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

[edger477]

With all this said, what is a SAFE maximum voltage for these estim boxes to output. I don't mind if the very very top of the volume knob hurts a tiny bit, but I don't want to use this without knowing what the safe upper limit of voltage is.

When considering safety, the most important safety limit is current. The most widely accepted limit for estim (below the waist) current is 50mA.

Now, the reasons we use transformers are:
1. galvanic insulation (both outputs are not connected to inputs in any way)
2. transforming amp output to reduce current and increase voltage

Our perceived sensations come mostly from voltage, that is why most often we take the lowest power tap on transformer (since it has most voltage and least current). Voltage on transformers without any load is not really meaningful value since 0.25w tap already has 795 Ohms internal resistance, so if you shorted its outputs, max current that it could produce would be determined by its power (0.25w) which means current x voltage = 0.25. So Ohm's law says that U = R x I, and in our case 0.25/I= 795xI which when solved (I = square root of 0.25/795) which is around 17mA. This is maximum current we could expect from lowest tap (it will be much less since body resistance is far far from 0).

To check what current you really have, you would need to connect output to a resistor of 600-1000 Ohms (this is approximation for body resistance) and check voltage (we can calculate current then based on Ohm's law). With load, your 0.25w tap might have lower voltage than the 0.5 since its power is very low, but maximum safe voltage with 1000 Ohm resistor would then be around 50V for 50mA "safe" current (0.05A x 1000 Ohm).

When I tried to submit answer I see that digled already mostly answered, but since I already wrote all this, I will post it too.

[f12345u]

Thank you for the information. Here's my build. It's almost finished, but I'm waiting on some WIMA caps to replace the input coupling capacitors on the amp board with some better ones and some 10uF chokes. The changes I made to the board dropped the gain output of the amp board down to +20db, as well as removing cross talk within the op amp. I also removed and bypassed the shitty onboard pots, which cleaned the sound up from the board a ton.

Before making these changes, my pots would only be at about 1/2 before maxing out the voltage when I played from my laptop at full volume (1vAC across gnd to signal line), and the pots would influence one another. Now I have the full range at max volume :D

This is only the second thing I've built, it's kind of ugly inside but I'm overall happy with it. I'm still a bit scared to use it because of the shock that I got, but I'm hoping it'll make for many fun times :D

[edger477]

Nice when you have knowledge how to turn shitty amp board into a decent one.

[f12345u]

So with the 10W leads, the box feels great, I CANNOT take it up past about half way without it being overwhelming but

With the massive heat sink and fan, stays very cool. I put on a 600hz sound at max volume for an hour and barely any heat was coming out of the vent.

I just need to play with electrode placement and how to estim, first time with it lmao.

[edger477]

have you tried less powerful leads? I use the lowest powers on my box, tried next and did not feel as good.

[f12345u]

yeah lmao, the 0.25w leads shocked the hell out of me. Too much voltage I guess.. It's good like this :D very good.

*Edit* This has been in the back of my head for a bit. I don't rightly understand how I could have gotten such a shock from this. The current would have been less, and I tested the voltage with the 1k ohm resistor and it did massively drop into a "normal" range. It's got me worried about my build's safety. I've used it probably a bit too much since finishing it up , and it WORKS, but I'm starting to think about tearing into it again.

[f12345u]

Figured I'd throw an update in. Using the 0.5 leads again, feels better. Smoother I guess. Just limiting the output with my bluetooth receiver to not get as spicy.

[edger477]

On high volume your transformers might have saturated and instead of proper sound produced just spikes. Always start from lower volume when testing.

[gagaga]

Hi fellow Milovanians, I'm sure glad the website works again!

