Comments on the Stepped Attenuator
Originally Posted by Cecala
What is heard when changing between steps from the headphones, does the sound quickly turn from on to off back to on?
Also going by my deduction, the displacements on the HR total 24 steps. Now the gain switch has 3 positions, so 3x24=72 actions. This would in theory give the ability to fine tune the sound.
Sorry about the delay in giving you some feedback on the stepped attenuator. I finally got the amp. I was under the impression that Fedex would move it through customs and dispatch it to me, but it seems that they are not set up to provide such civilised service. Anyway, I finally got my hands on the beasty last Friday. Let me make a few comments about the stepped attenuator for you.
As I turn the volume knob, it makes a physical click that I can feel. This thing is impossible to bump accidentally. In addition, with no source playing, I hear a pop through the headphones, much like the amp's turn-on thunk. The volume of this thunk seems to be related to the actual volume. With music playing, it is inaudible at low levels. there is never any break in sound from the source, just the little pop. I'm not worried in the least by this behaviour. I would think it is the nature of the beast as when changing from one discrete pair of resistors to another, you have to switch contacts at some point.
As for the step sizes, I don't believe you have anything to worry about. When I'm using the HD650's, I set the gain selector to medium (down) and I have had no difficulty finding a suitable listening level. When using the DAC as source, I find that a comfortable listening level is between 8 and 12 clicks (depending on the recording) from the lowest volume level. When listening to an analogue source, I have to go an extra 6 clicks or so to obtain the same level.
The low gain setting is not enough for the HD650's, but works well with my HD555's, HD25-SP's and even KSC-75's. These phones have impedances in the range 55-85 ohms (my 555's are the newer 55 ohm model).
the high gain setting is utterly unsuitable for any of the cans I have. With the HD650's I can turn the dial 4 clicks clockwise from the minimal setting and that's probably beyond where i'd want to be listening for any length of time. Moreover, with each step it jumps a huge amount. I was under the impression that the HD650's were no walk in the park for amps to drive, but there must exist some phones that are significantly more difficult to drive.
In summary, I believe that you should be able to find a gain selection that will appropriately match the step sizes of the stepped attenuator to just about any headphones you care to use with the amp so that you will have no difficulty selecting a desired volume level.
I hope my comments are useful.