Thule Audio's Universal Inrush Current Limiter for their Amplifiers - very special? - diyAudio
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Old 10th February 2010, 05:53 PM   #1
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Default Thule Audio's Universal Inrush Current Limiter for their Amplifiers - very special?

In serial to the good known NTC resistor especially for inrush current limiting there is additional a serial network that consist two diodes for bi-directional 0V7 voltage loss (sometimes four pieces for 1V4 voltage loss) and two caps.
Because I don't know the right keyword for this circuit, I haven't success by google to get more information. Is it an ordinary idea or is it very special?

I want to know the theory of operation and calculation advices for the necessary voltage loss and the capacity value refer to the individual inrush current behaviour of the transformer.

If there is to this inrush current limiting circuit a good known keyword, please let me know.

Thank you very much for your advices
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File Type: pdf Thule Audio Inrush current Lim.pdf (13.5 KB, 938 views)
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Old 10th February 2010, 06:11 PM   #2
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I do not know anything specific about the circuit, but maybe I can give you a vague clue of where to find out.
Kim Neeper once worked at Thule audio, which is now out of business, he started his own company a few years ago called Neeper Acoustics. You might find him here ((o Neeper Acoustics o)) - contact . Maybe he knows about the circuit or maybe he knows where to find Anders Thule, who was the engineer and designer behind all thule´s audio gear.

Good luck
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Old 10th February 2010, 06:42 PM   #3
Eva is offline Eva  Spain
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Those capacitors and diodes work as a high-pass filter that prevents the transformer from seeing the small DC component often found in mains voltage. The diodes protect the capacitor(s).

The circuit is commonly called a "DC filter", and its practical purpose is to prevent transformers from buzzing and leaking magnetic flux. It's particularly useful with high power toroids because they saturate easily when mains waveform contains some DC.
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Old 10th February 2010, 06:43 PM   #4
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I believe that is to keep DC off the transformer primary.
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Old 10th February 2010, 07:54 PM   #5
Dr_EM is offline Dr_EM  United Kingdom
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Quote:
Originally Posted by Eva View Post
Those capacitors and diodes work as a high-pass filter that prevents the transformer from seeing the small DC component often found in mains voltage. The diodes protect the capacitor(s).
That's what I was thinking, quite a neat idea. I may need to add one of these into my amplifiers as I periodically get an "aggressive" humming sound from the toroids inside which I attribute to DC on the mains.
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Old 10th February 2010, 08:13 PM   #6
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Quote:
Originally Posted by Eva View Post
Those capacitors and diodes work as a high-pass filter that prevents the transformer from seeing the small DC component often found in mains voltage. The diodes protect the capacitor(s).

The circuit is commonly called a "DC filter", and its practical purpose is to prevent transformers from buzzing and leaking magnetic flux. It's particularly useful with high power toroids because they saturate easily when mains waveform contains some DC.
I see - thank you very much. Now I have found some informations and circuit concepts therefore:
L C Audio Technology / DC Filter
Christian's Homepage (scoll down)
Soft Start and Standby Functions for your Aleph Amplifier (post # 10)
Buzzing mains Transformers - World-Designs-Forum
Mains dc filter instructions - World-Designs-Forum
What Hi-Fi? Sound and Vision - Mains DC Blocking help
dc filter
Getting rid of transformer hum [Archive] - Audioholics Home Theater Forums
High voltage engineering and testing - Google Bücher


Kurt von Kubik: thank you for this URL. I will ask them now regarded the software for Thule's costom pragrammable operating MCU's from Atmel - used in all pre- and integrated amplifiers from Thule Audio. I ask in this case this by this thread:
What happen to thule audio?
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File Type: pdf Main DC Filter.pdf (54.7 KB, 351 views)

Last edited by tiefbassuebertr; 10th February 2010 at 08:16 PM.
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Old 11th February 2010, 12:19 PM   #7
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The best Informations from URLs mentioned in my previous post I get from this two:
dc filter (basics - even from Mr. Nelson Pass about post #2)
Soft Start and Standby Functions for your Aleph Amplifier (schematic post # 10)

In the PDF attachement a stored website (in the meantime death) from a slightly different DC blocker topology:
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File Type: pdf Main DC Blocker.pdf (35.7 KB, 327 views)

Last edited by tiefbassuebertr; 11th February 2010 at 12:21 PM.
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Old 11th February 2010, 03:37 PM   #8
h_a is offline h_a  Europe
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As many said already that's the standard DC-filter, seen e.g. in Bryston amps.

Please use only these simple variants (single cap with a single diode bridge).

