Mark, which scope are you referring to? I'd like to know what you would deem worthy.
Don't you dare do that to me! My BA2018 is not done yet!!!!!! (on the other hand I can still make changes....eek!)
Good news. Problem is solved and this matched, premium board appears to be fixed.
Did two things: removed the resistors surrounding the 4 SMDs and carefully reflowed their legs using special precaution to make sure their continuity was clean and immediate. Then, while resoldering the Rs, noticed there were issues with both Q16 and Q18 -- the legs were not firmly soldered.
Made these changes and have been playing the BA2018 for an hour now and the left channel is staying rock stable in its volume -- soundstage is nicely stable as well.
So, THANKS folks. Those who stressed cold solder joints are the winners but all the help is appreciated.
Did two things: removed the resistors surrounding the 4 SMDs and carefully reflowed their legs using special precaution to make sure their continuity was clean and immediate. Then, while resoldering the Rs, noticed there were issues with both Q16 and Q18 -- the legs were not firmly soldered.
Made these changes and have been playing the BA2018 for an hour now and the left channel is staying rock stable in its volume -- soundstage is nicely stable as well.
So, THANKS folks. Those who stressed cold solder joints are the winners but all the help is appreciated.
I'd sure like to see your offset lower. That seems a bit high. Mine, for example, is at 0V.
I do see a few things that could be related. The yellow circles are a few sockets that look like they may need to be reheated or have solder added. The best check, of course, it to check the back side of the board. The red circles on Q3 and Q4 look like you might have shorted a few connections. Or it could be just a photo anomaly and those are the existing traces. Let us know!
I do see a few things that could be related. The yellow circles are a few sockets that look like they may need to be reheated or have solder added. The best check, of course, it to check the back side of the board. The red circles on Q3 and Q4 look like you might have shorted a few connections. Or it could be just a photo anomaly and those are the existing traces. Let us know!
On your scope it looks like the half of the sinus is cut away? Voltages in the PSU and on the amp board are for sure o.K.?
How do you feed the sinus signal in?
How do you feed the sinus signal in?
R11 and R12 are shown as 27 Ohm on the schematic. Seems likely!
Also (per your photo) check the joint on Q1. It appears to have a cold joint (even though this would only affect that particular channel.)
Also (per your photo) check the joint on Q1. It appears to have a cold joint (even though this would only affect that particular channel.)
I had not spotted your larger output transistors. 15 Ohms is correct, then.
Please check this post from 6L6:
https://www.diyaudio.com/community/threads/waynes-ba-2018-linestage.329240/post-7825436
Are you sure you are using the 5pF parts for C1 and C7? Somewhere in this thread is a mention (by 6L6) as to which one is which since I think both pairs of parts are sent and they look very similar to each other.
Please check this post from 6L6:
https://www.diyaudio.com/community/threads/waynes-ba-2018-linestage.329240/post-7825436
Are you sure you are using the 5pF parts for C1 and C7? Somewhere in this thread is a mention (by 6L6) as to which one is which since I think both pairs of parts are sent and they look very similar to each other.
Double check please R15,R16 and R30, R43 values.
Those decides the gain.
(47K/27K)+1
P.S.: I will recheck if that’s correct resistors for gain and calculus in 30 min when I reach PC and edit.
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