AC coupling vs. DC coupling
Printed From: Graham Slee Hifi System Components
Category: And the rest
Forum Name: Amplification
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Topic: AC coupling vs. DC coupling
Posted By: Analog Kid
Subject: AC coupling vs. DC coupling
Date Posted: 27 Mar 2009 at 8:48pm
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I have noticed many HiFi amp manufacturers proudly advertise their products being completely DC coupled. But why do they think this is such a great idea? And what are the advantages and disadvantages of each coupling method? |
Replies:
Posted By: Graham Slee
Date Posted: 29 Mar 2009 at 12:33am
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Ah, you must be refering to the "all capacitors are sh1t" brigade! It makes a difference from the "all solid state is sh1t" brigade! Better throw away all your Slee gear AK if you believe these sh1t stirrers... Please name a musical piece that features the "frequency" DC? ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Analog Kid
Date Posted: 29 Mar 2009 at 10:22am
No I don't believe them. I don't have the necessary knowledge to judge which method is better. I was just curious to know why so many manufacturers proudly advertise their amplifiers being DC coupled. But this whole discussion almost seems to take on a religious nature for you. All I wanted was a technical explanation of each method and to learn about the differences.  And by the by, there is a brigade on each side. There are also many people who think all valves are garbage. |
Graham Slee wrote:Posted By: mrarroyo
Date Posted: 29 Mar 2009 at 3:11pm
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I google ac vs dc and got the following, btw I did not understand it.
http://zone.ni.com/devzone/cda/ph/p/id/9 - http://zone.ni.com/devzone/cda/ph/p/id/9
http://agraja.wordpress.com/2007/01/04/dc-coupling-vs-ac-coupling/ - http://agraja.wordpress.com/2007/01/04/dc-coupling-vs-ac-coupling/
http://en.wikipedia.org/wiki/Capacitive_coupling - http://en.wikipedia.org/wiki/Capacitive_coupling ------------- Miguel |
Posted By: Analog Kid
Date Posted: 29 Mar 2009 at 3:47pm
I looked at the second link and got the following: "DC coupling allows both AC and DC signals through, while AC coupling accepts only AC signals. Issue in AC coupling: AC coupling rejects DC component in the signal, making the average value of the signal to zero." All three articles only explain the matter from a purely technical point of view. There is no specific information about how the two coupling methods apply to amplifiers and how each method affects the sound. |
Posted By: Graham Slee
Date Posted: 29 Mar 2009 at 6:33pm
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Well, you tell me! After all, you do have a Reflex don't you? Just what do you want from me by way of explanation? Blood?  I have posted the Novo review from WHF here. The Novo is AC coupled. As far as I know the rest are DC coupled. The Novo was the winner of the group test with a most involving and addictive sound.  Every single one of our products reviewed in WHF over 10 years has got 5 stars and at least one other has been group test winner against DC coupled competitors. Michael Fremer (ever heard of him...?) still uses his Era Gold V today 5 years after calling it miraculous! It also is capacitor coupled. I could go on, and on, and on... PS. A very thorough technical explanation is coming up  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 17 May 2009 at 8:27pm
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OK, here goes... there is no such thing as a DC coupled amplifier! Thought that would get you going Even if the input, output and negative feedback signals are DC coupled (instead of connected by capacitors) the return to supply path is AC coupled! How could it not be? So that's one right in the face of the "all capacitors are sh1t brigade". In fact, power supply return paths are eons worse than coupling capacitors! Don't believe me - google it! When it comes to power supply return paths the technique is called "decoupling" - get it wrong and you have an oscillator instead of an amplifier! Decoupling is used to "solidly fix" the power supply rails relative to each other so they don't budge a jot while at the same time sourcing or sinking power to the amp. It doesn't matter if it's a small signal amp or power amp. And it's done with..... CAPACITORS There, without going into a lengthy technical article you wouldn't understand (the technically minded can always do their homework...), that's part one of why DC coupling isn't the cure-all the advertising man (who isn't an engineer!), in complete ignorance and oblivious to any real science, claims! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 17 May 2009 at 10:59pm
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Here's a typical comment about one type of capacitor... "Electrolytic capacitors have no place in the high fidelity audio chain anyway. They are nonlinear and create distortion. Their only real purpose is as energy storage devices in power supplies" This guy has absolutely no idea but to all intents and purposes he looks like an expert and his webpage is well read because it came number one in a search. It comes number one because lots of people go there - sent by others.... So why if "Electrolytic capacitors have no place in the high fidelity audio chain" are they used in decoupling which is actually the return route to supply FOR THE SIGNAL? After all, "they have no place", except they do. Even a little low power preamp requires something in the order of 1,000uF for a low impedance return to supply - what is the alternative to an electrolytic? There is none! Therefore all amps must be "nonlinear" and "create distortion". Well here are the myth busters... Electrolytics do distort! They distort at their -3dB (or turnover) frequency! A decade or so above and their distortion is no different to most other capacitors - therefore set the turnover frequency a decade or so below the lowest pass frequency and they DO NOT DISTORT. This old timer obviously doesn't know that - he's just being a fashionable cap basher - vigilantes are dangerous... Electrolytics do not work at high frequencies! Partly right! At frequencies above 10kHz they start to become inductive - it's not a step-change - it happens gradually. BUT THEY'RE STILL A CAPACITOR! Because they are a massive pair of plates miniaturised by being made into rather elongated narrows foils wound up inside a can, they are inductive because they are a winding. Therefore at some high frequency their AC resistance rises, and I tell you now that high frequency isn't audible to the human race. However, it can leave a high gain circuit in trouble (phono preamps are very high gain and that's what I've been making for the last 30 years or so...), and that is the reason for bypassing - a film cap which can handle the highs gets placed across (in parallel) with the electrolytic. The lower inductance of the film cap in parallel with the higher inductance of the electrolytic results in an overall lower inductance. And that's how the signal is returned to the supply IN "DC COUPLED" AMPLIFIERS. Yes, I'm still talking about DC coupled - I haven't started talking about cap coupling as such. Now there are those who will say "but we're talking about power here". Listen, what power are you talking about? A neg 60dB signal from a preamp into a 30k power amp input isn't power! However, the so called "decoupling cap(s)" couple the return back to the power supply and we're talking nano-amps here! That's NOT POWER. So these "DC COUPLED" amps are superior? As the signal struggles through the "horrible" electrolytic(s) bypassed by a film cap (the bass and mid frequencies taking the electrolytic route)? No, that's not the case - capacitors are as important in audio as everything else is. You cannot serve two masters - if you serve the truth master like I try to, you cannot serve the money master - the money master knows it's best to knock the capacitor because that's where those who have money to spend have been brainwashed - so they all jump on the bandwagon! So here you have a lone voice? A guy selling cap intensive products that beat DC coupled circuits! But hey, he must have bribed them? Yes, he must have bribed them reviewers because the cap bashers are the multitudes and Graham Slee is all alone in what he says??? So google me! Yes google me. You have my address - I don't hide behind a nickname - I publish who and where I am. Go on - google me and look at my mansion! Oh, that's odd - he doesn't have one.... No, and I don't bribe reviewers - they like what they hear, and it's cap intensive. So unbrainwash yourself and in the next instalment I'll flesh out how coupling works and how decoupling is actually coupling. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 18 May 2009 at 3:34pm
Anyhow, back to the topic of AC v DC coupling. There are an awfull lot of "audio designers" and tweakers who either don't understand Kirchoff's Law, or never heard about it - but the rest of electronics depends on it! Therefore it applies to audio too! The amp output delivers current to its load but it just can't stop there - if it could you would only need one wire instead of two to your electric light! The load's other end is to ground and that has to connect back to the supply (or plural - supply rails, in a DC coupled amp). The signal would be quite messed up if it returned via the voltage regulator or transformer/rectifier circuit alone, so the so called decoupling capacitors are actually coupling capacitors that couple the circuit ground to the supply (supplies). ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 24 May 2009 at 4:29am
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This topic has now been hijacked twice by different writers who wish to "dirty" any attempt of explaining the true purpose of capacitors in an audio amplifier. They cited no scientifically acceptable facts to support their claims (or rubishing of this topic), but just rode the tidal wave that is sweeping "hi-fi-fo-fum". I see that as censorship of me and the truth when there is enough of the same on an incredible number of websites elsewhere which members if they so wish can avail of themselves. The laws of nature stand, and the laws written down by those who discovered them have not yet been scientifically challenged - in fact, everything electronic on earth and floating above it in orbit - your very lives! - depend on these laws. Those laws include that of Ohms, Faraday, Henry, and Kirchoff. We are being told here that they are wrong. I will not allow such lunacy on this community. As such the replies have been deleted and the individuals suspended. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 24 May 2009 at 10:33am
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Now, OK, for those non-technically minded I know it's hard to understand, but often the truth is hard to understand, but that should not be an excuse to let lies prevail, should it? Let me explain Kirchoff: he was a bloke like you and I. He observed something about nature. The result was he wrote it down and it became known as Kirchoff's Law. In other words, a law of nature discovered by Kirchoff. It is how people became able to design things like audio in the first place - that's before the "Jaberwocky" fashion "Church Loony" brigade took over. He noted that if a current flowed out of somewhere, it had to find its way back to that somewhere... Just like the waves on the sea! So it's a law of nature - not what some modern day twerp imagined and decided to con you with to take money off you. Kirchoff's Law is free of charge! Therefore those who want to make money and see the truth being stifled have attacked this topic - and those attacks have been deleted as this is a purely scientific topic! This topic is not about me saying AC coupled is better than DC coupled. It is an explanation aimed at you getting at the truth the way things actually are. I am doing this as time allows, so you will have to keep coming back and read each "instalment" as I can manage to fit it in with my hectic schedule. This morning I have been busy drawing diagrams which I will put to illustrate my next part. I will also cite references to prove the case. Thank you... ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Cyreg
Date Posted: 24 May 2009 at 10:38am
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Hmmm, Graham, if I remember it right (can't read it back now):
- The first comment by dvv was IMO sort of a popular general explanation between the differences of 2 types of design:
fully AC coupled(your favourite) and "DC" coupled(his favourite), but with having to use capacitors on mandatory places in the design.
(EDIT BY GRAHAM SLEE: I don't usually jump in on a member's reply but please note that one of our products is DC coupled - the Elevator EXP - and that's also one of my favourites) Shortly, I was thinking that it was a nice understandable suppletion on the AC vs DC subject.
On this first comment, it would be interesting to know where it went principally (laws of E) wrong, according to you, so we could all learn from that.
- With the second comment (also from dvv?) I thought it went much too far in stating his design was better (not explicitely) than yours and calling AC coupling "old fashioned" and not SotA and plugging his own favourite design.
I can understand that you deleted that post on this (YOUR) forum.
(enough other forums to make a point on design differences)
Maybe you will comment on this? Han
EDIT: Graham, your last comment came between me writing this and you posting ! ------------- TecnoDec/RB250/MP110>GramAmp2C/PSU1; Cyrus CD8SE; > Exposure 3010S2D INT > Harbeth C7ES-3 '35th Anniversary' cabling: IC 2x DNM V3; LScable Exposure DMF-two; Furu TP60 + MWaY and BlackCable pc's |
Posted By: Graham Slee
Date Posted: 25 May 2009 at 7:05am
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Don't ask me why (because I'll end up writing a book and I don't have the time) but Kirchoff is right simple to understand. He discovered that the net current at any one point in a circuit is zero! Yes 0. So that means that any current supplied from a given point to a load must return to that point. (current to load - return current = 0 or 1-1=0) The following explanations apply to both single and dual rail supplies but I have just shown the positive half (a single rail) to make it less complex and easier to understand.  OK, so if we take figure A we can see that if there was not the capacitor C, any AC current in the load would return via the transformer and rectifier diodes (by the way, those two flat things at the centre-tap and beneath the load basically mean the same point - ground/zero volts - they're connected together in reality). Not good if the load is an amplifier! There will be the switching current of the diodes at 100Hz and 50Hz mains frequency added to the music. So we insert capacitor C to return the AC (music being an alternating current) to whence it came. Still not perfect because the capacitor is charging from the rectifier then partially discharging into the load - that's called ripple which is superimposed on the signal. In figure B and C we have the voltage from figure A supplying two types of regulator which absorb the ripple but they are not a perfect short circuit at AC. They still need a capacitor to return the load current back to the starting point such that Kirchoff's law is fulfilled. Figure B is a shunt regulator. It has the lumped impedance of the series resistor and the source impedance of the rectifier capacitor (C in fig A) which is going up and down with the ripple and the transformer impedance and series diodes (in fact, I was tempted to include the path all the way back to the power station...), feeding the shunt transistor (you could replace the transistor with a FET/MOSFET if you wanted, or even a valve - they all work in very similar ways). The shunt transistor is neither on nor off but is adjusted by the regulation control circuit so that it gives the required output voltage. A bit like a pot! In fact, it is a potential divider. As such there is no direct route back to the starting point so to meet with Kirchoff's law the signal without capacitor C would flow back via the path of least resistance which is the capacitor in figure A, and back through the shunt regulator. Therefore, even with a shunt regulator Kirchoff shows us that capacitor C is required and the signal is coupled via that capacitor. The only thing that's wrong with a shunt regulator is that it consumes at least 10 times the power the load needs to be a stable source. It can also get very hot and badly rated components can overheat etc. In figure C we have the common or garden representation of a series regulator. The regulation control circuit contains negative feedback from its output to keep its output resistance low, but AC signal current in the load still cannot fully return via the regulator to its output - it can only source current. Therefore, without capacitor C, its only route is via the circuit feeding it - that of figure A and back through the regulator's pass transistor. Add capacitor C and AC signal current is returned back to its starting point, again fulfilling Kirchoff's Law. Next instalment I will show how Kirchoff is fulfilled in a simple amplifier schematic. For the time being the conclusion we can see so far is that the signal's current is always AC coupled - coupled via a capacitor, whether the amp itself is AC coupled or DC coupled! Kirchoff proves there is no such thing as a DC coupled amplifier! This will become even more apparent in my next posting. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 25 May 2009 at 7:37am
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Hi Han, I think dvv himself will be thankfull I removed his replies by the time I've finished my explanation/teach-in. Opinion is fine, but the laws of nature prevail. The question I was asked is what is best: AC coupling vs. DC coupling. I don't like to lie to my readers - I didn't want to answer the question in the typical BS arrogant way that has corrupted much of hi-fi. Therefore I have told the truth - there is no such thing as a DC coupled amplifier. Therefore the question cannot be answered because all amplifiers of music (being an alternating signal) are AC coupled. As many have commented, the power supply is often not considered part of the amplifier when it obviously is. However, that is where their learning often stops. This is quite convenient when wishing to argue a particular standpoint. On the other hand, the truth derived from the laws of nature removes opinion (what someone imagined and decided to indoctrinate in people for gain). As for the mandatory, nature's laws mandate. The laws of nature written down by men are not opinion. Kirchoff is not at odds with Faraday - Henry is not at odds with Ohm. But we see in hi-fi many people at odds with one another - don't we? Should not this be a lesson? Unfortunately man will often side with opinion rather than fact. If you don't believe that, then consider this: Only a few hundred years ago most seafarers believed the earth was flat and if they sailed too far they would fall off the edge of the earth. They put opinion before fact. The fact was that a few thousand years earlier a scribe had recorded in the Old Testament that the earth is like a ball spinning in space. Rather than accepting the Old Testament fact they limited their progress by listening to opinion. Much like people who do the rounds of the hi-fi forums? EDIT: As for "olde fashioned", we see from the last paragraph that the ancient scribe was bang up to date, and the more modern concept of flat earth was a misconcept...  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 27 May 2009 at 1:46pm
