diagnosis? sound distorted no bass

1997 BMW 328ic - Replaced the head unit with Kenwood unit & replaced OEM amplifier with new used OEM unit, also replaced all speakers - all this done around 5 years ago. This winter radio started sounding bad, bass notes just gone, and midrange sounds strange. Pulled headunit and hooked up to outboard speakers it sounds just fine. Ran it for 1/2 hour at some 85-90% and internal amplifier kept up, no noticeable distortion. Got to most of the speakers and each one I tested showed 4 ohms, so I think voice coils / speakers are OK. So where is the problem? I'm now thinking that it's the amplifier. However, bought another used amp on FleaBay, music sound almost the same - only slight improvement. Would you suspect "New" amp is also defective? What other possibilities are there that I can check? /Suppose you were an Idiot, and suppose you were a Congressman.... But I repeat myself -- Mark Twain

If there were NO changes to the wiring and equipment and everything WAS fine then, If the radio plays fine on all outputs by hooking a speaker directly to it and if each speaker meters fine then it's the LIKELY amp HOWEVER you said you metered most speakers not all. Meter them ALL. Also less likely but it could be wiring between the deck and amp or between the amp and speakers.Gary Sather

Amp power supply?

Did I read right... other speakers sound fine. but not the vehicle speakers? So try the vehicle speakers on another amp, else start with the speakers being at fault.

Sorry, I read that wrong, thanks Peter. Sounds like no mid-range on the speakers, try wiring directly to each of the speaker outputs at the amp from the head unit, that will confirm whether it's the speakers or the amp. Head unit to external speakers doesn't tell you anything except that the head unit and your external speakers are OK.

BUSTED! But, I figured that I needed to test each speaker (& the wiring to the speakers). I just hate to remove the inner door panels to get at the door speakers - lots of effort, and a dozen broken plastic clips/rivets. OK, so now I need to fabricate a pair of needle-thin test probes to (reliably) get into correct pairs in 30+ pin female connector that feeds the speakers. Fun Fun Fun Maybe I should literally use needles - can I solder them to copper wire? Will give it a try. Suppose you were an Idiot, and suppose you were a Congressman.... But I repeat myself -- Mark Twain

(Yes - I now know you can solder a steel sewing needle to copper wire) I've now checked each one of the 10 speakers, by bypassing the amplifier and feeding them signal from an outside source. Each speaker sounded fine, and, showed correct # Ohms. Thus speakers *and* wiring to speakers have been verified OK. This amp takes speaker-level input; Have now checked wiring from head-unit to Amplifier by hooking up an outboard speaker to each channel at the amplifier input. Each channel sounded fine. So wiring checks out. This leaves the amplifier as the problem, yes? Should I start by looking for bad caps?Suppose you were an Idiot, and suppose you were a Congressman.... But I repeat myself -- Mark Twain

Assuming it's a highish power Kenwood, why not dispense with the amp?

If it was manufactured anytime since 1990, it will be a high powered unit.

The Kenwood is rated around 20w/channel RMS - and it's probably pretty clean, though I haven't seen any specs on THD. It never occurred to me to run w/o the amp. Two negatives are (A) OEM amp is around 15 watts RMS @ speaker + had internal crossovers, w/o the amp, would have to install my own crossovers. (B) Hate to cut into the harnesses... Humm... just realized I could pull the PCB out of the amp out, then do all the rewiring inside the shell. Never have to cut any wire harnesses. Suppose you were an Idiot, and suppose you were a Congressman.... But I repeat myself -- Mark Twain