IC Suppliers

Dear Sirs,
Could you tell me where I could purchase an LM13600 used in your Comp-Lim. Maplin don't list it in their catalogue and I cannot find it in any other catalogue or shops.

Paul Dreczko
Surrey

The LM13600 should be available from most electronic component retailers. Two companies who stock it are:

Technomatic Ltd., (Contact Details)
Watford Electronics, (Contact Details)

Maplin do in fact stock the LM13700 which is pin compatible.

Wasp/Micro interface

Dear Sirs,
I have a query concerning the use of digital synthesisers with computers, in particular an EDP Wasp and a BBC micro.

I have successfully connected the two machines and written a program to play the synthesiser by entering music into the computer in conventional notation using the function keys and cursor keys.

However, communicating between the two machines in the opposite direction (i.e. reading codes into the computer from the Wasp) is totally unsuccessful.

There are two main problems:

1. When the connecting cable is plugged in, the Wasp will not sound at all when played from it's keyboard. If the trigger line is disconnected, then it will sound. I have partly solved this problem by using one of the timers on the 6522 VIA to pulse the trigger line.

2. The codes output by the Wasp appear to be completely random, and jump about. When the trigger line is pulsed automatically, as above, the notes representing the codes actually sound, producing a completely useless random burbling.

Does this sound like a faulty Wasp, or do I need additional components, a latch for instance? Perhaps I am reading the codes too often, or pulsing too fast. I wonder if any readers have encountered this problem, or better still, found a solution?

Nigel Williams
Kent

When a note is pressed on the Wasp, six digital pulse trains are output from the link socket, along with a 'Trigger' pulse train, the pulse width of which varies along the keyboard.

The correct digital data is read by latching the six signals on the positive going edge of the trigger pulse. This edge should be delayed by approximately 100uS to ensure that the data settles before being read.

Your computer should therefore be connected to the Wasp via a latch. A suitable circuit is shown below. The six bit code at the output of this latch will now only change when a new key is pressed.

MF1/Roland connections

Dear Sirs,
I am writing to you requesting some info regarding how I wire up the output lead from your MF-1 sync unit to the DIN connector on the back of my TR808 Drum machine in order that it may be triggered.

Mick Smith
Worcester

Dear Sirs,
I have now finished the E&MM project but am at odds as to how to connect it to my Roland TR606 Drumatic sync socket. The latter, as you probably know is a five pin DIN, but no mention of 'which pin is what' is provided in the Roland handbook. Can you help out?

Secondly, a correspondent in your letters page of August 1982 i$sue (R. Stacey of London) suggests a start/stop switch to be used with the MF1/TR606 combination - can you tell me where to wire this in. Thanks.

I must admit I'm 'dying' to get the project working! Thank you for a most interesting read each month.

Ed Conley
Liverpool

Both the Roland TR606 and TR808 have 5 pin DIN connectors for Start/Stop and Clock.

Pin 1 - Start/Stop (High level to Start)
Pin 2 - Earth
Pin 3 - Clock (Up to 12V)

Therefore the output of the MF1 should be connected to Pin 2 (Screen) and Pin 3 (tip) of the DIN.

Spectrum Synth Controller

Dear Sirs,
With ref to the 'Micro Music - Spectrum Synth controller' article in the November 1982 issue.

I note from the accompanying text that the trigger signal is +10V. I have a Moog Source, and am informed that the signal required would have to be at least +15V. Could you please advise me of the necessary alterations.

My Spectrum is the 48K version and thus I wondered if I would be able to expand the sequence length (preferably), or the number of sequences available, to utilise the full memory potential of the computer.

Can the sequences be linked or chained together to form a continuous program? Is looping etc., possible within the confines of the set up?

As I am not a master electrician, I would appreciate a PCB layout of the interface circuit.

Does the interface need an external power supply, or does it operate from the Spectrum's edge connector DC output?

M. A. Burton
Coventry

The Moog Source uses what Moog call an S-Trig or Switch Trigger, through a stereo jack.
Sleeve - ground
Ring - input
Tip - output

The machine is triggered when the ring and sleeve are shorted together. To trigger from the synth controller connect via an NPN transistor as shown below.

Micromusic articles are meant as a starting point to provoke ideas. The Sequencer program is designed to be extended and changed, adding sequences, chains and anything else you require. No PCB layout was given for the same reason, although an interface circuit will be published in the near future.

The interface does require a ±15V supply for the analogue side but the logic 5V can be supplied by the Spectrum.