Hi, i am building regulated power supply for guitar effect (compressor).
There is a bridge rectifier (db107) and a cap (4700uF).
The regulator has 220nF at input anf 100nf at output.
There is no hum, but a sibstantial hiss when I run the effect. Putting another 4700 uF at the regulator output reduces the hiss, but still something remains.
There is no hiss if I power the effect with a 9v battery.
Changed the electrolytic caps, but hiss remains.
What could be wrong?
Can I reduce noise further, if cascade 7812 and 7809 in series? (7812 feeding 7809)
Regards
There is a bridge rectifier (db107) and a cap (4700uF).
The regulator has 220nF at input anf 100nf at output.
There is no hum, but a sibstantial hiss when I run the effect. Putting another 4700 uF at the regulator output reduces the hiss, but still something remains.
There is no hiss if I power the effect with a 9v battery.
Changed the electrolytic caps, but hiss remains.
What could be wrong?
Can I reduce noise further, if cascade 7812 and 7809 in series? (7812 feeding 7809)
Regards
Either something is wrong with your copy of the 7809, or there is a problem elsewhere in what is powered by it. Try replacing the 7809 to see if that cures the problem. I have had no problem with any of the 78xx regulators. Be sure that the small value bypass caps you are using have short leads and are placed as close to the Vreg as possible.
This is the regulator (picture).
Small caps are close to the chip.
I tried with lm7812 (thats what i had around), and there is a bit less hiss.
Just guessing the reason - might be that the regulated voltage is closer to the rectified voltage ~18,5v.
The effect works with ~12.5 v as well.
7809 output was ~9.5
P.s. the effect behaves odd with switching psu's as well.
Does not work at all, making only squeak noise
Small caps are close to the chip.
I tried with lm7812 (thats what i had around), and there is a bit less hiss.
Just guessing the reason - might be that the regulated voltage is closer to the rectified voltage ~18,5v.
The effect works with ~12.5 v as well.
7809 output was ~9.5
P.s. the effect behaves odd with switching psu's as well.
Does not work at all, making only squeak noise
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Three pin regulators do generate output noise, which can peak in the 2kHz-50kHz range.
The frequency and magnitude of the peak depend on the capacitor connected to the output.
Your audio circuit probably cannot reject HF rail noise very well.
Some three pin regulators do require at least 10uF output capacitance.
Try a 100uF output capacitor, that should be enough to minimize the noise.
Also the input DC voltage must be more than 3VDC greater than the output voltage
for the regulator to work properly.
https://electrooptical.net/static/oldsite/www/sed/ErrolDietzRegulatorNoisePeaks.pdf
The frequency and magnitude of the peak depend on the capacitor connected to the output.
Your audio circuit probably cannot reject HF rail noise very well.
Some three pin regulators do require at least 10uF output capacitance.
Try a 100uF output capacitor, that should be enough to minimize the noise.
Also the input DC voltage must be more than 3VDC greater than the output voltage
for the regulator to work properly.
https://electrooptical.net/static/oldsite/www/sed/ErrolDietzRegulatorNoisePeaks.pdf
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Hiss is high frequency noise. The 78** and 79** regulators have quite a lot of high frequency noise in the output. The guitar effect unit is effectively operating at microphone signal levels and therefore quite susceptible to noise in the power supply.
The simplest solution is to put a low pass filter on the output of the regulator. This requires a resistor in series with the regulator output, followed by a shunt capacitor to ground. The effects unit probably only draws a few milliamps, so choose a resistor that drops 0.1 or 0.2 volts, say 18 ohms. The size of the shunt capacitor and series resistor sets the frequencies rejected.
Choosing 100 hertz for the corner frequency, the capacitor calculates out to a bit under 100µF. That should give >30dB of hiss reduction from 2kHz up. Put your 4700µF cap on the regulator input to smash ripple at the input to the regulator.
The simplest solution is to put a low pass filter on the output of the regulator. This requires a resistor in series with the regulator output, followed by a shunt capacitor to ground. The effects unit probably only draws a few milliamps, so choose a resistor that drops 0.1 or 0.2 volts, say 18 ohms. The size of the shunt capacitor and series resistor sets the frequencies rejected.
Choosing 100 hertz for the corner frequency, the capacitor calculates out to a bit under 100µF. That should give >30dB of hiss reduction from 2kHz up. Put your 4700µF cap on the regulator input to smash ripple at the input to the regulator.
