Circuit to drop 9vdc to 1.5vdc?

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Post by Cableaddict »

My electronics knowledge is pretty basic.

I want to run my Maestro Fuzz-Tone FZ-1A, which runs on 1.5vdc, off my pedalboard psu. It's a Voodoo Labs, so I could dial -down one of the outputs, but I'd be worried that it might accidentally get bumped up.

Is there a circuit diagram available for a simple 9vdc - to - 1.5 vdc converter, either stand-alone or something I'd build into the pedal? - Having variable voltage would be even better, though I could of course just swap-in a pot.

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Post by kleuck »

Just put a 7,5 volts zener in your pedal.
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Post by GuitarlCarl »

I'd just use the "dialed" down line on your supply, why think about "swapping in a pot" when you already have it in your supply? Put some tape on the "dial" so it can't get bumped. Extra benefit...dirt cheap.
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Post by kaycee »

Its easy enough to include a voltage regulator in your build. Just a couple of parts, the LM338T for example. Check page 7 of the datasheet for a schematic with part values:

http://pdf1.alldatasheet.com/datasheet- ... M338T.html

You could build it on a small piece of vero and then run off of your 9 volt supply or a battery and not worry about keeping an outlet dialled down to 1.5 or accidentally plugging in to a 9 volt supply and frying something (more likely it just won't work as the bias is out). I use this method for similar circuits and works fine.

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Post by mictester »

Cableaddict wrote:My electronics knowledge is pretty basic.

I want to run my Maestro Fuzz-Tone FZ-1A, which runs on 1.5vdc, off my pedalboard psu. It's a Voodoo Labs, so I could dial -down one of the outputs, but I'd be worried that it might accidentally get bumped up.

Is there a circuit diagram available for a simple 9vdc - to - 1.5 vdc converter, either stand-alone or something I'd build into the pedal? - Having variable voltage would be even better, though I could of course just swap-in a pot.
This is easier than you might imagine! Get (say) a 4k7 resistor and a red LED. Connect across a 9V supply, with the resistor connected to the +9V, so that the LED lights up. You'll find that you've got almost exactly 1.6V across the LED so connect the junction of the resistor and the LED as the + supply to the pedal and the other side of the LED as ground.

If you have a PNP version (which has the battery + connected to ground) you're going to have to use a slightly more involved circuit. Examine the fuzz box and let us know how the battery's connected up.
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Post by kleuck »

mictester wrote:
Cableaddict wrote:My electronics knowledge is pretty basic.

I want to run my Maestro Fuzz-Tone FZ-1A, which runs on 1.5vdc, off my pedalboard psu. It's a Voodoo Labs, so I could dial -down one of the outputs, but I'd be worried that it might accidentally get bumped up.

Is there a circuit diagram available for a simple 9vdc - to - 1.5 vdc converter, either stand-alone or something I'd build into the pedal? - Having variable voltage would be even better, though I could of course just swap-in a pot.
This is easier than you might imagine! Get (say) a 4k7 resistor and a red LED. Connect across a 9V supply, with the resistor connected to the +9V, so that the LED lights up. You'll find that you've got almost exactly 1.6V across the LED so connect the junction of the resistor and the LED as the + supply to the pedal and the other side of the LED as ground.

If you have a PNP version (which has the battery + connected to ground) you're going to have to use a slightly more involved circuit. Examine the fuzz box and let us know how the battery's connected up.
You can't do that as the led needs more current than the circuit itself will consume if you want as steady voltage, silly waste of power, as would be a regulator dropping 7,5 volts, even if the circuit does not consume a lot, the cost of the regulator is silly for such a simple task : the best trick by far is the Zener if you just want to drop a voltage
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Post by mictester »

kleuck wrote: You can't do that as the led needs more current than the circuit itself will consume if you want as steady voltage, silly waste of power, as would be a regulator dropping 7,5 volts, even if the circuit does not consume a lot, the cost of the regulator is silly for such a simple task : the best trick by far is the Zener if you just want to drop a voltage
You obviously know so much more about electronics than me. Perhaps I should retire.

Where does the 7V5 magically disappear to in your zener? How are you going to get a consistent voltage as battery voltage falls?

What is the current consumption of an LED powered with a 4k7 resistor? I'll give you a clue - it's ~1.6 mA. With the added 2 mA drawn by the fuzz circuit, your 9V battery will last for several months.

