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2006-11-17 ER6i's and StarComm Advance


An epic tale

Posted 17 November 2006 - 08:51 AM

First off, let me state that Jeff at Sportbike Effects ( has been GREAT in helping me troubleshoot this problem. He has sent new parts, cables, ear buds. He has conference called Tony, in England, to help resolve this issue. Jeff is a heads up man and deserves credit and our support. Also, there is a member of this forum whom I consulted and he provided invaluable data and insight into resolving this issue. I promised to not divulge his name and will honor my promise. If he wants to come forward that's up to him. To that person… THANK YOU. Hope to meet you in person some time and buy you a big steak and lobster dinner.

SUMMARY – (in case you don't want to read the diatribe below..) I bought a StarCommm Advance (SCA) unit and Er6i ear buds. Installed the SCA into a tank bag side panel and went riding. Worked great until the first hot day, then the audio went to crap. Unacceptably bad distortion. The unit would reset after cooling down, sound good again until the next hot day.

The problem was ultimately discovered to be an impedance mismatch between Er6i ear buds and the SCA amplifier. The SCA use 'differential amps' based at nominal load impedance of 32 ohms. The Er6i's impedance value is closer to 16 ohms. This caused the amp to work too hard; heat and distortion soon followed.

The final solution is use ear buds that have an impedance value equal to or greater than that of the SCA ear buds. Fortunately, the Er6 ear buds fit this bill. Also, the Er6 ear buds actually have better frequency response than the Er6i's.. and they come in black so they don't show grime as bad as the white Er6i's.

As always, YMMV. I know that some of ya'll out there ride in hot weather and have no problems using the SCA and ER6i combination. Good for you, but I didn't have the same experience.

One last thought; the SCA was re-designed for 2006. New design, new components.

For a detailed analysis, keep reading..

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StarCommm Failure


The audio level decreases to the point of being inaudible when ambient temperatures reach ~95 degrees F or above. Turning the volume up to audible levels results in severe distortion of the audio. After the StarComm cools down the problem disappears and good audio quality is heard. When ambient temperatures are cool, it works great. When hot outside, it does not work well at all.

A second, new, unit was sent to me and it does exactly the same thing as the first unit.


The StarComm resides in the side compartment of a Tourmaster tank bag.

I am not using rider to pillion, bike to bike, or anything else. Just 2 audio inputs; radar and mp3.


I've tried to isolate the problem to determine the cause. So far I've tested the following items:

  1. Thinking the temperature inside that compartment could exceed the maximum temperature stated by StarComm of 135 degrees F, I placed a RF remote thermometer in the side compartment with the probe taped to the new StarComm. The remote thermometer is RF enabled and consists of a transmitter and receiver. The receiver (and readout) was placed where I could monitor the StarComm temperature while riding. The maximum temperature observed was 108 degrees F inside the compartment. Ambient temperature, as read by FJR instrumentation, was 95 degrees F. The StarComm had failed at this point. This lead to more testing back at the house.
  2. With the StarComm failed,
    1. 3 different audio sources tested (All three devices were tested for good audio first by plugging the ER6i's directly. All 3 tested good.)
      1. Dell Axim mp3
      2. Portable Sony CD player
      3. Sony mini- disc
    2. Replaced audio input cable from audio source to StarComm.
    3. Used battery source other than bike; used a spare car battery.
    4. Removed the 'Remote' volume control.
    5. Adjusted StarComm controls per recommendations in manual.
      1. Vox off then at 0 – 100% in 10% increments
      2. Mic gains at 0 – 100% in 10% increments
      3. Volume control at 0% to ~ 30%
    6. Relocated the StarComm from the side panel away from the magnets thinking that perhaps the magnets were affecting the circuitry somehow.

Testing (continued)

None of these items fixed the problem. The next steps were to:

  1. Cool the StarComm down to typical morning temperatures, at about 60 degrees F. I did this by first taking the unit into the air conditioned house then into the refrigerator for ~ 5 minutes. When at 60 degrees F as read by the thermometer it was removed.
  2. The StarComm was then connected back at the bike, outside, with the StarComm perched on top of the tank bag, not in the side compartment.
  3. The temperature probe was taped to the StarComm and the temperature monitored as the unit heated back up to ambient temperature, ~95 degrees F.
  4. I monitored the audio while the temperature rose. At ~85 F, the audio level had decreased significantly. Turning the volume up yielded adequate level but some distortion.
  5. At 90 degrees F, total failure. The audio was severely distorted and to hear much of anything the remote volume control and/or internal volume control had to be placed at ~80% to hear audio.
  6. When at this state, I discovered that *sometimes* if I unplugged the audio source from the 'Audio' connection, let it sit for 10 or 15 seconds, then plugged it back in, that the audio came back loud and clear. Then, after about 30 seconds, the level would fade and the distortion begins.
  7. I repeated this test 3 times. Additionally, every morning the StarComm works great, every hot afternoon it fails.


