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In Reply to: RE: 'Tube sound' can be very misleading. posted by andy evans on December 14, 2015 at 09:20:39
All very true; but nearly all tube amps have a relatively high source impedance due to the output transformer. My own experiments, and some calculations tell me that at least 70% of the difference between tube amp with output transformers and direct coupled SS amps lies with the higher source impedance of the tube amps. The other 30% or so must lie somewhere else. A lot of candidates for that remaining 30% have been suggested; but many don't hold up.
One of the differences is that many tube amps have no input coupling cap, and the input goes directly to a tube's control grid, so you have a very high input impedance and minimal interaction with the preamp and interconnect's properties.
Film caps are a good idea in tube amps; but not practical in SS amps. I do add bypass caps to my power supply caps in my SS amps, and some commercial amps I have already had them.
It's good this thread is getting lots of opinions - that's why I posted in the first place.
Jerry
Follow Ups:
I don't know about your 70% and 30% ratio. What I can tell you is that a SIT amp which is single ended and uses a single device is pretty much as good as a good tube amp. I know - I've tried a direct comparison in my system which uses a 4P1L PSE amp. We threw in a 300b amp and a conventional transformerless PP solid state amp of good quality. The best performers were the 4P1L and the SIT.
But the SIT used an electrolytic output capacitor. The designer now wants to use an output transformer. The question then becomes how low can you get the output impedance of your output stage, so the OPT only has to do the minimum of step-down. In an "ideal world" you use an OTL tube amp, but that's a kind of circlotron - not single ended, so how important is single ended operation. That's another big design choice.
There are a number of factors here. Goes way beyond capacitors.
Unless you account for the source impedance of the various amps, you really don't know where you are, interaction-wise. In comparison's like that, you also need to know what the speaker's modulus of impedance curve looks like. Without that, all you have done is found a preference in a given system which may not be transferrable to other systems.
Jerry
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