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Old 29th March 2010, 12:20 AM   #1
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Default Swapping in transformer?

A particular monoblock power amplifier uses a 300 VA toroidal transformer, has 6 output devices and 80,000 uF of secondary capacitance. Would it be possible to swap in a 400 VA or 600 VA toroidal transformer without any other modifications or would other adjustments have to be made to utilize the larger transformers? What specifications must be considered to match a larger transformer with the system; output voltage and output current?
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Old 29th March 2010, 01:05 AM   #2
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Quote:
Originally Posted by jackfish View Post
A particular monoblock power amplifier uses a 300 VA toroidal transformer, has 6 output devices and 80,000 uF of secondary capacitance. Would it be possible to swap in a 400 VA or 600 VA toroidal transformer without any other modifications or would other adjustments have to be made to utilize the larger transformers? What specifications must be considered to match a larger transformer with the system; output voltage and output current?
Well, with the 400vac you will not noticed much, but with the 600vac you will noticed that when you turn it on the lights will flicked a little bit also you can pop some main fuses too (use slow blow fuses). for that reason you should use a "soft start circuit" it even help the life expectancy of your transformer too. it is not a must but I would suggest it. you can also use plain thermistors one in the hot and one in the neutral lines before the transformer (primaries).
I would use thermistors or soft start circuits with big transformers like over 500vac. This is just my opinion maybe I am wrong here. let see what the pro say about it.

PS:This is how I used two thermistors in line, the transformer is a 670vac
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Old 29th March 2010, 01:09 AM   #3
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Quote:
Originally Posted by jackfish View Post
A particular monoblock power amplifier uses a 300 VA toroidal transformer, has 6 output devices and 80,000 uF of secondary capacitance. Would it be possible to swap in a 400 VA or 600 VA toroidal transformer without any other modifications or would other adjustments have to be made to utilize the larger transformers? What specifications must be considered to match a larger transformer with the system; output voltage and output current?
Wow thats a lot of capacitance for a 300VA transformer.
I have a disco amplifier that uses a 1000VA transformer with 2 * 10,000uF and sounds great even when very loud.

With that much capacitance the turn on surge will be massive through a larger transformer. So it looks like you will probably need an anti surge protect circuit.
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Old 29th March 2010, 01:25 AM   #4
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Originally Posted by nigelwright7557 View Post
Wow thats a lot of capacitance for a 300VA transformer.
I have a disco amplifier that uses a 1000VA transformer with 2 * 10,000uF and sounds great even when very loud.

With that much capacitance the turn on surge will be massive through a larger transformer. So it looks like you will probably need an anti surge protect circuit.
Wow, 1K vac with just 10,000uf per channel that is way poor!. I use a 670vac transformer using 40,000uf and in my gainclone I used 10,000uf per rail(LM3875) using 300vac.
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Old 29th March 2010, 01:29 AM   #5
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Wow, 1K vac with just 10,000uf per channel that is way poor!. I use a 670vac transformer using 40,000uf and in my gainclone I used 10,000uf per rail(LM3875) using 300vac.
It still blows mains fuses unless they are 13amp.

While the transformer is 1000VAC the amp is only 800 watts peak so its running fine on 10,000's.
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Old 29th March 2010, 01:38 AM   #6
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Originally Posted by nigelwright7557 View Post
It still blows mains fuses unless they are 13amp.

While the transformer is 1000VAC the amp is only 800 watts peak so its running fine on 10,000's.
With that transformer and power,you should at least use 30,000uf per rail.you will improve bass big time.
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Old 29th March 2010, 01:41 AM   #7
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With that transformer and power,you should at least use 30,000uf per rail.you will improve bass big time.
The smoothing caps are on the main pcb and just fit, so to add more i would need to find room off the pcb. The box is full as it is.
I will bear that in mind for the next build.
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Old 29th March 2010, 01:50 AM   #8
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Originally Posted by nigelwright7557 View Post
The smoothing caps are on the main pcb and just fit, so to add more i would need to find room off the pcb. The box is full as it is.
I will bear that in mind for the next build.
Do you have a picture of your ps?. there is always room for more capacitance, lol.
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Old 29th March 2010, 01:53 AM   #9
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Do you have a picture of your ps?. there is always room for more capacitance, lol.
Its in a case and I would need to dismantle it to get pictures.
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Old 29th March 2010, 02:01 AM   #10
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Its in a case and I would need to dismantle it to get pictures.
I understand! Thanks anyway.
if you open your amp in the future, just try using "alligator clips" and give a test with more juice to your amp (capacitance) that way you do not need to solder anything. you will "feel" the difference.
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