I built rod elliot project 39 the soft start circuit. Right now the circuit is working. However the transformer i use for the soft start is driving me nuts. The transformer is center tapped 6VA 9-0-9V. I measured the transformer without anything connected and it gives me 9V ac. But when i connect the soft start circuit to it, one side gives me 9.3V ac and the other side gives me 18V ac. How could this be possible ? I tried checking the connections again and again but can't point out what is wrong. Can anyone tell me what i should check ?
Has the transformer ONLY 3 pins. 9-0-9 or is it two separate windings of 0-9 and 0-9 and has four pins 🙂
For a 6VA transformer, a softstart isn't neccesary anyway... you will be fine with an appropriately rated "T" type (slow blow/time delay/anti surge) fuse.
The transformer has 3 pins 9-0-9.
Jaycee the 6VA transformer i am talking about is to power the soft start circuit. The soft start circuit is made to power a 500VA transformer.
Jaycee the 6VA transformer i am talking about is to power the soft start circuit. The soft start circuit is made to power a 500VA transformer.
Hmmm... as ever wihout actually seeing something...
OK... meter on AC, transformer not conected to anything, and putting one meter lead on the center 0v ? (it usually is the center but not always) pin and reading with the other lead to either of the other pins should give 9 vac.
Connecting to the circuit, and repeat exactly and it has to be the same 🙂 perhaps slighly lower as now under load.
Your not measuring the rectified AC or anything ?
OK... meter on AC, transformer not conected to anything, and putting one meter lead on the center 0v ? (it usually is the center but not always) pin and reading with the other lead to either of the other pins should give 9 vac.
Connecting to the circuit, and repeat exactly and it has to be the same 🙂 perhaps slighly lower as now under load.
Your not measuring the rectified AC or anything ?
I did exactly as u said. 9V ac with nothing connected. But when i connect to the soft start circuit the meter gives me 9V ac on one side and the other side (the other pin) is 18V ac. The 0V pin is at the center. I put one end of the meter lead at the center, kept it fixed. The other lead to measure the 9V pins . I am very sure i did not put the meter leads across the 9V pins. This is so crazy..........ARGHHHHH. I don't understand why.
The soft start you gave seems like it is powered by the main transformer of the amp itself. Forgive me if i am wrong.
Hi Buzzy... all I can suggest is recheck... and put a link or something in so we can see what you have built and see what the DC voltages should be (as confirmation) 🙂
Something is going astray with the measurement, or something is floating etc...
Something is going astray with the measurement, or something is floating etc...
The circuit I was building was found here Soft-Start Circuit For Power Amps. The circuit is figure 2.
I have modified the rectifier part of the circuit to use a center tapped transformer. The way i modified and wired it is shown in the figure below.
I have modified the rectifier part of the circuit to use a center tapped transformer. The way i modified and wired it is shown in the figure below.
An externally hosted image should be here but it was not working when we last tested it.
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OK... quick guess... the connection to one of the secondaries is open circuit and it's running on just one of the windings, and you are measuring a "floating" connection on the anode of one of the diodes.
With it all connected (but off 🙂)measure the resistance from ground to each diode anode and compare... they should be the same.
With it all connected (but off 🙂)measure the resistance from ground to each diode anode and compare... they should be the same.
Hmm ok i shall measure the resistance when i get home. What is a "floating" connection ?. When i measured, it was on the transformer itself not on the soft start circuit at all. That is with the soft start circuit connected. One side gives me 18V ac voltage. Is it trying to play games with me ? HeHe.
I mean if the winding is open circuit. Those small transformers are easily damaged like that, a break in the wire at the pin.
You might well have connected one of the secondaries to the ground, instead of the centre tap. This would give the same result as Mooly's suggestion would give, & easily explain the 9V & 18V outputs.
If you measure things as Mooly suggested i think it'll all become evident shortly after applying a multimeter 😉
Best of luck 🙂
If you measure things as Mooly suggested i think it'll all become evident shortly after applying a multimeter 😉
Best of luck 🙂
If i correctly understand what you mean, you are saying that the connection between the 3 pins inside the transformer has become open ? I think i have done a continuity test using a multimeter and all the pins seem to be connected. I have to recheck this.
Erm......aren't ground and center tap the same thing ? Both are the 0V pin on the transformer right ?
That's what I mean, a break within the tranny. Recheck and reconfirm the AC is high on the suspect pin, then switch off and measure resistance from ground to the Anode of each rectifier. That way you are not disturbing anything.
Going off your circuit the AC on one pin can't suddenly increase... not in the normal sense.
I can think of bizzare scenarios, but it will be simple in the end 🙂
Going off your circuit the AC on one pin can't suddenly increase... not in the normal sense.
I can think of bizzare scenarios, but it will be simple in the end 🙂
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