adjusting bias...
As has been pointed out before, the process of adjusting the bias is slow and steady. Do not attempt to do it in 10 minutes, you'll end up way over-biased. Set it to perhaps 50% of what you ultimately want then walk away for an hour. Come back and adjust to half the difference between what you have and what you want, walk away for an hour...repeat 3 or 4 times, then leave it untouched for three or four hours, measure and adjust again...
...and do all this with the amp in it's 'normal' form...fans etc need to be on, case in place, anything that can change the dissipation of the heatsinks should be in place...
When the amp is at room temp, the bias will sit low until the heatsinks reach 'normal' temp, so you have to set the initial value appropriately. The bigger the heatsinks the longer this will take, 10's of minutes through an hour is not uncommon...
HTH
Stuart
As has been pointed out before, the process of adjusting the bias is slow and steady. Do not attempt to do it in 10 minutes, you'll end up way over-biased. Set it to perhaps 50% of what you ultimately want then walk away for an hour. Come back and adjust to half the difference between what you have and what you want, walk away for an hour...repeat 3 or 4 times, then leave it untouched for three or four hours, measure and adjust again...
...and do all this with the amp in it's 'normal' form...fans etc need to be on, case in place, anything that can change the dissipation of the heatsinks should be in place...
When the amp is at room temp, the bias will sit low until the heatsinks reach 'normal' temp, so you have to set the initial value appropriately. The bigger the heatsinks the longer this will take, 10's of minutes through an hour is not uncommon...
HTH
Stuart
right
Thanks Stewart. I just had sufficient time to try it the way I did. Will do a marathon session soon with fans and load and report back. From what happened does it appear that things are at least working?
Thanks Stewart. I just had sufficient time to try it the way I did. Will do a marathon session soon with fans and load and report back. From what happened does it appear that things are at least working?
Re: adjusting bias...
If you lower the resistance, does the Bias follow or is it an inverse relationship? What side of the pot should the wiper be on for lowest possible Bias?
Regards
Anthony
Stuart Easson said:
If you lower the resistance, does the Bias follow or is it an inverse relationship? What side of the pot should the wiper be on for lowest possible Bias?
Regards
Anthony
Re: Re: adjusting bias...
Am I the only one who uses the Wiki? I am certainly the only one who is editing it with info from this thread. I'm going to start putting my own personal notes in there for building this thing.
The answer to this question is in the wiki under "setting the bias" with links to where this was discussed before. Higher R = higher bias. While you are reading it, why don't you enter your data into the krell-o-tracker at the end?
Krell Build Wiki Link
Coulomb said:
Am I the only one who uses the Wiki? I am certainly the only one who is editing it with info from this thread. I'm going to start putting my own personal notes in there for building this thing.
The answer to this question is in the wiki under "setting the bias" with links to where this was discussed before. Higher R = higher bias. While you are reading it, why don't you enter your data into the krell-o-tracker at the end?
Krell Build Wiki Link
sounds like it's working to me...
...if you can also adjust the output offset using the other pot you are definitely in good shape, it means the DC levels are properly coupled from end to end, at which point you should be able to play music...
I have my bias pot installed so clockwise rotation increases the bias, but I am not using the same pots the layout was designed for, so beware. IIRC the track cutting stuff was to give clockwise==more bias.
...and yes I edit the wiki from time to time...;^)
Happy listening
Stuart
...if you can also adjust the output offset using the other pot you are definitely in good shape, it means the DC levels are properly coupled from end to end, at which point you should be able to play music...
I have my bias pot installed so clockwise rotation increases the bias, but I am not using the same pots the layout was designed for, so beware. IIRC the track cutting stuff was to give clockwise==more bias.
...and yes I edit the wiki from time to time...;^)
Happy listening
Stuart
bias
I did cut the tracks, and jumper where instructed. Yet, for me clockwise = less bias................
..........on my version of this Krell KSA-50 Clone.
I did cut the tracks, and jumper where instructed. Yet, for me clockwise = less bias................
..........on my version of this Krell KSA-50 Clone.
Of course it's a Krell Clone.
I did the track corrections as well and clockwise is lower bias.
Question:
Should the DC offset be set before biasing or does it matter?
Thanks, Terry
I did the track corrections as well and clockwise is lower bias.
Question:
Should the DC offset be set before biasing or does it matter?
Thanks, Terry
dc
Good, at least someone has the same results as me!
Terry, I think you should adjust the DC offset AFTER biasing because when you adjust bias you will affect the DC offset. I don't think it would do any good to adjust DC as you go because your DC setting would be messed up as soon as you change bias.
still4given said:
Good, at least someone has the same results as me!
Terry, I think you should adjust the DC offset AFTER biasing because when you adjust bias you will affect the DC offset. I don't think it would do any good to adjust DC as you go because your DC setting would be messed up as soon as you change bias.
Yep, you have to see it this way; the higher the resistance, the more bias slips the other way😉
Steen😎
Al,
The files syou sent for the board are corrupt and will not open. Can you resend them when you have a moment.....
Thanks!
Mark
The files syou sent for the board are corrupt and will not open. Can you resend them when you have a moment.....
Thanks!
Mark
Member
Joined 2002
I burned one of my driver resistors. The BOM calls for 25R 2w. I could only find 22R, 24R and 27R. I if substitute one of these which should I use? I would change out both of course.
Another question:
If using the light bulb trick ahead of the transformer, is it common for the light to start burning brighter when the bias is raised? It pulls the rails down to about 27VCD with the RE at .134V drop on 0.68R.
Thanks, Terry
Another question:
If using the light bulb trick ahead of the transformer, is it common for the light to start burning brighter when the bias is raised? It pulls the rails down to about 27VCD with the RE at .134V drop on 0.68R.
Thanks, Terry
I hate to ask this-- but why would a driver resistor go? Should I replace my 2 watters with a 5 watters to be safe before I button this thing up?
lgreen said:
Because if you Driver resistor did not go, it would be a passenger resistor? 🙂 🙂
Anthony