Bose Speaker Amps/radio face

[LancePearson]

Robert, I agree in general. When I have opened the tunnel to deal with the radio there is some 1/2" or 3/8" thick stuff in there that is dry and not rotted and the car's interior noise level and heat level is fine especially when compared to my 76 where I ripped it all out and did what you did. However, on the highway just forward of the tunnel when I drove the car home from my Atlanta purchase in December all 515 miles I kept hearing this sort of whooshing sound almost behind the radio. I did not know what it was but since have learned the ZF is a noisy tranny and that simply folding a microfiber towel and placing it on the ashtray access door and forward and up 4" across the front of the bottom of the center trim piece over the radio/hvac/dic stack stops the noise entirely. When I opened it up for the radio, sure enough it's all thin plastic and below the radio there is a sort of 1.5" or so by the radio head deep cave there which I believe can act a bit like a resonance chamber...the tube on a pipe organ so to speak under the right circumstances. All I did was use the .080 urethane foam adhesive with foil face to coat most of those plastic surfaces and the inside of the trim to try and stop what I think is inherent, resonance in the plastic surfaces which aren't thick enough to stop it. I'll probably put some on the bottom of the radio to absorb sound a bit more as well when I do the final stick it back in. I did not close any openings so air can flow if it is a design feature which I doubt but just in case....We'll see when I get the radio all the way done. Just waiting for something to arrive now and then I'll button it up and try it. I sure agree it's not worth redoing the cockpit. The cockpit so far is much cooler than the 76 was before I did this with thicker urethane on the cage floor and tunnel the way it is already so I'm not worried about that either. We'll see in a little while. I'm probably being obsessive about the noise.

In the 76 I also switched the two seats when I had them out to redo the floor and carpets. I'll probably switch the two seats next winter on the 91 as well though I may recover the driver's side with new leather. next year's project. In a month or so it's time to start using it, time to resume serious kayaking and time to start thinking about my Flying scot sailboat too!

Thanks for the information...it confirms what I'd thought about the cockpit.

[Schrade]

Originally Posted by LancePearson

a diagram service sent me the system diagram schematics today so I'll pass it along. It does not go inside the boards but is a fairly clear presentation of the system as I see it.Attachment 2228

I got board schematics there Lance, for the mainboard, and for the tape/CD board from Bob carstereohelp.com.

Your lights don't go through the board. Only way to check the missing incandescant bulbs is to pull them, and check the bulb filament for continuity, then check the Incand input (the solid gray input on the smaller HU connector), TO the first bulb socket, then the second (I don't know if the bulbs are in series, or in parallel). ON SECOND THOUGHT; THE FSM NOTE TO THE RIGHT SAYS NOT TO MEASURE IMPEDANCE TO THE UNIT - I DON'T KNOW IF YOU CAN ISOLATE THE INCAND CIRCUIT THROUGH THE HU

(in the 2 schematics, board header ID's P701 and P702 correspond to CN101, and CN102, respectively, to our HU header ID's.

Never mind my notes there; that's for the AUX Input mod...

The gray input

[LancePearson]

Shrade, I don't have the unit in front of me but the total head unit by Delco consists of three boards/electronic controls including the cd and cassette mechanisms if memory serves...there is one horizontal on the floor of or somewhere innside the the metal case I think (memory here or it could all be the mechanism controlled by the side board.)..will see. There is a second vertical one on edge with its length the depth of the head unit when put into the dash behind the two incandescent bulbs on the left side as you look at it when the top and two sided metal case is removed. Then, on the separate approx 1/2" deep face unit is a third, or another, green circuit board which screws to the back of the face with all it's buttons and light distribution plastic "runners" in place. All you see when looking at the back is the soldered pins instead of what is on the other side. I haven't removed it again at this point but will in time. Between it, the buttons and the plastic face they all reside in are two pieces of clear plastic with white lines on them which I believe distribute the dash lights controlled by the dimmer to the entire face and when the lights come on for the car, parking or headlights, then the dimmer switch controls them and they show an orange light throughout my radio (the basic lighting schemel across my dash gauges). I think it is the two fairly powerful little incandescant bulbs on the vertical board on the left side which generates that light. Each of the buttons also has a green lcd or led that lights on demand as well. The lights show three types on the schematic: Incand, LED, LCD....and normally display screens are lcd types I think but I'm in over my head without it open and in front of me. Every single light function works fine save the backlighting for the 1/2" x 3-4" long display area which by definition has to be a more subtle light source and I believe does not come from the two incandescent bulbs on the left side of the h.u.

The metal case to which the completed face unit with it's green board screwed to it attaches clicking in with its separate board is the face mounted on the h.u. metal head box then. There are pieces of insulating material to keep that board from touching the metal case itself. I don't remember exactly what's under the face board itself but the one thing in the entire radio function not working at the moment is the display window backlighting which is more or less a constant though gets brighter if memory serves when the headlights are on as well. It can probably only be lit by a source on that face board just described. Without the headlights there is backlighting there normally and right now in mine it is not there. So, if it's the two Radio Shack 50 miliamp bulbs referred to in Alchemist's post I put up here then I'll see that when my new/used radio arrives and I substitute it in place. Then I'll take my current which will become a backup h.u. apart and see what is on the inside of the face's board. I'm no EE but what I've seen so far does not look like the board for the face unit. Maybe wrong and maybe I'll have to eventually send it to one of the radio tuners, dr. don or Bob, to let them do it but right now it's an interesting puzzle. I'll let you know when I get my new/used unit and put it in assuming it works correctly as purchased says it does.

We'll see. Not often I spend this much time on one thing. I just have the dash open in that area now as it's too cold to drive at the moment anyway. Sound is terrific when I do try it though.

[HAWAIIZR-1]

Lance,

Thanks for all your posting about Bose stereo woes as it made me finally get off my arse this weekend to pull the two front amps to ship out for repairs. They were buzzing and hissing with no sounds otherwise. Initially I thought it was my plug wires or alternator not really looking into it to actually listen, but after disconnecting them it was easily known to be the problem. I replaced my head unit years ago with an aftermarket unit (JVC Chameleon) and it still works great even with back speakers only. I guess it never really bothered me since I don't listen to the stereo and always enjoy the music from the modified LT5. Again, thanks for motivating me to get this done.

Craig

[LancePearson]

Hawaiizr-1,
You are welcome. The speaker amps are really very easy to remove and replace..probably one of the easiest things I've done to date with either of mine and you will like the new amp on the speaker unit with the Bose speaker setup. I'm not a huge base guy but clear sound and hi fidelity when I'm listening to a book on cd or cd on a long drive or the radio and it is more than sufficient for me for that. I like the original look and is why I'm going to all the trouble.

[LancePearson]

One last thing..there are small bulbs around that face c. board and if you bend them you can make them inoperable as lights for the backlighting of the display which is almost certainly what I've done in my first attempt. He, Dr. Don, and I discussed the radios a little and he told me he was the JVC national audio Engineer as a career and quit to do the radio repair business 13 years ago since national companies don't service what they sell very well. The head unit in our case was made by Delco and the CDM unit was made by Bose as were the speaker amp units and they jealously guard the circuitry diagrams. He said that the front speakers are designed to give good mid base and high sounds and the rear speakers to give good base and mid high sounds as a system. Bose simply got rid of the energy of producing sound we don't want to hear. The amps are 50 amps going into 1 ohm speakers which if you put it into the traditional sound producing design would be the equivilent of about 100 amps of power in each amp. He says that he has taken any number of our corvettes where the owner says the amps are fine, gone through the amp boards on them one by one and the sound improves dramatically like it's a whole new radio and the system is good. Dr. Bose is a genius he says but he hired people to buy capacitors and resisters who bought poorly made (not doped effectively is his term) and they started leeching acid the moment they were put in use and then heat and activity over time makes them all fail. He uses components that do not do that he says and when done you have an outstanding audio system. I keep reading here where they are not good systems but I suspect that is the reaction to the many components and dealing with the capacitors which fail, etc. Once set up properly he says they are one of the best systems around. I will probably send my unit back to him since it will become my backup unit shortly and he'll go through it and clean it all up, put the bulbs in, for a very minimal fee and redo the lights on the display as well and return it.

He advises never to use anything other than water and a very soft rag like a microfiber rag to wash the radio face as it is an lcd screen just like your laptop and you can use soaps and sprays and turn them cloudy in an instant. Treat it like your laptop and you'll do fine.

If you did not realize it there is a mute sound system built into it as well. it uses the speakers as microphones, identifies some background sounds which are not good for the human ear and sends out sounds that cancel them in the course of using the radio as well as the SCV, Speed Corrected Volume feature.

Lance just passing on what I'm learning from experts.

[HAWAIIZR-1]

Originally Posted by LancePearson

Hawaiizr-1,
You are welcome. The speaker amps are really very easy to remove and replace..probably one of the easiest things I've done to date with either of mine and you will like the new amp on the speaker unit with the Bose speaker setup. I'm not a huge base guy but clear sound and hi fidelity when I'm listening to a book on cd or cd on a long drive or the radio and it is more than sufficient for me for that. I like the original look and is why I'm going to all the trouble.

Hi Lance,
I'm not surprised that some maintenance comes with owning this Bose system from an over 20 year old car. I think it is well worth it to rebuild so I did as I like the sound myself. I know if you want one of those really thumping systems it might be best to replace it all, but as you said I like Bose and the sound quality even for my home. I understand your wanting to keep it stock and nothing wrong with that with the original look. Thanks for sharing what you found out from Dr. Don about the history and information in detail for this system.

Craig

[LancePearson]

Part of why I like the Bose is that Dr. Bose and his systems use some cleverness rather than just the raw application of indiscriminate electrical power. I like rock and roll and jazz and often listen to books on cd discs on long drives or a local radio station though with the targa top off and in the back which it normally is I just listen to the motor and nature. I like the tuned application of the speaker enclosures and the fact that they aren't 12" in diameter to get the sound they get. Just, as you say, a matter of choice. Sound is like art, you like or dislike what you want and it varies widely for different people. Dr. Bose in the sound community is considered a genius for the approach he took but not everyone likes his approach.

My backup used new to me head unit is enroute and will be here late Thursday then I'll take a look at the one with the new face but no backlighting on the display and pack it up with a note and ship it to Dr. Don who will fix the backlighting issue and return it to me.

Have a great day...

[LancePearson]

I have a friend who is a serious audiophile...Kliptsch speakers, et al, and has his own sound meter and is a meticulous guy. While I'm quite content with my Bose in the Z, especially since I only use it when I'm under 50 mph and ride around with the Targa top out listening to the Borlas and the LT5 for the most part, here's what he and his audiophile buddies have to say: "If it has no highs and no lows, it must be Bose!" Made me laugh as these are the equivalent of wine snobs as applied to sound. it's true that Bose gets rid of some sound that they consider un necessary. It's also true that my friend worships at the holy grail of: "huge speakers and huge amps of 400 amps or more, minimum." Sort of different for me and to continue the wine analogy, not worth buying me $200 bottles of wine as my pallet is only good enough to manage the difference to about $40 a bottle.

He is very knowledgable and spends enormous amounts at home on speakers and headphones chasing "pure, full and rich sound."

I'm sorta content with what I have and then there's the beast and the borlas which is way better anyway.

Thought you'd enjoy the audiophile view...