Look for details of how susceptable LDOs are to instability and what steps the designer must take to help eliminate such.mtl777 said:
The improvemnts from adopting LDOs will appear miniscule compared to building a proper dual polarity supply for the existing regs. Let them work properly and the performance will improve.
Richie,
If the doubler were operating efficiently then the 9Vac effectively produces the same DC output as an 18Vac transformer.
The single rectifier (halfwave) allows the dual polarity to be generated. Another spoke in the efficiency wheel.
Hi Richie,
I did not mean that as a put down, sorry.
I have already said that Vac ~=regulated Vdc.
That takes account of ripple and droop and transformer regulation.
What it does not take account of are the high dissipations that can occur with high mains input voltage.
Bigger heatsinks than imagined/advocated may be required for the worst case senarios.
That's part of the reason I suggested using an off board pre-regulator, to ease the load on the sound card regulators.
I did not mean that as a put down, sorry.
I have already said that Vac ~=regulated Vdc.
That takes account of ripple and droop and transformer regulation.
What it does not take account of are the high dissipations that can occur with high mains input voltage.
Bigger heatsinks than imagined/advocated may be required for the worst case senarios.
That's part of the reason I suggested using an off board pre-regulator, to ease the load on the sound card regulators.
AndrewT said:
I'm getting confused now. In my understanding of the discussion so far, after rectifying and doubling the 9 VAC, you get 25.46 VDC (9 V x 1.414 x 2). Half of that, or 12.73V, goes to the positive regulator, and the other half goes to the negative regulator. But you need at the very minimum 15V for each regulator so 12.73V going into each of them is not enough?
Well done, now you see exactly why I keep banging on about how I cannot understand why they supplied a 9V wall wart with this unit, and how using LDO regs is pointless.
Andrew, no worries. You also raise some very valid points about heatsinking. (PS I also use the rule of thumb Vac ~=regulated Vdc).
Andrew, no worries. You also raise some very valid points about heatsinking. (PS I also use the rule of thumb Vac ~=regulated Vdc).
Hi,mtl777 said:
I'm getting confused now. In my understanding of the discussion so far, after rectifying and doubling the 9 VAC, you get 25.46 VDC (9 V x 1.414 x 2). Half of that, or 12.73V, goes to the positive regulator, and the other half goes to the negative regulator. But you need at the very minimum 15V for each regulator so 12.73V going into each of them is not enough?
two separate half wave rectifier/doublers, each producing opposite polarity. Each can operate off the available doubled voltage.
BUT, doublers do not work efficiently at higher currents. The component values become enormous for quite low output currents. The consequence for using lower value components is badly sagging voltage when current demand rises. I suspect that is the problem, the doubler allows the output voltage to sag so low that the regulator runs into Vdrop problems and fails to regulate for normal operational currents.
Send a proper voltage and current supply to the sound card and the problem will go away. Then decide whether improvements to the quality of clean voltage sent to the opamps is necessary and you won't have to compromise with only choosing the LDOs, you can choose the best regulator for the purpose that you think may improve the sound card.
AndrewT said:
Thank you so much for the explanation. So, with two separate rectifiers/doublers, each reg is being fed 25.46 VDC (9 VAC x 1.414 x 2), right?
That's good to know!
Are my existing regs (L7815CV and L7915CV) good? If I'm going to replace them without having to determine if replacement is necessary (because I don't think I'm knowledgable enough to make that determination), what better regs would you recommend as replacement?
Thanks again!
Hi,
all three terminal regs are not made equal, but they all perform in a similar manner and all suffer from the same problem:- All the connections are internal and all the components follow the temperature of Tc.
For a significant improvement I suspect you need to go discrete and possibly approach the performance of Pooge or better.
Go read Walt Jung and Jan Didden. But, listen to what a properly implemented power supply achieves with the current regulators.
