Help--Amplifier "pops" on power up??

jjkozlow · 3rd April 2005, 02:29 PM

I received a vintage 1981 RAM 510 solid state amplifier as a gift from my dad and am getting a loud "pop" when powering up (and a very faint pop on power down). My dad's had the amp for 20 years or so and said it's always done this from day 1 and that his speakers never were damaged by it, it was just an annoyance. I normally turn the preamp on 1st then the amp and tried to vice versa this and then I get 2 pops, once for the amp power up and once for the preamp power up. I tried waiting in longer intervals between the sequences and it makes no difference.
The woofers are moving a good inch or so during the pop, I guess I also want to know if I should just leave it all on to avoid potential damage. On the other hand, due to age, I don't want a fire or something if the amp dies someday.

I know start up/shut down amp pops are somewhat common, has anyone come up with a generic fix?

anatech · 3rd April 2005, 03:01 PM

Hi jjkozlow,
Have a look in the thread "output protection" just below. You are getting a DC offset as the voltage amp section in your amp settles down from power up.
-Chris

ChocoHolic · 3rd April 2005, 04:12 PM

Might be similar as here:
NAD 3130 amp popping speakers

jjkozlow · 3rd April 2005, 07:46 PM

Someone on AA suggested this fix:

"It's due to inadequate design of the power supply. You can probably cure it with a 1000v .01 ceramic/mica capacitor across the power switch pins, but I would not bet on it. "

Is that easily done, possible fix? I am about as amature as they come, but I can solder if given proper instructions.

anatech · 3rd April 2005, 08:09 PM

Nope,
The fault is the voltage amp stage being in a non-zero state as the amp powers up. The design is not natually happy with low DC offset so you need to disconnect the speakers until the amps settles down.
-Chris

EchoWars · 4th April 2005, 04:01 AM

Quote:

Someone on AA suggested this fix:

Figures.

jjkozlow · 4th April 2005, 02:09 PM

Thanks guys. 3 more questions then....

1) Could I just leave the amp on all the time? Any potential risks here?

2) Do I then just connect the speakers after the amp is stabilized? Could I use like a speaker selecter box instead and have it selected to "nothing" until the amp stabilizes and then swich it on?

and finally.....

Seeing how my dad's used it like this for 20 years and it never hurt anything, how likely is it that it could (over time) deterierate my speakers or hurt them? Is DC offset deadly to voice coils? The speakers are fused protected as well and the pop isn't tripping them.

Joel

Leslie Horn · 4th April 2005, 02:09 PM

Hmmm, output delay switching should be employed as a safety feature, not as a workaround to poor design!

Specifically, I'll bet dollars against dog biscuits that the voltage amplifier stages have poor CMRR
(common mode rejection ratio), or the input stage lacks good current mirroring, or both.

In any event, as the supply voltage ramps up, a transitional dc imbalance occurs in the earlier stages,
as an offset current. This gets amplified, and is passed on to the speakers, ultimately, as a pulse
or series of pulses. Not good! If the power supply voltage comes up fast enough,
this pulse or pulses will even propagate right through any coupling capacitors or infrasonic filters.

anatech · 5th April 2005, 12:10 AM

Hi jjkozlow,
Man I hate it "leaving the amp on 24/7" is suggested. Aside from wasting a great deal of power in some cases, it's not intelligent. You know there is no protection circuit in this admiditly old amplifier. Why tempt ... no, beg, fate?
Just because something is done incorrectly and has been for a long time does not mean it's okay to continue to do so. In over 25 yrs in service, I've seen more burned speakers and amps (insc claims) than I care to remember.
You must know your insurance will not cover damages caused by a none UL rated product. So this could cost you your house +. Your gamble.
You can use a speaker selector box just fine, but why not make it automatic? That way your wife and kids can use the stereo too.

Sorry about the soapbox but I've seen bad things happen too often.

-Chris

anatech · 5th April 2005, 12:13 AM

Hi Leslie,
Some products just need to settle down. I wouldn't call it poor design but a different transient state. On power up, nothing is defined. Especially when things start aging.
Besides, a preamp upstream could cause the damage even if the amp is perfect. Or a CD with defective muting transistors, on & on.

-Chris

3rd April 2005, 02:29 PM	#1
jjkozlow diyAudio Member Join Date: Mar 2004 Location: Michigan	Help--Amplifier "pops" on power up?? I received a vintage 1981 RAM 510 solid state amplifier as a gift from my dad and am getting a loud "pop" when powering up (and a very faint pop on power down). My dad's had the amp for 20 years or so and said it's always done this from day 1 and that his speakers never were damaged by it, it was just an annoyance. I normally turn the preamp on 1st then the amp and tried to vice versa this and then I get 2 pops, once for the amp power up and once for the preamp power up. I tried waiting in longer intervals between the sequences and it makes no difference. The woofers are moving a good inch or so during the pop, I guess I also want to know if I should just leave it all on to avoid potential damage. On the other hand, due to age, I don't want a fire or something if the amp dies someday. I know start up/shut down amp pops are somewhat common, has anyone come up with a generic fix?

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3rd April 2005, 03:01 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi jjkozlow, Have a look in the thread "output protection" just below. You are getting a DC offset as the voltage amp section in your amp settles down from power up. -Chris

3rd April 2005, 04:12 PM	#3
ChocoHolic diyAudio Member Join Date: Dec 2003 Location: Munich	Might be similar as here: NAD 3130 amp popping speakers

3rd April 2005, 07:46 PM	#4
jjkozlow diyAudio Member Join Date: Mar 2004 Location: Michigan	Someone on AA suggested this fix: "It's due to inadequate design of the power supply. You can probably cure it with a 1000v .01 ceramic/mica capacitor across the power switch pins, but I would not bet on it. " Is that easily done, possible fix? I am about as amature as they come, but I can solder if given proper instructions.

3rd April 2005, 08:09 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Nope, The fault is the voltage amp stage being in a non-zero state as the amp powers up. The design is not natually happy with low DC offset so you need to disconnect the speakers until the amps settles down. -Chris

4th April 2005, 02:09 PM	#7
jjkozlow diyAudio Member Join Date: Mar 2004 Location: Michigan	Thanks guys. 3 more questions then.... 1) Could I just leave the amp on all the time? Any potential risks here? 2) Do I then just connect the speakers after the amp is stabilized? Could I use like a speaker selecter box instead and have it selected to "nothing" until the amp stabilizes and then swich it on? and finally..... Seeing how my dad's used it like this for 20 years and it never hurt anything, how likely is it that it could (over time) deterierate my speakers or hurt them? Is DC offset deadly to voice coils? The speakers are fused protected as well and the pop isn't tripping them. Joel

4th April 2005, 02:09 PM	#8
Leslie Horn diyAudio Member Join Date: Feb 2005 Location: -124.22760W, 40.64431N	Hmmm, output delay switching should be employed as a safety feature, not as a workaround to poor design! Specifically, I'll bet dollars against dog biscuits that the voltage amplifier stages have poor CMRR (common mode rejection ratio), or the input stage lacks good current mirroring, or both. In any event, as the supply voltage ramps up, a transitional dc imbalance occurs in the earlier stages, as an offset current. This gets amplified, and is passed on to the speakers, ultimately, as a pulse or series of pulses. Not good! If the power supply voltage comes up fast enough, this pulse or pulses will even propagate right through any coupling capacitors or infrasonic filters.

5th April 2005, 12:10 AM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi jjkozlow, Man I hate it "leaving the amp on 24/7" is suggested. Aside from wasting a great deal of power in some cases, it's not intelligent. You know there is no protection circuit in this admiditly old amplifier. Why tempt ... no, beg, fate? Just because something is done incorrectly and has been for a long time does not mean it's okay to continue to do so. In over 25 yrs in service, I've seen more burned speakers and amps (insc claims) than I care to remember. You must know your insurance will not cover damages caused by a none UL rated product. So this could cost you your house +. Your gamble. You can use a speaker selector box just fine, but why not make it automatic? That way your wife and kids can use the stereo too. Sorry about the soapbox but I've seen bad things happen too often. -Chris

5th April 2005, 12:13 AM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Leslie, Some products just need to settle down. I wouldn't call it poor design but a different transient state. On power up, nothing is defined. Especially when things start aging. Besides, a preamp upstream could cause the damage even if the amp is perfect. Or a CD with defective muting transistors, on & on. -Chris

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