Will I need a transformer for this DIY Amplifier? - Page 2

Dxvideo · 31st July 2009, 10:24 AM

I have a 30x2v AC 225VA toroid, and it gives 41-42v DC depends on load. However I have never thought to apply it a chipamp! I think its dangerous..
What if the mains increases only up to 240v???

AndrewT · 31st July 2009, 10:37 AM

the rated input voltage to rated output voltage ratio is critical if you want to run at close to the National maximum voltage specification.

I reckon a 240:28Vac 300VA transformer (6% regulation) feeding a pair of 3886 chipamps will be just above the +-42Vdc maximum quiescent specification. But when significant power is drawn from either or both amplifiers then the supply will drop below the +-42Vdc spec maximum.

I recommended 240:28Vac a long time ago as the maximum to supply an 8ohm loaded pair of chipamps and got shouted down as far too big a supply voltage.

Measure what you have and monitor temperatures, but if you choose to run above National's specification maxima then the risks and consequences are wholly of your own making.

pacificblue · 31st July 2009, 11:12 AM

The trouble with the 2x30 V transformer is that it is recommended in National's AN-1192, but people tend to overlook the fact that it is only recommended in combination with 8 Ohm speakers and with profound heatsinking. As long as an amplifier is not permanently connected to a dedicated driver in an active speaker or similar set-up, you can not be sure that it will never be connected to a 4 Ohm load. Just as little as you can be sure that nobody will ever turn the volume up, while your amplifier is connected to a 4 Ohm load, when it should not be.

odysseybmx414 · 31st July 2009, 01:44 PM

all is why that voltage shouldn't be recommended to a beginner. 18-0-18 will give him the ability to drive different loads, different volumes, with assurance that the chips are not getting very hot as long as he uses a sink that isn't incredibly small.

kizm0 · 31st July 2009, 08:22 PM

Alright..I'm still having a hard time understanding this but..

With some googling I found this:

http://www.newark.com/jsp/search/pro...FC-GB100000001

http://www.newark.com/jsp/search/pro...FC-GB100000001

guitvinny · 31st July 2009, 08:43 PM

It's not so hard, you have basically 3 things to check :

- Primary winding, is it for 120 or 240 V
- Secondary winding, in your case 18 - 0 - 18
- VA rating, which is *grossly* the power the transformer can handle

The 2nd one from Newark looks very nice, the first one can only deliver 4 VA... its going to fry.

netbug · 31st July 2009, 08:59 PM

This is what I'm running in a dual 3886 chipamp
25v+25v 250va
http://www.parts-express.com/pe/show...number=122-625

Safe using 8ohm speakers a decent heatsink

As stated earlier 18v+18v would be safe for 4ohm

http://www.parts-express.com/pe/show...number=122-620

kizm0 · 31st July 2009, 09:44 PM

Didn't have to get to other people sending me their parts, but oh well.. Thanks a lot. I now have a better understanding of Transformers.

31st July 2009, 10:24 AM	#11
Dxvideo diyAudio Member Join Date: Nov 2003 Location: Turkey	I have a 30x2v AC 225VA toroid, and it gives 41-42v DC depends on load. However I have never thought to apply it a chipamp! I think its dangerous.. What if the mains increases only up to 240v??? __________________ Best regards, Ozgur

31st July 2009, 10:37 AM	#12
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the rated input voltage to rated output voltage ratio is critical if you want to run at close to the National maximum voltage specification. I reckon a 240:28Vac 300VA transformer (6% regulation) feeding a pair of 3886 chipamps will be just above the +-42Vdc maximum quiescent specification. But when significant power is drawn from either or both amplifiers then the supply will drop below the +-42Vdc spec maximum. I recommended 240:28Vac a long time ago as the maximum to supply an 8ohm loaded pair of chipamps and got shouted down as far too big a supply voltage. Measure what you have and monitor temperatures, but if you choose to run above National's specification maxima then the risks and consequences are wholly of your own making. __________________ regards Andrew T.

31st July 2009, 11:12 AM	#13
pacificblue diyAudio Member Join Date: May 2008	The trouble with the 2x30 V transformer is that it is recommended in National's AN-1192, but people tend to overlook the fact that it is only recommended in combination with 8 Ohm speakers and with profound heatsinking. As long as an amplifier is not permanently connected to a dedicated driver in an active speaker or similar set-up, you can not be sure that it will never be connected to a 4 Ohm load. Just as little as you can be sure that nobody will ever turn the volume up, while your amplifier is connected to a 4 Ohm load, when it should not be. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

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
Arc Welder Transformer used to power Amplifier	John Biles	Solid State	53	18th July 2011 04:17 PM
transformer amplification amplifier	damianl	Solid State	19	11th October 2010 10:00 PM
Need to replace the transformer in this amplifier	Kramerguy	Solid State	35	23rd December 2008 07:54 PM
Is this transformer good for power amplifier	ostie01	Solid State	10	14th August 2006 02:53 PM
amplifier without transformer	csl113	Solid State	2	17th June 2005 02:28 PM


	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

31st July 2009, 01:44 PM	#14
odysseybmx414 diyAudio Member Join Date: Feb 2005 Location: Watertown, NY	all is why that voltage shouldn't be recommended to a beginner. 18-0-18 will give him the ability to drive different loads, different volumes, with assurance that the chips are not getting very hot as long as he uses a sink that isn't incredibly small.

31st July 2009, 08:22 PM	#15
kizm0 diyAudio Member Join Date: Jul 2009	Alright..I'm still having a hard time understanding this but.. With some googling I found this: http://www.newark.com/jsp/search/pro...FC-GB100000001 http://www.newark.com/jsp/search/pro...FC-GB100000001

31st July 2009, 08:43 PM	#16
guitvinny diyAudio Member Join Date: Nov 2005 Location: Québec	It's not so hard, you have basically 3 things to check : - Primary winding, is it for 120 or 240 V - Secondary winding, in your case 18 - 0 - 18 - VA rating, which is grossly the power the transformer can handle The 2nd one from Newark looks very nice, the first one can only deliver 4 VA... its going to fry.

31st July 2009, 08:59 PM	#17
netbug diyAudio Member Join Date: May 2009 Location: roseville, ca	This is what I'm running in a dual 3886 chipamp 25v+25v 250va http://www.parts-express.com/pe/show...number=122-625 Safe using 8ohm speakers a decent heatsink As stated earlier 18v+18v would be safe for 4ohm http://www.parts-express.com/pe/show...number=122-620

31st July 2009, 09:44 PM	#18
kizm0 diyAudio Member Join Date: Jul 2009	Didn't have to get to other people sending me their parts, but oh well.. Thanks a lot. I now have a better understanding of Transformers.

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

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