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

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

Post by cl13a »

Image
This design is a variation of TroniC's MidiStim from the SmartStim forums.
https://www.smartstim.com/forum/viewtop ... 59&t=37175

eBay bare minimum Parts list:
1. "US TPA3116 Digital Power Amplifier Board 2*50W DC24V Two-Channel Stereo Digital" - $8.49
2. Speco T7010 $13.99 x 2
3. 3.9 ohm 10W resistor (3 pieces) $5.60
4. UL Listed 12V 3A 36W AC Adapter Power Supply $8.99
5. 20 Pairs 2mm Gold-Plated Bullet Connectors $5.45

Total before tax for eBay bare minimum: $56.54
-----------
Added 10/3/2020: Parts Express replacements drop the price to just $43.12 before tax! ($6.95 economy shipping included)
1R. TPA3116D2 2x50W Class D Stereo Amplifier Board with Volume Control $7.98
2R. 70V 10W Speaker Line Matching Transformer $5.19 x 2
3R. 4 Ohm 10W Resistor Wire Wound 5% Tolerance $0.83 x 2
4R. 12V 5A DC Switching Power Supply Grounded AC Adapter with 2.5 x 5.5mm Tip Positive Plug (also UL listed) $9.97
5. 20 Pairs 2mm Gold-Plated Bullet Connectors $5.45
1P. 2.5 x 5.5mm Power Jack to Screw Terminals $0.73

(edited on 10/22/2020, seems like the 5V 2A adapter went out of stock.) You can save some money if you already have a 12V supply and a way to wire it to the amplifier.
Big thanks to hosenguy for helping verify this wiring diagram!
Image
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This assumes you already have a soldering iron (soldering is easier than you think), wire, a 3.5mm audio cable, and something to mount the components to.
I recommend also getting some silicone wire for the electrode leads though since it's very flexible:
22 AWG 15ft x3 $7.59

Other instructions:
  • Be careful, you are passing electricity through your body. However, the risk is very low if your electrodes stay below the waist.
  • There will be a bunch of other wires on the side of the transformer with the 0.5W tap, just insulate the ends with tape or something and move them out of the way.
  • The two major changes to the original MidiStim are a different amplifier and lower power resistors. I measured less than 2 watts at the input of the amplifier so it seems that 25W resistors aren't needed (maybe you need them if you're trying to shock your entire leg or something?).
  • You can use a virtual audio mixer like Voicemeeter Banana (or other versions of Voicemeeter) to adjust left-right volume bias by passing the E-stim audio into the virtual input and then changing the L-R bias. Then you route the virtual input to the audio output that goes to the amplifier. Make sure all the audio devices going in and out of Voicemeeter are set to the same sampling frequency and bit depth (like 2 channel, 16 bit, 48000Hz) or else you'll have audio skipping and crackling.
  • EarTrumpet is a useful app to have in general, it provides an easy interface to move programs to different audio outputs.
You should take this with a grain of salt since I am not an electrical engineer, but this setup works for me. Please correct any errors if you see any.

Ultimately I hope this helps get more people into E-stim since there is huge potential in it. The current E-stim teases on Milovana are just the beginning and they are already amazing!
Last edited by cl13a on Thu Oct 22, 2020 6:57 pm, edited 3 times in total.
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Re: Low-cost (~$60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by cl13a »

It may be possible to get this below $50 which would be a milestone for sure:
This transformer seems very similar to the Speco but is just $5.19
https://www.parts-express.com/70v-10w-s ... r--300-040
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Re: Low-cost (~$60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by hosenguy »

Regarding the cheaper transformer:

I spent a bit of time trying to compare the spec sheet of the cheap one with the Speco T7010.

The only spec I found looking for the T7010 is a generic system spec for an audio system used in commercial installations.

The Speco T7010 was the standard for many years, then came offshoring from the US of A and cheaper transformers.
The basic T7010 is now distributed from Hong Kong and is OK, but it no longer has a spec sheet that shows anything other than its power handling and impedance taps. They do not currently include the frequency response or winding information anywhere that I could find..
The cheaper one at least includes the frequency response which is typical for this type of transformer for it's intended use.

