Running Harmon Kardon with no factory head unit

As some will know, I have installed an aftermarket Kenwood head unit connected to a 20GB MP3 Kenwood Keg.

I had planned to replace the Harmon Kardon amplifier & speakers with aftermarket, but after a lot of pain & grief with Tweeter, I was left with an aftermarket head unit and factory amp – but the Harmon Kardon amp will only work when connected to a factory head unit, so I had to keep it installed:

This install lasted a while, then “scooterboy” provided me with a factory head unit which I was able to strip down to a minimum – enough to still run the Harmon Kardon amp, but “hideable”:

 

While this system worked, it remained awkward. With a volume control on the Harmon Kardon amp (controlled by the steering wheel remotes via the stripped down factory head unit) and a second volume control on the Kenwood head unit, it was confusing for other people (sorry Keith!)
I tried setting the Kenwood to a fixed high level and using the steering controls only to adjust volume, but then I lost the “loudness” low volume emphasis function of the Kenwood.
I could not set the Harmon Kardon to a fixed high level, since the factory head unit always reverts to a medium volume when it is turned off/on. So for a while I would start the car, use the steering controls to increase the Harmon Kardon level to maximum, then use the Kenwood volume control the rest of the time. One problem with this was losing the speed compensation of the Harmon Kardon amp, which does not work when its volume is already at max.

So finally I have spent a few days developing what I long ago planned to do – a circuit that controls the Harmon Kardon amp the way I need; the circuit is based on “EZcal”, a product made by my company. In the picture the case is removed because I have not finished development yet (the program does not yet remember adjustments that I make when power is turned off).

The circuit is programmed to send appropriate iBus messages to the Harmon Kardon amp, so that it powers up with near full volume – enough headroom left over for speed compensation to work, but loud enough that the Kenwood head unit output gives good sound with “loudness emphasis”. As the picture shows, I can use the EZcal keypad to alter the Harmon Kardon “mode”.
I need to do a bit more work, but this is much more workable – I can finally install the PAC SWI-X thingy so that the steering wheel controls can directly control the Kenwood head unit. Oh – I can also now remove & discard the stripped down factory head unit (unless “scooterboy” wants it back!)

 

TECHNICAL INFO:
Harmon Kardon / Radio communications in 2003 MINI Cooper S.
===============================================
When power is applied, the radio sends a broadcast message – presumably indicates that it is turned on.
68 04 FF 02 04 95 Radio->all …
Next the DSP sends a message to the radio – presumably indicating that it is present.
6A 04 68 02 01 05 DSP->Radio …

So now the radio knows it needs to operate in “Harmon Kardon” mode. In this mode the front speaker outputs are fixed at a medium volume level, with no bass/treble/fade/balance applied. Instead the audio control settings are transmitted to the amplifier and are applied to the incoming signal there. The radio sends an initial sequence of settings:
68 04 6A 36 AF 9F Radio->DSP “initialize begin?”
68 04 6A 36 60 50 Radio->DSP “bass=center”
68 04 6A 36 C0 F0 Radio->DSP “treble=center”
68 04 6A 36 80 B0 Radio->DSP “fade=center”
68 04 6A 36 40 70 Radio->DSP “balance=center”
68 04 6A 36 E4 D4 Radio->DSP ????
68 04 6A 34 09 3B Radio->DSP “mode=spatial”
68 05 6A 34 90 00 A3 Radio->DSP “driver mode off”
68 04 6A 36 A1 91 Radio->DSP “initialize end?”
The values for bass, treble, fade and balance are the current settings – not necessarily “center”. The “36 AF” message at the beginning perhaps sets some flags; this message stops the amplifier putting out any sound, because the radio sends it when it is turned off. It probably also sets all the audio controls to default, and sets the volume to zero. The “36 A1” at the end presumably allows the amplifier to start running.

The radio now sends a sequence to set the volume. This is set with one or more messages that increase the volume by between 1 and 15 steps:
68 04 6A 32 F1 C5 Radio->DSP “volume+15”
68 04 6A 32 F1 C5 Radio->DSP “volume+15”
68 04 6A 32 31 05 Radio->DSP “volume+3”
So the volume is now at “33”; the maximum volume that can be sent by the radio is “63”.

The radio / amplifier system is now operating.

The volume can be adjusted up/down. The radio sends messages to increase or decrease the volume by 1-15 steps; it must keep track of how many steps are needed:
68 04 6A 32 10 24 Radio->DSP “volume-1”
68 04 6A 32 40 74 Radio->DSP “volume-4”
68 04 6A 32 10 24 Radio->DSP “volume-1”
68 04 6A 32 30 04 Radio->DSP “volume-3”
68 04 6A 32 11 25 Radio->DSP “volume+1”
68 04 6A 32 61 55 Radio->DSP “volume+6”
68 04 6A 32 11 25 Radio->DSP “volume+1”
68 04 6A 32 51 65 Radio->DSP “volume+5”
After this sequence, the volume would be at “36”.

The audio controls can also be adjusted; bass/treble/fade/balance are all adjusted using the “36 xy” code where the “x” part indicates the audio function and the “y” part indicates the setting:
36 60 “bass=center”
36 6y “bass=boost”; y=2/4/6/8/A/C
36 7y “bass=cut”; y=2/4/6/8/A/C
36 C0 “treble=center”
36 Cy “treble=boost”; y=2/4/6/8/A/C
36 Dy “treble=cut”; y=2/4/6/8/A/C
36 80 “fade=center”
36 8y “fade=front?”; y=1/2/3/4/5/6/8/A/F
36 9y “fade=rear?”; y=1/2/3/4/5/6/8/A/F
36 40 “balance=center”
36 4y “balance=left?”; y=1/2/3/4/5/6/8/A/F
36 5y “balance=right?”; y=1/2/3/4/5/6/8/A/F
I would guess that all the audio controls can vary to “F”=15, so that it might be possible to get more bass/treble boost by sending a “36 6F” or “36 CF” code.

The amplifier mode can also be adjusted using the “34 0y” code where the “y” part selects the mode:
34 08 “MINI H/K”
34 09 “SPATIAL”
34 0A “ELECTRONIC”
34 0B “INSTRUMENTAL”
34 0C “FESTIVAL”
Other values of “y” seem to have no effect.

The “driver mode” can also be adjusted on or off:
34 90 “DRIVER MODE OFF”
34 91 “DRIVER MODE ON”
Some modes do not allow the driver mode to be turned on; the radio always sends a “34 90” code when the amplifier mode is changed.
Turning driver mode on when it’s not allowed seems to have no effect.

If the radio is turned off, a “final” message is sent to the amplifier:
68 04 6A 36 AF 9F Radio->DSP “initialize begin?”
This silences the amplifier even if it is not powered off! Strange, since the radio also sends a voltage to control the amplifier.

(I also created a document listing the pin connections of the Harmon Kardon amp, copied from data on www.minitis.com: Harman Kardon Amplifier Connections)