Let’s talk about voltages

Yorkie · August 2021

I've got like a million questions on voltages in pedals. But before we begin, let us pretend for a moment that I don't know anything about engineering or physics, and just tell me what the hell is going on.

Not untrue. I do have some degrees, but for the purpose of this thread I think it's better if we assume that I don't know anything.
So here we go. Please feel free to answer or comment on any or all of the questions; or question the questions, whatever feels right.

- Why did folks start to use 9V for all-analog, transistor-based pedals?
- Why do we keep using 9V nowadays in many all-digital pedals?
- Would USB-rechargeable pedals make sense? I've seen some TC Electronic ones use USB for data transfer, but not for charging.
- I know there are some pedals that use higher voltages (those with valves?). Wouldn't USB-C – which has got power delivery modes of up to 20V@5A – provide a one-size-fits-all alternative? e.g. supply 5V to some pedals, 9V to others, 20V to the valve-based ones?

Please contribute!
Jon

menamestom · August 2021

I like high voltage.

When we touch, when we kiss.

digitalkettle · August 2021

I prefer concrete shoes, cyanide, tnt…

Yorkie · August 2021

menamestom said:

I like high voltage.

When we touch, when we kiss.

Cirrus · August 2021

Why 9v? I suspect it might have something to do with this little feller;

Duracell Plus Power Battery 9V

ecc83 · August 2021

9V: Because the first transistor radios used the PP3 battery which MAY have been invented for that very purpose? The Germanium transistors of the day had a collector-emitter Vce of around 20V so, since they used audio transformers, 10V was about all they could stand.

USB rechargeable: Very inconvenient if you have a gig and forgot to charge it! The best option IMHO is 4x AA rchbl and a built in DC-DC converter to develop~10V. You should also always have the option to fit bog S alkalines.

Higher voltages just give you higher operating levels which you don't need at the front of an amp and most FX loops run at -10dBV (300mV) if properly designed.

Lastly, guitarist are VERY conservative you change formats at your commercial peril!

Dave.

ICBM · August 2021

Yorkie said:

- Why did folks start to use 9V for all-analog, transistor-based pedals?

As said above, because the original portable transistor devices - radios mostly - used either PP3 or PP9 batteries, which are made with six 1.5V zinc-carbon cells in series. (Hence why not 10V, or another 'more round' number.)

Yorkie said:

- Why do we keep using 9V nowadays in many all-digital pedals?

Because the power supplies already exist so it's convenient. It's also simple to regulate 9V down to the 5V most digital chips use while leaving enough headroom for the analogue input and output stages.

Yorkie said:

- Would USB-rechargeable pedals make sense? I've seen some TC Electronic ones use USB for data transfer, but not for charging.

More complexity and potential unreliability than the job needs. The great beauty of a 9V battery is that you can change it in seconds if you need to. You can even nip out of the venue to a handy all-night shop if you've forgotten to bring a spare one!

Yorkie said:

- I know there are some pedals that use higher voltages (those with valves?). Wouldn't USB-C – which has got power delivery modes of up to 20V@5A – provide a one-size-fits-all alternative? e.g. supply 5V to some pedals, 9V to others, 20V to the valve-based ones?

It might be a worthwhile idea, but the historical incompatibility of pedals built before it was introduced would hinder uptake, I think. It wouldn't be particularly attractive to small builders either, the extra circuitry to sense and control the voltage is not something most would probably want to try implementing... since I suspect it's one of the main reasons even something as relatively simple as buffered bypass switching is rarely used.

Danny1969 · August 2021

The trouble with USB C is you would need a relatively complex bit of circuitry in the pedal to tell the charger what voltage is required and how much current the pedal can take (USB C is designed really for rechargeable devices so the charger needs to know how quick it can safely charge whatever it is connected to.
In most drive, compressor pedals etc the circuit required to handshake with the PSU would be more complex than the actual pedal circuit. And make the pedal much more unreliable, plus add a load of noise.

I write off a lot of laptops boards because this handshake portion of the circuit is quite easily damaged, leaving a laptop stuck at 5V rather than 20V it needs.

If you consider something like a Tubescreamer, it's not really a 9V circuit. You can run it form 3V or 20V as long as the caps are within their max voltage. The actual circuit operates at half the supply, it's biased in the middle so it can swing positive and negative directions in order to follow the positive and negative waveform from the guitar. So 4.5V is a kind of fake 0V that can be swung below or above by roughly 4V either way. If you connect a 5V battery then the bias network would set it at 2.5V as the actual bias is normally achieved with a simple resistor voltage divider. If 2 identical value resistors are put in series across a voltage difference then their junction will be half that voltage difference. If you use a lower voltage you won't notice until your signal is larger than the circuit can amplify without hitting the voltage limit of it's rails. Then it will run out of headroom and distort. That's what headroom is .... how much voltage swing between barely registering and clipping the rail. The higher the voltage rail the more headroom .... but big headroom in a pedal is pointless as the input of the amp will clip before the pedal a lot of cases.

For my own designs I tend to use 12V AC because it's relatively easy to get a dual supply from a single ended AC meaning I can run the internal circuit at +12 - 0 - 12V which simplifies coupling opamps and allows a larger swing for line level circuits.

Yorkie · August 2021

ecc83 said:

Lastly, guitarist are VERY conservative you change formats at your commercial peril!

Agreed, I know I am too... just to be clear, I am not wanting to implement or commercialise any of these ideas, just seeing if they would make any sense.

Yorkie · August 2021

Danny1969 said:
I write off a lot of laptops boards because this handshake portion of the circuit is quite easily damaged, leaving a laptop stuck at 5V rather than 20V it needs.

Sounds terrifying, considering how many USB-C devices I own. Hopefully designs will get better/safer with time.

If you consider something like a Tubescreamer, it's not really a 9V circuit. You can run it form 3V or 20V as long as the caps are within their max voltage. The actual circuit operates at half the supply, it's biased in the middle so it can swing positive and negative directions in order to follow the positive and negative waveform from the guitar. So 4.5V is a kind of fake 0V that can be swung below or above by roughly 4V either way. If you connect a 5V battery then the bias network would set it at 2.5V as the actual bias is normally achieved with a simple resistor voltage divider. If 2 identical value resistors are put in series across a voltage difference then their junction will be half that voltage difference. If you use a lower voltage you won't notice until your signal is larger than the circuit can amplify without hitting the voltage limit of it's rails. Then it will run out of headroom and distort. That's what headroom is .... how much voltage swing between barely registering and clipping the rail. The higher the voltage rail the more headroom .... but big headroom in a pedal is pointless as the input of the amp will clip before the pedal a lot of cases.

For my own designs I tend to use 12V AC because it's relatively easy to get a dual supply from a single ended AC meaning I can run the internal circuit at +12 - 0 - 12V which simplifies coupling opamps and allows a larger swing for line level circuits.

Fascinating. Where can I read about the relationship between voltage and headroom? I don't immediately understand what headroom means.

Yorkie · August 2021

ICBM said:
It might be a worthwhile idea, but the historical incompatibility of pedals built before it was introduced would hinder uptake, I think. It wouldn't be particularly attractive to small builders either, the extra circuitry to sense and control the voltage is not something most would probably want to try implementing... since I suspect it's one of the main reasons even something as relatively simple as buffered bypass switching is rarely used.

I suppose this would make more sense in a completely new line of digital-only pedals, where the USB-C cable could serve not just for power delivery but data transfer, keeping the audio in digital form until the last pedal, which would have to be a DAC of some sort... or a class D amplifier. It actually sounds kind of terrifying.

Any makers reading this: please forget I've said it, it's a really, really bad idea.

Jon

Cols · August 2021

I thought that was a really interesting question, and a great example of the expertise of the forum in giving the background of 9V and pitfalls of USB power.

There are USB rechargeable power supplies now available, but no idea if they’re any good.

Yorkie · August 2021

Cols said:

I thought that was a really interesting question, and a great example of the expertise of the forum in giving the background of 9V and pitfalls of USB power.

Image: https://gifs.cackhanded.net/ghostbusters/no-studying.gif

Not just the expertise, but the patience most folks here show with newbies like me. I would never have posted these questions on a different forum. This is a truly special place.

Jon

Danny1969 · August 2021

It was a good question and I honestly think out country does need a rethink about power in general. The trouble is in this country we implement something out of necessity to suit the situation at the time but then refuse to budge from it, even when those circumstances are no longer relevant and it's detrimental and wasteful to stick to it.

Take the mains rings in a house. It was good idea after the war as it saves on copper and back then everything ran on 240 but it's not the best or safest way to run a house now. Only around 10% of the stuff in a house actually runs from a native 240V, the other 90 % has to rectify this voltage to 320V DC and then switch it down to something that is usable for modern electronics.

The American system has a lot of flaws (lack of fuses in plugs etc) but the way they implement their 240V is a lot better with a centre tap. So most things run from a safer 120V around the house with the full 240V generally going to big things like aircon units and washing machines.

Take lighting in a modern house. We can easily generate a perfectly good low voltage from solar panels / storage batteries more or less perfect for modern LED bulbs but in out current setups this low voltage is stepped up to 240V with an inverter only to be sent to the bulb and electronically switched back to 5V or so within the bulb. That's around 15 to 20% power lost to heat in pointless conversion.

At some point hopefully there will be a rethink as the complexity and cost of our common electronics could be reduced and safety improved if we redesigned our mains system to suit the way we live now.

ecc83 · August 2021

Sorry Danny, I don't agree. 120V is not THAT much less lethal than 240V (and 240 garners some respect?) For any given appliance power rating current for 120V is doubled and thus cables have to be heavier (an IEC cable would e.g. only be rated to 1.2kW) Copper losses are proportional to current so transformers would be less efficient unless you made them bigger for a given VA.

I would aver that our '13A' ring main system is the most efficient and safe in the world. Then, if you Google it you will find that 230/240V is the MOST common supply across the world. The Americas are really the only significant market for the puny voltage!

Headroom: Just the extra signal handling capacity above the 'normal operating level'. That last in a the guitar world is a bit vague but is generally taken as 300mV/-10dBV and so the headroom is usually 20dB =x10 above that or +9.5dBV/3.0V say +10dBV for jazz?

In the pro studio world OP level is +4dBu, about 1V and so headroom is 10V/ +22dBu (yes! I know the decibbale is a bit hard to follow! You don't need to know)

Dave.

ecc83 · August 2021

Yorkie said:

Cols said:

I thought that was a really interesting question, and a great example of the expertise of the forum in giving the background of 9V and pitfalls of USB power.

Not just the expertise, but the patience most folks here show with newbies like me. I would never have posted these questions on a different forum. This is a truly special place.

Jon

Pleasure Jon. You will also find Sound on Sound forum and homercording.com equally civilized.

Dave.

Danny1969 · August 2021

ecc83 said:

Sorry Danny, I don't agree. 120V is not THAT much less lethal than 240V (and 240 garners some respect?) For any given appliance power rating current for 120V is doubled and thus cables have to be heavier (an IEC cable would e.g. only be rated to 1.2kW) Copper losses are proportional to current so transformers would be less efficient unless you made them bigger for a given VA.

I would aver that our '13A' ring main system is the most efficient and safe in the world. Then, if you Google it you will find that 230/240V is the MOST common supply across the world. The Americas are really the only significant market for the puny voltage!

Headroom: Just the extra signal handling capacity above the 'normal operating level'. That last in a the guitar world is a bit vague but is generally taken as 300mV/-10dBV and so the headroom is usually 20dB =x10 above that or +9.5dBV/3.0V say +10dBV for jazz?
In the pro studio world OP level is +4dBu, about 1V and so headroom is 10V/ +22dBu (yes! I know the decibbale is a bit hard to follow! You don't need to know)

Dave.

Dave, the supply to an American house IS 240V, or rather 220 ish to 235 is typical. It's just also centre tapped so rooms that only require 120V can have it and for a given skin / flesh resistance 120V will push half the current through your body and the skins zener effect is also harder to trigger due to the reduced voltage.

Anything that needs 240V in a north American house is either wired directly into the wall or uses one of 3 special high voltage plugs.

They also don't tend to use mains rings on circuits so don't suffer the fault where someone can breach on end of the ring leaving the rest of it only capable of carrying half the current without anyone being any the wiser in older installations.

Headphones · August 2021

I must point out that next to nothing does this:

"has to rectify this voltage to 320V DC"

Absolutely not 90%. Perhaps 0.009%...