You cannot possibly design in modifications and improvements if you don't know how it works in it's present state.
all three terminal regs are not made equal, but they all perform in a similar manner and all suffer from the same problem:- All the connections are internal and all the components follow the temperature of Tc.
For a significant improvement I suspect you need to go discrete and possibly approach the performance of Pooge or better.
Go read Walt Jung and Jan Didden. But, listen to what a properly implemented power supply achieves with the current regulators.
that little clue tells us you have not done your homework.
You cannot possibly design in modifications and improvements if you don't know how it works in it's present state.
AndrewT said:
From this it seems that changing to the same three-terminal type regs, even if they're better quality, will not make a significant improvement that I can hear, so it is pointless.
I'm afraid that would be too much for my present level of knowledge. Here's my final solution that I'll be contented with:
1. Replace the 9 VAC 41 VA wall wart with 12 VAC 41 VA.
2. Replace the rectifier diodes (the four 1N4001's next to each other near the 9 VAC input connector) with Schottky types like the MBR1100, for a lower voltage drop.
What do you think? Your comments on this are greatly appreciated.
Thanks!
I understand that feeding the voltage directly to the regs is best, but as I stated before, I'm afraid I'm not knowledgable enough to do such a seemingly drastic change to the circuit. Therefore, I just want a simple solution that would work. With that in mind, do you think my proposed solution is good enough? Also, regardless of whether it will give an improvement or not, is that part about replacing the four 1N4001 rectifier diodes with Schottky types alright and safe to do?
Thanks!
Thanks!
If you are capable of replacing these diodes and replacing the regulators then you will find that running four wires from an off board (external) PSU to the regulator input pins and zero volts power ground will be far easier.mtl777 said:
I have no idea whether LDOs and Shottkys will solve the sound card problem of running out of regulator Vdrop. I depends on just how badly the V doubler is performing.
AndrewT said:
Is that all? Do I need to remove any capacitors or disengage any existing connections or traces to the regulators? What happens to those 1N5818 diodes attached across the ground and output pins of the regulators -- should I just leave them in exactly the way they are attached now? BTW, someone told me that those diodes "serve as current limiters." Don't know exactly what that means.
Regardless of whether it will solve the problem or not, I just want to know if replacing the four 1N4001 rectifiers with Schottky's is safe and will not destroy anything.
Thanks!
In all of these discussions of different alternative solutions we may have forgotten one very important thing: the 5V supply to the digital stages (ADC and DAC chips)! The 1010's PSU has two +5V (L7805CV) regs to implement this, and I wonder what the effect of the different solutions would be on these regs. For example, if I were to implement the suggestion to send a direct supply from an external regulated source to the +/-15V regs (bypassing the half-wave rectifier/doublers), what happens to the 5V regs? Where will they get their power from? And if I were to implement the use of a higher voltage 12 VAC wall wart, would this still be safe for the 5V regs?
The 1010's PSU has two +5V (L7805CV) regs to implement this, and I wonder what the effect of the different solutions would be on these regs. For example, if I were to implement the suggestion to send a direct supply from an external regulated source to the +/-15V regs (bypassing the half-wave rectifier/doublers), what happens to the 5V regs? Where will they get their power from? And if I were to implement the use of a higher voltage 12 VAC wall wart, would this still be safe for the 5V regs?
It is just possible the 5V regs get their input from the rectified and smoothed 9Vac supply without the use of a Vdoubler. This would be a good way for them to do that but would cost more in components and in PCB space. It should be easy to find the input trace of the 5V regs and measure the voltage. Do the same for the 15Vregs.mtl777 said:In all of these discussions of different alternative solutions we may have forgotten one very important thing: the 5V supply to the digital stages (ADC and DAC chips)!
Another tack.
+-15V allows output signal of almost 10Vac.
What other circuits run off the +-15Vdc?
If these are reduced to +-12Vdc, then the maximum output drops to 8Vac. Do you need any more than 2Vac to your next receiver?
If this is feasible then you gain three extra volts for the regulator to operate properly.
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