So working with brand new amplifier big and famous that had a customer complain about sound
initial test proved the amp was too cold
Checked bias according to the manufacturer and found low ....
Manufacturer need 8mv per transistor but found only 2.5
So adjusted bias and all appears to work fine .....
Placed a question to the chief engineer ( Turkish ) ( ?????? ) about it, since this is not only famous but also very expensive amp
And the answer was that may be from transportation trimmers have been moved Trimmers areBB top quality 10
turn
Please comment your opinion for this bellow
initial test proved the amp was too cold
Checked bias according to the manufacturer and found low ....
Manufacturer need 8mv per transistor but found only 2.5
So adjusted bias and all appears to work fine .....
Placed a question to the chief engineer ( Turkish ) ( ?????? ) about it, since this is not only famous but also very expensive amp
And the answer was that may be from transportation trimmers have been moved Trimmers areBB top quality 10
Please comment your opinion for this bellow
- Weird that both trimmers would happen to move in the same direction to lower the bias in both channels by the same amount, although it isn't impossible, and depending on how the Vbe multiplier is designed (schematic?), it may be very sensitive to even a tiny movement of the trimmers.
- Are there specific instructions, such as "run at full power for X minutes, let cool down for Y minutes, then measure and adjust"? Some are meant to be adjusted cold, others after some specified warm-up schedule.
- Generally you're supposed to measure with no load attached (and of course no input signal applied), otherwise DC offset may skew the measurement.
- Now that you've adjusted it, is it stable?
- Are there specific instructions, such as "run at full power for X minutes, let cool down for Y minutes, then measure and adjust"? Some are meant to be adjusted cold, others after some specified warm-up schedule.
- Generally you're supposed to measure with no load attached (and of course no input signal applied), otherwise DC offset may skew the measurement.
- Now that you've adjusted it, is it stable?
Oh, sorry. Again, very unlikely but not impossible. Multi-turn trimmers do have a certain amount of play, which you can notice when you change direction and it takes half a turn or so to engage again, so I guess if you drop it from a sufficient height...
Or the famous designer of the expensive amplifier doesn't want to admit to bad QC. Also not impossible.
Or the famous designer of the expensive amplifier doesn't want to admit to bad QC. Also not impossible.
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I'd go with that.
The other option is extremely unlikely, like - impossible in this universe!
They both move the same direction, the same amount? And from a setting for 10mV to 2.5mV is not just some play.
Apply Occam's Razor and there's no question.
Jan
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There might also be an effect of supply voltage differences affecting the bias (ideally it shouldn't, but not everything is ideal).