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

[JakofClubs]

Thank you - this was really helpful for me! What is the point in switching the outputs using the 3P3T vs only switching the power with the SPST? It seems to add unnecessary complexity, so there must be some benefit.

If the circuit stored a lot of power, switching off the outputs might be a good idea to immediately cut the output. But the amps commonly used (class D amps) store very little power, so just killing the power cuts output immediately. Also, some amps "pop" a little when you turn them on or off.

[InfamousPlantain]

Hi Everyone!

Has anyone ever integrated @mantrid's high pass filter into the current v2 lolol design?

viewtopic.php?p=288013#p288013

I have some confusion because I don't think mantrid ever mentioned that he has the 4ohm resistor setup in between the amp and transformer like we do. Would it affect anything here?

In addition, do I put this high pass filter before or behind the 22ohm "smoothing" resistor in relation to the amp?
EDIT: Oh wait, he did say in here that it didn't matter: viewtopic.php?p=322776#p322776

My imagining is something like this currently....

thanks!

[JakofClubs]

Here's some pictures from my last build with a simplified schematic. It switches between three different high-pass filters.

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Spoiler: show

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This build feels really good, but I'm not sure if it's the smoothing resistor and high-pass filter (which were good improvements), or that I used a better transformer. Quam TCH-70. It's supposed to be a "high fidelity" part. Not sure if it's that or just a better turn ratio (primary to secondary turn ratio).

It uses an "on-on-on" DPDT switch to switch between three high-pass filter capacitor values. 100up, 220uv and 330uf.
The different capacitor values change the cutoff frequency and feel a bit different. I did this to see what capacitor feels best, but it depends on the track which feel best.

[InfamousPlantain]

Hey, this is great! Thanks so much. It will take me a little to digest this. You seemed to have dropped off the 10ohm resistor part of the high pass filter spec ... unless you're relying on our existing 3.9ohm one to do the job.

Or

I could have grossly misunderstood the purposes of each resistor and that setting it up the way I did would probably end up negating something...

[JakofClubs]

Hey, this is great! Thanks so much. It will take me a little to digest this. You seemed to have dropped off the 10ohm resistor part of the high pass filter spec ... unless you're relying on our existing 3.9ohm one to do the job.

Or

I could have grossly misunderstood the purposes of each resistor and that setting it up the way I did would probably end up negating something...

I'm pretty sure when you add Mantrid's protection circuit, it takes the place of one of the resistors.

They say the best way to get the right answer on the internet is to post the wrong answer, I assume someone will chime in and correct me

[bobhill]

Hello all!

I'm continuing work on assembling my box, using lolo's V2 design. I couldn't get the 100v/10w transformer and got the Parts-Express 70v/10w used on other designs (330-040). I'm wondering about the transformer connections. Some use the 8 ohm and 0.62v leads and others, such as this, use 4 ohms and larger voltage - 10 volts on this one. Those are pretty large disparities, so any advice is appreciated. I've read these threads many times and an answer using technical electrical engineering discussion is beyond my knowledge.

Along those lines, I haven't received the 3.9 ohm resistor yet. Is the unit usable without that until those parts arrive?

Thanks - BH

[JakofClubs]

Hello all!

I'm continuing work on assembling my box, using lolo's V2 design. I couldn't get the 100v/10w transformer and got the Parts-Express 70v/10w used on other designs (330-040). I'm wondering about the transformer connections. Some use the 8 ohm and 0.62v leads and others, such as this, use 4 ohms and larger voltage - 10 volts on this one. Those are pretty large disparities, so any advice is appreciated. I've read these threads many times and an answer using technical electrical engineering discussion is beyond my knowledge.

Along those lines, I haven't received the 3.9 ohm resistor yet. Is the unit usable without that until those parts arrive?

Thanks - BH

On the transformers, it ends up being about the primary to secondary turn ratio, so various combinations could work. I'd recommend sticking to the 8 ohm and 0.62v leads. You want the 3.9 ohm resistor to make sure the amp always sees a minimum of 3.9 ohms. I wouldn't use it with out it.

