diff --git a/demos/smb/apu_sim.s b/demos/smb/apu_sim.s
index b13136a..35fbb78 100644
--- a/demos/smb/apu_sim.s
+++ b/demos/smb/apu_sim.s
@@ -48,8 +48,8 @@ Tmp1        equ   130
             jsr   APUStartUp
 
             sep   #$30
-            lda   #1
-            jsl   APU_STATUS_WRITE              ; turn on the first pulse channel by default
+            lda   #$f
+            jsl   APU_STATUS_WRITE              ; turn on the first four channels by default
             rep   #$30