Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

[hosenguy]

Actually the issue is matching impedances. The 8 ohm output is slightly safer for the amplifier output so it does not get overloaded. But I do not know of any reason you should not match the transformer impedance to the amplifier. If you have a 4 ohm output then it can certainly be used to hook to the same 4 ohm value on the transformer. I would not expect any change in the sensation either way.

The output of the transformer is usually .625 because that impedance transfers the signal to the human the best in most but this is a personal choice and the 1.25 watt is also useful and often used. The sensation is usually more powerful on the .625 watt tap but some transformers and some humans have different impedance so you should try various taps to see what you prefer.

A bigger issue that affects the sensation is the value of the series resister in the output circuit. The smaller the value the sharper the sensation - sorta like a stinging feeling. The larger the value then the smoother the feeling.
The reason for this is that the signal is mostly a voltage with a small resister while it becomes more current based with the larger resister value.

The best thing about building your own stim device is that you can tune it as you go until it is the best for you!

[JBK]

Thank you, this is the info I was looking for :) I have been wondering whether fine-tuning the series-resistor was a thing. Apparantly it is! Hopefully I can pick up some other resistors and a rotary switch to change between them. Same thing for the transformer outputs (0.625W - 1.25W). That would make for a very versatile box :)

When you say that a higher series-resistance makes for more current-based play, do you mean that the voltage drop over the resistor becomes bigger while the current stays pretty much the same (as the 1-2 Ohm difference in resistor is meaningless compared to body-resistance)?

[hosenguy]

The technical definitions are really meaningless to the end result.
However a voltage source holds the voltage constant and the current goes up and down as the load changes.
A current source has a steady current and raises and lowers the voltage as the load changes.
These are general definitions of pure resistive circuits. The body adds a really complicated combination of capacity and changing impedances due to your tissue conditions, trode connectivity, instantaneous signal level, and more. Note that impedance and resistance are not the same. Additionally these definitions don't really address the intended signal changes from the amplifier input signal, they assume the amp output is constant for a changing load. Stimming provides both a changing output form the source and a changing load in the human!

I tried to find a dissertation about this related to medical devices as that is the research that exists, but could only find this and it is not in depth enough for conversion to stim theory, but if you read this you might learn that understanding the science is not at all as fun as stimming via experimentation.

https://media.lanecc.edu/users/thorpeb/ ... print.html

This is information I have available for review.
https://mega.nz/folder/wBsFVKaK#HQqojgl6Fps0QMBeVfg4Vg
Look at the drawing called "my stimbox schematic 1b.pdf"

Here you see R 1 which is the series resister we are discussing.
You also see an R 2 resister not included in this build. This is not often included in cheaper designs but contributes a lot to the creation of a current vs. voltage source and I recommend a 10 TO 15 ohm at the same wattage as R 2.
With this arrangement you will not need to change the transformer taps after you find the most powerful one which should be the .625. HOWEVER changing the series resister R 1 from around 2 ohms to a max of 6 ohms will make a lot of change! You could even short it out for a real sharp signal - in my experience. If you go higher than 6 ohms for the series resister you will likely have a loss of power.

I hope this provides a little perspective you can use and not just frustration that the science is not a fixed thing!

[maps524]

If you want to plug a TENS cable you have into this stim amplifier you should buy a connector to match the cable and modify the BOM to the different receptacles. The TENS usually have a coaxial connector and I would not try to find or install those. It would be much cheaper to buy a new set of leads I would guess. I often buy the recommended connector in a project to have it to look at to see what I can use with it. In this case the picture should be enough to clarify this.

