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Old 20th October 2005, 10:41 PM   #1161
troystg is offline troystg  United States
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0.1R + 3.3nF

Those 2 in series placed across the Bridge rectifier or the main supply caps?


Edit:

Or better yet, a link to a picture for morons.
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Old 20th October 2005, 11:19 PM   #1162
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Quote:
Originally posted by rabstg
0.1R + 3.3nF

Those 2 in series placed across the Bridge rectifier or the main supply caps?
Across the bypass caps on the chip.
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Old 20th October 2005, 11:26 PM   #1163
DcibeL is offline DcibeL  Canada
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Quote:
Originally posted by motzu'
One strange issue - one of the chips is getting a litlle bit warmer than the other one .Sensible warm ! Also the chips are warm if the amp is left alone with the power on but with no input at all...

...Could it be a high frequency oscilattion heating my chips differentelly and also heating the chips even with no signal ? Should I move to Rev_C ?
If there is no electrical problem with your amp (ie. oscillations), I would say that there is way too much thermal paste between the chip and the heatsink. Too much goo will actually decrease the thermal conductivity between the chip and the heatsink (because the goo is not as thermally conductive as metal), and could possibly be the reason behind the heating. Is it the chip you are measuring as being hotter, or is the heatsink itself hotter? It looks like the chips are nice a flush against the heatsink, but if there is even the smallest gap between the chip and sink there will be very little thermal conductivity between the two.

Are the resistors in the feedback path high tolerance 0.1% resistors as stated in the schematic? If not, there is potential for oscillations causing heat as well.
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Old 21st October 2005, 12:41 AM   #1164
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Hi All,

Carlos has some very interesting experiences with snubbers no doubt and others as well I am sure. But it is not an accident they are not included in the circuit. This is not conjecture, but design. This is not promises of "tighter, clearer, better" it is execution.

But for now please try the snubber if your curiosity has you, just don't expect the promised improvements, or you will be sure to hear them.

Adding the snubber will not hurt (well not much anyway), so no harm will come to try it, but if you wish to make comparisons make sure you review/measure the modified amp directly against an unmodified amp before you subscribe to subjective impressions and grandiose promises.

The reason is, it is easy to fool yourself with euphonics simply because you expect a change to occur. It is pure psychology.

Just remember this is very much an engineered amp, and it has been executed in a precise and deliberate way. Remeber that adding or changing components without a thorough understanding of all of the principles involved as well as a thorough undstanding of the circuit is something that is fun, but not necessarily better.

Anyway I will not denegrate those who try, God knows I did. With every value Carlos has suggested, with side by side comparisons. In every case the amp has always performed well, but the snubbly version certainly did not perform better in any way that I could hear, nor anyone else who listened.

If the snubbers really had any positive effect in this circuit, they would be on the PCB, at least mine. The absence is not because they were not tried, quite the opposite.

Cheers!
Russ
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Old 21st October 2005, 10:09 AM   #1165
motzu' is offline motzu'  Romania
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Carlos - I'll make a try with snubbers. About the psicho effect we shall see. Finnaly we are DIY'ers so there is room for experience, any time

All the components were selected as in Mauro specs. Yes the resistors in feedback are 0.1% . In fact they were the only resistors brought very late because i need to place a special order for them.

About the thermal paste , the pictures were token in a earlier stage of development, when the contact between the chips and radiator was imperfect.

In that moment the chips were getting hot but the radiator , not.

Now I've rectified with sand paper the PCB border and in this way I've moved closer to the radiators. The interface between the chips and the radiator is one piece ox 2x3cmx1mm cooper with a tiny layer of Titan thermal grease/paste on both sides.

Still the left chip is getting warmer than the right one. Unfortunattely i don't have an oscilloscope, but in the audible range there is no problem or hum

Dcibel - the radiator is warm as well as the chip.

What about the bass ? Should I move to REv_C ? Still I don't get it why the amp is - pretty - warm when there is no signal.

Thank you everyone for the answers
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Old 21st October 2005, 10:20 AM   #1166
UnixMan is offline UnixMan  Europe
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Exclamation "My_Ref" is NOT a Gainclone !!!

Quote:
Originally posted by motzu'
Finished my first Gainclone Rev_A

Pictures ( warning, each one, full size - about 800k !!!) at :

ftp://ftp.dallnet.ro/public/hi-fi&stuff/Gainclone/

For the sake of correctness, once again: Mauro's "My_Ref" design is NOT a Gainclone !!!

It may be "categorized" as a chip amplifier (in that it make use of a chip amp), but definitely it has NOTHING to do with a Gainclone other than using (also) the LM3886!

So, please, please, STOP referring to it as a gainclone!
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Old 21st October 2005, 10:30 AM   #1167
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Wink snubber-o-mania

Quote:
Originally posted by Russ White
But it is not an accident they are not included in the circuit. ...
Hah ! I knew from the beginning there is somthing wrong ! But now I see - a bunch of elcaps and NO SNUBBER !!! IŽll get my iron immidiately and ... ... ... Oh sh*t, no more resistors and filmcaps in parts bin. So I forget it.
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Old 21st October 2005, 10:32 AM   #1168
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motzu-

I would try a few things to investigate. Try disconnecting your input and output wires from the board, then power the amp up. Does it still get hot the same way? (This is to rule out possible wiring issues.)

Also, it's worth the effort to reexamine the bottom of your circuit board very closely, looking for small solder bridges between joints. They are very easy to miss (I do).

Assuming neither of these bears fruit, you could try swapping the LM318s between the channels to see if the issue follows them. If so, replace the "hot" 318 (I know it's not the 318 getting hot, but one could be "bad" and cause the problems).

Keep us posted, and good luck!
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Old 21st October 2005, 01:12 PM   #1169
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hi motzu',

1. all the connections, input RCA, and Power output have to be isolated by the chassis. Am seems me that you have the power GND connected to the chassis...
2. Check the RCA connections, I have seen a red connected to the GND...
3. Check all the resistors, ( R9 and R32 =47Kohm 01 % ) R5 and R28 seem me from 4k7 but they have to be 22Kohm, checks and measures all the values...
4. The heatsink has to be ALWAYS connect OR to chassis (main gnd) OR to trafo GND.


Your problem is a caused oscillation by LM3386, because you have not put the correct resistors. Uses the "original" My_rev revA circuit to check all...

FOR ALL:

My_ref it's a mid-difficulty electronic project, and requires an adeguate ability

BEFORE turn on the circuit, verify all the components and the connections are correct


ciao

Mauro
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Old 21st October 2005, 03:56 PM   #1170
troystg is offline troystg  United States
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Agreed, no GC I have heard sounds like this.

I will try the zener voltage mod and the snubber mod ONLY because both are relatively minor additions / changes that are reversible.

Last night I played the Audio Quest recording of "The Mighty Sam McClain(?)".

My wife listened with me. She quit doing that 10 yrs ago. I asked why she was "here", and she said she was listening. I discreetly said "WHAT!". And she replied "this sounds nice".

Women have WAY better hearing than men, and for her to say it sounds nice, over rides ANYTHING I may have said.
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