[Richard Laws]

Mr Kenyon,

I'm the proud new owner of a 94 MKIV. However, I've been experiencing some speaker audio problems The problem began with intermittent audio on the two front speakers. Currently, I've lost all audio on the two front channels.

The problem then spread to the rear channels. On power up, the rear channels work fine, but after 2 to 3 minutes of operation, the rear channel begins to fade, until there is no audio output at all. Kind of sounds like a thermal problem on the rear channel, but I'm not sure if I should beging at the amp (wherever it is) or the haed end.

I thought perhaps, the problems I'm experiencing may have been experienced by other Supra owners, and the culprit component(s) identified.

Also, if there is a link or some info you could copy to me on the MKIV basic system layout, and component locations, I'd greatly appreciate it!

Rich L.

 

[Ear Candy]

Your amp is singing the swan song.

You will need a new factory amp or an aftermarket one. That is most likely the cause, if what you descrided are the only things occuring.

 

[ThomasKenyon]

Well, the factory MKIV system consists of a headunit with just a low voltage signal comming out. That signal is sent via a harness to a small 5 channel amplifier under the passenger seat. The amp then powers each of the 5 channels. (The front tweeters and the door mid are wired in series)

With a few more questions, I should be able to hone in on your problem.

When the front speakers "fade out" is it both at the same time or does one go out and then the other??

Does the "fading" out occur gradual or abruptly?

When all speakers are playing, do they sound OK or do they sound distorted?

Do the speakers fade out at high volume or at any volume??


I have seen both the factory headunit and the amplifier have problems similar to what you have described.

More than likely it is either of the two and not the speakers themselves causing the problem.

Thomas Kenyon
Custom Sounds
San Antonio, Texas

 

[Richard Laws]

Thanks for your prompt response -- I really apprecaite it!

To answer your questions:

When the front speakers "fade out" is it both at the same time or does one go out and then the other??

I'm not sure, because when I bought the car, the driver's side front speaker was already out -- no audio, never. The passenger front, would work intermittently and sound fine when it did, at all volume levels. Then it started "crackling" with no audio output at all, as a matter of fact, it would "crackle" with the volume set to min at the headend, and the fade and balance completely isolating the speaker.

Does the "fading" out occur gradual or abruptly?

The rear channels fade out rather abrubtly -- from perfectly good audio out, to muffled attenuated audio, to no audio at all, within 30 seconds. The initial volume level doesn't seem to be a factor, because I tried to get by with just minimum volume, and it still occured.

When all speakers are playing, do they sound OK or do they sound distorted?

When all speaker did play (Minus the driver's front, which never did), the audio sounder fine with no distortion.

Is there a slick way to verifty the low-level audio out of the headend? Can the low-level audio out of the factory headend, be RCA'd into an aftermarket amp? If I am able to verify the headend is not the culprit, and the problem is in fact the amp, is there an aftermarket equivalent (or better yet, upgraded) 5-channel amp, you'd recommed for this particular application? If so, are there any special considerations I have to make to send the proper low frequencies to the factory sub?

Thanks a lot!
Rich L.

 

[ThomasKenyon]

Sorry for the long delay... musta been side tracked.. sorry.

Well, after reading the description of your problem I am really leaning to the factory amplifier being the problem. I believe this to be the problem because of the fact that the speakers (when they play) sound fine. I have seen this problem before in Lexus' and Supras that use the same setup.

As far as the tying into a new amplifier.... yes, it is possible. I would however, use a line level convertor on the signal side so that you can adjust the signal going into your new amplifier easily. Any decent small 5 channel amplifier will do a good job and if you want, I could sell you a stock Supra amp and return it for a refund if it wasn't the problem.

Call me at the shop and I'll try and help you out!!

Sorry for the delay!

Thomas Kenyon
Custom Sounds
San Antonio, Texas
210-340-4000