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AcuraTLSQ 3rd August 2014 02:52 AM

Alpine 3545 off/on/fizzle out

Due to lack of time and my novice repair skills I have had two 3545's re-furbed to hopefully reliable working order. Not modded just re-capped, repaired to as close to OEM spec as possible. I also have a third going thru the process now. One thing I have noticed from all three is the odd way these amps turn off. Remove remote power with music playing and the music stops, starts again, and then fizzles out. On all three. 3 different test benches. ( 2 re-furbed, 1 as it came off the Alpine assembly line) Obviously I could time the system on/off so that there is no input to the amps when they turn off, both times, but it just seems odd.

Are the amps mute circuits aging and not staying engaged long enough? Perhaps a component is not dissapating correctly? Any ideas where to even start?

I was taught early on that an amp should be silient when turning on and off if you want your system silent. i.e. turn the amp on last and off first in the timing sequence.

Thank you for any input


Perry Babin 3rd August 2014 12:37 PM

Is this a problem in the vehicle where there is no output from the head unit when the head unit is switched off?

The emitter voltage on Q618 should go to near 10v when the amp is muted. In normal operation, the emitter would be near 0v.

AcuraTLSQ 3rd August 2014 03:29 PM

These have not made it into a vehicle yet but the off/on/fizzle out has been confirmed on three different test benches just to eliminate a bench issue and confirm it is an amp issue, in all three. Two have been re-furbed, one is still 100% OEM. Perhaps this is why Clark is the only person I am aware of to use these in a competition vehicle. He figure out how to solve this issue?

I use a Phoenix Gold DDi10 to sequence the entire systems on/off timing. The amount of time between components is adjustable. Normally the PG DDi10 is configured so all components except the amps turn on first with an up to 13 second delay to let everything stabilize and then the amps turn on. On turn off it is exactly the opposite. The PG DDi10 turns the amps off immediately then turns everything else off with up to a 13 second delay. Both on/off delays time is adjustable. It might be possible to finely adjust the timing so the head unit turns off while the amp is silent and before it turns back on and fizzles out so nothing is heard IF all amps turn back on and fizzle out at nearly the same time. I am positive if I reverse the timing sequence and turn the amps on first and off last you will hear the other equipment turning on/off.

The PG DDi10 has constant power/ground but is turned on/off itself by either a switch or simply the head unit.

Nit picky I know but I am picturing a tweeter getting fried by a turn on/off 'pop' generated by a hot system that has been playing for several hours. I drive this car frequently on 2-4 hour road trips. The old 3545's might need a different, less used home but I'm going to give it a shot.

I will check the emitter voltage.

Thank you as always Sir!

Perry Babin 3rd August 2014 06:06 PM

The problem seems to be that the amp is being used in a way that the designers didn't anticipate. If used with a standard head unit being controlled as it was designed, the amp would likely power down completely silent.

AcuraTLSQ 5th August 2014 03:10 AM

Possibly? Surely a designer would account for the amp turning off with the possibility of it still having input?

From the tech working on the amp:

Q618 actually has -5 volts on it when the amp is playing.During mute it jumps to 12 volts and then slowly drops as the caps discharge.The problem I see is that Q618 has resistors built into it which is causing a bleed back to the base where R671 is.This in turn un mutes it briefly.
If I change the value of C612 and C610 It seems to fix the problem.I just have to tweak the values so it doesnt stay on too long.

Perry Babin 5th August 2014 03:42 AM

Possibly? Surely a designer would account for the amp turning off with the possibility of it still having input?

Name a single head unit that produced any output more than a fraction of a second after the head unit is switched off.

R806 seems like it could be causing problems.

Negative 5v is OK. Some muting circuits go to negative 15v when the mute is defeated. What's important is that the voltage is not enough to drive the muting transistor into conduction.

AcuraTLSQ 5th August 2014 04:02 AM

Never timed one or thought about it to be honest. Good point BUT anything switching 'off' with the amp still on has the potential for noise. I just use amps that are silient and sequence the system on/off accordingly. If the amp is off the rest is a mute point. Pun intended. :)

I wil pass the info on to the tech.

Perry Babin 5th August 2014 05:41 AM

When you switch off a (good quality) head unit, transistors immediately clamp the signal on the RCAs.

EnvisionAudio 5th August 2014 04:52 PM

Only here because I was asked... ;)

I remember this fizzle issue with many amps. Perry is right (when is Perry not right??): the audio level is usually low or off as soon as the amp is commanded to power down. :drink:

Randy62 5th August 2014 07:32 PM

Good point guys.

I am running a sine wave to the amp through a function generator trying to find the reason for this problem with these amps.But since there should be no audio signal at the RCA's when powered down then it shouldn't be an issue.
One thing I did find,the caps in question were way out of spec and when I replaced them the output of the amp dropped about 80% when it did come back out of mute for the brief period of time.

The amp stays muted for about 3 seconds then it comes back on for about a second.The +/-15v regulators get their voltage directly from the main caps so they stay on until the voltage drops below a certain threshold.The timing between the regulator voltage shut down and the muting base drive is what is so critical.

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