Well, the official Senn HD650 tech specs claims for a bandwidth from 10Hz to aprox 40kHz, the graph pointed by WWence is this:
An externally hosted image should be here but it was not working when we last tested it.
At 20Hz you can see values above 0dBr, it's true that lower than to 40Hz, but I think that saying that Senns cut to 40Hz is like saying they have a bandwidth from 40Hz to 400Hz.
I agree with WWence about the quality of headphones bass, but comparatively the change has improved it (at this point I'm talking about .47microfarad caps, not 1microfarad ones). Of course testing the change with both headphones and amp/speakers should be the right thing, and I'm going to follow this address.
But in my opinion the key is not in the cap size (that of course is important and must be given in mind), the key is in the nature of the cap. CD6000 sounds different with Silmics that with Auricaps, that's a reality. Beyond this point we enter in the field of subjectiveness and tastes, and here I have to admit an improvement in the quality of sound.
Said this, I think this post is stating very useful facts for those who want to tweak many Marantzes sharing the HDAM output caps, I'll try to summarize them:
· Both Elna Silmic 220microF act as DC coupling non polarised 110microF cap.
· Objectively, the replacement of these caps for a non polarised cap modifies the quality of sound.
· Many DC measurements drop values of milivots in the HDAM output, what should not be a problem if these caps are removed, but some cincurmstances could increase this value which could be dangerous for devices attached to the CD output.
· Both caps, with the next resistor in series with ground, perform a high pass filter. If these caps are replaced attention should be placed in selecting the right size to mantain the cutoff frequency of the original filter.
At this point I have a doubt: if resistor in series with GND forms a high pass filter with the caps, should this resistor be removed if Silmic caps are removed? I understand that that resistor is not useful if caps are removed.