First Amp...First DIY Audio project...

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#44
I have a total of three fuses on the PSU circuit. One fast blow 3A on the AC and two slow blow 3A on each DC rail. I have not tried it with out fuses. Out of curiosity, why do you ask?
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I have been building my GCs without fuses on the DC and was wondering if adding a fuse made any difference sonically. Seeing its easy to remove a fuse than add a fuse I was wondering if you had tried. 😉

I tried 1000 uF, 1500 uF, and 6000 uF. In this case, the bigger the better. The purpose of the caps is to act as a tank cap to reduce 60 hz or 50 hz (depending on what part of the world you're from) in the DC. They are crucial in my opinion. I'm really surprise to hear that you're not using any caps from DC to ground and that it works well.
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In traditional amp design, bigger the caps are considered better. For the GCs OTOH, having less or no caps on the PSU seems to be the go as long as the 1000uF caps (1500uF in your case) are very close to the chipamp.
 
#45
Doovieman said:
I'll send all the PCB artwork/CAD drawings to anyone who wants them this weekend...problem sets, labs, and exams call...gotta love being a student 😉 As far as protection, I use an inline fuse on the AC and two fuses on the DC (one per each rail). I can send a schematic of the powersupply circuit as well if people are interested.

Doovieman
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id like some of that plz
 
#48
I thought I had emailed everyone that requesed files...guess not, if I forgot to email you, please email you email to me again. Thanks and sorry for the delay. Also, as I mentioned in a few previous postings, my friend helped out on this project and built his own version of this amp (though slighly modified). What I forgot to mention was that he's actually a member of this forum. So all the compliments are equally distributed to Julester 😉

Doovieman
 
#51
Re: Details not received

avguy said:
Hi Doovieman,

I have not received the details still. Can you please send the details to me. Please


Avguy
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Avguy-
As I posted above, I thought I had sent everyone the files. If I have not, please resend me your email. I am still waiting for an email address from you.

Doovieman
 
#52
any reason for the 0.33uF - 22kohm RC filter on the input? seems limiting in the extreme! i get an f3 of 86.5hz!!! are you using these on fullrange speakers? i would think it should be an order of magnitude lower. changeing 22k to 220k would fix that, i'd stay closer to 100k for minimum noise (the noise curves on resistors seems to start picking up at around 100k, so i try to design with 10k-100k). 100k should give an f3 near 20hz, which i guess is ok.
 
#54
theChris said:
any reason for the 0.33uF - 22kohm RC filter on the input? seems limiting in the extreme! i get an f3 of 86.5hz!!! are you using these on fullrange speakers? i would think it should be an order of magnitude lower. changeing 22k to 220k would fix that, i'd stay closer to 100k for minimum noise (the noise curves on resistors seems to start picking up at around 100k, so i try to design with 10k-100k). 100k should give an f3 near 20hz, which i guess is ok.
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Yeah. The reason for the input cap is AC coupling. As far as the low pass, in theory, your right. However, my source impedances are so low that it doesn't matter. With regard to the "second DC blocking filter" I assume you're referring to the 1k - 47 uF. If you read the previous postings, I explained that I thought that the chip was bass light so I put a large cap down there to extend the low end frequency response.

Doovieman
 
#55
Very nice work Doovieman,

I’m planing of building the NIGC similar to what you did. I’d like to try it without the 47uF NFB cap. I’d like to have the least amount of caps needed in the circuit. So if I can remove the electrolytic cap would be my preference. My only concern is the output offset voltage. So far the guys that build it without the cap report pretty good results - http://www.diyaudio.com/forums/showthread.php?s=&postid=257590#post257590 (scroll to the bottom of the tread). Have you tried that and what’s the output offset voltage you get in your present setup.

Thanks
Greg
 
#56
Doovieman said:



Yeah. The reason for the input cap is AC coupling. As far as the low pass, in theory, your right. However, my source impedances are so low that it doesn't matter. With regard to the "second DC blocking filter" I assume you're referring to the 1k - 47 uF. If you read the previous postings, I explained that I thought that the chip was bass light so I put a large cap down there to extend the low end frequency response.

Doovieman
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it's a highpass, and the source impednace being low has nothing to do with the RC filter ii refer to. no clue how you extended you bass response by adding the cap to act as another highpass filter! notice the gain is lowest at DC... seems like the input RC network would be the prime location for any light bass. do you have an EQ turned up to compensate? the f3 i got was 83hz, definatly in the audible range.
 
#59
theChris said:



it's a highpass, and the source impednace being low has nothing to do with the RC filter ii refer to. no clue how you extended you bass response by adding the cap to act as another highpass filter! notice the gain is lowest at DC... seems like the input RC network would be the prime location for any light bass. do you have an EQ turned up to compensate? the f3 i got was 83hz, definatly in the audible range.
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Sorry, meant highpass. The 47 uF replaced a 22 uF. The greater the cap, the more you extend the low end response. Can't really figure out which filter you're referring to when you say "RC filter ii."

The filter on the input blocks out low frequencies...I don't like listening to 10 Hz so I popped that in there 😉! In retrospect the resistor to ground could probably go. The second filter ensures DC unity gain.
 
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