The (high-cap.) unregulated PSU for chipamps

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#621
Chuck...

There are two camps on regulated vs. unregulated. Search Nuuk's GC discussion.

Some feel that E-cores are quieter than toroidals. Some don't.

Some think that batteries are quieter. Some don't. batteries don't just sit there. They belch, burp and fart during the discharg and charging phase. There are rational discussions of battery power on this forum. It boils down to sealed lead acid as the contender. Other battery types (NiCad, LI, etc.) are too noisy.

Start building and see for yourself. The CarlosFM unreg snubberized discussed in this thread is VERY quiet.
 
#622
I am having a lot of DC offset problems with this amp.....
Last night I measure more then 4.0 Volts ....... 😱 :att'n:
The chip got hot very quickly :hot:

Now I am runing with a 4,700uF cap in the output :dodgy:
It sounds like rubbish 🙄 :dead:

I need to solve the problem.... here I go, back to work on it :smash:



PS: I also have a 2,2uF cap in the input....

PS2: With the cap in the output the chip is runing cold 😉
 
#623
Now I have -40 mili Volts of DC offset 😀
( I measure it with the ground connected to the +Vin )


With the source(CD player) connected I had 4V :bigeyes: 😛 And lots of heat :hot:




I let it play all afternoon at almost full power and the chip didn't get very hot 😎
This single ended prototype it's runing with a 650VA trafo, 45.000uF near the trafo and 3.980uF near the chip ( I used small caps ). ( per rail )
( great bass... fast and deep 😀 )
 
#626
Carlos, what is the normal DC offset of the LM3886 in single ended ?

Now I am having -1.0 to 2.0 in the scale of 200 mV.
( with cd player connected and without the input cap(2.2uF) )




PS: I having the same values that I add in differential mode :bigeyes:
 
#627
What is the output voltage of this PS, just 1.41 x input? Is there any drop after rectification?

Also how would you estimate the voltage swing would it just be the swing from the mains and the unloaded transformer voltage to loaded?
 
#636
Hi, Carlos.
I want to build an amplifier, unregulated PSU based on LM4780 paralleled chips and your schematics.
Can you help me to determine the best solutions?
1) Can I use without any harm to sound quality 10nF MKT caps to bypass diodes on bridge rectifiers (KBPC3506)?
2) I've found that amplifier when it's turned OFF discharge PS caps for about 5-10 minutes, so may I omit bleeders resistors in your design. What do you think?
3) May I use 1mF+1Ohm10W+10mF with 1 BR except 4,7mF+1Ohm10W+10mF+10mF with 2 BR in PSU for each voltage
rail and 1mF+100nF on chip's PSU pins for one channel 100W amplifier with 4Ohm load and with 400VA trafo
for two channels?
P.s. I want to try Panasonic FM caps for high frequency response. Some people claims that Panasonic FM is the best in filtering high frequencies, but with 50V rating 1000uF is the biggest value.
4) Also, perhaps it will be wise to use MOVes or some NTC thermistors to limit inrush current. Could you tell me where I have to place them on your schematic?
5) Which component of 0,1Ohm+3.3nF, 100nF, 2,2mF have to be the closest to the IC?
6) Concerning your LM3886 schematic, will it be better to use C1-1uF and R1-47k?
As I know using DC blocking caps with value more than 1uF will degrade a sound quality.
7) Don't you think that: Ri and R2 must be equal value in order to minimize DC Offset on Output? And an input impedance at your LM3886 schematic is seemed to be too low, thus any noise can be injected into the amplifier and will affect the THD+N performance?

Thanks for answers.
Everyone else is invited for comments too.

Best Regards.
 
#639
steenoe said:


Sounds like fun, but we don't have to!
You have made all the hard work already😉



Well, your guidelines were followed all the way, I think.
And with great result, I might add!!
Here is a pic of the rearside of those amps, in case you care?
The binding posts were ordered from Taiwan, of all places!!
Very cheap, and very good quality. Can take a serious speaker-cable.

Steen.
Click to expand...


carlosfm said:


You mean something like this?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39039&highlight=

Yes, in most situations it improves the sound.
Click to expand...

hello carlo
i did a gc lm3886, bass good but bad mid and treble, so i searched the web and searched a lot of information from yours post, so i will build another one after a few question, 1. the attached file shows from you, 3300u and 10000u, can i 820u x4, and 820u x 12, because i bought a lot last mouth.........
and after building the psu and unregulator(same as yours), what is the number of capacitor that for lm3886 between +v and pin 1,5 and -v and pin 4? i saw steenoe's gc use very small cap..
thanks alot.
 
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