Trimming, tweaks
I haven't got any suggestions for real tweaks. I'm not a big fan of this kind of voodoo but if you have, please feel free to email them to me. Maybe they can be useful for others.
Trimming
If you change C17 and C18 ( pre amp) and C41 and C42 (correction amp) you can trim the slew rate and by that also sonic properties. It's wise to have the speed adjusted to perfect step response. It's not recommended to have the amp too fast with overshoots.
Preamp with BC550/560, MM-mode
14V/1,0µs (14 V/µs), 330 pF, perfect step
14V/0,6µs (23 V/µs), 220 pF, perfect step
14V/0,5µs (28 V/µs), 150 pF, perfect step
14V/0,25µs (56 V/µs), 100 pF, minor ringing
Preamp with BC550/560, MC-mode
14V/1,0µs (14 V/µs), 220 pF, perfect step
14V/0,25µs (56 V/µs), 100 pF, perfect step
14V/50ns (280 V/µs), 0 pF, perfect step
In MC-mode the amp has no slew rate limiting and therefore a nice clean step response.
DC-voltages in an amp with feedback
Use a multimeter 10 Mohms inimpedance. All values are voltage across the component.
+-15.0 V supply voltage were used.
Pre amp, Left channel, MM-mode, BC550C, BC560C in all positions, OP07 as DC-servo, no input bias servo, input not shorted.
DZ1, 6,96V
DZ2, 6,96V
DZ3, 7,08V
DZ4, 7,09V
R1, -9,5mV, current into the amp. NPN-transistors have slightly lower Hfe than PNP. Total resistance is 47 kohms, 0,2uA, input bias current.
R6, 491mV, 4,91uA
R7, 438mV, 4,38uA
R8, 5,85V, 1,500mA
R9, 5,88V, 1,508mA
R10, 5,86V, 862uA
R11, 5,90V, 868uA
R12, 4,80V, 857uA
R13, 4,83V, 862uA
R14, 200mV, 2,00uA
R15, 299mV, 2,99uA
R16, 5,64V, 376uA
R17, 5,61V, 374uA
R18, 5,64V, 376uA
R19, 5,61V, 374uA
R20, 5,64V, 376uA
R21, 5,61V, 374uA
R22, 5,64V, 376uA
R23, 5,61V, 374uA
R24, 508mV, 747uA
R25, 518mV, 762uA
R26, 1,65V, 750uA
R27, 9,15V, 91,5uA
R28, 3,65V, 36,5uA
R29, 9,12V, 91,2uA
R30, 3,62V, 36,2uA
R31, 1,68V, 764uA
R32, 1,56V, 1,418mA, (1,1kohms)
R33, 1,58V, 1,436mA, (1,1kohms)
R34, 926mV, 9,26mA
R35, 926mV, 9,26mA
R38, 834mV, 14,9uA
R39, 855mV, 15,3uA
R42, 325mV, 14,8mA
R43, 319mV, 14,5mA
R44, 321mV, 14,6mA
R45, 319mV, 14,5mA
R46, 316mV, 14,4mA
R47, 323mV, 14,7mA
C3, 6,46V, Vbe, T1 580mV
C4, 6,40V, Vbe, T2 550mV
C19, 5,28V
C20, 5,30V
H1, 1,82V
PREAMP_OUT_L, <+-0,2mV, changing with temperature fluctuations and air movements
DC-ADJUST_L, -5,66V, can go between +12-13V to -(12-13)V depending of balance.
Pre amp, Right channel, MM-mode, BC850C, BC860C in all positions, OP07 as DC-servo, no input bias servo, input not shorted.
DZ11, 7,14V
DZ12, 7,11V
DZ13, 7,05V
DZ14, 7,18V
E1, -3,1mV, current into the amp. NPN-transistors have slighty lower Hfe than PNP. Total resistance is 47 kohms, 66nA, input bias current.
E6, 479mV, 4,79uA
E7, 513mV, 5,13uA
E8, 5,98V, 1,533mA
E9, 5,98V, 1,533mA
E10, 6,03V, 887uA
E11, 6,00V, 882uA
E12, 4,90V, 875uA
E13, 4,90V, 875uA
E14, 255mV, 2,55uA
E15, 302mV, 3,02uA
E16, 5,73V, 382uA
E17, 5,72V, 381uA
E18, 5,73V, 382uA
E19, 5,72V, 381uA
E20, 5,74V, 382uA
E21, 5,72V, 381uA
E22, 5,74V, 382uA
E23, 5,71V, 381uA
E24, 470mV, 691uA
E25, 469mV, 690uA
E26, 1,527V, 694uA
E27, 1,527V, 694uA
E28, ----
E29, ----
E30, ----
E31, ----
E32, 1,388V, 1,262mA, (1,1kohms)
E33, 1,394V, 1,267mA, (1,1kohms)
E34, 748mV, 7,48mA
E35, 752mV, 7,52mA
E38, 666mV, 11,89uA
E39, 727mV, 12,98uA
E42, 373mV, 16,95mA
E43, 373mV, 16,95mA
E44, 381mV, 17,32mA
E45, 367mV, 16,68mA
E46, 383mV, 17,41mA
E47, 368mV, 16,73mA
G3, 6,56V, Vbe, V1 580mV
C4, 6,56V, Vbe, V2 580mV
C19, 5,54V
C20, 5,74V
H3, 1,80V
PREAMP_OUT_R, see below!
DC-ADJUST_R at +15 V gives -0,177V at output, -15 V gives -0,0185V. Can go between +12-13V to -(12-13)V depending of balance. This particular amp needs some adjustment in the offset adjusting range ,
Comments about the measurements
You can see a difference between hole mounted transistors and surface mounted ones. Places where the dissipated power is low there are no major differencies but in the output stage the transistors get much hotter due to less effective cooling. Otherwise the performance is more or less identical.
Correction (RIAA) amp, Left channel, BC550C, BC560C in all positions except for the input stage BC847BS, OP07 as DC-servo, input shorted.
DZ5, 6,99V
DZ6, 6,98V
DZ7, 7,03V
DZ8, 6,60V
R93, 0,92mV, current into the amp. NPN-transistors have slighty lower Hfe than PNP. Total resistance is 680 ohms, 1,35uA, input bias current.
R56, 1,14V, 11,4uA
R57, 1,10V, 11,0uA
R58, 5,24V, 1,344mA
R59, 5,25V, 1,346mA
R60, 9,71V, 1,428mA
R61, 9,10,V 1,338mA
R62, 5,25V, 772uA
R63, 5,28V, 776uA
R64, 4,28V, 764uA
R65, 4,33V, 773uA
R66, 183mV, 1,83uA
R67, 209mV, 2,09uA
R68, 446mV, 656uA
R69, 451mV, 663uA
R70, 1,45V, 659uA
R71, 1,47V, 668uA
R72, 1,31V, 1,191mA (1,1kohms)
R73, 1,32V, 1,200mA (1,1kohms)
R74, 667mV, 6,67mA
R75, 665mV, 6,65mA
R78, 629mV, 11,23uA
R79, 687mV, 12,22uA
R82, 338mV, 15,36mA
R83, 337mV, 15,32mA
R89, 0,96mV, from the inverting input,
C30, 5,84, Vbe T38 600mV
C43, 5,64V
C44, 5,27V
H2, 1,89V
+15 V at pin 6, IC2 (without an opamp) gives +81mV at output, -15 V gives -79mV. Can go between +12-13V to -(12-13)V depending of balance.
