Hi everyone!
I've encountered a big problem that I can't solve by myself.
I need to start telling you it's not stompbox related, but it's about an "alternative" source of power for my active bass.
Long story short, my bass devours two 9V batteries in a couple of months, so I decided to go recheargable using a lithium battery from an "old" smartphone.
I've bought a charging circuit for lithium batteries (with overcharge protection, and all the other safety functions) and a step up dc-dc converter, 'cause the battery is 3.8V 3000 mah, taking it to 18V I got around 600 mah (more or less what normal batteries provide) so I should be all set.
I've made all my soldering, everything works and the readings are ok, 18V are coming out of the dc-dc converter and feeding my baby bass, that unfortunately has become a noise machine, the signal to noise ratio is like 1:1.
When I use normal 9V batteries it's almost dead silent even with all the potentiometers cranked up, nothing, now with this lithium battery it's basically unusable.
What did I do wrong? Am I missing something? Is there some kind of extra ground connection to be made? Should I simply give up the lithium battery idea and stick to disposable ones?
I've successfully put a lithium battery inside a boss odb3, making it a power supply for other pedals too, and got no issues, no extra noise added when using it.
Now why is the same circuit acting differently on a bass?
I've already tried to change the circuits, maybe there was a faulty one, but still got the same results.
I've made a video so you can hear and "see" the noise I'm talking about, here it is
I hope I'm not off topic 'cause I don't know where else to ask for help with this!
Thanks to anyone willing to help!
QuoteAm I missing something?
Do you know how step-up converters work in general and what configuration yours uses in particular? Do you have a scope?
How shielded is the new circuitry? I would think that some of the oscillation in the converter would be leaking into the audio amp. It would need to be well shielded I would think, with a well grounded shield.
Hi Brainless, welcome. there are a lot of sharp people in here with decades of combined power design experience, so I think you'll get some good advice once they see the post.
Can you post a schematic of what you have? A pic of exactly what your setup is? For instance - is this unit all installed in the bass yet, or is it on the desktop? Is there any kind of shielding around the electronics? Are you near a PC/laptop when you get this noise? Near any transformers, ANY sort of noise-making equipment? The more info the better.
I suspect it's the converter, too, maybe harmonics of the switching frequency down in the audio spectrum. Proper shielding would be a way to potentially fix this; the more you amplify, the more you amplify any noise present, too!
It sounds like broadband noise (either white or pink) and your spectrum analyser doesn't seem to be showing any distinct peaks, leading me to agree with all the previous comments about shielding. If your step-up converter has an inductor in it, this will bring all the environmental electromagnetic noise into your power supply, which can then leak through to the audio path.
If this is the case (I might be wrong):
The most rigorous way to remove noise is to prevent it getting into your circuit in the first place, ie. proper grounded shielding around the converter and other active electronics in your bass.
The next best thing would be to prevent the noise getting from the power supply into the audio signal, and we would need more details about the design of your step-up converter for this. If you look at the schematic of most modern pedals (not fuzz pedals!) then you will see a variety of passive components are normally configured as filters to remove power supply noise before it powers op-amps, transistors, ICs etc.
If the converter itself is generating the noise, filtering may still be possible. The DC voltage is not as consistent as a battery, it often oscillates a little bit around the target voltage to give you 9V+/- a few mV at any given moment.
Its possible that when you did this modification to your Boss ODB3, placing it inside the metal housing of the pedal provided enough shielding to remove audible hiss.
Quotemy bass devours two 9V batteries in a couple of months
This shouldn't be unless you play 24/7. Do you remember to take the jack plug out of the bass when not playing? Usually, that automatically switches the batteries off.
Quote from: anotherjim on November 05, 2021, 09:08:04 AM
Quotemy bass devours two 9V batteries in a couple of months
This shouldn't be unless you play 24/7. Do you remember to take the jack plug out of the bass when not playing? Usually, that automatically switches the batteries off.
Jim taking a pencil into space while everybody else tries to design the zero-G pen...
Also you can buy rechargeable 9V batteries!
P.S. I know how incorrect the story about NASA and Soviet writing technology is, but it's a good allegory.
Thanks everyone for answering!
So let me answer back at my best...
I'm just a noob when it comes to electronics and circuits in general, I can solder, but I don't know the basics for creating a working circuit of any kind, so I simply watched a couple of videos and read infos here and there and thought I could make this thing easily.
Quote from: FiveseveN on November 05, 2021, 01:53:17 AM
Do you know how step-up converters work in general and what configuration yours uses in particular? Do you have a scope?
I don't know how they work and I don't have a scope, the only info I can give you is the actual amazon link to the ones I've bought ( http://www.amazon.it/gp/product/B071H9NRTW ).
Quote from: DIY Bass on November 05, 2021, 04:05:37 AM
How shielded is the new circuitry? I would think that some of the oscillation in the converter would be leaking into the audio amp. It would need to be well shielded I would think, with a well grounded shield.
The new circuit isn't shielded in anyway, 'cause I simply didn't know you're supposed to shield such circuits and I don't really know how to shield it aniway, 'cause I'm a gigantic noob that watches youtube videos of people doing things the wrong way, I guess :icon_mrgreen:
Quote from: GibsonGM on November 05, 2021, 05:37:47 AM
Hi Brainless, welcome. there are a lot of sharp people in here with decades of combined power design experience, so I think you'll get some good advice once they see the post.
