QED A240CD lacking bass.

pastedavid · 31st January 2010, 08:32 PM

Howdy.

I have a QED A240CD which works OK-ish, but really lacks what I'd call 'full bass'. It does output bass as low as the music source will provide, it's just not loud enough to compete with the rest of the audio spectrum. It's not the speakers or the source used - I have tested for this - it is definitely the amplifier.

I have it on Internet Authority(TM) that electrolytic caps don't last indefinitely -- and the life my amp leads (in the garage) probably won't help their longevity -- could this be the cause of the great bass drought?

Having said that, it's been pretty weedy since I bought it, so maybe it's just a weedy amp.

Thanks in advance for any help or suggestions offered.

Dave.

nigelwright7557 · 31st January 2010, 10:43 PM

Could be a design fault.
The feedback loop electrolytic should be quite a large value.
I have seen them as low as 1uF when I use a 220uF to stop losing bass.

Mooly · 1st February 2010, 07:05 AM

Get a CD with test tones on it, or use a signal generator of constant output and test it

Use a dummy load, 4.7 ohm wirewound would be ideal.
Use either a 'scope or a meter that is accurate over the audio band on AC and set the output to around 3 volts rms and make sure the output is the same at say 10hz and 20hz as it is at 50, 100, 1000 etc.

pastedavid · 1st February 2010, 11:19 AM

Thanks Nigel, I'll have a look for that.

pastedavid · 1st February 2010, 11:21 AM

Well, that certainly sounds like a plan, but... I don't have a sig. gen. or a o/scope!

Actually, thinking about it, I have an old unused laptop lying around... I can feel a plan coming together!

Cheers Mooly.

Mooly · 1st February 2010, 01:03 PM

You are welcome

brainf · 2nd February 2010, 04:21 AM

I recapped mine around two years ago. I replaced the original filter caps with 5600uF and the standard rectifiers with fast, soft recovery types.

The input (10uF) and feedback (1uF) bipolar capacitors in the power amp section are also electrolytic and should be replaced as well.

It was a worthwhile effort and expense

pastedavid · 3rd February 2010, 11:18 PM

So you have direct experience with this then, Brainf? Most encouraging! I think I shall take my time with this mini project and enjoy the task.

Also, what a great reason to make a new pair of loudspeakers!

Thanks.

brainf · 4th February 2010, 07:07 AM

Quote:

Originally Posted by pastedavid

So you have direct experience with this then, Brainf? Most encouraging! I think I shall take my time with this mini project and enjoy the task.

Also, what a great reason to make a new pair of loudspeakers!

Thanks.

Yes, it's a nice little amp and had pretty good reviews in its day.

Your post caught my eye because lacking bass it is not!

I have a scanned schematic with me should you like a copy. My pet project with the QED is to give it a new lease of life with updated and uprated components. Like you, I'm taking it slow too (backlog with other projects).

cheers!
leslie

pastedavid · 4th February 2010, 03:15 PM

Well thank you for the offer, Leslie. I will certainly take you up on it. It will be of great benefit to go into this project with a bit more knowledge on my side!

My email address is pastedavid at googlemail dot com with the obvious at and dot replaced with their proper equivalents!

Thanks again for your help,

David.

31st January 2010, 08:32 PM	#1
pastedavid diyAudio Member Join Date: Jan 2010 Location: N.W. England	QED A240CD lacking bass. Howdy. I have a QED A240CD which works OK-ish, but really lacks what I'd call 'full bass'. It does output bass as low as the music source will provide, it's just not loud enough to compete with the rest of the audio spectrum. It's not the speakers or the source used - I have tested for this - it is definitely the amplifier. I have it on Internet Authority(TM) that electrolytic caps don't last indefinitely -- and the life my amp leads (in the garage) probably won't help their longevity -- could this be the cause of the great bass drought? Having said that, it's been pretty weedy since I bought it, so maybe it's just a weedy amp. Thanks in advance for any help or suggestions offered. Dave.

31st January 2010, 10:43 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	Could be a design fault. The feedback loop electrolytic should be quite a large value. I have seen them as low as 1uF when I use a 220uF to stop losing bass. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

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1st February 2010, 07:05 AM	#3
Mooly diyAudio Member Join Date: Sep 2007	Get a CD with test tones on it, or use a signal generator of constant output and test it Use a dummy load, 4.7 ohm wirewound would be ideal. Use either a 'scope or a meter that is accurate over the audio band on AC and set the output to around 3 volts rms and make sure the output is the same at say 10hz and 20hz as it is at 50, 100, 1000 etc.

1st February 2010, 11:19 AM	#4
pastedavid diyAudio Member Join Date: Jan 2010 Location: N.W. England	Thanks Nigel, I'll have a look for that.

1st February 2010, 11:21 AM	#5
pastedavid diyAudio Member Join Date: Jan 2010 Location: N.W. England	Well, that certainly sounds like a plan, but... I don't have a sig. gen. or a o/scope! Actually, thinking about it, I have an old unused laptop lying around... I can feel a plan coming together! Cheers Mooly.

1st February 2010, 01:03 PM	#6
Mooly diyAudio Member Join Date: Sep 2007	You are welcome

2nd February 2010, 04:21 AM	#7
brainf diyAudio Member Join Date: Feb 2007 Location: Manila, Philippines	I recapped mine around two years ago. I replaced the original filter caps with 5600uF and the standard rectifiers with fast, soft recovery types. The input (10uF) and feedback (1uF) bipolar capacitors in the power amp section are also electrolytic and should be replaced as well. It was a worthwhile effort and expense

3rd February 2010, 11:18 PM	#8
pastedavid diyAudio Member Join Date: Jan 2010 Location: N.W. England	So you have direct experience with this then, Brainf? Most encouraging! I think I shall take my time with this mini project and enjoy the task. Also, what a great reason to make a new pair of loudspeakers! Thanks.

4th February 2010, 03:15 PM	#10
pastedavid diyAudio Member Join Date: Jan 2010 Location: N.W. England	Well thank you for the offer, Leslie. I will certainly take you up on it. It will be of great benefit to go into this project with a bit more knowledge on my side! My email address is pastedavid at googlemail dot com with the obvious at and dot replaced with their proper equivalents! Thanks again for your help, David.

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