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Chip Amps Amplifiers based on integrated circuits

This is not just another gainclone
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Old 12th March 2003, 08:16 PM   #1171
Peter Daniel is offline Peter Daniel  Canada
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2Bak,

What circuit are you using?

As soon as I connected In+ directly to ground I started to have interference problems, I was picking some radio frequencies. The circuit was OK when using Thorsten schematic with resistor and capacitor to ground on positive input. On my first amp I grounded the chassiss by connecting it to mains ground with an extra wire from PS. On my later amps I connected the chassiss to the signal ground by not isolating one of the negative binding posts (in one channel only)

Yesterday, a friend of mine who's using very efficient Altecs, noticed that when using his cordless phone near the amp, the channel which negative output was not connected to the chassiss was picking up hum. So I advised him to connect both channels negative posts together and it solved the problem. Still, it makes me wonder why?
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Old 12th March 2003, 08:29 PM   #1172
Cradle22 is offline Cradle22  Germany
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Hi!

I have to tell you all what caused my problems...!!!

I use the small heatsink cases from Conrad, and drilled holes for all my (insulated) connectors into one of the frontplates of this casing...

Of course I checked that the LS-connectors, cinch connectors... had no connection to chassis... or so I though...

The smooth finish of the aluminium casings is not conductive ! So, measuring resistance or (what do you call the small diode-test on multimeters) showed no connections...

But all the time the LS connectors which directly connect to (both) ICs had connections to chassis, and so also connections to each other... I think that could have caused a lot of the problems I described in all my numerous (often annoying, I would think) postings...

But I can't widen those holes enough in order to ensure non-conductive connector mounting since it is to late and I do not want to wake my neighbours with my dremel rotating at 25000 rpm...

But at least now I can sleep soundly , with great expectations for my GC tests, and hey! it even made me test my OPA548...

So, thanks to all, sometimes dumbness is intelligence's worst enemy...

Arndt
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Old 12th March 2003, 08:30 PM   #1173
Elkaid is offline Elkaid  Canada
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from Peter D.
Quote:
Some people commented that their GC don't have enough bass. This amp has all the bass you would ever need, with perfect gradation, punch, tightness and whatever else you might need.
I just finished mine based on the LM3875 and it's almost perfect to my taste. No noise even at full volume, no ground loops... well you get the point.

However I found out that my Gainclone is a little "shy" on bass reproduction. What could be the factor causing this lack of bass ?

I'm using a 1uF input cap. 10K & 220K resistor and finally 2 X 1000uF caps.

Thanks !
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Old 12th March 2003, 08:38 PM   #1174
Equilibrium is offline Equilibrium
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Quote:
Originally posted by Elkaid

I'm using a 1uF input cap.
Make it 4.7 and see what happens.

Can I get an Amen?
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Old 12th March 2003, 08:39 PM   #1175
GringoAudio is offline GringoAudio  Canada
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Elkaid asked:


QUOTE]What could be the factor causing this lack of bass ?[/QUOTE]


Lack of a real power supply perhaps?? Add a couple of 4700uF caps in parallel with your 1000uF ones. No bass problem with my 20000 uF per rail supply.
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Old 12th March 2003, 09:06 PM   #1176
Elkaid is offline Elkaid  Canada
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Amen

I read somewhere that 1000uF per rail was enough... I found that suspicious but I thought that those guys are more exprimented than me... Anyway, I'll add 20000uF per rail right away ! I'll also try those 4.7uF input caps

Thanks guys
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Old 12th March 2003, 09:16 PM   #1177
Cradle22 is offline Cradle22  Germany
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The only plausible explanation I ever read about 1000uF being enough (apart from caps sitting directly at IC, thus leading to short paths and faster recovery), is that BECAUSE 1000uF are not enough capacitance to totally control the bass on strong bass impulses, the amp SOUNDS better. Better in the ways of less defined, warmer, louder.
Of course if you like razor sharp bass impulses, dry enough to punch the dust out of your couch, that will not suffice...

But over all people like to compare the GCs with tube amplifiers, having a warm, not too anaylticals sound (although without breaking in time I found the GC pretty analytical...)
So, just try it out... But when you add a lot of capacitance to the main supply, reduce the cap directly at the IC (no need for big caps, smaller and faster ones are better, maybe 220uF bypassed...).

I will definitely try this with some SlitFoils lying around

And report the differences, please!


G' Night,

Arndt
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Old 12th March 2003, 09:49 PM   #1178
Peter Daniel is offline Peter Daniel  Canada
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One way to get more bass is reduce supply voltage. Some people commented that my amps running on 18-0-18 v AC have too much bass.
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Old 12th March 2003, 09:52 PM   #1179
Elkaid is offline Elkaid  Canada
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Thank you very much

I added 20 000uF per rail and the bass came back
However, i used 4 X 10000uF 'cause I had only that on hand but it's still pretty good ! (You suggested more caps with smaller value)

I'm still curious about the impact of the 4.7uF input cap suggested by Equilibrium. This will be my next experience !

After that, the only thing left will be to add some windings around my transformer to light up a blue led perhaps

Regards,
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Old 12th March 2003, 10:05 PM   #1180
2Bak is offline 2Bak  Denmark
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Quote:
Originally posted by Peter Daniel
2Bak,

What circuit are you using?
This one without any modifications.
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