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Chip Amps Amplifiers based on integrated circuits

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Old 21st May 2004, 07:43 PM   #1
Vikash is offline Vikash  United Kingdom
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Default Newbie GC complete

...you guys must be fed up seeing that title.

This is was one hell of a buzz. I can't believe I built an amplifier. yay to me .

I used old parts where possible, so this one channel has cost < 10. I followed the NS schematic more or less. It's an absolute mess but it works fine. There is the slightest hum that can be heard only when my ear is put right near the woofer, but I'm hoping that will go once I sort all the wiring up and fix everything in place. I recall measuring the DC offset to < 4mV which looks too good to be correct?

I was somewhere between pessimistic and realistic in my expectations, and although I won't claim some superioior GC sound (well those caps must be 15 years old to begin with) I must say I am impressed.

I've heard a few tracks, and I feel there is an ever so slight lack of bass (but then again I'm listening on a pair of JBL control 1's at the moment) but the midrange already seems to outdo my midfi mini system. I could hear digitization effects in one (poorly compressed) mp3 track which I'd never picked up on before, and I made out some new sounds in another that I'd never really noticed before. The last time I experienced this was when hearing a pair of Logan ESL's for the first time.

Cheers to Nuuk in particular. Your site is a GC newbie's best friend
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Old 21st May 2004, 08:40 PM   #2
ekd is offline ekd  United States
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Default Be careful!

This can become the most dangerous type of addiction... An affordable one.

Ditto. Nuuk's site was my diving board as well...

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Old 21st May 2004, 10:10 PM   #3
Ropie is offline Ropie  United Kingdom
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Old 21st May 2004, 10:46 PM   #4
ekd is offline ekd  United States
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Default I got bad news...

The guy hanging on the wall over there says there is no way out...

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Old 22nd May 2004, 08:10 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Tee hee - there is no escape from the Decibel Dungeon!

Well done Vikash and welcome to the club.

May I suggest replacing those old caps when you can as they are probably more important in the GC design than some other amps where there is more capacitance.

And thanks for all your kind comments on DD. I hope to be adding some new stuff on GCing very soon now.
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Old 22nd May 2004, 01:21 PM   #6
mAJORD is offline mAJORD  Australia
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congrats.

im still trying to be convinced that my GC could be as good as a more expensive discrete design. even tho it sounds great.

It dosn't fit with me
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Old 22nd May 2004, 02:34 PM   #7
Vikash is offline Vikash  United Kingdom
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Quote:
Originally posted by Nuuk
May I suggest replacing those old caps when you can as they are probably more important in the GC design than some other amps where there is more capacitance.
At present, the caps are 5600uF. I've seen small value caps placed close to the pins of V+ and V- (in addition to the smoothing caps). What is the purpose of this? Are they used when the PSU caps are far away?

Also, I found a difference when putting a 22uF cap close to pin 8 (and the resistor afterward). What is the name of function of this cap (I know it's not a smothing or snubber cap etc.)?

Lastly, I haven't the faintest idea what the resistors I've used are rated at. Is there a minimum requirement for any of them?

Nuuk, I have a few suggestions about your GC FAQ which you may want to take on board. Perhaps I will email you a list of the things that wern't obvious to me which may help others too...
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Old 22nd May 2004, 03:19 PM   #8
Nuuk is offline Nuuk  United Kingdom
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The 1000 uF caps are generally recommended because that level of capacticance has been found to give the best sound by most GC builders.

Some argue for more but it is felt that higher values 'slow' down the sound or affect the tonal balance.

Except for the 0.22 R on the output (if you use one), the other resistors can be 0.125 watts. I suggest a minimum of 3 watts for the 0.22R.

Yes, please contact me (use the form on DD) with any suggestions for the FAQ page.
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Old 22nd May 2004, 04:16 PM   #9
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Quote:
Originally posted by Nuuk
Some argue for more but it is felt that higher values 'slow' down the sound or affect the tonal balance.
Nice subtle spin there, Nuuk, ever thought of going for Alistair Cambell's old job?
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Old 22nd May 2004, 05:17 PM   #10
Rarkov is offline Rarkov  England
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I'll let you know about the capacitance when my GC4s are complete.

GC1 & 2 - 5600uF on a seperate supply followed by 1000uF at the rails. This was to reduce the indution of 50Hz by the umbilical cords.

GC3 - 1000uF at rails only (Tube buffered)

GC4 - 10000uF at PSU + 1000uF at rails. Same chassis.

I have tended to find that the extra capacitance on the PSU and th compulsary 1000uF at rails sounds best. Not "slow" or adversly affected in the least. I am yet to listen to my nearly completed GC4s so I can't comment when the PSU is in the same chassis. See my website for details. I should note that all of these designs are monoblocks.

Gaz
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