hi all,
i managed to blow the phono outputs on my headunit the other week (think
wires touched in the boot when i had the system out and a carpet in the
back).
now got a brand new head unit,no sound at all from the sub (have changed
phono leads etc.),driven by an old kenwood amp.
my 6x9s driven by an alpine amp sound ok up to about 1/3 volume,then the
sound goes really crappy,distorted,volume fades in and out(the front
speakers are powered from the head unit and are fine).
both amps power up fine,and no fuses were blown the other week there when i
suspect the wires touched(phono and live,probably).first thing i knew about
it was when i refitted the stuff and had no sound.
so.........is it possible that i've fried the amps (without blowing the
fuses) ??

In article ,
"RgvKid" wrote:

hi all,
i managed to blow the phono outputs on my headunit the other week (think
wires touched in the boot when i had the system out and a carpet in the
back).
now got a brand new head unit,no sound at all from the sub (have changed
phono leads etc.),driven by an old kenwood amp.
my 6x9s driven by an alpine amp sound ok up to about 1/3 volume,then the
sound goes really crappy,distorted,volume fades in and out(the front
speakers are powered from the head unit and are fine).
both amps power up fine,and no fuses were blown the other week there when i
suspect the wires touched(phono and live,probably).first thing i knew about
it was when i refitted the stuff and had no sound.
so.........is it possible that i've fried the amps (without blowing the
fuses) ??

You could have damaged the amp if significant current flowed through the
RCA connectors. It might be easy to repair. My guess is that part of
the input protection is shorted and you're hearing the thermal fuses
kick in.

"Kevin McMurtrie" wrote in message
...
In article ,
"RgvKid" wrote:

hi all,
i managed to blow the phono outputs on my headunit the other week (think
wires touched in the boot when i had the system out and a carpet in the
back).
now got a brand new head unit,no sound at all from the sub (have changed
phono leads etc.),driven by an old kenwood amp.
my 6x9s driven by an alpine amp sound ok up to about 1/3 volume,then the
sound goes really crappy,distorted,volume fades in and out(the front
speakers are powered from the head unit and are fine).
both amps power up fine,and no fuses were blown the other week there when
i
suspect the wires touched(phono and live,probably).first thing i knew
about
it was when i refitted the stuff and had no sound.
so.........is it possible that i've fried the amps (without blowing the
fuses) ??

You could have damaged the amp if significant current flowed through the
RCA connectors. It might be easy to repair. My guess is that part of
the input protection is shorted and you're hearing the thermal fuses
kick in.

Input protection shorted??? Thermal Fuses?

I have been in countless audio devices and have never seen _input_
protection "short", you can drive all inputs right up to the rails. But
almost all have output protection!

If he can't get enough output how can the thermal protection come in to
play? Unless he has no bias on the outputs, but, if you loose bias chances
are you have torched the output devices and it won't work anyway.

He may have damaged the input buffer op amps, if they are cap coupled they
will not transfer DC offset to the final drive and kick in the DC
protection. This is rare. Some amps have a resistor designed to act as a
fuse right off the center conductor of the RCA, this may have come open. As
for the amp that distorts at moderate volume I would suspect a failed power
supply in the low voltage section or an open driver transistor that won't
allow the amp to go into class B, It's fine operating in class A but when it
passes it's bias point to class B he looses 1/2 waveform.

Chad

In article ,
"Chad Wahls" wrote:

"Kevin McMurtrie" wrote in message
...
In article ,
"RgvKid" wrote:

hi all,
i managed to blow the phono outputs on my headunit the other week (think
wires touched in the boot when i had the system out and a carpet in the
back).
now got a brand new head unit,no sound at all from the sub (have changed
phono leads etc.),driven by an old kenwood amp.
my 6x9s driven by an alpine amp sound ok up to about 1/3 volume,then the
sound goes really crappy,distorted,volume fades in and out(the front
speakers are powered from the head unit and are fine).
both amps power up fine,and no fuses were blown the other week there when
i
suspect the wires touched(phono and live,probably).first thing i knew
about
it was when i refitted the stuff and had no sound.
so.........is it possible that i've fried the amps (without blowing the
fuses) ??

You could have damaged the amp if significant current flowed through the
RCA connectors. It might be easy to repair. My guess is that part of
the input protection is shorted and you're hearing the thermal fuses
kick in.

