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Page 1: Project Kick-Off
June 1, 2007
This projects started as a braindump when thinking about output capacitors. Having built several phono amps last years where capacitors, both their values and manufacturer, make the difference between bad and good sound I still not like the idea of having massive electrolitic output capacitors on the output of a headphone amp.
And just like there are Output Transformer Less (OTL) amplifiers one starts to think: Would it be possible to build an amp without output capacitors. The answer is of course "Yes". But the question is would it be safe to do so for humans and their cans and secondly would it sound better than amps with these large value output caps. Since high voltages are dangerous for humans, and even small DC voltages are dangerous for headphones, we'll have to look for a push-pull design. I also searched on the web at well known places and found some information there as well.
I call the project "Zero" as using no output transformer and no output capacitor means that the DC at the output must be 0V.
But there is a seconde reason for this project. Some time ago I bought some batches of Russian tubes on eBay and I still did not find a good reason to use them. Mainly because after all it was not so simple to find really detailed datasheets for these tubes and secondly because I bought them for a power amp and I decided that for the moment this was not the time to build a power amp after all.
Well, the 6P43P power penthode looks a lot like the EL84 but is not identical or a direct replacement. Although this tube is advertised on eBay as a EL84 clone, it simply isn't. The 6P14P would be the better tube. On the other hand, I do not have a direct requirement for the EL84 other than that it sounds good, after all I'm not looking for a replacement tube of an existing amp. And the 6P43P is reported to be a very good sounding tube, with hi power and low voltage requirements.
The problem is that there is very little information available for the 6P43P tube and not all information is consistent as well. However, it's behaviour (triode setting) is very good so I do not expect to many difficulties (after initial bias settings etc.). Initial simulations can be done with EL84 models making changes afterwards.
The intended driver tube, the 6N6P is also not very well known. It is a medium mu tube which sometimes is referred to as the little brother of the 6H30 tube. The latter is more powerful and is quite popular with headphone DIY enthusiasts. The 6H30 is also expensive, but this is not a major problem as it has a very long life (10,000 hrs). The 6N6P is rated as at least 2000 hours, and that's good enough for the moment.
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Page 2: Circuit Design >> |