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

[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?

[edger477]

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

How loud is it? If you don't start to hear it until like half of volume (does amp have pot?) then is fine as the signal to noise ratio will be such that this noise will never be noticeable.

You want to measure max input you can have from your sound card without distortion (if it is ok sound card that does impendance matching for headphones or you use line out, it will probably be 100%), check that with speakers, as you won't be able to know if input is too high and distorted once you connect transformers.

If you can play sounds fine and without discernible distortion you can move on with building box.

[gagaga]

If you can play sounds fine and without discernible distortion you can move on with building box.

I finished building the box and tested it... WOW, it feels great!

There is one negative point: It's almost too strong for me! I reach my limit with the sound card at 20% and the pots around 10%.
For safety, SNR and usability I'd like to operate the sound card and the pots at higher values. E.g. for the unlikely case when my laptop "decides" to play a system sound at 100%. Is there an easy way to reduce the amplification power of the box? E.g. by using different transformer ratio than the one shown here?

I guess I could also turn down the pots on the amp (next to the signal inputs) - but they are very cheap and don't produce stable results, so I'm not sure touching them is a good idea.

[edger477]

For safety, SNR and usability I'd like to operate the sound card and the pots at higher values. E.g. for the unlikely case when my laptop "decides" to play a system sound at 100%. Is there an easy way to reduce the amplification power of the box? E.g. by using different transformer ratio than the one shown here?

You should be using the lowest power output on transformer (I see you use 10W, I am using 1.25 or 1.75)
Then test again.
You should be using 12V power supply, not 24 (as with 24 amp works at full power).
If still too strong, you can try using 8 Ohms as input on transformer. Also, parallel resistor should be not needed for this amp and removing it should result in no difference in preceived sensations.

If still too strong, set pots on amp to about what is max you want to have outputed ever, then measure the resistance and find similar resistor to solder in place instead of them.

[gagaga]

You should be using the lowest power output on transformer (I see you use 10W, I am using 1.25 or 1.75)
Then test again.
You should be using 12V power supply, not 24 (as with 24 amp works at full power).
If still too strong, you can try using 8 Ohms as input on transformer. Also, parallel resistor should be not needed for this amp and removing it should result in no difference in preceived sensations.

If still too strong, set pots on amp to about what is max you want to have outputed ever, then measure the resistance and find similar resistor to solder in place instead of them.

Very clear instructions and hints,

[gagaga]

I have a question about the transformer (sorry if this has been asked already):
Is there a difference between using the 10W+4Ohm, 5W+8Ohm or 2.5W+16Ohm connections?
All three combinations have a winding ratio of ~15:1, so is the transformed voltage and current very similar in all three cases?

[edger477]

I have a question about the transformer (sorry if this has been asked already):
Is there a difference between using the 10W+4Ohm, 5W+8Ohm or 2.5W+16Ohm connections?
All three combinations have a winding ratio of ~15:1, so is the transformed voltage and current very similar in all three cases?

Hi, assumption of current and voltage being transformed similarly is correct, but does not mean the output is same since the input might be different.
The main difference will be in the impendance that amp sees, and therefore in the transformer input current. Normally the amount of power the amps produce is inversely proportionate to the load connected, so doubling the resistance means halving the power. It is good for making more use of volume pots if your signal becomes too strong early (on low volume).

Also, if you have serial resistor, and then use 8 Ohms or more resistance, check if total resistance is within amp specs, many say that load is 4-8 or 4-16Ohms, so you'd have to remove serial resistor to use those.

The secondary difference might or might not be different internal resistance of the output windings. I know that each of output taps on my transformer has different static resistance and I use the lowest power / highest resistance one (1.25w or whatever is lowest) since there is several hundred Ohms of internal resistance there that is helpful as buffer when surface area changes, you accidentally short the electrodes etc, it is basically good match for the load of human body that is connected.