White noise generator for tinnitus treatment

I am looking for a white noise generator to help my mother who has tinnitus. As far as I can determine from the (limited) published literature, the white noise generator works by distrac­tion only. You may find the following website useful:

http://www.gold-line.com/pwn1.htm

As far as the medical literature is concerned, the condi­tion is poorly understood and treatment options are limited. I suspect someone tried white noise on a patient, it worked, and it then found its way into the literature. My understanding is that low level noise helps in retraining the brain. Anyway, what can you suggest? (G. M., via email).

We have not described a white noise generator but we have described a pink noise generator in the January 1997 issue and it was also featured in our recent publication "Electronics Test­Bench". It should serve the purpose although it would be easy to remove the "pink" filter components to make the noise "white".

White noise has a uniform energy spectrum; it rises at 3dB per octave. Pink noise is white noise with a 3dB/octave filter applied to give equal energy per octave. As far as tinnitus is concerned, the effect of pink noise would be exactly the same as white noise.

Frequency change for Tandy R/C cars I have recently purchased two radio-control cars for my children from Tandy Electronics. The problem is that the two cars are both on the same frequency, 27.145MHz . I had thought of changing the crystal in one of the cars but it only has one in the trans­mitter, not the receiver. What should I do? (C. O., via email). If there is only one crystal in the system and it is in the transmitter, it is possible that the receiver is a super-regenerative type with a bandwidth of around 2-3MHz. That means that you can only operate one receiver at a time on the 27MHz band. According to our R/C guru, Bob Young, this is how radio-control began back in the olden days. They flew one model on 27MHz and the other on 40MHz. Then along came superhets and changed everything. According to Bob Young, if it is one of the modern super-regen receiver chips, it could possibly have a bandwidth of only 200kHz which may make it possible to squeeze one transmitter in at the bottom (26.995MHz) and another at the top on say, 27.255MHz. If you want to try it, Silvertone Electronics can supply crystals cut to those frequencies if required, at $21.50 each. See their advertisement elsewhere in this magazine.

Query on UHF
remote switch

I am interested in the "UHF Remote Switch" featured in the December 1989 and August 1990 issues of SILICON CHIP. Before procuring photocopies or back copies of the relevant articles I have a couple of queries.

I understand that the RF transmitter is based on discrete components. Does the design for the RF receiver portion use a pre-built module or is it also based on discrete components? If it uses a pre-built module, do you know if this is still easily obtainable?

I am particularly looking for a design for the RF section of a 308MHz remote-control receiver to interface with an MC145028 that uses readily available parts and I favour one that uses discrete components. (J. P, via email).

The design in question is very old and you might want to use a later one. The transmitter has a Motorola 41342 encoder chip which may not be available now. The receiver does not use a prebuilt module. Later designs do. Check out the designs in February 1996.

More 12V outlets from PC PowerHouse

I am in the process of building the PC PowerHouse, described in the December 1999 issue of SILICON CHIP. I would like to change the 5V outlet to 12V (thus having two 12V outlets).

Another idea I have would be to purchase a used PC power supply and (either with or without the PC Powerhouse kit) use this unit to supply another two or more 12V outlets (without a PC). How can this be done? I don’t have much need for the lower voltages. (A. Z., via email).

If you don’t want the lower voltage outputs, you can have up to three 12V outputs simply by placing a link across each of the 3-terminal regulators. If you want to use a PC power supply direct and you only want 12V, you don’t need the PC PowerHouse at all – just use the 12V directly from the power supply.

High energy ignition will not start car I purchased the High Energy Ignition kit from Jaycar Elec­tronics, assembled it without any problems, connected it into my daughter’s Datsun 200B and the car will not start. It spins over OK but there is no spark getting to the plugs. The Jaycar people have looked at it and couldn’t see anything that was obviously wrong with it. They gave me a replacement IC in case the original was faulty but this didn’t help. Do you have any suggestions? (D. M., Canberra, ACT). You really need to do a bench test on the ignition system, with a coil fitted. You do not say whether the car has points but you need to simulate the closing of the points (or whatever the pickup is) to see that a spark is being delivered by the coil. The coil should have a spark gap from the HT connection to one of the primary terminals. You can do this with a paper clip and arrange for a gap of no more than 6-8mm. If you operate the coil without a spark gap, you may blow it internally. We doubt whether the IC would be at fault. The most common problems with any kit are missed solder joints or shorts due to fine solder splashes across the tracks.

