Amplifier and Speakers

[Kevv]

Hello

I've recently lost most of the sound in my car, happened quite suddenly aswell while driving.
I only have working speakers in the front dashboard, not all but a few of them, and when i put my ear on the speakers in the car i can just hear static noise.
I took the doors interior off and took disconnected the big speaker and the small one cause they werent working, the big one worked slightly, it was more static but i could make out the faint music.
I used Ohm on between the connections and both of them were on 3.7-3.8 Ohm, im guessing thats normal?
If the impedance is O.L its broken right?

Also disconnected the AMP and opened it to see if any capacitors were popped or if the circuit board had been fried, but nothing, also 30A fuse wasnt blown either.
i used 20V DC between Brown/red and Brown/blue which were the wiring on the big speaker in the back door right side, and no voltage, so can it be the amp? and how to i easily check?
i checked youtube and they all have equipment i dont have like tone generator or whatever. and i dont have an external power supply to test, only the car.

Im out of ideas what the reason can be, can it really be the wiring or the connections in the Symphony stereo unit?

I have non-BO speakers and unit is a regular Symphony III i think, no MMI or anything.

Anyone experienced a similar problem, or have any idea what other process of elimination i can use.

Sincerely Kevin.

[MongoMcG]

Test your battery. The cause could be Audi's Energy Management System shutting down the MOST-bus because the battery voltage is low. The MOST-bus is "Media Oriented System Transport" which is a high speed optical data transfer bus via fiber cable.

Your voice coil impedance of 3.7 ohms is fine if you had no other load at the speaker (you should not during measurement). A bare speaker impedance measurement with a multimeter usually measures around 15% lower than the speaker's rated impedance. That is about 3.4 ohms for the Audi's 4 ohm speakers. Actual mileage may vary.

If the integrated chip(s), aka IC(s), that do the actual amplification have failed, it's possible there will be no visual evidence inside the amp. You can test voltages at the IC's as well as input and output to narrow it down the the IC(s). If you (or an electrical engineer friend) are not familiar with these procedures, then it may be time to hit up eBay or Wolf Auto Parts for a used unit.
https://wolfautoparts.com/catalogsea...57&q=amplifier

Re: the battery - here is a note from the Factory Service Manual:
Most control modules, which are needed for the audio system, are connected to the energy management system. This means the MOST-bus switches off if there is a poor energy balance in the vehicle. Depending on the state of the battery, there are different switch-off levels which have an effect on the different control modules. Audio output is not possible after a switch-off level has been activated.

Good luck! There are cats on this forum much smarter than me about the car's electrics. Hope they have some ideas to share.

[Kevv]

Battery is quite new, and it read 12.43 Volts, so everything is good, should be about 2.1v per cell and its 6 cells so 2.1v x 6 = 12.6, im guessing this isnt an issue then.
All im left with is either input from the media unit to the amp or the output of the amp, and since i read 0v dc on the output then im guessing its the Amp, but my gut feeling isnt buying it.

[MongoMcG]

Yeah, grab that model number off you current amp and check the used market. I see them selling for as low at 50 bucks for non B&O amps at Wolf and eBay. At that price I'd give it only about an hour of troubleshooting before pulling the trigger on a replacement. The downside is 50 or 60 bucks plus shopping time versus the the search for the unknown, and once found it may not be repairable for less than $50 or $60. It's still early, so the forum could chime in with other ideas.

[Smac770]

Sounds like you have Symphony radio -> J525 amp -> standard sound system (tweeter+woofer in the four corners, plus dash center channel and rear subwoofer on rear deck (sedan) or in spare tire well (wagon)). If you just had the 8-speaker basic sound system, you wouldn't have an outboard amp in the left rear.

If any of the speakers are working at all, then the issue is either with the not working speakers or the J525 amp.

The J525 to the standard sound system has 6 output channels:

Audi standard sound system.jpg

If you wanted to confirm, you'd determine a speaker set that was working correctly, swap wires on the 32-pin plug to move the working speaker set to the other 5 channels and see which channels worked and which didn't. To check if the speaker set had an issue, put a non-working speaker set on a known working channel and see if it now works.

J525 CAN standard pinout.png

[Kevv]

I see, im guessing its the amp since the cuttoff was like instant and the non working speakers have 4ohms still .. i will test anyway, thanks alot folks!

[cybernet99]

check to see that water has not leaked down and onto the amp. That is one of the common issues with the placement of the amp. I had it happen to me while on a massive road trip. Took the amp out of the car, opened it up and found some "white" corrosion on the back of the pcb board in the amp. bought a toothbrush and some tooshpaste, scrubbed away at it for a while, wiped it all off, put it back in plugged in and was back to working 100%. :)

[Kevv]

The amp is dry but i got time to meassure voltage today and there is 0 volts pre amp out from the radio unit, and i am wondering if thats normal, i mean im meassuring 0 volts post amp aswell on the same circuits.. so can it be the radio unit itself?

I dont know what voltage pre amp should be, 4-6 volts?

[MongoMcG]

I am a sound mixer and video editor who has wired few studios with the actual engineers. Pre amp output voltage in professional systems range from 2 to 10v, peak to peak, depending on application. I would guess (and it is a guess) output voltage in a car preamp is not much more than .5 to 1v, peak to peak - maybe reaching up to 2v for high end car audio. The voltage here is kinda' like the size of a pipe for fluids - how much audio (or pressure) gets passed through to then be amplified, if that makes sense; and my guess is factory car audio does not use a big pipe.

You are measuring AC voltage with some sort of single frequency sine wave signal passing through the audio system, correct? Also, your Digital Multi Meter should indicate "TrueRMS" somewhere on the body or in the documentation. If it doesn't, you may need to use only a 60Hz test signal because that seems to be a frequency that most DMM's can get a voltage read on (in EU it may be 50Hz). If you do not have a test signal generator (true sine wave) then you might get away with playing something on your phone (square wave) to determine if there is any kind of voltage at all. I wouldn't bet on it, but it's been a couple of decades since I've been that deep in the weeds. I'm sure there are how-to videos and write-ups on the inter webs.

If your lucky you'll find a buddy with a known good audio system from which to swap one part at a time to test components. You'd find the offending piece before the first intermission of the hockey game on the garage television.

[Smac770]

One, make sure you're doing AC voltage, not DC voltage. DC voltage on analog audio signal lines (amp input, amp output) should be near 0. Mongo points out some of the caveats with measuring AC with consumer "tools". They are made cheaper by making them suitable just for the most common usage, home wiring (50Hz/60Hz AC). Analog audio is not just 50Hz or 60Hz.

Looking for low voltage signals out of the radio, so you have a Concert or Symphony unit in the dash with a J525 amp unit in the left rear? It's the same output pins on the radio unit to the speakers or to the amp, just a coding bit flips the output between high voltage (to drive speakers) or low voltage (to pass to the amp). But never found anyone having posted what the actual voltage range is. 4V wouldn't surprise me; but you'd only measure that at peak output.

[Kevv]

I meassured the voltage on the output on the speakers that wasnt working and i got 5.1 volts same as the output i had, without turning the volume button ofc. and then i measure while i turned the volume and i only got radio unit voltage, like 6v on max.
So i ordered a new used amplifier and it only works on the front left door now.

Its pretty straight forward right? i had a bad amp and ordrered an even worse amp ?

[MongoMcG]

It sounds that way (pun intended). Hopefully a decent vendor that will swap the bad part.

[Smac770]

You can't just swap the radio or amp units in these cars, component protection will kick in. You have to have the component protection reset. Though I'd do a scan first and see if any DTCs are coming up besides CP such that there might be an issue with the unit.

[MongoMcG]

Thank you, Smac, for covering when I post something dumb.

[Kevv]

How do i reset the componenet protection? Dont you need a read/write unit for this?
Not something the regular person has access to.

Also what type of Amplifier is this? how many channels, and can i replace with another new non-audi amp.

[Gunnark100]

How do i reset the componenet protection? Dont you need a read/write unit for this?
Not something the regular person has access to.

For "component protection off" you need audi dealer or person with similar tools(not vcds job).

[Smac770]

If you have Symphony and not MMI, then you don't have the MOST optical ring transport system. You instead have four copper preouts (+/- pairs) as noted in the pinout above, signal from radio. So you could certainly run that to an aftermarket eq/crossover/amp solution to replace your factory J525. If you wanted to bother with all that.

[Kevv]

I see, im guessing this AMP isnt component protected, dunno what makes me say that but it worked on 1 channel, the one i bought that is.

I have Concert, i guess thats symphony III? but yea no MMI, and i feel like i almost have to since i get sent used AMPS that are shit, since they're not tested, or seems like.

[Smac770]

Concert is concert (single-disc), symphony is symphony (six-disc), not the same thing, but both are the same infotainment system architecture.
The J525 is certainly component protected, but the nature of the component protection exhibit varies. Might be one side of the car is muted, might be the audio is interrupted every few seconds, might be the audio works except for entertainment sources, etc.