Every so often the old Workbench file overflows with the amassed trivia of various odds and sods that I always meant to put in but never got round to. In a belated fit of spring cleaning I collected all the junk together and was just about to throw it out when I was struck by a thought – why not stick them all together as one of my famous pot pourri selections?

Electronic Tuners

One of the most useful gadgets to have come on the market in recent years is the electronic guitar tuner. Early models had just a single input socket, which made mid-set tuning a rather cumbersome and time consuming performance, with the guitar being plugged back and forth like a yo-yo. With this type of tuner there are two different ways of making life (and tuning) easier, depending on the way you prefer to tune on stage. If you like to tune whilst hearing the guitar through the amp then a simple Y cord will do the trick. Unfortunately this tends to load down the amplifier input if the input impedance of the tuner is less than a couple of hundred thousand ohms, causing a loss in volume. A much more usable system incorporates a switch to isolate the guitar from the amplifier whilst you are tuning. It also short circuits the amplifier input to cut out the residual hum that usually a rises when the amplifier lead is left unconnected.

The switch used is a DPDT miniature toggle switch which can either be fitted, along with a second jack socket, directly into the guitar or put into a separate case into which the guitar, tuner and amplifier are plugged. Fig. 1 shows the circuitry. Obviously if the switch is fitted into a separate case it should be put in the line between the guitar and any effects pedals that may be used. In this case the connection labelled 'amplifier' in fig. 1 should go to the input of the first effect unit in the chain. If you're into footswitches then the DPDT switch could be a floor mounted footswitch (perhaps incorporated into the Workbench effects pedal board that I know you all built last year!), otherwise a small plastic box (like a Tic-Tac box) could be used.

With all this sophistication in switching it would be a shame to have to grovel around on the floor or at the back of the stage to actually see the tuner. As a suggestion try strapping the tuner to your mike stand with masking tape – don't use Sellotape, it leaves the stand and tuner all sticky and gungy.

Those people with in-line tuners such as the Boss TU12 will already have the advantage of not having to plug their guitar back and forth, but because the amplifier is connected, silent tuning is not easily achieved. Once again the problem can be overcome by putting a switch in the output line from the tuner. As before this switch has to cut the signal line from the tuner to the amplifier and also to short down the amplifier input to ground. The most useful place for this switch is taped in the tuner line, right next to the tuner. Fig. 2 shows the idea. The switch used is a miniature SPDT – if this is not easily found then one side of a DPDT switch could be used. Alternatively a footswitch could be used – these are most commonly available in the DPDT version.

So there we are. I've finally done something positive about improving East-West relations, showing thousands of working musicians how they can combine Western and Eastern music by simultaneously playing not only the Sounds of Silence but also that well known Chinese number Tu-ning.

Effects Send and Return

A common question that I'm often asked is 'How can I fit echo Send and Return sockets to my amplifier?'. In practice this is quite a simple job. Making sure the amplifier is unplugged from the mains, remove the case and find the back of the master volume pot. You should find that there are three leads soldered to it. At one end there will be the ground lead which is connected back to the amplifier chassis; this is commonly a co-ax screen wire. The lead to the middle terminal will be connected to the input of the power amplifier section and the lead at the other end of the pot will come from the preamp output – it is this lead that we need to interrupt. For this mod you will need the following parts: a length of stereo co-ax long enough to go from the back of the master volume pot to the amplifier's back panel. Two mono, switched jack sockets (plastic type).

The wiring is shown in fig. 3 – the two jack sockets are simply mounted close together at a convenient point on the back panel. The system is of the signal interrupt type which means that the 'mix out' output of the echo unit must be connected to the return socket, with the 'input' socket of the echo connected to the send socket. If the 'echo out' output were to be used the straight signal would be lost and only the echoes would emerge from the amplifier.

If, as sometimes happens, the effect seems very weak and diluted the problem will almost certainly be due to an impedance matching problem. If you look at the back, or round the edge of the volume pot, you should find the resistance stamped or printed on it, eg 4K7 1g which translates to 4,700 ohms, logarithmic track. The echo may have an input impedance of say 100K (100,000 ohms), and this vast difference gives rise to the loss in volume and clarity. The way round this problem is to fit matching transformers before and after the send and return sockets. A quick look back to March's Workbench should give you all the information you will need to do this. In the example I quoted a 5K:100K matching transformer between the pre amp and the send socket would cure half the problem whilst, assuming an echo unit output impedance of 50K, a 50K:5K transformer between the return socket and the pot will solve the other half of the problem.

Converting a reverb system

For those people having, say, a PA amp with a reverb which is switchable for each channel you can work a dodge by fitting echo send and return sockets in the reverb line. When jack plugs are put into the send and return sockets it disables the reverb and converts all the reverb select switches to echo select. The reverb depth control now becomes an echo volume control. The loss of reverb under these circumstances is not too critical as the deeper echo effects tend to mask the reverb effect anyway. If the echo is left switched in the reverb on/off switch can be used for the echo. As this echo system is of the 'add on' rather than 'interrupt' version, the channelling of the echo unit's 'echo only' output into the return socket will give a deeper effect. With no plugs in the send and return sockets, the reverb system reverts to normal operation.

The conversion is fairly straightforward – the wiring details are shown in fig.4. The input and output transducers look like very small transformers mounted at either end of the reverb spring unit. The co-ax lead that is connected to the input transducer is desoldered and extended to link to the send socket. A second co-ax lead is taken back from the socket to the input transducer. Similar treatment is meted out to the output transducer and return socket. If you can't tell the input and output transducers apart don't panic, just wire it up anyway and do a practical test by plugging in the echo unit one way round and then the other. Once you know which way round the sockets are you can label them accordingly.

Effects Pedal Repairs

There are very few things that can go wrong with effects pedals, the main problems arise with the jack sockets, the low voltage power socket and the footswitch unit. Unfortunately there is no agreed standard between the various manufacturers and as the majority of pedals on the market are made in the Far East, exact replacement parts are not readily available through component shops. There really is very little choice, you must get the correct part as things are packed so tightly in the pedals that non-genuine replacements simply won't fit in most cases. Luckily getting the correct parts is not particularly difficult, any shop that stocks the particular make of pedal should be able to order them for you. If you run into trouble using this method you could try contacting the manufacturer's or importer's service department direct. I've found them very helpful and one firm in particular, who I'm not allowed to mention, (alright it was the Ibanez importers, Summerfields) gave what I can only describe as exceptional service – 24 hours after my phone call I had the part.

So there we are. I've finally cleared the junk off my desk. I feel a lot better for that, don't you?