SteveHolt -
P3 is to adjust the distortion spectra only, it has nothing to do with setting output bias.
You need to neutralize it, count turns from one side to the other and stop halfway. Don't touch it again.
P1 and P2 are where you set the bias and the offset.
The two pots work as a sort of teeter-totter to control both the offset and bias, in concert with each other. One does not do bias and the other doesn't do offset, instead you twiddle both to get both readings where you need it.
The best thing to do is get (3) voltmeters. Place one on the output to measure offset. place the other two on the N and P channel source resistors.
Turn both the pots evenly (it might take what feels like many turns) until you start seeing voltage across both source resistors. Turn them up to 0.2v. Now adjust one pot until you make the offset zero. This will certainly change the bias. That's normal.
Continue to increase the bias about .1v at a time, and then eliminate the offset. You will take two steps forward and one step back. Again, that's normal.
Once it's to 0.4, with zero offset, put the lid on and let it sit for 1/2 hour. Then adjust the bias to 0.47v across the source resistors with zero offset, and you are done.
Check it again in about a week.
P3 is to adjust the distortion spectra only, it has nothing to do with setting output bias.
You need to neutralize it, count turns from one side to the other and stop halfway. Don't touch it again.
P1 and P2 are where you set the bias and the offset.
The two pots work as a sort of teeter-totter to control both the offset and bias, in concert with each other. One does not do bias and the other doesn't do offset, instead you twiddle both to get both readings where you need it.
The best thing to do is get (3) voltmeters. Place one on the output to measure offset. place the other two on the N and P channel source resistors.
Turn both the pots evenly (it might take what feels like many turns) until you start seeing voltage across both source resistors. Turn them up to 0.2v. Now adjust one pot until you make the offset zero. This will certainly change the bias. That's normal.
Continue to increase the bias about .1v at a time, and then eliminate the offset. You will take two steps forward and one step back. Again, that's normal.
Once it's to 0.4, with zero offset, put the lid on and let it sit for 1/2 hour. Then adjust the bias to 0.47v across the source resistors with zero offset, and you are done.
Check it again in about a week.
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@steveholt: P1 and P2 control the bias on the output devices, and the two devices interact with each other as their individual bias levels change. So as you increase bias on the MOSFET connected to the positive rail, the output is driven overall positive and vice versa.
P3 is to be ignored after setting halfway (ohmmeter is the best way to do this and before installation and power up, ideally). On initial powerup if you have followed procedure correctly you should get zero voltage across the source resistors, and turning the pots P1 and P2 should increase this voltage. It typically takes many turns to get this going, five or more turns, but if you are running out of range even at maximum bias (maximum resistance) you may need to tweak the drain resistors on the input FETs. An ohmmeter is good for verifying pot resistance because those little screws keep turning even after hitting the endstops.
As the bias goes up you will see that the offset will constantly change. When you hit close to the desired bias level, you may have to make tiny adjustments to the bias to get everything to level out (the exact bias will be slightly different for both halves). At this point you might want to involve P3 as it affects the symmetry between the top and bottom halves of the circuit, and tune for maximum symmetry (exactly same bias levels on both sides of the supply) once the amp is fully warmed up.
I have managed offsets below 10mV with single F5, I see no reason why same or better is not possible with the Turbo.
P3 is to be ignored after setting halfway (ohmmeter is the best way to do this and before installation and power up, ideally). On initial powerup if you have followed procedure correctly you should get zero voltage across the source resistors, and turning the pots P1 and P2 should increase this voltage. It typically takes many turns to get this going, five or more turns, but if you are running out of range even at maximum bias (maximum resistance) you may need to tweak the drain resistors on the input FETs. An ohmmeter is good for verifying pot resistance because those little screws keep turning even after hitting the endstops.
As the bias goes up you will see that the offset will constantly change. When you hit close to the desired bias level, you may have to make tiny adjustments to the bias to get everything to level out (the exact bias will be slightly different for both halves). At this point you might want to involve P3 as it affects the symmetry between the top and bottom halves of the circuit, and tune for maximum symmetry (exactly same bias levels on both sides of the supply) once the amp is fully warmed up.
I have managed offsets below 10mV with single F5, I see no reason why same or better is not possible with the Turbo.
Single FE. Cascode, because it was there. Will hook up store boards in V3 tonight, hopefully. ONce again plugged the damn PSU up wrong. Had positive going into ground slot. with negative rail correct, G to G, poitive rail to ground, full power, all was fine. It even had little bit of bias on outpus. No worries. Listening to music now. I cannot say that V3 is big step over V2. For those who need the power, think you would have different results. V2 gives you the signature sound of the Turbo series. From there, it is about more power.
Nope, but they will. Just have to give them a cut diagram. I have tools that I can do it with. I asked him about anodizing, but there is a $300 minimum. Next bacth I order, I will pay to have them tap the holes. I hate tapping holes and I alwys go all the way through. Hidden tap is much more difficult. Rather than buy the tools I am going to see how much it cost. Funny^6 sinks enclosure will be dual monoblocks with single heatsink, like ACA. THE BAX will be monblocks with dual 8" tall, 18" deep.
Buzz,
Looking good. How big is that heat sink? Looked like you you have one channel's worth of output FETs (8) on it.
Regards,
It is 6" tall by 18" deep. The layout of Tea's boards limits its abilties, but that is the only issue. I like the compact and clean layout. This amp will go head to head with BA3B. Whoever wins gets its own new set of sinks sized just right. The sinks in the pica are being pushed 187watts, dissipation. If spread out, they would be fine. Now they are hot to touch at 5 seconds during full on play. Kids cut temp probe and temp gun is on fritz(spilled milk, literally)
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