Another GC project

[GregGC]

http://www.diyaudio.com/forums/showt...023#post279023

Take a look at R1/C1. That is LF Filter. Use 10k/100pF. Connect them directly ont the RCA connector of the amp.

My concern is that that interference signal was not present before, or if it was, the housing of the amp you had before was doing better job shielding the amp. So if you have different type of housing now, that very well can be the problem.

Try adding R1/C1 to your amp and see if you get some improvement. Another thing to try would be to bypass the 1000uF caps with 47nF. On each 1000uF connect 47nFcap in parallel.

Let see if you get any improvement.

[uvodee]

very last option the bypassing

still the same,

the time of clean music seems to reach about 3 to 5 minutes then it starts to slightly crack and then the louder humm comes forward and pushes all the other sound to the back......

[uvodee]

turn the power off and on the sound is back to perfect for 3 to 5 minutes.....


it truly drives me crazy




J-P

[GregGC]

Originally posted by uvodee
turn the power off and on the sound is back to perfect for 3 to 5 minutes.....


it truly drives me crazy




J-P

Sounds like a capacitor that's bad or backwards. Check if any of them gets warm. Is the problem evident in both chanels at the same time? Do you have input cap?
Does it hapen if there is no input signal. Turn it on donCan you show me the exact sch. of the amp?'t play any music and see an see if the noiseigoing to appear.

Did you mesure the powersupply voltages when no input signal is present (when you first tun the amp on and after it starts making all the noise?

It could be a bad solder joint too.

Measure the voltages please.

[uvodee]

Sounds like a capacitor that's bad or backwards. Check if any of them gets warm.

Checked them = nothing gets warm, even the LM feels cold!


Is the problem evident in both chanels at the same time?
I started with only one channel this time, so I h cannot answer that one

Do you have input cap?

I used " the ultimate gainclone schematic, second time.

Does it happen if there is no input signal. yes and no, as long as there is no signal everything stays quiet but when the music arrives then after 3 to 5 minutes i get the crackling followed by hummmmmm...

Turn it on donCan you show me the exact sch. of the amp?
sure, here it is...

't play any music and see an see if the noiseigoing to appear.

Did you mesure the powersupply voltages when no input signal is present (when you first tun the amp on and after it starts making all the noise?

toroid power ingoing is 41 volts , after the bridge it is 60.5 volts


It could be a bad solder joint too.
I checked them so many times i had to replace the LM because I broke off some tips.....
\
Measure the voltages please.
I will do so and I will also measure the dc offset. now that I found out how to do it ( with a 10 ohm R)


Gee, I must have been very very lucky with the first amp 2 channels, I built it, connected it and it played right away. This time it seems like climbing the Kilimanjaro!


Jean-Pierre

[uvodee]

Sounds like a capacitor that's bad or backwards. Check if any of them gets warm.

Checked them = nothing gets warm, even the LM feels cold!


Is the problem evident in both chanels at the same time?
I started with only one channel this time, so I h cannot answer that one

Do you have input cap?

I used " the ultimate gainclone schematic, second time.

Does it happen if there is no input signal. yes and no, as long as there is no signal everything stays quiet but when the music arrives then after 3 to 5 minutes i get the crackling followed by hummmmmm...

Turn it on donCan you show me the exact sch. of the amp?
sure, here it is...

't play any music and see an see if the noiseigoing to appear.

Did you mesure the powersupply voltages when no input signal is present (when you first tun the amp on and after it starts making all the noise?

toroid power ingoing is 41 volts , after the bridge it is 60.5 volts


It could be a bad solder joint too.
I checked them so many times i had to replace the LM because I broke off some tips.....
\
Measure the voltages please.
I will do so and I will also measure the dc offset. now that I found out how to do it ( with a 10 ohm R)


Gee, I must have been very very lucky with the first amp 2 channels, I built it, connected it and it played right away. This time it seems like climbing the Kilimanjaro!


Jean-Pierre

[uvodee]

sorry, here it is..

the only thing I changed (from the very beginning) is the pot. The value I use is 25 K.
For making the ground stars I use very small copper washers where every wire (cap etc..) is safely soldered onto. I make 2 stars and they are connected to each other.

I have used 3 different sources to test now : 1) portable cd player, 2) Pioneer cd player (25 disc changer) and 3) a very very cheap dvd player

the best sound comes from the cheap dvd player but the result after a few minutes is always the same whatever source it comes from .... crackling followed by Hummmmmmmmm

[GregGC]

Thanks for the sch.
Let see what you measure as a DC output and rail voltages as the amp starts making noise.
Does the pot position afect the noise in any way? I'd put a 22k to 47k resistor from +in (pin 7 to gnd) just to make sure that the pot is OK and it provides constant gnd path for +in.

[uvodee]

the pot position does not make any difference.
I replaced the pot with a 50 k R ... no difference.
I can do this because all the sources come with a volume pot


I have to start all over again cause I ruined 2 LM's in the last 36 hours due to pin breakage....


J-P.

[GregGC]

Today decided to do some experimenting with values and sch. changes.

Found that removing the cap and keeping the gain just above 20 gave the best results (base and HF balance). More base and the highs are more refined.
The 1k resistor keeps the DC offset at the output to a nice low level when the attenuator is at low levels. With the shown res. values (had to decrease them to 3.3k/68k to keep the offset low) the DC offset is in single digits at all levels but the highest volume setting (it's around 25mV at max. volume).
Found that gain at just above 20 gives more refined highs and deeper base than gain of 30.
C6 was never installed on the first place. Didn't needed. So, the less parts the better.

So, I think, for my taste this is a better performing version of the amp. No DC should be present at the input of the amp though.