How to vary spring reverb time

I have built two of the reverb units described in the January 2000 issue into a single enclosure for my band co-member and we are quite impressed with the performance. The only issue we have is that for vocal use, the reverb length is too long, thereby muddying the sound. Is there a simple mod which will address this problem ? I guess what I’m after is a "reverb duration" control. (J. S., via email).

 The reverb delay is fixed by the springs and cannot be adjusted easily. You could try reducing the length of the springs but that brings the risk of permanently damaging the unit.

Optical fibre project suggestions

There is a lot of debate at present regarding mobile phone radiation. Even the hands-free kits are suspected of channelling radiation into the ear and possibly being worse than not using them. How about a project which uses a fibre link between the phone and the hands-free earpiece and microphone? With no wires there would be nothing to conduct the RF emissions. I realise there would be challenges with power and size but I’m sure something could be achieved. (I suppose a cheaper option is to put a ferrite choke in the cable somehow.)

A related project suggestion is for a fibre-optic stereo transmitter/receiver. For example, my CDs are in the house but I’m doing some work in the shed. Wouldn’t it be great to be able to listen to them there? I figure a fibre-optic cable from the house to the shed, an appropriate transmitter plugged into the amplifier (line-out probably), a receiver in the shed plugged into a second amplifier (line-in). There would then be no worries with earth loops or long speaker cables or induced noise, etc

A neat extra (which would considerably increase the cost no doubt) would be to make it duplex so that using a remote control in the shed, I could control the CD player which is in the house (similar to what you can do with B&O gear which I would love to own but cannot afford).

And how about an opto-isolator for modem lines so that they don’t have to be unplugged from the modem every time it looks like a storm? (M. B., via email).

 It does seem possible that the lead for the hands-free mobile phone kit could act as a "counterpoise" and thereby contribute to stronger radiation of the mobile signal. An optical fibre solution would be tricky and would require a separate battery supply as well. Your alternative suggestion of a choke in the lead could be a simple and effective solution.

As far as your CD player is concerned, the most effective solution would be to use its optical output (if it has one) and feed it to a D/A converter in your shed. However, while it could be done, the cost is likely to be more than the price of a portable CD player – you can buy them for around $125 now.

And as far as an optical isolator for phone lines is concerned, it would only remove the lightning protection issue from the modem to the isolator; after all, the isolator would still need a mains supply and it is the potential difference between the phone lines and the mains supply which blows modems.

How to avoid blowing the bass barrel I’m presently building my second Bass Barrel subwoofer (as described in the August 1997 issue) but this time I’m making it from MDF board. Why? Cos I blew the first one up! And since I had put it all together with Liquid Nails there was not much chance of pulling it apart to change the drivers! I drove the original one with one channel of a stereo integrated amp (at least 120W into 4W) and I think it was a bit much! What is the nominal rating of the barrel? And what size amplifier module would you suggest? I have built the Altronics sub-woofer controller as well and would like to build a small amplifier inside it to make it a self-contained unit. I am thinking of using the 50W stereo module described in the February 1995 issue and then using one channel to drive each speaker as the Altronics controller can provide in-phase and out-of-phase outputs. I would rather have the amplifier a bit too big than too small. (D. A., via email). We would suggest that you feed no more than 50W into the Bass Barrel system. If you drive each speaker with 50W you will blow it for sure.

Dolby decoder kit wanted

I am currently upgrading my hifi system and I am looking at upgrading to a surround sound system. As a kit builder I am wondering if SILICON CHIP is going to do a decoder for Dolby analog, digital or other in the near future, or whether this sort of technology is beyond the scope of a kit.

I have had a look for the "Dolby Pro Logic Surround Sound Decoder Mk.2" kits but have been unable to source this particular project. (D. H., via email).

 Our last Dolby project was in November & December 1995 and the project has now been discontinued. Since then Dolby decoders have dropped markedly in price and so another Dolby decoder project would not be viable.