Can you post a schematic of what you have? A pic of exactly what your setup is? For instance - is this unit all installed in the bass yet, or is it on the desktop? Is there any kind of shielding around the electronics? Are you near a PC/laptop when you get this noise? Near any transformers, ANY sort of noise-making equipment? The more info the better.
I suspect it's the converter, too, maybe harmonics of the switching frequency down in the audio spectrum. Proper shielding would be a way to potentially fix this; the more you amplify, the more you amplify any noise present, too!
I don't have a schematic, I just put together 2 circuits bought on Amazon thinking they'll just work, 'cause I'm a noob, so if you wanna I can give you the link to the charging circuit (the dc-dc step up converter is the one I've already linked) http://www.amazon.it/gp/product/B0859W9LMB
I've installed everything in my bass, the circuits in the battery cavity, which has no shielding whatsoever, and the battery in the potentiometers cavity, which should be shielded since the back of its cover is covered with aluminum foil.
(https://i.postimg.cc/SnSN3tST/asaa.jpg) (https://postimg.cc/SnSN3tST)
(https://i.postimg.cc/mtDTS18J/qassqqd.jpg) (https://postimg.cc/mtDTS18J)
The noise was always there, didn't change if I move away from the pc, or the amplifier, or anything, my setup has always been dead silent, bass preamp + power amp + 4x10 cabinet, not even bad ground noise, now this costant noise came to ruin everything
Quote from: aleks_tedstone on November 05, 2021, 06:20:41 AM
It sounds like broadband noise (either white or pink) and your spectrum analyser doesn't seem to be showing any distinct peaks, leading me to agree with all the previous comments about shielding. If your step-up converter has an inductor in it, this will bring all the environmental electromagnetic noise into your power supply, which can then leak through to the audio path.
If this is the case (I might be wrong):
The most rigorous way to remove noise is to prevent it getting into your circuit in the first place, ie. proper grounded shielding around the converter and other active electronics in your bass.
The next best thing would be to prevent the noise getting from the power supply into the audio signal, and we would need more details about the design of your step-up converter for this. If you look at the schematic of most modern pedals (not fuzz pedals!) then you will see a variety of passive components are normally configured as filters to remove power supply noise before it powers op-amps, transistors, ICs etc.
If the converter itself is generating the noise, filtering may still be possible. The DC voltage is not as consistent as a battery, it often oscillates a little bit around the target voltage to give you 9V+/- a few mV at any given moment.
Its possible that when you did this modification to your Boss ODB3, placing it inside the metal housing of the pedal provided enough shielding to remove audible hiss.
Now that you mentioned it, the ODB3 was noisy at first with the battery and the circuits inside, but not like the bass, it was a more constant hiss around 5khz that kinda modulated if I touched the converter, then went away as soon as I've turned the ODB3 in a power supply for other pedals (simply shorted pin 2 and 3 on the PSU socket, so it's no longer a power input but a power output) and plugged another pedal to it, so I guess the noise issues in that case were solved by adding another pedal to the equation, maybe it acted like an extra ground? I don't know, I didn't bother to find out in this case 'cause I'll be using both pedals while playing anyway, so...
Quote from: anotherjim on November 05, 2021, 09:08:04 AM
Quotemy bass devours two 9V batteries in a couple of months
This shouldn't be unless you play 24/7. Do you remember to take the jack plug out of the bass when not playing? Usually, that automatically switches the batteries off.
I always unplug the jack from the bass, even when we make like 5 minute breaks during rehearsals
I know it shouldn't devour them so fast, but still it did , 2 batteries lasted 2 months playing like 2 hours a day, 2 days a week, so let's say around 36 hours total in 2 months, I measured the current drawn by the preamp circuit, it's around 16.5 mah with the jack plugged in, and 0 with the jack unplugedd, there's no issues with its preamp circuit, by the search I've made online it appears to be a common issue with this bass, which has been in some way solved with later versions by changing the preamp circuit.
So it's 16,5 mah x 36 hours = 594 ma , which is what a common 9V battery provides more or less.
Oh, the bass' a Peavey Millennium AC BXP by the way.
Quote from: aleks_tedstone on November 05, 2021, 10:14:19 AM
Quote from: anotherjim on November 05, 2021, 09:08:04 AM
Quotemy bass devours two 9V batteries in a couple of months
This shouldn't be unless you play 24/7. Do you remember to take the jack plug out of the bass when not playing? Usually, that automatically switches the batteries off.
Jim taking a pencil into space while everybody else tries to design the zero-G pen...
Also you can buy rechargeable 9V batteries!
P.S. I know how incorrect the story about NASA and Soviet writing technology is, but it's a good allegory.
I really don't get this comment...
Rechargeable 9V batteries aren't the best solution IMHO, they don't deliver the full 9V, it's always 8.75 or something like that, plus I wanted to make something with the lithium batteries laying around here, I like tinkering with stuff and learn something new in the process, so had this idea...
I hope I've provided enough infos to understand what's causing the noise and how to solve this, most of you wrote about shielding, so what should I exactly do now?
Thanks a lot!!!!
Yes, 9V rechargeables can be a pain, not the full 9V (most of my regular 9V don't read that, LOL)....but you avoid the boost circuit, which uses switching to jack up your voltage. That switching represents "ON OFF ON OFF", meaning a current is drawn, then stopped, then drawn etc...very very rapidly. This switching current causes an EMF around the wires it's associated with...this can couple into nearby wires and circuits, causing a whine, hum, noise...the switching frequency is generally much higher than 20kHz, the limits of human hearing, but harmonics from it can be heard. That may be your problem, without the shielding (and sometimes with it). There is a whole field of study in making this stuff quiet!
