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Old 26th November 2015, 06:05 PM   #1
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Default Uneven output from LL1677

Hi,
When measuring Lundahl LL1677 (4/4+4) as plate load/phase inverter for a E55L stage (despite that datasheet only note SE to SE application), I found out that output of the 2 phases are only even at lower frequencies (<1kHz) but go unevenly at higher frequencies (especially at 10kHz and up).
Anyone here have experienced similar issue and know how to solve it?
Thanks,
Duong
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Old 26th November 2015, 08:12 PM   #2
hpeter is offline hpeter  Slovakia
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schema?
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Old 26th November 2015, 09:48 PM   #3
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Quote:
Originally Posted by hoangduongo View Post
Hi,
When measuring Lundahl LL1677 (4/4+4) as plate load/phase inverter for a E55L stage (despite that datasheet only note SE to SE application), I found out that output of the 2 phases are only even at lower frequencies (<1kHz) but go unevenly at higher frequencies (especially at 10kHz and up).
Anyone here have experienced similar issue and know how to solve it?
Thanks,
Duong
the datasheet
" http://www.lundahl.se/wp-content/upl...heets/1677.pdf "
limits the current to < 100mA, and recommends 80mA

Whats you current ( and schematic ) ?
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Old 27th November 2015, 02:12 AM   #4
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Originally Posted by petertub View Post
the datasheet
" http://www.lundahl.se/wp-content/upl...heets/1677.pdf "
limits the current to < 100mA, and recommends 80mA

Whats you current ( and schematic ) ?
The schema is very simple, just a E55L (8233) in triode mode with this LL6277 as plate load. B+ is 200V, first I ran at 45mA idle current but it showed signs of saturation at below 100Hz so I reduced current to 30mA now. The secondary windings are loaded with two 82k resistor now.
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Old 27th November 2015, 02:51 AM   #5
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Along with uneven outputs, there's considerable phase shift at higher frequencies as well. Included is waveform of the 2 output from secondary windings (blue channel is inverted for easier comparison).
And I tried terminating the whole secondary winding with a LC network (22k series with 300pF) as suggested in datasheet, it did help a bit with the output level but the phase shift is still there.
Duong
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Old 27th November 2015, 10:36 AM   #6
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If they have specified it to be SE to SE then they haven't paid particular attention to matching the parasitics of the windings. You cannot realistically expect this transformer to behave in any other way than it is. You should be using a SE to PP transformer.

Shoog
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Old 27th November 2015, 04:11 PM   #7
hpeter is offline hpeter  Slovakia
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you havenīt still provided schematic, exact pinout how you wired the transformer..

already measured my irons, symmetrical output. i think you wired something wrong
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NOW: XMOS_U8/PCM5102A > LL1544A > ECC803JJ 12AX7WB_SOV > 2A3_SOV > LL1660 > STAX SR207//STAX SR007 ## LL2748 -> 394A

Last edited by hpeter; 27th November 2015 at 04:33 PM.
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Old 28th November 2015, 11:12 AM   #8
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Originally Posted by hpeter View Post
you havenīt still provided schematic, exact pinout how you wired the transformer..

already measured my irons, symmetrical output. i think you wired something wrong
Here's the schema, pretty ordinary I think. The LL1677 is wired follow schema in datasheet, as shown in photo.
And the load on secondary is no longer 82k, I tried replacing them with 10k per leg as you can see in photo, this helped balancing the output up to approx. 25kHz, but I lost a lot of output, distortion probably goes up and the phase shift is still there.
I really hope I wired something wrong, not because this IT is designed solely for SE to SE application
Thanks,
Duong
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Old 28th November 2015, 11:42 AM   #9
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In this situation heavy loading (10K) will probably not effect the distortion much. Not loading transformers enough is often the source of many response issues which represent far more distortion than when adequately loaded. Equal response out to 25khz is probably the best response you can expect and will be more than adequate for HIFI.

Have you checked for ringing on square wave response at various frequencies - this can be a much more serious issue with transformers.

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Old 28th November 2015, 11:49 AM   #10
jane is offline jane  Norway
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Quote:
Originally Posted by hoangduongo View Post
And the load on secondary is no longer 82k, I tried replacing them with 10k per leg as you can see in photo, this helped balancing the output up to approx. 25kHz, but I lost a lot of output
Lower drive impedance could make a difference.
Try to decouple the 100R cathode resistor.
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