Output transformer for 845, GM70, 813 and FU-13 - cheap and good - diyAudio
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Old 23rd September 2010, 08:53 AM   #1
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Default 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
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Old 23rd September 2010, 09:03 AM   #2
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Here a my tests result with a 845 Valve Art at only 900V 90mA on 8ohm
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Old 23rd September 2010, 01:17 PM   #3
45 is offline 45  Italy
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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.

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Old 23rd September 2010, 05:03 PM   #4
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100Hz THD butthe distortion is of the 845 not of transformer
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Old 23rd September 2010, 05:18 PM   #5
45 is offline 45  Italy
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Quote:
Originally Posted by audiodesign View Post
100Hz THD butthe distortion is of the 845 not of transformer
Yes, it is basically the same as at 1KHz.

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Old 23rd September 2010, 06:07 PM   #6
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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
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File Type: gif 845plot_900v_90mA.gif (76.9 KB, 771 views)
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Old 23rd September 2010, 06:34 PM   #7
SY is offline SY  United States
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So, is this an advertisement for transformers that you (or an associate) are selling?
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Old 23rd September 2010, 06:57 PM   #8
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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.
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Old 24th September 2010, 01:01 AM   #9
anatech is offline anatech  Canada
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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.

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Old 23rd October 2010, 07:39 AM   #10
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News, first measurements on driver stage with Fiat choke

GM70 amplifier with Fiat transformers

EMU input
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