Back to the "teach-in" What do we see above? Yes, an AC coupled amp! How can that be then? The amp (the triangle symbol) is connected directly to the load (speaker, next stage, headphone etc) and the load is connected to ground. So it should be a DC coupled amp... But where is ground connected to? As we've seen, Kirchoff's Law says that the net current at any point in a circuit is zero, and therefore, as the signal current is taken from the point just above the capacitor C, it must return to that point. It cannot go the wrong way up a one way street which is what a voltage regulator of any variety is - and electricity will always find the path of least resistance which Faraday proved, so it returns via the (so called) decoupling cap, which as you can see, is in series with the signal, and hence the DC coupled amp is really a capacitor or AC coupled amplifier. Figure D just shows one half the supply, in the next installment I will show you both sides of the supply as I compare dual and single rail amps. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 28 May 2009 at 7:35am
(this reply may be edited to add or clarify information) In the above diagram we see the Kirchoff current paths in a "DC coupled" amplifier. Circle 1 is the positive half cycle. Circle 2 is the negative half cycle. Each half cycle is capacitor coupled necesitating a power supply capacitor value large enough to "match" the load the formula: C= 1/ 2pi ƒR (this board doesn't do the pi sign) C is the required capacitor value ƒ is the lowest frequency wanted R is the load  In this diagram we see the Kirchoff current paths in an AC coupled amplifier which uses a single rail supply. Again we see circle 1 and 2 indicating the positive and negative half cycles. We can see that on the positive half cycle the signal current is returned via two capacitors instead of one. This in my opinion is the chief problem in AC coupled design - understanding of this fact. Two equal value capacitors in series half their value (two 1,000uF caps in series equate to 500uF). Therefore whatever the value the above formula comes up with, the value has to be doubled for the same bass response. On the negative half cycle there is only the output cap to negotiate and that has become twice the value we need, but it is at half the lowest turnover frequency so that should hardly matter... The point here being that the turnover frequency really needs to be set much lower than the lowest frequency to be faithfully reproduced. At one tenth, the phase of the wanted frequency will be phase shifted minimally (6 degrees) so no cancellation due to doppler effect will occur. The disadvantage is going to be the capacitor size - 20,000uF is the value required to give the equivalent of 10,000uF and will have a turnover frequency down to 2Hz, thus reproducing bass down to 20Hz accurately. If good quality capacitors are chosen - which will be expensive (I am not talking boutique here) the AC coupled amplifier will sound just as good as the DC coupled amplifier. However, in my experience of AC coupled amplifiers, I have never seen a 20,000uF output cap yet! Therefore I can only conclude that the "DC coupled is best" myth has evolved due to an omission by AC coupled amp manufacturers... Make the output and supply caps big enough and you'll have the same sound! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 28 May 2009 at 8:01am
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Damping Factor At this point I thought I ought to explain about damping factor. Damping factor isn't a measurement but a ratio of amplifier output impedance versus speaker impedance. It assumes that a loudspeaker cone will be controlled by the amplifier output impedance thus preventing overshoot of the cone - a form of braking. (I have never been able to measure this and cannot find any evidence that it has been measured) In an AC coupled amp, looking back from the load into the output, the 20,000uF output capacitor is seen as (in this example) having a series impedance of 0.4 Ohms at 20Hz (from the formula in my last reply). The output impedance of the amplifier itself will be in the region of 0.02 Ohms, so by simple maths we see the ration of speaker to output impedance it "sees" is around 20:1 (damping factor 20). In a DC coupled amp there is no series capacitor and therefore the damping factor will be 8/0.02 = 400. The above ommits Kirchoff's law! There is as we have discovered series impedance contributed by the power supply capacitor. If we take this into consideration we see that with the 10,000uF capacitor the damping factor is just 10! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 29 May 2009 at 2:14am
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Spot my deliberate error? I said the AC coupled example would have a damping factor of 20 and the DC coupled example would have a damping factor of 10... If you have been following my words closely you should be questioning that. What I ommited was to include the Kirchoff capacitor, which being in series on the positive half cycle, makes the sum of capacitances 10,000uF on the AC coupled example too - and the damping factor 10! However, that's only on the positive half cycle - on the negative half cycle it is still 20. And this is a clue to possibly why AC coupling has to date suffered some bad press: if the turnover frequency is too close to what's audible that "subtle" non-linearity between positive and negative half cycles will I'm sure be heard as a phase anomally. As for electrolytic capacitor distortion - if the cap is big enough so its turnover frequency is well below the lowest frequency from the source, then the added distortion has been measured by quite a few people at something like 0.0025% - swamped by the distortion of the majority of amps and preamps! At HF electrolytics do resonate between 10kHz and 100kHz but that's where the bypass capacitor - a good quality film cap - comes in. DC coupled amps use them on the power supply caps because they say it makes a difference... ...to me that justifies all I've said above! Kirchoff is accepted! And not accepted depending on the type of doctrine being hyped  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: tg [RIP]
