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Getting more bass boost I have recently completed the 50W Stereo Amplifier and preamp, and it works very well. Having stated it works very well, I would like greater or more bass boost. What components should I change to increase bass response? Also, if I wished to tape record, say, “phono”, it would seem that “phone” to “tape out” bypass the preamp and amplifier. Can you help please? (M. D., Beechboro, WA). • You can increase the available bass boost and cut at very low frequencies by reducing the 22kΩ resistors at each end of the bass pot (VR2) to 10kΩ. However, doing this is also likely to increase the possibility of amplifier overload on problem but this could then make the warranty void. Even when the washing machine is switched off at the ma­chine, there is still interference but not so severe, so the machine has to be switched off also at the power point. I have contacted other people via my CB radio that have the same problem so it is generalised and I was disappointed with the reply from Fisher & Paykel who made it sound as if mine was an isolated case. I thought that because it was a problem affecting the public in general you might be able to suggest some form of suppression that could be added externally to stop or at least reduce the interference. The suggestion by the SMA that none of the affected items be used when the washing machine is being used is unacceptable in 1996. (J. C., Waroona, WA). • We agree that the interference does seem rather severe. At this stage we can only suggest that you invest in a good line filter; it will need to have a rating of at least 10 amps and should be capable of coping with any surge current from the motor. Single channel operation for VHF receiver I am a fanatical reader of your magazine which I am getting from a relative of mine in Australia. As a student of 94  Silicon Chip bass-heavy program material. A better approach, which will increase the apparent bass boost and cut, is to reduce the .01µF capacitor shunting VR2. This will raise the turnover frequency of the bass control so that it has a more audible effect at higher bass frequencies. Try a capacitor value of .0068µF. We should point out that raising the bass turnover frequen­cy in this way will increase the interaction between the bass and treble controls. In virtually all amplifiers, when the tape monitor function is used, the amplifier circuitry is effectively out of the pic­ture. The only exception is if you are taping a record and then the RIAA preamplifier is in circuit. electron­ics, I am very interested in RF communications devices and I found an article from your magazine, the VHF Monitor Receiver from the March 1989 issue. I would be very obliged to you if you can send me any schematics to modify it in order to operate it as a single channel receiver. (L. P., Athens, Greece). • There is no need to make any modification to the circuit to operate it as a single channel. Just use a multi-turn trimpot to tune it to the wanted channel. Message recorder variations I bought the 16-Second Solid State Message Recorder at the time it was published in October 1993. Then, in October 1994, the Talking Headlight Reminder circuit was published. I kept the two magazines inside each other, with the idea of using the message recorder for the headlights at a later date. Now that I have examined the two, I notice that the updated ISD1416 has a record pin (27) and a playback pin (23). In the Message Recorder circuit, pin 27 gets connected to the positive rail to play back and to the negative rail to record. Could I still use the 555 of the later circuit to turn on a PNP transis­tor between pin 27 and the positive rail to make the older chip work for the headlights? Do you have any ideas about this please? (D. S., Caloundra, Qld). • The Solid State Message Recorder was published in July 1993, while a version from Dick Smith Electronics was published in the October 1993 issue. We are not sure which you are referring to. However, for the October 1993 version we recommend connecting the pin 27 input of the recorder to play back as selected by S1. The cathode (K) of LED1 should go to ground and the Vccd pin (pin 28) to a switched positive supply. This could be obtained directly from the pin 3 output of 555 timer IC1 for the Talking Headlight Reminder. If you are using the July 1993 recorder, the pin 3 output of the 555 can connect directly to the S1 play switch. TV pattern generator output is distorted I have a problem with the Colour TV Pattern Generator which I have put together in the correct format. The seven separate patterns, except the dot pattern, appear on the television but there is a lot of distortion on the screen and, therefore, the patterns don’t show up as being clear. I get a lot of vertical distorted lines with zig zags and it’s off frequency. Could you please advise me as to where the problem might be? (M. S., Chis­wick, NSW). • From your description of the symptoms it appears likely that the circuit is affected by hum breakthrough from the power supply. The most common cause of this is the failure to use a plugpack transformer of adequate rating. It needs to be rated at 500mA or more. A 300mA unit is inadequate. Notes & Errata 175W Power Amplifier, April 1996: to further increase the safety margin in the event of amplifier failure, we suggest that the fuses be changed to 3A instead of 5A when 8Ω loudspeakers are used. Photographic Timer, April 1995: the bridge rectifier specified as “WO4” does not have the same pinout as the DIP rectifier depicted on the PC overlay on page 27. If a WO4 type is used, two of the leads will have to be swapped and sleeved so it can be SC installed in the PC board.