diff --git a/src/devices/bus/odyssey2/voice.cpp b/src/devices/bus/odyssey2/voice.cpp
index 5a89e7a6160..ea7c328a7ca 100644
--- a/src/devices/bus/odyssey2/voice.cpp
+++ b/src/devices/bus/odyssey2/voice.cpp
@@ -49,7 +49,7 @@ void o2_voice_device::device_add_mconfig(machine_config &config)
 {
 	SPEAKER(config, "mono").front_center();
 
-	SP0256(config, m_speech, 3120000);
+	SP0256(config, m_speech, 3.12_MHz_XTAL);
 	m_speech->data_request_callback().set(FUNC(o2_voice_device::lrq_callback));
 	// The Voice uses a speaker with its own volume control so the relative volumes to use are subjective, these sound good
 	m_speech->add_route(ALL_OUTPUTS, "mono", 1.00);
@@ -83,11 +83,23 @@ const tiny_rom_entry *o2_voice_device::device_rom_region() const
 	return ROM_NAME( o2voice );
 }
 
+
+//-------------------------------------------------
+//  mapper specific handlers
+//-------------------------------------------------
+
 WRITE_LINE_MEMBER(o2_voice_device::lrq_callback)
 {
 	m_lrq_state = state;
 }
 
+READ_LINE_MEMBER(o2_voice_device::t0_read)
+{
+	// conflict with subslot T0
+	int state = (m_subslot->exists()) ? m_subslot->t0_read() : 0;
+	return state | (m_speech->lrq_r() ? 0 : 1);
+}
+
 void o2_voice_device::io_write(offs_t offset, uint8_t data)
 {
 	if (offset & 0x80 && ~m_control & 0x10)
@@ -97,4 +109,8 @@ void o2_voice_device::io_write(offs_t offset, uint8_t data)
 		else
 			m_speech->reset();
 	}
+
+	// possible conflict with subslot IO (work ok with 4in1, not with chess)
+	if (m_subslot->exists())
+		m_subslot->io_write(offset, data);
 }
diff --git a/src/devices/bus/odyssey2/voice.h b/src/devices/bus/odyssey2/voice.h
index 139dc7d9a78..38aec123679 100644
--- a/src/devices/bus/odyssey2/voice.h
+++ b/src/devices/bus/odyssey2/voice.h
@@ -19,19 +19,19 @@ public:
 	o2_voice_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock);
 
 	// reading and writing
-	virtual uint8_t read_rom04(offs_t offset) override { if (m_subslot->exists()) return m_subslot->read_rom04(offset); else return 0xff; }
-	virtual uint8_t read_rom0c(offs_t offset) override { if (m_subslot->exists()) return m_subslot->read_rom0c(offset); else return 0xff; }
+	virtual uint8_t read_rom04(offs_t offset) override { return (m_subslot->exists()) ? m_subslot->read_rom04(offset) : 0xff; }
+	virtual uint8_t read_rom0c(offs_t offset) override { return (m_subslot->exists()) ? m_subslot->read_rom0c(offset) : 0xff; }
 
 	virtual void write_p1(uint8_t data) override { m_control = data; if (m_subslot->exists()) m_subslot->write_p1(data); }
 	virtual void write_p2(uint8_t data) override { if (m_subslot->exists()) m_subslot->write_p2(data); }
 
 	virtual void io_write(offs_t offset, uint8_t data) override;
-	virtual DECLARE_READ_LINE_MEMBER(t0_read) override { return m_speech->lrq_r() ? 0 : 1; }
+	virtual uint8_t io_read(offs_t offset) override { return (m_subslot->exists()) ? m_subslot->io_read(offset) : 0xff; }
+	virtual DECLARE_READ_LINE_MEMBER(t0_read) override;
 
 protected:
 	// device-level overrides
 	virtual void device_start() override;
-	virtual void device_reset() override { }
 
 	virtual void device_add_mconfig(machine_config &config) override;
 	virtual const tiny_rom_entry *device_rom_region() const override;