Take your time with the adjustments. You need to have the lid on except when you take it off quickly to make an adjustment and then replace the lid again. So there is a lot of waiting for temperature to stabilize.
As for the P3 I suggest you leave it alone for now. Its proper adjustment requires tools for measuring the distortion characteristics. You also have to be very careful with P3 since it changes the bias as well.
Here's 6L6's video demonstrating the adjustment of the P3 pot:
Adjusting P3, Nelson Pass Burning Amplifier BA-3 - YouTube
As for the P3 I suggest you leave it alone for now. Its proper adjustment requires tools for measuring the distortion characteristics. You also have to be very careful with P3 since it changes the bias as well.
Here's 6L6's video demonstrating the adjustment of the P3 pot:
Adjusting P3, Nelson Pass Burning Amplifier BA-3 - YouTube
Thanks for the tips. I probably have better than 12 hours playing with bias / DC offset. I let it cook for an hour after I finally got to a point I was happy and it was stable . I might be 3 mv high on on channel a 1 high on the other. Under a mv of offset in one channel and under 2 in the other.
I worked hard for it. I'll have to watch the video later. I'll go with it as is for now as you suggest.
I worked hard for it. I'll have to watch the video later. I'll go with it as is for now as you suggest.
I have a set back, re tying everything into place has shifted something. I know there are iffy pads on front end boards. Previous builder opened power holes up to accommodate 12 GA wire. It was the root of all my initial problems. I repaired trace ( pad) and it was solid until I started pulling everything back in place to dress . If I play with it enough I can likely get it right but the right repair is replacing the 2 front end boards and the wire from the power supply to the front end boards. I sent an email to the diy store to see if they'll just sell me a pair of FE boards.
I'm taking a deep breath and a step away for a day . Last night I was frustrated. After a night of sleep , ( well most of a night).
I've accepted the situation and dealing with it. I appreciate all the help , advice and patience you've given. I'll linger in the background for a few days to see how I can best go forward. I understand my problems and know how to fix.
Now I'm sorry for not building this from scratch myself. Another of life's lessons.
I'm taking a deep breath and a step away for a day . Last night I was frustrated. After a night of sleep , ( well most of a night).
I've accepted the situation and dealing with it. I appreciate all the help , advice and patience you've given. I'll linger in the background for a few days to see how I can best go forward. I understand my problems and know how to fix.
Now I'm sorry for not building this from scratch myself. Another of life's lessons.
Pulled that board. Did some creative bridging. I believe i got it solid ( getting to the point where i have enough stuff to build a second less transformer and chassis) . Is there some common wisdom regarding how high you can safely bias this? I understand shooting for 350mv. I have it baking but it creeps to 355mv or so. Is that an uncomfortably high setting? I know if a tweak it down, its going to start the baking process over. I am hoping to avoid.
Nelson's words:
The point at which the diodes conduct is temperature dependent, so you will want to set the bias so that it makes a nice transition above the bias point and doesn't run away when the amplifier gets hot. If you are competent, fearless and also own a fire extinguisher, you can find this point. Just run the amplifier into a reasonably low impedance until it gets good and hot – as hot as you plan to let it get - ever. Then adjust the bias to a point below where the idle current starts to really take off. You should find that this point is around 0.4 volts across the 1 ohm resistors. If you are afraidy-cat, then just set it at 0.3 volts, and conservatively fuse the AC line.
I gave up on 350mV and set mine to 310mV ( that way I'm not afraidy-cat) and don't need a fire extinguisher.
The point at which the diodes conduct is temperature dependent, so you will want to set the bias so that it makes a nice transition above the bias point and doesn't run away when the amplifier gets hot. If you are competent, fearless and also own a fire extinguisher, you can find this point. Just run the amplifier into a reasonably low impedance until it gets good and hot – as hot as you plan to let it get - ever. Then adjust the bias to a point below where the idle current starts to really take off. You should find that this point is around 0.4 volts across the 1 ohm resistors. If you are afraidy-cat, then just set it at 0.3 volts, and conservatively fuse the AC line.
I gave up on 350mV and set mine to 310mV ( that way I'm not afraidy-cat) and don't need a fire extinguisher.
I haven't disappeared.
I did find doing the 20 minute cook method ( near 0mv offset, around 350mv bias, when I left it overnight , I found bias drifted up around 360mv and the DC offset shifted about 10mv. Being cautious ( fraidy cat?) I'm not comfortable that high (360) I've been backing it down in hits twice a day. Nelson has set me straight that I shouldn't worry much about DC offset ( I had been shooting for 0mv)
He said he wouldn't worry about anything under 10mv also he said while testing distortion on certain drivers, he got lowest distortion at over a volt of DC offset. I'll still try to stay very low. The twice a day testing , tweaking is a slow go. I think I'm close
I did find doing the 20 minute cook method ( near 0mv offset, around 350mv bias, when I left it overnight , I found bias drifted up around 360mv and the DC offset shifted about 10mv. Being cautious ( fraidy cat?) I'm not comfortable that high (360) I've been backing it down in hits twice a day. Nelson has set me straight that I shouldn't worry much about DC offset ( I had been shooting for 0mv)
He said he wouldn't worry about anything under 10mv also he said while testing distortion on certain drivers, he got lowest distortion at over a volt of DC offset. I'll still try to stay very low. The twice a day testing , tweaking is a slow go. I think I'm close
Just started my F5T build. Fingers crossed! (hopefully not the wires)
This will be used with a pair of LX Mini speakers I've already constructed. I also put together the Pass Active Crossover for them and added a 6-24 ACN board in the same box for output to sub woofers. It was an eye-opener even using a pair of Crown XL amps to power everything. Love your ACN Mr. Pass. And your buddy Seigfried did some pretty awesome work too. These do not sound or act like typical speakers. I will use my existing F5 for the high end drivers and the F5T for the low end. I have to think that will a noticeable improvement over the Crown class D amps that I typically use to power subwoofers.
This will be used with a pair of LX Mini speakers I've already constructed. I also put together the Pass Active Crossover for them and added a 6-24 ACN board in the same box for output to sub woofers. It was an eye-opener even using a pair of Crown XL amps to power everything. Love your ACN Mr. Pass. And your buddy Seigfried did some pretty awesome work too. These do not sound or act like typical speakers. I will use my existing F5 for the high end drivers and the F5T for the low end. I have to think that will a noticeable improvement over the Crown class D amps that I typically use to power subwoofers.
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The store kit is now using TIP31 and TIP32 in place of these transistors:
F-5T V1/2 Transistor Kit – diyAudio Store
I personally would go with substitutes for the cascodes instead of risking fakes on ebay.
F-5T V1/2 Transistor Kit – diyAudio Store
I personally would go with substitutes for the cascodes instead of risking fakes on ebay.
CL60 Vs CL70
I have completed an F5, it sounds great. Around 1 in ten power-ups the fuse in the isolation switch blows and needs replacing (1.25A slow). I live in Europe with 220Vac line voltage , I wonder whether I should replace the CL60 with a CL70 with increased the resistance from 10 Ohms to 16 Ohms (RT), the only secondary effect I can see is that the CL70 will sustain a reduce current of 4A. Before I implement this change does anyone have experience here?
I have completed an F5, it sounds great. Around 1 in ten power-ups the fuse in the isolation switch blows and needs replacing (1.25A slow). I live in Europe with 220Vac line voltage , I wonder whether I should replace the CL60 with a CL70 with increased the resistance from 10 Ohms to 16 Ohms (RT), the only secondary effect I can see is that the CL70 will sustain a reduce current of 4A. Before I implement this change does anyone have experience here?