Where does such clearly false data come from? I thought they'd changed presidents.

ecc83 · August 2021

Danny1969 said:

ecc83 said:

Sorry Danny, I don't agree. 120V is not THAT much less lethal than 240V (and 240 garners some respect?) For any given appliance power rating current for 120V is doubled and thus cables have to be heavier (an IEC cable would e.g. only be rated to 1.2kW) Copper losses are proportional to current so transformers would be less efficient unless you made them bigger for a given VA.

I would aver that our '13A' ring main system is the most efficient and safe in the world. Then, if you Google it you will find that 230/240V is the MOST common supply across the world. The Americas are really the only significant market for the puny voltage!

Headroom: Just the extra signal handling capacity above the 'normal operating level'. That last in a the guitar world is a bit vague but is generally taken as 300mV/-10dBV and so the headroom is usually 20dB =x10 above that or +9.5dBV/3.0V say +10dBV for jazz?
In the pro studio world OP level is +4dBu, about 1V and so headroom is 10V/ +22dBu (yes! I know the decibbale is a bit hard to follow! You don't need to know)

Dave.

Dave, the supply to an American house IS 240V, or rather 220 ish to 235 is typical. It's just also centre tapped so rooms that only require 120V can have it and for a given skin / flesh resistance 120V will push half the current through your body and the skins zener effect is also harder to trigger due to the reduced voltage.

Anything that needs 240V in a north American house is either wired directly into the wall or uses one of 3 special high voltage plugs.

They also don't tend to use mains rings on circuits so don't suffer the fault where someone can breach on end of the ring leaving the rest of it only capable of carrying half the current without anyone being any the wiser in older installations.

Yes Dan, I am aware of their dual voltage system. Seems rather complicated for domestic supplies? We of course have 3ph supplies for heavy users but that entails no special wiring as of course 3p comes from the subs...Which are massive and very efficient unlike I would guess a load of 'pole pigs' (that seem prone to blowing up if Hollywood is to be believed!)

Yes, peak rectified 240V is 340V as near as but will not be anywhere near that on load. The growth of very reliable SMPSUs has improved the efficiency of 'small' supplies greatly. At full load they are not that much more efficient than a well designed toroid and rect/caps supply but they draw next to nothing off load.

Err...HOW can you have an "end of a ring"?

Dave.

Danny1969 · August 2021

Yes Dan, I am aware of their dual voltage system. Seems rather complicated for domestic supplies? We of course have 3ph supplies for heavy users but that entails no special wiring as of course 3p comes from the subs...Which are massive and very efficient unlike I would guess a load of 'pole pigs' (that seem prone to blowing up if Hollywood is to be believed!)

Yes, peak rectified 240V is 340V as near as but will not be anywhere near that on load. The growth of very reliable SMPSUs has improved the efficiency of 'small' supplies greatly. At full load they are not that much more efficient than a well designed toroid and rect/caps supply but they draw next to nothing off load.

Err...HOW can you have an "end of a ring"?

Dave.

Forget the load, that's not the point, the point is you now need bulk caps rated at that working voltage, load or no load. For any given value of capacitance, the higher the working voltage the more expensive it will be

As for one end of a ring consider a typical mains ring and then disconnect one end to simulate someone cutting through it with a plasterboard saw.
Your mains ring will still work, all sockets will still work, you will be none the wiser but it will now only be capable of half the current it was before.

ecc83 · August 2021

"As for one end of a ring consider a typical mains ring and then disconnect one end to simulate someone cutting through it with a plasterboard saw.

Your mains ring will still work, all sockets will still work, you will be none the wiser but it will now only be capable of half the current it was before." Oooo! That's bit of a stretch! Still, UK 2.5mm is very conservatively rated and so will safely carry the current SHOULD someone put a~7kW load on the end and the breakers will trip long before our cables catch fire!

I take you point about HV caps but they HAVE proved very reliable. How many millions in PC supplies? I sort I agree about a secondary LV supply for LV DC kit* but the average Joe has enough trouble with 'audio volts and mains volts' The potential for disaster causes me the galloping ***ts!

*I have a 12V DC system in my garden, runs a porch security light and will run other stuff. Rescued car batteries on solar panels.

Dave.

crunchman · August 2021

A 12 or 24V DC system in the house for lighting and smaller devices would be good. LED lights don't need 240V, and most modern digital electronics don't. 24V would probably be better as the higher voltage would require lower currents, and there would be less losses.