Switched capacitor speed control for fan

We have a ceiling fan about 10 years old (maybe a bit less). It came with a multi-tap choke control, which was not installed. Instead, a solid-state Clipsal fan control was used, together with a SPDT centre-off Clipsal switch, enabling the fan to be run full bore, bypassing the control, or through the vari­able control. This was done purely for aesthetic reasons. The original choke control has been lost.

Now the solid-state control has died (the fan works when the switch is set to bypass the control but won’t work via the control). The new fans one buys now use a multi-position switch to switch in different capacitor values in series with the fan.

I would like to replace the faulty solid-state control with one of these capacitor ones, as it will free up a position in the switch plate, to be used for an extra light. Will the new capacitor controls (a Clipsal one) work with the older fans or are the motors different now? I don’t want to just go out and buy a capacitor control only to find it either won’t work or it ruins the fan motor.

Of course, it may well turn out to be cheaper to buy a new fan, the way prices of things are these days. (J. B., via email).

Trying a switched capacitor control could be a bit of a lottery – we don’t know whether the new fan motors differ sub­stantially from the old one.

Why don’t you just fix the solid state control? It is likely to need a new Triac. We published an article on fixing light dimmers in the November 1996 issue. You can also buy switch plates which will accommodate three switches – or one switch either side of the dimmer module. We can supply the November 1996 issue for $7.70 including postage.

By the way, Triac fan speed controllers are now available quite cheaply from hardware stores.

Adding a kill switch to the 5 Band equaliser I was considering adding the 5-band equaliser from your December 1995 issue, to my mixing console. I was wondering if I insert a notch filter or similar on each of the bands to effectively cancel them when not needed; similar to the kill switches found on DJ mixers. Or maybe I could extend the ranges from the usual ±15dB on each band. A kill switch beside each pot control would also be effective. Is this possible? (E. Z., via email). The kill switch probably does not introduce a notch at the frequency selected but simply restores the equaliser band to flat. This could be implemented by switching the wiper of the control pot to a second resistive divider across the pot. The resistors would each be 22k. Extra boost and cut can be achiev­ed by changing the 10k resistor between pins 10 & 14 of IC1. A larger value will in­crease the boost and cut. Adding a fixed resistor in series with the pot will restrict the control range. One in the top will restrict the boost and one in the bottom will restrict the cut.

More range wanted from speed controller

I have just successfully completed the Universal Motor Speed Controller described in November 1992 and put it to good use. However, the power tool I am using with it does not run at full speed. In fact, the measured output line voltage with the tool running is only 145VAC.

I am using a Dremel Moto-Tool, rated at 110W and 0.48A, running at 30,000 RPM. Is this as expected or is there a modification to the controller that I could make? (G. C., via email).

The unit is working pretty much as expected. The circuit is essentially a controlled rectifier and so in theory, the maximum output voltage to the motor is about 170VAC.

If you want control over the full range of a motor, including full speed, you need to build the 10A 240VAC speed controller described in the November 1997 issue. We can supply this issue for $7.70 including postage.

Zener diode tester availability

I am inquiring as to who may still be supplying the kit for the Zener Diode Tester described in the March 1996 issue of SILICON CHIP. If there is no supplier, where can I obtain the harder to get parts such as the Philips transformer assembly and its parts, the 1N4936 fast recovery diode and the 56V 3W zener diode. (D. S., via email).

