diff --git a/src/mess/drivers/esq5505.c b/src/mess/drivers/esq5505.c
index a302a43f076..c4f1a6e1fa9 100644
--- a/src/mess/drivers/esq5505.c
+++ b/src/mess/drivers/esq5505.c
@@ -810,6 +810,9 @@ static INPUT_PORTS_START( vfx )
 #endif
 INPUT_PORTS_END
 
+#define ROM_LOAD16_BYTE_BIOS(bios,name,offset,length,hash) \
+		ROMX_LOAD(name, offset, length, hash, ROM_SKIP(1) | ROM_BIOS(bios+1)) /* Note '+1' */
+
 ROM_START( vfx )
 	ROM_REGION(0x40000, "osrom", 0)
 	ROM_LOAD16_BYTE( "vfx210b-low.bin",  0x000000, 0x010000, CRC(c51b19cd) SHA1(2a125b92ffa02ae9d7fb88118d525491d785e87e) )
@@ -840,8 +843,8 @@ ROM_END
 
 ROM_START( sd1 )
 	ROM_REGION(0x40000, "osrom", 0)
-	ROM_LOAD16_BYTE( "sd1_410_lo.bin", 0x000000, 0x020000, CRC(faa613a6) SHA1(60066765cddfa9d3b5d09057d8f83fb120f4e65e) )
-	ROM_LOAD16_BYTE( "sd1_410_hi.bin", 0x000001, 0x010000, CRC(618c0aa8) SHA1(74acf458aa1d04a0a7a0cd5855c49e6855dbd301) )
+	ROM_LOAD16_BYTE( "sd1_21_300b_lower.bin", 0x000000, 0x020000, CRC(a1358a0c) SHA1(64ac5358aa46da37ca4195002cf358554e00878a) ) 
+	ROM_LOAD16_BYTE( "sd1_21_300b_upper.bin", 0x000001, 0x010000, CRC(465ba463) SHA1(899b0e83d0788c8d49c7b09ccf0b4a92b528c6e9) ) 
 
 	ROM_REGION(0x200000, "waverom", ROMREGION_ERASE00)  // BS=0 region (12-bit)
 	ROM_LOAD16_BYTE( "u34.bin", 0x000001, 0x080000, CRC(85592299) SHA1(1aa7cf612f91972baeba15991d9686ccde01599c) )
@@ -855,10 +858,15 @@ ROM_START( sd1 )
 	ROM_LOAD( "u36.bin", 0x000000, 0x080000, CRC(c3ddaf95) SHA1(44a7bd89cd7e82952cc5100479e110c385246559) )
 ROM_END
 
+// note: all known 4.xx BIOSes are for the 32-voice SD-1 and play out of tune on 21-voice h/w
 ROM_START( sd132 )
 	ROM_REGION(0x40000, "osrom", 0)
-	ROM_LOAD16_BYTE( "sd1_410_lo.bin", 0x000000, 0x020000, CRC(faa613a6) SHA1(60066765cddfa9d3b5d09057d8f83fb120f4e65e) )
-	ROM_LOAD16_BYTE( "sd1_410_hi.bin", 0x000001, 0x010000, CRC(618c0aa8) SHA1(74acf458aa1d04a0a7a0cd5855c49e6855dbd301) )
+	ROM_SYSTEM_BIOS(0, "410", "SD-1 v4.10")
+	ROM_LOAD16_BYTE_BIOS(0, "sd1_410_lo.bin", 0x000000, 0x020000, CRC(faa613a6) SHA1(60066765cddfa9d3b5d09057d8f83fb120f4e65e) )
+	ROM_LOAD16_BYTE_BIOS(0, "sd1_410_hi.bin", 0x000001, 0x010000, CRC(618c0aa8) SHA1(74acf458aa1d04a0a7a0cd5855c49e6855dbd301) )
+	ROM_SYSTEM_BIOS(1, "402", "SD-1 v4.02")
+	ROM_LOAD16_BYTE_BIOS(1, "sd1_32_402_lo.bin", 0x000000, 0x020000, CRC(5da2572b) SHA1(cb6ddd637ed13bfeb40a99df56000479e63fc8ec) ) 
+	ROM_LOAD16_BYTE_BIOS(1, "sd1_32_402_hi.bin", 0x000001, 0x010000, CRC(fc45c210) SHA1(23b81ebd9176112e6eae0c7c75b39fcb1656c953) ) 
 
 	ROM_REGION(0x200000, "waverom", ROMREGION_ERASE00)  // BS=0 region (12-bit)
 	ROM_LOAD16_BYTE( "u34.bin", 0x000001, 0x080000, CRC(85592299) SHA1(1aa7cf612f91972baeba15991d9686ccde01599c) )
@@ -956,7 +964,7 @@ DRIVER_INIT_MEMBER(esq5505_state,denib)
 CONS( 1988, eps,   0, 0,   eps,   vfx, esq5505_state, eps,    "Ensoniq", "EPS", GAME_NOT_WORKING )   // custom VFD: one alphanumeric 22-char row, one graphics-capable row (alpha row can also do bar graphs)
 CONS( 1989, vfx,   0, 0,   vfx,   vfx, esq5505_state, denib,  "Ensoniq", "VFX", GAME_NOT_WORKING )       // 2x40 VFD
 CONS( 1989, vfxsd, 0, 0,   vfxsd, vfx, esq5505_state, denib,  "Ensoniq", "VFX-SD", GAME_NOT_WORKING )    // 2x40 VFD
-CONS( 1990, sd1,   0, 0,   vfxsd, vfx, esq5505_state, denib,  "Ensoniq", "SD-1", GAME_NOT_WORKING )      // 2x40 VFD
-CONS( 1990, sd132, sd1, 0, vfx32, vfx, esq5505_state, denib,  "Ensoniq", "SD-1 32", GAME_NOT_WORKING )   // 2x40 VFD
+CONS( 1990, sd1,   0, 0,   vfxsd, vfx, esq5505_state, denib,  "Ensoniq", "SD-1 (21 voice)", GAME_NOT_WORKING )	// 2x40 VFD
+CONS( 1990, sd132, sd1,0,  vfx32, vfx, esq5505_state, denib,  "Ensoniq", "SD-1 (32 voice)", GAME_NOT_WORKING )	// 2x40 VFD
 CONS( 1990, sq1,   0, 0,   sq1,   vfx, esq5505_state, sq1,    "Ensoniq", "SQ-1", GAME_NOT_WORKING )      // 2x16 LCD
 CONS( 1990, sqrack,sq1, 0, sq1,   vfx, esq5505_state, sq1,    "Ensoniq", "SQ-Rack", GAME_NOT_WORKING )   // 2x16 LCD