[IDEA] Hybrid amplifier: tube + class D

[STUDI]

Design assumptions:
Sensitivity is sufficient for commercial level (-10dBV / 316mVrms).
Output power: 2 * 32W/8Ω at 24V supply
Bandwith -0.5dB: better than 20Hz-20kHz
Bandwith -3dB: better than 10Hz-45kHz 


Measurement:
Software: RMAA 6.4.5 on Windows 10 x64
Audio interface: Focusrite Scarlett 2i2 2gen.
Load: real speaker sets
Supply: industrial power supply 24V/100W, manufacruter: Delta


Results for full undistorted power

Noise RMS:
L: -85.6dB
R: -84.2dB

Noise RMS (A):
L: -86.9dB
R: -85.5dB

Noise peak valuse:
L: -71.8dBFS
R: -70.1dBFS

DC offset:
L: 0.00%
R: 0.00%

THD:
L: 0.366%
R: 0.387%

THD+noise:
L: 0.367%
R: 0.387%

THD+noise (A):
L: 0.483%
R: 0.509%

IMD+N:
L: 0.407%, R: 0.356%

IMD+N (A):
L: 0.251%, R: 0.271%

IMD+N (swept freq):
5kHz: L: 0.422%, R: 0.450%
10kHz: L: 0.226%, R: 0.240%
15kHz: L: 0.175%, R: 0.184%

Crosstalk
100Hz: L->R: -58.6dB, R->L: -65.1dB
1kHz:  L->R: -66.1dB, R->L: -67.3dB
10kHz: L->R: -62.6dB, R->L: -51.8dB

Noise level:


THD:


IMD:




Results for ~-12dB level

Noise RMS:
L: -73.0dB
R: -72.6dB

Noise RMS (A):
L: -74.5dB
R: -73.8dB

Noise peak valuse:
L: -58..4dBFS
R: -48.8dBFS

DC offset:
L: 0.00%
R: 0.00%

THD:
L: 0.103%
R: 0.111%

THD+noise:
L: 0.112%
R: 0.120%

THD+noise (A):
L: 0.138%
R: 0.149%

IMD+N:
L: 0.123%, R: 0.114%

IMD+N (A):
L: 0.079%, R: 0.089%

IMD+N (swept freq):
5kHz: L: 0.120%, R: 0.128%
10kHz: L: 0.083%, R: 0.126%
15kHz: L: 0.080%, R: 0.083%

Crosstalk
100Hz: L->R: -62.9dB, R->L: -67.7dB
1kHz:  L->R: -68.7dB, R->L: -66.1dB
10kHz: L->R: -65.6dB, R->L: -51.4dB

Noise level:


THD:



IMD:



Note:

The distance from the right speaker system to the tubes during measurements is less than 50 cm, from the left one about 80 cm. Please note that the microphone of the tubes affects the crosstalk.

The DC voltages of the SPICE simulation match better than 10% with the measurements of the assembled prototype.

*$

.SUBCKT 6S51N  1 2 3 ; P G C (Triode) 21 May 2004 by GaLeX
+ PARAMS: MU=54.72  EX=1.248  KG1=123.5  KP=99.63 
+ KVB=300.0  VCT=0.00 RGI=1500
+ CCG=4.2P  CGP=1.8P CCP=2.5P
E1 7 0 VALUE=
+{V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(V(2,3)+VCT)/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1}
RCP 1 3 1G    ;
C1 2 3 {CCG}  ;
C2 2 1 {CGP}  ;
C3 1 3 {CCP}  ;
D3 5 3 DX     ;
R1 2 5 {RGI}  ;     
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS