Post by Deleted on May 12, 2013 6:39:31 GMT
I buy'd MRS25 resistors - but which are recommend to use HOLCO or similar resistors like this www.hificollective.co.uk/components/prp_pr9372_metal_film_resistors.html?
For C1 100pF I have film capacitor, polypropylene (Mouser 505-FKP2100/100/2.5),
for C2 68pF I have MICA (Mouser 598-CD15ED680GO3F) in my stock - are this OK?
You could use those singles for the output resistors . I would use a normal good quality DIP 8 socket for the offset corrector I.C. but make sure that it's pins are long enough to protrude right through the 3mm thick PCB. The same applies to all terminal blocks. I would use normal .5W MF resistors for all except the LS352 emitter resistors, where .1% tolerance types would be an advantage.
Alternatively, you could get a couple of packs of that value (150 ohms) and match pairs for that location with your DMM.. The exact value isn't crucial, but being closely matched is worthwhile.
Due to the thickness of this PCB it isn't a good idea to fit sockets or pins that will need to be replaced later. A solder flux pen is also good to use for some of the through layer holes.
Double check everything you do with the layout diagram before soldering them in. You can bend the leads under the PCB to hold them in place while you confirm that everything is correct.
I find it best to do both PCBs at the same time with resistors etc. Insert a resistor on one PCB, then insert the same value resistor at the same location on the other PCB for example.
At a later date you may wish to try higher quality resistors at a couple of locations such as the 4.7K and 10K in the feedback network. Don't forget the 2.2nF to 4.7nF across the 1M resistor of the offset corrector under the PCB. The capacitors you mentioned will be fine. An OPA134 MAY give a lower DC out than an AD744, as well as be a smidgin quieter.
The 1N5819 diode should be replaced by an SF11 or SF12 (or ES1D Surface mount type) low forward voltage diode, and the 82 ohm emitter resistor in the V.A.S replaced by 120 ohms. This gives improved front end tracking with temperature.