That makes sense. I'm off to buy some new leads. Thanks for the reply

[JBK]

This is information I have available for review.
https://mega.nz/folder/wBsFVKaK#HQqojgl6Fps0QMBeVfg4Vg
Look at the drawing called "my stimbox schematic 1b.pdf"

Here you see R 1 which is the series resister we are discussing.
You also see an R 2 resister not included in this build. This is not often included in cheaper designs but contributes a lot to the creation of a current vs. voltage source and I recommend a 10 TO 15 ohm at the same wattage as R 2.
With this arrangement you will not need to change the transformer taps after you find the most powerful one which should be the .625. HOWEVER changing the series resister R 1 from around 2 ohms to a max of 6 ohms will make a lot of change! You could even short it out for a real sharp signal - in my experience. If you go higher than 6 ohms for the series resister you will likely have a loss of power.

I hope this provides a little perspective you can use and not just frustration that the science is not a fixed thing!

My R1 is 4,7 Ohms and R2 is 15 Ohms. 4,7 already seems pretty high if the range is around 0-6 Ohms.
It is indeed complicated material. I'll stick to the experimentation

I also need to experiment further with trode positioning. I just can't seem to get it right.

[chromesoldier]

FYI, I built my own stim device about 10 years ago.
My background is in electrical engineering and it includes designing and maintaining numerous commercial audio systems.

This is really good news for lowering the cost of stimming!

If you don't mind I have some questions about the Parts Express version. The only experience I have with something similar was soldering a few things in shop class, so these may be some very basic questions.

I have never used an estim before and want to try and make the Parts Express version with the Tri-phase on/off switch that shorts the common outputs that was mentioned in this topic.

1) Most of the connections seem straight forward with the screw terminals. However, for both sides of the 4Ω resistor do you just solder them?

2) When adding the Tri-phase switch like in

Spoiler: show

to short the common outputs. How do you connect the wires that goes in between the common outs? Do you just use wire nuts? Also which common out becomes the negative electrode when using Tri-phase?

3) How do you add the electrodes, some of the electrodes I seen on amazon are 2mm female is that what the 2mm bullet connectors are for? Would you add a female bullet connector to the end of the transformer wires, then get another cable with two male bullet connectors and then attach the electrode to it for more length?

Also if anyone could upload a video of making one of these from scratch, or maybe just a few pictures of a finished one of these it would probably help me and other beginners that have never done this kind of thing before.

[CaliPhotoDude]

So a few answers based on completing mine (ok completed is a bit of an overstatement, it works fine but it is currently mounted on pieces of scrap wood until I decide what I want to add before figuring out a final box for it.)

1. On the resistors I soldered wires to both ends just to simplify my life. One end is connected to the amplifier output and the other using a wire nut to the transformer. Once I figure out my box I will likely trim the wires down and figure a way to probably mount the resistors to some piece of metal just to spread the heat a bit. They don't really get hot except with pretty long use or certain types of more constant files.

2. On the tri-phase switch. I attached the transformer output, a wire to the switch and a wire to the socket from both left and right channels to each side of a SPST switch using wire nuts so when the switch is open they don't connect but when the switch is closed they connect. At that point it doesn't matter which socket you use since they are both essentially wired exactly the same when the tri-phase is on.

3. For the leads I bought both 2mm and 3mm banana plugs from Amazon. I also bought 3mm banana plug female sockets and some 22 gauge wire and made my own leads. I used the 2mm because they will work with the standard TENS pad connectors.
Wasn't especially hard to solder. The 3mm works better as the box side because the female jacks are cleaner.

The second larger switch on the right is a DPST switch to basically kill the power to the red/primary leads.

Things I am considering doing to finalize is possibly adding a second amplifier so I could have independent control of each channel. Still debating that. Also would likely add one of those cheap MP3/Bluetooth boards because the headphone jack on the amplifier is super annoying because it is too stiff.

Here are a couple pictures of the messy state that mine is currently in. Please forgive the rats nest disaster. It works but it sure ain't pretty right now.

Hopefully this helps a little bit even if things are still not really finalized.

FYI, I built my own stim device about 10 years ago.
My background is in electrical engineering and it includes designing and maintaining numerous commercial audio systems.

This is really good news for lowering the cost of stimming!

If you don't mind I have some questions about the Parts Express version. The only experience I have with something similar was soldering a few things in shop class, so these may be some very basic questions.

