LJA4170AA/BA Amplifier Musings
 

http://www.braveknight.com/images/LJA4170BAPCB.jpg

Just some random Harman Kardon amplifier musings.


I finally opened up my TJA4170BA amp from my '97 XK8 with "upgraded" Kommon Hardon stereo system. On my car the amp failed as it will not shut off and always draws more than 2 amps even when its supposed to be idle. So the battery will die quickly with it still hooked up. Obviously that is not normal.

The amplifier uses (4) Toshiba TA8233BH Output IC's. These are dual channel chips good for 30 watts a channel rated at 2 to 4 ohms. So that means the amplifier has a max of 240 watts available between all 8 amplifier circuits. Each IC has its own circuit to self power down when it sees no power at pin 4 of the IC. The Jag schematic shows the same line that signals the power antenna also goes to the amp and that likely is what signals the amp to shutdown also.

The crossovers are "active" and not "passive". All the crossover duties are handled by (10) quad 741 op amps with R/C networks to set the crossover frequency points. The AA/AB amps are likely identical except for some different values here.

There are only 5 line level inputs coming from the head so the 741 op amps crossover section also is used to derive the 8 channels to drive all the speakers.

There are a total of forty 6db/octave crossover poles available and they are usually put in series to get 12/18/24 etc slopes. Will take a little tracing to see how they divide these up.

Each woofer does have its own 30 watt channel so they are not in series or parallel.

There is also a regulator and s noise filter on the incoming DC onboard.

As my amp draws so much at idle thats indicative of a shorted output IC as these will not draw that much at idle even if they don't shutdown.

These chips are only $9.95 each with free shipping and anyone with decent soldering skills can replace them. I ordered a couple and will report back after I find the culprit and replace it.


Dave

Seems I forgot to update this thread. Replacing the Toshiba TA8233H fixed it and its stayed working since then. These chips can be had as cheap as $5.99 with free shipping on ebay. Cheap fix if you can solder and have one of these amps with a continuous power draw or a dead channel or 2. In the previous post I made a typo and said the chip was a Toshiba TA8233BH but the B was for brain misfire. The correct chip number is Toshiba TA8233H.


Dave

Glad it worked out for you.

Nice circuit analysis and explanation.

So are you dissecting some of the other weak sisters any time soon?

The SLM is known to have driver chips die :)

An older thread, but definitely interesting.

I've often wondered if there are any opportunities to "hot rod" this amplifier a bit by upgrading capacitors, etc or even the ICs (e.g. is there a better quality IC)?

If so, obviously one couldn't push the envelope too far as the stock speakers will be the next limit, unless they were upgraded too.

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The 741 IC's are not known to be the best sounding but I doubt you'd really hear any improvement changing them assuming the rest of the original stereo is left intact. I'd rather just change everything - speakers, head unit and amp. If anything just to have something besides radio and CD as sources. The trunk mounted player is virtually useless from a convenience standpoint and in my small town there are no decent radio stations worth turning it on for. I'd much prefer being able to use a flash disk I can load at home and an android based head unit that can do internet radio etc. That and the original speakers have foam cones that rot and both my rear speakers do nothing but rattle so I need new speakers anyways. If I ever get around to changing it all out I'll try and keep it so someone else can always revert back to the old equipment if they really want to but once its been replaced I won't miss it at all. As it is now I rarely use it because of the lack of anything decent to hear on it.


Dave

I actually don't mind the rear mounted CD changer as 6 CDs last me a long time, plus if you change it to a later MP3 capable player you can play 100s of songs. And I think the stock system when in good shape sounds very good. I wish it just had a bit more power, but most of the time is it ear splitting loud at full volume.

I've also got bluetooth going through my stock head unit right now via an FM transmitter, which isn't the highest fidelity, but actually doesn't sound too bad. So I stream Pandora, etc.

I picked an ancient Alpine Ai-Net "injector" the other day that is designed to go between the head unit and CD changer, triggered by 5-12V to switch between the CD changer and a set of aux RCA inputs so you can insert another source while tricking the controller/head that the CD player is still there. I don't know if it will work, but hope to test it soon.

If the stock HK amplifier can't easily be upgraded, I probably won't bother, but one could also slip in a nice aftermarket amplifier with a bit better electronics without pushing the power too much and keep the stock speakers. But that would take some work to build a converter to plug into the stock harness.

Thanks for dissecting the HK amp. That was very informative!

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Al, As a dedicated audio "Tweaker" I've wondered the same thing too. It sounds as though Dave was not too hot on the idea of upgrading the ics but if there are better ones out there I'd be surprised if you couldn't hear a difference. I just did this with my subwoofer crossover at home, but that was designed in the 1970s. While this wouldn't be a 30 year leap forward in technology for our xk8 amps, I've seen countless examples of audio manufacturers using cost effective parts. Replacing these with super high quality parts (teflon capacitors, vishay nude resistors, high qualitycopper terminals) makes a huge improvement.

These amps are non standard inn so many ways, I guess we'd have to open up the amp to look for these cost effective weak links to evaluate what we could go after. In fact I've been wondering where the power supply main capacitors are and if there is space to double the value-almost a guaranted for improvement on any amp.

From the photo Dave was kind enough to post, it looks like the op amps are the best shot at trying to improve things. Someone can correct me here if I remember wrong, but we have to be sure it is not an uncompensated device or it can ossilate. Signal path capacitors and resistors would be another improvement option. The connectors are so customized they are off the table.

Have you, Al, done any research on best/cutting edge technology op amp replacements for this one?

The 741's are 30 y/o tech. They can be replaced with NE5534AN's but you have to put a 22pf cap on pins 5 and 8 or they will oscillate.
You can also use LME49710 or OPA627 which are better yet but they ain't cheap.
Replacing the cheap electrolytics with upper line Panasonic electrolytics will help some. Not enough room to change them to polypropylene or teflon and teflons don't come easy in higher values. Or cheap.
I'm a rabid audiophool when it comes to home audio...


Dave

Great feedback guys! I am not as advanced an electronics tinkerer as you likely are, but I regularly rebuild old tube components & consoles and rehab decades old solid state gear like a 1976 Marantz 2215 for my son. But I'm an amateur, just replacing like-for-like per the service manual or minor upgrades as noted above such as capacitors, resistors, etc. So any real re-engineering I leave to the experts to give me step-by-step instructions so I can learn something new and don't release the "magic blue smoke" :)

I'd be very interested in what options are available, and how, to get some modest output and sound quality improvements from the OEM HK amp. For me it's a lot more fun, challenging and interesting to keep things looking stock (cars or other audio gear) but hide improvements inside.

As a note, my application is for a 1997 XJR(6) so my HK amplifier model# is slightly different, but I'm sure effectively the same.

The part number for my generation is: LNA4170AB or LNA4170BA

I'll have to see if I can get a salvage one and open it for comparison if interested.

.

Dave, great info thanks. When you advise to use the cap to prevent oscillation you mean pin to ground, not pin to pin right? .

I have a pile of OPA2604 op amps laying around. As I understand they are based on the 741, though they are dual opamps. Would they work too?

I appreciate your help. The way I figure it, every little improvement helps with the audio, sometimes you change something and the improvement is an unexpected quantum leap forward.

John

And yes between pins 5,8 on a 8 pin NE5534. They are compensation pins. Most 741 circuits used for crossover/eq use are set for unity gain and NE5534 needs some gain to be stable so the cap between 5&8 compensates. If you use one of the other choices those caps shouldn't be used.

I just realized that the amp uses the 14pin version of the 741 and all the upgrade ones I mentioned are 8 pin for swapping with the 8 pin 741's. So an adapter would have to be made to use those. I will see if there are any drop in's that would be worth the upgrade. Thats what happens when I don't have my coffee first.


Dave

Well, the OPA627 are about $30 a piece, which while not cheap wouldn't break the bank if they offered a significant improvement (note, significant :) ) over stock and the LME49710

The LME49710 is $3-7 each, which is not a big deal at all from my perspective.

And as long as they'll fit, quality Panasonic caps cost more to ship than purchase :)


Very curious to hear which of the improved OP Amps you think would be an easy drop-in and give good bang-for-buck.

Here's some interesting threads on the subject of these particular chips (of course many more if one Googles, almost like "oil threads" :p )

LME49710 vs OPA627s ?

NE5534 replacement - National LME 49710?



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Hi Dave, hope you're still following this thread? :D

Steve ( thejagwrangler ) just pointed me to your post as I seem suffering from a similar problem. My 2003 XKR Convertible is equipped with the navigation and premium sound system.
I was able to identify that the remote amplifier in the boot does not shut off when its supposed to, draining about 1.6A all the time. The cooling fan inside also keeps running.

When I pull the Fuse of the Radio Head Unit, it turns off - so I guess the probability is high that there's a remote control line, which keeps it turned on.

Unfortunately the cars schematics are not detailed enough to identify the remote control line. Do you know by accident?

I would like to try fixing it before exchanging the amplifier module.

BR
Ralf


PS: I did something similar some time ago for my home stereo... this is a 7x 100W Channel Class-D Power amplifier

https://cimg3.ibsrv.net/gimg/www.jag...3bca3e03b8.jpg
B&O IcePower 7x100W Class-D