I have built the circuit below to auto soft-start a Charlize amp
The idea is that there is 330 ohms in series with the 12 volt power supply until the relay shorts the resistor, allowing full voltage to the amp. I have used a single pole relay rated at 8 amps.
When tested on its own it works OK but when the amp is connected, the relay repeatedly trips every few seconds. Can somebody suggest a way to fix this problem or even tell me what is happening?
An externally hosted image should be here but it was not working when we last tested it.
The idea is that there is 330 ohms in series with the 12 volt power supply until the relay shorts the resistor, allowing full voltage to the amp. I have used a single pole relay rated at 8 amps.
When tested on its own it works OK but when the amp is connected, the relay repeatedly trips every few seconds. Can somebody suggest a way to fix this problem or even tell me what is happening?
Thanks Ritchie - it appears to work OK! 🙂
I had no idea such genius lurked just across the county border!
I had no idea such genius lurked just across the county border!
TBH the 555 has a more elegant edge, but this could be worth a try as a comparison.
Ignore the transistor type - use something like a BD139.
You could add R1 and D1 to your circuit to give a faster reset.
An externally hosted image should be here but it was not working when we last tested it.
Ignore the transistor type - use something like a BD139.
You could add R1 and D1 to your circuit to give a faster reset.
That looks interesting, All I have is a TIP3055 which I hope works, but what values would you use for a 3-4 second delay?
Thanks for the circuit.
Thanks for the circuit.
The low-gain 3055 will I think need too much base current so R2 would need to be much smaller, hence C7 much larger for the same delay. A 2N2222A will drive any relay with ease, the 2N3904 shown most small relays.
An improvement for better reproducibility and longer delays without big caps is a zener in the base lead; the transistor won't turn on until the cap has charged to (Z+0.7)V rather than only 0.7V. Pick one about 60% supply to ease calculations.
An improvement for better reproducibility and longer delays without big caps is a zener in the base lead; the transistor won't turn on until the cap has charged to (Z+0.7)V rather than only 0.7V. Pick one about 60% supply to ease calculations.
Thanks Ritchie, I'll give it a try when I can find time. My hi-fi projects list is growing longer every week! 
cpemma's comments are all good. He beat me to it 🙂 I've also thought about using a little power Darlington from the TIP range as this would raise the threshold a bit as well as requiring less base current. You could even try a MOSFET.
richie00boy said:
This thread covers both those features with a stripboard & pcb pattern for the darlington version. 😀
Why do you guys even bother to mess with relays and resistors in the power line? Use a simple delay circuit to unmute the amp after the input coupling caps have charged up. I posted one a while back in this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=76504&highlight=
Michael posted the circuit the Super-T uses as well.
Michael posted the circuit the Super-T uses as well.
You seem to have missed the point of a soft-start... which is to prevent surge currents, thereby extending component life. Nothing to do with turn on thumps.
Ummm... this is a "soft start" for a small Tripath amp, not a transformer. Therefore, there is no large surge current at all. The whole point of this "soft start" circuit is in fact to get rid of the turn on thump that you hear because the amp is enabled before the input coupling caps are fully charged due to the input stage being biased at 2.5V.
That's what I have done Brian using Nuuk's Timer Circuit with the relay and my AMP3 because the AMP3 has mute pins, but instead of the power soft start, using it to switch on and off the mute pins.
I am also using Nuuk's and Carlos's preamp and takes a second or two to get it's act together and a 4 second mute for the AMP3 works well. No nasty noises from the preamp and no thump from the AMP3.
I am also using Nuuk's and Carlos's preamp and takes a second or two to get it's act together and a 4 second mute for the AMP3 works well. No nasty noises from the preamp and no thump from the AMP3.
You don't need a relay to drive the mute pin because it draws almost no current at all. But if it works then there isn't really any need to change it! All of the TA202X chips have mute pins, so it's possible with any of the amps that use those chips.Bearman said:
The "soft start" name that most people use for this application is quite misleading. I like to call it thumpless or pop-less turn on.richie00boy said:
A valid point, and that's what I was going to do. But Yeo of DiyParadise prefers to use the resistor trick and recommended me to do the same. As I am building this Charlize up for somebody else, I followed Yeo's advice. 😉
What's pin 11 (mute) of the TA2020 connected to on the Charlize amp? Chances are it's connected to pin 18 (fault) so that the chip is muted if the fault protection is tripped. If it's not connected to anything you could jumper in a wire to that pin to control the chip's mute function. If it is connected to the fault pin you could just as easily cut the trace and jumper in a wire to control the mute pin. That's what I would do.
Just so you know, the mute pin is active high. It would have been nicer if Tripath made the mute pin active low so you could easily keep the amp muted with a pull down resistor then pull the pin high once the 5V rail reaches 5V, but not much we can do about that.
Just so you know, the mute pin is active high. It would have been nicer if Tripath made the mute pin active low so you could easily keep the amp muted with a pull down resistor then pull the pin high once the 5V rail reaches 5V, but not much we can do about that.
Brian, I just use the relay as a switch. The AMP3 has mute jumper pins on the PCB so I don't have to lift any legs or anything, just a two pin connector on the jumper pins, and run that to the relay. On power up, the pins are not shorted, then after 4 sec. the relay shorts the mute connection.
If the relay fails, there is no current to cause problems and it just mutes the amp.
If the relay fails, there is no current to cause problems and it just mutes the amp.
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