Hi AndrewT:
I removed the volume pot today and connected the + inputs from the chassis directly into the amplifier boards. The sound improved, but I still feel a difference in power from one channel to the other. The "bad amp" is still not as powerful as the "good amp", very noticeable at lower volume levels, I can hear sound from speaker connected to "good amp" but the speaker connected to "bad amp" is barely producing any sound.
I've been doing research on the matter because the main goal of this experiment was basically to learn, and I read somewhere that they mention a "feedback resistor". Which is this resistor in my PCBs?. Anyhow, I have checked resistance and capacitance of all components in the "bad amp" and all the readings I've got are OK.
I have another question?. Why do I use AC voltage when measuring inputs, outputs?.
I thought it was all DC after the PSU....?.
Thank you again, Professor.
I removed the volume pot today and connected the + inputs from the chassis directly into the amplifier boards. The sound improved, but I still feel a difference in power from one channel to the other. The "bad amp" is still not as powerful as the "good amp", very noticeable at lower volume levels, I can hear sound from speaker connected to "good amp" but the speaker connected to "bad amp" is barely producing any sound.
I've been doing research on the matter because the main goal of this experiment was basically to learn, and I read somewhere that they mention a "feedback resistor". Which is this resistor in my PCBs?. Anyhow, I have checked resistance and capacitance of all components in the "bad amp" and all the readings I've got are OK.
I have another question?. Why do I use AC voltage when measuring inputs, outputs?.
I thought it was all DC after the PSU....?.
Thank you again, Professor.
AndrewT:
Another question:
I tried to measure the AC voltage in the inputs at the volume pot, amp PCBs and the outputs at the chassis speaker connectors. It is really hard to do it with music because it is constantly moving, I need a constant sound, a beep or something, do you know where I can get a file with a sound that I can use to do this measurements and obtain an accurate value so I can compare exactly one channel to the other?.
Another question:
I tried to measure the AC voltage in the inputs at the volume pot, amp PCBs and the outputs at the chassis speaker connectors. It is really hard to do it with music because it is constantly moving, I need a constant sound, a beep or something, do you know where I can get a file with a sound that I can use to do this measurements and obtain an accurate value so I can compare exactly one channel to the other?.
LM3886
Thank you, AndrewT.
Did you read my previous post?.
Is there anything else I should check in the "bad amp" that would help me determine the cause of the power output difference between the two PCBs?.
Since I connected the + inputs directly to the amps, now I control the volume using the volume pot at the source, I'm using a iPod and a QLS QA350 Wave Player as sources, when I set the volume all the way up I noticed that the "bad amp" doesn't get near as hot as the "good amp", so something is definitely wrong....
I see that these LM3886 have some protection measures built-in, but in case this activate, is there any way to reset the chip to back to normal?.
Thank you, AndrewT.
Did you read my previous post?.
Is there anything else I should check in the "bad amp" that would help me determine the cause of the power output difference between the two PCBs?.
Since I connected the + inputs directly to the amps, now I control the volume using the volume pot at the source, I'm using a iPod and a QLS QA350 Wave Player as sources, when I set the volume all the way up I noticed that the "bad amp" doesn't get near as hot as the "good amp", so something is definitely wrong....
I see that these LM3886 have some protection measures built-in, but in case this activate, is there any way to reset the chip to back to normal?.
For all of you interested in a "tone generator", I found a free software you can download:
Audio Frequency Generator FREEWARE
AndrewT/Pacificblue;
I'm going to get measurements with this tone generator, I will post them soon.
Audio Frequency Generator FREEWARE
AndrewT/Pacificblue;
I'm going to get measurements with this tone generator, I will post them soon.
AndrewT/Pacificblue:
I switched the input cables at the PCBs, I have also switched the speaker terminal cables, the problem remains in the same "bad amp".
I downloaded that audio frequency generator above and connected the laptop to the amplifier, I checked the AC voltage at both inputs, the value is about the same, 0.179 volts in Left amp, 0.174 in Right amp.
Now, when I checked the output voltage at the speaker terminals, I found a difference of 6 volts between the two PCBs. The "bad amp" outputs 6 volts less than then "good amp". I checked this at the speakers terminals, and also from pin #3 at both LM3886.
My guess, the bad LM3886 got damaged because of the heat, I just realized that the heatsink in "good amp" was always touching the aluminum sheet I placed in front of the amplifier boards, while the "bad amp's" heatsink never touched it.
