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Are line harmonic suppression filters ever used for audio amplifiers?
Are line harmonic suppression filters ever used for audio amplifiers?
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Old 19th September 2019, 05:39 AM   #1
Hari is offline Hari  India
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Default Are line harmonic suppression filters ever used for audio amplifiers?

Line frequency harmonic supression filters are quite common in power electronics for industrial use where lots of AC motors, inverters and welding and other power euipmenets are used. These usually supress the harmonic freunccy from 3rd to 20th harmonic and allows pure sine wave to the load. The fundamental frequency here is 50Hz and harmonic supression will be for 150Hz and above.

Are such kind of filters also relevant for use with audio gear? Actually i tried building one with CFL chokes and capacitors and found the tube amplifier power transformer pretty cold even after 2+ hours of use. Also the sound was free of any harshness and sparkle and the mids very very open and less listening fatigue. Would be glad to hear from experts here. I am not sure if this is how music should be as the extra sparkle from the music has just vanished for the better.

Last edited by Hari; 19th September 2019 at 05:41 AM.
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Old 19th September 2019, 07:24 AM   #2
TBTL is offline TBTL  Germany
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Apart from EMI compatibility, if the there is a problem with strong harmonics in an audio device, the problem would be that these somehow manage to enter the audio signal path, which reveals itself as hum or buzz. The power supply itself does not care too much about what the input wave looks like.

Last edited by TBTL; 19th September 2019 at 07:27 AM.
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Old 19th September 2019, 08:17 AM   #3
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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EMI filters are employed with switch mode power supplies to stop interference from the power supply entering the household supply and then the national grid/supply lines or whatever your country calls it.
The have no effect on the amplifiers ability to have improved sound!
A simple 100nF 250v class X capacitor across the supply to your valve amplifier is sufficient to remove any mains born noise.
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Old 19th September 2019, 09:56 AM   #4
Hari is offline Hari  India
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Thanks TBTL, Jonsnell for your reply.

I am not referring to any EMI or RF noise that gets picked up in the supply line from the utility company to our home wall outlet but the harmonics of the fundamental 50Hz frequencies which are quite a bit till 11th or 19th harmonics. This would be less to do with the power supply of the amplifier as they do have large capacitors and small ones to filter the ripple. The harmonic filter mostly i think is helping the amplifier transformer as they are now not heating up as before - so implying low core and eddy current losses. Also i am getting quite a different sound with and without this filter. Without the filter, the transformer is warm in 15 mintues and quite hot in 45 minutes. Now they are barely warm with 2+ hours of use.

As most of us are tuned to listen to coloured sound, first listen with this harmonic filter will give a feeling of something is suck out of music with reduced sparkle, brillance and less energy. But after careful listening for 15+ minutes i am feeling much relaxed, enjoyable and pleasant. Even my wife and daughter noticed this and asked me why the setup is now very quite unlike before. Looking for answers.

Last edited by Hari; 19th September 2019 at 09:59 AM.
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Old 19th September 2019, 11:44 AM   #5
ApolloZhang is offline ApolloZhang  Europe
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Thought the harmonic suppresors are these kinda active filter that samples the harmonic frequence and inject the opposite wave via an IGBT into the powerline, but it seems Hari you are talking about a LC Filter on the powerline? IMO it is a very common product for the commercial HiFi market, can reduce harshness and brightness in the treble. But those products are mostly named power conditioner and cost lots of money.
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Old 19th September 2019, 01:10 PM   #6
Hari is offline Hari  India
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ApolloZhang, thanks for confirming. I have used a simple LC filter for this and it reduces the harshness quite a lot.
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Old 19th September 2019, 02:06 PM   #7
Pano is offline Pano  United States
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Are line harmonic suppression filters ever used for audio amplifiers?
Are your filters before or after the transformer? After the rectifiers?
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Old 19th September 2019, 02:45 PM   #8
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Be care about the use of such filters. If they enters in resonance between them and the power trafo or any reflected capacitive or inductive suceptance from the secondary(ies), at the line frequency or their harmonics, unexpectedly high voltages or currents can flow in the circuit causing burning, explosion or fire.
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Old 19th September 2019, 04:19 PM   #9
Hari is offline Hari  India
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Quote:
Originally Posted by Pano View Post
Are your filters before or after the transformer? After the rectifiers?
They are before the transformer on the primary side. May be i shall post a schematic and image tomorrow.

Last edited by Hari; 19th September 2019 at 04:23 PM.
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Old 19th September 2019, 04:22 PM   #10
Hari is offline Hari  India
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Quote:
Originally Posted by Osvaldo de Banfield View Post
Be care about the use of such filters. If they enters in resonance between them and the power trafo or any reflected capacitive or inductive suceptance from the secondary(ies), at the line frequency or their harmonics, unexpectedly high voltages or currents can flow in the circuit causing burning, explosion or fire.
Thanks for informing. This filter is in parallel to the transformer primary and offers high impedance for 50Hz and from 150Hz onwards a relatively low impedance for the harmonics. This needs to be switched on/off along with the amplifier for resonance to match exactly at 50Hz else they will fail. I have been using it for past one week and have not seen any component heating of the choke or the capacitors, though i have used them around 2 to 3 hrs on a daily basis past one week. I will keep a note and post again.
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