Hi!
When thinking about using a 9V battery instead of the Zener to improve noise I stumpled about the idea to use a voltage divider.
As I understand the zener is a more general solution, especially if everybody can use different transformers and thus get different supply voltages.
However, given I know my supply voltage - say 48V DC - I could also use a voltage divider consisting of 80k6 Ohms instead of R5 (originally 3k32) and one gets 9.04 V over the 18k7 resistor in place of the original 9.1V zener.
(I took a randomly high total resistance to get more easily the correct values and lower the current going straight to ground)
Further the resistors can be matched and thus give better channel equality.
Any downsides to this?
Any things I'm missing?
Would be great if somebody could comment!
Thanks a lot! Have fun! Hannes
When thinking about using a 9V battery instead of the Zener to improve noise I stumpled about the idea to use a voltage divider.
As I understand the zener is a more general solution, especially if everybody can use different transformers and thus get different supply voltages.
However, given I know my supply voltage - say 48V DC - I could also use a voltage divider consisting of 80k6 Ohms instead of R5 (originally 3k32) and one gets 9.04 V over the 18k7 resistor in place of the original 9.1V zener.
(I took a randomly high total resistance to get more easily the correct values and lower the current going straight to ground)
Further the resistors can be matched and thus give better channel equality.
Any downsides to this?
Any things I'm missing?
Would be great if somebody could comment!
Thanks a lot! Have fun! Hannes
I'm afraid it is a bad idea... if you use a voltage divider to control the regulation in a regulated supply, you'll get in trouble. The whole point of the regulation is to trade voltage for less ripple. If you have the resitors on the unregulated supply, you'll get all the ripple there transferred to the gate of your regulating mosfet. If you place it on the regulated side, I don't think you'll get any voltage at all.
If you really want to do this, I think you could improve the performance by adding a big (relative to the resitors) capacitor in parallel with the resistor which replaces the zener.
I think you'll get better performance from decoupling the zener with a capacitor - try search the forum on this topic.
If you really want to do this, I think you could improve the performance by adding a big (relative to the resitors) capacitor in parallel with the resistor which replaces the zener.
I think you'll get better performance from decoupling the zener with a capacitor - try search the forum on this topic.
A voltage divider give a perfect voltage without output current
Hi.
Looking at the schematic. D1 is connected to the Base of a bipolar transistor. A BJT is drived by an input current. In the worst case, the input current is 10 mA. The used zener diode provided 28 mA. So, that's good.
If you use a voltage divider, V = E - RI <=> V = 40 - ( 80,6.10^3.10.10^-3) <=> V = 40 - 806 ==> Can we do it ?
A voltage divider must be followed by a buffer. A voltage divider is a theorical thing.
Let's D1 maybe it can induce some noise but no problem BJT are not the most sensible to the noise.
--------------
http://passdiy.com/pdf/pearlphono.pdf At the end of the page 2, regulator schematic.
Hi.
Looking at the schematic. D1 is connected to the Base of a bipolar transistor. A BJT is drived by an input current. In the worst case, the input current is 10 mA. The used zener diode provided 28 mA. So, that's good.
If you use a voltage divider, V = E - RI <=> V = 40 - ( 80,6.10^3.10.10^-3) <=> V = 40 - 806 ==> Can we do it ?
A voltage divider must be followed by a buffer. A voltage divider is a theorical thing.
Let's D1 maybe it can induce some noise but no problem BJT are not the most sensible to the noise.
--------------
http://passdiy.com/pdf/pearlphono.pdf At the end of the page 2, regulator schematic.
Thanks for your replies!
Well also it seems that large value resistors add noise - I never thought that a Zener would have noise on about the same level.
So next idea is to use the 6.9 V LM329 precision voltage regulator that seems promising to me. The drawback is that the discrete opamp needs to be adjusted accordingly (to cope with the lower voltage reference).
I read the DIY opamp article on passdiy, but didn't find any hints on how to calculate the necessary resistor values.
Any idea what resistors need to be changed to deliver the same regulated voltage with the lower voltage reference?
Thanks a lot! Have fun! Hannes
PS: info will be added to the pearl wiki - so the first giving me the values/equations will become famous! C'mon guys!!
Well also it seems that large value resistors add noise - I never thought that a Zener would have noise on about the same level.
So next idea is to use the 6.9 V LM329 precision voltage regulator that seems promising to me. The drawback is that the discrete opamp needs to be adjusted accordingly (to cope with the lower voltage reference).
I read the DIY opamp article on passdiy, but didn't find any hints on how to calculate the necessary resistor values.
Any idea what resistors need to be changed to deliver the same regulated voltage with the lower voltage reference?
Thanks a lot! Have fun! Hannes
PS: info will be added to the pearl wiki - so the first giving me the values/equations will become famous! C'mon guys!!