I have ordered another LM3886TF to replace it, and I'm finding out about bigger heatsinks to replace the ones I am actually using.
I have to resolve all these issues before I move on to the "input selector board" and "speaker protection board", and put this contraption inside an enclosure.
I switched the input cables at the PCBs, I have also switched the speaker terminal cables, the problem remains in the same "bad amp".
I downloaded that audio frequency generator above and connected the laptop to the amplifier, I checked the AC voltage at both inputs, the value is about the same, 0.179 volts in Left amp, 0.174 in Right amp.
Now, when I checked the output voltage at the speaker terminals, I found a difference of 6 volts between the two PCBs. The "bad amp" outputs 6 volts less than then "good amp". I checked this at the speakers terminals, and also from pin #3 at both LM3886.
My guess, the bad LM3886 got damaged because of the heat, I just realized that the heatsink in "good amp" was always touching the aluminum sheet I placed in front of the amplifier boards, while the "bad amp's" heatsink never touched it.
I have ordered another LM3886TF to replace it, and I'm finding out about bigger heatsinks to replace the ones I am actually using.
I have to resolve all these issues before I move on to the "input selector board" and "speaker protection board", and put this contraption inside an enclosure.
Pictures...
Here, the pictures of the amplifier. Right now the volume potentiometer is disconnected because of the issue I'm having with the Right Channel amplifier outputing 6 volts less than the Left Channel amplifier.
Again, there is no hum or any kind of noises in this amplifier, it sounds amazing, detailed, crystal clear sound. The only issue is what I have mentioned above. I know the wires are messy, I will do a better job when I put it in the enclosure.
Here, the pictures of the amplifier. Right now the volume potentiometer is disconnected because of the issue I'm having with the Right Channel amplifier outputing 6 volts less than the Left Channel amplifier.
Again, there is no hum or any kind of noises in this amplifier, it sounds amazing, detailed, crystal clear sound. The only issue is what I have mentioned above. I know the wires are messy, I will do a better job when I put it in the enclosure.
Attachments
Hi Pemo:
This issue is driving me nuts.... I thought that too, I resoldered the LM3886 in the bad PCB, I don't know if this really makes a difference but I've used the Cardas Quad solder, I have checked capacitance and resistance in each component, all values are fine, same goes to continuity... I even checked resistance in both speaker outputs, from pin #3 to speaker terminals, I get 0.7 Ohms in each....
I'm waiting for the new LM3886TF chip I just ordered from Hong Kong (there it is $4.00, here in US is $8.50 plus shipping) to replace it and recheck it. I think I need heatsinks like yours, but I don't even know where or how to get them. Do you happen to have a part number, Pemo????.
I am trying to get heatsinks from www.heatsinkusa.com , just something double the size of what I'm using, these chips get ultra hot, the ideal would be something like yours, if you could only come up with part numbers....
Thank you, Pemo.
This issue is driving me nuts.... I thought that too, I resoldered the LM3886 in the bad PCB, I don't know if this really makes a difference but I've used the Cardas Quad solder, I have checked capacitance and resistance in each component, all values are fine, same goes to continuity... I even checked resistance in both speaker outputs, from pin #3 to speaker terminals, I get 0.7 Ohms in each....
I'm waiting for the new LM3886TF chip I just ordered from Hong Kong (there it is $4.00, here in US is $8.50 plus shipping) to replace it and recheck it. I think I need heatsinks like yours, but I don't even know where or how to get them. Do you happen to have a part number, Pemo????.
I am trying to get heatsinks from www.heatsinkusa.com , just something double the size of what I'm using, these chips get ultra hot, the ideal would be something like yours, if you could only come up with part numbers....
Thank you, Pemo.
Hi my Brave friend,
I like the heatpipe stuff in those heatsinks. There are a lot of surplus stores online that sell HP heatsinks with fans (just remove the fans). I liked the copper ones, but the nickel ones might work as well.
The heatsinks from heatsinkusa are a very good value. I really think that heat is not the cause, but.....
Just to clear off all doubts. Why don´t you desolder the amp and install it in the other board.
Once I had a problem with a cable. I never noticed that it was (how to say it) almost cut and caused a similar problem.
What else can you check, hummm. If I think of something I'll let you know.
RGDS
PEMO
PROBLEM SOLVED!!!!!
Okey, guys, I have solved the issue I was having with one channel sounding louder than the other....
I tried last night the advice provided by Pemo, I wanted to desolder the LM3886TF in the "bad amp" to resolder it in the "good amp" PCB.
It was impossible, I tried sucking all the solder in every leg with a solder remover, then I used a solder wick, but I just couldn't remove the chip, so I left it alone, I replaced the thermal paste and the heatsink and connected it back in the chassis.
I was disappointed because I thought that I was going to have to replace the whole entire PCB, including LM3886TF and all its components, but when I turned it on, both amplifiers were working great again.
This was definitely a HEAT ISSUE, I guess the "bad amp" was getting hotter than the other one, and it prevented it from producing full power output, perhaps AndrewT and Pacificblue can offer a better explanation to this phenomenom.
Then I decided to put some aluminum folder to get rid of the gap between both amp's heatsinks and the aluminum sheet in the chassis, and after I did that I realized that now I have hum that can be heard in the chassis and in both speakers. This is a temporary solution, I will be getting bigger heatsinks soon, but how can I get rid of the annoying hum now?. The two heatsinks have some "terminals", if I solder a piece of wire on each and run it to the "star ground", would that be OK to eliminate the hum?.
Thank you....!
Okey, guys, I have solved the issue I was having with one channel sounding louder than the other....
I tried last night the advice provided by Pemo, I wanted to desolder the LM3886TF in the "bad amp" to resolder it in the "good amp" PCB.
It was impossible, I tried sucking all the solder in every leg with a solder remover, then I used a solder wick, but I just couldn't remove the chip, so I left it alone, I replaced the thermal paste and the heatsink and connected it back in the chassis.
I was disappointed because I thought that I was going to have to replace the whole entire PCB, including LM3886TF and all its components, but when I turned it on, both amplifiers were working great again.
This was definitely a HEAT ISSUE, I guess the "bad amp" was getting hotter than the other one, and it prevented it from producing full power output, perhaps AndrewT and Pacificblue can offer a better explanation to this phenomenom.
Then I decided to put some aluminum folder to get rid of the gap between both amp's heatsinks and the aluminum sheet in the chassis, and after I did that I realized that now I have hum that can be heard in the chassis and in both speakers. This is a temporary solution, I will be getting bigger heatsinks soon, but how can I get rid of the annoying hum now?. The two heatsinks have some "terminals", if I solder a piece of wire on each and run it to the "star ground", would that be OK to eliminate the hum?.
Thank you....!
Well, as you can see it, all the wires are like spaghetti plate!. The wires caring AC should be Twisted really well and also as close to the chassis as possible. The inputs wires should be as far as possible from AC lines and transformer! any noises picked up by the input wires...WILL BE AMPLIFIED
!!! also "ground loops" are big problems too.Spaghetti is just right...!
Hi Lanchile:
Yes, the whole thing looks like a mess, I knew that as soon as I'd post the pictures I was going to get a lot of criticism, I am ready for it...
Now, the amazing thing is that even though the cables are a complete mess, I didn't have any hum or noises of any kind. I introduced hum last night when I added the two pieces of aluminum foil to the gaps between the heatsinks and the sheet holding the switch and volume pot.
All this issues will be addressed when I put this thing in a enclosure, but I need you guys help in the meanwhile. Can you please tell me where the ground loops are?. Can you please tell me if soldering ground cables to the heatsinks will get rid of the hum I have now that I didn't have before?.
Thank you, Lanchile.
Well, as you can see it, all the wires are like spaghetti plate!. The wires caring AC should be Twisted really well and also as close to the chassis as possible. The inputs wires should be as far as possible from AC lines and transformer! any noises picked up by the input wires...WILL BE AMPLIFIED
Hi Lanchile:
Yes, the whole thing looks like a mess, I knew that as soon as I'd post the pictures I was going to get a lot of criticism, I am ready for it...
Now, the amazing thing is that even though the cables are a complete mess, I didn't have any hum or noises of any kind. I introduced hum last night when I added the two pieces of aluminum foil to the gaps between the heatsinks and the sheet holding the switch and volume pot.
All this issues will be addressed when I put this thing in a enclosure, but I need you guys help in the meanwhile. Can you please tell me where the ground loops are?. Can you please tell me if soldering ground cables to the heatsinks will get rid of the hum I have now that I didn't have before?.
Thank you, Lanchile.