what rate of transformer i should use?

motbuddy · 12th March 2010, 07:37 AM

hi,
If i would like to try on this quasi-complementary circuit shown below,what rate of transformer should i choose? in a way of VA. The link of this circuit is as below
http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html

quasi1.JPG

thanks.

Aldotin · 12th March 2010, 08:50 AM

A 20...30VA rated transformer with ~22V secondary will do the job!

Good luck!

motbuddy · 12th March 2010, 08:52 AM

how do u actually calculate that value?or by experience?
But the circuit label a +30V ,isnt it needs +30V?

thanks.

nigelwright7557 · 12th March 2010, 11:05 AM

If the amp is 10watt then you need a bit more in VA due to losses into heat in the heatsink. I usually allow 50% for that so I reckon a 15-20VA transformer would do the job.

wakibaki · 12th March 2010, 11:59 AM

Quote:

Originally Posted by motbuddy

how do u actually calculate that value?or by experience?
But the circuit label a +30V ,isnt it needs +30V?

By experience + calculation.

A 10W amplifier usualy means 10 watt sinewave (RMS) power. But music is not sinewave, it has less power.

A 10 watt amplifier with 50% efficency wastes 10 watts in heat.

For an IC (chip) amp, transformer VA ~ 2 * amplifier watts is a guess.

The amplifier will work. If it gets hot, we put in a fan and buy a bigger transformer for next one. If it's a hot day, maybe the transformer goes bang anyway, so often we make it too big, just in case.

+30V is +30V, but transformer VA is ~. Approximate.

w

motbuddy · 15th March 2010, 03:19 AM

Quote:

Originally Posted by Aldotin

A 20...30VA rated transformer with ~22V secondary will do the job!

Good luck!

Do u mean that we dont have to follow the circuit which mention +30V as input power?

thanks.

motbuddy · 15th March 2010, 03:23 AM

could a transformer with a rating 30V, 30VA be chose?

thanks.

motbuddy · 15th March 2010, 10:58 AM

after survey around the shop, i decide to buy a 24VA transformer with secondary voltage equals to +30V. Can it be?

thanks.

Aldotin · 15th March 2010, 12:40 PM

Quote:

Originally Posted by motbuddy

Do u mean that we dont have to follow the circuit which mention +30V as input power?

thanks.

~22V (22Vac) gives +30V

motbuddy · 15th March 2010, 01:03 PM

Quote:

Originally Posted by Aldotin

~22V (22Vac) gives +30V

sorry, i really not understand this. how could a 22Vac gives +30V?

ok this is my plan for the power supply part. I plan to use a +30V 24VA transformer and connect to a bridge rectifier(1N4007 will be use) and filter cap(not sure what value to put,any idea?) to get +30Vdc. Am i correct?

thanks.

12th March 2010, 07:37 AM	#1
motbuddy diyAudio Member Join Date: Jan 2010	what rate of transformer i should use? hi, If i would like to try on this quasi-complementary circuit shown below,what rate of transformer should i choose? in a way of VA. The link of this circuit is as below http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html quasi1.JPG thanks.

12th March 2010, 11:05 AM	#4
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	If the amp is 10watt then you need a bit more in VA due to losses into heat in the heatsink. I usually allow 50% for that so I reckon a 15-20VA transformer would do the job. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

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12th March 2010, 08:50 AM	#2
Aldotin diyAudio Member Join Date: Dec 2009	A 20...30VA rated transformer with ~22V secondary will do the job! Good luck!

12th March 2010, 08:52 AM	#3
motbuddy diyAudio Member Join Date: Jan 2010	how do u actually calculate that value?or by experience? But the circuit label a +30V ,isnt it needs +30V? thanks.

15th March 2010, 03:23 AM	#7
motbuddy diyAudio Member Join Date: Jan 2010	could a transformer with a rating 30V, 30VA be chose? thanks.

15th March 2010, 10:58 AM	#8
motbuddy diyAudio Member Join Date: Jan 2010	after survey around the shop, i decide to buy a 24VA transformer with secondary voltage equals to +30V. Can it be? thanks.

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