Class D step-up possible?

Conrad Hoffman · 25th April 2011, 02:35 PM

I want to step up the output voltage of a class D amp. Did some searches and didn't like the answers

that said the output transformer needs to pass the lowest audio frequency. Can somebody explain this in more detail? If the output transformer passes a suitable HF PWM signal it seems possible. No doubt I'm missing something- never worked with class D. I thought isolation amps that want down to DC used a method like this. Been wrong before though.

Thanks,
CH

nigelwright7557 · 25th April 2011, 08:29 PM

You would need to take the output after the class d inductor so would need a normal audio transformer. Of course stepping up the voltage also steps down the current so it wont be any louder.

Conrad Hoffman · 26th April 2011, 03:05 PM

Why can't I step up the PWM signal, then filter it after the transformer? This isn't for a dynamic speaker application. Think more like electrostatic, but not quite so high a voltage. I want to get up to a kV or so without having to start with a HV supply or switch that much voltage.

Thanks,
Conrad

Pafi · 26th April 2011, 05:25 PM

PWM signal contains audio freq components also. This is the reason why it can be restored by a simple filtering.

theAnonymous1 · 26th April 2011, 06:08 PM

I'll admit I'm a complete idiot with severe comprehension problems, but I feel like taking a guess at this one.

Is it that the inductor would have to be large enough to pass the lowest audio frequencies, which in turns means the inductance would be unsuitably high?

Eva · 26th April 2011, 09:54 PM

The PWM signal contains all the audio frequencies plus the carrier HF. Feeding the unfiltered PWM signal to a big transformer is not a good idea due to possible EMI (leakage inductance would do the output inductor job).

The transformer needs a big enough core and a high enough amount of primary turns to prevent saturation at low frequencies. Exactly as every other audio step up/down transformer.

nigelwright7557 · 26th April 2011, 10:00 PM

One way to do it is to take the pwm out and feed it into more power transistors fed with a higher voltage.
This might need an interface because of the change in voltage.

Conrad Hoffman · 27th April 2011, 12:11 AM

Well, this just doesn't sound promising. Back to the drawing board- maybe just go where I want to go directly with a tube amp.

Eva · 27th April 2011, 01:19 AM

Driving electrostatic panels?

Conrad Hoffman · 27th April 2011, 01:55 PM

No, non-audio instrumentation application, but very similar to electrostatic drive.

CH

25th April 2011, 02:35 PM	#1
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	Class D step-up possible? I want to step up the output voltage of a class D amp. Did some searches and didn't like the answers that said the output transformer needs to pass the lowest audio frequency. Can somebody explain this in more detail? If the output transformer passes a suitable HF PWM signal it seems possible. No doubt I'm missing something- never worked with class D. I thought isolation amps that want down to DC used a method like this. Been wrong before though. Thanks, CH __________________ I used to be an audiophool like you but then I took an arrow to the knee.

25th April 2011, 08:29 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	You would need to take the output after the class d inductor so would need a normal audio transformer. Of course stepping up the voltage also steps down the current so it wont be any louder. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

26th April 2011, 03:05 PM	#3
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	Why can't I step up the PWM signal, then filter it after the transformer? This isn't for a dynamic speaker application. Think more like electrostatic, but not quite so high a voltage. I want to get up to a kV or so without having to start with a HV supply or switch that much voltage. Thanks, Conrad __________________ I used to be an audiophool like you but then I took an arrow to the knee.

26th April 2011, 06:08 PM	#5
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	I'll admit I'm a complete idiot with severe comprehension problems, but I feel like taking a guess at this one. Is it that the inductor would have to be large enough to pass the lowest audio frequencies, which in turns means the inductance would be unsuitably high? __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

26th April 2011, 09:54 PM	#6
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	The PWM signal contains all the audio frequencies plus the carrier HF. Feeding the unfiltered PWM signal to a big transformer is not a good idea due to possible EMI (leakage inductance would do the output inductor job). The transformer needs a big enough core and a high enough amount of primary turns to prevent saturation at low frequencies. Exactly as every other audio step up/down transformer. __________________ I use to feel like the small child in The Emperor's New Clothes tale


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

26th April 2011, 05:25 PM	#4
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	PWM signal contains audio freq components also. This is the reason why it can be restored by a simple filtering.

26th April 2011, 10:00 PM	#7
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	One way to do it is to take the pwm out and feed it into more power transistors fed with a higher voltage. This might need an interface because of the change in voltage. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

27th April 2011, 12:11 AM	#8
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	Well, this just doesn't sound promising. Back to the drawing board- maybe just go where I want to go directly with a tube amp. __________________ I used to be an audiophool like you but then I took an arrow to the knee.

27th April 2011, 01:19 AM	#9
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Driving electrostatic panels? __________________ I use to feel like the small child in The Emperor's New Clothes tale

27th April 2011, 01:55 PM	#10
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	No, non-audio instrumentation application, but very similar to electrostatic drive. CH __________________ I used to be an audiophool like you but then I took an arrow to the knee.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Home built 1" dome tweeters, with step-by-step pics	flyingtele	Multi-Way	3	3rd April 2011 09:11 PM
Difference between Class H 2 step and 3 Step	Maxco	Solid State	3	24th January 2011 07:26 AM
Step up voltage on class d	ASLHK	Class D	4	7th September 2008 01:02 AM
my first step to class A amp -aleph3 3ow.	space2000	Pass Labs	11	20th June 2008 08:24 AM
DC step down converters vs. Class D amps	fokker	Class D	2	31st July 2006 02:28 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read