resistor type I´m using the right one? I´m using a 1kOhm 5W ceramic resistor, other builds use a resistor with a metal heat sink.