I have never used an estim before and want to try and make the Parts Express version with the Tri-phase on/off switch that shorts the common outputs that was mentioned in this topic.

1) Most of the connections seem straight forward with the screw terminals. However, for both sides of the 4Ω resistor do you just solder them?

2) When adding the Tri-phase switch like in

Spoiler: show

to short the common outputs. How do you connect the wires that goes in between the common outs? Do you just use wire nuts? Also which common out becomes the negative electrode when using Tri-phase?

3) How do you add the electrodes, some of the electrodes I seen on amazon are 2mm female is that what the 2mm bullet connectors are for? Would you add a female bullet connector to the end of the transformer wires, then get another cable with two male bullet connectors and then attach the electrode to it for more length?

Also if anyone could upload a video of making one of these from scratch, or maybe just a few pictures of a finished one of these it would probably help me and other beginners that have never done this kind of thing before.

[chromesoldier]

Thank you for the information!

Your pictures are very helpful, now it seems like it is even easier then I thought.

In your top down picture is the part at the bottom mounted in the wood something like this?
https://www.parts-express.com/2.5mm-Met ... k-090-5018

So a few answers based on completing mine (ok completed is a bit of an overstatement, it works fine but it is currently mounted on pieces of scrap wood until I decide what I want to add before figuring out a final box for it.)

1. On the resistors I soldered wires to both ends just to simplify my life. One end is connected to the amplifier output and the other using a wire nut to the transformer. Once I figure out my box I will likely trim the wires down and figure a way to probably mount the resistors to some piece of metal just to spread the heat a bit. They don't really get hot except with pretty long use or certain types of more constant files.

2. On the tri-phase switch. I attached the transformer output, a wire to the switch and a wire to the socket from both left and right channels to each side of a SPST switch using wire nuts so when the switch is open they don't connect but when the switch is closed they connect. At that point it doesn't matter which socket you use since they are both essentially wired exactly the same when the tri-phase is on.

3. For the leads I bought both 2mm and 3mm banana plugs from Amazon. I also bought 3mm banana plug female sockets and some 22 gauge wire and made my own leads. I used the 2mm because they will work with the standard TENS pad connectors.
Wasn't especially hard to solder. The 3mm works better as the box side because the female jacks are cleaner.

The second larger switch on the right is a DPST switch to basically kill the power to the red/primary leads.

Things I am considering doing to finalize is possibly adding a second amplifier so I could have independent control of each channel. Still debating that. Also would likely add one of those cheap MP3/Bluetooth boards because the headphone jack on the amplifier is super annoying because it is too stiff.

Here are a couple pictures of the messy state that mine is currently in. Please forgive the rats nest disaster. It works but it sure ain't pretty right now.

Hopefully this helps a little bit even if things are still not really finalized.

[CaliPhotoDude]

That is the exact part actually.

Thank you for the information!

Your pictures are very helpful, now it seems like it is even easier then I thought.

In your top down picture is the part at the bottom mounted in the wood something like this?
https://www.parts-express.com/2.5mm-Met ... k-090-5018

[Hypno99]

Working on building my own DIY e stim. I have trouble finding a audio transformer who is sold in Germany and has a good quality / is affordable. Anyone has some experience ?

[JakofClubs]

Working on building my own DIY e stim. I have trouble finding a audio transformer who is sold in Germany and has a good quality / is affordable. Anyone has some experience ?

These two are on the old approved transformer list.

https://www.conrad.com/p/elma-tt-iz1892 ... pcs-516104

https://www.conrad.com/p/pa-audio-frequ ... 0-w-335533

[Richi1412]

Hello and good moring all together

Working on building my own DIY e stim. I have trouble finding a audio transformer who is sold in Germany and has a good quality / is affordable. Anyone has some experience ?

this is the one that i used for all my 3 DIY estim units.

https://www.reichelt.de/de/de/-bertrage ... rager&&r=1

[InfamousPlantain]

I liked it so much a did a cleaner, minimal design with the recommended amp from SmartStim.com

Spoiler: show

So, after rereading this and the other thread many times, I finally built the variation @JakofClubs posted above (thanks!) ... almost exactly like it...

