Index: src/mess/machine/coco.c
===================================================================
--- src/mess/machine/coco.c	(revision 31169)
+++ src/mess/machine/coco.c	(working copy)
@@ -679,15 +679,19 @@
 	/* determine the sound mux status */
 	soundmux_status_t status = soundmux_status();
 
+    /* the SC77526 DAC chip internally biases the AC-coupled sound inputs for Cassette and Cartridge at the midpoint of the 3.9v output range */
+    bool bCassSoundEnable = (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL1));
+    bool bCassPlaying = ((m_cassette->get_state() & (CASSETTE_MASK_UISTATE | CASSETTE_MASK_MOTOR | CASSETTE_MASK_SPEAKER)) == 
+                         (CASSETTE_PLAY | CASSETTE_MOTOR_ENABLED | CASSETTE_SPEAKER_ENABLED));
+    UINT8 cassette_sound = ((bCassSoundEnable && !bCassPlaying) ? 0x40 : 0);
+
 	/* determine the value to send to the DAC */
 	m_dac_output = (m_pia_1->a_output() & 0xFC) >> 2;
-	UINT8 sound_output = single_bit_sound + (status == SOUNDMUX_ENABLE ? m_dac_output << 1 : 0);
-	m_dac->write_unsigned8(sound_output);
+	UINT8 dac_sound =  (status == SOUNDMUX_ENABLE ? m_dac_output << 1 : 0);
+	m_dac->write_unsigned8(single_bit_sound + dac_sound + cassette_sound);
 
 	/* determine the cassette sound status */
-	cassette_state cas_sound = (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL1))
-		? CASSETTE_SPEAKER_ENABLED
-		: CASSETTE_SPEAKER_MUTED;
+	cassette_state cas_sound = bCassSoundEnable ? CASSETTE_SPEAKER_ENABLED : CASSETTE_SPEAKER_MUTED;
 	m_cassette->change_state(cas_sound, CASSETTE_MASK_SPEAKER);
 
 	/* determine the cartridge sound status */