If you don't want to buy and use and look at 50mA LEDs, you can connect a resistor in parallel to the LED, chosen such that 49/50ths of the total current flows in the resistor, and 1/50th of the total current flows in the LED. Now you get a very, VERY dim LED. And if you implement this new resistor with a 25-turn trimmer potentiometer, you can adjust the LED brightness all the way from very dim to very bright, and every brightness in between.
precision not really mandatory, 0.5 to 1 second delay is all that is needed..
yes, increasing C4 gives a longer delay, but not really necessary...
the delay should be the same with or without load..
I use a delay on the soft start bypass of ~200ms.
It works for all sizes of transformer and all amounts of smoothing capacitance after the rectifier.
I have used shorter and longer soft start delays and all seem to work.
I have not used long period delays for the soft start and I don't blow the close rated fuse.
The speaker delay is much longer, 3seconds to 6seconds is typical.
It works for all sizes of transformer and all amounts of smoothing capacitance after the rectifier.
I have used shorter and longer soft start delays and all seem to work.
I have not used long period delays for the soft start and I don't blow the close rated fuse.
The speaker delay is much longer, 3seconds to 6seconds is typical.
why i dislike the use of NTC on soft start boards....
An externally hosted image should be here but it was not working when we last tested it.
Now that the F5's are in place, I could focus on building a Soft Start module Toecutter V3 design...using stock values, worked first time..thanks 6L6 for the visual details...I was using CL60's until now...no problems yet...I played the amp for like whole day (Pretty loud continuously)...the CL60's wouldn't get hot at all on a 600VA teddy. Where I live, there are power issues, voltage fluctuates, power outages etc...the local power generators kicks in..in about 10 - 20 secs, CL60's were able to bear this abuse and kept the teddy sane. Now this soft start circuit is simple and works fine...I tried testing it by powering up and down and then up almost instantaneously, I realised the relay gets engaged pretty fast...I assume ~200ms, but disengages slow.... takes close to a second...any power off and on cycle before 1 sec, results in blowing of fuse/trips my circuit breaker...I went through all the pages in this forum, couldn't find anything related to fast discharge of the the circuit...for relay to disengage faster..I think AndrewT might be suggesting the aux transformer based solution for this reason only...but it would interesting to understand how the discharge mechanism could be controlled.
You can create a second circuit that is a start delay after power is applied. A second relay on the input power controlled by a simple timer set to a long enough duration to allow the t hermistors to cool and become functional again.
These are not thermistors, but circuit resistors...they get hot in due course of operation...my question was if it was normal for these to get hot...assume they could be..as they are 3W ones, but my suspect is the LED resistor...ideally it should not...
Where I live, i am able to find in numerous clones of this relay...all we need is 24V 10A ones..as per the schematic, K1.1 & K1.2 are just 2 parts of one single relay only.
Soft Start stopped working
The amplifier with soft start was working great for a few years. Recently it started showing the following symptoms:
The amplifier with soft start was working great for a few years. Recently it started showing the following symptoms:
- I'm using the external switch at PWR_SW1 and PWR_SW2. When I flip that switch, I don't hear a "click" anymore.
- Voltage OUT of the transformer is low, and clipped.
- The 4 big 180 ohm resisters get super hot.
- The LED does not light up.
- whole amplifier works fine when I bypass the soft start.
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