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Another option is putting a lower noise regulator in its place like the LM317 series which can be adjusted to the correct voltage .
Output noise ( percentage of Vo ) 10Hz to 100KHz=0.003%.
I agree its unusual to get this from a "78/79" used them for years but the 317 is quieter.
Are you buying them from a major good source as I have seen some bad voltage regulators other people have fitted because they were very cheap and they were a bit below genuine specifications.
Output noise ( percentage of Vo ) 10Hz to 100KHz=0.003%.
I agree its unusual to get this from a "78/79" used them for years but the 317 is quieter.
Are you buying them from a major good source as I have seen some bad voltage regulators other people have fitted because they were very cheap and they were a bit below genuine specifications.
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Got 7809 from the nearest local store, didnt think much about it. Just a common part.
I will try the idea for the lowpass at the output. Resistor in series don need to be high power. With 22 ohms and 4700uF at output (I keep the 4700 at bridge rectifier as well), the lowpass corner would be bellow 1 hz
There is some reason that 7812 yileds less noise than 7809 (except parts quality).
If 78xx generate noise, the more voltage the regulator has to drop, the harder it works, the more the generated hiss amplitude is.
Probably the hum reduction is better, but I dont hear hum anyway, just hiss.
Cascading two 78** won't remove the regulator noise, it would just split the work in between. Reducing power/ heat dicipation and hiss generated by each.
But, the best case would be to have the louder hiss of the two regulators at output.
What do you think about LM723 or UA723? (UA723 does not have resistor values in the datasheet)
Other ppl proposed that it is low noise. This one or something similar, low current regulator, depend what I can find nearby.
But I will first try the lowpass at output.
I will try the idea for the lowpass at the output. Resistor in series don need to be high power. With 22 ohms and 4700uF at output (I keep the 4700 at bridge rectifier as well), the lowpass corner would be bellow 1 hz
There is some reason that 7812 yileds less noise than 7809 (except parts quality).
If 78xx generate noise, the more voltage the regulator has to drop, the harder it works, the more the generated hiss amplitude is.
Probably the hum reduction is better, but I dont hear hum anyway, just hiss.
Cascading two 78** won't remove the regulator noise, it would just split the work in between. Reducing power/ heat dicipation and hiss generated by each.
But, the best case would be to have the louder hiss of the two regulators at output.
What do you think about LM723 or UA723? (UA723 does not have resistor values in the datasheet)
Other ppl proposed that it is low noise. This one or something similar, low current regulator, depend what I can find nearby.
But I will first try the lowpass at output.
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Adding a low pass filter after the regulator sounds like a good idea to try.
Another thing that could help somewhat is to put a low pass RC filter also before the 7809 regulator. This would also somewhat lower the voltage if it is high (depending on current). This is more of hum reduction than hiss, but might create better working condition for the regulator.
Another thing that could help somewhat is to put a low pass RC filter also before the 7809 regulator. This would also somewhat lower the voltage if it is high (depending on current). This is more of hum reduction than hiss, but might create better working condition for the regulator.
It's not unusual for a design with low PSRR and high gain to exhibit power supply noise at the output node.
If your design draws (more or less) a constant current from the supply, the best option is a noise shunt. It's a simple design with a single low-power transistor and a handful of passives. You can hunt for Wenzel noise shunts, there are a few examples used for the illustration depending on the quantum of current needed.
If your design draws (more or less) a constant current from the supply, the best option is a noise shunt. It's a simple design with a single low-power transistor and a handful of passives. You can hunt for Wenzel noise shunts, there are a few examples used for the illustration depending on the quantum of current needed.
Added low pass at the output (27ohms/ 4700 uf) and it is pretty much done.
If I turn the gain all the way up, it is still quite nasty noisy - above the bass guitar amp floor noise.
But I use it at arount 1/4 gain and difference (effect on/ bypass) is neglible.
No more time for this project, I will leave it like this.
Someday - a better PSU in another enclosure
If I turn the gain all the way up, it is still quite nasty noisy - above the bass guitar amp floor noise.
But I use it at arount 1/4 gain and difference (effect on/ bypass) is neglible.
No more time for this project, I will leave it like this.
Someday - a better PSU in another enclosure
The thing that is wrong here is using 100nF cap on the output - such a very-low-esr/ low uf part positively-provokes oscillation in these kind of reg (and that's is why adding 1000uf in parallel further downstream may have made things a little better.
