Testing the sx amplifier using my sound card, i see that distortion is higher than expected. On the other hand distortion graph is flat from 20Hz up to 30KHz+
Any idea Andrew?
Any idea Andrew?
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I think much of the "distorted" output is measurement error.
You have a measured distortion and a measured hum+harmonics.
All of these are exceptionally high.
You need to trace where the measurement errors are getting in.
You have a measured distortion and a measured hum+harmonics.
All of these are exceptionally high.
You need to trace where the measurement errors are getting in.
I don't think so because with same measurement setup other amplifiers looks OK.
See attachment.
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then look at your PSU wiring first. Get rid of that hum.
It will measure bad with a DMM set to 199.9mVac
It will measure bad with a DMM set to 199.9mVac
Thimios
Good that you have an opportunity to measure your amp. I think Andrew is correct - there is some problem there. Have you got a scope? Can you look at the output? I would imagine with your ear next to the speaker you could hear some noise etc.
Good that you have an opportunity to measure your amp. I think Andrew is correct - there is some problem there. Have you got a scope? Can you look at the output? I would imagine with your ear next to the speaker you could hear some noise etc.
Yes i have.
What you want to scope?With or without signal?
I have remove the GND lift and here is the new graph.
Putting my ear in close contact with speaker i can't hear hum.
In any case problem is the high distortion not the hum.
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Rhinitis,
You have very significant hum components on you amp. There is a problem there.
1. Find the root cause of the hum ( notice the harmonics as well)
2. Then we can try to address the distortion coming front the 1k signal
One idea: what is your bias current set at? If it was very high you could get these issues
Output offset ok?
Voltages correct - eg the 10V front end supplies?
Can you check the power supply rails for hum? If one had hum and the other none it might point us to a problem.
Decoupling caps ok - you don't have one that might be badly leaky?
Do you perhaps have some HF oscillation?
You have very significant hum components on you amp. There is a problem there.
1. Find the root cause of the hum ( notice the harmonics as well)
2. Then we can try to address the distortion coming front the 1k signal
One idea: what is your bias current set at? If it was very high you could get these issues
Output offset ok?
Voltages correct - eg the 10V front end supplies?
Can you check the power supply rails for hum? If one had hum and the other none it might point us to a problem.
Decoupling caps ok - you don't have one that might be badly leaky?
Do you perhaps have some HF oscillation?
One other idea: ground loop between your amp and the sound card. Can you connect a speaker to the output when you have the sound card connected.
Well the hum is gone ,at least the big one .Removing the ground lifter and rearrange the measurement setup.
The distortion is here.
The bias is as required 450mV/0.66R=680mA for each tran.pair
+/-10v is ok.
Offset=0mV.
I tried speaker connection when sound card is connected ,all ok nothing heard.
The distortion is here.
The bias is as required 450mV/0.66R=680mA for each tran.pair
+/-10v is ok.
Offset=0mV.
I tried speaker connection when sound card is connected ,all ok nothing heard.
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Is there a post describing the difference between the v1.0 boards and the v2.0 boards? I ordered the v1.0 boards and a short 2 weeks later, I saw a post regarding new boards. Talk about poor timing.
And yes, I've searched quite a bit to try and find the post regarding the version upgrade.
And yes, I've searched quite a bit to try and find the post regarding the version upgrade.
thimios
Have you tryed to keep the main signal a bit bellow the 0dB at the main scale (-5dB or -10dB, just in case to not overdrive the line-in) ?
(prapobly you did)
Have you tryed to keep the main signal a bit bellow the 0dB at the main scale (-5dB or -10dB, just in case to not overdrive the line-in) ?
(prapobly you did)
Bonsai ,it is the same SX
Borys ,yes i tried different levels but distortion is always high.
I tried ,0db,-3db,-6db.
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Hi Thimios,
May I ask what type of equipment you use to test for THD? I would love to be able to do that.
Thanks, Terry
May I ask what type of equipment you use to test for THD? I would love to be able to do that.
Thanks, Terry
Why are you using your ear as a measuring instrument?
Use a DMM set to 199.9mVac and measure the Hum+Noise.
OK Andrew, i have done this.The measurement is near to 5mV (DMM)
look new measurements with more capacitors added
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5mVac for hum + noise is a disaster.
expect a correctly wired power amp to give <0.1mVac Hum + Noise.
Yes 40dB less and your ear could not detect that error in the wiring.
expect a correctly wired power amp to give <0.1mVac Hum + Noise.
Yes 40dB less and your ear could not detect that error in the wiring.
The mains frequency and its harmonics sitting as side bands around the test tone and its harmonic products manifested an inter modulation problem. If the measurement gear is known to be good, the bad THD result is then real. This amp is not in a good order and needs a careful check up.