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Old 2nd April 2010, 06:28 AM   #1
bunshi is offline bunshi  United States
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Default Weird way of powering a sub for cheap - quick question.

I can buy a cheap, old stereo receiver on CL for about 20$.

I want to build a sub, and I don't want to buy an expensive plate amp for it. Since my yamaha HT receiver doesn't power a sub, can I just buy an extra receiver from CL and use it to just power my sub with minimal negative effects?

-Bunshi
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Old 2nd April 2010, 07:09 AM   #2
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I have done this. You will still need an XO.

Jack Hidley is selling exNHT Foster plate amps for $35. That is probably better value.

NHT drivers and electronics surplus sale

dave
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Old 2nd April 2010, 07:24 AM   #3
bunshi is offline bunshi  United States
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You are right that I still need an XO.

What I'm going to do is use the active XO in my yamaha receiver as per Zaph (these are also the speakers I built). He just has a section on using an active subwoofer. EDIT forgot link: http://www.zaphaudio.com/audio-speaker18.html

Thanks for the feedback!
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Old 2nd April 2010, 05:13 PM   #4
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Older amps tend to need PSU caps replacing, to release their full potential. Being electrolytics, they dry up and lose capacitance. Replacing them with new ones of the original value will help things. If you want to take things further, raising the value may help. I found it did with my newer amp - it used to have 2x3,300uF caps, now it's 2x10,000uF. This greatly improved power output before distortion, so trying something like that might work too.
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Old 22nd April 2010, 11:44 AM   #5
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Default Can you explain this please

Quote:
Originally Posted by planet10 View Post
I have done this. You will still need an XO.


dave
Hi
Completely new to this, but have had the same thought about how to power a sub. I had assumed the Sub out from the HT would be fine into (almost any?) amp. The above suggests not. Can someone explain what else is needed and why.

Thanks

Lewis
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Old 22nd April 2010, 01:19 PM   #6
vadi is offline vadi  Austria
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I'd guess that the sub-out only works on DolbyDigital tracks for example. The LFE track shouldn't contain higher frequencies but for any other source, you'd need a XO. You'd probably want a subsonic filter too.
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Old 22nd April 2010, 01:38 PM   #7
jwmbro is offline jwmbro  United States
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Quote:
Originally Posted by Renovator View Post
Hi
Completely new to this, but have had the same thought about how to power a sub. I had assumed the Sub out from the HT would be fine into (almost any?) amp. The above suggests not. Can someone explain what else is needed and why.

Thanks

Lewis
This will probably depend on what HT Receiver you are using.

My Yamaha RX-V659 outputs a lowpassed signal out of its LFE out jack.

Which is why I am currently using an RCA splitter connected to the back of a cheap stereo amp to drive my two prototype subwoofers.

I can report, it works just fine. I tested test tones (30Hz, 50Hz, 140Hz, 440Hz) with the speakers turned on and off, and can report that, when the speakers are off, there is no output at 440Hz and hardly any at 140Hz, which is in accordance with what you would expect from a 100Hz lowpass at the subwoofer.

So I can report nothing negative from using a Home Theater receiver and a cheap stereo amp for the sub(s).

Just make sure your receiver lowpasses the LFE-out.
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Old 23rd April 2010, 11:46 AM   #8
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This is what I do. My Adire Tempest tubesub is powered by 2x50W amplifier and I've never felt the need to try it with more power.

As mentioned, the only thing missing is an adjustable rumble filter which could be useful to protect your driver in a ported design. This cuts the frequencies below eg 20Hz. You are probably trying to get as low extension as possible, that's why this filter is preferably adjustable.
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Old 23rd April 2010, 11:58 AM   #9
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You don't need a low pas s filter , your receiver will have one built in.

If you want to do it really cheap ,do what i did:

My first build

I am currently running mine off a 2 x 50W amplifier ( lm3886 chipamp) and i have to confess it is actually MORE than enough , but i am in for another project so i am going to build a stronger amp for it anyway.

I would suggest using two woofers then using both channels on you amplifier out like i did.

The woofers i used wasn't really effecient for lower than 60Hz so i EQ's the !@# out of it with a linkwitz transform and 2 way paramteric filter. But if you buy a halfway decent sub yours should by just fine.
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Old 23rd April 2010, 12:04 PM   #10
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you can set most receivers ( i do on mine) to also use the sub when listening to music.

So that when you are using only stereo lower than 80hz still goes to the sub.
On my Rotel 985rsp stereo sub mode is switchable. As i would guess most receivers can do.

So you have three options.

1) no sub at all
only 5 channel out and sub channel will be put on front/large speakers

2) sub + 5 channels for 5.1 source
2.0 for 2 channel source

3) sub + 5 channels for 5.1 source
2.1 for 2 channel source

I tend to switch between mode 2 and mode 3 depending on mood.
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