I’m not an engineer but, as I understand it, there are two arguments for setting the -3db point that low. They both center on the frequency range of 20 to 20k because that is commonly considered to be the range of human hearing. Even though there is not much, if any, musical information at those extremes.
The assumption is that you want a 20hz signal to be flat at 20hz, not rolled off. So you set a -3db point such that the signal starts to roll off at 20hz. The result is that it will be -3db at 2hz. The second argument is that phase anomalies can occur at up to 10x the -3db rolloff point. So a -3db point of 2 Hz or thereabouts is commonly used in order to eliminate that possibility. So there will be no phase issues from 20hz and up.
The engineers will, no doubt, tell us that these phase anomalies can be measured but whether or not they are audible, I have no idea. And I’m not sure I would even know what to listen for.
Perhaps @Merlinb or some of the other more technical types here will provide more details. Or you might want to search or start a thread and ask.
Generally, I agree with you, though. Lots of emphasis is placed on specs and performance at the extremes. That’s why I suggested using an online frequency generator to determine, from a practical standpoint, what range of frequencies a person can actually hear with the speakers they use.
I have not always set that low of a -3db point myself. For example, I’ve set the rolloff higher in an amp when I was concerned that too low of a rolloff might cause a small OT to saturate. That's done by changing values of the coupling cap and grid resistor. But when I have used rolloff points ~2 Hz or even a bit lower I can’t say that I’ve heard any problems either. Though I don’t use vinyl so I have no issues with turntable rumble.
The cost of a low rolloff point vs a higher one is essentially the same since they're just different combinations of cap and resistor values. So, even if I can’t hear any difference, I’ll go with one that eliminates the possibility of theoretical / technical issues.
I'm planning to use it as a headphone amp as well as the preamp for Pass aleph j. This is a solid state class A power amp. My interconnect cables are 0.5 meters
Last edited:
It should work well with a SS amp. If you were using a tube amp with cables that aren’t long, I was going to suggest that the cathode follower section was not really necessary.
I don’t know much about headphone amps so I’m not sure if it can be used for that purpose or not. I would wonder if it produces enough output and if its output impedance is low enough for headphone use.
Perhaps others will comment.
Well, for getting -3dB at 20 Hz, you want C = 1 / ( 2 x Pi x 20 x R ), where R is the headphone impedance and Pi is 3.1415.
For example, for 30 ohm headphones, C = 1 / ( 2 x 3.1415 x 20 x 30 ) = 265uF (use 270uF).
Use a DC voltage rating greater than the total power supply value, 350VDC would be good, with positive lead to the follower.
For example, for 30 ohm headphones, C = 1 / ( 2 x 3.1415 x 20 x 30 ) = 265uF (use 270uF).
Use a DC voltage rating greater than the total power supply value, 350VDC would be good, with positive lead to the follower.
If i put 30 Ohm as a load, my output amplitude will be almost equal to the input amplitude. If i substitute the load to 30kOhms, everything is fine. Should there be some modifications done in order to proper pair with headphones?