[bobhill]

Hello all!

I'm continuing work on assembling my box, using lolo's V2 design. I couldn't get the 100v/10w transformer and got the Parts-Express 70v/10w used on other designs (330-040). I'm wondering about the transformer connections. Some use the 8 ohm and 0.62v leads and others, such as this, use 4 ohms and larger voltage - 10 volts on this one. Those are pretty large disparities, so any advice is appreciated. I've read these threads many times and an answer using technical electrical engineering discussion is beyond my knowledge.

Along those lines, I haven't received the 3.9 ohm resistor yet. Is the unit usable without that until those parts arrive?

Thanks - BH

On the transformers, it ends up being about the primary to secondary turn ratio, so various combinations could work. I'd recommend sticking to the 8 ohm and 0.62v leads. You want the 3.9 ohm resistor to make sure the amp always sees a minimum of 3.9 ohms. I wouldn't use it with out it.

I was offline for a while and just saw this - thank you!

[bobhill]

Ok, I was able to get everything together and working. More on that later.

EDIT: I used lolol2's V2 design, but with the 70w/10v transformer used in the other thread.

EDIT 2: It's a Class II AC Power Unit - with the double squares

US Parts list:
Project box: https://www.amazon.com/dp/B06XSMK61Q
AC Power unit: https://www.amazon.com/dp/B073QTNF9F (Mine is marked as Class II - double squares)
Amplifier: https://www.amazon.com/dp/B07TSKNCSV
Parts Express 70w/10v Transformer (x2): https://www.amazon.com/dp/B0002KRA1U
On/Off Switch (3PDT): https://www.amazon.com/dp/B07MTTVH3W
Tri-phase switch: https://www.amazon.com/dp/B07SVWYKG1
10k Pots and volume knobs: https://www.amazon.com/dp/B07DHKBGLG (Found these later and would have purchased them: https://www.amazon.com/dp/B082FCXJZ2)
50w/22 ohm resistor (x2): https://www.amazon.com/dp/B07FDZH85J
50w/3.9 ohm resistor (x2): https://www.amazon.com/dp/B07FF3GYWC (Longer lead time - I also found this on overstock.com available more quickly)
Power in jack: https://www.amazon.com/dp/B08CVF3QXL
Input jacks (RCA): https://www.amazon.com/dp/B08ZLQHGNS
Output jacks (4mm banana): https://www.amazon.com/dp/B091TDC1LM
Output plugs (4mm banana): Bought some like these at Home Depot (https://www.amazon.com/dp/B07RJ3NX5Y )
Lead wires (2mm TENS): https://www.amazon.com/dp/B075MS5L66 (cut off 3.5mm jack and attach banana plugs above. The lead wires are too thin and will come out pretty easy, so you will need to patch to a thicker wire – I plan to do this with some spare 18 AWG lamp power cord wire)
Input (from PC) cable: https://www.amazon.com/dp/B01D5H8KO2

Miscellaneous work stuff:
Wire: https://www.amazon.com/dp/B089D3T1JD (I bought 26 AWG, but would get 24 if I did it again – just a little easier to work with)
Soldering kit: https://www.amazon.com/dp/B07S61WT16 (This one is pretty basic and there are plenty similar ones on Amazon, but it worked fine. I bought flux and rosin core electrical solder at Home Depot.)
Helping hands: https://www.amazon.com/dp/B08DLGTZNZ (DON’T GET THIS ONE – I found the arms difficult to adjust, would get something with “wire” arms)
WAGO solderless connectors: https://www.amazon.com/dp/B07NKSHVF6 (DEFINITELY GET THESE!!!)
Solderless/Heat shrink connectors: https://www.amazon.com/dp/B089D79FQL (I haven’t used, but probably will – these are pretty cool)
Mini Heat Gun: https://www.amazon.com/dp/B07G4VMSHW (Very helpful)
Alligator clips (for testing): https://www.amazon.com/dp/B096S2JXYW (I got these later, should have purchased with other materials)
Multimeter (if you don’t have one, you will need for testing): https://www.amazon.com/dp/B01N9QW620

Notes:
Project box: It’s a tight fit, perhaps someone else will find a better one. Also, this box has a LOT of little pre-set screw posts on the bottom, so you will need some material as a base. I found a thick plastic yard sign at Home Depot that worked well and was thin enough to cut with scissors – barely.
Power in jacks: I used a 2.5mm three pin jack first and could not get power to the board. This 2.1mm two pin jack worked on first try. It’s tight with the power unit at first, but works easily now. (The power unit says either will work.)

[fl0w]

...
Power supply
IT IS VITAL THIS IS CLASS 2
...

For future reference and beginners like me, there seems to exist two standards confusingly named Class 2 and Class II.
I believe, please someone correct me if I'm wrong, that what's vital is that it is Class II, or at least that seems to be what's used by medical equipment anyways. Whether Class 2 is of importance or not I don't know...

https://www.cui.com/blog/class-2-vs-cla ... r-supplies

[harryc]

...
Power supply
IT IS VITAL THIS IS CLASS 2
...

For future reference and beginners like me, there seems to exist two standards confusingly named Class 2 and Class II.
I believe, please someone correct me if I'm wrong, that what's vital is that it is Class II, or at least that seems to be what's used by medical equipment anyways. Whether Class 2 is of importance or not I don't know...

https://www.cui.com/blog/class-2-vs-cla ... r-supplies

Have edited it now, apologies to any confusion it caused
I too was a complete beginner and had no idea there was a difference

[diglet]

I'm intending to build a stim box, but I have questions. After researching I landed on this schematic:



D1: TVS 1.5kE15CA
cap: bipolar 330uf (according to mantrid, this results in a cutoff of around 110 Hz)
Resistors: I think the worst-case power on R22 is 4.5W (very unrealistic, assuming 12V RMS with 12V PSU), so I choose a 5W resistor to save space. R3.9 is 50W
Conrad 100V transformer elma TT IZ1892 as recommended
amp: TPA3116D2 XH-M543 as recommended.
plan is to use separate switches for power/A/B and 3 pots (master, A, B). 3.5mm jack input. Maybe upgrade to an amp with Bluetooth later.


Questions:

• I'm surprised we need a transformer with this much iron. Is saturation a concern with smaller transformers?
• Some boxes have the 3-phase switch before the transformers, or the TVS diode and power switch after the transformers, what are the advantages/disadvantages of each?
• Some users have capacitors and resistors near the volume pots example here, iirc these turn the pot into log or reverse-log pots. Is this recommended? Is the volume range/sensitivity on the default build satisfactory? Do people use the pots on the stim box at all, or just volume control on the computer/xtoys?

[fl0w]

Some users have capacitors and resistors near the volume pots example here, iirc these turn the pot into log or reverse-log pots. Is this recommended? Is the volume range/sensitivity on the default build satisfactory? Do people use the pots on the stim box at all, or just volume control on the computer/xtoys?

I was wondering the same thing and found this on /r/estim wiki

Potentiometer mod: this mod adds a 10K ohm fixed resistor between the hot terminal and wiper of a 10K ohm linear-taper potentiometer to make adjustments less-sensitive to small knob rotation. To eliminate any interference that can be picked up by the audio-input cable, a 470 pF capacitor is added between wiper and amplifier's audio-input ground. For longer life, choose potentiometers with plastic or CERMET resistance elements.

[diglet]

I performed some calculations, assuming 40w max output power.


linear: normal 10k pot.
antilog: 10k pot + 10k loading resistor between + and wiper, as in MEGA schematic.
log: 10k pot + 1k loading resistor between - and wiper, as recommended for audio applications to approximate a log pot.

My guess is that if you stim mostly at low power, antilog is better as it gives more sensitivity in the lower range. If you stim mostly at high power, log is better as it gives more sensitivity in the higher range. This amp seems very powerful, which seems to favor the antilog setup. Will have to perform some "experiments" before making final decision...

[JakofClubs]

[*]I'm surprised we need a transformer with this much iron. Is saturation a concern with smaller transformers?

I believe the transformers were selected for their turn ratio and trial and error.