The kit for the Zener Diode Tester is no longer available. The PC board can be obtained from RCS Radio. Phone (02) 9738 0330. The EFD20 transformer is available from Farnell Electron­ics; phone 1300 361 005. Cat­alog numbers are 200-270 for the core (2 required), 200-281 for the bobbin (1 required) and 200-293 for the clips (2 required). The 56V zener (368-428) and the 1N4936 diode (366-950) are also available from Farnell.

Fault in high efficiency fluorescent inverter Can you please assist me with the fluorescent light inverter published in November 1993. I have construct­ed the unit to suit a 36-40W tube. The light came on OK and a short while later it failed. I replaced the 5A input fuse and as soon as light came on, the fuse went again. Can you help? (P. W., via email). With the fluorescent tube out of circuit (disconnected) check that the inverter produces 340V between the drain of Q3 and source of Q4. If not, check that transformer T1 is wound correct­ly. Windings for the primary are wound by terminating wires at pins 4 & 5 of the transformer and winding both wires for four turns and terminating at pins 7 & 6 respectively. The secondary at 136 turns starts and finishes at pins 2 & 1 respectively. Check that the transformer is correctly oriented on the PC board. Check the voltages at pin 1 of IC2 and pins 12, 11 & 8 of IC1. These should all be at 12V with respect to ground. Also check the orientation of the diodes and that the zener diodes are in their correct positions.

Cheaper transformer for 500W amplifier

I was interested in building the 500W amplifier described in SILICON CHIP during 1997. I just want to find out if I could substitute a cheaper transformer or if there is some other way I could power the amplifier for a lower price.

Just recently, I went to the Altronics website and saw they have a 50V + 50V 500VA toroidal transformer (Cat M-5750). Is this transformer going to suit the design? (B. B., via email).

A 500VA transformer is nowhere near big enough if you really want 500W output. The rule of thumb is that a class-B amplifier is about 60% efficient at maximum power and if you do the sums, you need 833VA. That’s why we specified 800VA. Also 50V a side is a big reduction on the 57V specified and that would mean a reduc­tion in power output of about 23% or about 380W maximum. We’re afraid there isn’t any easy answer.

TENS kit wanted

I’m after a TENS kit as featured in SILICON CHIP, August 1997. I have tried Dick Smith Electronics but have been told they are no longer available. Could you help in obtaining one please? (T. S., via email).

While this kit is no longer produced, all the parts should be readily available. The PC board can be purchased from RCS Radio. Phone
(02) 9738 0330 or www.cia.com.au/rcsradio

Ultra-low distortion amplifier query

I bought a pair of low distortion amplifier modules (pub­lished by SILICON CHIP in March & May 2000) from Altronics, thinking that they would be perfect for a subwoofer project I am doing. Unfortunately, I bought the modules sight unseen, having not read the original articles. I need to use the modules to drive 4 loads and note that this impedance is not recommended.

Can any modification be performed to improve reliability (force more equal current sharing)? Your article notes that emitter resistors were tried on the output devices but they increased distortion.

In my application, ultra-low distortion is not needed and I won’t be feeding them anything above 200Hz. My intended bass driver has dual voice coils. The plan was to feed each voice coil from a separate amplifier. (P. H., via email).

There is no easy or effective modification to make these modules suitable for 4 loads. The ideal choice would have been to pick our Plastic Power module (175W into 4) published in April 1996 but not available from Altronics. Your best course may be to ask for a credit and buy the Altronics Mosfet amps (K-5170) which are rated for 200W into 4. Their distortion is nowhere near as low (despite being quoted at .007%) but they would be quite suitable for your application.

Fuses for toroidal transformers

Last week, the transformer on our church equaliser went open circuit on the primary side. No other faults were noted and the fuse was intact.

As a new transformer is $60-80 and 10 weeks away, I was advised to substitute a 15V toroid, which I have done (Jaycar MT-2086). The EQ unit had a 150mA 3AG fast-blow fuse which blew immediately at power up when testing the toroidal transformer but with a higher-rated fuse the transformer is putting out the correct voltages.

