That is a ground loop breaker to reduce ground loop hum when connecting the PCB to chassis ground at that point. I use a crimped loop connector there to a star chassis ground on mine. Works well - a very quiet hum-free amp. Note the green wire on the top right corner of each board.
@asuslover - pretty sure this is a 2 layer board. No need for 4 layers on a basic chip amp.
Indeed Roland, but the best indicators are: (1) Smoke, and if the IC survives (2) meassure the performance.
Today I have browsed Aliexpress to find the reviews. Fakes, if the reviewers have tested. For a tenfold lower price one cannot expect anything else. But the human mind is strange, wants to believe in the absence of the cash. And 12 bucks aren't a fortune by any means.
I put my Xmas amp back on rotation and connected to my compact bookshelf TLs - foamcore ones as prototypes for wooden ones coming soon. This amp really sounds great. Can’t find fault with it. Smooth and easy to listen with bass grip and nice highs. More people should build this amp. It’s cost effective and easy to assemble.
If something is cheaper than it costs from the manufacturer, then you have to ask yourself why someone is selling it so cheaply.
I only know 3 reasons for genuine goods.
1. The parts are used and have been recycled.
2. The parts are sold by a closeout dealer or as leftover/overstock.
3. The dealer does not know what the parts are worth and sells them too cheaply.
Everyone else would deliberately put money on it and why should a dealer subsidize the buyer 1, 5 or 8 $ per component?
@Berlusconi This amp was first offered as free boards and the gerbers are still in the first post, so anyone can get boards made. Some parts may be is short supply but the posts here often include a work around. I build one and really like the sound of the amp.
Thanks @Signal lost for the info. Actually I have got boards from PCBWay and have built a pair of boards which are, for time being, under development and testing. What I meant is that it would be helpful to others who would like to have them too.
By the way: gerbers in the OP aren't the latest version - the most recent gerbers are in some later post. I've realised that when it was too late, the boards have already arrived from China.
Cheers! 😎
By the way: gerbers in the OP aren't the latest version - the most recent gerbers are in some later post. I've realised that when it was too late, the boards have already arrived from China.
Cheers! 😎
Don't worry @Signal lost, that was all my fault, before the New Year season. I'm too quick reader, except when signing contracts. 😉 .
Last evening i fired one channel up to see if it was good.
I didn't recieve my trafo yet, so i use an old 2x18v giving around +23 / -23.
The DC offset is a little high at this voltage, tonight i will see if the other channel act the same.
I will not really bother doing anything about until i have the right trafo on it.
My R15 is 47.5Kohm, and if i have the same offset on both channels i will assume i need to lower this resistor to something lower.
Well i found some American country and feed the channel directly from my Topping starting at -99dB.
Amp. is playing nicely on my shop speaker(mono ofcause), and i actually heard music 🙂
I tried giving it full (0 dB) and everything seems to play nicely, when pausing the Countrysong's, there are absolutely quiet, e.g. no hum, no nothing, which really surprised me i must say...
Let's see how it goes.
Jesper.
I didn't recieve my trafo yet, so i use an old 2x18v giving around +23 / -23.
The DC offset is a little high at this voltage, tonight i will see if the other channel act the same.
I will not really bother doing anything about until i have the right trafo on it.
My R15 is 47.5Kohm, and if i have the same offset on both channels i will assume i need to lower this resistor to something lower.
Well i found some American country and feed the channel directly from my Topping starting at -99dB.
Amp. is playing nicely on my shop speaker(mono ofcause), and i actually heard music 🙂
I tried giving it full (0 dB) and everything seems to play nicely, when pausing the Countrysong's, there are absolutely quiet, e.g. no hum, no nothing, which really surprised me i must say...
Let's see how it goes.
Jesper.
On one board I had trouble with DC offset and it turned out to be a damaged trace going to the op amp. X had helped me disable the servo by removing two components. This showed me that the servo was not working and i found the problem and fixed it with a jumper. I likely overheated that trace.
With power off, It would be wise to make sure all pins of the op amp are connected to the next component. If i can remember it was pin three was not connected to R16.
With power off, It would be wise to make sure all pins of the op amp are connected to the next component. If i can remember it was pin three was not connected to R16.
OK i found the post. My exchange with x starts at post 434.
both boards are working with the servo operating. The problem was no connection between left leg of C25 and pin 4 of U4. So no negative rail to the servo. Offset was -4.5V and it dropped to 6.1mv with a jumper from C25 to pin 4 of U4.
both boards are working with the servo operating. The problem was no connection between left leg of C25 and pin 4 of U4. So no negative rail to the servo. Offset was -4.5V and it dropped to 6.1mv with a jumper from C25 to pin 4 of U4.
Nice work! Your offset of 162mV is too high obviously. Your silent background amp is a good start though.
Let’s see what could be the issue. Schematic is here:
Retouch the solder joints from R16-R19 and make sure they are the correct values. Why did you change R15 to 47k?
EDIT :: Seem's i posted along with you XRK 😉
@Signal lost
Thank's for your'e reply's... I read it all around post 434, and i also tried firing up my other channel.
This channel gives approx. the same offset, and it's the same magic with volume at 0dB absolutely no hum or nothing 😀
I have installed a jumper at C17, which i removed on both boards... It does not seem to do much difference, and it's actually stated somewhere that if using DC serve, short C17 & C2, so i'am not sure if this i correct or not.
Well having the allmost same offset on both channels, telling me that everything is proberly assembled correct.
Now i just have to wait for the Toroidy transformer which i recieve in next week.
Jesper.
@Signal lost
Thank's for your'e reply's... I read it all around post 434, and i also tried firing up my other channel.
This channel gives approx. the same offset, and it's the same magic with volume at 0dB absolutely no hum or nothing 😀
I have installed a jumper at C17, which i removed on both boards... It does not seem to do much difference, and it's actually stated somewhere that if using DC serve, short C17 & C2, so i'am not sure if this i correct or not.
Well having the allmost same offset on both channels, telling me that everything is proberly assembled correct.
Now i just have to wait for the Toroidy transformer which i recieve in next week.
Jesper.