[sdiy] SSM2164 last time buys

[Tim Ressel]

Excellent work Oscar! This will be a relief to many I'm sure. The only question 
I have is does the current limiting resistor affect normal operation?

--TimR



----- Original Message ----
From: Oscar Salas <osaiber at yahoo.es>
To: Synth DIY <synth-diy at dropmix.xs4all.nl>; Scott Juskiw <maillist at tellun.com>
Sent: Mon, February 28, 2011 4:10:30 PM
Subject: Re: [sdiy] SSM2164 last time buys

Hello, I was thinking about it and I did again the tests.
I thought that it is about current and remembered that I did the test with a 
very little power supply that I have for the breadboard.

So, like in the past test, I put side by side a V1264 and a SSM2164 without 
connect the negative rail for two minutes connected, this time, to a big power 
supply HBB15 1.5A.
Both died.

So it is current, and the solution could be as easy as put a series limiting 
resistor in the positive supply. 


I did tests with another V2164:
Data-sheet says that supply current is 6mA as typical and 8mA as a maximum in 
class AB operation. I wanted worst case for make the test and measured a maximum 
of 10.8mA on positive supply with following settings:
class A operation
for all four VCAs:
signal input= V+ (+15V)
control voltage input= V- (-15V)

OK with those settings I started putting a 1K5 resistor in series with the 
positive supply. With the negative rail connected(normal) I read 8.8mA and 
without connect the negative I read 9mA. The best thing is that the chip doesn't 
die, nor goes hot!

Further I did several measurements reducing the value of the resistor, for 
example with a 510Ω resistor I read 10.6mA (normal) and 25mA without connect the 
negative rail. And the chip doesn't go hot!

The Chip starts going hot (measured by touching) with resistor=56Ω, without 
connect the negative rail you can read 115mA.
And dies with resistor=2Ω you can read more than 500mA and then falls to 0mA.

Ok, take my measurements as a orientation, think for-example that those chips 
had been used for several test. 


As a summary I would say:

A) With a resistor in series with the positive supply the chip is protected 
restricting the current. I would say that a value about 510Ω or 1K would do the 
job.

Question: There is any inconvenient in use a resistor? could it affect the 
performance of the VCAs

B) I didn't test it but another solution would be a resettable fuse but in this 
case stay within 10mA or 50mA per chip. Maybe better one fuse per chip.



Best Regards,

Oscar.
--- On Sun, 2/27/11, Scott Juskiw <maillist at tellun.com> wrote:

> From: Scott Juskiw <maillist at tellun.com>
> Subject: Re: [sdiy] SSM2164 last time buys
> To: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
> Date: Sunday, February 27, 2011, 7:49 PM
> I've had similar experiences with
> CoolAudio v2164 where it overheated a lot (and very quickly)
> when my negative supply was accidentally disconnected. BUt
> in my case, those chips are now worthless. Considering that
> some power supplies have been known to have one rail lock up
> on startup, this is a bad thing for anyone trying to use
> these chips in a module.
> 
> Is there a simple way to test for this "lack of negative
> supply" condition and disconnect the positive rail
> automatically before the chip becomes toast?
> 
> On 2011-02-27, at 9:31 AM, Oscar Salas wrote:
> 
> > Hello,
> > 
> > Regarding the SSM2164 I would like report my
> experience with the coolaudio v2164.
> > 
> > Time ago 3 quad VCAs of my system died. (They are Mike
> Irwin linearized  so 6 chips) I didn’t understand
> why. I read somewhere that the 2164 dies when the negative
> rail faults and forget it. Just replace them. I thought that
> maybe I shorted accidentally the negative rail with that
> result.
> > More recently another quad VCA, this time with new PCB
> layout, also did die. Just replaced the chips and now is
> working.
> > 
> > Well, I wanted to know why. I bought a pair of
> original ssm2164 and I did several tests. For example, I
> placed in a breadboard, side by side, a V2164 and a SSM2164
> without connect the negative rail for more than five
> minutes. Neither of both did die. 
> > The only thing that I can report is that the V2164
> went so much hot than the original SSM2164. I don't have a
> thermometer and temperatures were sensed with the finger :).
> The diference was very clear. The SSM2164 was hot but you
> could stay touching the chip. The V2164 you could not stay
> touching it nor one second, was really burning.
> > 
> > I didn’t found why the V2164 of my system died, nor
> if they were original SSM2164 they had died. 
> > What I found was a difference within them.
> > 
> > Other similar experiences?
> > 
> > Hoping that my English is understandable :) Best
> regards,
> > Oscar.
> 
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