is there a particular soft start kit you recommend as this is the first time iam having to use one and iam been readind around and some have said its not needed below 300va however i would rather be safer than sorry
There are many sch for a soft start.
All they need is:
Resistor to limit starting current
Relay to bypass the resistor after start up
Timer to set the delay for the bypass relay.
A small signal transistor to turn on the relay.
A PSU to drive that lot.
The resistor value depends on the fuse value you want to adopt.
The fuse value can be anywhere from 80% of full rated primary current to 300% of full rated primary current. I usually aim for 90% to 120%.
The timer can be a 555, or any similar timer chip. I do not recommend a directly driven RC for which the delay is VERY dependent on the mains voltage.
All they need is:
Resistor to limit starting current
Relay to bypass the resistor after start up
Timer to set the delay for the bypass relay.
A small signal transistor to turn on the relay.
A PSU to drive that lot.
The resistor value depends on the fuse value you want to adopt.
The fuse value can be anywhere from 80% of full rated primary current to 300% of full rated primary current. I usually aim for 90% to 120%.
The timer can be a 555, or any similar timer chip. I do not recommend a directly driven RC for which the delay is VERY dependent on the mains voltage.
I've all but finished the front two channels of my 5.1 badger setup. the stereo pair for L & R will be the first to complete. I've really enjoyed building it thus far.
In terms of soft start, I've been looking at that and protection with an Arduino based solution.
For soft start. I'm thinking of using an inverted output 0=soft start and bring an appropriately sized resistor into play for 10 seconds or so. That would include the Arduino boot time of a couple of seconds.
In terms of protection, I again was thinking an inverted Arduino output, IE: 0=protected, 1=systemLive. I was thinking of two things:
1/ a low pass filter set at 0.1hz or similar that would trigger DC protection and turn off the output and mute the input at a threshold voltage.
2/ either a hall effect unit or 0.1 ohm resistor to sense current at the output, and have a V by I map in the Arduino data segment that provides current values by bucketed voltage that cannot be exceeded, with allowable temporary exceptions to avoid a transient triggering it.
Both protection cases would turn off the output using a relay and maybe mute the input.
It must be said both of these are vapour-ware at the moment, and I'm not even looking at them in anger until I've got both channels working. Once I've got two working channels on my bench supply, I'll start to look at protection and soft-start and make available what I find both here and on my blog.
There's at least one assumption here that needs some thought and testing: can an AVR chip output be relied upon to be stable and in a known state very quickly after power up. This I have not yet tested.
If this works, the circuit would probably just be a couple of 5534's or 5532's to measure voltage across the sense resitor, a few resistors, cheap transistors to active the relays, two relays and an a Arduino Mini. I'd imagine the whole lot would be less than £50 and the PCB probably easily DIY'able.
In terms of soft start, I've been looking at that and protection with an Arduino based solution.
For soft start. I'm thinking of using an inverted output 0=soft start and bring an appropriately sized resistor into play for 10 seconds or so. That would include the Arduino boot time of a couple of seconds.
In terms of protection, I again was thinking an inverted Arduino output, IE: 0=protected, 1=systemLive. I was thinking of two things:
1/ a low pass filter set at 0.1hz or similar that would trigger DC protection and turn off the output and mute the input at a threshold voltage.
2/ either a hall effect unit or 0.1 ohm resistor to sense current at the output, and have a V by I map in the Arduino data segment that provides current values by bucketed voltage that cannot be exceeded, with allowable temporary exceptions to avoid a transient triggering it.
Both protection cases would turn off the output using a relay and maybe mute the input.
It must be said both of these are vapour-ware at the moment, and I'm not even looking at them in anger until I've got both channels working. Once I've got two working channels on my bench supply, I'll start to look at protection and soft-start and make available what I find both here and on my blog.
There's at least one assumption here that needs some thought and testing: can an AVR chip output be relied upon to be stable and in a known state very quickly after power up. This I have not yet tested.
If this works, the circuit would probably just be a couple of 5534's or 5532's to measure voltage across the sense resitor, a few resistors, cheap transistors to active the relays, two relays and an a Arduino Mini. I'd imagine the whole lot would be less than £50 and the PCB probably easily DIY'able.
From a quick read, it looks probable that it would work and the pins could be relied on to be low during boot:
Pin status at boot
Pin status at boot
We have already put together a complete softstart/protection system based on an Arduino. AVRs are perfect for this sort of task and are very reliable if done properly. We do current sensing by measuring voltage drop on a pair of emitter resistors through an optoisolator. Any direct connection between rail voltage and the microcontroller isn't a good idea.
http://www.diyaudio.com/forums/solid-state/264313-how-build-21-st-century-protection-board.html
http://www.diyaudio.com/forums/solid-state/264313-how-build-21-st-century-protection-board.html
Many thanks, I will take a look at this once Ive got two working boards! Will save me considerable time.
