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Chip Amps Amplifiers based on integrated circuits

LM3875 Kit Finished - Could use some more bass
LM3875 Kit Finished - Could use some more bass
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Old 16th March 2008, 10:04 PM   #11
Peter Daniel is offline Peter Daniel  Canada
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LM3875 Kit Finished - Could use some more bass Send a message via AIM to Peter Daniel
PS is the same for LM3875 and LM4780 and schematic can be found here: http://audiosector.com/lm4780%20psu.pdf

Rz and Cz on amp board are Zobel components and suggested values are 2R7 and 0.1uF.

Gaincard uses 10R and 0.1uF. I don't use Zobel network, as I prefer the sound without those components.
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Old 16th March 2008, 10:10 PM   #12
johan851 is offline johan851  United States
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Great, thanks.
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Old 16th March 2008, 10:37 PM   #13
johan851 is offline johan851  United States
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One more thing - I can't seem to find appropriate capacitors at Digikey or Mouser. Does anyone have suggestions for big caps in the 10mF to 22mF range?
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Old 16th March 2008, 10:50 PM   #14
seventenths is online now seventenths  United States
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If you're needing an immediate fix, Vetco in Bellevue has Nichicon 6800uF 35V in stock.



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Old 17th March 2008, 12:36 AM   #15
Steve M is offline Steve M  Australia
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I'm not sure extra power supply caps is going to make your chip amp give better bass 'output' (which they seem to lack?), it might improve tautness and bass 'quality' though.

I have an LM3876T amp which is the same as 3875, but with a mute circuit (which I have bypassed). I agree with you that they have weak bass. Reading between the lines in many posts on this forum, this seems to be a common complaint.

Although lacking a bit of bass, the beauty of chip amps is their excellent overall tonality, good soundstaging and sweetness ...attributes that are rare among solid state amps when compared to valve amps (which nearly always sound nicer).
Therefore, a lot of people on this site use efficient speakers such as Lowther & Fostex as they bring out the best in the chip amps, which is in the region of midrange and treble.

Regards,

Steve M.
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Old 17th March 2008, 02:27 AM   #16
BWRX is offline BWRX  United States
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Everyone complains about a lack of bass, but has anyone actually measured the frequency response of their amps? If so, what results do you have that show the chip is the cause of the "lack of bass"?

It's simple to measure using a computer for a sine wave generator and a true RMS multimeter with decent frequency response. An oscilloscope makes things even easier.
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Old 17th March 2008, 02:29 AM   #17
johan851 is offline johan851  United States
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Well, I can hear the frequency response, and it's not bad. The frequency response isn't the problem, it's a lack of control. Hard hitting bass passages, especially in classical music, sound lifeless and uncontrolled.

*Edit* Maybe lifeless isn't the right word. It's hard to describe...it lacks presence and authority. And every now and then it just sounds distorted.
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Old 17th March 2008, 02:54 AM   #18
johan851 is offline johan851  United States
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Would these be ok for carbon film resistors, or should I look for something else?

http://search.digikey.com/scripts/Dk...me=P22KBBCT-ND
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Old 17th March 2008, 06:46 AM   #19
dfdye is offline dfdye  United States
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Quote:
Originally posted by BWRX
Everyone complains about a lack of bass, but has anyone actually measured the frequency response of their amps? I
Touche!

I personally haven't measured, but I have a Gainclone sitting next to a
"Linkwitz" chipamp, and the latter subjectively has much better bass response IMHO--tighter and less strained. Again, to each their own, but for my taste, the Gaincard circuit doesn't reproduce bass on my speakers as I would like.

PS I hate carbon comp resistors too!
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Old 17th March 2008, 07:38 PM   #20
danielwritesbac is offline danielwritesbac  United States
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Lack of bass could mean lack of driver control.

This aspect can be adjusted by the rails capacitance. Try 220uF onboard the amp. Bear in mind that the tweeters lose control first, and can resonate or squeak. So, in case the woofer is in control but the tweeter isn\'t, then the rails capacitance is still too large.
For reference, 2200uF is going to sound a lot like a 1970\'s transistor amplifier, with floppy (boomy) bass and a beautiful warm sound.
Halfway in-between, the tweeters will squeak, and just right is about the next step smaller. The \"right\" spot probably also brings the amplifier heat output to about half as much.

You can also adjust by the capacitance of the input filter cap, wheras too large is a problem for driver control, and too small isn\'t quite enough low bass.

Its also possible to use a 100v (or better) bipolar cap from + to - rails at the amplifier board. This really acts as a filter, and I\'m not sure what the recommended capacitance size is or even if the practice is okay or not. For sure it will make some sort of change to driver control.
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