and I think I have some (circuit?) problem.
| Romy the Cat wrote:|
In the end of everything I was able to get very nice response. The response is nice and flat with 0dB at 18.1Hz and 0dB at 15.600Hz. It has plus 0.2dB from 1500 to 3500 which I feel is not a big deal. (Juts for my future reference: the values of the feedback capacitors have without de-soldering capS from the circuit are: 110pF= 136.2pF and 330pF=372pF)
This level of calibration is something I can dream of, as well as of this one (Fig. 1):
I have a massive +2.2dB peak around 35-50Hz. No matter what I do it's there, getting broader or narrower and slightly moving.
From 1kHz up I can flatten the things out very nicely. I scan the phono using (HF corrected) Hagtech iRIAA.
Since Jim mentions it wants to see 50R source, I've been driving it with 50R out of Tek SG505 generator
or with my sound card with unknown output R....all gives the same. I somehow start to suspect that I have
some circuit problem. I tried to measure aircaps in the circuit but my simple C-meter gets crazy and prefer not to desolder them
unless necessary. The big cap responsible for LF looks actually identical to Romy's and should give up to 390pF, so plenty of room.
Anyone have any idea what the heck may be wrong? Where does a ~50Hz low Q peak may come from?
Any help appreciated. Thanks,
PS There is one circuit change wrt the original: I use 1uF instead of 2uF output coupling cap.
Experimenting with Decca carts, I've temporaly disconected the SUT's and decided to check the RIAA calibration