I built the box outlined by lolol2 on page 12 of this thread. I haven't tested it on myself yet, but found some issues during initial testing:

1. To test the amp and signal lines I hooked up speakers to the amp (instead of the transformers). Through the speakers I hear a high pitched noise/tone. It's the same frequency as the fan, which I connected to the same 12V power supply: When I slow down the fan, the frequency I hear through the speakers also goes down. For now I removed the fan, but is it normal, that the amp picks up so much noise from the power line?
2. Without the fan I still hear a faint white noise fron the speakers, even with the pots turned all the way down. I guess it's because of the cheap amp? I hope it will be below the threshold of what I'm feeling.
3. To test the transformers and resistors, I hooked them up to the amp and removed the speakers. When feeding music to my box I can hear it inside the box. It's bad quality and it's faint, but it's definitely the same music. Does anybody know what element acts as a speaker and if this is something to worry about?

If you built the same or similar box, I'd appreciate your feedback very much!

[edger477]

To test the amp and signal lines I hooked up speakers to the amp (instead of the transformers)

Those are not normal and you don't want stray sounds. Maybe on max volume hearing rather silent noise is normal, but below half volume there should be nothing to hear. It might be that you have bad power supply that does not insulate output from the grid, which might be dangerous for using with estim box.

The music can be heard very silently from some components (chokes, sometimes even transformers) on high volumes. Again, if it can be heard below half volume it indicates either bad quality of components or something wrong in circuit (load too high or shorted output from transformer).

Easiest thing to check is power supply first.

[gagaga]

Those are not normal and you don't want stray sounds. Maybe on max volume hearing rather silent noise is normal, but below half volume there should be nothing to hear. It might be that you have bad power supply that does not insulate output from the grid, which might be dangerous for using with estim box.

The music can be heard very silently from some components (chokes, sometimes even transformers) on high volumes. Again, if it can be heard below half volume it indicates either bad quality of components or something wrong in circuit (load too high or shorted output from transformer).

Easiest thing to check is power supply first.

It's good to know, that this is not normal - thanks for your input, edger477!

The power supply is class 2 and from a reputable brand (as far as I can tell). But I agree, it's the easiest thing to check and also very important for safety. If that doesn't help, I'll probably swap the amp.

[edger477]

The power supply is class 2 and from a reputable brand (as far as I can tell). But I agree, it's the easiest thing to check and also very important for safety. If that doesn't help, I'll probably swap the amp.

Wait, did you refer to fan on the amp, or some fan that is connected to same wall output like power supply?

[gagaga]

Wait, did you refer to fan on the amp, or some fan that is connected to same wall output like power supply?

It's a 12V DC fan for the amp, but separate from the amp. I connected it in parallel to the amp (same power supply).

Since it's on the DC side of the power supply, the noise from the fan does not go through the power supply. Does this point to a bad amp, then?

[edger477]

Since it's on the DC side of the power supply, the noise from the fan does not go through the power supply. Does this point to a bad amp, then?

Not necessarily. The modern amps use a lot of feedback and something like fan on same power supply can interfere alot. I thought noise coming from grid, that is why I suspected PSU, but you have noise source on 12V line, so PSU is mostly irrelevant, as long as it has enough power.

Try adding a capacitor (whatever you have around, bigger is better, as long as it is more volts than 12) to the fan wires to try and flatten that noise. Also if you have some custom 12V plug to supply both fan and amp, make sure that your wires are thick enough (not thinner than those of PSU).

Of course if amp was 10$, there is high chance that it is simply of bad quality. If it works just fine without the fan, try getting one of those DC-DC stabilizers and power fan through that, and if still makes noise, you can reduce voltage on stabilizer to make fan spin slower where it will produce no noise.

[gagaga]

Try adding a capacitor (whatever you have around, bigger is better, as long as it is more volts than 12) to the fan wires to try and flatten that noise. Also if you have some custom 12V plug to supply both fan and amp, make sure that your wires are thick enough (not thinner than those of PSU).

Of course if amp was 10$, there is high chance that it is simply of bad quality. If it works just fine without the fan, try getting one of those DC-DC stabilizers and power fan through that, and if still makes noise, you can reduce voltage on stabilizer to make fan spin slower where it will produce no noise.

Thanks for your advice. Right now I'm focussing on reducing the faint white noise, which is present even without the fan.

It is indeed a 10$ amp. I wonder how I can get a good quality XH-M543. It seems paying more is not a garantee for better quality. Maybe ordering from another supplier and hoping for a different result?