Speed control won’t regulate

Could you please help me with a problem with the motor speed control published in the June 1997 issue? I purchased a kit and had no trouble with it until I damaged it (my fault). Rather than spend time fixing it, I purchased another kit and built it. However, it won’t regulate more than a couple of volts. In the test sheet they show pin 16 of the IC at +12V but in the circuit diagram it shows pin 16 grounded; the other readings seem close. Can you help please? (J. D., via email).

 Pin 16 of IC1 should be at ground as shown on the circuit. The mention of pin 16 being at 12V is a misprint and should say that pin 12 is at 12V.

You can test the circuit by measuring voltages. There should be +12V at pin 12, +5V at pins 14 & 15. Check that there is not a short between the drain and source pins of the Mosfets Q3 and Q4. Pin 13 of IC1 should be at ground.

Check also that the voltage at the wiper of VR1 can be adjusted from 0V to 5V.

Data logger interface

I am looking for a data logger to connect to the anemometer kit published in the March 1999 issue of SILICON CHIP. I bought and built a data logger kit (2V - 20V input) but need a way to read the pulses emitted from the reed switch on the anemometer into a frequency with an analog output so that I can take a sample every hour or so.

The reason for this is that I am involved in a student assignment to collect wind speed data from a site to gauge its suitability for a wind generator. I thought some sort of frequency counter with an analog output (meter) would do but have been unable to find one that reads pulses into frequency so far. (D. D., via email).

 The anemometer comprises a reed switch activated by a rotating magnet. A frequency meter does actually convert the pulses applied to its input into a frequency measurement. It does this by counting the pulses over a set period of time of, for example, one second. This would mean that the number of pulses is the frequency in Hz. So you do not need a unit to convert the pulses from the reed switch into a frequency which is then applied to the analog frequency meter.

We would suggest using the National Semiconductor LM2917 chip to do the whole conversion for you. It will convert the pulses from the reed switch into a voltage.

We used an LM2917 in the Gear Change Alarm published in the September 1998 issue of SILICON CHIP and the values used in that circuit would probably suit your application. Data for the device can be obtained from the National Semiconductor linear data book or search the web for data from the National Semiconductor site.

Knight Rider LEDs don’t switch direction

I built the Knight Rider from the May 1996 issue and it’s not switching direction. I see that the circuit diagram shows pins 5 & 6 on IC 3 at +12V but the PC board ties them to pins 3 & 8 and they are all at ground. Please explain. (S. D., via email).

 The J and K inputs to IC3 are shown tied high on the circuit but they are actually tied low on the PC board. This has no effect on the circuit operation. However, you are on the right track to finding the problem with your Knightrider circuit, since it is the IC3 flipflop which changes the direction of the LEDs.

Check your board for shorts between tracks, particularly near IC3. Check also that each LED is inserted with the correct polarity, particularly the LEDs at each end. The outputs driving these end LEDs at pin 11 and pin 15 of IC4 switch the flipflop (IC3) so the direction changes on each LED sweep.

Spring reverb sounds dead I have purchased and constructed a Spring Reverb as described in the January 2000 issue of SILICON CHIP. Generally, I found that the spring reverb effect is subjectively quite good and ‘sweet’ sounding. However, there seems to be a serious problem with the unit when used for my purposes. I play a guitar through the unit (guitar into input of unit, output of unit to amplifier input) and have found that I get a "dead" sound from the unit; my guitar seems to lose highs and dynamics. Note that this occurs even when I turn the reverb effect off which means that I am only really going through the final op amp/mixer. I have checked the frequency response of the unit with some test equipment (pink noise source and 1/3-octave band analyser) and have found it to be very good, as specified in the article. The guitar frequency range doesn’t really go above 10kHz so I cannot see how this would be a problem. Given this, I cannot explain why the unit sounds like it is cutting out highs and making the guitar sound dead. I can only assume that it has something to do with the transient/dynamic response of the unit. The guitar is a very dynamic instrument; when you hit the strings hard you get sparkly loud highs. Possibly, it is something to do with mismatched input or output impedances. Note that the pickups in my guitar have something like 10kΩ output impedance. Is there anything you can suggest which might help me out? Note also that I have found some information on this type of spring reverb on a website at http://members.tripod.com/~roymal/reverb.htm (J. A., via email). The dead sound from your Spring Reverb module could be due to the loading effect of the level pot VR1. Check that it is actually 50kW in value. If it is not high enough, it could cause problems. You could also use a 100kW type instead. Also try changing the .0039mF capacitor value to something smaller.

