DIY Estim Build Help

[Dabow]

Hello all. I have a coyote and I am looking to upgrade. I figure I can build my own unit as there are a lot of guides. I already have a soldering iron and some experience with home electric, but I am by no means an expert. I am however not an idiot and can troubleshoot things fairly well. I can also research things and ask the right questions until I figure it out. I seem to have found a decent resource here for some help. So far what I'm planning is based off of the 17 page Low-cost estim topic linked below. I like the idea of building a more potent rig up front so I don't have regrets later and need to rebuild. I like the webteases here and want to make sure what I build can utilize those and have enough kick to be both pleasurable and painful.

viewtopic.php?f=12&t=23322

Using that topic I can find the resistor and transformer quite easily on parts-express. The transformer appears to be commonly used in these diy projects, but the resistors seem to change. So if somebody has a better resistor let me know.

https://www.parts-express.com/4-Ohm-10W ... quantity=1
https://www.parts-express.com/70V-10W-L ... quantity=1
https://www.amazon.com/ALITOVE-Adapter- ... 687&sr=8-3

Up to this point I feel comfortable with what I'm looking at buying, but the amp and some of the other bits have me wanting to make sure I'm going to get the right thing. Now as far as the amp I want the flexibility to connect via bluetooth and with a wire. I would also like their to be a build in volume control. I haven't seen anything that has two knobs, some with one, and some with none. I like the alure of having less to wire. I also believe there's software out there that can change the volume of each speaker, but I don't have any experience with that yet. Up to now I've just been using xtoys with my coyote and I'm not sure xtoys connects well with a diy estim. I have found a few amps, but none of them seem to have all of the functionalities I am looking for. The first link only has bluetooth, but no audio jack. The second has no bluetooth. The third is just plain expensive when compared to the other units. I would love to hear from somebody with more experience if there is such an amp that I am just missing. If there is no such thing then I'd rather get the amp with the bluetooth only as I'd rather not be stuck to my laptop.

https://www.parts-express.com/2-x-50W-H ... quantity=1
https://www.parts-express.com/TPA3116D2 ... quantity=1
https://www.parts-express.com/Dayton-Au ... quantity=1

My other questions are pertaining to housing and everybody's favorite connectors from the wires to the body. As far as housing goes I am a woodworker and could build a small box to house all of this, but if there's something that can be bought I wouldn't complain about not having to build a wooden box, especially given a chunk of aluminum will dissipate heat better. In regards to connecting to my body I have two loops from my coyote kit, pads, and the egg that I like to use. I understand that the coyote uses 2.5 mm. I am pretty sure the loops can accommodate a smaller pin as it stretches. I'm just not sure if there a convenient kit of adapters that can be bought that won't cost me an arm and a leg like you see on the dedicated estim sites. I can easily wire my own stuff. Wire is easily bought locally, but I'm not sure about plugs and adapters. Thanks all.

Edit-I remembered after posting this that I have an old amp for a subwoofer from a while back. It's a rockford fosgate punch 160.2. I found the manual and linked it below. Maybe somebody could help me interpret it's specifications and give me some insight if that'd work. Offhand I'm not sure what's the difference between continuous vs dynamic power rating, but it does have a dynamic power rating at 4 ohms 77 watt x 2. It has a continuous power rating at 4 ohms 40 watts x 2. The manual indicates that it has a 20 amp fuse. I am not well versed in this stuff to know if this is an option or not. I'm not broke and can buy an amp if this doesn't work. This is just already in a case and ready to go. I'm also not sure how to power it. Is there a way to get a power supply or do I grab a 12v battery whenever I use it lol.

https://rockfordfosgate.com/rftech/libr ... ch_man.pdf

[Johankain]

Hello and congrats on deciding on building a diy e-stim device.

You seem to be mostly on the right track. Personally I would choose a resistor with a 20 W power rating. They seem to get pretty hot with some signals sometimes.

I highly recommend biting the bullet and doing the wiring internally to two separate volume knobs on the signal side, like
https://www.parts-express.com/100K-Line ... quantity=1

These come really useful when calibrating for webteases or other mp3 based stim content. Not as much needed with restim and funscripts. Anyway, they are useful and dont cost a lot. Remember to order some knobs for these too!

