Anyone familiar with the LM12CLK - any good?

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I have a car amp that uses an LM12CLK as a driver for each channel, so there are two LM12CLK's, each one driving two MJ15003 and two MJ15004 outputs.

One of the LM12CLK's appears to be dead/dying. The amp has always worked very well, but is now quite old. I was planning to repair it until I saw the price of LM12CLK's from not-quite reputable sources.

My question is, is an amplifier (150 watt x 2 @ 4 ohm car amp) that is using the LM12CLK worth repairing? Is that chip any good SQ wise? or should I be putting my money towards a new amp.

The amp in question is a MMatts SQ2150 if anyone is familiar with them. I have always been quite happy with the sound and power, but I am sure there are better amps available - I just don't know at what price.

Thanks!
 
I would check the outputs before replacing the driver.
Make sur that they are not shorted, open or leaky.
When you say dying then I assume that there is still sound coming out of the channel.

Just by the parts you describe it sounds like a simple current boosted design similar to the ones in these threads,

http://www.diyaudio.com/forums/chip...istors-amp-tda7293-come-also.html#post2904001

http://www.diyaudio.com/forums/chip...tda7293-2sc2500-2sa1943-push.html#post3914862

The LM12CLK was always a little on the expensive side but it was an impressive device for its day.
Then the LM3886 came about.

I have never heard one that I am aware of but the specs of your amp looks pretty good.

The initial cost of the chip is the only reason I never tried it out as I have always wanted too.

I don't know what the driver would cost if you could find one.
But if it is less then the cost of a new amp then I don't see any reason not to repair it.

From what I recall the LM12CKL was a pretty durable chip by itself so I don't suspect that is what is wrong, although I can't make that judgement without seeing the device first hand.

When I used to fix TV's people would spend the money to get their old set repaired because it just plain had a Great picture, and, in most cases had a better picture than what the newest ones had in the day (80's and 90'S).


FWIW

jer :)
 
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Yep. I plan to swap a known good lm12clk from a different amp to see if the issue persists. It could be the outputs, they are all working, but measuring the voltage across the emitter resistors, they do not seem to be sharing the load as equally as I am used to.
 
From the looks of the scope shots it could be oscillating because one of Outputs might be leaky causing the opamp to have a hard time too stabilize.

I suspect if the opamp was bad it wouldn't be doing anything at all.

If there is excess voltage on the emitter resistor(s) then that means that there is a lot of current flowing through them and a shorted transistor would cause that.

jer :)
 
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The factory outputs are MJ15003/4. I have a new, unopened pile of same batch MJ21193/4s here. Looking at the datasheets, my first impression is that these could probably work. I see they could be potentially lower gain, output capacitance is higer, and they may be faster (oscillation?)...

Based on general knowledge - are the MJ21193/4 are suitable replacement for MJ15003/4 in such a simple amp?

I have a used set of working TOS 2sd424/2sb554, and a working used set of Motorola MJ15022/23's. Both were pulled from working adcom equipment (and replaced with MJ21193/4 sets), but could be near end of life, or working but damaged (in each case the other channel was damaged so I replaced all. These appear to be a closer match to the MJ15003/4, but if the MJ21193/4 are suitable, I would rather test with (and use?) known new parts.

Thoughts?
 
If they worked in the Adcom without modification I don't see why they wouldn't.

If you already have then, then it wouldn't hurt to give them a try.
The current boosted opamp configuration is a pretty versatile circuit.
It is one of my favorite circuits to mess with.

Even if the output devices have a little bit of a lower gain (hfe) I am sure the LM12CKL will have no problem supplying the current required to drive them, as it is just a fraction of what it is capable of on it's own.

According to the spec's it looks like the MJ2119x's are more linear is all.

jer :)
 
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The amp still sounds great with the new outputs, but the initial problem remains when the input voltage (and rail voltage) rises within what was an acceptable level.


I can rule out the outputs now, which most likely puts the blame back on the LM12CLK. I guess I will be pulling one out of another amp to test.
 
Recently stumbled across these ICs

Hi,

Old thread...

Well I happened across a handful of these things and having had a little experiment with them I'm planning on using a few as regulators, and also toying with various ideas for amplifiers.

1) a follower/buffer driven by op amp or discrete stage. Local FB only.

2) a composite amp consisting of op amp gain stage, and LM12CLK as a follower. Global FB returned to the opamp, local FB in the output buffer....not sure if this will be in my scope of intelligence!

3) use the LM12CLK as power op amp eith no preceding gain stage.

Which one would you build, and why?
 
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