Get the wiring perfect, then dig into the shielding...I do all of my guitars with foil, and my single coil strats/tele's are quiet as can be (weren't before). I think the switch box could benefit from it, but HOW to do it so it's not terrible...? But the rest of your bass could use it as well, appears the control compartment isn't shielded. Has to be foil-lined, the WHOLE thing, incl. the cover, and all parts must make contact. Do a net search before we all talk about it :)
You also need to be prepared for some intense learning. It is tough to get any switching power supply to power low signal audio equipment without introducing noise, so you've accidentally picked a tough first project.
Switching power supplies switch the entire power on and off at ultrasonic or RF freuqencies, so they're perfectly suited to make and broadcast RF noise by conduction and by radiation. The comments you got about shielding and filtering are a reflection of this concept. Switching power noise is bad enough that the exact placement of every PCB trace and the location (physical and electrical) of every wire going to and from the power supply can make a difference in noise.
I say this to prepare you - it may not be only one thing, and it may not be easy. So look at it as a challenge, and go learn, learn, learn. It won't kill you, and it will definitely make you more knowledgeable and therefore stronger. :)
Quote from: GibsonGM on November 05, 2021, 05:44:24 PM
Get the wiring perfect, then dig into the shielding...I do all of my guitars with foil, and my single coil strats/tele's are quiet as can be (weren't before). I think the switch box could benefit from it, but HOW to do it so it's not terrible...? But the rest of your bass could use it as well, appears the control compartment isn't shielded. Has to be foil-lined, the WHOLE thing, incl. the cover, and all parts must make contact. Do a net search before we all talk about it :)
So I did my homework, serched the web, saw videos and stuff, here's the results:
I've shielded the battery cavity, nothing changed, the noise was still there as before.
(https://i.postimg.cc/5j0DzN5m/Whats-App-Image-2021-11-06-at-14-38-41.jpg) (https://postimg.cc/5j0DzN5m)
Ok, it wasn't beautiful to watch, but I can assure you there was continuity all over the cavity shielding and in the cover too, so...
Oh, another thing, the control compartment seems to be shielded with shielding paint and the cover with aluminum foil, so the problem should be elsewhere...but where? :icon_question:
Quote from: R.G. on November 05, 2021, 07:22:32 PM
You also need to be prepared for some intense learning. It is tough to get any switching power supply to power low signal audio equipment without introducing noise, so you've accidentally picked a tough first project.
Switching power supplies switch the entire power on and off at ultrasonic or RF freuqencies, so they're perfectly suited to make and broadcast RF noise by conduction and by radiation. The comments you got about shielding and filtering are a reflection of this concept. Switching power noise is bad enough that the exact placement of every PCB trace and the location (physical and electrical) of every wire going to and from the power supply can make a difference in noise.
I say this to prepare you - it may not be only one thing, and it may not be easy. So look at it as a challenge, and go learn, learn, learn. It won't kill you, and it will definitely make you more knowledgeable and therefore stronger. :)
Oh I'm ready to learn and dig deep, I thought this project would be an easy one, once again a noob thought!
Since shielding didn't work, what about filtering? I know nothing about it, so...
BTW, I've found something that could help, but I wasn't able to find an exact schematic:
There are Warwick basses that come with lithium battery and mini-usb charging socket right off the factory, those are the Masterbuilt Custom Shop ones, here's the explaination
I've managed to find the spare PCB from Warwick shop, but I'm not spending the 125 euros of course
https://shop.warwick.de/en/pickups/accessories-parts/bass-electronics/22064/warwick-parts-charger-pcb-for-rechargeable-lithium-battery
So, as I wrote before, I couldnt find the schematics for that PCB anywhere, Warwick gives just the preamp and the wiring ones, nothing else.
It'd be great to see what they put in it and how they managed to solve the noise problem (if they ever got one building this).
I'll keep searching, but unless there's some owner willing to share photos, I don't think I can find any specific infos
Further research led me to understand that charging board isn't from Warwick but it's Fishman's, apparently they got the license to use it or something, still no schematics anyway, but buying one now costs around 98 euros, still not doing it though.
I got 1 and a half more days to figure this out (rehearsal day), otherwise I'll be back to disposable 9V batteries, but I'm not giving up anyway!
have you tried a filtering cap and a low value resistor between the power supply and the active circuitry? a bit of power supply filtering cant do harm iirc
cheers
Quote from: iainpunk on November 09, 2021, 07:26:00 AM
have you tried a filtering cap and a low value resistor between the power supply and the active circuitry? a bit of power supply filtering cant do harm iirc
cheers
Yep, been there done that, didn't work :'(
I've also switched the battery, but the other one (a standard 18650 lipo) once connected made the bass "scream", there was a constant feedback like high pitched scream plus the usual noise, I really don't know why, I'm starting thinking the charging circuit might be responsible somehow...
are the batteries you use the ones th charger was designed for?
13650 cells are rated at a different nominal voltage (lower) than phone batteries. is it maybe that you use a too-low voltage battery here?
cheers
Quote from: iainpunk on November 09, 2021, 09:27:46 AM
are the batteries you use the ones th charger was designed for?
13650 cells are rated at a different nominal voltage (lower) than phone batteries. is it maybe that you use a too-low voltage battery here?
cheers
I'm using a phone battery and this circuit is made for any lithium battery from 3.7V to 6V, everything works fine, the battery fully charges and the step up booster gives an output of 18V, it's all working, except this damn noise coming from who knows where :icon_cry:
So, somebody suggested to add a zener diode to eliminate output ripple....
