A test that I commonly use on my servicing bench to verify performance of a repaired amplifier is as follows.
Take a Y-Lead and feed both channels with a music source.
Connect a single speaker between both output active terminals.
At medium volume setting, adjust the balance control to achieve nil output from the speaker.
Now adjust the volume up and down to gauge channel balance over the full volume range.
Turn the volume up to clipping to gauge behavior in overload condition.
Swing the tone controls to gauge tone control channel balance.
By adjusting the balance control left or right, speaker output level and absoloute polarity can be chosen.
By adjusting the volume control, the amplifier operating point can be chosen.
I find this quick and simple test to be very informative of the channel matching charcteristics of stereo amplifiers.
Eric.
Take a Y-Lead and feed both channels with a music source.
Connect a single speaker between both output active terminals.
At medium volume setting, adjust the balance control to achieve nil output from the speaker.
Now adjust the volume up and down to gauge channel balance over the full volume range.
Turn the volume up to clipping to gauge behavior in overload condition.
Swing the tone controls to gauge tone control channel balance.
By adjusting the balance control left or right, speaker output level and absoloute polarity can be chosen.
By adjusting the volume control, the amplifier operating point can be chosen.
I find this quick and simple test to be very informative of the channel matching charcteristics of stereo amplifiers.
Eric.
Useful amp test
Yes, cool it certainly is, especially for the amps. They are tested unloaded......
Jan Didden
Yes, cool it certainly is, especially for the amps. They are tested unloaded......
Jan Didden
Polarity & Level Settable Amplifier
Yes, this test will quickly and easily determine any non-matching of the two channels, and without test equipment and with real world music signals.
This test at clipping level is also particularly revealing.
Many amplifiers actually sound friendlier imo with an active load, and the ability to invert absoloute polarity easily is very handy.
With a four channel amplifier box (4 * LM3876 for example), and a dual gang linear pot, output level and polarity can be easily adjusted without any switching or other change in the replay system - see attached diagram.
Eric.
Yes, this test will quickly and easily determine any non-matching of the two channels, and without test equipment and with real world music signals.
This test at clipping level is also particularly revealing.
Many amplifiers actually sound friendlier imo with an active load, and the ability to invert absoloute polarity easily is very handy.
With a four channel amplifier box (4 * LM3876 for example), and a dual gang linear pot, output level and polarity can be easily adjusted without any switching or other change in the replay system - see attached diagram.
Eric.
Attachments
usefull etc
Well, if you feed the amps the same signal and connect a single speaker between both hot outputs, what is the current through the speaker after you have balanced the thing?
Jan Didden
Well, if you feed the amps the same signal and connect a single speaker between both hot outputs, what is the current through the speaker after you have balanced the thing?
Jan Didden
Dynamic Test
If the amplifiers are perfectly matched then no output from the speaker, BUT both amps are running at a non zero output level.
Eric
If the amplifiers are perfectly matched then no output from the speaker, BUT both amps are running at a non zero output level.
Eric
useful etc
Hey, come on, if the load current is zero, then the load is infinite, i.e. unloaded, OK?
Jan Didden
Hey, come on, if the load current is zero, then the load is infinite, i.e. unloaded, OK?
Jan Didden
Hi Jan,
Time for bed?😕
Rodd Yamas***a
Not OK. When the two channels are balanced, the voltage differential between the channels is equal to zero. Zero Volts = zero current, regardless of load.😉
Time for bed?😕
Rodd Yamas***a
Maybe this test would be more informitive if, for example, the output of each amplifer channel were loaded with an 8 ohm, wire wound, high wattage resistor. (OK give me just a little inductive loading here.)
This is a simple test I have used for years and does what you say it does but I have found it more revealing if I load the amplifer outputs and then use a high Z speaker or headphones across the outputs. (When using headphones remember to keep the volume low or add lots of series resistance, a pot would be good, to keep from blowing up your headphones or you ears.)
Have fun
Bruce
This is a simple test I have used for years and does what you say it does but I have found it more revealing if I load the amplifer outputs and then use a high Z speaker or headphones across the outputs. (When using headphones remember to keep the volume low or add lots of series resistance, a pot would be good, to keep from blowing up your headphones or you ears.)
Have fun
Bruce
Improved Testing
Hi Bruce, I agree both channels should have a proper speaker load.
I agree that if using enclosed headphones (to exlude speaker room sounds) you can have a more correct listen to the difference to the channels loaded with real world loudspeakers.
Resistive load on each of the two channels is not really a proper dynamic test.
Eric.
Hi Bruce, I agree both channels should have a proper speaker load.
I agree that if using enclosed headphones (to exlude speaker room sounds) you can have a more correct listen to the difference to the channels loaded with real world loudspeakers.
Resistive load on each of the two channels is not really a proper dynamic test.
Eric.
Hi Mrfeedback.
I don't use resistive loads, as you say they don't give a proper dynamic test. Not everyone has Genrad audio power meters with varible reactive loads though.
Later Bruce
I don't use resistive loads, as you say they don't give a proper dynamic test. Not everyone has Genrad audio power meters with varible reactive loads though.
Later Bruce
Beer Budget
"Not everyone has Genrad audio power meters with varible reactive loads though."
Me neither 😡
Eric.
"Not everyone has Genrad audio power meters with varible reactive loads though."
Me neither 😡
Eric.
roddyama said:
Not OK not OK. Not wanting to split too many hairs, but for me this is important. "Regardless of load", no the point is that the load for the amp is infinite. Maybe you wanted to say "regardless of impedance between the amp outputs", that I agree.
Goodnight Rodd,
Jan Didden
Mrfeedback
I just got lucky at a Hamfest. $10 each. He had no idea what he had and I got there first. I asked him if he was sure about the price. He just wanted to get rid of this old junk.
Some days your lucky. Some days your good. Some days it better to be lucky than good.
Later Bruce
I just got lucky at a Hamfest. $10 each. He had no idea what he had and I got there first. I asked him if he was sure about the price. He just wanted to get rid of this old junk.
Some days your lucky. Some days your good. Some days it better to be lucky than good.
Later Bruce
Yeah, I've grabbed some outstanding bargains that way, including a 500W+500W PA amp at auction for $2 and 12 NOS GE KT-66 at a flea market for $5.
Eric.
Eric.
- Status
- Not open for further replies.