Magazine Archive

Home -> Magazines -> Issues -> Articles in this issue -> View

Trigger Converter for the Yamaha SPX-90

Article from Home & Studio Recording, July 1986

A simple circuit enabling you to trigger the footswitch input of your SPX-90 from a positive trigger pulse.

Once again, technology has taken precedence over the end user's actual requirements, so when you want to use a simple trigger pulse to initiate one of the SPX-90s many functions, you can't... that is, you couldn't until now.

Figure 1.

MIDI is fine for polyphonic systems and makes a lot of sense for the control of monosynths, sequencers or complex drum machines, but when all you need to do is to trigger an event such as a sampled drumbeat, there is still no more practical method than the old trigger pulse. This coupled with the fact that most existing drum machines provide at least one trigger output should make it clear to the designer of any sampling device that a simple trigger input is clearly needed, no matter how many other MIDI marvels it may contain.

Fortunately, the SPX-90 does have a facility for triggering via an optional footswitch but this is configured such that the unit triggers when the switch is opened: a kind of reverse S-trigger action if you like. After minutes of intensive research I came up with the circuit below which will directly convert a trigger pulse such as is provided by Roland equipment into the form required to trigger the SPX-90. Indeed it was tested using the trigger output of a Roland TR707. There is no noticeable delay in the trigger circuit but the SPX-90 itself does take a couple of milliseconds to realise that it's been triggered, the outcome of which is that there is a barely perceptible delay. If you sample a snare drum and then play it back at the same time as the snare drum in your drum machine, you might detect a very short flam effect, but to be fair, the delay in the SPX-90 is a lot less than that found on some other currently available samplers and many users won't even notice it.

"There is no noticeable delay in the trigger circuit but the SPX-90 itself does take a couple of milliseconds to realise that it's been triggered..."

How it Works

The trigger input from your friendly drum machine is fed into the input with the result that T1 is turned on every time a pulse is received. The collector voltage of T1 then falls far enough to allow T2 to turn off which is the equivalent of the footswitch opening. Once the pulse has ended, T2 again conducts simulating a closed switch. No circuit layout is given; it is such a simple design that all the components could be strung between two jack sockets in a small plastic box or built up on a scrap of Veroboard. T1 and T2 may be virtually any general purpose NPN transistors and D1 any silicon diode, though specific values are given in the parts list. Likewise the type and wattage of the resistors is entirely unimportant. In order to save cost, the battery is switched on automatically whenever a jack is inserted into the input socket, so be sure to unplug the unit when it is not in use.

Parts List

T1, T2 BC107
D1 1N916
R1, R2 10K
R3, R4 100k
Stereo Jack Socket 1 off
Mono Jack Socket 1 off
PP3 battery clip 1 off
PP3 battery 1 off
Plastic Case 1 off

More from these topics

Browse by Topic:

Electronics / Build

Maintenance / Repair / Modification

Also featuring gear in this article

Previous Article in this issue

Ramsa WS-A10E-K Speaker System

Publisher: Home & Studio Recording - Music Maker Publications (UK), Future Publishing.

The current copyright owner/s of this content may differ from the originally published copyright notice.
More details on copyright ownership...


Home & Studio Recording - Jul 1986

Donated & scanned by: Mike Gorman

Feature by Paul White

Previous article in this issue:

> Ramsa WS-A10E-K Speaker Syst...

Help Support The Things You Love

mu:zines is the result of thousands of hours of effort, and will require many thousands more going forward to reach our goals of getting all this content online.

If you value this resource, you can support this project - it really helps!

Donations for July 2024
Issues donated this month: 14

New issues that have been donated or scanned for us this month.

Funds donated this month: £20.00

All donations and support are gratefully appreciated - thank you.

Magazines Needed - Can You Help?

Do you have any of these magazine issues?

> See all issues we need

If so, and you can donate, lend or scan them to help complete our archive, please get in touch via the Contribute page - thanks!

Please Contribute to mu:zines by supplying magazines, scanning or donating funds. Thanks!

Monetary donations go towards site running costs, and the occasional coffee for me if there's anything left over!

Small Print

Terms of usePrivacy