Amp wise I would recommend sticking to the tpa3116 based boards, as they are cheap, proven to work well etc. Bluetooth amplifier wise there is the problem that they often have power on, connection established or lost sounds which sure will not feel nice when they occur unexpected.

Parts express has a selection of enclosures to choose from. Just collect all the dimensions of the parts and design a layout for them in your head or on paper, to make sure they fit in the enclosure. Bigger enclosure makes the building a bit easier, but leads to a bulkier end product.
https://www.parts-express.com/electroni ... Heat-Sinks


Hand built wooden box would sure look cool though!

The amp you have laying around might work, but your device wull then be really bulky. And the amplifier probably is not as efficient as the tpa3116 chips. Which leads you to the need of bigger power supply.

[Dabow]

Thanks for the advice. I did find the below linked amp on Amazon based on your suggestion. It already has all the things I was looking for. So that’s nice.

https://www.amazon.com/Bluetooth-Subwoo ... 569&sr=8-4

Also found this resistor.

https://www.parts-express.com/4-Ohm-20W ... quantity=1

Thanks for the enclosure link as well. Lots of boxes that are super cheap and well worth the time savings. I could make a box with finger joints and a plywood face but that’d be more work than it’s worth. Maybe if I get a wild hair I’ll do it some day. Otherwise it’s easier to just buy a $5 box.

Going back to my car subwoofer amp. I happened to notice that my laptop power supply has a 19.5v 16.92 amp output. Do you think that would be able to power my subwoofer amp? At this point I would prefer to make my own unit from scratch, but color me curious.

[Johankain]

19 volts propably triggers overvoltage protection on a car audio amplifier. So maybe it works, maybe it does not. Or in case you ment the amplifier you linked in your last message it will work. However it is always recommend to use a double insulated powersupply while stimming. It is a safety thing, prevents you from connecting your body to mains power in any situation

I don't of course know what you were looking for in an amplifier, but the one you linked does not lose the need for wiring the potentiometers for the right and left channels. The amplifier you linked does have many knobs, most of them are useless when stimming. Bass and treble are not needed as well as the subwoofer channel.

https://www.parts-express.com/TPA3116D2 ... quantity=1

Ie. this amp does not have a lot of unused stuff, as the included volume knob can be used as kind of a master volume as it controls both channels at the same time. The separate potentiometers are still crucial when calibrating the channels individually.

[Dabow]

Thanks again for the response. My inquiry in regards to my laptop power supply was in regards to the subwoofer amp. I will be using my laptop for stimming so I will still need to buy a power supply for my new device. I was just curious more than anything.

I was aware that most of those knobs were just going to be decorative. I had looked at the amp that you linked, but I do want the ability to use Bluetooth as well as directly connect via wire. It seems that all of the amps on parts express (that I could find mind you) are one or the other. Not both. The amp that I found on amazon caught my eye because it does have Bluetooth as well as an aux input already on the board. It also has the master volume know and power input already installed on the board. Just more things I will not need to wire myself.

I do plan on buying the volume potentiometers (I believe that is the correct terminology). They look easy enough to install and I do agree that the feature of dual channel volume control is important. However if I do utilize Bluetooth how does one install the potentiometers on the input? I believe that is what you meant when you said the signal side. I have seen other diagrams where they were installed on the input side as well. Unless I confused your statement and you wire in the volume on the speaker side of the board.

