Better transistors for the class-A amplifier
For the 20W Class-A Amplifier, is it possible to use MJL1302A & MJL3281A transistors instead of the specified MJL21193 & MJL21194 devices? I presume the transistors I have are genuine On Semiconductor as they have a circle printed with "ON". (N. J., via email).
Offset problem in Studio 350 amplifier
I have constructed two Studio 350 amplifier modules (SILICON CHIP, January/February 2004) from kits supplied by Altronics. For each kit, adjusting VR1 never brings the output to 0V; rather it adjusts between 120mV to 10mV from one extreme to another. Curiously, one kit stays positive with respect to ground (+120mV to +10mV over VR1’s range) and the other stays negative (-10mV to -120mV). With VR1 in its centre, the offset is about +35mV in both cases. VR2 adjusts the idle current just fine.
I have not yet tried removing the 470W set-up resistors and applying a signal, as I am not particularly keen on using something that hasn’t passed its tests. I have checked all the voltages against those printed on the schematic in the article and they’re all within about 20%, although some only barely.
The power rails measure 72.5V rather than exactly 70V and I have not yet hooked up both amplifier modules at the same time. I am considering swapping the 2SA1084 transistors from the long-tailed pair in case they’re poorly matched enough to cause this issue. (M. J., via email).
Short circuit in
Comparing Rechargeable & Non-Rechargeable Cells
I have a question regarding conventional (non-rechargeable) batteries versus rechargeable batteries. Just taking standard "over the counter" cells as an example (AAA, AA, C & D), rechargeable cells always come with a mAh rating, whereas conventional batteries (heavy duty, alkaline, etc) do not. I know rechargeable cells are 1.2V and conventional batteries are 1.5V. But what I’m not clear on is which type of battery would produce the highest short-term peak current?
Obviously, if the internal resistances were identical, then 1.5V would "push" more current into a given load than 1.2V but is it that simple? Are the internal resistances similar in each type of battery?
Why don’t conventional batteries have an mAh rating and why do some toys say not to use rechargeable batteries? In my case I am looking at modifying a launch controller for model rocketry clustering. Launch controllers in rocketry are used to supply current to a Nichrome wire igniter-head, which in turn ignites the rocket motor. When clustering (ie, igniting more than one rocket motor simultaneously), it is essential that the controller provides a high current for a short period (1-3 seconds), otherwise the situation could arise where one or more motors may not ignite before lift-off occurs, which could lead to serious damage to both the rocket and the pocket, to say nothing of the potential hazard to spectators!
This leads to my final question: for a given number of cells (most controllers hold four AA cells), would the best solution be alkalines, rechargeables or the "newer" non-rechargeable Lithium cells? Any assistance would be greatly appreciated.
If used for a short time each day, they will provide more capacity than if used continuously. The current draw also changes the available capacity.
Rechargeable cells state the capacity because this information is needed to be able to recharge them and their capacity is fairly consistent over a wide range of applications.
Some toys cannot be used with rechargeable cells because they are voltage sensitive and may not work well with the lower voltage available from rechargeables. Rechargeables can also damage toys with motors because high current delivered to a stalled motor can burn it out. In general, rechargeables can deliver higher currents than non-rechargeable cells.
The current available from a cell depends on the chemistry and the manufacturer. Generally, Nicad cells can deliver the most current but these days NiMH cells can deliver high currents as well.
In general, if you have any device which can accept rechargeable cells and you use it a lot, then rechargeables are the better proposition.
I am really keen to build the Serial I/O Controller kit but there’s one question that has been plaguing my mind for months now. Is there any way to interface this card with a computer and have the card control functions of software on the computer?
What I am trying to achieve is finding a method of utilising this card to run batch files on my computer to do automated tasks should a condition change on the card’s inputs. Is this possible? If so, what modifications would I have to make. (J. H., via email).
Notes & Errata
PIR Sensor Triggered Mains Switch, February 2008: the O11 output mentioned in the text on pages 58 and 59 and on the circuit should be the O10 output.
Multi-Message Voice Recorder, December 2007: the resistor from pin 7 of the HK828 should be 47kΩ and the parts list should show nine 47kΩ resistors and only one 10kΩ.
UHF Remote Mains Switch Transmitter, February 2008: Transistor Q1 is a BC327 (PNP) as listed in the parts list. The circuit labelling is incorrect. In addition, the parts list should have 5 10kΩ resistors not 4.
Electricity Saving Box, November 2007: the formula published in Fig.6 (page 26) should read: q' = tan-1 (w (L - w2CL2 - CR2))/R = 59.98° which leads to cos(q') = 0.5.
The set of commands that are available are explained on page 78 of the November 2005 issue. For the application that you have in mind, a simple C program could be written that will run on the host PC. It would continuously monitor some condition, by periodically sending commands to the Serial I/O Controller, and it would analyse the received data. It would then take action, such as executing another program, if some condition is met.
In other words, the application you have in mind can be implemented but you will have to:
(1) Write a C program (or equivalent in some other high level language) to poll the Serial I/O Controller periodically and analyse its output;
(2) This program must run on the host PC and must be always running - the host PC will have to be on for a start.
(3) This program will preferably be loaded automatically by the OS (operating system) and work in the background.
As you can see, it can be done, yet the solution is not ideal, mainly because polling is an inefficient way to implement your application.
I was interested in the article on PC recording (SILICON CHIP, November 2007) as I am about to buy a new laptop computer for audiovisual work. You mention the audio testing software "Rightmark Analyser" but how would I test a new computer before purchase, to see if it is suitable?
What are the preferred specs for a laptop? Few of them appear to be media-orientated with AV sockets fitted. My old Pentium 400 had a separate Pinnacle sound card in one of the motherboard slots – this had a full set of RCA in/out connectors on the rear metal bracket.
I have spoken to four different computer suppliers and they say that any late model should do but can’t be sure. They’re a bit vague, refer me to someone else or don’t reply. Even a consultant who specialises in recording has not replied. Yet I’ve seen concerts being recorded straight into laptop computers.
Enquiries to the PC user group for technical specs are for members only. So maybe I should join then investigate this recording aspect. (P. S., Albert Park, Vic).
Generally, cheap laptops have cheap
and dirty sound circuitry but a high price is not always a guarantee of high quality. However, there are a number of ways of making sure you get a good one:
(1) Take a copy of the analyser program with you and ask to test it before you buy it. Most places will allow this and if they don’t then try (2) below.
(2) Make sure you get a "money back guarantee if returned within X days" deal and simply purchase the laptop. Take it home and analyse it. If it’s no good, take it back and demand one that works properly or you want a refund.
(3) In the unlikely event that both of the above are not possible, then get a high-quality music sampler CD that you know intimately and a set of high-quality headphones – the best you can get, even if you just borrow them. Play the CD and listen to it on a known system of high quality. Then try it on the laptop in question.
If you have good ears, then it should be readily apparent if the laptop is not up to spec – if you don’t, then the whole matter is rather moot anyway. Chances are that if the manufacturer has gone to the trouble of designing a good audio playback stage in the laptop, then the recording section will also be good.
As to what constitutes good specifications, just compare its performance with that of high-quality amplifiers: 20-20kHz within ±1 or 2dB; less than 0.1% distortion; -70dB hum and noise or better. There is no need to go overboard on specifications. The main thing is that the finished result sounds good. A poor quality laptop will soon reveal itself in this regard because results will simply not be pleasing to the ear, even when everything else is done correctly.
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