Here is detailed description of what was done:
I. Installation of a new motorized volume pot. Fortunately, it’s enough space for a pot that was sold with the kit. It turns out to be 4-channel so if one gets 2-channel one it should be half-inch shorter. The new pot needed a lock-up hole for the pin in the front panel and its shaft was longer than needed so I shortened it by 12 millimeters. Also the shaft should be knurled at a specific position which is different from the existing one.
Since the new pot doesn’t have center tap one couldn’t use loudness circuit with it; I removed its components, 0.1 mfd cap and 4.7 K resistor leaving the switch in place with nothing connected to it.
The small PCB attached to the pot has ribbon socket at the input and output. I removed the sockets and connected PCB inputs (they are labeled) to pins 2 and 5 i.e. middle terminals of the balance control, outputs to pins 9 and 2 of the line amp plate and the output ground to terminals 1 and 6 of the balance control AND to Pin 1 of the line amp plate.
II. Power supplies. Space for adding new components should be freed up and, since the preamp is stock, some components in the power supply have to be upgraded. So I decided to combine these two tasks.
The cap can and the filament filtering caps with rectifying diodes (someone replaced selenium rectifier long time ago) were replaces with Sheldon Stokes SDS power supply board mounted at the old filament caps space. The SDS board is mounted on 8 mm stands and I made new holes in the bottom plate for B+ wires. I didn’t use on-board fuse since I think running the mail AC line to the board and back might increase hum. Before the next step, I wired the whole thing and ensured the PAS powers up and works.
This freed up space for a remote power transformer which was installed atop of the cap can opening. Primary winding wires were soldered to the AC jack at the rear where power transformer wires are connected and the middle of the secondary ( green wire) was grounded.
III. Installation of the remote controller main plate. This is the biggest plate in the kit, and only reasonable place to install it is above tone control pots. Capacitors and wires connected to them could potentially interfere with installation; however, I bypassed tone controls (as recommended by Dynaco Doctor) so this was not a problem.
I used 20 millimeters bronze stands secured on front plate with M3 screws. Since screw heads didn’t fit in the tiny space between front plate and PAS faceplate I made indents in the front plate similar to those made for switches. Still, a couple of screw heads protruded too much so I partially filed them off.
IV. Installation of the infrared (IR) eye. The IR eye was carefully unsoldered from the controller plate and installed in the hole from the scratch filter switch. The horizontal dimension of the IR eye was a bit smaller than the faceplate switch opening. I found a polypropylene box with 1.5 mm-thick walls, cut a strip from it and made a square hole for the IR eye body. The eye was glued to the strip with epoxy glue in such a way that it protrudes as far as possible and the strip was mounted at the front of the faceplate using two existing scratch filter switch holes and screws. Excess of the epoxy glue was removed by a filer to allow tight mounting. Three wires were soldered to the eye terminals and soldering joints covered with heat shrink tubing. The other ends of wires were soldered to the controller plate. In the assembled preamp, the eye protrudes for 2-3 millimeters out of the faceplate which allow wide-angle remote operation.
V. Connections. The volume control pot has two-wire cable connected to a snap-in terminal; I just extended the wires. The transformer wires were connected to a similar snap-in terminal supplied with the kit. These wires should be managed better than they are now; I’ll deal with this later when ribbon connectors for input relays will be installed.
VI. The remote volume is working now and the next step was supposed to be installation of input relays. However, upon connection of the Dynaco to audio system I got quite strong hum using all inputs. The hum was independent of the volume control position. I checked all connections including ground and they seems OK. Then I checked if hum results from installing of remote control transformer by unsoldering it. It partially helps, i.e. the hum diminished but is still quite noticeable. What’s interesting is that the hum now diminishes if I increase volume and became quite weak if volume is at the MAX.
The transformer hum should be eliminated by the Faradey cage I'm going to make; however, the remaining hum is quite puzzling. Any ideas what might be the cause of it?
I. Installation of a new motorized volume pot. Fortunately, it’s enough space for a pot that was sold with the kit. It turns out to be 4-channel so if one gets 2-channel one it should be half-inch shorter. The new pot needed a lock-up hole for the pin in the front panel and its shaft was longer than needed so I shortened it by 12 millimeters. Also the shaft should be knurled at a specific position which is different from the existing one.
Since the new pot doesn’t have center tap one couldn’t use loudness circuit with it; I removed its components, 0.1 mfd cap and 4.7 K resistor leaving the switch in place with nothing connected to it.
The small PCB attached to the pot has ribbon socket at the input and output. I removed the sockets and connected PCB inputs (they are labeled) to pins 2 and 5 i.e. middle terminals of the balance control, outputs to pins 9 and 2 of the line amp plate and the output ground to terminals 1 and 6 of the balance control AND to Pin 1 of the line amp plate.
II. Power supplies. Space for adding new components should be freed up and, since the preamp is stock, some components in the power supply have to be upgraded. So I decided to combine these two tasks.
The cap can and the filament filtering caps with rectifying diodes (someone replaced selenium rectifier long time ago) were replaces with Sheldon Stokes SDS power supply board mounted at the old filament caps space. The SDS board is mounted on 8 mm stands and I made new holes in the bottom plate for B+ wires. I didn’t use on-board fuse since I think running the mail AC line to the board and back might increase hum. Before the next step, I wired the whole thing and ensured the PAS powers up and works.
This freed up space for a remote power transformer which was installed atop of the cap can opening. Primary winding wires were soldered to the AC jack at the rear where power transformer wires are connected and the middle of the secondary ( green wire) was grounded.
III. Installation of the remote controller main plate. This is the biggest plate in the kit, and only reasonable place to install it is above tone control pots. Capacitors and wires connected to them could potentially interfere with installation; however, I bypassed tone controls (as recommended by Dynaco Doctor) so this was not a problem.
I used 20 millimeters bronze stands secured on front plate with M3 screws. Since screw heads didn’t fit in the tiny space between front plate and PAS faceplate I made indents in the front plate similar to those made for switches. Still, a couple of screw heads protruded too much so I partially filed them off.
IV. Installation of the infrared (IR) eye. The IR eye was carefully unsoldered from the controller plate and installed in the hole from the scratch filter switch. The horizontal dimension of the IR eye was a bit smaller than the faceplate switch opening. I found a polypropylene box with 1.5 mm-thick walls, cut a strip from it and made a square hole for the IR eye body. The eye was glued to the strip with epoxy glue in such a way that it protrudes as far as possible and the strip was mounted at the front of the faceplate using two existing scratch filter switch holes and screws. Excess of the epoxy glue was removed by a filer to allow tight mounting. Three wires were soldered to the eye terminals and soldering joints covered with heat shrink tubing. The other ends of wires were soldered to the controller plate. In the assembled preamp, the eye protrudes for 2-3 millimeters out of the faceplate which allow wide-angle remote operation.
V. Connections. The volume control pot has two-wire cable connected to a snap-in terminal; I just extended the wires. The transformer wires were connected to a similar snap-in terminal supplied with the kit. These wires should be managed better than they are now; I’ll deal with this later when ribbon connectors for input relays will be installed.
VI. The remote volume is working now and the next step was supposed to be installation of input relays. However, upon connection of the Dynaco to audio system I got quite strong hum using all inputs. The hum was independent of the volume control position. I checked all connections including ground and they seems OK. Then I checked if hum results from installing of remote control transformer by unsoldering it. It partially helps, i.e. the hum diminished but is still quite noticeable. What’s interesting is that the hum now diminishes if I increase volume and became quite weak if volume is at the MAX.
The transformer hum should be eliminated by the Faradey cage I'm going to make; however, the remaining hum is quite puzzling. Any ideas what might be the cause of it?
Last edited:
