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

[ZeeWW]

I don't think there is much difference. That's why I bought a 3.5mm port. Also it is possible to put both connectors into the housing. So you can still switch between them if wanted.
My orders should arrive on the weekend so I can finally start building it, test it and write an how to build guide.

Any update on this @alexfayer? Thanks

[Dust]

I finally ordered all the parts over the week and wanted to build it all together but there are two parts I am not sure about.
First: How am I supposed to attach the heat sink to the amp? Just put it on the back with the clamp (but that seems to need a lot of force and I am afraid to break something)? Or should I put some thermal paste somewhere?

The second thing is more important I guess. I can't seem to figur out what connector is + and - on the AC port. I tried looking through the documentation of the product but that did not help to much. From the pictures I would guess that the one in the middle is - and the one on the left (with middle upwards facing) is +. Is this correct?

I already drilled all the holes in my case. Only the soldering is left to do :) (and could end in a complete disaster)

Btw is there a recommended test sequence for those DIY builds? I unfortunately don't have a multimeter or something similar but I can imagine that there are safer first things to do than attaching it right away to the genitals.

[lolol2]

1) Yes it's just clamped on the amp part, maybe stretch the clamp a bit, but it need to sit tight on.
I added some thermal paste but I guess this isn't necessary.

2) Please get a multimeter before you start.
Then plug in the power supply and just measure the voltage with the multimeter, you will only have one scenario where it will be +12V, when you swap the connectors you will get -12V. The third connector will not have any voltage as long the power supply is plugged in, this pin is designed when you have a setup with a power supply + an internal battery.

[Dust]

Then I guess it will take a bit more time until I finish the build^^.

[mantrid]

As announced earlier, I performed some measurements for better part dimensioning.

In the standard 3phase setup with 1kHz sinusoidal calibration signal I measured electrode currents of 35mA and 12mA at electrode impedance's of 100 Ohm and 270 Ohm.

I attached a spread sheet (created with gnumeric) which can be used to dimension the parts.

Remarks/usage hints:

• Transformer data (DC resistance of the windings and winding ratio) should be entered in rows 1 to 4
• Rows 5 and 6 depend on electrode setup. Based on my measurements the estim box should be able to drive 50mA @ 500 Ohm (which should contain sufficient margin)
• Rows 7 and 8 contain values of series resistor and capacitor
• Remaining rows are calculated data. Voltages and currents are effective values (0.707 times the peak values). Power values are average values. Calculations are correct if magnetic loss and impedance of the capacitor are neglectable which is true if the frequency is sufficiently above the cutoff limit. I verified the values in column F with an oscilloscope and a dummy load of 200 Ohm using 1kHz sinus test signal. Error is less than 5%.
• Important rows are marked yellow:
  • Row 14 (U_A) is most important. Cheap 12V amplifiers (without charge pump or transformer) can output up to +/-10V peak voltage which corresponds to +/-7V effective voltage. If volume of amplifier is turned up above this limit (depends on the volume range of the sound file) the signal is cropped and becomes almost rectangular at max. volume setting. I noticed that my setup is always in this saturated mode. The main problem is that phase modulation effects does not work properly. So I have to change a few things.
  • Its assumed that an estim box should be current controlled, i.e. independent from the load resistance R_L (row 5) (one can argue whether this is always optimal). The examples contain calculations for R_L=50 Ohm and R_L=500 Ohm @ 50mA. Amplifier voltage U_A should change as less as possible. This is achieved best with high transformation ratios n (row 4).
  • Row 16 is needed for the power rating of the series resistor. In practice estim signals are amplitude modulated, i.e. power rating does not need to be higher.
  • Last row is the cutoff frequency of the high pass filter. At this frequency a signal feels about half as intense as without filter. Recommend limits are 200 to 300 Hz.
• Sum of rows 17 and 18 are the power dissipation of the transformer. For the first transformer it is maybe a little bit to high (@ I_S=50mA). Third transformer (Digikey 237-2018-ND) is a good alternative.
• All Digikey transformers are high frequency transformers which are probably also save without capacitor. These transforms require the high pass filter for protection against overheating at low frequencies (imagine a DC signal ...)

I also attached a screenshot of the shopping card at digikey where I just ordered new parts. I have a 4 channel box but only need one channel with > 25 mA. That's why I choose different resistors and capacitors. The power ratings are higher than necessary because I caught the wrong row (15 instead of 16).

[Dust]

I tried to put everything together this weekend but I was not successful... The soldering just did not want to work. While building my own triphase cable I had no problems, but the cable this time around did not want to cooperate. I could not even properly tin the cable. Maybe I will try again with a thinner cable (the thickness seems to be the problem) or just by using crocodile clamps to connect everything. For now I have unfortunately put this project on ice...

[phoopha]

I tried to put everything together this weekend but I was not successful... The soldering just did not want to work. While building my own triphase cable I had no problems, but the cable this time around did not want to cooperate. I could not even properly tin the cable. Maybe I will try again with a thinner cable (the thickness seems to be the problem) or just by using crocodile clamps to connect everything. For now I have unfortunately put this project on ice...

Shame, I was looking forward to hearing how it went.
I'm also interested in building my own box, but have just got lost in all the details, parts, etc...