All good so far on the testing front. These amps gave my seas mimir test speaker a run for its money. I'd never seen it reach max excursion before.
I've just started to get ready to spec out my psu. I'm aiming for running the amps at +-50v. How much capacitance (ball park) would each amp rail need to drive a pair of 8 ohm speakers that have a low of about 6 ohm? I know this has come up before but I wasn't sure if the answer applied to one channel or two channels.
I was thinking 6800 x4 on each rail. Making 4 rail's for two amplifier's.
I've just started to get ready to spec out my psu. I'm aiming for running the amps at +-50v. How much capacitance (ball park) would each amp rail need to drive a pair of 8 ohm speakers that have a low of about 6 ohm? I know this has come up before but I wasn't sure if the answer applied to one channel or two channels.
I was thinking 6800 x4 on each rail. Making 4 rail's for two amplifier's.
I have what must amount to insufficient heat sinking on my Honey Badger, and despite trying to set the bias current on the low side, it apparently would not stabilize and after a few weeks, I had an incident of thermal runaway. I thought the compensation would prevent this from happening. I was just playing quiet music at the time.
Had I left this on when I was not home, I could have burned the house down and lost everything. I was nearby and shut it off as soon as I caught the smell of hot electronics. I don't know if anything was damaged... there was never any smoke... but even if nothing was damaged, I just don't think I will ever feel safe using my own home built amplifier again. It's a shame after all the money I put into this and it did sound good. I was pleased with the sound, but I can live with spending a bit more or having slightly less performance for the safety of my family and home.
I'm not so much looking for a solution. I don't think there is one for me. Just wanted to say what could happen.
Had I left this on when I was not home, I could have burned the house down and lost everything. I was nearby and shut it off as soon as I caught the smell of hot electronics. I don't know if anything was damaged... there was never any smoke... but even if nothing was damaged, I just don't think I will ever feel safe using my own home built amplifier again. It's a shame after all the money I put into this and it did sound good. I was pleased with the sound, but I can live with spending a bit more or having slightly less performance for the safety of my family and home.
I'm not so much looking for a solution. I don't think there is one for me. Just wanted to say what could happen.
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I recommend ±20mF for each 8ohms speaker.
4ohms would be ±40mF
I get to that from setting the input filter to one decade below 20Hz, i.e. 2Hz.
The NFB needs to be at least half an octave below that i.e.1.4Hz and the PSU needs to be another half octave below the NFB, i.e. <1Hz.
8ohms and 20mF is 1Hz. 4ohms and 40mF is 1Hz. Note this has nothing to do with power, a 50W chipamp and a 200W monster amp both need the same PSU to extend the bass down to 20Hz with minimal phase due to rolling off the frequency response.
Your 4off 6800uF exceeds that requirement and allows you to set the NFB RC to ~0.192seconds, eg. 150uF & 1k3 in the lower leg of the NFB. You could swap the 1k3 to 1k2, or 1k1 or 1k0 (all with 150uF) if you need to fine tune the amplifier gain.
ClassAB amplifiers have crossover distortion, in addition to all the other distortions. This can sound bad if not set up correctly.
The best way is to adopt "Optimal ClassAB" biasing. That depends on which output stage the amplifier uses. For an Emitter Follower (EF) output stage the bias voltage across the output emitter resistors should be set to ~<26mVre
D.Self has a section on his webpages describing this. He talks about the voltage across the two emitter resistors, so his examples shown a doubled voltage. D.Self also discusses CFP bias voltage, it is very much lower.
eg. adopt 0r47 for the EF emitter resistors (match them rather than take ±10% straight from your supplier) and set the bias voltage to 25mVdc.
A better way is to measure the THD and find the correct bias voltage that minimises crossover distortion (D.Self shows pics of what these look like)
The current is not the controlling factor. It is the VOLTAGE that needs to be set.
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A temperature switch on the main heatsink that shuts off the mains power is cheap.
A DC detect and speaker protect/isolation is a bit more expensive, but worth fitting. This can also be used as a speaker delay at start up and instant off if power fails.
Hi,
If you are looking for a simple solution, you can try APEX Audio NE555 protect ckt(just one IC, 2 to-92 transistors, few passives). http://www.diyaudio.com/forums/soli...mplifier-irfp240-irfp9240-62.html#post3044583 . It has start delay, DC protect and thermal shut-off, all on a very small PCB that can be fitted directly to speaker terminals.
one can also add short ckt detect on a small daughter pcb.
reg
Prasi