The Steel Guitar Forum

Keith, how does Goodrich do it?? They too are a relatively small operation but they have PC boards in their products - obviously hand soldered. Goodrich is probably not paying big bucks for their PC boards.

Jack, correct me if I am wrong, but I think all of the Goodrich equipment runs on batteries only. There is nothing wrong with hand soldering, except that the labor cost is high. I am constantly trying to hold a line on cost and price increases. Recently, I had a manufacturer jump the price of a part I was buying from $6.00 to $36.00. There is a limit to everything. I suppose they thought I "HAD" to have their part. I simply designed around it. Jack, by using batteries only, the Goodrich Company you mentioned, gets out of building power supplies. When you build a circuit that is powered from house current, there are a few more parts on the board.

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Some of the Goodrich products run on batteries or external (wall wart) power supplies, such as my MatchBro. I have a friend with a Goodrich volume pedal (not a photocell model) and I seem to remember it has a built-in power supply (I've never looked inside so I don't know what type of power supply it is) as I I recall is the AC power cord running out of it.

Well Jack, I stand corrected. I have not studied Goodrich products at all. I've just never seen one in use powered by anything but batteries.
The question at hand "TODAY" is this: The Peavey Pro-FEX II is powered by a 16 volt AC power wall wart. If you take a reading with a meter, the actual output of the Peavey 16 volt AC wall wart is 19.18VAC.
If this power is run through a voltage doubler, by someone plugging in the wrong plug, what happens. If we double 19.18, we get 38.36VDC. Then if we multiply that by 1.4, we get 53.70VDC. Now, if we have a dual polarity power supply, that puts half of the 53.70VDC on the plus and half on the minus. This means that there are 26.85volts DC on each side to ground, or 53.70 from plus to minus. The next question is wheather or not 7812 and 7912 voltage regulators would work and last, without heat sinks with 26.85 volts DC put on them? Next question after that is this: Will National Semi-Conductors LM2940 and LM2990--low drop out regulators work and last, without a heat sink with 26.85 volts put to them. When you design a power supply, you must assume that a musician will pug in the wrong thing. You must design it where nothing bad happens.

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Keith....

I think you are makeing this power/hum problem really a problem only for your-self..

Example:

I have a Profex II, I know it is a 16 volt AC unit. Why would I even think of trying to power it using a 38 volt 4 pin Dual power Wall-Wart? First, it wont fit. second, its the wrong voltage.

While understanding that you design and build verious pedals and other equipment(which we all know of and some of us are lucky enought to own), I wonder if you may be putting too much thought into design of the power supply section of these units? One of the above post suggested that we may be attempting to cover up the problem instead of realizeing that it's really a DC ripple thing. I agree that if a battery is used as a power supply, the hum factor goes away. (This thought dosen't take into condersation the width of a copper track and other design things on a PC board, at this point.)

I guess my main point is:

We have to accept a cost value in the production of a product, and in general, if the product is good, we go for it, if bad, we learn not to buy it.

I have several "BOSS" stomp box units, I power them with a single power supply (read as a Wall-Wart) and have no problems with them. (After opening them up, I see that most of them have a good filtering system, DC ripple circuits, My Profex II is a good example, If the wall-wart is in close proxcemity (sp?)to the front end, it humms like hell, if a few inches removed, it's quite as a mouse. Therefor, I know to keep it a bit removed from the unit.

A lot of hum problems that you may think are P/S related may be related to other things.

First, in response to making a + and - voltage from a 2 wire wall wart. This can be done by setting up a simple resistor network that splits the voltage in half. This voltage feeds an opamp that is set up as a buffer. The output of the buffer becomes your ground point. I have seen this done before, but not the best choice for audio stuff.
Second, I agree with the idea of just going to single voltage and setting up the bias point for audio using resistors to split the voltage in half. That's what's done in most stomp boxes. To get more headroom I would recommend going higher than the 9-10 volts that you get from a battery.
Third, I have seen 3 wire wall warts. That would be the best solution.