Any idea how and where should I do this? :icon_biggrin:
It doesn't look to me as if you have really done shielding - at least not what I had in mind. The charging PCB and the dc-dc converter need to be individually shielded from everything else. They need to be in metal conductive containers that don't short out anything on the boards, and which are themselves connected to ground. It is not enough just to have the cavities shielded.
Quote from: DIY Bass on November 10, 2021, 04:36:54 AM
It doesn't look to me as if you have really done shielding - at least not what I had in mind. The charging PCB and the dc-dc converter need to be individually shielded from everything else. They need to be in metal conductive containers that don't short out anything on the boards, and which are themselves connected to ground. It is not enough just to have the cavities shielded.
You really think the noise comes from not shielding the circuits?
On the Warwick bass doesn't seem there's that much shielding, I can try anyway of course...
Do you think using a can (like a coke one) to create each individual shielding would work? Otherwise what should I use?
I don't really think this shielding thing might solve this problem, cause on the odb-3 the shielding might be the pedal itself ok, but when I took the circuits out of it there's still no noise... Or maybe it's the battery that needs shielding? Cause in the odb-3 again the battery stays inside all the time, underneath the pedal circuitry, but from what I can remember even with everything exposed there was no noise.
I don't know, I guess I'll try this individual shielding of both circuits, any suggestion on how to do it?
"...That switching represents "ON OFF ON OFF", meaning a current is drawn, then stopped, then drawn etc...very very rapidly. This switching current causes an EMF around the wires it's associated with...this can couple into nearby wires and circuits, causing a whine, hum, noise...the switching frequency is generally much higher than 20kHz, the limits of human hearing, but harmonics from it can be heard. That may be your problem, without the shielding (and sometimes with it). There is a whole field of study in making this stuff quiet!"
ANY part of that bass that's involved in the electronics that isn't shielded can have noise coupled into it, leading to the hiss...one way to shield the battery is a metal battery box that is grounded. The power wires would need to be shielded too if they pass thru a 'blank' spot inside the bass. The controls, the pickups...all shielded. Foil will work, and work well, if done properly. All parts must be continuous, and the foil is grounded - but as said, whatever circuit you're putting inside doesn't short to it. There are probably many videos on this on Youtube. I've used spray adhesive to line cavities successfully.
Then you want to look at some form of 'star grounding' (another topic) to ensure how everything grounds...to 1 point only. So you don't get noise coming back on the ground line. This isn't a trivial or easy project, as I'm sure you're finding out! Nor one that someone can easily just 'tell you how to do it'...which is why the 9V battery is so popular...
Ok, thanks for the infos!
The only thing I don't get is why should I shield the whole bass when it's perfectly silent using 9v batteries, my logic would tell me to shield just the circuits generating noise, and maybe the battery, even though it should already be shielded.
That's something I can't really understand, but I guess I don't have the necessary knowledge to understand it, so I'll do my homework :icon_wink:
Thanks again!
So, shielding wasn't the solution, the noise it's not from a lack of insulation, the noise is from...well, I don't know, but with a simple RC lpf filter I managed to reduce it to an acceptable level.
But there's some "strange" effect happening:
As you can see/hear I've lowered the noise to a reasonable level, but a slightly compression (?) of the signal appeared, why so?
The RC lpf filter at 60hz is made of a 265 ohms resistor and a 10 uf 50V low ESR ceramic capacitor mounted on the pcb of the step up converter, right on the output, and so were all the other filters I've tried, same capacitor, different resistors.
Can someone at least explain why the compression (or whatever it is) of the signal? I've searched online, nothing, there's no info about such thing.
Any ideas?
Not enough info...what "LPF"? What are the values, and we need to see the schematic of how you assembled it.
Resistors limit current, perhaps they are limiting the power supply current here, and if the circuit is starved, distortion may result. It is basically losing headroom. You still get your 18V after the LPF? Just a guess cuz I can't see what you built.
I assume you mean KILOHERTZ when you write 'Hertz" in your vid? ;)
I suggested totally shielding your bass just cuz you are already in there doing it. And the switching supply is RIGHT THERE, literally on top of it. Noise will get into everything, couple into wiring etc. Anywhere wires are passing unshielded thru the body, they'd need to have an internal shield grounded at 1 end only, things like that.
Ambitious project, I can see it's kind of a PITA, LOL. I think I'd prefer a 9 or 18v battery, charge it while on-board, remove charger cable and play. But you are actually being exposed to some good stuff to learn about! Sometimes we just CAN'T get it quiet, no matter what we try.
For easy shielding, copper slug tape comes to mind. Gardening stores will have it (and Amazon). It's exactly like self-adhesive shielding tape, even has conductive glue and can be soldered but most have a wave pattern on one edge to confuse the slugs.
You should treat the output jack shield as the centre of a star ground connection. Shielding should only connect to the star from one end - don't allow currents to travel from one place to another via shielding.
Anyway, I would consider the possibility that all is not well with that bass guitars electronics. The noise could be worsened by it taking too much current due to a fault.
Did I see a picture showing the electronics in a potted block somewhere? If so, I'd want to chuck it away - you can't fix it.
There are circuits & kits & PCBs for better alternatives out there based on classics such as the Musicman/Ernie Ball models. I know a player with a Bongo bass & he hardly ever has to change its x2 9v batteries.
Quote from: GibsonGM on November 15, 2021, 12:54:14 PM
Not enough info...what "LPF"? What are the values, and we need to see the schematic of how you assembled it.
