[SonicTrance]

Here you go https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-180#post-13978373

 

[bloodhawk]

Here you go https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-180#post-13978373

You are awesome! <3 <3

 

[bloodhawk]

Does anyone have picture of the board without these resistors installed / list of the values in the order they are installed on the board -

Mainly the circled ones -

I am not able to confirm on my own amp, since there are a lot of wires/caps in the way.

 

[bloodhawk]

So kind of about to give up on troubleshooting his amp. Tested all the 330R resistors, and all of them check out just fine. Swapped around opamps, and the results were the same.

I didnt test out the voltages, since im not exactly sure which terminals to test the voltage between, now since this isnt my amp im trying to troubleshoot, i dont want to start poking and prodding terminals based on what i understand.

Will someone here be able to point me to exactly what to check for and in between what terminals?

 

[baronbeehive]

Does anyone have picture of the board without these resistors installed / list of the values in the order they are installed on the board -

Mainly the circled ones -

I can go better than that!
Left to right: 0.56, 106, 0.56, 1.9, 10, 10 - 10, 10, 106, 0.56, 0.56, 1.9 - - 106, 0.56, 0.56, 10, 10, 1.9, 10, 10, 1.9, 0.56, 106, 0.56
They're not mirrored between channels so that makes it slightly awkward.

I think they're all K ohms, I will check. Also the 2 values in bold might be reversed, I'll check that too.

 

[baronbeehive]

So kind of about to give up on troubleshooting his amp. Tested all the 330R resistors, and all of them check out just fine. Swapped around opamps, and the results were the same.

I didnt test out the voltages, since im not exactly sure which terminals to test the voltage between, now since this isnt my amp im trying to troubleshoot, i dont want to start poking and prodding terminals based on what i understand.

Will someone here be able to point me to exactly what to check for and in between what terminals?

Just check voltages on the 4 330R resistors, not the drop over the resistors. They should read around 100v on one side and 80v on the other. Then compare readings for the 4 circuits to see which one is out.

 

[bloodhawk]

I can go better than that!
Left to right: 0.56, 106, 0.56, 1.9, 10, 10 - 10, 10, 106, 0.56, 0.56, 1.9 - - 106, 0.56, 0.56, 10, 10, 1.9, 10, 10, 1.9, 0.56, 106, 0.56
They're not mirrored between channels so that makes it slightly awkward.

I think they're all K ohms, I will check. Also the 2 values in bold might be reversed, I'll check that too.

Damn ! Thanks a lot!

From some more troubleshooting, i have a feeling on of the bypass RIFA caps might not be upto spec or working properly. I cant test the capacitance with the cap installed the board, but tomorrow ill start take the bypass caps out one by one to see if thats the cause.

 

[bloodhawk]

Just check voltages on the 4 330R resistors, not the drop over the resistors. They should read around 100v on one side and 80v on the other. Then compare readings for the 4 circuits to see which one is out.

Voltages on the 330R's were matched up across left/right sections. SO that pretty much rules out the resistors. Even their values were consistent.

 

[baronbeehive]

Voltages on the 330R's were matched up across left/right sections. SO that pretty much rules out the resistors. Even their values were consistent.

That pretty much rules out channel imbalance then. One thing, the soldering looks to be OK. So that leaves the pot as far as I can see, don't know how you go on from here, someone else might have some ideas, at least it doesn't look serious!

 

[bloodhawk]

That pretty much rules out channel imbalance then. One thing, the soldering looks to be OK. So that leaves the pot as far as I can see, don't know how you go on from here, someone else might have some ideas, at least it doesn't look serious!

I doubt its the pot since, from what i understand, the pot come after the bias circuit.

I brought his amp back to my place today, and did some listening for a few hours, and seems like its not exactly a channel imbalance, but feels more like there is a hard roll off of the high end. Im not sure how to explain this properly.

But the main thing that really concerns me right now is the tube bias being 10-15mA lower on the right channel OR higher on the other one.

Im really leaning towards a bad / faulty cap. Probably one of bypass RIFA caps.

Also anyone know what exactly the TRIMPOTs are doing? Are they being used as a offset for the OPAMP auto biasing resistance?

 

[baronbeehive]

I doubt its the pot since, from what i understand, the pot come after the bias circuit.

I brought his amp back to my place today, and did some listening for a few hours, and seems like its not exactly a channel imbalance, but feels more like there is a hard roll off of the high end. Im not sure how to explain this properly.

But the main thing that really concerns me right now is the tube bias being 10-15mA lower on the right channel OR higher on the other one.

Im really leaning towards a bad / faulty cap. Probably one of bypass RIFA caps.

Also anyone know what exactly the TRIMPOTs are doing? Are they being used as a offset for the OPAMP auto biasing resistance?

The pot and biasing circuit are independent.

That roll off, would you describe it as a high frequency imbalance of some sort, seems even more likely to be the pot!

So what do the 2 meters read, also what tubes is he using

I believe the trimpots are for providing a baseline for the biasing.

Edit: Try flipping the gain switches, they're known to be problemmatic as well.

 

[klnglim]

My MK8SE just burnt again, any idea what happened? This is the third time already, may be bad luck for me. When begin turn on, look normal but after the second meter turn on the amp sound like something is burning and I straight turn it off immediately, the bulb seen normal, I have checked all the other component fine but the amp inside burn,cant find any reason what is going on?

 

[baronbeehive]

My MK8SE just burnt again, any idea what happened? This is the third time already, may be bad luck for me. When begin turn on, look normal but after the second meter turn on the amp sound like something is burning and I straight turn it off immediately, the bulb seen normal but the amp inside burn,cant find any reason what is going on?

I see you changed the layout, was it alright before and when did this happen, did it happen just after you did something?

 

[klnglim]

I see you changed the layout, was it alright before and when did this happen, did it happen just after you did something?

Before it was turn on, after second meter jump but meter show 0 with light and amp not working, that's why I changed take out the bypass cap

 

[baronbeehive]

Before it was turn on, after second meter jump but meter show 0 with light and amp not working, that's why I changed take out the bypass cap

If it was not something you did just before this happened you should check your solder joints, wires. Something is not making connection or is touching something else and shorting out.

Do you have a multimeter. If so you should check every solder joint you have made and make sure it is making proper connection with the board trace. That will rule out any problem solder work. Also check there is no solder particles lying around.

Finally make sure everything is connected up correctly.

Edit: Check especially the circuit which is reading zero, there is a faulty connection there somewhere.

This is disheartening kinglim, I'm sure it is something simple that can be put right!