Using mains transformer as output transformer - Page 4

Elias · 8th September 2008, 07:13 AM

The compensation current seems to be quite critical. Here's the response at -5%. Again at 20Hz.

Elias · 8th September 2008, 07:14 AM

And the same at +5%:

Elias · 8th September 2008, 07:16 AM

At 80Hz saturation seems to be reduced a bit, but still visible. Here's response without compensation at 0.5W 80Hz:

Elias · 8th September 2008, 07:20 AM

And 80Hz with compensation. Not only amplitude but also phase is corrected!

Using DC compensation freq response is much improved. Without compensation -3dB is at 80Hz. With compensation freq response is 0dB at 20Hz and -1.6dB at 20kHz. Cannot test lower than 20Hz with my signal generator, but it seems to go really low.

Overall quite promising results

- Elias

ErikdeBest · 8th September 2008, 07:28 AM

Hi Elias

Very interesting that you put your ideas to practice!

May I ask what method you used for DC compensation?

Erik

Elias · 8th September 2008, 08:34 AM

Hello Erik,

The compensation is very simple. I feed DC current from voltage source of about 270mA to the 43V secondary through 100ohm resistor. I know it loads the primary a bit, better would be using current generator with high impedance. That would be one of the next steps I'm planning to do. However, the impedance level propably is not a big issue.

- Elias

jerluwoo · 8th September 2008, 10:54 PM

Have you tried simply grounding the cathode through the secondary so that you have the same amount of dc through primary and secondary? Curious if this would have a cancelling effect on saturation or not.

john_ellis · 8th September 2008, 11:02 PM

Hi Elias

I don't think transformers like to be treated the way you supposed. If you are going to the trouble of adding a compensating DC current, why not operate two valves in Class A push-pull?

The problem is that the offset current does nothing for the signal, but adding another valve on the other primary winding would make use of that winding, give you twice the power, and reduce the DC all in one go.

cheers

John

316a · 8th September 2008, 11:02 PM

Quote:

Originally posted by Elias
And 80Hz with compensation. Not only amplitude but also phase is corrected!

Using DC compensation freq response is much improved. Without compensation -3dB is at 80Hz. With compensation freq response is 0dB at 20Hz and -1.6dB at 20kHz. Cannot test lower than 20Hz with my signal generator, but it seems to go really low.

Overall quite promising results
- Elias

Well done ! Are you going to share the design ? I'm surprised at your upper rolloff . I got -0.5dB down at 20khz using a 6B4G into a 230:9+9 Talema 30VA unit .

cheers

316A

poynton · 9th September 2008, 05:20 AM

Probably due to the size of the Tx

Andy

8th September 2008, 07:28 AM	#35
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Hi Elias Very interesting that you put your ideas to practice! May I ask what method you used for DC compensation? Erik __________________ my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!

8th September 2008, 08:34 AM	#36
Elias diyAudio Member Join Date: May 2003 Location: Where you live	Hello Erik, The compensation is very simple. I feed DC current from voltage source of about 270mA to the 43V secondary through 100ohm resistor. I know it loads the primary a bit, better would be using current generator with high impedance. That would be one of the next steps I'm planning to do. However, the impedance level propably is not a big issue. - Elias __________________ Reinventing the wheel ! Free wavelet software for audio analysis click here!

9th September 2008, 05:20 AM	#40
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	Probably due to the size of the Tx Andy __________________ If it ain't broke, break it !! Then fix it again. It's called DIY !

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8th September 2008, 11:02 PM	#38
john_ellis diyAudio Member Join Date: Sep 2006	Hi Elias I don't think transformers like to be treated the way you supposed. If you are going to the trouble of adding a compensating DC current, why not operate two valves in Class A push-pull? The problem is that the offset current does nothing for the signal, but adding another valve on the other primary winding would make use of that winding, give you twice the power, and reduce the DC all in one go. cheers John

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