I have a Heathkit AD-1308 audio spectrum analyzer with microphone that seems to work great. However, I want to use it to view the outputs of preamps and amps so see their performance across the audio spectrum using a sweep generator as the signal source. Such a set up would not utilize microphone and the unit has a switch to bypass the microphone and a DIN connector on the back to allow an external source input. I have the manual for it so I know which DIN pins are the ones to use for the external source in. However, the manual is not very clear on how much power the unit will take from external sources such as power amps. I would be driving the power amps into dummy loads and then measuring from there. I don't anticipate anything really high powered. Probably 100 watts max, but I likely wouldn't drive the amp to full power anyway.
Does anyone have any experience with this unit doing what I want to do?
Does anyone have any experience with this unit doing what I want to do?
Is that 20RMS into 8R? if so that's 50watts,
When I test amps for distortion etc I always test at less than 10% power, any more and large transients can push the amp into clipping causing voltage rails to collapse.
Lots of maybes here but this is what I was taught when I worked for Marantz.
Load testing the output stage was done into a dummy load with a scope.
When I test amps for distortion etc I always test at less than 10% power, any more and large transients can push the amp into clipping causing voltage rails to collapse.
Lots of maybes here but this is what I was taught when I worked for Marantz.
Load testing the output stage was done into a dummy load with a scope.
The manual says that the unit's external input impedance is ">10 K ohms". I want to use the unit to test the output linearity of tube preamps and power amps. Determining amp or preamp power output is not a factor, just linearity. Probably the highest power one to be tested would be a McIntosh MC275 or something similar.
I assume you are testing for frequency response over the full power range.
I would use a squarewave and scope? A squarewave will tell you if you have flat frequency response.
I would not use the SpecAn to test the output of the power amp at high power. I have seen things go wrong and take out the input of the SpecAn. If I was testing manually (not an automated test) I always used an attenuator on the input of the SpecAn so if anything went wrong it would take out the external attenuator not the SpecAn input.
I would use a squarewave and scope? A squarewave will tell you if you have flat frequency response.
I would not use the SpecAn to test the output of the power amp at high power. I have seen things go wrong and take out the input of the SpecAn. If I was testing manually (not an automated test) I always used an attenuator on the input of the SpecAn so if anything went wrong it would take out the external attenuator not the SpecAn input.
This is a tool for speakers and rooms. It is imprecise for amplifiers.
It expects a random noise source. Using a sweep sine will probably read wrong, maybe a -3dB/oct slope?
> outputs of preamps and amps ... using a sweep generator
Even in "slow" it can hardly read to 1dB. Decent amplifiers do not have such large error in a 40Hz-16KHz band. A sweep source and good cheap meter will read small tenths of a dB, and far beyond the audio band.
Speaker level is dozens of volts. Microphones are milliVolts. While it turns out this will take quite hot mike levels, I still would use a LOT of pad in front. 1000:1 may be a good start. If the preamps are not distressed by 100k load, use 100k:100r divider. If the RTA is battery power, you may use 50k:100:50k U-pad to get a pseudo-balanced input and more protection against ground faults and loops.
It expects a random noise source. Using a sweep sine will probably read wrong, maybe a -3dB/oct slope?
> outputs of preamps and amps ... using a sweep generator
Even in "slow" it can hardly read to 1dB. Decent amplifiers do not have such large error in a 40Hz-16KHz band. A sweep source and good cheap meter will read small tenths of a dB, and far beyond the audio band.
Speaker level is dozens of volts. Microphones are milliVolts. While it turns out this will take quite hot mike levels, I still would use a LOT of pad in front. 1000:1 may be a good start. If the preamps are not distressed by 100k load, use 100k:100r divider. If the RTA is battery power, you may use 50k:100:50k U-pad to get a pseudo-balanced input and more protection against ground faults and loops.
The manual says it can test amps, but I think you're right that it is really for testing speakers and adjusting equalizers.
However, in searching through my treasure trove of misc. equipment I've collected over the years, I found an Audio Control SA-3050A Third Octave Real-Time Spectrum Analyzer that I think will work much better. It also has a built-in pink noise generator. I tested it on a preamp and it seemed to work well.
However, in searching through my treasure trove of misc. equipment I've collected over the years, I found an Audio Control SA-3050A Third Octave Real-Time Spectrum Analyzer that I think will work much better. It also has a built-in pink noise generator. I tested it on a preamp and it seemed to work well.
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