Input protection shorted??? Thermal Fuses?

I have been in countless audio devices and have never seen _input_
protection "short", you can drive all inputs right up to the rails. But
almost all have output protection!

Car audio often has varistors on all low current connectors to protect
against shorts, overvoltage, and powerful ground loops. They'd cause
the sound to fade in and out if they were brought into action by another
fault.



If he can't get enough output how can the thermal protection come in to
play? Unless he has no bias on the outputs, but, if you loose bias chances
are you have torched the output devices and it won't work anyway.

He may have damaged the input buffer op amps, if they are cap coupled they
will not transfer DC offset to the final drive and kick in the DC
protection. This is rare. Some amps have a resistor designed to act as a
fuse right off the center conductor of the RCA, this may have come open. As
for the amp that distorts at moderate volume I would suspect a failed power
supply in the low voltage section or an open driver transistor that won't
allow the amp to go into class B, It's fine operating in class A but when it
passes it's bias point to class B he looses 1/2 waveform.

Chad

!

Car audio often has varistors on all low current connectors to protect
against shorts, overvoltage, and powerful ground loops. They'd cause
the sound to fade in and out if they were brought into action by another
fault.


many thanks for the input folks
i just thought (perhaps naively) the fuses were there to guard against this
sort of thing.i have yet to double-check all wiring to the amps,though
nothing has changed,far as i know.
this afternoon i will try swapping amp outputs to the speakers to see if the
older pioneer amp (the sub one) is actually outputting anything at
all,though i don't think it is,cos there wasnt a peep coming from the sub.
realistically i am now thinking the easiest thing to do is buy a 4-channel
amp to solve all the problems,cos the pioneer is ancient,and i've had the
alpine a good few years and it's only worth 20 odd quid,even if it was
working.
cheers,
col

"Kevin McMurtrie" wrote in message
...

Car audio often has varistors on all low current connectors to protect
against shorts, overvoltage, and powerful ground loops. They'd cause
the sound to fade in and out if they were brought into action by another
fault.


If it's low current then it's voltage driven, if there's very little current
then what heats up the varistor and causes the varistor's impedance to rise?
The input impedance of most amplifiers is so high thet injecting even a 1M
resistor in series with the signal path will cause little or no loss.

Chad

In article ,
"Chad Wahls" wrote:

"Kevin McMurtrie" wrote in message
...

Car audio often has varistors on all low current connectors to protect
against shorts, overvoltage, and powerful ground loops. They'd cause
the sound to fade in and out if they were brought into action by another
fault.


If it's low current then it's voltage driven, if there's very little current
then what heats up the varistor and causes the varistor's impedance to rise?
The input impedance of most amplifiers is so high thet injecting even a 1M
resistor in series with the signal path will cause little or no loss.

Chad

Nothing heats the varistors if it's working correctly and the inputs are
correct. It doesn't seem to be working correctly, though.

I'm not saying that I know the problem. I just added one thing to the
list to check. It could be a problem with an offset output, broken
overload detection, half-wave output, fried power supply, cooked HU
line-out amp, etc.

"Kevin McMurtrie" wrote in message
...
In article ,
"Chad Wahls" wrote:

"Kevin McMurtrie" wrote in message
...

Car audio often has varistors on all low current connectors to protect
against shorts, overvoltage, and powerful ground loops. They'd cause
the sound to fade in and out if they were brought into action by
another
fault.


If it's low current then it's voltage driven, if there's very little
current
then what heats up the varistor and causes the varistor's impedance to
rise?
The input impedance of most amplifiers is so high thet injecting even a
1M
resistor in series with the signal path will cause little or no loss.

Chad

Nothing heats the varistors if it's working correctly and the inputs are
correct. It doesn't seem to be working correctly, though.

I'm not saying that I know the problem. I just added one thing to the
list to check. It could be a problem with an offset output, broken
overload detection, half-wave output, fried power supply, cooked HU
line-out amp, etc.

Not to mention we could be playing doctor on a throw away amp

I have a smoked Soundstream reference 1000 on the bench now, talk about an
assload of output devices!!! That ain't gonna be cheap to fix!

But, then again, it wasn't cheap to buy

Chad