Just from the fact that Parts Express (reputable company) is selling it, and from the spec they have, I would think you could not tell the difference between these two transformers in a stim amplifier device.

FYI, I built my own stim device about 10 years ago.
My background is in electrical engineering and it includes designing and maintaining numerous commercial audio systems.

This is really good news for lowering the cost of stimming!
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Re: Low-cost (~$60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by lolol2 »

Thanks for adding another DIY design!
Always cool to see what people are using and see a really easy manual with a shopping list where nearly everyone can follow! :yes:

The only thing that I personally wouldn't like is an AMP with just a single volume button.
I always have different power levels for both channels, change always the balance in software when you turn up the volume sounds really laborious.

But when I see that the amp is $8.49... I would just buy two and use one for left and one for right :-D

This design should also be able to realize without any soldering for people who are not into this?
All components have already wires attached and you could just use cable clamps?

And I would recommend to add a triphase switch... should less than $3 and can make wire up way more easy.
My creations:
Spoiler: show

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

Videos:
06/2020 - Estim Sync Hero Vol. 01

Teases:
04/2020 - Estim Mansion under Quarantine
12/2019 - Estim Challenge
12/2018 - Estim Distraction
03/2018 - The Estim Tower - Endless Mode
01/2018 - The Estim Tower
05/2017 - The Estim Mansion
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Re: Low-cost (~$60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by BoundSquirrel »

This is great! Questions from one non-electrical engineer to others (and I think at least one actual EE :-) )

I have a DIY Midistim that I've posted the specs for here:

viewtopic.php?f=12&t=23035&p=284710#p284710

It there any reason that I can't swap out the SMSL SA36A separate amp for 2 x US TPA3116 (1/channel) internal amps linked in this build? Will the resistors and transformers behave the same as with the current amp? I suspect that they will, but as always, I don't want to zap my junk off. :no:
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Re: Low-cost (~$60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by cl13a »

hosenguy wrote: Sat Oct 03, 2020 4:04 am Regarding the cheaper transformer:

I spent a bit of time trying to compare the spec sheet of the cheap one with the Speco T7010.

The only spec I found looking for the T7010 is a generic system spec for an audio system used in commercial installations.

The Speco T7010 was the standard for many years, then came offshoring from the US of A and cheaper transformers.
The basic T7010 is now distributed from Hong Kong and is OK, but it no longer has a spec sheet that shows anything other than its power handling and impedance taps. They do not currently include the frequency response or winding information anywhere that I could find..
The cheaper one at least includes the frequency response which is typical for this type of transformer for it's intended use.

Just from the fact that Parts Express (reputable company) is selling it, and from the spec they have, I would think you could not tell the difference between these two transformers in a stim amplifier device.

FYI, I built my own stim device about 10 years ago.
My background is in electrical engineering and it includes designing and maintaining numerous commercial audio systems.

This is really good news for lowering the cost of stimming!
Thanks for your info!
Incredibly, the Parts Express parts were able to lower the cost before tax to under $40. Can you confirm if the wiring for the Parts Express transformer should look like this?
EDIT: Do not wire it like these pictures, this is wrong!
Image

Image
Last edited by cl13a on Sat Oct 10, 2020 1:12 am, edited 1 time in total.
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by hosenguy »

I am not certain which lead you are hooking the secondary to with this picture but I think I do not agree.

According to the spec for the transformer you should connect the primary side as you do clearly show. Black is common and grey is the 8 ohm lead.

The secondary should be connected with the black as electrode common as you show.
The electrode output should be connected to the lead marked 70V at 1.25 watt (orange) or the more often used 0.65 watt lead (purple).

I would like to see a review of this transformer when used to stim as it is designed in typical cheap method. It is listed as a 10W transformer but that is only true of the 25 W winding. This is a little odd but should not affect stim use as we do not require that connection. My very minor concern would be if it can really be called a 10 Watt transformer as advertised. Just a heads up as I would still use this if I were building a new box for myself.

https://www.parts-express.com/pedocs/te ... iagram.pdf

And for the nerds among us, note the way the transformer is drawn with the various wattages scattered about.

