The thing I really really don't understand right now is not even why only the right side is effected. It's how it can be, that this noise only ever disappears when I bring the amp to some repairman and then reappears if I'm at home or closeby. If the amp didn't work to begin with when I built it I would think maybe there's some sort of interference that somehow extends for kilometers around me, but this thing worked for two months with no issues, and the noise went away and came back once. I seriously don't get it.
Yeah, some problems can be very tricky to fix.
I meant slicing the circuit into pieces and mixing them together. I find it hard to explain, sorry. Think about the amp like a set of functional blocks: volume control and input, first stage, second stage, output and coupling caps. If then you can shift those around, you'll be able to pin point the issue to one of the blocks.
If I switch output stages left to right and the issue shows up in left channel, then you know that issue is a part of the output stage.
I meant slicing the circuit into pieces and mixing them together. I find it hard to explain, sorry. Think about the amp like a set of functional blocks: volume control and input, first stage, second stage, output and coupling caps. If then you can shift those around, you'll be able to pin point the issue to one of the blocks.
If I switch output stages left to right and the issue shows up in left channel, then you know that issue is a part of the output stage.
What could be different...?
I suppose if you focus on good old fault-finding principles, the results might be more fruitful...?? Cursing things for what appears to be like a science fiction novel will not result in any joy.
I'd still look at the bias pots very closely. See my previous post(s).
The testing should be done with inputs shorted and a resistive load (of some 30 ohms maybe / 5W) connected at the output.
I'd monitor the signal path from input towards the output with a 2-channel oscilloscope; one channel connected at the output, the other channel probing the said signal path. With valve gear, I wouldn't dare NOT to use differential probes.
If all looks good with resistive load, add a bit of capacitive load and see what happens.... (around 0.047uF will do). Turn the bias pot a bit, tap on it... did you do a sniff test (see my previous posts...)??
If the amp appears stable, add a sinewave at the inputs of some 0.5Vpp at 1kHz, and repeat the above with probes. A good old signal generator (so that you could adjust the input level to the amp) will be immensely helpful.
By the way, did any of those 2 fellas who tried to fault-find the problem do what I suggested above?
I suppose if you focus on good old fault-finding principles, the results might be more fruitful...?? Cursing things for what appears to be like a science fiction novel will not result in any joy.
I'd still look at the bias pots very closely. See my previous post(s).
The testing should be done with inputs shorted and a resistive load (of some 30 ohms maybe / 5W) connected at the output.
I'd monitor the signal path from input towards the output with a 2-channel oscilloscope; one channel connected at the output, the other channel probing the said signal path. With valve gear, I wouldn't dare NOT to use differential probes.
If all looks good with resistive load, add a bit of capacitive load and see what happens.... (around 0.047uF will do). Turn the bias pot a bit, tap on it... did you do a sniff test (see my previous posts...)??
If the amp appears stable, add a sinewave at the inputs of some 0.5Vpp at 1kHz, and repeat the above with probes. A good old signal generator (so that you could adjust the input level to the amp) will be immensely helpful.
By the way, did any of those 2 fellas who tried to fault-find the problem do what I suggested above?
Use the fact that only one channel has the problem to your advantage...
Even though it is a single tube for both channels, there is a way to do a "flip" to see if the problem jumps to the other channel. Pins 3 and 6 are the left/right cathodes of the 6AS7, they connect to the coupling electrolytics. You can try flipping pins 3 and 6 to the opposite capacitors. If the problem moves to the other channel then you know the problem is upstream from the capacitors. If it stays on the same channel then you know the problem is somewhere downstream from the cathodes.
Even though it is a single tube for both channels, there is a way to do a "flip" to see if the problem jumps to the other channel. Pins 3 and 6 are the left/right cathodes of the 6AS7, they connect to the coupling electrolytics. You can try flipping pins 3 and 6 to the opposite capacitors. If the problem moves to the other channel then you know the problem is upstream from the capacitors. If it stays on the same channel then you know the problem is somewhere downstream from the cathodes.
