Never spent much time measuring or worrying about damping factor, but decided to give it a try. I'm driving the DUT with a second power amp and isolation resistor, and then calculating the impedance and damping factor. No problem there.
Here's the quirk. With most amps, the residual signal seen at the DUT output is a clean sine wave. With my SWTP Tiger amp clone that signal is a bit asymmetric and distorted, enough to be obvious on the scope.
What do you think causes that? The amp works normally and has low distortion, though the DC offset is higher than people today like to see, maybe 100 mV or so.
Here's the quirk. With most amps, the residual signal seen at the DUT output is a clean sine wave. With my SWTP Tiger amp clone that signal is a bit asymmetric and distorted, enough to be obvious on the scope.
What do you think causes that? The amp works normally and has low distortion, though the DC offset is higher than people today like to see, maybe 100 mV or so.
Can you detail how they look like ?
For calculating damping factors, I found the method using the voltage change when loading a low value resistor connected to ground much more reliable.
Shorting the fuses might be kind of risky - you could increase their current rating. Are the output fuses included in the nfb loop? If not, that could help.
Hey, risk, what's the worst that could happen. The house is fused. I figure I can fix anything I built, or at least that was what I always told them at the McIntosh clinics when they tested my stuff back in the '70s.
Anyway, found it. It was fuse related, but not the fuse itself. I actually had to clean the fuse holder "spinner" and fuse ends with DeOxit to get the connection stable. After that, no more odd waveform.
Anyway, found it. It was fuse related, but not the fuse itself. I actually had to clean the fuse holder "spinner" and fuse ends with DeOxit to get the connection stable. After that, no more odd waveform.
Yes, in older equipment that's a persistent problem. I have an old Pioneer receiver that I use as a radio, and the switches keep acting up.
Even Cramolin hasn't been able to fix them, but it's not worth the time and effort to do much more.
Yes, that is the proper and most accurate method
In this case, it was fuse-related, but sometimes it is revealing: that is the case when the OP stage has a variable non-linear impedance dominating the distortion factors. Always good to know.
Regarding fuses, I always try to include them in the FB loop: even in perfect condition those little bastards manage to be non-linear.
I've always wondered why people don't put fuses in the loop, as the fuse is a significant source of resistance and low frequency non-linearity. What do you have to consider if the fuse is moved inside? Until it blows, probably not much. After it blows, no feedback. Should it by bypassed with a medium value resistor?
It's probably that when the fuse blows, you get a very faint sound in the speakers that sounds like the amp's blown.
The Dyna Stereo 400 did that, and I have to admit, it really was scary.
System damping factor measurement with a microphone?
Didn't want to start another thread about damping factor, so I will insert my question here...
I was wondering, when measuring a speaker with REW or some other software and looking for a difference of really low system df, with long thin wires against an amplifier with a very high damping factor and short thick wires?
What to look for in the measurement results?
Didn't want to start another thread about damping factor, so I will insert my question here...
I was wondering, when measuring a speaker with REW or some other software and looking for a difference of really low system df, with long thin wires against an amplifier with a very high damping factor and short thick wires?
What to look for in the measurement results?
Bypassing won't help, the fuse blows because the output load is heavy or a short. You'd better have current limiting on the VAS transistor when this happens or it might fail in turn.
Back to the question: asymmetric residual implies the amp's open-loop gain varies with output current polarity, due to mismatched gain for the drivers and/or output transistors.
Distorted residual may be due to variation of gain with current in older output devices?
Put another way injecting a current at the output probes the open-loop distortion on an amplifier.
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The impulse response should show more resonance (higher Q) for lower damping factor. In theory tapping the dustcap of the speaker should sound different with no amp connected, or highly damped amp connected or less well damped amp connected, as the electrical circuit interacts with the mechanical suspension. A speaker with stiff suspension will be less affected by electrical damping, all else being equal.
Then the thinner wire will add to the circuit's resistance and damping will be lower. As noted by Mark T.
It is exactly the same as adding a resistor in series with the amp output to lower damping.
Jan
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