Flexible I/O cards for PCs

I am building the I/O interface kit that was published in the July 1997 issue. However, there seems to be problem with getting the input from the hardware. Could it be because of the program (Basic listing) problem? I followed all the instructions and I can use the output part of the hardware with success. (H. H., via email).

 If the relays can be operated from the computer listing, then the address selection for IC1 would appear to be correct. The same address selection is used for the reading of data at the IC3 and optocoupler inputs. So therefore the software appears to run correctly.

Perhaps you have a problem on the PC board. Check that diodes D1-D8 are installed the correct way around and that the optocouplers are working. A low on an input should select a high at the corresponding collector output of the optocoupler. This voltage should also be at the respective Data input (D0-D7) of IC3.

Is there a hazard with leaded solder?

Of late my doctor friend passed me an article concerning the health hazard of workers in industry doing soldering work. The article covers lead poisoning. As we know solder contains lead. In most cases it is 40 percent lead and 60 percent tin.

I have the following questions in mind. Is there a risk involving soldering work? The fumes released from soldering generally contains flux. Do the fumes also contain lead vapour with it? My guess is there isn’t since lead is a heavy metal. The only thing we MUST remember to do is after soldering work is to wash our hands clean, to prevent contamination when we handle food.

To be safe why don’t we switch to using lead free solder? I found lead-free cored solder has 99.3 percent tin and 0.7 percent copper alloy. It has a melting point of 227 degrees. Dick Smith Electronics have it available (Cat N-1628).

Will the electrical joints using this type of solder be as good as 60/40 tin/lead alloy solder? I found solder joints using lead free solder to be not as shiny. Why is this so? Is it because tin is not as shiny as lead? Is this effect just cosmetic or does it have an effect on the tensile strength of the soldered joints?

One way to test this is to solder a piece of cable to a copper base and use a strain gauge to test the pull strength of the solder joints. Have you experimented with this sort of test?

Finally, has SILICON CHIP published an article in regard to the risk involving soldering work? (M. O., via email).

 We have not done an article on the risks of lead in solder and we are inclined to the view that they are very low. It seems that the main reason for the push for lead-free solder comes from Europe where they want to keep lead out of community land-fills.

Furthermore, we have the view that lead in solder is probably as much a health risk as lead in dental amalgam (ie, extremely low). Most dentists don’t believe amalgam is a risk.

Having said that, you should use a fan to blow the fumes away while soldering; depending on how hot your soldering iron is, there could be some lead in the vapour and yes, you should definitely wash your hands after soldering.

We have not done any work involving lead-free solder.

Snubber burnout in fluorescent inverter I have built and operated two of the high efficiency inverters for fluorescent lamps, published in the October 1993 issue. They have operated for the past 18 months but in January this year the 22Ω resistor in the snubber circuit went up in smoke at turn on. I did no more than take the fitting apart to fix it and it still works. In November I bought three more of these kits and assembled two, with the 22Ω resistor in one lasting only a few hours and it no longer works. The other now refuses to go after not being used for a couple of weeks. These later kits use a different toroidal core (T2) to the previous ones and they run very hot; ie, burn your fingers. Up until this stage I have been impressed with their performance. Can you advise? (M. F., via email).  The 22Ω resistor in the snubber could be changed to a 0.5W rating if you find that it does not last past 18 months of use. Your later kits with a different toroid for T2 are not likely to work properly since the characteristics of this core determine how the circuit operates. Unless the toroid has the same saturation and inductance factor, the oscillator frequency will not be consistent with the design. This will alter the frequency of drive to the fluorescent tube and alter the tube current. We can only recommend the RCC12.5/7.5/5 3F3 ring core for T2 as described in the parts list.

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