MP

Beerman, Eagle 4.11 has a free hobbyist version. I highly recommend it. http://www.cadsoftusa.com/freeware.htm MP

I am not aware that anyone has discontinued this device. Where did you get that information? You can get the Texas Instruments SN7407 for about 60 cents at digikey. I just checked their website and they had more than 500 in stock. MP

I have purchased these in the past. The legs are bent to an angle which permits them to snap into the circuit board for a snug fit. I have not seen any sockets for them, but perhaps they do exist. MP

Ante: I do not think this debate really belongs in this thread. Others are probably tiring from it. I will have to stop now. Please check out the link above for more on transistors. In answer to the question...since all of your transistors are on at the same time, your resistances are all in parallel and thus follow the rules of parallel resistors. You do not want one of them acting as a direct short because the others will no longer factor into the equation. In order to have 12 volts at 10 amp, you must have a total resistance of your circuit of 1.2 ohms when the transistors are turned on. (12/1.2 =10) otherwise you do not have 10 amps. If a transistor draws your total resistance down to 0.1 ohm, for example, then you are running 12/0.1 = 100 amps through this one transistor. The others will not react because all the current is flowing through the one. Adding small resistances to each leg of the circuit to balance the load will insure that the flow is equal. This is because of the parallel resistance formula. This is only one small area of the design math. There are many other factors also, like hfe of the transistor, DC current gain, MMP, etc. I hope that this explanation is helpful in resolving your questions. Please, back to the inverter. I am interested in the outcome. MP

rectify the radio signal so that it is DC. Actually, I used the term "1 transistor" to mean simple, but I am not sure that you even need a transistor. MP

You could store the message on a ISDxxxx record/playback chip. Instead of triggering the relay forr the horn, you could send the pulse to this chip and have it play the message. There seem to be a few of these chips with different numbers, so I replaced the number with xxxx. MP

I have not really been following this thread, but why not just use a one transistor radio receiver circuit and rectify the received wave with a diode to use it as a power source. (radio waves are everywhere). You should be able to get about 3 volts from this. You then only have to connect it to a low draw bulb or LED. 8) MP

Yes, I work in the consumer electronics industry. I have also seen the amazing things that the industry gets away with. ::)Consumer electronics is not based on good design. It is based on how much money the company can make. If you can leave out several 20 cent parts and sell several hundred thousand units that will still make it past the warranty period, then it is considered a good thing. The goal is met. One should never base good design on this. One can always base good profit on this. The only thing the resistors will do is control the amount of current flowing and insure that all paths to ground have the same resistance. When you have several paths to ground all open at the same time, the flow is going to take the least resistive path. That is a built in law with electronics. I appreciate your stubborness. In fact, I respect you for standing on your opinion. If you want to research this further, please show me an engineering article which backs up your claim. By the way, the MOSFETs are different. You do not need resistors on them. MP

You are correct. Most PC devices will not allow more than 5 volts. Some cards have over voltage protection, but I would not use a higher voltage as a test to find out if yours has protection. You should decide what your highest voltage will be. Is it 5 Volts Pk-Pk?, 10 volts Pk-Pk? When you have this figured out, then you just use a small transformer to drop it down. Sound is an AC voltage, so transformers work great for these. There are several types used for telephone equipment that will work fine for you. perhaps you want a 2:1 or similar. MP

Glad we could help. I trust the wedding is still on, then? ;D Take care! MP

Here are some choices: http://www.abra-electronics.com/catalog/chemicals/gc39.html http://www.rpelectronics.com/Default.asp?Main=/English/OnlineCat.asp?Menu=/English/Content/Categories/CatM_85.asp%26Detail=/English/Content/Items/835-100.asp http://doityourself.com/store/6713317.htm http://www.action-electronics.com/kester.htm#Flux http://www.advancedpcb.com/products_flux.htm I am only familiar with the rosin flux and that has been the industry standard for years. But there are several types such as easy clean up types. These might be better if you do not want to use alcohol to clean afterwards. Some are water clean up but I have an opinion about putting water on my circuit boards before they are protected. ;D MP

I do not work in that industry, but it is my understanding that high end eqipment for measuring such specs use transformers for attenuation. With a transformer, you get an exact replica of the sound wave but at a smaller level. Distortion in the sound wave would also be duplicated on the output. This without adding impedance to the circuit. MP

