Greetings Friends. I've been testing my single-ended project amps and have run across some questions about proper use. I'm using a Pyle USB ASIO interface, a dummy load made of thick film resistors wired to present 4- and 8-ohm loads, and an old Lenovo PC running REW.
I have a DSO138 oscilloscope and a Klein TRMS-capable meter to directly measure across the dummy load, and a 22:1 voltage divider inside the plug going into the audio interface to limit that voltage to <100mV. This is calibrated in REW and verified with the 'scope.
Ok. I can run Freq sweeps and measure distortion and get pretty graphs. But I'm realizing that without a standard, the measurements are arbitrary. Testing an EL84 Triode amp at 2w output will give a much higher distortion profile than testing a similar amp wired in Pentode at 2 watts, so it's not the output power that I'm after, it's a standardized input signal that I need.
A friend is a guitar amp tech and he recently did an IG post about measuring Guitar amp output power, where he mentioned that the standard input signal for measuring guitar amps is 1Khz @ 500mV. Is there such a standard for Hi-Fi amps?
When using REW, the measurement level can be set in Volts, dbFS, dbu, or dbV. Running a frequency sweep at 4v, for example, causes an input signal to be applied to the DUT that will result in 4v at the output. Setting the level using dbFS results in a similar outcome, arriving at a set output level. Would dbu or dbV give a set input? Am I barking up the right tree here?
Thanks
w
I have a DSO138 oscilloscope and a Klein TRMS-capable meter to directly measure across the dummy load, and a 22:1 voltage divider inside the plug going into the audio interface to limit that voltage to <100mV. This is calibrated in REW and verified with the 'scope.
Ok. I can run Freq sweeps and measure distortion and get pretty graphs. But I'm realizing that without a standard, the measurements are arbitrary. Testing an EL84 Triode amp at 2w output will give a much higher distortion profile than testing a similar amp wired in Pentode at 2 watts, so it's not the output power that I'm after, it's a standardized input signal that I need.
A friend is a guitar amp tech and he recently did an IG post about measuring Guitar amp output power, where he mentioned that the standard input signal for measuring guitar amps is 1Khz @ 500mV. Is there such a standard for Hi-Fi amps?
When using REW, the measurement level can be set in Volts, dbFS, dbu, or dbV. Running a frequency sweep at 4v, for example, causes an input signal to be applied to the DUT that will result in 4v at the output. Setting the level using dbFS results in a similar outcome, arriving at a set output level. Would dbu or dbV give a set input? Am I barking up the right tree here?
Thanks
w
Googling "RCA line amplitude in volts" resulted in "Normally RCA outputs are -10 dBV or about 0.3 volts for a maximum signal level." from a Reddit user...
If you trust Reddit...
But thanks, lots of conflicting info on the Google, I was hoping for a better source. Ha!
But thanks, lots of conflicting info on the Google, I was hoping for a better source. Ha!
The standard for testing amplifiers is usually 1 watt output. You adjust the input voltage to produce this level. To measure output wattage, you measure the peak-to-peak output, convert to RMS voltage, square the result and divide by the load impedance. For an 8 ohm load, 1 watt is around 2.8 volts RMS.
For typical tube amplifiers with normal input sensitivity, 200-400 mV of input signal will produce around 1 watt of output.
For a 2 watt amplifier, you'd probably want to measure at lower output, maybe 1/2 watt? Since at 1 watt your distortion is already going to be high... ;-)
For typical tube amplifiers with normal input sensitivity, 200-400 mV of input signal will produce around 1 watt of output.
For a 2 watt amplifier, you'd probably want to measure at lower output, maybe 1/2 watt? Since at 1 watt your distortion is already going to be high... ;-)
Try to use Multitone sw with a decent sound card. Then you need an attenuator of 20 dB ( or 40 dB switchable) to send the signal to the card.
It is a good setup to understand the performance