Since I am on the topic of input, how does one connect a laptop to the estim? I have a headphone jack that I assume is 3.5 mm. I assume that you can take a wire and simply split it. From there install your volume potentiometers and wire that into the board from there. I found an adapter linked below, but I feel like that can be done easily without the adapter.

https://www.parts-express.com/3.5mm-Ste ... 0-294?quan

These last links are purely to help me keep track of bit and pieces. I often open and close tabs as I cruise around and bookmarks are starting to get clogged. Just some banana plugs and posts.

https://www.parts-express.com/Gold-Plat ... quantity=1

https://www.parts-express.com/Gold-Bana ... quantity=1

[Dabow]

Sorry for the double post, but I bought some of my gear today with the exception of my power supply and amp. As I'm scanning through amps with the TPA3116D2 chip I noticed something that I overlooked previously. They are only rated at 2x50 watts with certain volt power supplies. Take that amp linked below. It does 50 watts at 21 volts and 4 ohms. The 21 volt and 24 volt are harder to find and more expensive, especially since I'm trying to verify they are double insulated. With the resistors and transformers that I bought what should I be looking for. What voltage/amp power supply should I be looking for to pair with a certain wattage amp? I feel like up until this point I have been thinking I have been doing 50 watts and need to get a power supply to match that or do I just get a 12v 5a power supply and not worry about it?

https://www.amazon.com/XY-Y50H-Bluetoot ... 151&sr=1-9

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

https://www.parts-express.com/4-Ohm-20W ... quantity=1

[darthjj]

I do plan on buying the volume potentiometers (I believe that is the correct terminology).

At least according to Tronic's schematic you should buy a linear potentiometer for estim signal control. A "volume potentiometer" is bound to have audio taper, which I think is more of a logarithmic curve. I have never tried audio pots myself, but I have built the "channel level" box from the schematic using linear pots and it gives good control over the whole range so I can at least vouch for that.

[Dabow]

Well that's to bad. I already bought them. Oh well they weren't expensive and they don't look difficult to install. Once I get all my stuff together I'll give it a try. If I want to change them out I don't think it'll be difficult to do. Thanks for the insight!

I'm still stuck on my amp/power supply. I found this amp that can get up to 40 watts per channel at 12 volts. If it's not a big deal I'll just order it. If it's a deal breaker I'll keep looking.

https://www.amazon.com/Bluetooth-Amplif ... C93&sr=1-1

[Johankain]

I'm sorry that I accidentally linked the wrong kind of potentiometer. I edited the link to not mess up anyone elses builds. They propably still work, just a bit more sensitive on the other end of the area.

40 watts will be enough, I believe I've seen some builds with just 25 watt amps.

Heck, I think the other build of mine is made with 2x30 watt wondom board

[Dabow]

Ya I'm not worried about it. They don't cost much and of all the parts to assemble they seem like the easiest. So if it becomes an issue I'll just switch them out.

[Dabow]

Started getting some of my components today. My power supply and board are coming tomorrow. I quickly realized that the box I picked out isn't big enough to house the transformers. So now I must decide between buying a new box vs building one. I wanted to just buy a box, but if all I'm buying is the box then it's probably not worth the cost of shipping unless I buy more stuff in the future. I also figured out that the rca cords I had on hand are to small a gauge. So I'll head into town tomorrow and buy more wire. I'll look to see if they are some electrical boxes that'll fix my needs or I'll just build the box.

A couple of questions regarding the build. Do people insulate the wire from the resistors? It's all uninsulated coming out of the resistor. I've already soldered the connection between the transformers and resistors and it feels wrong to just be exposed.

If I need to ground a component what should I ground it to?

Also back to the volume potentiometers. Still uncertain where to put it. The board itself has a single 3.5 mm input and the speaker outputs. I feel like the answer is directly after the speaker output.

Thanks!

[Johankain]

I don't remember needing any grounds. On the other topics there is the drawn schematic which will come handy.

Insulating the resistors connection would not hurt anything, but surely makes your build more reliable.

The potentiometers come to the 3,5 mm plug side. So snip your cable, peel and solder. They will sure burn if installed after the amp.

[edger477]

If I need to ground a component what should I ground it to?

No grounding. Components already have terminals (+/-) that need to be connected, and if i.e. they have a heatsink (some resistors have it), they will normally be insulated from both terminals (so you could screw them to same metal heatsink). Grounding anything would defeat the safety precautions of the build. The double-insulated power transformer is used to ensure none of the + or - terminals are connected in any way (there is no potential between) input (AC) and output (12/24v), and then transformers on the output of the amp are used to completely galvanically insulate the output circuit of estim from that DC input. Grounding anything just defeats the purpose of galvanic insulation since it connects "gnd" (-) of DC to something that might be connected to the grounding wire of the AC installation (and that one is only safe if whole installation in building is properly safe). By having estim terminals properly insulated from everything else, we ensure that the current can only flow between these terminals, and never from one of terminals to something else (i.e. grounding if you touch something that is grounded too).

[darthjj]

A couple of questions regarding the build. Do people insulate the wire from the resistors? It's all uninsulated coming out of the resistor. I've already soldered the connection between the transformers and resistors and it feels wrong to just be exposed.

I did not insulate the connectors on the heavy duty resistors since those are mounted on a metal plate. But all loose cables are fully insulated, with shrink tube to fill the gaps, and there is no risk of accidentally touching anything since the box is closed. The smaller resistors, which I mounted inline with some cables, are of course insulated with shrink tube covering the metal bits.

If I need to ground a component what should I ground it to?

Ask again when you have a specific component you think needs to be grounded :) On the output side nothing should be connected to anything else. There should be two closed circuits per channel: One loop between the amplifier speaker outputs and transformer primary side, and one loop between transformer secondary side and the electrodes (with your body closing the circuit). Nothing else should be connected to these circuits, with the one exception of when you're using triphase, but definitely no grounding.

Also back to the volume potentiometers. Still uncertain where to put it. The board itself has a single 3.5 mm input and the speaker outputs.

The single 3.5mm input is surely a stereo jack, so it has common audio signal ground, left channel, and right channel internally. If you look at the schematic I posted previously it has the symbol for this connector in the top left corner, with 3 wires coming out of it. You can also see that the signal ground joins the jack ground and both channels going into the amplifier, so it's perfectly fine to keep these as a single wire if your amplifier only has 3 inputs (left, right, ground) in the form of a 3.5mm jack instead of splitting it up to (left, ground, right, ground) as in the schematic.

I.e. you build the volume control something like this:

(either 3.5mm stereo jack, or separate channel inputs) -> volume controls -> 3.5mm stereo plug which goes into the amplifier

Using something like this: https://www.aliexpress.com/item/1005005892049362.html

I feel like the answer is directly after the speaker output.

I sincerely mean this in the best possible way; I beginning to worry about your safety :S Not saying you need the kind of skill to be able to design these schematics yourself, but you ought to at least know enough about power, voltages, currents and resistances to know that it would be a bad idea to connect it like that before even thinking about modifying the schematics. This combined with your somewhat vague question about potentially "needing to ground" something kind of makes it sound like you're either about to change something you don't fully understand, or that you might've misinterpreted the schematic. Even if you refrain from making any modifications, not knowing what you're doing still increases the risk of making some mistake. You might electrocute yourself or start a fire if you connect something wrong.

[Dabow]

I'm sorry. I'm definitely the knows enough to be dangerous type of person, which is why I'm asking a lot of questions before I begin. I want to make sure I understand what I'm doing any why I'm doing it. I'm following the low cost (~$40-50) build linked below, but that build does not have a left and right volume built into it.

viewtopic.php?f=12&t=23322

I can look at the part/schematics, look at other builds, and figure it out but I definitely wanted to know where this went and if it mattered. The volume potentiometers are one thing that was hanging me up. In my mind my card already had the single input and I hadn't even considered making my own left and right input going into my box, volume, then back to the single input. Hard to break out of the box I had created for myself in my head. For now I will not have the parts to complete my build with left and right volume control. My amp has the 3.5 mm input as well as bluetooth connectivity. I live in a rural area so hopping in the car and going into town is a 25 minute drive. I should be able to grab what I need when I go next. Until then I should be able to put my build together as outlined in the low cost build linked above and at least test it out.

The building your own DIY estim linked below is what confused me about grounding. I was looking at it trying to figure out what I was doing with the separate channel volume and saw that it had wire labeled ground, which I did not have the ability to wire to my board. It makes sense that it all goes into the 3.5 mm jack like you linked.

viewtopic.php?t=23302

All of the responses sure clear up the confusion I had lol. I guess saying something dangerous elicited some good responses. Thank you everybody for the help.