Spoiler: show

IMG_0969 (3).jpg (811.96 KiB) Viewed 3281 times

IMG_0970 (3).jpg (563.27 KiB) Viewed 3281 times

As a first time stimmer, geez, this thing was strong! I feel like I couldn't turn the nobsound amp's volume past 20%! Did I wire something off or is that somewhat expected? I mean, the wiring looks so simple in this setup, which was one of the reasons why I gravitated towards it.

On closer inspection, I do realize that I am using the originally recommended 10w resistors from the original build and not the 25w ones used in @JakofClubs' build, but would that cause that?

@lolol2, I did read about you mentioning the difference in volume required for anal trodes vs ones attached outside and I thought I encountered this issue. Made the mistake of calibrating on the anal one and got a pretty literal shocking experience on the glans one Recalibrated for glans, and no longer felt the anal one, unless I somehow got the anal one disconnected. This time around, I used all rubber loops. Would that contribute to the problem? @JakofClubs, do you notice this problem on your build with the nobsound amp?

Other n00b mistakes included not realizing that the drilled project box holes actually were conductive so I had to insulate all my banana plug jacks, realizing that I should probably insulate the banana plugs that attach to the electrodes, making a whole mess between lubes and electrogels, still trying to find that perfect sweet spot. I think I hit it sometimes, but lose it just as easy. That volume control is just too sensitive.

But at the end of everything, I did get a good release -- just not properly through the intention of the tease (@lolol2's legendary estim tower). Well, already planning "fixes" and thanks to @cl13a, @hosenguy, @JakofClubs, and everyone here for their shares!

[Electro]

On closer inspection, I do realize that I am using the originally recommended 10w resistors from the original build and not the 25w ones used in @JakofClubs' build, but would that cause that?

What is the ohm value of the resistor? The wattage value is basically how much energy the resistor can dissipate over a set period of time without overheating. You've got yours mounted to a good chunk of metal and the larger chassis mounted resistors became the 'go to' because they were easier to mount with the large screw holes. If your resistors say 3R9 or 3.9 ohm on them, they are the right value. The other varying factor is the transformer tap you are using. I am using the same configuration as you if your resistor value matches. I usually set my computer volume at "not 100%", often closer to 40% but I noticed that every laptop, phone, and MP3 player of mine has a different volume ramp rate and maximum volume to them. Set your devices volume lower and you'll find the top 3/4 or so movement of the volume knob on the amplifier has more wiggle room than the lower levels.

Hope this clears things up a little.

[InfamousPlantain]

On closer inspection, I do realize that I am using the originally recommended 10w resistors from the original build and not the 25w ones used in @JakofClubs' build, but would that cause that?

What is the ohm value of the resistor? The wattage value is basically how much energy the resistor can dissipate over a set period of time without overheating. You've got yours mounted to a good chunk of metal and the larger chassis mounted resistors became the 'go to' because they were easier to mount with the large screw holes. If your resistors say 3R9 or 3.9 ohm on them, they are the right value. The other varying factor is the transformer tap you are using. I am using the same configuration as you if your resistor value matches. I usually set my computer volume at "not 100%", often closer to 40% but I noticed that every laptop, phone, and MP3 player of mine has a different volume ramp rate and maximum volume to them. Set your devices volume lower and you'll find the top 3/4 or so movement of the volume knob on the amplifier has more wiggle room than the lower levels.

Hope this clears things up a little.

Actually, I ended up using a chassis mount version of the 4ohm 10w based on the partsexpress setup I guess. Setting the computer volume lower is a nice idea. I'll try that. Thanks!

When you say transformer tap, I think you're referring to the power source of the amp? It's a 19V laptop power supply that matches the specs of the one sold with the nobsound amp. I think I've read that lowering this to 12V, and thus limiting the output power of the amp, may help too?