Three-pole compensated blameless clone

[PMA]

THD is excellent, however THD+N is quite poor in comparison. What is the reason, amplifier noise or measuring system noise?

 

[LKA]

it will be clear when you look at the dac -> adc graph

Measurement : unbalanced 24bit 96k
DAC Topping D10s
ADC X-Fi HD USB

DAC -> FukAMP -> voltage_divider -> ADC
DAC output -13.5dBFS
ADC input -6dBFS

DAC -> ADC
DAC output -17.5dBFS
ADC input -6dBFS

 

[PMA]

OK, thank you. Did you measure amplifier output noise with shorted input? It is as important as low THD.

 

[LKA]

Noise measurements

Cosmos ADC unbalanced noise (input 50R) = 2.111uV or -113.5dBV

FukAMPv4 voltage amplification = 35.9x or 31.2dB
Simulated noise bw 20kHz = 26uV or -91.7dBV (ideal power supply)
Measured noise bw 20kHz (input 50R) = 29.8uV or -90.5dBV (SSR3 included)

 

[LKA]

I reduced the gain from 36 to 29, the residual noise is 25uV (-92dBV) unweighted BW20kHz ref@1Vrms (SSR3 is not part of the output)

WELL DONE

 

[LKA]

This is PCB v4.0, v4.1 is slightly modified (rc filter added to the 3ef driver/pre-driver power supply line)

 

[ingo50]

You make yourself a beautiful X-Mas gift!!
Frohe Feiertage!!

 

[LKA]

Square wave test.
4Vpp 10kHz, load 2R parallel 47n,100n,680n,2u2.
Measured after the output coil. (just 0.1uH)
Fantastic, completely tamed 3 pole TMC compensated VFA at 3MHz ULGF.

 

[LKA]

Another set. 40Vpp 10kHz.
no-load, 4R, 4R parallel 470n

 

[LKA]

Comparison of linear and switched power supply.

Linear power supply -> 2x3x10000uF/63V

The smps has two 150uF/400V input caps, later I plan to try 2x330uF/400V.
https://www.audiophonics.fr/en/smps-power-supply/smps500r-power-supply-module-500w-55v-p-6458.html

 

[chermann]

Did you try to level down the noise just use a RC filter...XRK did this afaik at the VSQA (quasi) amp.
e.g. 0,33R 3W ...not able to handle 100W into 4R but..

chris

 

[LKA]

Sorry, I don't understand what you mean.
The measurement BW with LPS was 20k and with SMPS 90k.

 

[chermann]

ah...okay...my bad...sorry...
i mean to lower the ripple noise of the SMPS

 

[LKA]

-120dBc mains ripple level is not bad, the HF level is even better (in conjunction with my amplifier)
IMHO, that smps is quite good (at that price level), it has regulated output

 

[HRDSTL]

For low-cost projects, why not? In a quality hifi amplifier I wouldn't even consider it, ...
The parts in SMPS speak for themselves, ...

 

[LKA]

Most linear powered amplifiers have worse ripple than the discussed smps+fukamp combo

 

[chermann]

okay..thanks for your explanation

 

[LKA]

Doubling the capacity of the HV rectifier (300uF/400V -> 600uF/400V) => mains related noise decreases by 10dB

 

[triplej]

For those of us who like to see the zero's... -121.6 dB THD is 0.00008% -100w 4r measured! Very impressive.

 

[HRDSTL]

Personally, I don't care if the amplifier has a distortion of 0.001% or 0.00008%, the sound performance is more important. I would also buy Fukamp boards, but there are 3 things that bother me.

1, Absence of quality polypropylene at the input
2, Wago terminal at the output, into which you can put a maximum of 1.5mm2, even with problems, ... (I prefer Faston)
3, Missing choke at the output, which you replace with a 30cm wire...