All those measurements with barely 60-70 dB dynamic range are pointless, they show absolutely nothing. All we know is that you have high distortion, we do not know if you have high order distortion components and we do not know if you have mains related hum components. The plots you show are in accordance with marketing plots in audio magazines.
It is possible to modify the harmonic decay of the distortion with a slight imbalance of the 2 feedback resistors or by using 2 less selected fet.
The peak of noise at -75dB 50Hz is a measurement problem not present on normal use.
The peak of noise at -75dB 50Hz is a measurement problem not present on normal use.
I agree...... I would say that if the majority of the THD is comprised of H2+H3+H4 (all musical) then the objectionable harmonics, H5 and beyond, are very, very small and therefore the amp should sound pretty good. The graph at #23 indicates that H5 and beyond are all below -77dB and the dominant harmonics are H2 and H3. They will mask the H5+H6+H7+..........+H20.
Tube amps have very high distortion, typically 0.5% or higher, yet people love them. I would say that people like 'effects boxes', only the technically minded go on about very low THD.
There is something about an amp presentation with low global feedback, less than 30dB. Perhaps it's distortion, but the presentation is very nice.
And as NP says, audio is entertainment, he doesn't worry too much about THD, and just hopes that everyone is having a good time..........
HD
Tube amps have very high distortion, typically 0.5% or higher, yet people love them. I would say that people like 'effects boxes', only the technically minded go on about very low THD.
There is something about an amp presentation with low global feedback, less than 30dB. Perhaps it's distortion, but the presentation is very nice.
And as NP says, audio is entertainment, he doesn't worry too much about THD, and just hopes that everyone is having a good time..........
HD
I would say that too Hugh and I dont find anything objectionable about someone liking low order harmonic distortion. hell, I like distortion, just not typically in my amplifiers. I do find it encouraging that more people are willing o admit this penchant, rather than the time honoured tradition of inventing unmeasurable 'meta effects' to explain why the amp is superior, in spite of measuring so much worse.
I will make in the next days some experiment to unbalance the 2 sections to create a perfect harmonic decay like single ended amplifiers.
For me it looks a lot like the push pull tube amp design topology bought to the modern era of Solid state devices.
Minimal or no negative feedback with the euphonic sound has been the staple of tube designs.
Hopefully you are able to fully replicate that euphonic tube like sound, helps move away from tubes and stop spending ridiculous amounts of money on obsolete technology.
Keep going.
Minimal or no negative feedback with the euphonic sound has been the staple of tube designs.
Hopefully you are able to fully replicate that euphonic tube like sound, helps move away from tubes and stop spending ridiculous amounts of money on obsolete technology.
Keep going.
After the summer break I restarted the experiments on this amplifier and the listening tests with my friends.
In a direct comparison with my Amplifier End which uses a tube as a voltage amplifier, an interstage transformer and the same output mosfets, the sound of this solid state amplifier remains more fatiguing.
This sensation was not present in the prototype which did not have the selected fet but had a higher distortion so I tried to unbalance the 2 feedback resistors and I obtained the desired effect by increasing the second harmonic.
Follows the measurements with various values where it is verified that a small variation is enough by adding 56K in parallel to 3k9 (result 3K65) on the negative line and we obtain the same harmonic decay of the amplifer end and another listening pleasure.
In a direct comparison with my Amplifier End which uses a tube as a voltage amplifier, an interstage transformer and the same output mosfets, the sound of this solid state amplifier remains more fatiguing.
This sensation was not present in the prototype which did not have the selected fet but had a higher distortion so I tried to unbalance the 2 feedback resistors and I obtained the desired effect by increasing the second harmonic.
Follows the measurements with various values where it is verified that a small variation is enough by adding 56K in parallel to 3k9 (result 3K65) on the negative line and we obtain the same harmonic decay of the amplifer end and another listening pleasure.
Attachments
This amplifier driving a 18000 euro loudspeakers, all happy of the incredible result!
Hi guys,
I have come quite a long way with my build. All boards are tested OK. It is time for the final assembly phase. A friend of mine works as a senior PCB CAB engineer. He was kind enough to design a board for the output stage power supply. I could not source the schottky diodes needed for rectification so I choose to use a low voltage drop rectifier bridge from Vishay along with some snubber caps.
/Dominic
I have come quite a long way with my build. All boards are tested OK. It is time for the final assembly phase. A friend of mine works as a senior PCB CAB engineer. He was kind enough to design a board for the output stage power supply. I could not source the schottky diodes needed for rectification so I choose to use a low voltage drop rectifier bridge from Vishay along with some snubber caps.
/Dominic
Have you unbalance the feedback like I suggest ?
Are you using a custom made transformers with many secondaries ?
Hi,
Yes, R18 = 3.9k//58k
I use two custom made audio grade transformers from Toroidy. 600VA: 4x25Vac for the output stage and 40VA: 2x18+2x9Vac for the driver stage (mounted under the driver stage board).
/Dominic
Yes, R18 = 3.9k//58k
I use two custom made audio grade transformers from Toroidy. 600VA: 4x25Vac for the output stage and 40VA: 2x18+2x9Vac for the driver stage (mounted under the driver stage board).
/Dominic