If you had that, then you could put solar panels on to feed it, with a battery for storage, and you wouldn't need all the inverters and other complications that come with a solar installation at the moment.

It would also be safer with less 240V wiring around the house. People doing DIY would have a lot less risk of drilling into a 240V cable.

ecc83 · August 2021

crunchman said:

A 12 or 24V DC system in the house for lighting and smaller devices would be good. LED lights don't need 240V, and most modern digital electronics don't. 24V would probably be better as the higher voltage would require lower currents, and there would be less losses.

If you had that, then you could put solar panels on to feed it, with a battery for storage, and you wouldn't need all the inverters and other complications that come with a solar installation at the moment.

It would also be safer with less 240V wiring around the house. People doing DIY would have a lot less risk of drilling into a 240V cable.

Nice idea but such a system would be 'noisy' prone to picking up mains hum and other clicks and RF noises so some filtering would be needed. Do not forget as well that digital circuits need 5V, sometimes at significant current and so converters will still be needed. You also have the massive logistical task of finding a standard connector for all this!

Yes, high voltages are dangerous but so too are low Vs with high current capacity, I know a guy who got his wedding ring welded to a car supply! However we distribute electricity it must be done with care and knowledge of the hazards.

ICBM · August 2021

crunchman said:

A 12 or 24V DC system in the house for lighting and smaller devices would be good. LED lights don't need 240V, and most modern digital electronics don't. 24V would probably be better as the higher voltage would require lower currents, and there would be less losses.

If you had that, then you could put solar panels on to feed it, with a battery for storage, and you wouldn't need all the inverters and other complications that come with a solar installation at the moment.

It would also be safer with less 240V wiring around the house. People doing DIY would have a lot less risk of drilling into a 240V cable.

But that would double the installation cost since you’d still need the 240V supply for the high-power appliances.

I also wouldn’t totally discount cable losses even over distances in a house, at the sort of currents a house full of 24V devices will draw in total.

Danny1969 · August 2021

This summer I was going to build a summer house at the bottom of the garden that could also function as a bit of an office. I had to shelf the idea when the cost of materials doubled but I did think out what I was going to do electricity wise and decided I could manage without the ball ache cost of 240V

So lights, laptop, printer, beer fridge, router are basically what's needed. I thought maybe I could build a large battery pack from 18650 cells, put some solar panels on the roof to charge it with the option of also charging from a mains cable if necessary Then put a 20V and a 5V rail around the place to power the various bits and pieces.
Heating would be an issue but my house is more than big enough so wouldn't bother using it in the winter.

JohnS37 · August 2021

Cirrus said:

Why 9v? I suspect it might have something to do with this little feller;

Yup. That’s it, right there.

Headphones · August 2021

What domestic system rectifies the mains direct?

I'm struggling to think of any.

A few industrial, but consumer/home?

More than the odd incorrect assumption in this debate (including that 110 is safe...).

ICBM · August 2021

Headphones said:

What domestic system rectifies the mains direct?

I'm struggling to think of any.

A few industrial, but consumer/home?

None I can think of after the 1950s - a lot of radios back then used direct rectification for the HT and series filament connections (like Christmas tree lights) for the valve heaters, so avoiding the cost of a power transformer, and meaning that they could also run from the obsolete pre-war 240V DC supplies that hadn’t been replaced yet.

There are even some old guitar amps that do - I’ve worked on a couple of very early late-40s/early-50s Selmers like that - as you can probably imagine, they’re very difficult to make safe for modern use.

Danny1969 · August 2021

Headphones said:

What domestic system rectifies the mains direct?

I'm struggling to think of any.

A few industrial, but consumer/home?

More than the odd incorrect assumption in this debate (including that 110 is safe...).

Everything with a SMPS rectifies the mains directly ... the 240V is put straight on the bridge rect

110V is safer (not safe) than 240V for obvious reasons relating to Ohms law

ICBM · August 2021

Danny1969 said:

Everything with a SMPS rectifies the mains directly ... the 240V is put straight on the bridge rect

Doh... yes of course

. The isolating transformer is downstream of the rectifier.

Cols · August 2021

I can’t believe that an interesting and relevant question about why we use 9V for guitar pedals has degenerated into a fierce-but-watching-paint-dry argument about domestic power supplies in less than 2 pages.

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