There exist so many DIY designs out there that are just dangerous (many diodes in series...) as they allow the reverse polarity of the cap to become larger than 1.6V-2V. At this point electrochemical reactions start in the cap, heat it up and let it explode if this voltage lasts long enough.

Stay safe, Hannes
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Old 11th February 2010, 08:37 PM   #9
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Quote:
Originally Posted by h_a View Post
As many said already that's the standard DC-filter, seen e.g. in Bryston amps.
Please use only these simple variants (single cap with a single diode bridge).
There exist so many DIY designs out there that are just dangerous (many diodes in series...) as they allow the reverse polarity of the cap to become larger than 1.6V-2V. At this point electrochemical reactions start in the cap, heat it up and let it explode if this voltage lasts long enough.
Stay safe, Hannes
You are right. Even the circuit topology of Bryston is highly controversial.
Therefore electrolytic capacitors with enhanced reverse voltage (above 2V) wanted and necessary.
The best solution are foil caps - I think; maybe the new Wima or
EPCOS Series http://www.epcos.com/inf/20/20/ds/MKT_B32520_29.pdf
mentioned about
220uF caps in MKT technology for PCB mounting

In generall, I have found now several variants of such DC blockers and I am a little confused. By all variants I discover shortcomings as follow:

1) An often observed anti-serial (back to back) interconnect of two electrolytics without parallel resistors for an equal sharing of each half-voltage I always missed, also about
Soft Start and Standby Functions for your Aleph Amplifier (go to PDF from post #10)
Even Mr. Nelson Pass don't mention this resistors by post #2 about
dc filter
As far as I know, an operation without the parallel resistance isn't permitted (except if there are should be electrolytic caps with integrated resistors)

2) back-to-back operation by electrolytics in series without anti-parallel voltage protection diodes

3) The opposite, i. e. anti-parallel diodes without electrolytics (ASR Schäfer)

4) anti-parallel electrolytics without diodes connected in anti-parallel for over voltage protection

5) anti-parallel electrolytics with diodes connected in anti-parallel. Mostly to see, also by Bryston and Thule Audio, but what advantage I get through anti-parallel electrolytics instead anti-serial (back to back) interconnect include parallel resistors ? Anti-parallel connected electrolytics I have never seen anywhere except this DC blocker stuff.

Currently, a lot more questions than answers. Because there are too many terms for this DC blocker circuit, it is very hard to get a sufficient overview.

What is now the royal way for such mains filter resp. mains DC blocker to block DC components from my otherwise singing and buzzing torodial main transformer ?
I guess a corresponding number of parallel EPCOS foil's MKT's together with the suitable anti parallel connected diodes (possibly suitable anti parallel connected diode serial networks of two or three serial diodes)
Or an complete other solution that meets the same purpose.

Here an URL collection in this subject

http://electrochem.cwru.edu/encycl/a...electr-cap.htm
(ELECTROLYTIC CAPACITORS - basic description)


DC-Offset, Elektronik - HIFI-FORUM (forum buzzing transformers)
Line Silencer (Horch - who knows URLs in english?)
http://www.horch-elektroakustik.de/P...20Silencer.pdf
Line Silencer

Power Controller (Omtec)
http://www.dienadel.de/cosmoshop/artikelpdf/27871_d.pdf

Diy Mains DC Blocker (DC-Netzfilter)
Netzfilter selber bauen: wer macht mit?, Elektronik - HIFI-FORUM (schematics)
DC Filter für 10€ (schematics)

ASR (some images)
Stammtisch für HiFi- und Musik-Freunde | Stromversorgung | DC-Offset im Netz: Gleichspannungsfilter


Bryston (schematic include DC blocking stuff)
http://bryston.com/BrystonSite05/pdf...28Nov01%29.pdf

Last edited by tiefbassuebertr; 11th February 2010 at 08:50 PM.
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Old 11th February 2010, 09:10 PM   #10
qsa is offline qsa  Germany
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Hallo tiefbassuebertr

sehe Du kommst aus meiner alten Heimat...ziemlich aufwendig die ganzen Netzfilter etc... Mit reiner Stromversorgung für den HI-FI Amp ist eine Menge Geld zu machen, meine EX fand Hi-Fi Messen auch immer sehr lustig...meiner Meinung nach mit eher zweifelhaftem Nutzen ausser hohen Kosten für den Enduser....aber ich sag mal nix weiter dazu wir wollen ja alle verdienen...bist auch im PA Forum aktiv?



Gruss

Last edited by qsa; 11th February 2010 at 09:15 PM.
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