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

Post by Electro »

"The two major changes to the original MidiStim are a different amplifier and lower power resistors. I measured less than 2 watts at the input of the amplifier"

It's not uncommon for me to see 15 watts while I'm stimming with my unit and that's not even in an intense session, a long one where I've cranked it up a bit, or especially if I am using a bipolar anal electrode because I really end up cranking the power in that case. I figure I could be putting 20 watts through there sometimes and most of that would be wasted through the resistor. Which also makes me think that getting a power supply lower than the rating of the amplifiers could go a little hairy if that power supply either hiccups or goes into foldback temporarily and someone turns up the volume and when the power supply leaves that mode, the person with the stim is going to get full power. You need to measure the power when you are stimming, I can't even feel anything if I'm putting 2 watts into the amp.

Showing pictures of PCBs is great for the budget conscious person who is familiar or willing to learn how to build one of these, but your instructions will get most people lost. We already have tons of people who want to enter the stim community who we tell it's easy to build, and when I'm telling people that it's easy, I'm thinking of a cased amplifier where the outputs go to the resistors, transformers, and out to electrodes. I think low cost is great but I think showing the easy to build version is the way to go because a decent suitable bookshelf speaker amp and power supply come in at about $50 plus the rest of the components and you've got people shying away from a DIY for units that cost hundreds more because they "don't know electronics".
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by cl13a »

Electro wrote: Mon Oct 05, 2020 1:19 am It's not uncommon for me to see 15 watts while I'm stimming with my unit and that's not even in an intense session, a long one where I've cranked it up a bit, or especially if I am using a bipolar anal electrode because I really end up cranking the power in that case. I figure I could be putting 20 watts through there sometimes and most of that would be wasted through the resistor. Which also makes me think that getting a power supply lower than the rating of the amplifiers could go a little hairy if that power supply either hiccups or goes into foldback temporarily and someone turns up the volume and when the power supply leaves that mode, the person with the stim is going to get full power. You need to measure the power when you are stimming, I can't even feel anything if I'm putting 2 watts into the amp.

Showing pictures of PCBs is great for the budget conscious person who is familiar or willing to learn how to build one of these, but your instructions will get most people lost. We already have tons of people who want to enter the stim community who we tell it's easy to build, and when I'm telling people that it's easy, I'm thinking of a cased amplifier where the outputs go to the resistors, transformers, and out to electrodes. I think low cost is great but I think showing the easy to build version is the way to go because a decent suitable bookshelf speaker amp and power supply come in at about $50 plus the rest of the components and you've got people shying away from a DIY for units that cost hundreds more because they "don't know electronics".
Thanks for the info! I haven't tried anything outside of conductive rubber loops, so that's probably why I saw maybe 1-2W at the most going into the amplifier before the feeling through the electrodes gets unbearably intense. Do you know how commercial E-stim devices work? The 2B can be powered with a 9V battery, so obviously it can't use more than a few watts.

And I see what you are saying, a lot of people will be scared off by the sight of a PCB, so I should explain how there isn't much of a difference between the bare amplifier board and one with a case and some connectors attached.
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by Electro »

Do you know how commercial E-stim devices work? The 2B can be powered with a 9V battery, so obviously it can't use more than a few watts.
My understanding is the commercial devices like the 2B use spaced pulses and operational amplifiers in the place of transformers. This makes for a smaller device, but it's also uses the electronics to modify the input audio(or chosen built-in routines) so that way it doesn't need to have the transformers to produce safety functions such as eliminating DC currents because the processing takes care of that.

I've been playing with the DG Labs Coyote and it's single lithium ion 3.7v 600mAh cell runs for 6 hours(haven't tested this fully yet with higher settings and a few longer duration sessions with both channels active with each session). So far I've tested using a single channel a few of the times because the audio input mode PLAYS MONO!!! :no: Both channels play the same thing and the interpretation of the audio is a complete joke. I need to do more testing to see what the heck it's trying to do with audio because it seems like stroking files do have a volume ramp effect and certain other files do seem to change the speed of the pulses. ..but this device feels tremendously different than a transformer-based directly audio derived device, less constant and smooth, and definitely more "pulsey/thuddy" most of the time. It spends more time in an "off" state by having blank spaces between shorter pulses, compared to an amplifier setup that will continuously play sine waves if that's what you play through it. When the feeling for the Coyote is supposed to feel more constant or smoother, it feels like it basically reduces the spacing between the pulses. I'm not sure if the 2B does that sort of thing to save energy and run off of a small battery or not. When you say a 9v battery? Are you talking like an alkaline 9v you'd drop into a smoke detector? ..or is it a built-in 3 cell LiFePO4 or 7 or 8 cell NiMh battery? weird for those to be called a 9 volt, but power tool manufacturers have done weird voltage conventions based off of rounding and non-nominal voltages(A123 cells in I think B&D tools if I remember right was one of the first) so I wouldn't put it past a E-Stim manufacturer to make something up.
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by cl13a »

