3dzapper Posted February 26, 2004 Share Posted February 26, 2004 As I stated above it either adds or sheds electrons consistant with it's RC circuit until charged to the negative potential of the wave or depleted to the positive potential. Rick Quote Link to comment Share on other sites More sharing options...
3dzapper Posted February 26, 2004 Share Posted February 26, 2004 "The square wave signal changes the potential between the source (B+ and signal) and the capacitor. The two are no longer balanced either making the capacitor 'overcharged' or 'undercharged' relative to the source. In either direction it is unbalanced so that DC passes through the capacitor again." Shawn, DC never passes through the capacitor. The capacitor recruits it's electrons from the external circuit. An open ended capacitor reads a DC potential because there is no electron supply. In a completed circuit the same end of the capacitor would read zero volts DC (or the bias drop accross the grid resistor due to grid current if any). Rick Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 26, 2004 Author Share Posted February 26, 2004 So how does all this happen without it disrupting the operation of the tube ?? This all could be true but in the real world of a amplifier I just don't see it happening. It looks good on paper and in the posts above but it just doesn't present itself in operation at least in my experience. The last thing a amplifier wants is DC leaking through a capacitor in any measurable amount. Unless of coarse were talking about such small amount that it can not be measured with normal test equipment and if so what exactly was the point of all this ? Craig Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 27, 2004 Share Posted February 27, 2004 Craig, "This all could be true but in the real world of a amplifier I just don't see it happening..... Unless of coarse were talking about such small amount that it can not be measured with normal test equipment and if so what exactly was the point of all this ?" Look at your square waves again.... Shawn Quote Link to comment Share on other sites More sharing options...
3dzapper Posted February 27, 2004 Share Posted February 27, 2004 Craig,That's how an amplifier works. The capacitor draws current from the grid bias resistor and it and the grid become more negative impeeding the flow of electrons from the cathode to the plate of the next stage. When the square wave shifts negative the electrons in the cap are repulsed back across the grid resistor making the grid more positive which allows more cathode to plate current. Any minute leakage in the cap is insignificant. A large leakage drops across the grid resistor making the grid much more positive and overloading that tubes circuit(RED PLATE!) Rick Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 27, 2004 Author Share Posted February 27, 2004 I give up nothing worse then being surrounded by EE's Quote Link to comment Share on other sites More sharing options...
3dzapper Posted February 27, 2004 Share Posted February 27, 2004 Just keep making them sound good!!!! Rick Quote Link to comment Share on other sites More sharing options...
chacal Posted February 27, 2004 Share Posted February 27, 2004 I've just spent the last hour and a half reading thru this entire thread. I learned something interesting about electronics and had more laughs than I can remember. The perfect 3-ring circus. Everyone, please don't stop. Keep the knowledge, learning, and the flames FLYING! And may the best ballwasher win......... Quote Link to comment Share on other sites More sharing options...
maxg Posted February 27, 2004 Share Posted February 27, 2004 Yup I am with Chacal on this. On page 3 I thought - well - that's capacitors explained - next? Since then the only thing I have understood are the insults (and not all of those - Ballwasher as an insult is new to me). One thing that really confuses me: "You read Gerbache wrong. In his post he wasn't refering to a DC component over which an AC signal is riding" Say what? If there is DC and AC passing along the same circuit (can this happen?) then the AC will be continuously discharging the capacitor and DC will be flowing merrily through - at least from the link on page 3. As must be apparent from this post - I really dont belong in this thread - why am I writing this? Oh and put me in the camp that likes both Kelly's posts and Paul Parrot's - minority of one? I am just such an easy going guy.... Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 27, 2004 Share Posted February 27, 2004 Craig, Look at the square waves coming out of your amp. Again that flat top is like a DC component that passed straight through you amp. Stop doubting that it happened, you measured it and saw it happening. Now figure out why. This is exactly the reason you need to understand *why* a cap. blocks DC after it charges up. Or put another way why the cap could potentially pass square waves through them at all which have that DC like flat top. Once you have that basic understood then that understanding also answers your question of how a cap with a constant DC on it can pass square waves. Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 27, 2004 Share Posted February 27, 2004 One more thing... "I don't see that happening ! If it did it would disrupt the bias of the output tube wouldn't it ?" Have you ever tried to set the bias on any of your amps with music playing through them? If so what do you see on the meter? Shawn Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted February 27, 2004 Share Posted February 27, 2004 What I got out of this is all AC current has a DC component to it, and AC current actually can be thought to be a summation of time integrated DC current. Tell me I'm wrong and I'll jump off a bridge to ease my migraine. The theory end of this makes me feel pregnant or constipated - at least it's not both at the same time! I think most of the people here are like me - we hit the WTF button and then hit the "thank the Lord I don't work too deeply in this field" button immediately afterwords I like turning these tube amps on and getting gloriuos sounds without too many deep thoughts, kinda like being a blonde Quote Link to comment Share on other sites More sharing options...
