[SOLVED] How much ripple rejection do you need for an audio circuits power supply regulator?

[obrien135]

How much ripple rejection do you need for an audio circuits power supply regulator? Will an LM7812 work OK?

 

[alexan_e]

Ideally you want as much as possible, a dc source would be the best source and sometimes they use that in moving coil pre-pre amplifiers (50-100uv output moving coil turntable heads) and as you go up to a pre amplifier and to a power amplifier the input signal gets stronger and the ripple can be worse.

For example in power amplifier we usually don't use a regulator, just big capacitors with a symmetric power supply and some kind of filter between the input and power stages.

Note that the ripple rejection is not the only factor, output impedance is very important and especially ic regulators are very bad in that area especially in high frequency, so discrete regulators are preferred.

Jung regulator has many fans and there are many modified circuits too.
You may find this useful Op-Amp Based Linear Regulators
Or you can make a simple one Precision +/-15V regulator for pre-amp or headphone amp
You can also do a search in diyAudio

Alex

 

[FvM]

Note that the ripple rejection is not the only factor, output impedance is very important and especially ic regulators are very bad in that area especially in high frequency, so discrete regulators are preferred.

Good point, some of those OP based regulators are even worse regarding output impedance, showing a resonance peak in the MHz range. That happens, because they have a rather high loop bandwidth, but the loop isn't compensated sufficiently for the capacitive load. Common IC regulators are most likely better in this respect.

 

[obrien135]

So an op amp series pass regulator will usually have a better ripple rejection spec than a three pin regulator like a 7812?

 

[alexan_e]

I don't know any exact figure and it also depends on the design used.
You can use a 7812 if you want something simple or a discrete regulator circuit if you want better sound quality, it depends on your needs.

Alex

 

[FvM]

Looking at the 78xx datasheet, that specifies about 70 dB 120 Hz ripple rejection, you can surely perform better with a good designed regulator. But I wonder, if it's a straightforward way to achieve high audio performance. A powerstage, also e.g. for a headphone, should be designed to have a high power supply rejection in addition. A preamp shouldn't be supplied by the unfiltered regulator output, it would use post filters, possibly with capacitance multipliers. Then 70 dB ripple rejection and e.g. 1 mV hum at the regulator output won't harm.

 

[alexan_e]

If you are going to use the 7812 then it is better to use lm317 which has 10db better ripple rejection (80db) if you use a decoupling capacitor of 10uf in the adj pin.

I have simulated the Jung regulator which has an lm317 in the input and then with the opamp adds an extra 50db for a total of about 130db ripple rejection (this is also the result of measurements in the Jung article ).
I think that the output impedance will be better and this is supposed to give better transients and sound better.



http://www.at-view.co.uk/pdfs/ALWSR rev2.9 rev009a.pdf modified version with full schematics and construction info

Alex