[alexfayer]

So finally a small update from me. I discarded the high-pass filter because it did not work and I did not have the motivation to fix it so I created a "classic" unfiltered Estim unit. The picture should describe everything needed.
The parts are already described by lolol2 in the first post. The only different part is the 3.9ohm resistor. Make sure to get a fan if you stim for longer periods.

estim.png (689.51 KiB) Viewed 4967 times

[phoopha]

On the left side of the diagram, am I right in thinking they are individual channel inputs, rather than something like a 3.5mm stereo have? Likewise, on the right side, are they individual outputs? I think that's the bit that confuses me the most.

[Electro]

On the left side of the diagram, am I right in thinking they are individual channel inputs, rather than something like a 3.5mm stereo have? Likewise, on the right side, are they individual outputs? I think that's the bit that confuses me the most.

Yes, they are, but they could easy be replaced with the connectors of your choice. I personally simplified by own design of my most recent build and bought a Nobsound amplifier that uses the TPA3116 amp chip. https://www.amazon.com/Nobsound-Channel ... 00WTOAC1M/
This saved on buying and wiring a few of the extra pieces and I just bought a 3.5mm to RCA cable. The amp is currently $33 and has a 5% "coupon" thing too. Be sure you use a 12 volt *double insulated* power supply (should have a depiction of a square inside a square). At least 3.8 amps should cover it.

[phoopha]

On the left side of the diagram, am I right in thinking they are individual channel inputs, rather than something like a 3.5mm stereo have? Likewise, on the right side, are they individual outputs? I think that's the bit that confuses me the most.

Yes, they are, but they could easy be replaced with the connectors of your choice. I personally simplified by own design of my most recent build and bought a Nobsound amplifier that uses the TPA3116 amp chip. https://www.amazon.com/Nobsound-Channel ... 00WTOAC1M/
This saved on buying and wiring a few of the extra pieces and I just bought a 3.5mm to RCA cable. The amp is currently $33 and has a 5% "coupon" thing too. Be sure you use a 12 volt *double insulated* power supply (should have a depiction of a square inside a square). At least 3.8 amps should cover it.

How would that amp fit in to the wiring diagram in this thread, or does it do away with everything else bar the cables?

[bobhill]

How would that amp fit in to the wiring diagram in this thread, or does it do away with everything else bar the cables?

I was wondering the same thing.

[Electro]

How would that amp fit in to the wiring diagram in this thread, or does it do away with everything else bar the cables?

The amp is essentially everything to the left of the resistors.

So you need a double insulated power supply, 12 volts, 4-5 amps, something like this
https://www.amazon.com/110V-220V-Conver ... B073QTNF9F
Power supply plugged into the amp. You'd then connect your device(laptop/phone/mp3) with a 3.5mm to RCA cable to the amp. The output of the amplifier goes to everything on the right right starting with the resistors.

[Brickx]

Just refound this website and got TeaseAI up and running and i would like to add a E-stim device, because there is so many info on this site i'm not quite sure if i got it right:

I know my way around a soldering iron and i know a little bit about electronics so i think it will be allright, i just want to double check my plans:

Wat i already have is MUSE T-Amp: i believe it's a TA2020 Based 2x 15 watts, there is no balance for the input signal, but is that necessery??

My plan is to build a separate small box with this in it:


i think i would be using:
(i'm getting confused due to different designs)

cables offcourse
banana plugs to interconnect the boxes, (so i can use the standard speaker outputs already on the amp)
2x resistor: https://www.conrad.nl/p/ate-electronics ... uks-421308
3.9 Ohm, 25 watts (is that correct, because i also see a 1Kilo ohm 50 watts resistore being used?)
2x elma TT IZ 1892 Impedantie: 4 - 16 Ω Primaire spanning: 0,625 -1.25 -2,5-5.0-10 V
or should i be using these: https://www.conrad.nl/p/monacor-tr-1756 ... or-1332826 ?
A simple switch for tri-phase setup.

i'm i on the right way and is this complete?

because i read about an highpass filter and a voltage limiter, but that is not in here and it sounds safe to add these to the box

and does anybody know how these very small plugs are named that connect to those rubber electric band thingies

[Electro]

Just refound this website and got TeaseAI up and running and i would like to add a E-stim device, because there is so many info on this site i'm not quite sure if i got it right

TeaseAI has EStim teases? I know Spicy has a E-Stim Systems 2B interface connection, but doesn't have any stim files for audio output. Which TeaseAI teases are you looking to use?

Regarding the 'no balance for the input signal' - I don't think this matters much myself, I've rarely felt the need to adjust it and I only really do if I want to boost volume for a bipolar anal electrode, but even if I don't the feeling is still there. I make the adjustment in software, my operating system's sound settings has a balance function and many audio applications do to.

Regarding the rest of your bill of sale, do you know anyone who has all of that in the exact combination? If not, you could run into problems with matching components. Too weak of an amp and it might fail, too much resistance with a lower powered amp might reduce total output, the wrong turns ratio for the power output and resistance combination might cause an issue with this not feeling like it should. You are talking about adding combinations of additional components that could bleed off power or introduce undesired characteristics to the stim. Looking at two plans for a stim box and picking and choosing one resistor from one, a transformer from another, a random amp, and a few extra random components like a high-pass filter is a great way to end up with an unknowns about what you'll get and if it doesn't all work the way you expect it to, don't expect much support from anyone because nobody has that combination of stuff. It's all a system, change one thing and it can affect the balance of power needs from rest. The solution to when it doesn't work out as expected ends up being to replace those components so they match a good known proven configuration, which means you'll be buying equipment again to get the right combination that should have been bought in the first place. Good luck.