Output transformer for 845, GM70, 813 and FU-13 - cheap and good

audiodesign · 23rd September 2010, 08:53 AM

see measurements on:

GM70 amplifier with Fiat transformers

300 euro for a pair

audiodesign · 23rd September 2010, 09:03 AM

Here a my tests result with a 845 Valve Art at only 900V 90mA on 8ohm

45 · 23rd September 2010, 01:17 PM

It looks good at medium-low frequencies, although there is no info about distorstion at low frequency, for example. From the measurements and the other specs it appears to have significantly higher losses in treble region.
The great difference in primary and secondary DC resistances (the secondary resistance translated to the primary is about 325 ohms) makes me think that most of the useful winding space has been used to minimize the primary DC resistance.
As a starting point for me, the configuation for overall minimal losses is half space for the primary and half for the secondary because there is the possibilty to minimize the forgotten AC resistance of the windings which adds up to the DCR.
Basically here the high end response has been traded-off for more bass performance. It's a necessary compromise in affordable high power SE amps however this not necessarily is a bad thing for the final sonic performance.

45

audiodesign · 23rd September 2010, 05:03 PM

100Hz THD butthe distortion is of the 845 not of transformer

45 · 23rd September 2010, 05:18 PM

Quote:

Originally Posted by audiodesign

100Hz THD butthe distortion is of the 845 not of transformer

Yes, it is basically the same as at 1KHz.

45

audiodesign · 23rd September 2010, 06:07 PM

Yes, with the 900V and 90mA at 11.4Vrms we are near to the limit of the output characteristics of 845, near to A2 class operation with higher distortion level.

In the future I will make other test at 1100V and 70mA

SY · 23rd September 2010, 06:34 PM

So, is this an advertisement for transformers that you (or an associate) are selling?

audiodesign · 23rd September 2010, 06:57 PM

I would like to promote this article and get feedback about it.

This transformer have an insteresting price and it sound like more expensive products.

Like for all my projects I don't get money for this promotion.

I receive only materials to test and review with a good price reduction.

anatech · 24th September 2010, 01:01 AM

Hi audiodesign,

Quote:

I receive only materials to test and review with a good price reduction.

No matter what you want to call it, this is still paid advertising.

Still, nice to show members what is available and foster discussion. Of course, that can be a two edged weapon if they don't measure up.

-Chris

audiodesign · 23rd October 2010, 07:39 AM

News, first measurements on driver stage with Fiat choke

GM70 amplifier with Fiat transformers

EMU input

23rd September 2010, 08:53 AM	#1
audiodesign diyAudio Member Join Date: Sep 2005	Output transformer for 845, GM70, 813 and FU-13 - cheap and good see measurements on: GM70 amplifier with Fiat transformers 300 euro for a pair

23rd September 2010, 06:34 PM	#7
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	So, is this an advertisement for transformers that you (or an associate) are selling? __________________ If there's a sucker born every minute, where do the rest of them come from?

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23rd September 2010, 01:17 PM	#3
45 diyAudio Member Join Date: Dec 2008 Location: United Kingdom	It looks good at medium-low frequencies, although there is no info about distorstion at low frequency, for example. From the measurements and the other specs it appears to have significantly higher losses in treble region. The great difference in primary and secondary DC resistances (the secondary resistance translated to the primary is about 325 ohms) makes me think that most of the useful winding space has been used to minimize the primary DC resistance. As a starting point for me, the configuation for overall minimal losses is half space for the primary and half for the secondary because there is the possibilty to minimize the forgotten AC resistance of the windings which adds up to the DCR. Basically here the high end response has been traded-off for more bass performance. It's a necessary compromise in affordable high power SE amps however this not necessarily is a bad thing for the final sonic performance. 45

23rd September 2010, 06:57 PM	#8
audiodesign diyAudio Member Join Date: Sep 2005	I would like to promote this article and get feedback about it. This transformer have an insteresting price and it sound like more expensive products. Like for all my projects I don't get money for this promotion. I receive only materials to test and review with a good price reduction.

23rd October 2010, 07:39 AM	#10
audiodesign diyAudio Member Join Date: Sep 2005	News, first measurements on driver stage with Fiat choke GM70 amplifier with Fiat transformers EMU input