Is it possible that the higher bias in the ba3 mosfets made the sound a bit more cleaner and opened up in the higher frequencies?
so maximum gain from input to output of the combination of vol pot plus pre-amp is the gain of the pre-amp. Does that maximum gain cause the power amp to clip when the source sends a maximum signal?
Only when you find that you have an unclipped maximum signal and you have turned the vol pot to maximum and still you don't think it is loud enough.
If you reach a rotation where it is loud enough, then you don't need any more gain.
What is the voltage gain inside the Power Amplifier?
What is the maximum signal that the Power Amplifier can send to the speaker?
You NEED both of these to make any sensible estimate of the maximum input signal that leads to clipping of the output.
Have you read this Forum article?
Did you implement any of it's recommendations?
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html
The F4 has no gain, it is a power buffer. My build is running on +-30V when loaded. I just measured the rails with music playing. Unloaded they are around +-32V
I just increased the bias on the output mosfets of the preamp (which increased the transconductance) and due to the design of the circuit increased the gain on the preamp. I now get almost as loud as I need.
I will have to increase the bias a bit more, but for that I need larger heatsinks on the mosfets, being ordered right now!
I have around 250mA CCS on each regulator, it was already chosen to leave some room for higher bias.
1V across each mosfet is 50mA. So 100mA in total per each rail. I have some room to increase. 70mA should be enough I believe and 140mA still just over 1/2 of the CSS.
Your pre-amp ideally should have a maximum output that just exceeds the maximum input of your power follower.
Check the specifications of both to see your requirements.
Once you know that you can work back to the gain required in your pre-amp to just reach clipping as the vol pot hits the end stop of the attenuator.
Check the specifications of both to see your requirements.
Once you know that you can work back to the gain required in your pre-amp to just reach clipping as the vol pot hits the end stop of the attenuator.
I will have to implement the cascode in the BA3 to make it able to increase the rails over 30V to have overhead to drive the power amp.
Nice article about gain, thanks!
That should have been revealed during your project research before you bought any components !!!!
It was actually. But since it is a non documented add on to the ba3fe I've decided to build it first as described in the article and build guide and will now start to implement the cascode. The psu can be configured between 23 and 37V for each rail so that was taken care of from the beggining!
And I could actually go up to 32V on the ba3 without any change acording to Mr. Pass who describes the toshiba jfets as very robust and able to.withstand such higher voltages as long as they have proper ventilation!
The cascode is a better solution though!
Trouble
Hi!
Hope someone have an idea about what the problem is.
I was playing around with my ba-3 preamp, and a distortion analyzer.
I think i damage the jfet or the mosfet when i was adjusting the p3😕.
The problem is the output gain on the right channel is much lower than the left channel.
Here is an example: If i calibrate my soundcard in arta to -3dB´, i got it on the left channel from the ba-3 but the right channel i got -4dB.
(switching the left cable, same signal, 1000 hz tone )
I can adjust the right channels output (dB) with P3 if i turn it to max.
The second problem is that i can not adjust the harmonics on the right channel.
What shall i started with to find the problem?
You shall not playing around with things that working good;🙄
Tommy
Hi!
Hope someone have an idea about what the problem is.
I was playing around with my ba-3 preamp, and a distortion analyzer.
I think i damage the jfet or the mosfet when i was adjusting the p3😕.
The problem is the output gain on the right channel is much lower than the left channel.
Here is an example: If i calibrate my soundcard in arta to -3dB´, i got it on the left channel from the ba-3 but the right channel i got -4dB.
(switching the left cable, same signal, 1000 hz tone )
I can adjust the right channels output (dB) with P3 if i turn it to max.
The second problem is that i can not adjust the harmonics on the right channel.
What shall i started with to find the problem?
You shall not playing around with things that working good;🙄
Tommy
No, you SHOULD play with things, that's how you learn!
What's the bias and DC offset. Are you tracking those as you adjust P3?
Thank's 🙂
Learning to what, not to do...😀
maybe i did a mistake and turn the wrong pot, not P3
The bias diff, Q3 0,8v, Q4 0,4v.
I could rase the bias to 0,8v on the Q4.
I think i shall leave it until tomorrow.
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P3 effects offset, which effects bias/offset relationship if you don't re-level after playing with P3. Adjust the harmonic with P3 then reset your bias/offset and check again.
Also, massive DC offset (caused by adjusting P3) would effect voltage swing. Not sure if bias effects gain or not.
Also, with enough heatsink you can run more bias than .8V. I settled on 1.25V.
Also, massive DC offset (caused by adjusting P3) would effect voltage swing. Not sure if bias effects gain or not.
Also, with enough heatsink you can run more bias than .8V. I settled on 1.25V.
Okej started from the beginnig with a higher bias, about 1,1v.
The left channel is pretty good with 2mV diff between the npn and pnp.
Right channel is another story i got a diff about 90 mV npn and pnp (at zero offset).
The problem started when i was playing with the P3 pot.
Could i have damage the mosfet on the right side?
Excuse me for the all the beginner question..🙂
It's my first build.
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90mV difference in the bias or 90mV offset? If it is the bias it might be normal if the mosfets are not matched.
There is no problem if the bias is a few mV different in each channel. You will never get a pair to have the exact same bias voltage and get 0 offset because these are not perfect complementary pairs.
P3 Setup
In my case it was worth the effort to setup the ba-3 (and F5-t) with a dominant second harmonic.
With my gear it gave the sound a clear warm pleasant character.
I got a little hum in the speaker when i not playing, but i can live with that.🙂
Thank's to the DIYaudio community, and Nelson Pass!
Happy listener 😀🙂
In my case it was worth the effort to setup the ba-3 (and F5-t) with a dominant second harmonic.
With my gear it gave the sound a clear warm pleasant character.
I got a little hum in the speaker when i not playing, but i can live with that.🙂
Thank's to the DIYaudio community, and Nelson Pass!
Happy listener 😀🙂
I have rebuild it little. Earth ground to chassi, then cl60 between chassi and the audio ground (PSU). From psu i split the ground cable to rca (isolated from chassi ground) and pcb, some kind of star ground.
However when i rebuilt it with the cl60 between the chassi ground and music ground the hum problem was gone. 🙂
However when i rebuilt it with the cl60 between the chassi ground and music ground the hum problem was gone. 🙂
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