That is only assuming that a) this particular regulator can still be improved substantially just by changing the voltage reference and b) that a battery does not have any noise, which is not correct. For further improvements, if at all possible, you would need to look at the whole power supply, potentially include pre-regulators, try shunt regulators and cap multipliers, etc..
Thanks for your replies!
Changing batteries is not the problem! It's going to last forever, since - after removing R5 - it only feeds the leakage current of the 3300uF cap.
After much reading it seems that batteries are also noisier as one might think - but less noisy as the zener as Wayne stated once (link is in the pearl wiki).
I thought a voltage divider would be great and extremely simple - but I didn't know that metal film resistors of some kOhms would create noise of the same magnitude of the zener.
Well what does create less noise and would perfectly fit into the pcb, would be the lm329 subsurface zener. It delivers only 6.9 V, so I thought that adjusting the resistors in the regulator should be easy and would also fit perfectly into the pcb.
I'm just looking for a simple yet powerfull solution.
Unfortunately I still don't know how to fix the gain of the voltage regulator
Maybe somebody more clever than me could help out!
Cheers, Hannes
Changing batteries is not the problem! It's going to last forever, since - after removing R5 - it only feeds the leakage current of the 3300uF cap.
After much reading it seems that batteries are also noisier as one might think - but less noisy as the zener as Wayne stated once (link is in the pearl wiki).
I thought a voltage divider would be great and extremely simple - but I didn't know that metal film resistors of some kOhms would create noise of the same magnitude of the zener.
Well what does create less noise and would perfectly fit into the pcb, would be the lm329 subsurface zener. It delivers only 6.9 V, so I thought that adjusting the resistors in the regulator should be easy and would also fit perfectly into the pcb.
I'm just looking for a simple yet powerfull solution.
Unfortunately I still don't know how to fix the gain of the voltage regulator
Maybe somebody more clever than me could help out!
Cheers, Hannes
Great! Thanks a lot!
I guess R12 needs to be adjusted as well?
As I see it, Q1 is a variable resistor and its resistance is set by the voltage reference with the aid of Q2.
Seems that Q12 is sort of feedback, set by the voltage divider R10/R11. Since Q12's emitter is on the same potential as the emittor of Q2, I think this controls the voltage drop over Q2 and thus the voltage fed to Q1.
Last I guess R12 and R6/R7 finetune the sensibility of the Q2/Q12 regulator.
Is any of this correct?
Have fun! Hannes
PS: and of course now there's the question wether a 7 V voltage reference that needs to amplified by additional 22% (when compared to the zener) still gives less noise.
I guess R12 needs to be adjusted as well?
As I see it, Q1 is a variable resistor and its resistance is set by the voltage reference with the aid of Q2.
Seems that Q12 is sort of feedback, set by the voltage divider R10/R11. Since Q12's emitter is on the same potential as the emittor of Q2, I think this controls the voltage drop over Q2 and thus the voltage fed to Q1.
Last I guess R12 and R6/R7 finetune the sensibility of the Q2/Q12 regulator.
Is any of this correct?
Have fun! Hannes
PS: and of course now there's the question wether a 7 V voltage reference that needs to amplified by additional 22% (when compared to the zener) still gives less noise.
Well after reading Ron Mancini's article on that topic, one could insert an 50 Ohms resistor in series. However this affects the regulator impedance? But probably not an issue here?
After some extensive searches/readings about that whole noise topic, the summary is terrific...no simple answer to the question what replacement for the zener gives less noise.
I think the lm329 would give less noise even if it has to be amplified by additional 30% (6.9 V vs. 9.1 V of the zener). Maybe connecting additional 50 Ohms in series would yield together with the 3300uF cap a nice RC-filter - but well this is just my impression. The cutoff-frequency of below 1 Hz is indeed impressive.
What about R9 (220 Ohm, connecting to the basis of Q2) then?
Remove it and use these 220 Ohm in series instead of the 50 Ohm?
Since I don't have any noise measurement equipment I cannot check wether all of this would really give some reasonable benefit.
I'm hoping somebody with more brain and experience could confirm my idea.
Cheers, Hannes
After some extensive searches/readings about that whole noise topic, the summary is terrific...no simple answer to the question what replacement for the zener gives less noise.
I think the lm329 would give less noise even if it has to be amplified by additional 30% (6.9 V vs. 9.1 V of the zener). Maybe connecting additional 50 Ohms in series would yield together with the 3300uF cap a nice RC-filter - but well this is just my impression. The cutoff-frequency of below 1 Hz is indeed impressive.
What about R9 (220 Ohm, connecting to the basis of Q2) then?
Remove it and use these 220 Ohm in series instead of the 50 Ohm?
Since I don't have any noise measurement equipment I cannot check wether all of this would really give some reasonable benefit.
I'm hoping somebody with more brain and experience could confirm my idea.
Cheers, Hannes
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