Well, all the infos are there, what values do you need? I wrote both the resistor and the capacitor values, where I put 'em, the frequency cutoff, what else am I missing?
I don't have a schematic of the step up converter, so...
Quote from: GibsonGM on November 15, 2021, 12:54:14 PM
Resistors limit current, perhaps they are limiting the power supply current here, and if the circuit is starved, distortion may result. It is basically losing headroom. You still get your 18V after the LPF? Just a guess cuz I can't see what you built.
Yep, the output is still 18V, the LPF only takes 0.02 V away, so I had like 18.05 V now it's 18.03 V
Quote from: GibsonGM on November 15, 2021, 12:54:14 PM
I assume you mean KILOHERTZ when you write 'Hertz" in your vid? ;)
No, I mean Hertz where I wrote Hz and Kilohertz where I wrote Khz, why?
Quote from: GibsonGM on November 15, 2021, 12:54:14 PM
I suggested totally shielding your bass just cuz you are already in there doing it. And the switching supply is RIGHT THERE, literally on top of it. Noise will get into everything, couple into wiring etc. Anywhere wires are passing unshielded thru the body, they'd need to have an internal shield grounded at 1 end only, things like that.
I get it, the fact is there's no need to do it, the bass is silent and doesn't pick up any noise with normal batteries, so I should achieve the same result with a lithium battery since that's the only thing that's changing (that, and the circuitry to charge and step up of course, but I've already tried shielding those circuits and it's useless as well).
Quote from: GibsonGM on November 15, 2021, 12:54:14 PM
Ambitious project, I can see it's kind of a PITA, LOL. I think I'd prefer a 9 or 18v battery, charge it while on-board, remove charger cable and play.
Well, that's what I'm trying to achieve, to have the battery (and the circuits) permanently inside the bass, charge it when needed, then remove charger cable and play, I thought it was clear, maybe I didn't explain it clearly...
Quote from: anotherjim on November 15, 2021, 01:50:02 PM
For easy shielding, copper slug tape comes to mind. Gardening stores will have it (and Amazon). It's exactly like self-adhesive shielding tape, even has conductive glue and can be soldered but most have a wave pattern on one edge to confuse the slugs.
You should treat the output jack shield as the centre of a star ground connection. Shielding should only connect to the star from one end - don't allow currents to travel from one place to another via shielding.
Again, thanks for the infos, shielding's not the solution here
Quote from: anotherjim on November 15, 2021, 01:50:02 PM
Anyway, I would consider the possibility that all is not well with that bass guitars electronics. The noise could be worsened by it taking too much current due to a fault.
Did I see a picture showing the electronics in a potted block somewhere? If so, I'd want to chuck it away - you can't fix it.
There are circuits & kits & PCBs for better alternatives out there based on classics such as the Musicman/Ernie Ball models. I know a player with a Bongo bass & he hardly ever has to change its x2 9v batteries.
There's no fault in the bass circuitry, with normal batteries it works perfectly, it's just a very consuming preamp, it is been made like that, nothing wrong, nothing to fix, in fact it sounds great and I don't wanna change it, I'd just like to have a recheargable battery to power it so I don't have to buy thousands of 9V batteries and pollute :icon_biggrin:
Anyway...
I've tried another step up converter, this one's bigger and apparently more precise and reliable, and in fact the output doesn't need the LPF filter like the other one, it's still less noisy by itself, but again the minimun noise is still there with almost the same curve as the filtered one, but the compression is gone (as one should've expected of course since there's no LPF involved this time)
Here's the new step up converter based on the XL6009 mosfet
(https://i.postimg.cc/5XsWMvQY/TZT-Boost-Buck-DC-DC-regolabile-Step-Up-Down-Converter-XL6009-modulo-di-alimentazione-20-W-5.jpg) (https://postimg.cc/5XsWMvQY)
Here's its noise eq:
(https://i.postimg.cc/zyYDtnZn/newconv.jpg) (https://postimg.cc/zyYDtnZn)
The absurd thing that happened is this:
Let's sum it all up, so now I have a lithium 3.8V 3000 mah battery connected to the input of a charge/protection circuit based on TP4056, the circuit output going to a step up converter circuit based on the XL6009 with the output set to 18V going to the bass preamp, everything exposed outside of the bass
with no shielding whatsoever.
It gives enough power for the bass to work but there's still that minimum noise, and like on the filtered circuit, the noise is low enough to be ignored, but I want a clean signal, so (here's the mindblowing solution) I randomly noticed that by touching the metal plate of the XL6009 mosfet with a screw the noise gets lowered, so I connected an alligator clip test lead to it, and with its other end I touched bass ground, output disappeared, touched circuits ground, same thing, I went randomly touching spots until I touched battery positive on the charging circuit, and magic happened! The noise was GONE!!!!!!!
The eq curve became the same as the one with the 9V disposable batteries, the noise was finally gone.
But why???
How is it possible?
I'm too noob to understand what's going on here, I'm glad the noise is gone, but at this point I wanna know why!
Thanks to anyone who will explain to me what's going on here (hopefully without telling me I gotta be shielding the circuits, and the bass, and myself, and my house... :icon_mrgreen:)
(https://htmlimg2.alldatasheet.com/htmldatasheet2/1132229/XLSEMI/XL6009E1/770/3/XL6009E1.png)
Hmmm...
That tab is the switch output. Connecting it to battery + ought to bypass the boost coil and the switch shorts the battery, yes? The battery wire on the charger is always connected to battery +?