Electro wrote: Wed Oct 21, 2020 3:00 am When you say a 9v battery? Are you talking like an alkaline 9v you'd drop into a smoke detector?
Yeah, it's that kind of 9V (the "PP3" form factor). Very interesting insight about the commercial devices, I guess the DIY transformer-based setups are the most "pure" in terms of audio processing.
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by BamaSwitch »

[/quote]
viewtopic.php?f=12&t=23322&p=288189#p288189
I made a build list based on the MidiStim from smartstim, all the parts there can be shipped to the US (eBay listings). And the Parts Express version is $43.12 (it should work but I will say that as of this post nobody has tested those components before).
[/quote]

Thanks! I had started with that version but the amplifier board has already sold out and I could find a drop in replacement. Do you know a good one?

Other than software, is there an easy way to add a knob to each side for volume control?
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by cl13a »

BamaSwitch wrote: Thu Oct 22, 2020 7:27 pm Thanks! I had started with that version but the amplifier board has already sold out and I could find a drop in replacement. Do you know a good one?

Other than software, is there an easy way to add a knob to each side for volume control?
https://www.ebay.com/itm/TPA3116-TPA311 ... 2072658051
($12.99)
I think this should work, and it has per-channel volume control, but no 3.5mm input (so you will have to buy a 3.5mm port and solder to the included wire). The volume potentiometers seem inconvenient though, but you could just remove them and solder bigger potentiometers in their place (make sure they are the same resistance range).
----------------------
Alternatively, you could buy this 2 pack for $15.98:
https://www.ebay.com/itm/2Pcs-TPA3116D2 ... 4322961217
And you'd get splitters for power and 3.5mm audio. You'd use one amp for left channel and one for right channel. This would also work for anyone who doesn't want to do soldering.
----------------------
Here's something almost identical to the originally listed one, if you want to use software ($11.99).
https://www.ebay.com/itm/Original-XH-M1 ... 2478291721
You may also be able to just put a potentiometer inline after each transformer to get hardware volume control per-channel but I am not aware of how much power it would need to dissipate.
Anyways, if you need any parts and they are available at Parts Express, buying the parts and amp from Parts Express will probably be better since the amp is $7.98 there. Definitely get a UL-listed power supply if you don't have one.
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Re: Low-cost (~$40-60) DIY Stereo E-stim for Audio Input (based on TroniC's MidiStim)

Post by hosenguy »

For several reasons I would not use the first recommendation. https://www.ebay.com/itm/TPA3116-TPA311 ... 2072658051
This is too much power for safe use.
It also changes the required skills and drawings to build.
Note: There are concerns about the complexity of a bare board and understanding of the original build already posted.

If you redesign this I would use the 2 separate amps.
Each of the other boards should also be acceptable choices.

There is a reason that the other site recommends a specific design and choice of parts. They have to support building the device and they need to know that it will work before you start the build!
If no one else has used a specific board that you choose, then PLEASE write a review, good or bad, and we will thank you for that.

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

Post by BamaSwitch »

hosenguy wrote: Fri Oct 23, 2020 6:48 pm For several reasons I would not use the first recommendation. https://www.ebay.com/itm/TPA3116-TPA311 ... 2072658051
This is too much power for safe use.
Thanks!! As luck would have it, I've ordered two of the boards already. :\'-( But I don't want to fry the bits!! :no:

I have also purchased two of the transformers listed in the original post.

I'm willing to trash (set aside) the two boards if they aren't safe and get another alternate. Better safe than sorry.
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