NO.
Remove the 0.1uFfilm/ceramic on the reg output - and use ONE cap of 10-100uf or more of basic, cheap, not 'low -ESR', electrolytic; that's all it takes!
HTH.
(This is an aspect that comes up again and again here; but also so very easy to avoid)
NO.
Remove the 0.1uFfilm/ceramic on the reg output - and use ONE cap of 10-100uf or more of basic, cheap, not 'low -ESR', electrolytic; that's all it takes!
HTH.
(This is an aspect that comes up again and again here; but also so very easy to avoid)
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Yes, in some types of three terminal regulators, there is a zone of capacitance where instability is triggered.
It may work ok with no capacitance, or a lot, but not with some intermediate range of values. This is true
of many feedback amplifiers, which the regulators are. It's not a good idea to go without any at all though,
as a capacitive load further downstream could trigger the instability. Usually 10uF is sufficient, though some
types will have lower noise with more load capacitance.
It may work ok with no capacitance, or a lot, but not with some intermediate range of values. This is true
of many feedback amplifiers, which the regulators are. It's not a good idea to go without any at all though,
as a capacitive load further downstream could trigger the instability. Usually 10uF is sufficient, though some
types will have lower noise with more load capacitance.
That's it, the 100nF with very low ESR at the output makes the regulator sing (aka oscillate). Remove it, replace it with an 100uF electrolytic, and it will shut up.
P.S. Too late
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Syn08 is right , I am surprised that on an audio website that talks so much about capacitors so little basic electrical understanding is known.
First Principles= most capacitors are composed of the properties of Resistance -Capacitance-Inductance , easily seen on a quality electronic component tester .
I have just tested several standard electrolytics all contain a significant amount of inductance , along with this I tested some quality polypropylene capacitors they too contained inductance and not in insignificant amounts either .
Read up on how they are manufactured its interesting .
Now you could class those "qualities " as parasitic but in certain circumstances they actual provide electrical "help " to a circuit --not all but they have their points.
As an example as pointed out by JLH who only used a series wirewound resistor at the output stating this resistor provided just enough inductance to overcome output interfacing conditions.
First Principles= most capacitors are composed of the properties of Resistance -Capacitance-Inductance , easily seen on a quality electronic component tester .
I have just tested several standard electrolytics all contain a significant amount of inductance , along with this I tested some quality polypropylene capacitors they too contained inductance and not in insignificant amounts either .
Read up on how they are manufactured its interesting .
Now you could class those "qualities " as parasitic but in certain circumstances they actual provide electrical "help " to a circuit --not all but they have their points.
As an example as pointed out by JLH who only used a series wirewound resistor at the output stating this resistor provided just enough inductance to overcome output interfacing conditions.
I had an electrolytic cap at the output from the very beginning.
4700 uf. Such a big value is not recommended for regulators output, but the bigger the better (noisewise, tried).
100-470 uF at output makes no difference, compared to 100nf
Using the output cap in a low pass, makes it signlificangly better. The lower the corner frequency, the better (tried).
Now it is a first order RC low pass @ ~1,5 hz. A higher order would be better, to get the regulator noise bellow the amp noise floor.
I would like to try RCRCRC(RC) or LCLC or any LC/RC combination, non regulated (since the problem is a generated hiss, not the mains hum), as well as ua723 regulator, but no time for this now.
4700 uf. Such a big value is not recommended for regulators output, but the bigger the better (noisewise, tried).
100-470 uF at output makes no difference, compared to 100nf
Using the output cap in a low pass, makes it signlificangly better. The lower the corner frequency, the better (tried).
Now it is a first order RC low pass @ ~1,5 hz. A higher order would be better, to get the regulator noise bellow the amp noise floor.
I would like to try RCRCRC(RC) or LCLC or any LC/RC combination, non regulated (since the problem is a generated hiss, not the mains hum), as well as ua723 regulator, but no time for this now.
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As mentioned above, low ESR ceramic and MP capacitors on a regulator output might cause some regulators to oscillate. Easy to just cut away the 100nF cap and see if it improves things. You don't need it with the big RC filter. (I can't tell from the above discussion if you still have it in place).
I will try to be concise.
1.
With many companies, there are two types of every 78xx and 79xx : A and C. For example, L7809A and L7809C by ST Microelectronics and MC7809A and 7809C by On Semiconductor.