If you want to compensate for the drooping battery voltage, you can configure any FET as a Norton diode to feed the resistor and LED.... I'm sure that this expert "kleuck" will be able to explain how to do that....
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Post by kleuck »

mictester wrote:
kleuck wrote: You can't do that as the led needs more current than the circuit itself will consume if you want as steady voltage, silly waste of power, as would be a regulator dropping 7,5 volts, even if the circuit does not consume a lot, the cost of the regulator is silly for such a simple task : the best trick by far is the Zener if you just want to drop a voltage
You obviously know so much more about electronics than me. Perhaps I should retire.

Where does the 7V5 magically disappear to in your zener? How are you going to get a consistent voltage as battery voltage falls?

What is the current consumption of an LED powered with a 4k7 resistor? I'll give you a clue - it's ~1.6 mA. With the added 2 mA drawn by the fuzz circuit, your 9V battery will last for several months.

If you want to compensate for the drooping battery voltage, you can configure any FET as a Norton diode to feed the resistor and LED.... I'm sure that this expert "kleuck" will be able to explain how to do that....
First, the topic is not "How can i have a 1,5 volts regulated supply from a 9 volts one" but "Circuit to drop 9vdc to 1.5vdc?"
So, the voltage would not be more or less consistent with a Zener dropper or not : just the same.
Second : it's in all books that if you want a steady voltage and current from a simple led regulator, the led must be feeded with something like 10 times the current consumed by the circuit itself, but i begin to think that you actually did not read a lot of theory about electronics....
If you try to take more, the resistor will become the dropper, and will drop voltage a lot more than you want.
It's pretty obvious : you can't feed a low impedance circuit with a higher one, in other words : you can't take more current than the power circuit can give.
Otherwise, we could built 50 watts amps with a 10 watts power transformer.
Obviously stupid.
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Post by earthtonesaudio »

Just dial it down with the Voodoo Labs supply. There's no reason to be worried about accidentally bumping up the voltage because that particular circuit can take it, although it may sound weird.

Do make sure to use the correct polarity of power though.
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Post by JakeAC5253 »

The Voodoo Labs only goes down to 3v per channel. Just use Ohm's Law to figure out how much current the unit is going to take, and then Ohm's law again to construct a voltage divider for the power input circuit.

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Post by kleuck »

With a voltage divider, if you want a steady voltage, it's the same as with a Led regulator : you need a voltage divider with a lower impedance than the pedal itself, it's a waste of power, needs 1 watts resistors, etc.
Added to that : all these tricks are TWO components tricks, at least (a decoupling cap would be a good idea in all cases >> 3 components) where the Zener trick only needs one component (two with a noise-killing cap)
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Post by earthtonesaudio »

Have you actually tried a series zener in this circuit, kleuck? I doubt it would work. The current consumption of a FZ-1A is on the order of a couple hundred micro-amps, and that number will vary depending on how the gain pot is set, and from one unit to the next, and with temperature. Zener impedance rises as you decrease their current, so at this current the zener will be a nonlinear and high-impedance voltage source; the circuit will not work correctly.

Incidentally, if you used a resistive divider (9V input, 600 ohms series, 100 ohms shunt) the current in the divider will be 12.8mA (which is at least 50x the circuit current), and the power dissipated in the 600 ohm resistor will be about 100mW which means you can use 1/8W resistors without exceeding their power rating (although I would use 1/4W resistors anyway for better safety factor, lower noise).
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Post by kleuck »

earthtonesaudio wrote:Have you actually tried a series zener in this circuit, kleuck? I doubt it would work. The current consumption of a FZ-1A is on the order of a couple hundred micro-amps, and that number will vary depending on how the gain pot is set, and from one unit to the next, and with temperature. Zener impedance rises as you decrease their current, so at this current the zener will be a nonlinear and high-impedance voltage source; the circuit will not work correctly.

Incidentally, if you used a resistive divider (9V input, 600 ohms series, 100 ohms shunt) the current in the divider will be 12.8mA (which is at least 50x the circuit current), and the power dissipated in the 600 ohm resistor will be about 100mW which means you can use 1/8W resistors without exceeding their power rating (although I would use 1/4W resistors anyway for better safety factor, lower noise).
Ho if the consumption of FZ-1A is that low, you may be right -i do not have one so i did not test with this circuit, i did with others- and in this case, the LED regulator would be the best solution indeed, but it's not a "generic" solution at all.
But are you sure that Zener would behave in a non-linear way ? 0,2 mA is not that low -will give it a test.
Anyway, with power supply, we can afford to waste 2 mA or more.
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Post by kleuck »

Edit : just tested with a 8,2 volt zener (i do not have lower value at the time, it's a BZX85C) from 0,1 to 0,4 mA, and the voltage drop actually varies, but from 7,99 volts to 8,02 volts...0,03 volts for a 400% variation in current doesn't look like a big issue for me :)
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Post by GuitarlCarl »

