I plan on building the Pooge 5.51 voltage regulator noise reduction circuit.My question is :What adjustment(s) need to be made to possibly use a 7805 5 vdc regulator?Is the 1k trim pot allowing for voltage output adjustment?
Mike
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5336&highlight=jung+regulatorurl
Mike
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5336&highlight=jung+regulatorurl
Quick mod
Add a cap across R861, with an impedance that's low relative to it's value.
It reduces noise significantly at higher frequencies, and lowers output impedance an order of magnitude.
In this form it's a VERY good sounding regulator.
You could try a TL431 as a reference, set to it's min o/p (2.5V), or just a zener of suitable value.
Andy.
Add a cap across R861, with an impedance that's low relative to it's value.
It reduces noise significantly at higher frequencies, and lowers output impedance an order of magnitude.
In this form it's a VERY good sounding regulator.
You could try a TL431 as a reference, set to it's min o/p (2.5V), or just a zener of suitable value.
Andy.
You kind of leave me with missing info.Higher frequency from what to what?
Pooge etc
I don't think you can give a hard freq value. Basically, the feedback divider (the two resistors that divide down the output voltage to the base of the comparator transistor) also divide down the error voltage with the same ratio. That decreases the accuracy of the loop with the same ratio. Now, for DC, that is not critical. I mean, you probably don't worry about an output voltage of 15.2 or 14.88 instead of 15. But the ac errors (noise, ripple) you really want to be zero. So when you put a cap over the top resistor, the AC feedback ratio can be made 1, that is, ALL ac errors are fully fed back to the base of the comparator transistor. But of course that only happens when the cap impedance is zero, which for a practical cap cannot be realised.
At the same time, realise that the performance of these circuits deteriorates with rising frequency. At low freq, it is probably good enough to do without the effect of the cap, but above 1 kHz or so, the cap can start making a contribution.
Taking into account these factors, I use rule of thumb to make the cap such a value that it starts to work at 1kHz, so at 1kHz Xc should be the value of the upper resistor. But there is not much stopping you taking a (much) larger cap.
Hope this helps,
Jan Didden
I don't think you can give a hard freq value. Basically, the feedback divider (the two resistors that divide down the output voltage to the base of the comparator transistor) also divide down the error voltage with the same ratio. That decreases the accuracy of the loop with the same ratio. Now, for DC, that is not critical. I mean, you probably don't worry about an output voltage of 15.2 or 14.88 instead of 15. But the ac errors (noise, ripple) you really want to be zero. So when you put a cap over the top resistor, the AC feedback ratio can be made 1, that is, ALL ac errors are fully fed back to the base of the comparator transistor. But of course that only happens when the cap impedance is zero, which for a practical cap cannot be realised.
At the same time, realise that the performance of these circuits deteriorates with rising frequency. At low freq, it is probably good enough to do without the effect of the cap, but above 1 kHz or so, the cap can start making a contribution.
Taking into account these factors, I use rule of thumb to make the cap such a value that it starts to work at 1kHz, so at 1kHz Xc should be the value of the upper resistor. But there is not much stopping you taking a (much) larger cap.
Hope this helps,
Jan Didden