Introduction

This page is a description of what I use in my shack (barn) for audio. I have several different radios an each of those have their own audio amps and speakers. Some of the speakers, like for the Heathkit systems (HR-1680, SB-101) are pretty large (5" x 7" Oval). They sound OK, but nothing special. Other units (IC-735, HTX-100) have small internal speakers. They produce enough sound but sounded kind of tinny. To complicate things even more, there are the radios (HW-8, HW-7) that are meant to be used with headphones and external audio filters that I would like to use with all of them.

I initially made a relatively simple switching interface that I refer to as the Key/Audio Switch. Since I was switching audio signals I thought it would also be nice if I could switch the destination of my keys. I further expanded it so that I could choose from several different keys.

Schematic

In the drawing below, CB1 and CB2 are Connector Blocks that contain two rows of four phono jacks. CB3 is a >Connector Block that contains one row of four phono jacks. The Connector Blocks are mounted on the rear of the chassis and the switches are mounted on the front of the chassis.

On CB2 (far left connector block), six of the phono jacks are allocated for Audio Input. The other two are used for routing the audio to/from a External Filter. The rotary switch (S1) selects one of the six audio sources and sends it to the Filter In/Out switch. If no external filter is used, the switch should be in the Bypass position. If, however, if CB2-J7 and CB2-J7 are connected to an external filter, the Filter In/Out switch can be used to put the external filter in and out of the circuit.

The selected audio is then passed to the Audio Output selector switch, S3. The Audio Output selector switch selects one of six possible destinations (CB1-J1 to CB1-J6).

CB1-J7, CB1-J8 and front panel Key jack, are reserved for a Key input. This can be from a straight key, semi-automatic key (Bug), or keyer. For my purposes, I used CB1-J7 to select my Heathkit HD-1410 keyer and CB1-J8 to take input from my Computer Interface. I only used the front panel Keyjack for testing out new keys or keyers. So, as long as all of the input devices operate in a similar manner, they can all stay connected at the same time. The Key Selector switch (S4) selects a destination for the keying signal. Again, as long as all of the destinations are keyed in a similar manner, there isn't any issue. Just don't try to mix keying types, like cathode keying and grid block keying.

Physical

The scaled drawing below (80 pixels/inch), shows how the box of connectors and switches actually looked. The view of the front panel is from the front and the view of the rear panel is from the rear. So to look at things properly you have to swap left and right, when you are going from front to rear. For example, when dealing with the Key Output switch on the left of the front panel. The connector block (CB3), which shows on the right in the drawing below, is actually on the left of the rear panel, when viewing from the front.

I have a rack of shelves that hold my equipment. This switch box is mounted in the center, under the bottom shelf. There is only enough room for a flat keyboard to slide underneath. This makes it seemingly difficult to connect things up, without seeing the rear panel. But it turns out, that isn't true. With switch box mounted under the shelf, the drawing below allows me to easily feel which connector is which. I can wire everything up without ever seeing the rear of the switch box.