I am honestly sorry, but being very much still ignorant in this hobby means I understand very little of what you are suggesting I do, plus I do not have oscilloscopes, signal generators or anything like that..
For starters I tried flipping the output channels like suggested, and the noise did indeed flip from the right channel to the left.
Yes, I have double checked and made sure my house's voltage is 240V, and that's how I wired the transformer per manual instructions. I have also tested that the ground is working well, which it is (I tested this in each of the 4 different houses I tested the amp at).
Even though this doesn't sound like it would matter in my situation, I was suggested to replace the octagonal socket with a better one, if only to completely rule out the possibility of having a bad connection there. I have done so earlier this afternoon, but nothing has changed and the noise is still there like before.
Even though this doesn't sound like it would matter in my situation, I was suggested to replace the octagonal socket with a better one, if only to completely rule out the possibility of having a bad connection there. I have done so earlier this afternoon, but nothing has changed and the noise is still there like before.
That said, I believe the last guy I brought my amp to did check with an oscilloscope, but I wouldn't be able to say how exactly he tested. Plus, the issue just wasn't there while he looked into it..
Hello there!
If this is not too late, in my opinion there will be 2 components to look after:
Firstly, I suspect the red small LED in the cathode of the first tube....but they are very sensitive to soldering-desoldering, keep those for last.
Secondly, the output capacitor could fail, can I see what component is there? I don't have time to sail between pictures. IF they are not of good quality I shold advise to change them both, anyway.
So, even if I suspect the LED's first, they are way too sensitive to roll, but you can swap the capacitors and if there's no change, try to swap also the led's, HLMP6000. I would just desolder the pins in contact with 12AU7 and reverse, you may damage for good the leds if you overheat them. Try to be as quick as possible with those when you desolder them.
If not so experienced, use some pliers when desoldering, they will absorb the heat and protect the plastic case of the led.
Even if you will fix it - and I'm almost sure the cause of that crackling couldn't be somewhere else, if you are sure about the tubes, I recomend to add those 1M resistors indicated above and maybe some 0.1....0.47uF non polarized film capacitors in parallel with the 100uF output caps, especially if they are not the best quality...they will improve the high frequency response. Be sure to get 250V rated or more...in my amps I tend to use overrated capacitors, even at 400V, they are not much more expensive than lower voltage ones and if you also have some expensive headphones, any safety add should be welcome.
If this is not too late, in my opinion there will be 2 components to look after:
Firstly, I suspect the red small LED in the cathode of the first tube....but they are very sensitive to soldering-desoldering, keep those for last.
Secondly, the output capacitor could fail, can I see what component is there? I don't have time to sail between pictures. IF they are not of good quality I shold advise to change them both, anyway.
So, even if I suspect the LED's first, they are way too sensitive to roll, but you can swap the capacitors and if there's no change, try to swap also the led's, HLMP6000. I would just desolder the pins in contact with 12AU7 and reverse, you may damage for good the leds if you overheat them. Try to be as quick as possible with those when you desolder them.
If not so experienced, use some pliers when desoldering, they will absorb the heat and protect the plastic case of the led.
Even if you will fix it - and I'm almost sure the cause of that crackling couldn't be somewhere else, if you are sure about the tubes, I recomend to add those 1M resistors indicated above and maybe some 0.1....0.47uF non polarized film capacitors in parallel with the 100uF output caps, especially if they are not the best quality...they will improve the high frequency response. Be sure to get 250V rated or more...in my amps I tend to use overrated capacitors, even at 400V, they are not much more expensive than lower voltage ones and if you also have some expensive headphones, any safety add should be welcome.
Hello. I appreciate your input. Fortunately I was able to solve my issue a while ago, but forgot to update this thread.
The culprit was the resistance in the right channel output path, right after the 12AU7 socket. Replacing that (and afterwards installing the speedball) completely removed the noise from the output.
Thank you so much for anyone who gave me their input!
The culprit was the resistance in the right channel output path, right after the 12AU7 socket. Replacing that (and afterwards installing the speedball) completely removed the noise from the output.
Thank you so much for anyone who gave me their input!
