Second Noise Source

You know the sound, if you play a Snare and a Clap together. It’s a little bit flanging. The reason for this is, that the Clap and the Snare use the same Noise-Source.

You can hear the effect in the following Demo.

Noise Demo
0:00-0:07: Only Clap
0:07-0:15: Clap and Snare with original Noise Source
0:15-0:22: Clap and Snare with second Noise Source
0:23-0:30: Clap and Snare with original Noise Source
0:30-0:35: Clap and Snare with second Noise Source

To stop this effect, Steda has created a second Noise Source in style of a additional PCB.

This PCB is designed like the original Noise Source from the Roland TR-909

From the TR-909 Service Manual (Image is from the Solder-Side)

BOM List for the second Noise PCB (Same names like the Roland Voice PCB)
2x CD4006 (IC32, IC33)
1x CD4070 (IC31)
3x 10K resistor (R182, R183, R184)
1x 33K resistor (R185)
1x 47k reistor (R187)
1x 100K reistor (R186)
2x 1N4148 diodes (D48, D49)
1x 100n ceramic cap (C48)
1x 100p ceramic cap (C47)
1x 4.7 uF electrolytic capacitor > 25V (C46)

If you want to have the possibility to switch between the original and the advanced sound, you need a ON/ON Switch additional (Like this

The Noise-Board need +15V and GND. You can find it in the Clap Section on the Voice-PCB. You can also use any +15V Source you want. Check Voltages before you solder the cables to the PCB. In my case, the Signs on the Bridges are wrong. +15V = GND and GND = +15V.

To use the new Noise-Source , you must cut the Leg from Resistor R208 from the site, that’s going to the original Noise-Source. For a better Understanding, on the lifted Leg of R208, the new Noise Source must be soldered. Its a good idea that you use shrink tubing. (Don’t be irritated, in this Picture, the second cable is soldered on the Solderpoint of R208 to the Switch. If you don’t want it switchable, the Cable in side of the R208 Sign must not be connected!)

If you have done all steps correct, you are done 🙂 Congratulation, your Clap and Snare are not in a relationship anymore 🙂
Assemble the Voice-PCB back in the case. To mount the Noise PCB, I use a spacer and mount it with one screw on the Voice-PCB.

If you want the sound switchable, drill a hole in the Cover of the Cartridge. like this

The Switch has 3 Legs. Regular, Leg 2 (the middle Leg) are the Base. Leg 1 and 3 are the signals that’s switched to Leg 2.
To the Leg 2, you solder the Cable that comes from the lifted Leg of R208. To Leg 1, the Cable that you solder on the free hole from R208. This is the free hole that you have cut the leg from R208.
On Leg 3, the Cable from the new Voice Source.

Now you can switch to normal and advanced Mode:
In normal Mode, you connect the R208 to the regular connection.
In advanced Mode, you switch the lifted Leg from R208 to the new Noise Source.

If you have no Noise PCB, don’t be sad. Ask Steda Electronics about one or build it on a Vero-Board. A good picture of the traces are here .
The Layout is a little different like Steda´s PCB but its the same Thing.