First, the topic is not "How can i have a 1,5 volts regulated supply from a 9 volts one" but "Circuit to drop 9vdc to 1.5vdc?"
Dude, it's gonna run a pedal, I'd want it to be consistent.
You can't do that as the led needs more current than the circuit itself will consume if you want as steady voltage, silly waste of power,
What is the current consumption of an LED powered with a 4k7 resistor? I'll give you a clue - it's ~1.6 mA.
Of course sometimes it's ok to have a silly waste of power...
Anyway, with power supply, we can afford to waste 2 mA or more.
(I think he just wants to argue...)
in this case, the LED regulator would be the best solution indeed, but it's not a "generic" solution at all.
Did he just admit Mic's answer was the best solution??? AHHH but it's not generic... Wait...generic?
Added to that : all these tricks are TWO components tricks
How about a cost break down too... dude, it's a resistor and a led, I have those in my parts bin...
Really I like kaycee's solution best. Why skimp on parts?
Next crap I guess your gonna tell me is my telecaster can be made brighter by putting 500k pots in it... :slap:
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Post by kleuck »

Yes, perhaps Mictester's solution is the best (but imo with higher current for the LED, i'll explain) so what ?
Voltage would not be more or less consistent with a series dropper if you take it from a power supply you know, theoretically at least.
A telecaster sometimes needs to be brighter, a friend has one with an Alnico 3 kit, and it was a little dull and a little weak comparedto his other Tele, it came back to life when, i replaced the two pots with 1M ones :)
Back to the LED/ZENER tricks, as pointed out earthtonesaudio, with such low current i'm not sure either would be good solutions.
Yesterday, i tested the voltage drop in the zener function of the consumption and it was consistant, but that's only one parameter, and indeed i don't know what would be the actual zener's impedance.
It can be an issue, as i saw a few times ago, as it can be with a LED :
I tried to bias a triode in a guitar amp with an led, as it's sometimes done in Hi-Fi amps, and though it's an elegant solution, it did'nt work well with 0,5 mA through the tube, theres was a significant lack of lows.The reason is that an LED can't be considered to have a low impedance if it's current is under about 5 mA, so it was not a good AC short-circuit, not the same impedance for all the bandpass (which is the main reason to use a LED this way)
So with the LED technique here, i would not choose 1,6 mA but more like 4-5 mA.
With a Zener dropper, the same issue i encountered with my amp can occur, but the only way to know would be to compare the solutions with actual circuits.
Actually the best solution here is perhaps the resistive voltage divider, as the impedance of it at least will not vary with frequency.
Not "Generic", sorry not the right word i suppose, i just want to say that you can afford 2 or 5mA consumption from the dropper/regulator as the circuit is a low consumption one, but with another consuming 2 or 3 mA (which is still low for a pedal) it would be crazy to use a regulator with 20 or 30 mA, as would be the use of a LM338, huge and meant for high current when you can use a tiny 78L02 and a diode.
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Post by earthtonesaudio »

I think the real problem here is there are too many acceptable solutions to the 1.5V from 9V question.

So the "best" answer depends on what your criteria are. Some example criteria would be Price, Component Count, and Performance.

Say you want the best performance: You can buy a low dropout 1.5V regulator. Those typically require a tantalum cap on the output and a regular electrolytic cap on the input. The performance will be better than a battery for the most part, but the cost is considerably higher than the other solutions because you probably don't just have one lying around; it will be a special order.

Say you want the cheapest solution: The 2-resistor divider will get the job done. It doesn't provide any line or load regulation, and to make it work reasonably well you have to make the current though the divider much greater than the current through the circuit. With the FZ-1A this is not a problem because static current in the fuzz is less than half a milliamp. You could make your divider flow 10x the circuit current, about 5mA (resistor values would then be 1500 and 300 ohms) and call it done. You would then add a BIG cap from their junction to ground (several hundred micro Farads at least) to keep the fuzz from oscillating.
The resistor+LED also works, maybe a little better than the two-resistor divider, but with the same limitations.
The series zener will work provided if passes enough current. Kleuck's test seems to confirm that it will work, at least with the specific diode he used. Probably should still use a big cap to ground to keep the power supply impedance low, but be careful: when that big cap is discharged and you initially apply power, a LOT of current will flow through the series zener. Low-power zeners in this configuration will have a shorter life span than high power zeners.

The lowest parts count is a wash. You can satisfy any of my listed criteria with just 3 components.


