I have a VX150 here. I used to have three of them years ago but sold them. This one had the VCA input cards.
I have recapped this unit as the caps on the main board were going high esr and low capacitance. I stupidly put in 10uF cap in the feedback path on each channel! Of course when I tested frequency response it was down 3db at 20Hz! Anyway, I installed 100uf and then was fine.
I'm surprised how bad the VCA input cards cripple the amplifier. Distortion figures were not that good. 0.05% at 1Khz mid power. This climbed to a very bad 4% at 30Khz!! Also I had to drive it with 5v to get full output! I pulled out the VCA boards and jumpered the links and now much better. Distortion at 1Khz is 0.0045% mid power and the same at 20Khz. Also no hiss even with headphones.
Bias, DC offset and CMR adjusted to spec.
I have recapped this unit as the caps on the main board were going high esr and low capacitance. I stupidly put in 10uF cap in the feedback path on each channel! Of course when I tested frequency response it was down 3db at 20Hz! Anyway, I installed 100uf and then was fine.
I'm surprised how bad the VCA input cards cripple the amplifier. Distortion figures were not that good. 0.05% at 1Khz mid power. This climbed to a very bad 4% at 30Khz!! Also I had to drive it with 5v to get full output! I pulled out the VCA boards and jumpered the links and now much better. Distortion at 1Khz is 0.0045% mid power and the same at 20Khz. Also no hiss even with headphones.
Bias, DC offset and CMR adjusted to spec.
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Knowing how these VCAs worked these numbers are absolutely fine and no surprise.
HH products were common in the musical industry.
Naturally nobody was interested in 30kHz THD.
So there is no point figuring THD at 30 KHz.
Btw, did the manufacturer state anything better than you measured?
HH products were common in the musical industry.
Naturally nobody was interested in 30kHz THD.
So there is no point figuring THD at 30 KHz.
Btw, did the manufacturer state anything better than you measured?
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Probably a compressor or soft clipping - same thing really, but different reasons
Brian
There would have been plenty of intermodulation going down to 20Khz. The distortion was also quite bad at 20Khz and it sounded like it too! Brittle..
Yeah, some sort of compressor in it with remote controlling. Hiss was bad with the cards installed.
These HH VX amps are simple. Typical Hitachi Lateral MOSFET driver stage. Just five small signal transistors for, LTP, current mirror and bias. Opamp for balanced input. Bias spec is quite high and does produce a bit of heat on the output heat sinks. A generous transformer and reservoir caps.
Yeah, some sort of compressor in it with remote controlling. Hiss was bad with the cards installed.
These HH VX amps are simple. Typical Hitachi Lateral MOSFET driver stage. Just five small signal transistors for, LTP, current mirror and bias. Opamp for balanced input. Bias spec is quite high and does produce a bit of heat on the output heat sinks. A generous transformer and reservoir caps.
This must have ruined your day.
Imagine, NO BASS! 🙄
Unbearable!
Some need ear transplants at those horrendous levels.
Let me see.
Second harmonic is @ 60kHz
Third is @ 90kHz.
And so on.
I bet those piercing unbearable harmonics ruin anybody's Musical experience.
What drive was needed to get, say, 90% output?
It is very common to design and setup limiters so amp does never actually reach clipping so signal needed to do so is not a realistic representation of actual use.
Specially since these are PA type amplifiers.
They will be driven hard all the time, operators will try to extract maximum power but limiters avoids ugly clipping.