Hi,
I built a 500W valve amp with 6x KT120 and get this:
Whats that around the fundamental? Intermodulation distortion? I didn‘t see this in this way in other amps.
Thats the fft at 504W
Thanks
Christian
Or may it be reflections in my cables or something like that? It looks a little bit like the Empire State Building.
For comparison, here is a Dared Tube VP350 (mono) amp which has similar distortion, but at much lower power levels.
compare that with a McIntosh MC240:
I was just trying to point out that sometimes you see “groupings” of spurs around the harmonics with tube gear and sometimes you don’t. I don’t see it very often with SS amps.It looks like the spurs are 100hz away from the harmonics at 1khz, and you have a 100hz spur…
Thanks a lot! The over all level of distortion is ok, may be I can‘t hear it.
I noticed that your gained changed from 40dB to 53dB- that is a lot for a power amp. If for some reason you are playing at 500w, it’s going to be quite loud and I doubt you would hear the distortion…
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It‘s not only the power amp, but with the bass preamp over all.
I found an article about IMD:
The effects on my fotos are IMD, but I’m not shure it is audible or not.
Forwatt,
The frequencies around the 1 KHz fundamental are at 100 Hz intervals. I see a 50Hz spike and surmise you are in a 50 Hz power country. 100Hz would be the ripple frequency of a full wave rectified power supply, therefore I’m guessing this is power supply ripple intermodulating with your 1 KHz fundamental. Have a closer look at your power supply filtering, especially the ground/return paths. As a thought experiment imagine every inch of wire to be a 10 Ohm resistor not a zero-loss perfect conductor. This will force you to clean up your layout PDQ. Star grounding. Also use the analyzer to look at earlier stages, driver and phase splitter to see if your small signal stage filtering is adequate. The Push-pull output should cancel supply ripple, but the single ended stages will not.
Dale
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Be sure to block the DC when measuring earlier stages.
Dale
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Would it be sufficient in this case to block DC with two condensators 1uF 1600V (symm signal and ground)? Assuming an input impedance of 100k results a corner frequency of app. 1,5Hz.
But I own a Micsig Diff Probe DP10013 V2, which withstands voltages up to 1500V.
Very detailed article- thanks for posting it!
Hi VAR,
I just saw some videos in your YT channel, testing two amps
McIntosh
Cary
The fft look very similar to my 500W KT120 and they are good amps, aren‘t they?
My 500W amp is an instrumental bass amp based on a Hiwatt DR400, same LTPI but a driver with 12BH7 and separate BIAS regulation.
@Forwatt- Your amp is pretty impressive looking- a lot of work went into it for sure…But an instrument amp like that is a whole different beast than the home audio gear I typically deal with. … I am not a fan of the Cary SLM 70 amp that you pictured- needing a pair of them for what they cost each for <30w/8ohms. It sounded ok despite how it looks- just can’t rattle the pictures off the walls. I am not sure which McIntosh SS amp you are showing, but it looks like it is doing ok with that kind of power output and it would be one that was probably pretty much in original condition. SNR is not the greatest but at those power levels probably not a big factor… I have yet to run across of Mcintosh gear that I didn’t like. Thanks for watching.
It‘s the MC352 from your video
That is actually my personal amp, but it could have been a few others. It’s rated at 350w into 2,4 or 8ohms, so it was being pushed a bit. It looks a lot better at its rated power:
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Hi,
today I measured
my Trace Elliot VA350 (400W) and Hexavalve (300W). In higher power regions I saw the same IMD as at my 500W Valve Amp. It seems to be normal at high power valve amps.
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