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HPF on a TA2020 |
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scott_fury 
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Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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 Topic: HPF on a TA2020Posted: 18 July 2014 at 2:26pm |
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Hello!
I've been doing a few tests on my 12V rig, and have been putting a sine wave through the car audio crossover I'm using to split the signal into a couple of TA2020 amps. Basically the crossover I have is rubbish. I have no high pass filter at all, and would like to have something that removes anything below 50-60Hz if possible? The amp I have is a cheapo ebay Yuangjing type TA2020...   By the looks of it, the signal comes from the input through the volume pot and the a 1,8uF cap and then onto the resistors before getting to the TA2020 chip. I've had a look at a few posts and admit my eletronic skills are basic, but have been led to believe that the cap on the input can be swapped in order to change the HPF to around 50Hz? All the ciruit diagrams I have seen (mainly the Lepai) show the input cap as 2.2uF, and I have read a previous post that says if this was changed to a 100nF and 47nF cap in parallel, this would do the job? Basically, is that 1,8uF cap the one that would need replacing, and would a couple of these do the job? http://www.maplin.co.uk/p/multilayer-metallised-polyester-film-100nf-capacitor-dt98 http://www.maplin.co.uk/p/multilayer-metallised-polyester-film-47nf-capacitor-dt97f THANKS!!! Edited by scott_fury - 18 July 2014 at 2:35pm |
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bitSmasher
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Joined: 23 June 2012 Location: Melbourne Status: Offline Points: 2296 |
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Posted: 18 July 2014 at 4:56pm |
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really interested in this idea, have that amp too just waiting to do something with it - if I you can work out a HPF it'll help with my silly suitcase system idea
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scott_fury
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Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Posted: 18 July 2014 at 5:55pm |
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I haven't found any reliable info on it, but the Lepai TA2020+ has an input impedance of 47k ohms, so actually a 100nF capacitor should cut off at 33.8Hz at -3db. A 47nF and a 22nF in parallel would give a cutoff at 49Hz at -3db, which is probably better for small 12v rig.
Just not 100% that the 1,8uF Cap is the one to swap? Got to use my rig tomorrow, so won't risk anything tonight, but the only way to know might be to just suck it and see!  Edited by scott_fury - 18 July 2014 at 6:30pm |
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mini-mad
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Joined: 13 July 2012 Location: london Status: Offline Points: 6903 |
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Posted: 18 July 2014 at 9:35pm |
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suck it and see.... run pink noise through your computers sound card and use a free spectrum analyser programme for ya fone and see how ruff the two caps panned out.... couldnt hurt could it!
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If it sounds like a gorilla is trying to escape, turn it down.
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scott_fury
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Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Posted: 18 July 2014 at 10:23pm |
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"They couldn't hit an elephant at this dist....." Famous last words. |
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mini-mad
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Joined: 13 July 2012 Location: london Status: Offline Points: 6903 |
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Posted: 18 July 2014 at 10:30pm |
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strap on a set and get on with the modding!..... one of the other forums i frequent "if it aint broke, mod it til it is!" Edited by mini-mad - 18 July 2014 at 10:30pm |
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If it sounds like a gorilla is trying to escape, turn it down.
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lutkeveld
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Joined: 23 September 2013 Location: The Netherlands Status: Offline Points: 517 |
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Posted: 18 July 2014 at 10:33pm |
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Just keep in mind that a 1st order filter doesn't have a perfect rolloff. It starts way after the point you choose. So if you don't want any rolloff before 50hz, you shouldn't choose 49hz.
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scott_fury
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Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Posted: 18 July 2014 at 11:38pm |
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Thanks for the advice lutkeveld. Honestly, I'm not sure what I want until I hear it, so may have to play about until I find a good balance between removing some of the unwanted or not needed low frequencies to help my drivers perform a little better, and still keeping enough of the low end to satisfy my desire for bass! The quick play I did with a tone generator showed that drivers and tuning of the box works really well from 60Hz up, so would be happy to lose anything else underneath.
My vague understanding is that a first order filter would have a slope of 6db/octave? It would be 50Hz at -3db and 25Hz at -9db? Maybe these would be better.... http://www.maplin.co.uk/p/wima-polypropylene-metal-foil-1250v-0068uf-capacitor-n41cn http://www.maplin.co.uk/p/wima-polypropylene-metal-foil-1250v-0047uf-capacitor-n40cn The 0.047uF cap should have a cut-off at 72Hz at -3db. If the slope is 6db/Octave then it would be about 36Hz at -9db? Looks like either of these might just fit in the place of the 1,8Uf Wima cap that's already in the amp... or is that asking too much? |
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scott_fury
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Posted: 18 July 2014 at 11:52pm |
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I've learnt everything I know by breaking everything I own |
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mini-mad wrote: