Before I even try powering it on I think I'm going to address the issues that I have around the zener diode region
The problematic right side is alot worse in terms of scorching
But I had noticed the left channel has heat stress also, just now
So
With a bit of AI I found what probably needs to be done
If someone wouldn't mind giving a human eye over this as I have removed dynamic bias so the board will be subjected to alot more heat stress over time
@bigskyaudio what are your thoughts?
The problematic right side is alot worse in terms of scorching
But I had noticed the left channel has heat stress also, just now
So
With a bit of AI I found what probably needs to be done
If someone wouldn't mind giving a human eye over this as I have removed dynamic bias so the board will be subjected to alot more heat stress over time
@bigskyaudio what are your thoughts?
Attachments
I dont know if anyone has any input..
Im not getting any idle MV on any emitter resistors on the modded driver board nor the original untouched!
now ive been using the modded side for testing and im getting sound after all the work, i pissed about rebuilding dynamic bias to same issue, replacing opamp etc
i have now completely removed opamp, r140 and r94, jumpered c83, put a trimmer on tvr one and set between 800-1000 ohms, tvr 2 has a 220ohm resistor
now when i play music quite loud i get mv up to around 13/14, however it basically zeros out when no source
i believe the amp is just playing in class b, ?
anyone have any ideas as ive spent a week trying different things
Im not getting any idle MV on any emitter resistors on the modded driver board nor the original untouched!
now ive been using the modded side for testing and im getting sound after all the work, i pissed about rebuilding dynamic bias to same issue, replacing opamp etc
i have now completely removed opamp, r140 and r94, jumpered c83, put a trimmer on tvr one and set between 800-1000 ohms, tvr 2 has a 220ohm resistor
now when i play music quite loud i get mv up to around 13/14, however it basically zeros out when no source
i believe the amp is just playing in class b, ?
anyone have any ideas as ive spent a week trying different things
At this point laup, I would return that to the factory for service. Or, maybe you'll figure things out.
As I said before, don't mess with a well engineered product unless you're going to return it to factory condition. Engineers design things a certain way for very good reasons. The second you begin second guessing a good engineering team, you are on your own. Badly engineered stuff - sure. But be certain you're a better engineer than the people who designed it in the first place.
You were determined to upgrade this amp following the advice of others, so I stepped out.
As I said before, don't mess with a well engineered product unless you're going to return it to factory condition. Engineers design things a certain way for very good reasons. The second you begin second guessing a good engineering team, you are on your own. Badly engineered stuff - sure. But be certain you're a better engineer than the people who designed it in the first place.
You were determined to upgrade this amp following the advice of others, so I stepped out.
I fixed the issue with the right channel not turning on for 5 mins, however the untouched left driver board gives the basically the same readings which is baffling me. ..
Really? Even if I pull out the original and measure it, and set the new pot to that value?
Yes, really. This should be pretty obvious to anyone skilled in electronics. Also, know your parts.
Look at a 10 turn control, look at a 270° control (single turn). Do you see a difference in the moving contact size? What difference could that make do you think?
They make a few 10 turn controls that can handle more wiper current, but not many. Most folks buy the cheap ones. 10 turn trimmers are meant for low current potentiometer use (ie - no current flow).
Now, what advantages will a 10 turn control bring to the table? I'll tell you one thing from experience, you can't tell approximately where it is by looking at it. I just set bias current for a tube amplifier that uses 10 turn pots. They are a pain to keep the tool on (I'm using the specific tool made for them). It takes far longer to get the current into the proper range and if you have to go from control to control, it takes much longer. 10 turn controls are for precision, and actually not often needed for that if the circuit is designed properly to begin with. We use them for test instruments and process control.
Is bias current a precise adjustment? No it isn't, it varies with temperature and supply (mains) voltages. You set it close, but it won't be at that value in an hour, or tomorrow.
Okay, how about DC offset? Okay, another non-critical adjustment. It's often okay below 50 mV, I like to adjust it close to zero, but again it will probably move from there. Hmmm, what else? Power supply regulator voltages? Nope, they just need to be stable and close. How about current limiting? Nope. Again, close t the ball park, non-critical again.
There are no adjustments in an audio amplifier that requires the precision of a 10 turn control, none. In fact, a 10 turn control is often less reliable than a single turn. You also cannot tell visually if the control is in a "normal" position for that equipment. These are all negatives, strong ones.
So give me a case for using a 10 turn control that doesn't involve improper circuit design. You can have fine adjustment by using resistances in series or in parallel with a single turn control. This is proper design.
Look at a 10 turn control, look at a 270° control (single turn). Do you see a difference in the moving contact size? What difference could that make do you think?
They make a few 10 turn controls that can handle more wiper current, but not many. Most folks buy the cheap ones. 10 turn trimmers are meant for low current potentiometer use (ie - no current flow).
Now, what advantages will a 10 turn control bring to the table? I'll tell you one thing from experience, you can't tell approximately where it is by looking at it. I just set bias current for a tube amplifier that uses 10 turn pots. They are a pain to keep the tool on (I'm using the specific tool made for them). It takes far longer to get the current into the proper range and if you have to go from control to control, it takes much longer. 10 turn controls are for precision, and actually not often needed for that if the circuit is designed properly to begin with. We use them for test instruments and process control.
Is bias current a precise adjustment? No it isn't, it varies with temperature and supply (mains) voltages. You set it close, but it won't be at that value in an hour, or tomorrow.
Okay, how about DC offset? Okay, another non-critical adjustment. It's often okay below 50 mV, I like to adjust it close to zero, but again it will probably move from there. Hmmm, what else? Power supply regulator voltages? Nope, they just need to be stable and close. How about current limiting? Nope. Again, close t the ball park, non-critical again.
There are no adjustments in an audio amplifier that requires the precision of a 10 turn control, none. In fact, a 10 turn control is often less reliable than a single turn. You also cannot tell visually if the control is in a "normal" position for that equipment. These are all negatives, strong ones.
So give me a case for using a 10 turn control that doesn't involve improper circuit design. You can have fine adjustment by using resistances in series or in parallel with a single turn control. This is proper design.
I appreciate your explanations and agree with all of that as general practical advice!
Sure, don't willy-nilly swap out 100 ohm pots. But I'm still going to continue swapping out touchy single turn 5k pots in Adcom 5200 and 5400 amps for multi-turn pots (25 turn Bourns 3296) for dialing in bias and DC offset.
Sure, don't willy-nilly swap out 100 ohm pots. But I'm still going to continue swapping out touchy single turn 5k pots in Adcom 5200 and 5400 amps for multi-turn pots (25 turn Bourns 3296) for dialing in bias and DC offset.
Might I suggest padding the values so you can use a single turn more easily? Just increase series resistors in value so the pot doesn't have as much range. Multiturn controls don't fit the footprint anyway.
Yamaha had the same darned problem, their pots had too much range. We called it "Yamaha syndrome" as we were authorized warranty.
Yamaha had the same darned problem, their pots had too much range. We called it "Yamaha syndrome" as we were authorized warranty.
Ok I jumpered tvr2
And put a pot back on tvr1
The course is very brutal with a 2kohm pot
However I have mv on emitters now however I cannot go over maximum 8mv
As u can see on picture I have dc of set and emitter readings
Seems protection kicks anything higher
I can play music very loud and the emitters go above to around 14mv which is ok
However if bias is set above 8mv I get no output
Any ideas?
And put a pot back on tvr1
The course is very brutal with a 2kohm pot
However I have mv on emitters now however I cannot go over maximum 8mv
As u can see on picture I have dc of set and emitter readings
Seems protection kicks anything higher
I can play music very loud and the emitters go above to around 14mv which is ok
However if bias is set above 8mv I get no output
Any ideas?