gerbache Posted February 27, 2004 Share Posted February 27, 2004 I think the phrase DC component might be confusing some people. In a music signal, there isn't any DC (at least there'd better not be!). The entire signal can be represented as a bunch of sine waves. When we start using square waves, there's still no steady state DC component. In other words, if we hook up a DC voltmeter, it'll still read 0 volts. The thing is that the flat part of the waveform is the same thing as a DC signal until it switches from positive to negative, or vice versa. The reason the capacitor passes this is not because it's leaking DC, but because it's happening so fast. It's absolutely true that in most amplifiers, when you reach steady state (as in, it's all warmed up and the voltages have settled down), a steady DC signal will be rejected. Trouble is that a square wave is not a steady DC signal. It's changing between positive and negative constantly, so the capacitors don't have time to charge up to a steady value, like they do with normal DC. Still, they will attempt to charge, and if the wave is slow enough, you can see it's effects on the scope. Quote Link to comment Share on other sites More sharing options...
maxg Posted February 27, 2004 Share Posted February 27, 2004 "Trouble is that a square wave is not a steady DC signal. It's changing between positive and negative constantly, so the capacitors don't have time to charge up to a steady value, like they do with normal DC. Still, they will attempt to charge, and if the wave is slow enough, you can see it's effects on the scope." So all of this is only appropriate for discussing square waves and not for discussions of normal playing of music? Thankfully I dont listen to square waves on my system - I am kinda traditional like that and listen to music (wiggly waves I believe - to get technical for a moment). Quote Link to comment Share on other sites More sharing options...
gerbache Posted February 27, 2004 Share Posted February 27, 2004 Exactly. For the purposes of music, any coupling caps in the amp will block all the DC present. In fact, pretty much all of this discussion is particular to watching square waves on a scope, but it does help to explain some of what we see when we're watching square waves. In theory, the lower frequency waves will probably be rolled off slightly, just like we've seen from Craig's first post, and at the high frequencies, they should look just like a high pass filter, which means that the sharp edges will be rounded out, without any "ringing," where they bounce above and below the wave. Again, this is just like how the square waves looked from the first post in this thread. Quote Link to comment Share on other sites More sharing options...
maxg Posted February 27, 2004 Share Posted February 27, 2004 "Exactly" Yippee!!!! Thanks Gerbie... Its all irrelevent - I dont need to know this - and from what you are saying neither does Craig!! So we presume he is right - his amps probbly sound great - just dont buy them if you want to listen(?) to square waves... Much relief all round really.... So what is the function of a square wave analysis? On second thoughts - dont answer that question....I dont want to know. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted February 27, 2004 Share Posted February 27, 2004 Max, To further confuse you, the capacitor charging/discharging process is the same wether you are listening to music or square waves. The waveforms are amplified by the ups and downs of the voltage on the signal grid of the output tube. Music just contains less harmonics than a square wave. In a way you do listen to some square waves also. When you are listening to a concert and a cresendo drives your amp into clipping, the tops of those waveforms are transmutated into square waves with all their odd order harmonics and DC wavetops. This is what blows out tweeters if the amp power is sufficient. But, that said, the origins of this discussion are questioning the effect of capacitive coupling on the waveshape of a square wave on an occilliscope. Rick Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted February 27, 2004 Share Posted February 27, 2004 ---------------- On 2/27/2004 8:41:36 AM maxg wrote: Thankfully I dont listen to square waves on my system - I am kinda traditional like that and listen to music (wiggly waves I believe - to get technical for a moment). ---------------- Max, you have no idea how much that 1K square wave high pitch that goes "heeeeeeeeeeeeeeeeeeeeeeeee" if fun to listen at. Quote Link to comment Share on other sites More sharing options...
maxg Posted February 27, 2004 Share Posted February 27, 2004 3d, "When you are listening to a concert and a cresendo drives your amp into clipping, the tops of those waveforms are transmutated into square waves with all their odd order harmonics and DC wavetops. This is what blows out tweeters if the amp power is sufficient." Probably never happens on my system because the amp is 70 wpc and even though my speakers are probably only 90-92 db/w/m I sit about 3 metres from the speakers at constant levels around 80 dB at the listening position. Never seen a peak go over 95. Paul, Is there a Living Stereo recording of that 1 KHz signal? This is obviously a gross omission from my collection. As an aside - on the Clearaudio test record I picked up one of the tracks is there to test/demonstrate dynamic range. According to them there is a 40 dB range on the track - aint tried it yet - may be a problem for my amp if it is that big - would probably kill a low watt SET stone dead. IF I get the time I may rip it to MP3 and let others wreck their systems with it. Quote Link to comment Share on other sites More sharing options...
Parrot Posted February 27, 2004 Share Posted February 27, 2004 Max, I have lots of recordings with a greater than 40dB range. If you're concerned about the safety of your system, play it quieter than normal first time through, and then you'll know what you're facing. A low watt SET amp isn't going to be damaged by playing it either. It'll clip like crazy, but that's nothing new. Plenty of low watt SET people have no idea when they're hearing clipping, and in that case ignorance is bliss. Quote Link to comment Share on other sites More sharing options...
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