Hey All,
I'm currently building a single ended amp that uses +9 volts bias on the grid of the voltage amplifier. Therefore, I need an input cap to contain the DC. But what to use? Obviously, I don't need a 600 volt cap in this position so the obvious choices used as coupling caps would be overkill. I was thinking of using a 200 volt Wima .22uf MKP but are there better options?
I'm currently building a single ended amp that uses +9 volts bias on the grid of the voltage amplifier. Therefore, I need an input cap to contain the DC. But what to use? Obviously, I don't need a 600 volt cap in this position so the obvious choices used as coupling caps would be overkill. I was thinking of using a 200 volt Wima .22uf MKP but are there better options?
Any polypropylene cap like the MKP series should be just fine. 0.22uF is a value that should be easy to find. No need for something esoteric.
Note, please, every cap will decrease quality of input signal also with combination with big input potentiometer /like 50 kohm and more/.
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here's my choice for input caps :
film caps : wima mkp10 / blackbox, vishay 1837, ampohm, etc
oil : russian (K75 / K40Y), what else? 😕
film caps : wima mkp10 / blackbox, vishay 1837, ampohm, etc
oil : russian (K75 / K40Y), what else? 😕
Plastic caps are good, but polyprop' is the worst of the bunch. However, capacitor distortion improves with dielectric thickness, i.e voltage rating, so a 200V polyprop should be almost as good as a 50V polystyrene. In any case, any distortion it produces will be buried below the distortion of the valve. Choose your poison.
The best choice here would be a teflon capacitor like the russian FT-1 or FT-3 - they have lower distortion and sound better than other plastic or PIO caps.
My second choice here would be a polystyrene cap (russian K71 for example).
K75 sounds OK but I think it adds something to the music. K40 PIO sounds good but has less micro-details than plastic caps (it doesn't matter in a power amp, but it matters in a preamp or headphone amp, where resolution is important).
Wima MKPs sound just average (that is, not very good).
My second choice here would be a polystyrene cap (russian K71 for example).
K75 sounds OK but I think it adds something to the music. K40 PIO sounds good but has less micro-details than plastic caps (it doesn't matter in a power amp, but it matters in a preamp or headphone amp, where resolution is important).
Wima MKPs sound just average (that is, not very good).
Bingo. A coupling cap (assuming that the time constant with the input resistance is reasonably high) has negligible voltage across it so cannot cause distortion. And actual experiment bears this out.
http://www.ebay.com/itm/20-x-0-22uF-100V-5-Mylar-Film-Capacitors-/250866896226
20 of them. Do a blind test and you won't hear a difference
20 of them. Do a blind test and you won't hear a difference
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I have been preaching this message for what seems like years.
I see two eminent Members supporting my viewpoint.
But, I ask, why do the majority of the Members seem to ignore the science and believe otherwise?
that's not supported by measurement evidence, or even audiophile guru "wisdom"
Mylar/polyester would be in the running for "the worst of the bunch" of plastic dielectrics, polypropylene is usually ranked right next to polystyrene by both measrured properties and golden ears
polycarbonate is now rare and suspect in "audio quality" anyway due to the polar molecular structure
polypropylene is the default "quality audio cap" dielectric until you want to spend stupid money to impress
and as mentioned a big step for distortion reduction is minimizing the signal V across the cap - so "supersize" - increase the value to drop fc another order of magnitude below audio
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If the input tube really is biased at +9 volts then the input impedance will be very low due to to the diode action of the grid/cathode so you will need a very high value capacitor. Any distortion the capacitor introduces will be swamped by that produced by the tube operated in this region.
Cheers
Ian
Cheers
Ian
This bias value (+9V) looks to me like E180F datasheet recommendation. Yet Uk in that case is 630 ohm * (13 mA+3,3mA)=10,26 V. So the question is what Uk is.
I'm not really a tube guy, but for tube amps with output transformers, wouldn't a coupling cap need to provide the proper high pass roll off to prevent LF distortion in the output transformer? In this case the type and quality of the cap would probably be important. But that isn't in any way an endorsement of expensive boutique parts. On the contrary, I see no reason to use $100.00 caps made of some kind of blessed who knows what, that are 3 inches long and 2 inches in diameter, when superior devices of known and consistant quality are available from commercial suppliers.
Mike
Mike
I found that caps could make a difference. However some ordinary caps turned out to be fine compared to boutique and expensive caps. In fact some polyester caps were as good as polypropylene caps.So you need to test them yourself and don't be surprised if you find it hard to hear any difference between them!😉
The coupling cap which matters (a little) is the one which defines the LF rolloff, as that one may have significant signal voltage across it. Hoever, if 'significant' is still only 100's of mV then little harm will be done whatever cap is used.
The strange biasing of the E180F (suggested by the datasheet IIRC) suggests to me that it suffers from high sample variation and/or high grid current (and conceivably thermal runaway - although unusual in a small signal valve).
The strange biasing of the E180F (suggested by the datasheet IIRC) suggests to me that it suffers from high sample variation and/or high grid current (and conceivably thermal runaway - although unusual in a small signal valve).
I mean not like RC group, Every cap color the sound and decrease quality of pure sound. And on another side - potentiometer with big nominal decrease quality of sound in low volume....
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