With KiCad, and I suppose any design package, you need to know the physical size of the components. So hopefully, the following is not off-topic. Most component choice results in a decision on component size, and that will affect the layout and physical arrangement.
If I do a PCB design in KiCad for the Leach amp, and post it, then would you like SMD or normal components? KiCad is new to me, so I'd appreciate any pointers. You will notice that there is a major load of doo doo on the net (and in the shops) about speaker-lead quality, oxygen free copper, "audio-gade" capacitors etc. The more research I do on this, the more convinced I become that we are being hoodwinked. For example, super-low loss speaker cables can actually cause an amp to oscillate at supersonic frequencies because the L/C characteristics move the poles and basically mess with the amp design. Some blind tests have revealed ordinary lamp-cord sounds better! Similarly, snubber caps look like a waste of time. None of the maths, physical measurements or simulations show anything other than infinitesimal differences. Very high bandwidth amps can be prone to oscillation. Speaker wires are NOT transimission lines at ANY audio frequency. self inductance of caps is also insignificant especially with today's construction; 6nH of inductance per cm of lead wire totally swamps the calculations. Unfortunately the list goes on. So I am pleased to see you tell me of some of the tweeks that actually make a difference. But I'd like to know why. :) Do you know why to use metal film resistors? Would SMDs be better these days for any of the components? In no particular order, what I think is important in component selection is: 1) Nominal value. 2) How its characteristics change with temperature? 3) What electrical / thermal stresses can it take? 4) Physical size. 5) How does it deviate from its ideal model? 6) Build quality and therefore reliability. 7) How the characteristics change over time. 8) Is it a very specialised component? with 1) only some components need to be tight tolerance. If you make everything 1%, then it just makes it expensive. Although tight tolerance can sometimes imply better quality and reliability. with 2), if the value changes with temperature, and you go for tight tolerance, then there had better be some temperature compensation, or you may as well use a cheaper component. Almost all practical calculations and component specifications involve temperature. Hfe (Beta) of a bipolar transistor actually goes up with T, some resistive devices fall with T, some increase, Random noise increases with T. with 3) These are the parameters that stop your equipment blowing up when voltages and currents and heating takes place. The biggest characteristic that is effected is probably physical size. with 4) See 3 ! Of course, this is also where component construction technology comes in. The most notable being capacitors. How big would a paper-oil 8000uF capacitor be? with 5) It depends on the use as to the effect. As noted above, at audio frequencies, self inductance of a cap does not have a measureable effect in most (of all?) circumstances. However, the characteristics of a mica capacitor make it ideal for the Miller-Cap. 6) and 7) are self explanatory except that sometimes smaller is better, and sometimes not! with 8) specialised components might not be in the market for a long time. So your design could be rapidly uneconomical to repair. Point 8) is one reason that I like the Leach design. It's simple. Simple can often lead to better results. Some off-PCB notes: I am interested to know more about the issues you had with the transformer. I don't know what is a "constant voltage transformer". Why would the hum be bad? Was this a physical hum? If so then this is because of loose laminations, and unaccaptable eddy-current losses in the iron. The iron could be poor quality for a transformer. If so it was probably inefficient. Or it might have been fixed by physical sheilding if the hum was electromagnetic radiation from the transformer picked up in the early stage of the amp. I can't fathom how the transformer can affect base response unless the losses were so great that the supply voltage was affected. Any ideas on that? Voltage is voltage, and current is current. If these are available to the components upon demand and at required levels, then how can one supply sound better than another? I reckon an amp driven by 15,000 mice in a wheel would sound just the same as one supplied by electricity from an oil-fired power station providing that the mice were well fed, we have a few 'subs' and we don't run out of oil. Toroids tend to be low-noise, compact but draw a large surge current on turn on. They are very efficient. The radiate less because of small or insignificant air-gaps which otherwise radiate flux, and the construction gives good sheilding. Maybe the high efficiency of the toroid reduces its regulation. (No load voltage as a ratio to load voltage). Regulation is inversely proportional to efficiency, size, $$! Regulation is directly proportional to temperature. By "audio ramping and thump supression" do you mean a slow-start power supply? So should I find, CAD, and post a circuit for a slow-start PSU too? On Sunday 14 October 2007 05:43:48 KeepIt SimpleStupid wrote: > It's a nice amp. You'll like it. I taped it in 1980 > or so. Just like everyone else, I made subtle > changes. > A couple notable ones: metal film resistors where > possible. 10 turn pot for bias adjustment. I added > audio ramping and thump supression as well. > > The power supply makes a big difference in the sound. > I used a 20 AMP constant voltage transformer and the > AMP sounded great and the hum was horrible. I then > changed to a somewhat under rated quad custom made > torroidal transformer and the AMP was quieter, but not > as bassey. > > I accidently mad a mirror image of the board and > because the design is so symmetric, I was able to use > it with a few external changes and switching the NPN > and PNP transistor positions. > > Go for it. > > --- j3r3m3l33 <[EMAIL PROTECTED]> wrote: > > Has anyone KiCAD'ed this amp: > > > > http://users.ece.gatech.edu/~mleach/lowtim/ > > (http://www.pavouk.org/hw/leachamp/en_index.html) > > > > The second link's author said he did it in Eagle. > > > > By all accounts is a nice unit when built. I've > > asked > > the author where to get manufactured PCBs but no > > reply > > yet. So failing that, unless someone here has > > already > > entered the design into Kicad, then I might do it > > and > > post the result. > > > ___________________________________________________________________________ >_________ Catch up on fall's hot new shows on Yahoo! TV. 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