Beefing up a receiver for a 4ohm load?

Marcel_D · 22nd December 2010, 08:47 PM

I garbage picked this Teac A-X750 stereo receiver and I just finished going through it cleaning the pots and whatnot. Sounds pretty decent, other than the fact that turning the Treble knob all the way up seems to create a ~30Hz oscillation at maximum volume.

I think I blew both my tweeters in my DIY speakers after that happened.

I also have this Klipsch sub which is rated at 4 ohms and its class D amp has died without a trace of failure so I want to take the Teac receiver and use it as a sub amp. Just temporarily at least. It's rated for a minimum of 8 ohms per channel, so I was basically wondering what it would take to make 1 channel of this thing be able to handle a 4ohm load rather than an 8? Like since I'll be running only 1 channel, the PSU should be fine right? It would see a single 4ohm load the same way as 2 8 ohms.

What else would it take? Some bigger outputs and biasing resistors?

Tekko · 22nd December 2010, 08:57 PM

For sub use you have join the two channels with two 1ohm or less resistors at the speaker outputs and just parallel the inputs and hook that to a subwoofer filter.

nightanole · 22nd December 2010, 08:58 PM

Normally the 4ohm/8ohm switch changes the B+ to keep the watt output the same. So you might be ok as long as you dont turn it up too high.

Other then that you would have to rewire the b+ inside the unit to put out 1/3 less voltage.

You should be fine as long as your keep the output at 2/3's or less.

Marcel_D · 22nd December 2010, 09:13 PM

Quote:

Originally Posted by Tekko

For sub use you have join the two channels with two 1ohm or less resistors at the speaker outputs and just parallel the inputs and

Last night I was searching the web trying to figure how to bridge any old amp and the whole time I was wondering why can't I just parallel the outputs? So the purpose of that resistor is to keep one channel from trying to drive the other? Or what is it for?

And nightanole, I was thinking the same thing. Just don't do anything and keep the volume relatively low. Back in my dumber days, I tried to drive a pair of 4ohm 10" car subs in parallel off an old Harman Kardon 40wpc integrated amp. Let's just say the only sound it produced was the clicking of the protection switches every time I turned up up past 1/4 of the way. It was like no sound, then click.

Tekko · 22nd December 2010, 09:19 PM

Yes and in case the two channels have a different dc offset. Same principle as when you parallel LM3886's and other chipamps, current sharing.

Marcel_D · 22nd December 2010, 10:14 PM

How about 0.1ohm, 1W?

So if the DC offset is wildly different (I'll check it), there could be a nasty bit of current flowing with this low of resistance yeah? So why not use like a resistor with a huge resistance instead?

22nd December 2010, 08:47 PM	#1
Marcel_D diyAudio Member Join Date: Oct 2007	Beefing up a receiver for a 4ohm load? I garbage picked this Teac A-X750 stereo receiver and I just finished going through it cleaning the pots and whatnot. Sounds pretty decent, other than the fact that turning the Treble knob all the way up seems to create a ~30Hz oscillation at maximum volume. I think I blew both my tweeters in my DIY speakers after that happened. I also have this Klipsch sub which is rated at 4 ohms and its class D amp has died without a trace of failure so I want to take the Teac receiver and use it as a sub amp. Just temporarily at least. It's rated for a minimum of 8 ohms per channel, so I was basically wondering what it would take to make 1 channel of this thing be able to handle a 4ohm load rather than an 8? Like since I'll be running only 1 channel, the PSU should be fine right? It would see a single 4ohm load the same way as 2 8 ohms. What else would it take? Some bigger outputs and biasing resistors?

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22nd December 2010, 08:57 PM	#2
Tekko diyAudio Member Join Date: Jan 2005	For sub use you have join the two channels with two 1ohm or less resistors at the speaker outputs and just parallel the inputs and hook that to a subwoofer filter.

22nd December 2010, 08:58 PM	#3
nightanole diyAudio Member Join Date: Feb 2009	Normally the 4ohm/8ohm switch changes the B+ to keep the watt output the same. So you might be ok as long as you dont turn it up too high. Other then that you would have to rewire the b+ inside the unit to put out 1/3 less voltage. You should be fine as long as your keep the output at 2/3's or less.

22nd December 2010, 09:19 PM	#5
Tekko diyAudio Member Join Date: Jan 2005	Yes and in case the two channels have a different dc offset. Same principle as when you parallel LM3886's and other chipamps, current sharing.

22nd December 2010, 10:14 PM	#6
Marcel_D diyAudio Member Join Date: Oct 2007	How about 0.1ohm, 1W? So if the DC offset is wildly different (I'll check it), there could be a nasty bit of current flowing with this low of resistance yeah? So why not use like a resistor with a huge resistance instead?

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