User guide
True to the Music
Radial Engineering Ltd. Workhorse User Guide
16
CARD-EDGE CONNECTOR SPECIFICATIONS
The following details the pin confi guration as used in the Workhorse. The ‘Old’ refers to the published API/VPR specifi cations. The ‘Current’ 
refers to the various racks we have investigated on the market. The ‘New’ is the Radial standard as outlined in the Workhorse Open Source 
Document.
Pin #  Old API Specifi cation  Current use in market  New Radial Specifi cation
1  Chassis Ground  Chassis Ground  Chassis Ground 
2  Output +4dB Hot  Output +4dB Hot  Output +4dB + Phase 
3  Output -2 Hot  - - -  - - -
4  Output Cold  Output Cold  Output +4db - Phase 
5  A- Ground  A- Ground  Analog Ground
6 Stereo link Stereo link Stereo link
7  Input -2 Cold  - - -  ¼” TRS Omniport - Ring
8  Input +4dB Cold  Input +4dB Cold  Input +4dB - Phase 
9  Input -2 Hot  - - -  ¼” TRS Omniport - Tip
10  Input +4dB Hot  Input +4dB Hot  Input +4dB + Phase 
11  Gain adjustment  - - -  Radial Buss feed
12  +16VDC supply  +16VDC supply  +16VDC supply
13  Power Ground - 0V ref  Power Ground - 0V ref  Power Ground - 0V ref
14  -16VDC supply  -16VDC supply  -16VDC supply
15  +48VDC Phantom  +48VDC Phantom  +48VDC Phantom
Due to the lack of clear standards, we have worked within the 
limitations of keeping the old standards while making the Workhorse 
as fl exible as possible. For instance Pin-3 has been left open 
because sometimes (on some modules) it is paralleled with Pin-2. 
This arrangement eliminates problems between other modules. We 
also discovered that sometimes Pin-7 and Pin-9 can be paralleled 
with Pin-8 and Pin-10, so the Omniport™ jack will not interfere.
The BUSS FEED (Pin-11) is simply whatever signal the designer 
will want to send to the buss (main out of module typically) and is 
essentially an amplifi er feeding a 4K7 resistor to Pin-11. That is 
connected to the inverting (virtual earth) input of an op-amp (in the 
mix section of the rack) with a 4K75 feedback resistor. This is called 
a ‘Virtual Earth Mix Buss”. It is low noise and less prone to problems. 
We chose 4K7 because it is lower noise than a higher value and 
because the Rupert Neve Designs Portico series has a 4K7 Mix 
Buss on all of their modules. This provides cross-compatibility 
between Radial and Rupert Neve Designs. 
The BUSS output on Pin-11 of each Radial module connects to a 
level and pan control in the master mixer area. By being able to 
mix together the output of what may be several modules in series 
various new effects may be created. For example if the Phazer phase 
adjustment tool is in a series chain of modules, it can be used as a 
radical EQ to phase cancel the tone by creating a nulling effect. 
Pin # 
1  Channel 8 Hot
2  Channel 8 Ground
3  Channel 7 Cold
4  Channel 6 Hot
5  Channel 6 Ground
6  Channel 5 Cold
7  Channel 4 Hot
8  Channel 4 Ground
9  Channel 3 Cold
10  Channel 2 Hot
11  Channel 2 Ground
12  Channel 1 Cold
13  Not Used
Pin # 
14  Channel 8 Cold
15  Channel 7 Hot
16  Channel 7 Ground
17  Channel 6 Cold
18  Channel 5 Hot
19  Channel 5 Ground
20  Channel 4 Cold
21  Channel 3 Hot
22  Channel 3 Ground
23  Channel 2 Cold
24  Channel 1 Hot
25  Channel 1 Ground
-
+
1
-
+
G
-
+
G
2
3
-
+
G
-
+
G
4
5
-
G
-
+
G
6
7
-
+
G
-
+
G
8
13
14
25
1
Pin # 
1  Channel 8 Hot
2  Channel 8 Ground
3  Channel 7 Ground
4  Channel 6 Hot
5  Channel 6 Ground
6  Channel 5 Ground
7  Channel 4 Hot
8  Channel 4 Ground
9  Channel 3 Ground
10  Channel 2 Hot
11  Channel 2 Ground
12  Channel 1 Ground
13  Not Used
Pin # 
14  Channel 8 Ground
15  Channel 7 Hot
16  Channel 7 Ground
17  Channel 6 Ground
18  Channel 5 Hot
19  Channel 5 Ground
20  Channel 4 Ground
21  Channel 3 Hot
22  Channel 3 Ground
23  Channel 2 Ground
24  Channel 1 Hot
25  Channel 1 Ground
+
1
+
GG G G
+
G
2
3
+
G
+
G
4
5
G
+
GGGG
6
7
+
G
+
G
G
G
8
13
D-SUB CONNECTOR FOR UNBALANCED 
SUMMING MIXER INPUT
D-SUB CONNECTOR FOR CARD SLOT I/O
1
2
3
4
5
-16VDC
COM
+48VDC
+16VDC
COM
CONNECTOR WIRING
HOT (+)
COLD (-)
GROUND
1
2
3
HOT (+)
GROUND
COLD (-)
XLR Connector
TRS ¼” Phone Connector
5-Pin XLR Power Connector










