288 watts per channel out of my Pioneer SX-1250

288 watts is 2.6 dB above 160 watts (if I pushed the right buttons on the virtual calculator). Probably about right for 1 kHz for an FTC-rated "160 watt" amplifier, I would think.

I would also think that looking at the THD (either as such or via a spectrum analyzer display for the harmonic component levels) would be a better measurement of the onset of clipping than eyeballing a sine wave(?).
 
one could have a little bit more than normal if voltage settings are off. for example having 240 volts on a unit set for 220 volts.

usually the rail voltage drops a fair amount, so there will be some explanation why this amount of difference between 2 of the same amps would be there..
 
FWIW, I built a simulation model for the power amplifier in the SA-9900 amp which is very similar in design to the SX-1250 amp. I changed the regulated the supply voltage to +/- 65 VDC and the unregulated supply voltages to +/- 73 VDC (assuming that it’s a little higher than the specified 70 VDC for the 1250 due to mains voltage). I added resistance to the unregulated supplies to provide a drop of roughly 9 VDC at full power with an 8 ohm load (not sure if this is realistic or not). Under these conditions, the most I can squeeze out of the simulated amp is 192 watts at 1 KHz just before visible clipping sets in. At 4 ohms, the unregulated supply drops by 15 VDC and the output power is 288 watts.

Les.
 
Les, essentially the same numbers this actual SX-1250 on my bench is giving. Whether this SX-1250 is preconditioned or not, the figures are the same- there's plenty of heatsink area and this thing can run all day at full power.

OP, please confirm your loads are in fact exactly 8 ohms, non-inductive, you have very short, thick, ultra low resistance wire and terminals of high quality.
 
OP, please confirm your loads are in fact exactly 8 ohms, non-inductive, you have very short, thick, ultra low resistance wire and terminals of high quality.

Exactly 8 ohms, non-inductive, 6 ft long and 16 gauge nothing-special-about-it speaker wire. Terminals are nothing special. Decent, middle of the road consumer grade wire and terminals.

SX1250 isnt set up to accept more than 16 gauge.

I will set this up again this weekend and take pics.
 
One problem is relating 1% THD to your "eyeball" view of the waveform. I don't know what 1% distortion would look like on a sine wave. Perhaps, despite looking fairly clean, it is actually 10% THD (or whatever) not the 1% point that has been measured in other tests.
 
I won't say that my method is the best, but I don't believe that you can necessarily see a <10% distortion in a sine wave.
I prefer to overlay the input and output waves, if I can detect a difference then there's distortion. You should be able to see clipping the same way.
 
for watts it's actually this:
Volts X Volts X .707 / dummy load ohm rating = Amplifier Output

48 X 48 X .707/ 8 = 143 watts

This is more likely since the 1250 is rated at 160. Watts are measured at RMS vs peak to peak
 
I would say the ops metered 288w is about right for 1 channel @ 1,000 Hz, 8 ohms, driving the amp to max output, which has WAY more than the THD spec for FTC.

288w peak x .707 = 204w RMS, With 2 amps operating perhaps 188w, 180w from 20 - 20,000 hz and maybe 168w at the rated distortion. If it required an input voltage over 120v to do this, it may not meet FTC ratings today by my estimate.

Soooo...Perhaps the op should replace it with something better...I will take it off his hands and even pay for shipping
 
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Perhaps the op should replace it with something better...I will take it off his hands and even pay for shipping

Wow even at FedEx air rates this would be a deal. They only want 517 to get it from Phila to Omaha, about half a country away. Reasonable but can you get the OP to bite? He now has a 288 wpc Pioneer receiver he is very proud of and will use it in good health, we hope.
 
Wow even at FedEx air rates this would be a deal. They only want 517 to get it from Phila to Omaha, about half a country away. Reasonable but can you get the OP to bite? He now has a 288 wpc Pioneer receiver he is very proud of and will use it in good health, we hope.

Yes, But that $517 is peak...x .707 that's only $366 RMS (route my street)

Seriously though, 160 wpc FTC @ 8 ohms with a receiver that is stable into a 4 ohms, Has an excellent FM Tuner, Loaded with features and flexibility, Very good sound, and a beautiful front...What's not to love about Pioneers SX 1250 Receiver.

Being a Fan of vintage Pioneer, Even their SX 737 IMO was also a real gem with many of the attributes of it's big brothers, but with less power.
 
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What's not to love about Pioneers SX 1250 Receiver.
If you compare it to a Sansui G-9000 (what I deem as important and nice to have features), missing a narrow IF filter, a FM MPX noise filter, power meters, jfet f/e on the phono amp, minor stuff :) They added meters to the 1280 and used a slightly high rail voltage.
When measuring o/p pwr it always a good idea to also measure THD/IMD as a reference point, state your measuring equipment make/model.
 
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Volts X Volts / dummy load ohm rating = Amplifier Output

48 X 48 / 8 = 288

Impressive!
How do you measure? You drive an 8ohm resistor and you get 48V peak ( sine wave swing from -48V to +48V) without clipping?

Power = (1/2) V^2/R=144W

OR P=(1/2)X I X V. where I peak = 48V/8= 6A. So (1/2) X 6A X 48V = 144W.
 
What's not to love about Pioneers SX 1250 Receiver.

Being a Fan of vintage Pioneer, Even their SX 737 IMO was also a real gem with many of the attributes of it's big brothers, but with less power.

The fact that it is not the good looking 160wpc Pioneer, the SX-5590, that Black/Silver® is sweet gear. In the x3x series that 737 is the sweet one. Nice flip switches instead of the push buttons.
 
Remember that the SX-1250 power supply is similar to the SX-1980, not the smaller SX-1280 power supply. It's capable of pushing the output without a significant voltage droop on the rails, thus its 4ohm capability.
 
Pioneer SX-1250 Specifications
Tuning range: FM, MW

Power output: 160 watts per channel into 8Ω (stereo)

Frequency response: 10Hz to 50kHz

Total harmonic distortion: 0.1%

Damping factor: 30

Input sensitivity: 6.5mV (mic), 2.5mV (MM), 150mV (DIN), 150mV (line)

Signal to noise ratio: 75dB (MM), 90dB (line)

Output: 150mV (line), 30mV (DIN), 1V (Pre out)

Speaker load impedance: 4Ω (minimum)

Dimensions: 556 x 186.5 x 464.5mm

Weight: 29.2kg

Year: 1976

,Mike. :smoke:
 
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