L7809A has much lower noise than L7809C. Also, the regulations are better. MC7809A has the same noise as MC7809C and L7809A. The regulation of MC7809A is better than this of MC7809C. Also, the output impedance of any MC7809 is 1mOhm as compared to the output impedance of any L7809, which is 18mOhms.
Generally, the A type is better than the C type.
2.
No capacitor is big enough. For input and output capacitors, those who want to go crazy, can get a huge Nichicon LS || FW || FG || KZ ( MUSE ). KZ ( MUSE ) is the most important. Any output and input capacitors best be paralleled with low ESR ceramics, such as Murata X7R, NTE ( 100V ), TDK, etcetera. 10uF || 1uF || 0.1uF || 10nF || 1nF || 100pF || 10pF.
Nichicon LS can go to tens of mF.
3.
When the regulators are in regulation, the impedances are as stated. When out of regulation, the impedance is higher as defined by the built in output resistors. Because the output capacitors are big, the built in amplifier can easily go to saturation, driven by the noise. When amplifiers are in saturation, they may be noisy.
5.
As mentioned, 317 can get a good value capacitor at the adjust pin. 78xx, however, has an Aluminium back, which is grounded internally ( and or externally ) and can shield. The front, however, is plastic and cannot.
4.
Internet says the higher the current of 78xx, the higher the noise. The current can be decreased by :
4a. A heavy RC filter and a common collector buffer. The regulation will not be very good because of Ube. Not a big deal for constant current. 7810, 10V, can be used to make 9.3V. An additional Germanium Schottky can be added to make 9V. Consider the tolerance of 7810, though. Type A have lower tolerance than Type C.
4b. A better way to decrease the current of 78xx is to add an overhead transistor ( this is a standard way, well discussed elsewhere and in documentation, see " Output Current Boost " ). A 100Ohm resistor will take 7mA to make 0.7V and 10mA to make 1V. Thus, the regulator will provide only 7 to 10mA and the transistor will add the higher output current. The base emitter current will be provided by the regulator too. TTA004 can be used for low output currents, 2SA1943 for high. MJ2955 is not as good, yet, comes in a better package and can be easily attached to chassis.
1.
With many companies, there are two types of every 78xx and 79xx : A and C. For example, L7809A and L7809C by ST Microelectronics and MC7809A and 7809C by On Semiconductor.
L7809A has much lower noise than L7809C. Also, the regulations are better. MC7809A has the same noise as MC7809C and L7809A. The regulation of MC7809A is better than this of MC7809C. Also, the output impedance of any MC7809 is 1mOhm as compared to the output impedance of any L7809, which is 18mOhms.
Generally, the A type is better than the C type.
2.
No capacitor is big enough. For input and output capacitors, those who want to go crazy, can get a huge Nichicon LS || FW || FG || KZ ( MUSE ). KZ ( MUSE ) is the most important. Any output and input capacitors best be paralleled with low ESR ceramics, such as Murata X7R, NTE ( 100V ), TDK, etcetera. 10uF || 1uF || 0.1uF || 10nF || 1nF || 100pF || 10pF.
Nichicon LS can go to tens of mF.
3.
When the regulators are in regulation, the impedances are as stated. When out of regulation, the impedance is higher as defined by the built in output resistors. Because the output capacitors are big, the built in amplifier can easily go to saturation, driven by the noise. When amplifiers are in saturation, they may be noisy.
5.
As mentioned, 317 can get a good value capacitor at the adjust pin. 78xx, however, has an Aluminium back, which is grounded internally ( and or externally ) and can shield. The front, however, is plastic and cannot.
4.
Internet says the higher the current of 78xx, the higher the noise. The current can be decreased by :
4a. A heavy RC filter and a common collector buffer. The regulation will not be very good because of Ube. Not a big deal for constant current. 7810, 10V, can be used to make 9.3V. An additional Germanium Schottky can be added to make 9V. Consider the tolerance of 7810, though. Type A have lower tolerance than Type C.
4b. A better way to decrease the current of 78xx is to add an overhead transistor ( this is a standard way, well discussed elsewhere and in documentation, see " Output Current Boost " ). A 100Ohm resistor will take 7mA to make 0.7V and 10mA to make 1V. Thus, the regulator will provide only 7 to 10mA and the transistor will add the higher output current. The base emitter current will be provided by the regulator too. TTA004 can be used for low output currents, 2SA1943 for high. MJ2955 is not as good, yet, comes in a better package and can be easily attached to chassis.