Anyway, it was probably the capacitance of whatever touches the switcher tab that reduced the noise, so you might find a small value ceramic capacitor across the battery terminals - may be 10nF or smaller is needed.
Regards screening. The simplest thing to do is have the wires tightly twisted, although if it's extra-flex wire (probably the battery) it won't want to stay twisted.
Quote from: anotherjim on November 16, 2021, 05:42:20 AM
Hmmm...
That tab is the switch output. Connecting it to battery + ought to bypass the boost coil and the switch shorts the battery, yes? The battery wire on the charger is always connected to battery +?
The battery wires on the charger are both always connected to the battery, yes.
I don't know if it shorts the battery, the charger circuitry has protection against it, plus measuring with a multimeter it seems like the battery positive it's already connected to that switch cause there's continuity when checking...
Quote from: anotherjim on November 16, 2021, 05:42:20 AM
Anyway, it was probably the capacitance of whatever touches the switcher tab that reduced the noise, so you might find a small value ceramic capacitor across the battery terminals - may be 10nF or smaller is needed.
You mean a capacitor between positive and negative should do the same? Should it be ceramic, electrolytic or what? You think the alligator clip wire capacitance is doing it? If that's the case then I think the capacitor should be connected between the battery and the charger circuit just on the positive and not between positive and negative, as I wrote before there's continuity between the battery positive and that mosfet switch, so I guess the battery negative isn't involved here, right?
When high frequencies are around (the converter does 400kHz and there will be higher harmonics of that) audible noise seems to happen even though the source is supersonic. The HF can act as a carrier for noise that is audible, when it meets semiconductors the noise can be detected from the HF like a good old radio receiver.
The type of filter capacitor used becomes critical at higher frequencies. A 10nF ceramic disc can outperform a 10uF electrolytic. The reason is the inductance of the structure of the capacitor. At HF inductance raises the ESR. An electro cap is a wound component - it has something of an inductor coil about it while the ceramic disc is just what it looks like but even that has some self-inductance. A belt & braces approach to filtering employs an Electro (>=10uf) with a large ceramic (100nF) and a smaller ceramic (10nF).
There could be plenty of places to fit an extra capacitor. The converter already has some ceramic caps on in and out power connections but the application example (many cheap modules are the datasheet example circuit) shows 105 value or 1uF which will be an MLCC type. Adding 10nF disc caps across those should be better. Adding a cap to the switcher tab has implications for its switching performance - could cause trouble rather than help, but won't hurt to try.
Note that as all this noise is AC, it often does not matter if the + supply or ground are used to terminate a filter cap. There should be low impedance for AC between supply and ground.
Capacitance isn't the only way to filter. Ferrite rings over the wires raise the RF impedance in the wire blocking it. These are those lumps moulded in the ends of some USB cables for instance. If you were putting this together as a commercial product, you will have to do this stuff anyway to limit radiation to the outside world.
Wire has self-inductance and at very high frequency, there is the "skin resistance" so your croc clip lead may not act as the short circuit it appears to be, but more of a load impedance. This has implications when messing around trying stuff and if you touch anything your body capacitance and resistance will change the effects.
So, I was happy and thought I found the solution....
Oh I was wrong!
Connecting the SW to the battery positive just lasts 5 seconds, then the noise builds back up.
At this point the only thing I got rid of is the compression, and that's just by changing the step up converter with the other one...
Now while trying random things, I've put a resistor of around 300 ohms between the positive input and the positive output of the step up converter, noise gone, of course the resistor was getting hot so I took it off (no soldering, just croc leads), but what does it mean?
I'm kinda getting tired of this "solutions" without meaning....
Oh, there's 'meaning', but you have to be a rocket scientist to really deduce what it is! All these circuits can generally be modeled as resistances, inductances and capacitances, in series or parallel. All the poking around you're doing is changing some ratio of those here and there, affecting the outcome. Not that it's easy to know exactly HOW you're changing them...but sometimes that stuff gives clues.
I used to read old ARRL Ham Radio handbooks, which dealt with this a lot because radio involves much higher freq's than we deal with. It was pretty eye-opening (but complex). A resistor can exhibit properties of having a capacitor in parallel and/or an inductor in series with it, depending on what frequency signal you're passing thru it, for example. Parts are NON IDEAL in the real world because of how they're constructed and the laws of physics, meaning they come with other baggage...run 2 wires too close to each other, they can become an unwanted (or 'parasitic') capacitance. Drop an R in the right place (even by accident), you might shunt the parasitically coupled junk away by making an accidental filter...that's why finding your noise is so difficult, esp. at a distance...it's frustrating. Read about "non ideal properties of basic components", and that may give some meaning...
:icon_sad: :'(
Damn I opened a Pandora's box here!!!
Yup, you SHORE did, ha ha. In the end, some light reading about those parasitic effects - even if you don't fully understand it - might be enough to get the gist of what goes on. It's why LM386 amplifiers feedback and squeal, and so on. Applies to audio signals, power supplies like yours...it's also why correct wiring runs and shielding and the like are so important! Design and build 'good practices'...
Quote from: Thebrainless on November 16, 2021, 01:41:10 PM
So, I was happy and thought I found the solution....
Oh I was wrong!
Connecting the SW to the battery positive just lasts 5 seconds, then the noise builds back up.
At this point the only thing I got rid of is the compression, and that's just by changing the step up converter with the other one...
Now while trying random things, I've put a resistor of around 300 ohms between the positive input and the positive output of the step up converter, noise gone, of course the resistor was getting hot so I took it off (no soldering, just croc leads), but what does it mean?