I believe that StarComm has thermal related problems with the new for 2006 StarComm. I think all other possibilities including power source, cabling, audio sources, etc. have been eliminated from the equation.

The device works when cool, fails when hot. The failure has been reproduced across various days and even across units. A component is not living up to its temperature specification, the circuit needs be redesigned, or ventilation holes need be drilled into the aluminum casing for improved circulation.

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A phone call to Tony Starling was made. Tony stated that StarComm1 Advanced uses a differential amplifier design and not a 'earth ground driven' system as is commonly found in the audio industry. This is done to maximize output from the amplifiers.

Tony stated that in a few cases, using earth-ground headset caused problems with the SC1 and the fix was to use the proprietary ear buds offered by SC1. Tony stated that the ER6i's are 'earth ground driven' and are mis-matched for use with the SC1.

Testing has shown that using the SC ear buds 'fixes' the problem but causes another, namely, that the SC1 ear buds have inferior frequency response and poor efficiency as compared to the ER6's. They SC1 buds are very tinny with poor bass response. IMHO, they are terrible.

The question I have now is "Can ER6i's be modified to facilitate use with a differential amplifier system?". What is the difference between the proprietary ear buds and a conventional system?

Update: I consulted with an electrical genius type of guy who frequents the board. I promised to not state his name. He can identify himself if he wants to, but THANK YOU to him.

The problem appears to be impedance mismatch between the SC ear buds and most other devices, causing the amplifier to push more current than it's capable of. This causes excessive heat and finally break down, resulting in distortion.

For a test, it was recommended I purchase a Radio Shack volume control, and adjust it so that the overall resistance of the circuit would match the impedance of the StarCommm ear buds. So, I measured the StarCommm ear buds and other devices too, and ended up with the values listed in the table below. Note: this is a dc resistance measurement, not truly an impedance measurement, but it's close enough for generic troubleshooting.

Brand Impedance (ohms)

StarCommm 32

ER6i 16

ER6 48

Sony over the ear 8

I adjusted the volume control so that the overall resistance of circuit (ear buds + volume control) was > 32 ohms then went for test ride in the heat. And….. no failure! But, unfortunately, this testing was done last September, and the ambient temperatures never got past 100F.

While this 'solution' appears to work, I didn't like the volume control dangling out there. This started a search to find high quality ear buds that higher than 'normal' impedance values.

Imagine my surprise when I found the ER6 ear buds. They have 48 ohms, well over the 32 ohms of the StarCommm ear buds, and by specs, they also have better frequency response. And, they come in black. So I bought a pair, installed them, sans volume control, and to date they have worked great. No distortion, better bass, and the fit and feel are identical to the ER6i's. I liked the 6i's 'pine cone' noise suppressor, the piece that fits in the ear, so I robbed them off the 6i's and installed them on the ER6's.

After 3 months of running the SCA and Er6i combination, I like it better than the Er6i's. Better bass response, the black color doesn't show grime, and the unit has yet to fail. 2

Also on

StarComm audio amp has output impedance (Z) of 32 ohms.

Etymotic ER6 is 48 ohms (and are discontinued) Etymotic ER6i is 16 ohms and caused amp thermal run away. and is also discontinued.

Replacement for ER6i is hf5 (my selection, like balanced armature sound over moving coil) and Z = 16 Ohms. OK, no I'm off to find some way of matching these imbalanced impedances.

From Wiki I find a circuit that looks promising and easy to build -

where Ra =

and Rb =

Given that Z1 = 50 Ohms (stated that Z1 must be > of two Z's) Z2 = 16 Ohms I think I calculate correctly that -

Rb = 19.4 Ohms
Ra = 41.2 Ohms
Does this look correct?
Is there a simpler solution?
Should I be using another technique e.g. circuit design type? (Man, it's been a loooooong time since I played elec tech... )
Thanks in Advance,

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