There is a constant minimum of power being drawn that is enough to keep the thermistor constantly at a low resistance state so this problem of thermistors acting like limiters with tiny amount of power being drawn is not a problem.
Member
Joined 2002
the second a class a amp is powered on, it's pulling current. It stop's when you turn it off OR unplug it.
In fact it does not have to go through all that crap. When a relay 'takes the thermistor out' it means that the relay is in parallel with the thermistor and after soft start has served its purpose the relay closes and the thermistor goes to high resistance since power now passes through the relay. Making it simple in this situation is only a nuisance at the time of the build and does not effect the performance of the amp.
edit: this is in reference to the soft start circuit. Speaker protection can be implemented in awful ways and there are also good ways which do not get in the output signal.
Finding out i didnt build an amplifier properly
by frying my > $500 drivers is not what i would want.
Regards,
Klaas
by frying my > $500 drivers is not what i would want.
Regards,
Klaas
I cannot confirm that.
Since it is directly connected to the mains, I cannot, with my equipment and my level of expertise, devise a safe method to confirm if that is true.
I don't believe what you have concluded about low resistance is true.
I doubt anyone would argue with you on that statement.
What is it that you meant to post?
Andrew
Lets keep the discussion in the context of the thread. The MiniA.
The CL60 which is the thermistor that has been referred to starts at 10R and goes to much lower when current passes through it. It is a 5A rated device. At 25%/50%/75%/100% of its 5A capacity it will have a resistance of 1.09/0.44/0.2/ 0.18 R.
After reading the datasheet though I wonder how great of a choice they are as they are rated for a long life when used to limit current for inrush charging of capacitors of 5000uf at 120VAC.
edit: well, then again they only take this terrible beating when the circuit is first turned on. The datasheet, I believe, is speaking more toward users of switching supplies where the thermistor is subject to charging the caps in an abrupt manner many times a second. Maybe CL60 is fine for the life of this amp.
Lets keep the discussion in the context of the thread. The MiniA.
The CL60 which is the thermistor that has been referred to starts at 10R and goes to much lower when current passes through it. It is a 5A rated device. At 25%/50%/75%/100% of its 5A capacity it will have a resistance of 1.09/0.44/0.2/ 0.18 R.
After reading the datasheet though I wonder how great of a choice they are as they are rated for a long life when used to limit current for inrush charging of capacitors of 5000uf at 120VAC.
edit: well, then again they only take this terrible beating when the circuit is first turned on. The datasheet, I believe, is speaking more toward users of switching supplies where the thermistor is subject to charging the caps in an abrupt manner many times a second. Maybe CL60 is fine for the life of this amp.
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Oh I certainly don't know if it is audiable, but with say 500mA drawn on the AC side, there will be a resistor of reasonably high resistance (compared to useing one that is smaller), dead squat in between my primaries. If I remember the datasheet stuff correctly, it doubles the impedance of the primary side, is that audiable?
Damn, I see now the C60 is only 1 ohm, I better fork out and get the proper thing then.
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An additional question could be:
will the resistance in the primary side lead to modulation of the transformer supply voltage when amplifier demand changes?
will the resistance in the primary side lead to modulation of the transformer supply voltage when amplifier demand changes?
Woot, I'm picking up my transformer tomorrow, finally. Damn backorders.
I'll be running 2x15Vac 225VA trafo with a total of 45000uF per rail, in a CRC filter. Judging from my chipamp build, a slow-start isn't going to be needed, but I'll see when I power up the PSU for a test.
I'll be running 2x15Vac 225VA trafo with a total of 45000uF per rail, in a CRC filter. Judging from my chipamp build, a slow-start isn't going to be needed, but I'll see when I power up the PSU for a test.
My case is almost finished.
The power supply is only.... 12V/0/12V 300VA and 120000uf
Need a few more bits so I can finish by psu board
I only hope my 300x100x40mm heatsink are up to the task.
Ric
The power supply is only.... 12V/0/12V 300VA and 120000uf
Need a few more bits so I can finish by psu board
I only hope my 300x100x40mm heatsink are up to the task.
Ric
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Member
Joined 2002
why would yuo connect your new amp that you just built to a nice pair of speakers ? the first thing to to is test it, measure all aspects and points, then connect to a pair of (TEST) speakers. ..
I never connect a amplifier to a pair of nice speakers until it has been tested and working fine.
My alephs that i have built never have given me any problems at all, so i use speaker protection ? NOPE, do i have ac mains protection ? NOPE ! do i have vu meters or other stuff tied to it ? NOOOO PPPPPEEEEEEE..
the mini was suppose to be a simple amplifier design, still is if you stick to the build properly.
use good
caps / resistors
Matched Fets
good quality tansformer
take your time to build it and test it.
should work for many years...
mine still do..
I hope you mean you have a 12V AC transformer, to get you in the region of 15V DC. You need at least 15V and 1A to get the output fets into their optimal operational mode.
I'm so averse to blowing drivers, I still have not tried the mini with my Kirkseaters.
Ups sorry that I was not clear, is it is 12V/0/12V AC 300VA.
Ordered the rest of the parts today hope they arrieve before Saturday.
Ordered the rest of the parts today hope they arrieve before Saturday.
I think is time for a bit of Heavy Metal porn...
I still need to make the vents on the top plate.
The board inside is the one for the cap bank the rectifiers are going on the bottom plate between the trafo ant the board.
Ric
I still need to make the vents on the top plate.
The board inside is the one for the cap bank the rectifiers are going on the bottom plate between the trafo ant the board.
Ric
Attachments
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Yes you're right
Couple of hours of drilling/cutting/filing and a couple of blisters for each side
Now imagine that with wife breading down your (mine) neck.
Doing psu board will come back later
Ric
Board ready to be etched
Made a small mistake in my Farnell order and don't have enouth 0.47 resistors and forgot the 2K2 bleeder ones.
I like it to (wife breading on my neck) but not when I'm working...
Ric
Made a small mistake in my Farnell order and don't have enouth 0.47 resistors and forgot the 2K2 bleeder ones.
I like it to (wife breading on my neck) but not when I'm working...
Ric
