a low noise phono preamp power supply using 4 TL431
hi! When I read the TL431 application sheets, I found 2 usable ideas for the a phono power supply, which I want to share with you. The TL431 behaves like a regulated Z diode, with a additional transistor it can supply more current. With X1 and X2 the output voltage can be set.
A shunt regulator needs a current limiting resistor. Here, a constant current source is used, which has a high internal resistance for AC. With Y1 and Y2 the current of the current source will be set, the constant current output needs to be a little higher than that what the preamp needs, lets say 15mA if the preamp needs 10mA. The circuit can deliver up to 100mA, with small heat sinks on the BD139/BD140 , without heatsinks it can deliver maybe 50mA, which is sufficient for the most phono RIAA circuits, and the voltage can be up to +/- 30V. I made a circuit board layout, and build several power supplies with it.
Until today, they work fine. I use a "wall wart" transformer to keep the high mains voltage out of the preamp housing. Please note, that this powersupply is short circuit proof, if designed carefully. If there is more interest, I can dig in my files for some pictures. Armin
hi! When I read the TL431 application sheets, I found 2 usable ideas for the a phono power supply, which I want to share with you. The TL431 behaves like a regulated Z diode, with a additional transistor it can supply more current. With X1 and X2 the output voltage can be set.
A shunt regulator needs a current limiting resistor. Here, a constant current source is used, which has a high internal resistance for AC. With Y1 and Y2 the current of the current source will be set, the constant current output needs to be a little higher than that what the preamp needs, lets say 15mA if the preamp needs 10mA. The circuit can deliver up to 100mA, with small heat sinks on the BD139/BD140 , without heatsinks it can deliver maybe 50mA, which is sufficient for the most phono RIAA circuits, and the voltage can be up to +/- 30V. I made a circuit board layout, and build several power supplies with it.
Until today, they work fine. I use a "wall wart" transformer to keep the high mains voltage out of the preamp housing. Please note, that this powersupply is short circuit proof, if designed carefully. If there is more interest, I can dig in my files for some pictures. Armin
Attachments
Last edited:
A pretty straightforward application for the the TL431, but it does certainly not qualify as low-noise: the base noise of a TL431 is already pretty high, but here without additional filtering it will be multiplied by the ratio of the voltage-setting divider.
If your preamp is happy with it, good for you, but some preamps have a PSSR close to 0dB, even negative sometimes, and they would have their performance seriously degraded with such a supply
If your preamp is happy with it, good for you, but some preamps have a PSSR close to 0dB, even negative sometimes, and they would have their performance seriously degraded with such a supply
I am using a zener regulator plus 220 ohm resistor into 470uf cap. this feeds the RIAA op amp. 82db signal/ noise ratio MM cart.
Is the RC filter after the Zener diode, or is the capacitor just in parallel with the Zener?
The former would have lower noise.
The former would have lower noise.
Last edited:
I use sPlan 7.0 for schematics. Its easy to use, and not expensive. For printed circuit layouts I use sprint layout 6.0, from the same company, abacom. And I have a old version of "Lochmaster"
This is for breadboard layout.
This is for breadboard layout.
by the way, any interest in a other power supply schematic from me, its a dual OP regulated shunt regulator with current source of course , I hope that I did not post this schematic here in this forum before.
This schematic is for low voltage, max. +/-30V .
Its affected by a high voltage shunt regulator, which I build from the preamp cookbook, Allen Wright. But this low voltage shunt regulator does also negative voltage regulation.
This schematic is for low voltage, max. +/-30V .
Its affected by a high voltage shunt regulator, which I build from the preamp cookbook, Allen Wright. But this low voltage shunt regulator does also negative voltage regulation.
There are far better ways to use TL431s in that circuit - such as, get rid of them all!
Keep the capacitance multiplier idea, but instead, learn how to do those well - say, with a zener diode to 0v from the first resistor, then a dab of R-C decoupling, followed by small-value R (4.7-10ohm) in series from that point to the transistor base.
6 cheap components /rail - and better performance.
Keep the capacitance multiplier idea, but instead, learn how to do those well - say, with a zener diode to 0v from the first resistor, then a dab of R-C decoupling, followed by small-value R (4.7-10ohm) in series from that point to the transistor base.
6 cheap components /rail - and better performance.
It's not there yet - but keep R1/T1 (R11, T2 other channel) and start from there.
TL431s still have certain uses, but are poor references for current sources, and very poor references for shunt regs using gain; in part because they are noisy out of the box; and in larger part, because they have limited internal gain that needs to be worked-around, and that requires significant 'compensation'.
My view is - it's a very poor choice for general recommendation for a pre-amp PSU. I think the OP can get better results, with less : )
TL431s still have certain uses, but are poor references for current sources, and very poor references for shunt regs using gain; in part because they are noisy out of the box; and in larger part, because they have limited internal gain that needs to be worked-around, and that requires significant 'compensation'.
My view is - it's a very poor choice for general recommendation for a pre-amp PSU. I think the OP can get better results, with less : )
with a TL431 a very simple circuit can be build, because it contains a OP, and a reference voltage. This is the reason why I chose it. With a circuit that consists of single elements, OP and reference it gets more complex, but the result should be better.
Here is a schematic from me, with the finished board and a phono RIAA ampliefier with the board
Here is a schematic from me, with the finished board and a phono RIAA ampliefier with the board
Attachments
Typically a zener's noise level is several µV/√Hz at low audio frequencies, 60dB worse than a good opamp for instance. (I measured some 10V ones at 5mA and saw about 2µV/√Hz at 100Hz and below)
This is why you put a capacitor across a zener in almost any situtation. The original TL431 circuit just needs some
decoupling across the TL431's to quieten it down.
This is why you put a capacitor across a zener in almost any situtation. The original TL431 circuit just needs some
decoupling across the TL431's to quieten it down.
Last edited: