SSM2142 Failures?

[thermionic]

Hi,

A while back I seem to remember someone here (Jakob maybe?) say that the ubiquitous SSM2142 line driver didn't like being connected to discernable DC offsets and was prone to fail if so treated. I've recently had to replace a couple of non-working SSM2142s. I have no idea what prompted them to fail, but one was completely dead and the other was (slightly bizarrely) outputting 1dB below what it should have (can't remember if THD was raised, but I double-checked and the output jumped by a dB when I subbed a new IC).

So...this has made me wonder about whether specifying the 2142 in a new design is a good move? Would a more rugged solution be (albeit less convenient) to lash up a balanced buffer from a couple of, say, OPA2134? The 2142's spec is decent, but I doubt a buffer comprised from the 2134 would measure any worse - in fact, maybe better.

Have you seen many 2142 failures? In some designs where the other ICs aren't socketed, the 2142s have been socketed...an admission they're prone to failure, or just a pragmatic decision, bearing in mind they are the interface with the outside world and may get connected to all kinds of unsavoury equipment?

Thanks in advance.

edit - Oops! Dropping balls today... Meant to post this in the DB... Please move if it's convenient.

 

[analag]

Hahaha...I used to use em. Sorry for laughing but after experimenting with the drivers and receivers, I gave up. I'd much rather stuck an Edcor  1:1 in there.

 

[thermionic]

You stopped due to mystery failures, right?

Personally, I like a nice transformer. However, sometimes the space isn't there. Not to mention that some people seem to demonise transformers for the colouration they add.

edit - is the DRV134 a more reliable solution?

 

[SSLtech]

They tend to curl up their pins if they see DC pushed back at them. -It doesn't even have to be a particularly high current that picks a fight; it's as if they see the voltage and start to self-destruct.

A hideously common failure that I see is on location video gear, where people plug the outputs into a mic preamp ("I'll stick a pad on it, then I've got loads of gain range!!!") -but on so much location gear, phantom or T12 is set by hidden DIP switches, and people forget and just leave it on...

With that in mind, I've found that putting a DC blocking cap in each output leg (with the + plate facing the outside world) ...and a little resistance in each leg to guard against shorts... seems to be all the protection they need to enjoy happy and productive lives.

So, in each leg I habitually add a DC blocking cap, a 50Ω series resistor and a high-value 'bleed' resistor to ground so that the caps don't HOLD charge after being disconnected from a phantom mic pre.

The DRV134 seems to be more robust than the 2142; I suspect that the THAT 'outsmarts' version may be similarly better, but haven't tried any 'destructo-tests' to prove this.

 

[Andy Peters]

So, in each leg I habitually add a DC blocking cap, a 50Ω series resistor and a high-value 'bleed' resistor to ground so that the caps don't HOLD charge after being disconnected from a phantom mic pre.

This seems to be standard -- just size that DC block so phantom power doesn't eat it.

-a

 

[SSLtech]

Yep, and the 'bleed' resistor can also help by pulling it down from 48V somewhat.

 

[CJ]

this was floating around a while back, can't vouch for it, never built it, passive massive,

however, it might stimulate some ideas,

 

[njm]

A company I used to work for used 2142s and we had one customer who kept coming back with blown 2142s on his outputs. I can't remember what kept blowing them up though! Sorry

The thing that annoys me with these chips is they are load dependent.
http://www.thatcorp.com/Line_Driver_Comparison.shtml

 

[CJ]

oops, wrong side,  :-*

 

[justanalogue]

One of those went out in my SPL Goldmike, replaced both channels with That's 1646, slightly improved the quality.

Willem.