## 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.