Here are some good links on voltage multipliers: http://www.tpub.com/neets/book7/27m.htm http://braeg.piranho.com/e_s/2theory/2_6_1_voltage_multiplier.htm Yes, all of the capacitors should be the same value. The circuit depends upon the direction of voltage from the rectifiers charging the capacitors, which depend upon the charging rates to be the same. The voltage multiplier could become unstable with different capacitor values. MP

THD is a measurement done at a particular output impedance. You are expecting a certain number of watts at 4 ohms. You will see measurements on stereos that will vary such as 0.1% THD into a 4 ohm load or 0.1% THD into an 8 ohm load. If you change the output load, you will change the distortion factor. When you put your resistor divider on the output of the preamp, you put a 100ohm resistor to ground. You just changed the output impedance of your amp. Now it is not 4 ohm or 8 ohm, but instead, it is a 100 ohm impedance. This is what changed your spec for total Harmonic Distortion. Not the amplification factor. MP

Another tip I will add: (1) Use liquid solder flux on the pins before you solder. You can clean them later with alcohol. It will leave a nice clean connection and cause the solder to flow faster. (2) If you get solder between the pins causing a short, use solder wick to absorb the excess solder. Flux will also help this to go faster and cleaner. MP

Yes, that is exactly what I meant. The diagram in the article you have posted also gives a little better detail regarding the reason behind this. MP

Current does not go up and down in a path. It remains the same. Perhaps I do not understand the question? MP

For those who have been searching the web for the material I spoke about in the last post, I contacted 3M to get an update on the product. Here is the reply I have received today: ************************************ snip Thank you for your inquiry of 3M! The product you are searching for was called Dynamark II. 3M discontinued this product line 7/8 years ago. No replacement is available either. There are a couple of our distributors who did find a similar type product from OUS. You could try them. VPC at 800-447-1944 and Metal Photo at 800-482-7758. ************************************ If anyone finds the similar product and a web link, please post it here for all. MP

I would not leave them out. Why should the current run through these 2N3055s equally? There is nothing there to cause it. There is no balance here. The resistors will cause current to flow equally through all of them. If 1 2N3055 is doing all the work because it has the least resistance, you have a problem, don't you agree? MP

The heart of your circuit can be a 555 timer. A resistor and cap determine the time, so you can have the switches determine which resistance is used. I have attached a link or a tutorial on a post somewhere in here. Use the search function for 555 and you should find it. You should be able to prototype the circuit on a bread board in one evening and complete the project by the next. MP

what do you mean by reasonable? Do you mean parts availability? Ease to build a circuit? Component count? Converting an AC signal to a DC signal is as easy as rectifying it and adding a few bypass caps. This is pretty much standard throughout the frequency range. MP

maestrodamuz, I think you will want to relabel the voltages in and out of the LM317. I think you mean positive voltages here. ;) MP

Here is a schematic and board layout that was donated by someone to the Eagle site. It is free to use. It looks like the project, but might be a little different. If you have the free version of the eagle, you can view it or even edit it to be what you want. If you do not have the free version of Eagle, go to http://www.cadsoftusa.com/ and download it. ICL7107.zip

I do not have the data sheet, but I do have this information: 2SJ50 - 160V, 7A, 100W P-Mosfet in TO-3 case. 2SJ55 - 180V, 8A, 125W P-Mosfet in TO-3 case. and in case you have this also: 2SJ56 - 200V, 8A, 125W P-Mosfet in TO-3 case. Hope it helps! MP

Although I know nothing about the Spectra software or your particular circuit, here is some general information regarding this. Total Harmonic Distortion is directly related to your amplification circuit. If you need to use an attenuation circuit, you will always have the characteristics of that circuit added into the mix. If you can find a pattern such as the circuit always reduces the THD by 0.2%, then you can compensate with a calculation. What kind of a circuit are you using to accomplish attenuation? Many companies drop down the voltage with a transformer (sound is an AC signal). High end sound equipment uses Balun transformers to change high and low impedance devices to match each other. You can find lots of information on the web regarding this principal. Any time you use op-amp or transistor circuits you are changing this THD spec. Hope this is helpful. MP