Re: Resistor, in special de low inductance ones, special units
Very interesting, Carlos.
I know you have practical real experiences from some areas (high freq, RF radio techniques )
that others may not have (Lineup and such persons
).
A reflectometer, I guess is something what is commonly used
for Tuning Antennas - can be Receiver or Transmitter antenna.
I do not know if I am right ....
So what you are telling is, we can use something similar, or even one of those boxes,
to see what happens in between the Amplifier Output and Loudspeaker Input.
I say again:
INTERESTING
Christmas - in north and south
Christmas - in Brasil and North Europe
under same sky
--- your lineup ----
destroyer X said:
Very interesting, Carlos.
I know you have practical real experiences from some areas (high freq, RF radio techniques )
that others may not have (Lineup and such persons
).A reflectometer, I guess is something what is commonly used
for Tuning Antennas - can be Receiver or Transmitter antenna.
I do not know if I am right ....
So what you are telling is, we can use something similar, or even one of those boxes,
to see what happens in between the Amplifier Output and Loudspeaker Input.
I say again:
INTERESTING Christmas - in north and south
Christmas - in Brasil and North Europe
under same sky
--- your lineup ----
Hi,
If you are thinking about removing 400W (2 x 200W) from a heatsink I would suggest using a fan or two (or more).
If you test your amp at 50W RMS output on two channels for a few minutes, a dummy load mounted on a large passively cooled aluminium heatsink will still get very hot.
80mm fans are cheap and plentiful from old PC power supplies. When running at 5~9 Volts (less than 1200rpm) they are relatively silent, and will provide enough extra cooling for whatever power resistor + heatsink combination you'll be using.
The oil idea is nice in theory but in practice, in your workshop it could cause a big mess. The first time you spill oil (coffee, milk, soup, whatever) on your workbench or on the floor of your workshop you understand that.
Using real speakers is fine if you are testing < 0.1W output; which imho is not really an adequate output level for power amp testing. At 1W with an average speaker one is getting 90dB, which is already unbearably loud for even a few seconds, for my fragile ears, at least.
Just my $0.02...
If you are thinking about removing 400W (2 x 200W) from a heatsink I would suggest using a fan or two (or more).
If you test your amp at 50W RMS output on two channels for a few minutes, a dummy load mounted on a large passively cooled aluminium heatsink will still get very hot.
80mm fans are cheap and plentiful from old PC power supplies. When running at 5~9 Volts (less than 1200rpm) they are relatively silent, and will provide enough extra cooling for whatever power resistor + heatsink combination you'll be using.
The oil idea is nice in theory but in practice, in your workshop it could cause a big mess. The first time you spill oil (coffee, milk, soup, whatever) on your workbench or on the floor of your workshop you understand that.
Using real speakers is fine if you are testing < 0.1W output; which imho is not really an adequate output level for power amp testing. At 1W with an average speaker one is getting 90dB, which is already unbearably loud for even a few seconds, for my fragile ears, at least.
Just my $0.02...
"Using real speakers is fine if you are testing < 0.1W output; which imho is not really an adequate output level "
I use a 150W dummy load. It is adequate for amplifiers up to 600W on music program material.
To listen to the output near full power I just use a 10W 70V line transformer. You can hook up a rotary switch for 10W, 5W, 2.5W, 1.25W, 0.625W to your speaker. A typical big hi-fi amp delivering 150W on program material will have 6dB less output on these taps, ie: 2.5W on the 10W tap.
I use a 150W dummy load. It is adequate for amplifiers up to 600W on music program material.
To listen to the output near full power I just use a 10W 70V line transformer. You can hook up a rotary switch for 10W, 5W, 2.5W, 1.25W, 0.625W to your speaker. A typical big hi-fi amp delivering 150W on program material will have 6dB less output on these taps, ie: 2.5W on the 10W tap.
"I would think the transformer has a very different impedance from that of a speaker? "
That's missing the point. The reason we test a repaired amplifier is to stress for weak parts.
Loads simulating real speakers are of use when designing inexpensive amplifiers that you are trying to cut every cent out of the BOM. That does not really describe the DIY crowd.
"Doesn't it affect the load as seen by the amplifier?"
The main 8R 150W resistor is the real amplifier load, the 8K load presented by the 0.625W tap on the 70V transformer may be ignored.
That's missing the point. The reason we test a repaired amplifier is to stress for weak parts.
Loads simulating real speakers are of use when designing inexpensive amplifiers that you are trying to cut every cent out of the BOM. That does not really describe the DIY crowd.
"Doesn't it affect the load as seen by the amplifier?"
The main 8R 150W resistor is the real amplifier load, the 8K load presented by the 0.625W tap on the 70V transformer may be ignored.
test loads
i was fortunate enough to find a 250w 8r dale resistor in a pile of junk parts i got at a yard sale, along with a pair of 100w 8r loads mounted in a box with banana terminals on one side of the box.
as far as a "real world" load, parts from an old crossover could be used to simulate the resonances of a real speaker.
i was fortunate enough to find a 250w 8r dale resistor in a pile of junk parts i got at a yard sale, along with a pair of 100w 8r loads mounted in a box with banana terminals on one side of the box.
as far as a "real world" load, parts from an old crossover could be used to simulate the resonances of a real speaker.
Re: test loads
I think that, unclejed613
would be as good test load as anything other people use.
The 90% available alternative to using real loudspeakers with real music and/or test records
is that we will use some ordinary quality power resistors.
As I stated in my post before before,
no need to use expensive SPECIAL LOW INDUCTANCE power resistors.
Because cheap ordinary wire wounded power resistors,
will be less far from the inductive load of real speakers / crossovers.
As long as normal power resistors can take power of test
in a good and safe way,
we should use this simple but not in compare bad method.
Regards & new year
lineup
unclejed613 said:
I think that, unclejed613
would be as good test load as anything other people use.
The 90% available alternative to using real loudspeakers with real music and/or test records
is that we will use some ordinary quality power resistors.
As I stated in my post before before,
no need to use expensive SPECIAL LOW INDUCTANCE power resistors.
Because cheap ordinary wire wounded power resistors,
will be less far from the inductive load of real speakers / crossovers.
As long as normal power resistors can take power of test
in a good and safe way,
we should use this simple but not in compare bad method.
Regards & new year
lineup
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