I have been pondering balancing speaker output by setting the bias so the speaker outputs voltages are equal,
rather than the bias voltages being equal while monitoring the bias voltages for longevity sake of the output transistors,
I can do this with my sound generator and oscilloscope.
Equal input to both channels while looking at the voltages of both outputs.
Seems like a a great way to compensate for ,minute L-R circuit differences.
rather than the bias voltages being equal while monitoring the bias voltages for longevity sake of the output transistors,
I can do this with my sound generator and oscilloscope.
Equal input to both channels while looking at the voltages of both outputs.
Seems like a a great way to compensate for ,minute L-R circuit differences.
NO!
If you do as you're suggesting, you'll likely damage your amp.
Find a service manual and follow its instructions.
Edit: I'll back away a bit from my initial alarm. If you're tweaking offset error, that's more benign; first impression was that you were looking at bias current.
None the less, follow SM instructions. You want the DC across each speaker to be 0V. Matching their errors will not help life of the output devices.
If you do as you're suggesting, you'll likely damage your amp.
Find a service manual and follow its instructions.
Edit: I'll back away a bit from my initial alarm. If you're tweaking offset error, that's more benign; first impression was that you were looking at bias current.
None the less, follow SM instructions. You want the DC across each speaker to be 0V. Matching their errors will not help life of the output devices.
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Yes, don't mistake bias for offset - set the bias wrong and you might fry the amps, or even have it oscillate and fry your tweeters. Set the offset wrong and speakers will be offset from their rest position a bit. Many amps don't have offset adjustment as the offset is low enough anyway.
Bias adjustment should be done as documented for the particular amp type.
Bias adjustment should be done as documented for the particular amp type.
Changing the bias does not change the audio gain or the audio balance.
Only the DC current, and sometimes the DC output offset voltage.
Only the DC current, and sometimes the DC output offset voltage.
I was able to compare input sine wave to out put sign wave.
I learned a lot.
I am wondering.
If I input 5k sine wave to both channels,
and adjust bias voltages so they are equal, and then compare
magnitude of both output channels with o-scope and adjust bias to output
signal rather than bias voltage for a truly balanced L&R signal.
thoughts
I learned a lot.
I am wondering.
If I input 5k sine wave to both channels,
and adjust bias voltages so they are equal, and then compare
magnitude of both output channels with o-scope and adjust bias to output
signal rather than bias voltage for a truly balanced L&R signal.
thoughts
"Truly balanced L&R signals" implies identical channels with respect to gain and frequency response, and trimming voltage offset differences changes nothing regarding channel matching. A voltmeter will measure offset error far more accurately than a scope. A scope is a wonderful instrument to have, but not the best tool for DC output nulling.
Remember, 0V across the speakers is the objective. Consider a hypothetical: say you had precisely matched channels--- truly balanced L&R signals--- but with 10VDC riding on each channel. Would this be desirable?
Remember, 0V across the speakers is the objective. Consider a hypothetical: say you had precisely matched channels--- truly balanced L&R signals--- but with 10VDC riding on each channel. Would this be desirable?
of course not,
My plan is as follows-
zero dc offset on both channels,
measure the bias resistors, both channels, 10 times,
removing the high and low resistances, then averaging 8 readings of each channel,
That way i can calculate Transistor current, knowing, nominal resistance and current values,
I can compensate for resistance difference between transistors, thus matching the current via voltage
for the individual resistances..
thus as example, Last years tweak......
note that 15.09 emitter current is < than15.15 nominal emitter current,
I am thinking the current should be nominal or greater, thus the mv should be 10.2 and 10.3ma
instead of 10.1 and 10.2ma;
thanks for listening.
My plan is as follows-
zero dc offset on both channels,
measure the bias resistors, both channels, 10 times,
removing the high and low resistances, then averaging 8 readings of each channel,
That way i can calculate Transistor current, knowing, nominal resistance and current values,
I can compensate for resistance difference between transistors, thus matching the current via voltage
for the individual resistances..
thus as example, Last years tweak......
| 5_13_23 | Left | R emit | Right | Units | Left | DC Offset | Right | |
| 1 | 0.66862 | 0.67315 | ohm | 0 | DC mv | 0 | ||
| 2 | 0.66890 | 0.67352 | ||||||
| 3 | 0.66897 | 0.67356 | SPL db | |||||
| 4 | 0.66905 | 0.67359 | Left | Stereo | Right | |||
| 5 | 0.66918 | 0.67367 | 64.0 | 67 | 64.0 | |||
| 6 | 0.66921 | 0.67386 | ||||||
| 7 | 0.66949 | 0.67398 | ||||||
| 8 | 0.66951 | 0.67399 | ||||||
| 9 | 0.66980 | 0.67419 | ||||||
| 10 | 0.66991 | Nominal | 0.67423 | |||||
| R emit | 0.669 | 0.660 | 0.674 | ohm | ||||
| E emit | 10.1 | 10.0 | 10.2 | mv | ||||
| I emit | 15.09 | 15.15 | 15.14 | ma |
I am thinking the current should be nominal or greater, thus the mv should be 10.2 and 10.3ma
instead of 10.1 and 10.2ma;
thanks for listening.
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