9.Tube Buffer Maintenance
Buffer Assembly Overview
The TPB.V1 Tube Preamp Buffer (the “Buffer”) is composed of 2 separate printed circuit boards: a) a power supply board, and; b) a tube board. Both boards are connected via wires to the rear panel. The 2 boards plus the rear panel plus a 2 inch spacer board form the entire buffer assembly.
The 2 boards slide into and out the enclosure via slotted grooves which hold the boards in place. The tube board is the top most board and goes into the 3rd set of slotted grooves down from the top. The power supply board goes into the bottom most slotted groove.
The entire buffer assembly is accessed and removed from the enclosure by withdrawing/sliding all parts of the assembly out from the rear of the preamp at the same time. Putting the assembly back into the enclosure is essentially the reverse of removing it.
Removal of Buffer Assembly
We recommend the following procedure:
- Remove the 4 socket head screws from the corners of the rear panel.
- Remove the single socket head screw located between the 2 tube holes in the top side of the enclosure.
- Grasp the rear panel and gently pull/slide the rear panel and attached boards out of the enclosure. Stop after the assembly has been pulled out roughly 3 inches.
- Turn the entire enclosure on to its side with the bottom of the enclosure facing you and the partially removed rear panel/assembly located to your left.
- Find the 2 inch wide spacer board that had been in the same bottom slot as the power supply board. Set the spacer board aside for now.
- Turn the entire enclosure over on its other side with the top of the enclosure facing you and the partially removed rear panel/assembly located to your left.
- While gently tilting the bottom edge of the rear panel back to left to better see the power supply board observe the series of small wires plugged into the pins of the power supply board (ignore the heavier white plastic connectors. Find the 2 wires plugged into the 2 right most pins of the power supply board pin header J4 as shown in the layout diagram below. The pins are labeled J4.LED+ and J4.LED-. These 2 wires run back into the enclosure towards the front and attach to the blue LED located in the front panel. Carefully note which colored wire goes into which pin. Gently remove the 2 wires from the 2 right most pins but pulling them by their square ends. Leave those 2 wires disconnected.
- Continue to gently pull the rear panel/buffer assembly out of the enclosure. At some point the tube board will be completely removed from its slots. Gently fold the tube board up and to the left such that it is now to the left of the rear panel making it easy to view the power supply board which is still partially inserted in the slotted enclosure.
- If you wish you can now turn the entire assembly and enclosure back so that its now laying with its bottom down as it would normally. You should be able to clearly see the first few inches or so of the power supply board at this point.
- Further withdraw the power supply board/assembly until approximately half of the large round toroidal transformer is now outside of the enclosure. Stop withdrawing the buffer assembly. You don’t have to fully remove the power supply board for most maintenance activities but you can if you like.
Changing Mains Voltage
The Buffer can accommodate either 120 or 240 VAC mains voltage input. To change the mains voltage level you will first have to remove the buffer assembly per the instructions above.
Mains voltage level is set by placing jumpers on J1 as shown in the power supply circuit layout shown below. J1 is located on the left side of the power supply board (facing the board from the rear) immediately after the Z1 mains filter (large silver rectangular cube) and right next to the left edge of the round toroidal transformer. The left side of the power supply board is the top side of the image shown below.
The Buffer has 3 separate fuses.
The mains fuse is located in a drawer that is part of the IEC power input with integral switch located externally on the left side of the rear panel. This mains fuse is rated at 3 amps.
There are 2 internal fuses, F1 and F2.
F1 is the tube heater fuse. It’s located immediately next to the Z1 mains filter as shown in the diagram above. The F1 fuse is rated at 2.5 amps.
F2 is the plate/auxiliary power fuse. It’s located on the opposite side of the power supply board from the J1 mains voltage header. The F2 fuse is rated at 200 milliamps (0.2 amps).
Changing The Gain
The gain setting can be changed by changing the gain setting jumper position on the buffer’s Tube Board as shown in the circuit board layout shown below.
The TPB.V1 usually ships with its gain set at the default 0 dB setting. There are 2 additional optional gain settings; +3 dB and +6 dB.
Please note that there are 4 separate sets of gain jumpers with only 2 sets shown in the image below. For single-ended buffers only one set of gain jumpers will be present adjacent to each tube (2 total jumper sets). For balanced buffers, there will be 2 sets of gain jumpers adjacent to each tube (4 total jumper sets). Jumpers must be set the same on all sets of jumpers.