StereoStim troubleshooting.

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Nezhul
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StereoStim troubleshooting.

Post by Nezhul »

Hey. So I finally got around to assembling my own box, and I will say right away I'm not an expert in all that stuff. But I'm using a schematic/guide that I found a few years back on SmartStim forum, or something like that.

Anyway, my question probably doesn't really relate to the box itself, but to an additional feature I've added and wired. See, I wanted separate volume control for each channel. The way I decided to do it is by controlling channel volume before it even gets to the Amplifier.

Basically what I have is a standard 3.5 3-pin jack input. I then put each channel through their own variable resistors (turn-handle type), and have 2x RCA cables as an output. The RCA are then plugged into the Amp, and the rest you can probably guess - pretty standard power box schematic with audio transformers and so on.

Anyway, that volume control system can actually be tested independently. I can simply take the RCA outputs, convert them back to jack 3.5 via a cheap thingy bought in a store, and listen to the output audio. And when I test it like that it works flawlessly, just as you'd expect - when I turn the handle the volume in that channel gradually decreases, until it finally fades out completely. The decrease is linear and without kinks.
So I'm pretty sure I did that part good.

But when I plug in the entire system and test the actual trodes, here's what happens:
When channel audio is at maximum, the trodes put out the stim just as you'd expect. I had a e-stim before, so I know the sensation. The Amplifier has its own Master volume control which I can regulate, and I can't go much past the half volume, because it gets too intense. So the output stimulation is STRONG, and again, the volume control gradually increases the stim just as you'd expect.

However my separate channel controls act awkwardly. As I mentioned, at max they put max volume. But if you turn them lower just a tiny bit - the decrease is too fast. Basically, within a couple degrees of turning the stim gets completely shut down, and I can even crank up the Master Volume on the amp all the way. It's as if my amplifier just doesn't understand an output lower than certain volume. Which shouldn't be the case - my sourse audio is rather loud, actually.

Here's the amp I use:
https://www.banggood.com/HIFI-Class-2_0 ... rehouse=CN

Am I doing something wrong?
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Re: StereoStim troubleshooting.

Post by Bonkgr »

Hello,

Sounds like you did pretty well making your own box, good job!

The "volume" controls you wired in before the amp are not really volume controls at all...In the audio world, we would call those gain controls, and what you are really doing is controlling the input to the amplifier which will change the output exponentially; which means that the drastic change that you experience from moving them just a little indicates that they are working correctly.

Normally in an amplifier circuit, the gain control would be installed to control the input levels so that you don't over-load the amplifier (and the speakers). You would set it during initial installation and setup, and pretty much just leave it alone (unless you needed to tweak it a little). So, you could try smaller resistance values with finer adjustments (maybe search out some actual gain pots to accomplish what you want).

Or, if you truly want a dual channel volume and master volume control, it would depend on how the amp is wired, but I would probably wire them in series between the master volume outputs and each individual channel output.

My opinion is that I would probably try to keep it relatively simple. I would eliminate the master volume control and only install individual channel volume controls between the amplifier and the outputs. That is the way most boxes seem to be set up anyway.

Good luck, let us know how it turns out!
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Re: StereoStim troubleshooting.

Post by Nezhul »

Thanks for the reply!

Thing is, the master volume control is built-in into the amplifier (see link). I'm not actually that confident disassembling it and re-wiring it. In fact, this is my first soldering experience ever.

So what you basically say is that turning the knobs of my separate channel controls affects the amp exponentially? Never would've thought about it.

I didn't quite understand you explanation how to fix it though. Could you elaborate a bit further? Also, is it possible to find variable resistors that with range not 0-100% but something like 80-100? If I understand corectly, if I wired those in - then it would work much better.

I'm not really good in such things though. If you gave me some links or materials to read, or pointed out which specs I should look at when choosing components, I would very much appreciate it. :blush:
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Re: StereoStim troubleshooting.

Post by Nezhul »

Or, perhaps, I could wire volume controls directly after the AMP and before it gets to the transformer? Would that work?
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Re: StereoStim troubleshooting.

Post by hosenguy »

I have successfully built many amplifiers and I am an electrical engineer. So I hope this helps.

First the building of an amp may seem simple it can be proven that it is not by the sheer numbers of discussions that have gone on here and on the Smartstim site regarding problems. So if you are only having a problem with additional controls you are really in pretty good shape.