There are other possible solutions if you relax the requirements a little. For example, an LM317 will provide a regulated 1.3V output if you connect its adjustment pin to ground. Input/output caps may not be necessary for this application so you have a very good 1.3V supply with just one component. But then again 1.3V is not the same as 1.5V... maybe this matters, maybe not (NiMH batteries are often 1.2V when fully charged).
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Post by DrNomis »

kleuck wrote:Yes, perhaps Mictester's solution is the best (but imo with higher current for the LED, i'll explain) so what ?
Voltage would not be more or less consistent with a series dropper if you take it from a power supply you know, theoretically at least.
A telecaster sometimes needs to be brighter, a friend has one with an Alnico 3 kit, and it was a little dull and a little weak comparedto his other Tele, it came back to life when, i replaced the two pots with 1M ones :)
Back to the LED/ZENER tricks, as pointed out earthtonesaudio, with such low current i'm not sure either would be good solutions.
Yesterday, i tested the voltage drop in the zener function of the consumption and it was consistant, but that's only one parameter, and indeed i don't know what would be the actual zener's impedance.
It can be an issue, as i saw a few times ago, as it can be with a LED :
I tried to bias a triode in a guitar amp with an led, as it's sometimes done in Hi-Fi amps, and though it's an elegant solution, it did'nt work well with 0,5 mA through the tube, theres was a significant lack of lows.The reason is that an LED can't be considered to have a low impedance if it's current is under about 5 mA, so it was not a good AC short-circuit, not the same impedance for all the bandpass (which is the main reason to use a LED this way)
So with the LED technique here, i would not choose 1,6 mA but more like 4-5 mA.
With a Zener dropper, the same issue i encountered with my amp can occur, but the only way to know would be to compare the solutions with actual circuits.
Actually the best solution here is perhaps the resistive voltage divider, as the impedance of it at least will not vary with frequency.
Not "Generic", sorry not the right word i suppose, i just want to say that you can afford 2 or 5mA consumption from the dropper/regulator as the circuit is a low consumption one, but with another consuming 2 or 3 mA (which is still low for a pedal) it would be crazy to use a regulator with 20 or 30 mA, as would be the use of a LM338, huge and meant for high current when you can use a tiny 78L02 and a diode.

Leds typically need a maximum of 20mA to light, the brightness of the led varies in proportion to the supply current, being a Diode, it will exhibit a constant voltage-drop across it, if you use a resistor-and-led to drop 9V down to 1.6V, and are worried about impedance effects, there's a simple solution, just bypass the led with a 470uF/16V electrolytic capacitor, you can use the led as a power on indicator too.... :hmmm:


And, if you are running, or plan to run, the FZ-1 off a 9V/200mA plugpack adaptor you can use an LM337T 3-Terminal adjustable Voltage-Regulator to regulate the nominal 9VDC down to 1.75V, because you're running the FZ-1 off an adaptor, current consumption will no longer be an issue.... :hmmm:
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Post by DrNomis »

earthtonesaudio wrote:I think the real problem here is there are too many acceptable solutions to the 1.5V from 9V question.

So the "best" answer depends on what your criteria are. Some example criteria would be Price, Component Count, and Performance.

Say you want the best performance: You can buy a low dropout 1.5V regulator. Those typically require a tantalum cap on the output and a regular electrolytic cap on the input. The performance will be better than a battery for the most part, but the cost is considerably higher than the other solutions because you probably don't just have one lying around; it will be a special order.

Say you want the cheapest solution: The 2-resistor divider will get the job done. It doesn't provide any line or load regulation, and to make it work reasonably well you have to make the current though the divider much greater than the current through the circuit. With the FZ-1A this is not a problem because static current in the fuzz is less than half a milliamp. You could make your divider flow 10x the circuit current, about 5mA (resistor values would then be 1500 and 300 ohms) and call it done. You would then add a BIG cap from their junction to ground (several hundred micro Farads at least) to keep the fuzz from oscillating.
The resistor+LED also works, maybe a little better than the two-resistor divider, but with the same limitations.
The series zener will work provided if passes enough current. Kleuck's test seems to confirm that it will work, at least with the specific diode he used. Probably should still use a big cap to ground to keep the power supply impedance low, but be careful: when that big cap is discharged and you initially apply power, a LOT of current will flow through the series zener. Low-power zeners in this configuration will have a shorter life span than high power zeners.

The lowest parts count is a wash. You can satisfy any of my listed criteria with just 3 components.


There are other possible solutions if you relax the requirements a little. For example, an LM317 will provide a regulated 1.3V output if you connect its adjustment pin to ground. Input/output caps may not be necessary for this application so you have a very good 1.3V supply with just one component. But then again 1.3V is not the same as 1.5V... maybe this matters, maybe not (NiMH batteries are often 1.2V when fully charged).

I agree, it really depends on how much money you want to spend on the solution, there's no one "right" way to do it... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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