[jackman]

Hi Guys,

Ever since I moved into my new place, about a year and a half ago, my amp and preamp (Aragon 4004 amp and 24K pre) emit a low level mechanical hum from their respective transformers.  It's not audible from the speakers and is not noticeable when music is playing at normal levels but I'd appreciate any suggestions on how to eliminate or reduce it, DIY.

I'm thinking about getting the Channel Islands device which is supposed to filter out dc but I don't want to spend $300 if I can find a diy solution.  Your suggestions are appreciated.

Also, I'm thinking about changing the electrolytic ps caps because the existing ones are very old.  They are probably >15 years old.  The exisiting ones are 40 mfd, 120volts but I can't seem to find direct replacements.  The closest I could find are these from Apexjr at 68000 mfd, 100volts.  Will these work or should I try to find a closer replacement?  Any suggestions on capacitor suppliers?  Please note, I'm only using the amp to power my subwoofers in my active system. 



http://apexjr.com/capacitorsR.html#Computer

I've also seen the following caps from musicaldesign that are closer to the ones in my existing amp but they are much more expensive (see bottom of page):

http://www.musicaldesign.com/electrolytics.htm
Thanks!

Jack

[peranders]

You may need this, a DC trap?

[jackman]

You may need this, a DC trap?

How can I purchase one of those?  Can't figure out how to order.

Thanks,

J

[peranders]

You could send an email... 

[Haoleb]

If the filter capacitors are indeed 40uf (which is a very low amount of capacitance for filter capacitors) then 68,000uf is WAY to big. Do you mean 40,000uf? (same as mfd)

[jackman]

If the filter capacitors are indeed 40uf (which is a very low amount of capacitance for filter capacitors) then 68,000uf is WAY to big. Do you mean 40,000uf? (same as mfd)

Yow!  Sorry, it's 40,000uf.  Can I sub 68,000uf without causing any problems?  It is a robust design with dual transformers and looks to be heavy duty. 

[mgalusha]

Jack,

Another DIY alternative: http://www.audiocircle.com/index.php?topic=50908.10

Also see here: http://diyparadise.com/dablok.html

Mike

[jackman]

Jack,

Another DIY alternative: http://www.audiocircle.com/index.php?topic=50908.10

Also see here: http://diyparadise.com/dablok.html

Mike

Thanks Mike, I really appreciate your suggestions and the contribution you make to this site.  I'll let you know what happens!

J

[Haoleb]

Heres another version. I found the schematics for this on DIY audio.com I am not sure I would use it for a power amp though. Im only using it on my preamp. In conjunction with an isolation transformer so it really doesnt do anything since its inline after the transformer but I figure it cant hurt.

http://www.audiocircle.com/index.php?topic=48552.20

[Christopher Witmer]

You can increase the capacitance from 40,000uf to 68,000uf with no problem. However, if you are going from 120VDC to 100VDC caps, you might be cutting the margin of safety too low on the voltage rating of the caps. (I can't say for sure as I don't know the details of your amplifier.) As a general rule I would NOT recommend replacing your present P/S caps with lower voltage caps unless you know exactly what you are doing.

-- Chris

[jackman]

You can increase the capacitance from 40,000uf to 68,000uf with no problem. However, if you are going from 120VDC to 100VDC caps, you might be cutting the margin of safety too low on the voltage rating of the caps. (I can't say for sure as I don't know the details of your amplifier.) As a general rule I would NOT recommend replacing your present P/S caps with lower voltage caps unless you know exactly what you are doing.

-- Chris

Chris,

Thanks for the feedback.  I have been too busy to make the change, but I appreciate your advice.  So a 20 VDC difference in voltage rating may affect the safety of the amp?  I'm going to have to look for 120vdc caps. 

Does anyone have any recommendations of a good supplier of ps caps with 120vdc rating?  I've checked out Apexjr.com and a couple other sites but the other sites are either too exensive or they don't have proper rating.

Thanks,

Jack

[JoshK]

Best way to know is know what your rail voltages are in your amp.  Panasonic TSHA caps are about as good as they get if you can find the appropriate size. 

nevermind, the TSHA's don't come that big in that voltage rating. 

[mgalusha]

Jack,

I was able to locate a 4004 power supply schematic and it shows 4 x 19,000uF/80V caps, not 40,000/120V. It shows 70V on the rails so the 80V caps would be fine but I'm a bit confused by why your amp has 120V caps. Large high voltage electrolytic caps are expensive, they are large and cost more to manufacture. Like Josh I like the big Panasonic's, they work very well and are not over the top expensive.

PM me if you and and I'll email the schematics I found to you.

Mike

[mgalusha]

Hmm... looking at the main circuit schematic there are a pair of 47uF/100V caps on each rail to ground. You originally said 40mfd and the revised it to 40,000uF. Not sure if these are the same ones but I don't see anything that needs a 120V cap based on voltage.

mike

[jackman]

Hmm... looking at the main circuit schematic there are a pair of 47uF/100V caps on each rail to ground. You originally said 40mfd and the revised it to 40,000uF. Not sure if these are the same ones but I don't see anything that needs a 120V cap based on voltage.

mike

Hi Mike,

I bought the amp used and the pevious owner must have changed the PS caps.  The new ones are those big blue ones and are 120v caps.  Maybe I don't need to change them.  The caps in the picture are pretty inexpensive.  I might just get them and swap them for the existing ones as a fun summer project.

Thanks,

Jack

This is a stupid question but is there a way to test the PS caps or determine age?  Thanks again.

J

[Christopher Witmer]

Re: testing caps -- definitely not a stupid question, but Google is your friend:

http://www.google.com/search?hl=en&q=testing+capacitors

-- Chris