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.
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.
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.
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.
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.
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.
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.
Actually, thinking about it, I have an old unused laptop lying around... I can feel a plan coming together!
Cheers Mooly.
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 🙂
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 🙂
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.
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
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.
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.
@ brainf,
hello, I was following this thread because I recently bought a QED 240CD, would it be too cheeky of me to ask a copy of the service manual? Thanks a lot.
my email address:
giuliano.gasparini at wspgroup.com
hello, I was following this thread because I recently bought a QED 240CD, would it be too cheeky of me to ask a copy of the service manual? Thanks a lot.
my email address:
giuliano.gasparini at wspgroup.com
QED 240CD Schematic
@ brainf,
I recently bought a QED 240CD too, and found this thread. Would it be too cheeky of me to ask a copy of the service manual too? Thanks a lot.
my email address:
pimd42 at hotmail.com
@ brainf,
I recently bought a QED 240CD too, and found this thread. Would it be too cheeky of me to ask a copy of the service manual too? Thanks a lot.
my email address:
pimd42 at hotmail.com
@brainf
Hello. I have a similar amp the A270 and every 2 years it blows a transistor near the input stage. I'm always curious to see a schematic to try to address the issue. If you still have the A240 manual, please email : mfrimu at gmail dot com
Thanks
Hello. I have a similar amp the A270 and every 2 years it blows a transistor near the input stage. I'm always curious to see a schematic to try to address the issue. If you still have the A240 manual, please email : mfrimu at gmail dot com
Thanks
@brainf
Hope this isn't getting too tedious for you but I have 2 QED 240 SAs, both with one channel down. I found one faulty pre-amp transistor in one but it hasn't sorted the fault. A schematic would be incredibly useful. Would you mind sending one to paulyrob at email dot com please?
Thanks in ants
Hope this isn't getting too tedious for you but I have 2 QED 240 SAs, both with one channel down. I found one faulty pre-amp transistor in one but it hasn't sorted the fault. A schematic would be incredibly useful. Would you mind sending one to paulyrob at email dot com please?
Thanks in ants