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

[Electro]

You'll want it to be a 2 prong(no ground) double insulated(square within a square symbol) and agency listed(UL for example in the US, or similar depending on the country) for safety.

12v 4 amps is ideal
...but your 3 amp power supply would be fine if it reliably stays at 12 volts under load

[edger477]

The one you posted has the symbol... if it is real :)



So you can use that one.

[Corndogville]

You'll want it to be a 2 prong(no ground) double insulated(square within a square symbol) and agency listed(UL for example in the US, or similar depending on the country) for safety.

12v 4 amps is ideal
...but your 3 amp power supply would be fine if it reliably stays at 12 volts under load

Thanks guys! I just ordered this 12v 4a one, as it was listed as "Amazon's Choice", let's hope it's good, and safe!

https://www.amazon.com/COOLM-100-240V-A ... r=1-4&th=1

Man these transformers are HUGE!!! It's a bit scary. The ones in my Davey box were the size of my fingertip.

This is the right thing, right?

https://www.parts-express.com/70V-10W-L ... quantity=1

I have a feeling this is going to be unlike anything I've experienced before, and I wouldn't probably know the difference even with the parallel resistors (though I will leave them out as you wise folks recommended).

I'm using the outside wires on both sides of the transformer, right? (0.5 on the trode side and ??? on the amp side?)

I have an old Radio Shack project box that I will probably mount the stuff to. It has a choice of 2 lids, aluminum and plastic. I'm guessing I should try and mount everything to the aluminum lid? So it can act as a big heat sink? Anything I need to worry about in terms of isolation? I was considering heat shrink tubing the resistors over completely, so they couldn't touch the alum plate, but if that's overkill or a dumb idea, let me know. I'll be trying to wire it all up in a few hours, got company coming over, lol.

At least I can take it for a test run with the adapter I have on hand.

My plan is to use 2 mono jacks, so I can use the old 2B cables. If I want to do triphase (the only thing I know as that's what my D box is), is it ok to just clip both negative wires into an alligator clip with a single wire electrode on the other end, for the common?

[edger477]

I'm using the outside wires on both sides of the transformer, right? (0.5 on the trode side and ??? on the amp side?)

amp comes to the SEC C and 4 Ohms (black and white), and the electrodes come to PRI C and 70V-0.62W (black and purple). That should give you the best ratio. Pay attention that primary common is on other side.

is it ok to just clip both negative wires into an alligator clip with a single wire electrode on the other end, for the common

Yes

[Corndogville]

OK, so when we get to SEC C time (seewhatIdidthere?) it's this side?



Thanks!!!

[Corndogville]

I'm using the outside wires on both sides of the transformer, right? (0.5 on the trode side and ??? on the amp side?)

amp comes to the SEC C and 4 Ohms (black and white), and the electrodes come to PRI C and 70V-0.62W (black and purple). That should give you the best ratio. Pay attention that primary common is on other side.

is it ok to just clip both negative wires into an alligator clip with a single wire electrode on the other end, for the common

Yes

Again, so the black common that goes to the electrode is on the opposite side of all the other wires we're using? Just want to confirm so I don't fry something.

Also, is it safe to use nylon zip ties to secure the transformers, at least temporarily, or do they get hot enough to melt them? Sorry if that's a stupid question. I wanted to try a test layout before I go through the trouble of drilling holes and trying to line stuff up in the enclosure. Judging by my old box, I'm guessing they shouldn't get that hot.

What do I do about the extra wires from the transformer? Clip them at the source or no? (Edit: I'm clipping off the stripped end and double shrink tubing them, one smaller piece to cover the cut wire, and one longer piece (same diameter) to cover well over both ends. Then I'll twist tie them all together for each separate transformer)

Was hoping to try it out tonight (as in nowish, haha) if I can make sure I'm doing it right

[edger477]

Again, so the black common that goes to the electrode is on the opposite side of all the other wires we're using? Just want to confirm so I don't fry something.

That is how it looks like by the markings on the pictures.

Also, is it safe to use nylon zip ties to secure the transformers, at least temporarily, or do they get hot enough to melt them?

If transformer gets that hot then something is very wrong.

I'm clipping off the stripped end and double shrink tubing them, one smaller piece to cover the cut wire

On mine I did similar, I put shrink tubing down near transformer and then folded wire back into it, did that with each wire, and then one large shrink tubing for all of them.

[Corndogville]

Again, so the black common that goes to the electrode is on the opposite side of all the other wires we're using? Just want to confirm so I don't fry something.

That is how it looks like by the markings on the pictures.

Also, is it safe to use nylon zip ties to secure the transformers, at least temporarily, or do they get hot enough to melt them?

If transformer gets that hot then something is very wrong.

I'm clipping off the stripped end and double shrink tubing them, one smaller piece to cover the cut wire

On mine I did similar, I put shrink tubing down near transformer and then folded wire back into it, did that with each wire, and then one large shrink tubing for all of them.

Thanks for coming to the rescue again!

I don't want to fry my corndog!

[Corndogville]

Again, so the black common that goes to the electrode is on the opposite side of all the other wires we're using? Just want to confirm so I don't fry something.

That is how it looks like by the markings on the pictures.

Also, is it safe to use nylon zip ties to secure the transformers, at least temporarily, or do they get hot enough to melt them?

If transformer gets that hot then something is very wrong.

I'm clipping off the stripped end and double shrink tubing them, one smaller piece to cover the cut wire

On mine I did similar, I put shrink tubing down near transformer and then folded wire back into it, did that with each wire, and then one large shrink tubing for all of them.

OK, I finished the thing, I think. The output jacks are just hanging loose right now, but I shrink tubed all the solder connections, so hopefully nothing can touch anything when I test it. The amp board's currently held in place by the wires, lol. I used green and black for the power connector. Since most folks seem camera shy about their messy builds, I figured I'd take one for the team:

Ebox1.jpg (195.17 KiB) Viewed 12606 times

Ebox2.jpg (230.7 KiB) Viewed 12606 times

I shrink tubed the entire length of the legs of the amp side of the resistors, leaving just enough to go into the terminal block, and clamped them, leaving me plenty of stiff but flexible leg to help me do cable management with. I tagged the other ends down with hot glue, to keep the resistor touching the aluminum plate, as a heat sink, if that makes any sense. The resistors aren't exposed anywhere. The transformers and power jack are held down with zip ties. I tested the board with my on-hand AC adapter to make sure the power light lit. The fixed voltage adapter is coming sometime today, but I'm just gonna test the box with what I have on hand.

If I don't post back soon, I died.

[Corndogville]

If I don't post back soon, I died.

I only died in the Shakespearean sense! That thing is strong! It works really well. Only quirk I noticed is if you wiggle the plug in the stereo input jack, it'll give you a nasty shock! Simple solution is just don't do that (at all really, but) at least when a file is playing! LOL

Thanks again for the help folks! I can safely throw the old 2B and Davey Box in the garbage. Will keep the Tens 7000 cos sometimes it's fun to go old school.

I'll have to go back and revisit the teases and files that felt too weak to be useful before.

Now all I have to do is figure out how to drill the holes right to put the enclosure over it. The box part is plastic, and a bit thicker than the lid. I'll post a pic when I manage to get it all zipped up, but you get the idea. Hehe

[Corndogville]

I've noticed it seems a bit harsh, especially if you're not entirely into it and are trying to ease in. Even trying to run it at low volumes doesn't work...it just kinda goes from "this doesn't feel like anything" to "woah Nellie!"

Also, now I finally know what people are talking about when they refer to "hot spots", yikes.

Wondering if the parallel resistors would mellow it out a bit. I have run it at full, the 2nd time I tried it (meaning, I don't want to make it too weak either), but if I had done that last night when I wasn't entirely there, it would have just roasted my dick.

I don't know what changed, if anything.

I did notice the regular resistors get a bit warm to the touch, after it's run a while, but not hot.

[edger477]

Are your electrodes having same surface area? If not then smaller one often feels harsh, it is normal.

[Corndogville]

Are your electrodes having same surface area? If not then smaller one often feels harsh, it is normal.

Interesting, I was using 2 regular stick on electrodes (R - tailbone and common perineum) and a steel ring or silver solder ring (L) for glans. Left was what felt harsh, with either, but I only had hot spots with the steel ring (which isn't as fitted), probably because of varying erection status.

jgjyyg.jpg (125.38 KiB) Viewed 12444 times

I did order some small stickies, both strip style and small circles, so hopefully one or the other will balance it out.

I also have a candle snuffer glans trode I made that I'll have to look around for (basically like a bell with no clapper, which I put inside of a stretched balloon to hold it in place. It should cover a lot more surface area.

[SniffyWally]

Hi all

I'm building a DIY Stereo E-Stim unit based on Tronic's Midstim, and I have a couple of questions.
Not so "low cost", though. Spent around £220 after buying all the components, wire, connectors, nuts & bolts, enclosure etc.

The Build:

I've opted for 2 x Fosi Audio TPA3116 V1.0G amplifiers (£50 each), and will only be using 1 channel from each, as I wanted individual channel controls rather than having to tweak balance at the source (a laptop with USB audio interface). I would hate having to jump back and forth between box and laptop to tweak balance and level. Individual channel controls is so much better IMHO. This also avoids "one wrong move of the mouse and scream!" issues. I probably could have added pots to control each channel's input level into 1 Amp instead to make it smaller and cheaper, but I wanted to keep any soldering to a minimum. I liked the look of the Fosi volume control, and I liked the idea of going straight into the Amps via the RCA outputs of my USB audio interface, so I chose 2 amps, and will only be using 1 of the 2 stereo channels of each amp.
For the transformers I opted for the Omnitronic ELA-T10 as these were available through Amazon.
I went super overkill on the serial resistors. 2 x 4 Ohm 100 Watts. Yes, you read that correctly. 100 Watts each. I plan to do without a heatsink and mount them to a thin wood sheet on the top of the box, so I wanted a large amount of radiating metal around each resistor to prevent any potential overheating. No parallel resistors or high pass filter arrangement.
The Amps will be fixed to the top of the box at the front, with the heat resistors on a thin sheet of wood further behind (leaving a nice gap for connections in & out of the Amps). Transformers and main connector blocks will be located inside the box (transformers at the back for even weight distribution) with various small holes drilled in the box lid for wiring. External connectors for 'trodes mounted on the top of the box to the right of the Amps. Lever nut wire connectors used throughout, as I find these far more reliable than banana sockets or 3.5mm plugs (dodgy connections = ouch! and more ouch!), with the only exception being the connections to the resistors which I plan to solder.
Quite a large ABS plastic enclosure 300 x 250 x 120 mm to fit all the stuff I need on the top. A bit of a monster.
Everything's ordered and I'm only now awaiting delivery of the transformers before starting the build.

Questions regarding transformer connections:

I would appreciate it if the more experienced builders on Milovana could answer these queries, if possible.

1. The Amps spec a 2-8 Ohm loudspeaker load. TroniC's Midistim schematic shows a 3.6 Ohm series resistor into the 8 Ohm winding of the transformer, which will produce a combined impedance of around 11.6 ohms. With my 4 Ohm serial resistors this will be 12 Ohms. Are there any issues with me connecting a load 1.5 x the specified impedance to a TPA3116 based Amp? Has anyone done this without any issues, or experienced issues when turning the volume up such as "soft clipping" (adding some additional HF content) or "hard clipping" (adding significant HF content)? NB the Amps are powered by 12-24V DC and I will be initially using the supplied 19V 4.74A PSUs for each Amp, but may change those out later (one Amazon buyer commented the PSUs were low quality / unreliable). Should I be looking to change these PSUs for another type?

2. Have other box builders used the 4 Ohm transformer winding instead of 8 Ohms, in order to keep within an 8 Ohm load for their Amps? I understand this will make it a bit more "current driven" (a plus point) but would lower the output power resulting in having to turn the amp up, increasing the power dissipated by the serial resistors (a minus point). I could see 2 options for this:

a) Use the 4 Ohm winding and keep to the 1.25 Watt winding. I calculate the maximum output voltage will drop by 62.5% which is quite significant, i.e. halving the primary winding, and the serial resistor is now using up 1/2 not 1/3rd, of the amp's output. Resulting in turning up the amp quite a bit to compensate, radiating away more heat via the serial resistors. I'm not sure what this arrangement might do to change the voltages / currents passing through the body.

b) Use the 4 Ohm winding but switching from the 1.25 Watt to the 2.5 Watt winding so as to maintain the same turns ratio shown in TroniC's schematic. I calculate the output voltage will drop by 25% rather than of 62.5%, which is far less significant and will only requires a small amp volume increase to compensate for it. Again I'm not sure what this arrangement might do to change the voltages / currents passing through the body.

Have other box builders tried alternative windings like this and could they advise their findings and suggest the best option? Are there any other arrangements that you find work best?

3. In general, presuming you are using TroniC's arrangement of tappings, inputting stereostim source files with peaks normalised to near-maximum levels, and with typical genital / anal trode connections, what level do you typically end up turning the signal source and Midistim amp up to, during a stim session? Has TroniC built in some overhead into his design to cater for low level inputs so with normal level files do you find you have to turn down the signal source in order to give you a good degree of control over the output level via the volume pot?

Answers would be much appreciated.

SniffyWally

[diglet]

Hi all

I'm building a DIY Stereo E-Stim unit based on Tronic's Midstim, and I have a couple of questions.
Not so "low cost", though. Spent around £220 after buying all the components, wire, connectors, nuts & bolts, enclosure etc.

...

I measured with an oscilloscope what the effect is for higher values of series resistor. There are no unexpected results for my chinese TPA3116 clone. I know the specs say 2-8ohm load, but it's really 2 ohm or higher.

btw, the 4 ohm winding indicates the inductance of the speaker that should be attached, not the resistance of the winding. The inductance of the transformer is frequency dependent, I measured mine (4ohm) at 16 ohm at 500hz and 27 ohm at 1000hz. Because of this trying to do math with the winding ratio and resistance is complicated, really need to measure it in action.

I use the 8ohm/10w winding because according to my measurements it outputs slightly more (maybe 10%?) power than 4ohm/10w at typical skin resistances and I found myself occasionally clipping the audio. I'm not sure which one is better, you will have to experiment.

The input sensitivity depends on how your amp is tuned. My amp has a potmeter to adjust the amplification, I adjusted it on first use such that maximum volume on my computer is clipping a bit. You may need to open your amp to do this.

I recommend using a 12V PSU, 19V is probably much more than you need. If you find yourself maxing out, you can always upgrade.