Date Posted: 29 May 2009 at 9:48am
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Definitely following closely, unfortunately questioning might require a little more time to digest what, for me at any rate, has been something of a 24 course banquet. I think I feel rather as poor Lucabeer did after his innocent question about 78 replay and appropriate stylus etc. Long unused synapses are still reluctantly clicking into place rather as rusty railway points might. Your explanation is not at all over technical and seems pitched at an appropriate level, still the totality of the thesis you present takes a little time to comprehend. Thank you for taking the time to prepare this lengthy discourse, I have found in the past, that the attempt to formulate one's own understandings and practices in order to pass them on to others as a coherent whole, has often been personally rewarding in enhanced understanding for myself. I hope this has been the case here, as this has obviously taken a deal of time and thought to prepare and put down in writing. |
Posted By: Graham Slee
Date Posted: 03 Jun 2009 at 8:27pm
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General reply in the spirit of the topic... "Interestingly enough, there is strong indication to us that in many situations the power supply electrolytics also need the same careful attention as do signal path units" ("Picking Capacitors" Walt Jung and Richard Marsh, Audio 1980) It seems that back in 1980 top engineers were only just about to discover Kirchoff's Law, even though they were supposed to have done it as part of their qualifications! In mathematics both sides of the equation are supposed to balance to yield the required result aren't they? By having the other side of the equation hidden from me by an incredible amount of foolish hi-fi opinion (strike that! I actually mean BS!), my progress over the years was limited. That BS is something many want to keep alive for some purpose or another. To all those people, a very big thank you for ensuring the good things in life were, and to a big extent still are, placed on hold until I was/still am able to clear a path and see through it. And guess what? Your S stinks! (to the BS'ers if you didn't understand who I was shouting at) ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 04 Jun 2009 at 12:15am
Hi tg, It has been very rewarding - it even helped me understand the subject better... What spoiled it and will continue to spoil it is the knowledge that there are "experts" out there who will/did argue it's wrong when the rest of the world of electronics functions because it is true. Is this why the truth is such a lonely place? ...350 members and they hardly ever visit... different story on the black-magic sites ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 08 Jun 2009 at 1:25am
And as a finale on this topic, here's a slide from Analog Devices saying very much the same... The page link is http://www.analog.com/static/imported-files/rarely_asked_questions/moreInfo_raq_analogBreadboarding.html - http://www.analog.com/static/imported-files/rarely_asked_questions/moreInfo_raq_analogBreadboarding.html So you can see if anybody "is fancying himself" (latest comment emailed to me from one of the thread hijackers - sad isn't it?) it must be the crew at Analog... (edit) Must add, I like this bit (at the above page)... "When the components of a breadboard of this type are wired point to point in the air (a type of construction strongly advocated by Robert A. Pease of National Semiconductor [Reference 1] and sometimes known as "bird's nest" construction) there is always the risk of the circuitry being crushed and resulting short circuits, also if the circuitry rises high above the ground plane the screening effectof the ground plane is diminished and interaction between different parts of the circuit is more likely. Nevertheless the technique is very practical and widely used because the circuit may so easily be modified." Bob, the inventor of the P45 opamp in the 60's recently got his P45. Oh well... ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: tg [RIP]
Date Posted: 08 Jun 2009 at 10:35am
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Mrs Murphy sounds like an emminently sensible woman - I would agree with her sentiments. Good read, thanks for the link. |
Posted By: less
Date Posted: 10 Jul 2009 at 11:46pm
Guilty! But I have been having my own problems Thanks for the explanations though Graham. ------------- I don't do mediocrity! Les Sutherland |