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In Reply to: RE: Tube sound - how much is due to the caps? posted by Bold Eagle on December 13, 2015 at 06:58:28
The first thing to say here is that you seem to start with a preconceived notion of what 'tube sound' is. This may include all the usual adjectives like 'warm', 'euphonic' etc. This may be true of warm sounding tubes like 12AX7 or EL84 but it isn't true of DHTs like 2a3, 10Y, 4P1L etc. DHTs are more detailed and more alive - transparent rather than warm. They are also more faithful to the original timbre of acoustic instruments and voices.
The second thing is that it depends on the capacitors. A teflon capacitor like FT-3 will be more neutral and transparent than a lower quality film cap or some of the generic paper in oil caps.
The third thing is that it depends on the capacitors in the power supply. Polypropylene capacitors right through the PSU will sound cleaner than larger electrolytics.
The fourth thing is that while most tube equipment used cathode bypass caps, you can eliminate these by fixed bias (batteries etc) or filament bias in the case of DHTs.
And obviously you can eliminate coupling caps by transformer coupling so all you are left with is the polypropylene caps in the PSU.
You are right to say that caps can colour the sound, but there are a number of ways around this, both with better caps and better circuits which can eliminate a lot of them. So miraculously you end up with tube amps that don't have a tubey sound at all. Voila.
Follow Ups:
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
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
Interesting post to say the least!But they all have been so far on this subject!
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