I'm kinda getting tired of this "solutions" without meaning....
Some switching converters need a minimum load anyway but also any fast voltage spikes on the output will be weak and a load resistor will pull those spike voltages lower but not drop the 18v (just make it work harder) unless the current rating of the converter is exceeded. 300R dissipates 1W at 18v so hot and wasting 60mA from the battery.
Anyway, I have a feeling the problem lies with the bass preamp. Knowing it's going to be used with battery power, the designer probably didn't waste space on power supply filters, so any extra filtering should be as close to the preamp as possible.
First, find out how much current the preamp takes. Put a 10R resistor in series with the + or - power lead to the preamp and switch on. Measure the DC voltage across the 10R. Do Ohms law: current = voltage/resistance and report back.
Quote from: anotherjim on November 17, 2021, 05:26:16 AM
First, find out how much current the preamp takes. Put a 10R resistor in series with the + or - power lead to the preamp and switch on. Measure the DC voltage across the 10R. Do Ohms law: current = voltage/resistance and report back.
The preamp takes 16.5 mah, measured with the 2 disposable 9V batteries.
It's more than certain that the preamp was made without thinking about any other power source than 9V batteries I'm afraid :icon_frown:
Another Q
Does the PSU negative supply connect to the output jack ground? Measure resistance of this, please. Normally, you'd expect a preamp negative to go directly to ground but they may have done something clever that could catch us out.
Quote from: anotherjim on November 17, 2021, 01:06:15 PM
Another Q
Does the PSU negative supply connect to the output jack ground? Measure resistance of this, please. Normally, you'd expect a preamp negative to go directly to ground but they may have done something clever that could catch us out.
Yes, the negative from the 9V battery plug goes straight to the sleeve of the bass jack, the ring is conneted to ground, the tip I don't remember, so the circuit is closed only when a jack is in.
Ok, do you think you can find something like this in your part of the world...
https://www.amazon.com/YoCoo-Supply-Filter-Transmitter-Quadcopter/dp/B01KZHGWRW
An
LC power filter for DC-Converters.
It will work best wired as close as possible to the preamp.
Quote from: anotherjim on November 17, 2021, 04:51:01 PM
Ok, do you think you can find something like this in your part of the world...
https://www.amazon.com/YoCoo-Supply-Filter-Transmitter-Quadcopter/dp/B01KZHGWRW
An
LC power filter for DC-Converters.
It will work best wired as close as possible to the preamp.
Found that same part, 10€ shipped, it'll take one full month to arrive... Maybe it's better/faster/cheaper to diy it?
What is it made of, an inductor and a large capacitor, and what's that smd?
I've also found that there's a circuit used to eliminate ripple which is called "capacitance multiplier", made by a low value resistor and a capacitor plus an npn transistor or a mosfet, but I can't find info on what transistor choose and which values should I go for...
I've got a couple of transistors here, but who knows if they fit or not?
I'd have suggested DIY straight away, but inductors like that aren't all that well known to most of us here *. I just think an LC filter will be more effective than anything we might make with an RC filter and not waste battery power. A inductor in series is perfect for reducing high frequency noise as its impedance rises with increasing frequency while it's DC resistance is low so doesn't drop much voltage or get hot like a resistor would.
* Edit - the inductor is probably 100uH. Something like this...
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=246_250&products_id=1877
The SMD part you can see is a ceramic capacitor. As I mentioned, an Electrolytic type will not filter out RF frequency.
Almost certainly these filters are copied from a suggested application circuit in some manufacturers product data, but need to find some. The exact inductor value used ought to match a target noise frequency but a generic filter will probably come near enough.
If you want to try making an RC filter...
68R in series with the + preamp power wire. this will drop about 1v at 16mA
A 220uF electrolytic capacitor after the resistor connecting to - preamp power wire.
A 100nF ceramic capacitor added in parallel to the 220uF.
If necessary, a 10nF ceramic in addition to the 100nF to increase RF filtering.
Now, the above may not solve your problem in one hit, but it should be fitted anyway. The reason is that not all interference problems will be apparent at home. There could be things on stage that might radiate noise at you, and you might radiate noise at them. So you really should screen everything.
Quote from: anotherjim on November 18, 2021, 01:15:05 PM
I'd have suggested DIY straight away, but inductors like that aren't all that well known to most of us here *. I just think an LC filter will be more effective than anything we might make with an RC filter and not waste battery power. A inductor in series is perfect for reducing high frequency noise as its impedance rises with increasing frequency while it's DC resistance is low so doesn't drop much voltage or get hot like a resistor would.
* Edit - the inductor is probably 100uH. Something like this...
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=246_250&products_id=1877
The SMD part you can see is a ceramic capacitor. As I mentioned, an Electrolytic type will not filter out RF frequency.
Almost certainly these filters are copied from a suggested application circuit in some manufacturers product data, but need to find some. The exact inductor value used ought to match a target noise frequency but a generic filter will probably come near enough.
If you want to try making an RC filter...
68R in series with the + preamp power wire. this will drop about 1v at 16mA
A 220uF electrolytic capacitor after the resistor connecting to - preamp power wire.
A 100nF ceramic capacitor added in parallel to the 220uF.
If necessary, a 10nF ceramic in addition to the 100nF to increase RF filtering.
Now, the above may not solve your problem in one hit, but it should be fitted anyway. The reason is that not all interference problems will be apparent at home. There could be things on stage that might radiate noise at you, and you might radiate noise at them. So you really should screen everything.