I recall some time ago reading that toroids have a high inrush current and require higher-rated fuses than conventional transformers but cannot find reference to the information any­where. I note that the LP Doctor described in January 2001 uses a 1A slow-blow despite the obviously minimal current of the operat­ing circuit and assume the fuse type is to prevent the problem I am observing. Should I use a slow-blow type fuse? (G. C. via email).

The fuse in the LP Doctor is wrong. It should have been 150mA slow-blow. We suggest that you use the same value for your EQ unit. The article on fuse protection in toroids was published in the March 1995 issue. We can supply it for $7.70 including postage.

Turbo timer runs at switch-on

I have installed the Turbo Timer, described in the November 1998 issue, on a Toyota 2.2 litre 4-cylinder diesel. The problem is that the timer appears to be running as soon as I start the engine for the correct time but it does not run when the engine is turned off. I have checked the wiring a couple of times but cannot find a fault. I must have made a mistake somewhere. Can you please assist? (D. S., via email).

There is possibly a wiring error on your Turbo Timer, with the 87 and 87a terminals on the relay (RLY1) transposed. Alterna­tively, the ignition voltage may not fall quickly when it is switched off due to an accessory that is connected to the igni­tion which has some storage capacitance.

You could try placing a 100 5W wire wound resistor between terminal 87a of RLY1 and 0V (ie, chassis). This should discharge any capacitance across the ignition supply.

Ballast resistor runs very hot

I recently installed a High Energy Ignition System (de­scribed in June 1998) into a Subaru Fiori and while the unit works very well, the temperature of both the ballast resistor and the coil worry me a little.

The resistor is so hot it will blister skin if touched and while the coil is not as hot, it is still quite warm.

I realise that the average DC current will be greater now (about twice) and that the unit is current limited. I am still concerned about the long term effects of the high temperatures, particularly on the resistor. Any comments? (B. S., Canberra, ACT).

Any high power wirewound resistor will run at very high surface temperatures when running at more than 50% of its rated power. You could always reduce the current limit figure somewhat and also ensure that airflow around the coil and ballast resis­tor is as unrestricted as possible.

Connecting the theremin to a guitar amplifier

I just purchased a Theremin kit (described in the August 2000 issue) and was wondering if I could replace the line out from an AV type plug to one that could plug into a guitar amp? (L. J., via email).

Yes, you can connect the There­min to a guitar amplifier but you will need to reduce the signal level. Connect a 10k resistor in series with the 10F output capacitor and replace the existing 10k resistor at the output with a value of 1k. This will reduce the Theremin’s output from a nominal 500mV to 50mV.

Running two tubes with the fluoro inverter

I intend to purchase a kit for the high efficiency fluores­cent inverter from Altronics but I have a question about it. Will this kit run two 20W tubes in parallel? (J. H., via email).

In existing form, the inverter will not drive two tubes in parallel because once the first tube ignites, there will be insufficient voltage to ignite the second.

The only way to do it would be to have a common 340V supply and then build separate driver circuits (involving transformer T2 and Mos­fets Q3 & Q4) for each tube. The easiest way to do that would probably be to purchase an extra PC board (from RCS Radio) and use the driver end of the second board to power the second tube.

Notes and Errata LP Doctor, January 2001: the specified fuse is wrong. It should be 150mA slow-blow.PIC Programmer and Checker­board, March 2001: the text on page 69 (third column) refers to jumper J2 and switches SW3 and SW4. These should be JP2, S11 and S12, respectively. The circuit diagram and overlay are correct. On the PC board, there is insufficient space to fit the 2200µF 25V filter capacitor but a value of 1000µF 25VW will be adequate. Also the 10k pullup resistor for RA4 on the LCD adapter is not low enough to give reliable operation. Use a value of 4.7k instead.Bass Blazer, February 2001: some filter PC boards (code 01102011) may not have a connection between pin 4 of IC6 and V+. This connection provides power to IC6. If your PC board has this error, use a short length of fine insulated hook-up wire to connect IC6 pin 4 to the cathode end of D9. The relevant PC artwork on our website has been corrected.

WARNING SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable.