Archive for Other Parts

Oberheim OB-Xa Program ROM Set

OB-XA-R1

Click the link below to download the installation guide

OB-XA-R1-Installation-GuideDownload

This is a set of two replacement program ROMs for the Oberheim OB-Xa synthesizer, preprogrammed with the latest OB-Xa software revision (XA-GA0 and XA-G1) released in February 1982.

The new ROMs are based around modern CMOS EEPROM devices manufactured by Atmel Corporation (now a part of Microchip), adapted to a 24-pin DIP footprint with a custom PCB and gold plated pins. These devices are fully compatible with the original NMOS UV EPROMS (ST M2732A-2), have TTL and CMOS compatible inputs and outputs, and offer a significant reduction in current draw: up to a 68% decrease under normal operating conditions, and up to a 94% decrease in standby mode.

All ROM boards are hand assembled in the USA and tested in an Oberheim OB-Xa to guarantee their functionality.

If you are ordering these to repair an OB-Xa with a nonfunctional computer, please note that in our experience it is not uncommon for these units to have one or more dead logic ICs on the upper or lower control boards. Thus, it is possible that your original ROMs are fine, but another component in the system has failed.

ROM CRC-32 Checksums:
XA-GA0: F8268EA0
XA-G1: B32DCB5D

Technical notes about the waveform comparison screenshots:

This image compares how data line 0 changes when the CPU accesses the original XA-GA0 ROM versus the new XA-GA0 ROM. Two equivalent opcode fetches are shown in each screenshot. A CMOS Z80 CPU was used in this case, but the original NMOS Z80 will also work fine with these new ROMs.

From top to bottom, the waveforms shown are the chip select/output enable signals going to the ROM (active low and tied together in the OB-Xa; pins 18 and 20), data line 0 (pin 9), the M1 output from the Z80 CPU (pin 27), and the Z80 clock input (pin 6).

Per the Z80 user manual, the CPU initiates an opcode fetch (M1 cycle) with the falling edge of the M1 line (purple). One half clock cycle later (green), the CS/OE line (yellow) goes low, forcing the ROM to assert the data pointed to by the current address onto the data bus (blue; D0 is shown). Note how the original NMOS ROM has brief “glitches” in the data output when the CS/OE line changes while the new CMOS ROM does not; this is inconsequential to the operation of the CPU, as the data bus is sampled with the rising clock edge of state T3, by which time the data lines are at a well-defined logic level. The period of slow rise seen on the data line is also normal and inconsequential; this occurs whenever the data bus is in a high-impedance state and climbs to supply at a rate determined by the time constant of the pull-up resistors and bus capacitance.

4-in-1 Capacitor Insulator Kit

Insulator board and hardware for floating 4-in-1 capacitor boards

This kit can be used to isolate our 4-in-1 can capacitor replacement PCBs from chassis ground. This is useful in cases where the original installation used an insulated can floating from chassis.

Includes one insulator PCB for 1-3/8 inch diameter cans with 46 mm CTC mounting holes, two nylon #6-32 screws, and two nylon #6-32 hex nuts.

4-in-1 Can Capacitor Kit (Wide)

Replaces multi-section cans with 46 mm CTC mounting holes. Fits four 7.5 mm lead spacing, 16 mm diameter capacitors

This kit is intended as an easy way to replace old multi-section can capacitors around 1-3/8″ diameter (approx. 35 mm) with 46 mm CTC mounting hole spacing. These cans were often used in vintage audio and radio equipment, such as McIntosh, Marantz, Heathkit, and Dynaco.

The capacitor board fits up to four 7.5 mm lead spacing, 16 mm diameter radial capacitors. Smaller 5 mm lead spacing capacitors will also fit. An alternate version of this kit designed specifically for 5 mm lead spacing, 12.5 mm diameter capacitors is also available.

The negative leads of all capacitors are connected to a thick outer copper ring and two plated mounting holes. This means the negatives will be tied to chassis ground by default. If you need to isolate this board from chassis, take a look at our isolation kit.

Includes one capacitor mounting board, one spacer board, 5 wiring turrets (one extra), a mounting hardware kit, and a link to installation instructions. Capacitors are not included. In order to save on paper and toner, we are now including a link to a PDF copy of the installation guide. If you would prefer a hard copy, please let us know and we’d be happy to accommodate.

Based on the IPC-2221B standard, this kit is not to be installed in circuits that will see peak voltages greater than 600 V.

Specifications:

  • Board material: FR-4 Kingboard KB-6165F (TG150, CTI >175)
  • Board finish: HASL (Lead-free solder), matte black solder mask
  • Copper thickness: 2 oz.
  • Screw hole spacing: 45.95 mm center-to-center
  • Screw hole size: 3.5 mm (#6-32 machine screw fits snug)
  • Wiring/turret hole size: 2.4 mm
  • Width: 55.39 mm
  • Length: 39.50 mm
  • Board thickness: 1.6 mm
  • Height from surface of mounting board to top of a turret: 7 mm
  • Spacer board diameter: 39.5 mm
  • Spacer board thickness: 2.0 mm
  • Capacitor lead spacing: 5 mm to 7.5 mm
  • Max capacitor diameter: About 16 mm
  • Capacitor lead hole size: 1.2 mm
  • Diameter of turret’s hole: 1.63 mm

Note: Dimensions are nominal values. Outline dimensions may vary by ±0.15 mm, and hole sizes by ±0.076 mm

3-in-1 Can Capacitor Kit

Replaces multi-section cans with 1.5 inch CTC mounting holes. Fits three 5 mm or 7.5 mm lead spacing, 12.5 mm diameter capacitors

Click the link below to download the installation guide

3-in-1-CGDownload

This kit is intended as an easy way to mount new radial electrolytic capacitors when replacing 1 inch diameter multi section can capacitors with 1.5 inch mounting hole spacing CTC. This design was modeled after an Astron A-25-65 can. These were often used in vintage radio equipment.

Up to three different caps can be installed, and they all share a common lead located in the center. The center common lead has a trace connecting it to one of the mounting holes, making it convenient to tie to chassis ground; if you need to isolate this board from chassis ground, take a look at our insulation kit. The spacer board sits between the new caps and mounting board and adds clearance between the turrets and cans of the caps. Four turrets provide a robust post for wires and other components to attach to when installing.

If you use a positive-common configuration, be wary that the cans of electrolytic caps are often tied to the negative lead (cathode), but not always. Thus, voltages may exist between the cans depending on the circuit, so space them apart as needed.

Based on IPC-2221B guidelines, this board is not to be used in circuits that may see peak voltages above 450 V assuming a typical negative-common configuration.

Specifications:

  • Board material: FR-4 Kingboard TG150 (CTI >175)
  • Board finish: HASL (lead-free solder), green solder mask
  • Copper thickness: 2 oz.
  • Screw hole spacing: 37.79mm center-to-center (Approx. 1.5 inches)
  • Screw hole size: 3.8mm (#6-32 fits slightly loose to allow adjustment)
  • Wiring/turret hole size: 2.4mm
  • Width: 47.59mm
  • Length: 34.14mm
  • Board thickness: 1.6mm
  • Height from surface of mounting board to top of a turret: 7mm
  • Max capacitor diameter: 12.5mm
  • Capacitor lead spacing: 5mm and 7.5mm
  • Insulator board diameter: 29mm
  • Insulator board thickness: 2mm
  • Insulator board hole size: 4.2mm for turrets, 2.6mm for capacitor leads
  • Diameter of turret’s hole: 1.63mm

Note: Dimensions are nominal values. Outline dimensions may vary by ±0.15mm, and hole sizes by ±0.076mm.

4-in-1 Can Capacitor Kit

Replaces multi-section cans with 46 mm CTC mounting holes. Fits four 5 mm lead spacing, 12.5 mm diameter capacitors

Click the link below to download the installation guide

4-in-1-CGDownload

This kit is intended as an easy way to replace old multi-section can capacitors around 1-3/8″ diameter (approx. 35 mm) with 46 mm CTC mounting hole spacing. These cans were often used in vintage audio and radio equipment, such as McIntosh, Marantz, Heathkit, and Dynaco.

The capacitor board fits up to four 5 mm lead spacing, 12.5 mm diameter radial capacitors. An alternate version of this kit designed for larger 7.5 mm lead spacing, 16 mm diameter capacitors is also available.

The negative leads of all capacitors are connected to a thick outer copper ring and two plated mounting holes. This means the negatives will be tied to chassis ground by default. If you need to isolate this board from chassis, take a look at our isolation kit.

Includes one capacitor mounting board, one spacer board, 5 wiring turrets, a mounting hardware kit, and a link to installation instructions. Capacitors are not included. In order to save on paper and toner, we are now including a link to a PDF copy of the installation guide. If you would prefer a hard copy, please let us know and we’d be happy to accommodate.

Based on the IPC-2221B standard, this kit is not to be installed in circuits that will see peak voltages greater than 600 V.

Specifications:

  • Board material: FR-4 Kingboard KB-6165F (TG150, CTI >175)
  • Board finish: HASL (Lead-free solder), matte black solder mask
  • Copper thickness: 2 oz.
  • Screw hole spacing: 45.95 mm center-to-center
  • Screw hole size: 3.5 mm (#6-32 machine screw fits snug)
  • Wiring/turret hole size: 2.4 mm
  • Width: 55.39 mm
  • Length: 37.96 mm
  • Board thickness: 1.6 mm
  • Height from surface of mounting board to top of a turret: 7 mm
  • Spacer board diameter: 27 mm
  • Spacer board thickness: 2.0 mm
  • Capacitor lead spacing: 5 mm
  • Max capacitor diameter: About 12.5 mm
  • Capacitor lead hole size: 1.2 mm
  • Diameter of turret’s hole: 1.63 mm

Note: Dimensions are nominal values. Outline dimensions may vary by ±0.15 mm, and hole sizes by ±0.076 mm

Ohm’s Law/Joule’s Law PCB Wheel

This is a 10 cm diameter wheel made of FR-4 (typical PCB material) that combines Ohm’s Law and Joule’s Law into one handy reference chart. To calculate one of the inner quantities, use two known quantities and the appropriate outer expression. Example: the power dissipated by a 1 kOhm resistor with 100 mA flowing through it is P = I2R = 0.12 A * 1000 Ohm = 10 W. This particular relationship is called Joule heating or Joule’s first law.

The reverse side features the likenesses of Georg Simon Ohm and James Prescott Joule. Electrical engineers, technicians, and hobbyists alike utilize these laws on a daily basis.

Available in green/gold, black/gold, red/gold, and laser etched wood. Note: The wood version does not have the portrait of Ohm and Joule on the back.

“If I have seen further, it is by standing on the shoulders of giants.”

— Excerpt from a 1675 letter from Sir Isaac Newton to Robert Hooke

Specifications:

  • 1.6 mm thick FR-4, immersion gold finish (wood version is 5 mm thick)
  • One hole provided for mounting or hanging

If you know a friend or family member who would appreciate a PCB medallion with custom artwork on it as a gift (e.g. a picture of a pet, loved one, etc.), we’d love to help you get some manufactured. They also make great Christmas ornaments. Please contact “parts (at) proaudioe.com” for more information. We can order as few as 5 PCBs.