I've already tried rc filtering, a bunch of different frequencies, the only one really effective that doesn't square the bass signal is the one at 60hz, only downside is the noise is still there, low enough to be playable on the clean channel, but to high when going overdrive, since I'm in overdrive 99% of the times...
I guess I'll try the LC filter then, that 101 inductor seems to be 100uh, I can get a bunch of them no problem, the question here's the values of other components besides that big electrolytic... Plus I've read an LC filter should be set on the frequency of the switching supply, but how do I find such frequency? Then how do I decide components values? I'll keep looking for infos then at some point I'll try random values like I did with the RC filter, and let's hope for the best!
I'm not sure what you already tried, since I or anyone else here really knows if you've taken many of the suggestions here seriously/literally and how or where you tried them. I know you say you tried RC filter but have you made and fitted the one I just recommended? Did you screen the wires & cavities? I'm trying to tell you it should be done and kept whether or not it fixes this particular noise problem. And what about the guitars pickup cavities - are they screened.
Proper filtering requires taking measures you may never know you need.
The datasheet I posted of the converter chip shows a 400Khz oscillator.
The inductors are cheap - try them!
There's no reason not to try inductors in series with the negative power wires as well as the positive.
Quote from: anotherjim on November 19, 2021, 04:47:49 AM
I'm not sure what you already tried, since I or anyone else here really knows if you've taken many of the suggestions here seriously/literally and how or where you tried them. I know you say you tried RC filter but have you made and fitted the one I just recommended? Did you screen the wires & cavities? I'm trying to tell you it should be done and kept whether or not it fixes this particular noise problem. And what about the guitars pickup cavities - are they screened.
Proper filtering requires taking measures you may never know you need.
The datasheet I posted of the converter chip shows a 400Khz oscillator.
The inductors are cheap - try them!
There's no reason not to try inductors in series with the negative power wires as well as the positive.
I understand, I haven't shielded everything yet, just tried on the circuits and saw little to none improvement, so I thought it might be avoided since to shield every cavity is a PITA, but still I've ordered adehesive brass tape to eventually do it...
Your filter I haven't yet tried, I've tried simple Rc filters like this
(https://i.postimg.cc/2LDs49vz/rcf.jpg) (https://postimg.cc/2LDs49vz)
With always 10 uf 50V capacitor and various resistors to change frequencies (I've posted video results earlier anyway).
I just think "if the only variable I've added to the equation is those circuits, the problem must be found there, not in the bass shielding or preamp or whatever"
I've tried shielding the step up circuit by enveloping it in an aluminum case isolated from the circuit and going to ground, it changed nothing, so again why bother keeping it?
Maybe my approach here is wrong, I don't know, but I'm going with what I try and learn, and if something useless...
Anyway, as I wrote before, Iìm waiting for the shielding tape so I'll be shielding the F out of the whole bass, I know that won't hurt so it's something I'll be doing for sure.
I've looked further into voltage regulators and stuff, so I'm waiting to get a 7818 chip, to try if putting it to regulate the voltage after the step up converter might work.
It might be an overkill, or at least a waste of current, cause 7818 has a drop of around 2V, so the step up must be set to around 20V in order to get a clean and stable 18V after it, that means lower current available from the battery, if I got it right, but it's a little price to pay in case this will work...
Then I'm waiting for a circuit which includes both lithium charger/protection and step up converter in the same small pcb, maybe it'll work better with less noise? I'll see...
If I think about all the money spent on circuits and stuff until now, it'd have been the same as if I bought the fishman battery pack, but where's the fun then?! :icon_mrgreen:
Oh, talking about that, here's a close up of it's circuits, but it's just one side and it's all smd, so it's pretty impossible for me to understand what's going on
(https://i.postimg.cc/BLLFxM3w/750-Fluence-Uni-BP-detail2.jpg) (https://postimg.cc/BLLFxM3w)
I'm having fun anyway, kinda frustrating fun sometimes, but still I'm learning a lot...
So let's wait for all the stuff the arrive then I'll try those other solutions!
VICTORY IS MINE!!!
I've managed to solve the problem, now the bass is more silent than before, with no square signals, no strange noises, even the normal noise to signal ratio has improved.
All it took was to use the bigger dc dc converter that has less noise on its own, and put a voltage regulator right after it, before hitting the preamp.
So It's lithium battery - charge/control circuit - step up dc dc converter - voltage regulator circuit - preamp.
Here's the voltage regulator circuit:
(https://i.postimg.cc/yJDMt5qM/18-volt-power-supply-circuit.jpg) (https://postimg.cc/yJDMt5qM)
It's a simple circuit found online, nothing crazy, but I thought that a stable DC could be the solution, and apparently it is!
The only downside is the 7818 IC works with a higher voltagethan 18 V to give a stable 18 V on the output, so the converter is set to 19.3 V in order to have a stable 18.1 V, there's a loss of 1.2 V , so apparently I've got 590 mah from the battery instead of 630 mah, I've lost 2 and a half hours of playing, but gained a clean and stable signal, so it's a great bargain IMHO!!!
I've managed to cram the circuits in the bass battery cavity, and the battery sits just above the potentiometers in their cavity, so from outside it's a clean job, If you want photos lemme know, I could also make a video about this journey as well, since it was my goal from the beginning....
Thank you everyone for all the infos and suggestions, even though you guys are a little too worried about shielding :icon_lol: but I know it helps as well.
Now the next project will be....
:icon_question: :icon_question: :icon_question: :icon_question: :icon_question: :icon_question:
I'm surprised it requires that much regulation, but then - I'm not surprised :) Great work!