From what I can tell without a schematic of the exact hookup you have made, I suspect that there is a "signal ground" reference problem. Each of the controls you added should have a set of 3 connection posts on them. The signal from the source that you are using to feed the signal would usually be connected to one side of the control, often called "signal hot", and the other outside connection would be signal ground. Usually ground is the shield in a stereo patch cord with the 3.5 connector. The center of the pot goes into your amplifier as the hot signal. You also need the shield to continue on to the amp as the signal negative or ground. This is also done with the other channel of stereo the same way. Because there is only one shield in the cable you describe it must go to both volume controls.

I have seen this sympton when a control comes un-soldered from a printed board.

There are linear controls and also logarithmic type made for special uses. For stimming the linear ones work best and provide a smoother adjustment. The linear ones should work in a linear fashion if working correctly.

Good luck!
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Re: StereoStim troubleshooting.

Post by Nezhul »

I think I have a Logarithmic Pots, because they were supposed to control audio volume, and due to how sound is percieved they needed to be logarithmic. Should I switch them to linear?

Also my current setup is this: I have 2 POTs looking like this:
Image
I also have a standard 3-pin jack socket, and 2x RCA cables as output.

I place the POTs on the table with shafts sticking up and pins pointing down.
The right pin of both POTs, the ground of Jack and both grounds of both RCA cables I solder together.
To the medium pins I solder signal (core) cables from the RCA (obvioulsy, 1 to each pot).
To the left pins I solder the jack socket channel outputs (1 channel to each pot)
I also have a metal aluminum case, so I don't need to solder the ground to the casing of the POT, like it is described sometimes.

This seems like the same setup you described. So I don't think the problem is there.
Thanks for the reply BTW. The AMP/Power box themselves work well, it's just channel controls that I really wanted and can't figure out.

I also can't go to smartstim because I forgot password to my old account, and I can't retrieve it or register a new one - I simply do not receive e-mails from smartstim. Funnily, I do receive their "funding drive" e-mail like every month, but when it comes to sending me password reset link or account confirmation - they fail for some reason.
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Re: StereoStim troubleshooting.

Post by Bonkgr »

Nezhul made some good points. I would make sure that you have linear pots. You can try different values as well...Usually they come in 250 or 500 k Ohms (you probably want 250k linear pots). Try looking here:

https://www.allparts.com/Potentiometers ... t5vCnnk%3D

I would definitely put them between the output of the amplifier and the audio transformers. I would also wire them in parallel to the signal. So, you would have the ground side going to ground, and the signal output wire from the amp would be soldered to the input of the pot, along with the signal input side of the audio transformer.

That will effectively bypass the pot (so you are not sending the signal through the pot) and lower the volume as you turn down the resistor in the pot because you are sending more of the signal to ground as you decrease the resistance.

It sounds a little backwards, but I've wired guitars like that, and it works great! You might have to play around a little, but it sounds like you are most of the way there.

Shielding is also very important, and make sure everything has a good ground.

FYI, I've also noticed that listening to a sound tells you very little about how it will feel through a stereo stim unit.
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Re: StereoStim troubleshooting.

Post by Nezhul »

Thanks!
I managed to get through to Smartstim and found a solution there.

You basically can wire it to the Jack input, before the amp like I have here. But you indeed need a linear 10k POT, as well as 10k resisrot and a 470pF, 50-100v capacitor.
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Re: StereoStim troubleshooting.

Post by lawman5297 »

Nezhul, You are on the right track, use the info for the level controls found on smartstim. I have built several of these and the design on SS works great, nice and smooth with no spikes or sudden jumps. This is the type of pot you should be using for this.

http://www.digikey.com/product-detail/e ... ND/2537832

You should turn you amp up as high as possible (my are at 100%) as well as the source and use the pots to control the input levels.
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Re: StereoStim troubleshooting.

Post by hosenguy »

Nice job!

Hope you enjoy for a long time!
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Re: StereoStim troubleshooting.

Post by Nezhul »

Hopefully not as much as your avatar enjoys it.

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Re: StereoStim troubleshooting.

Post by Afapp »

My 2 cents, use linear pots not log pots. turn your pre amp pots to 100%. Adjust your amp volume and then adjust channels for A/B perfection.
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Re: StereoStim troubleshooting.

Post by Nezhul »

thanks!
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