Eros with Flux magnetics ER head

[Doc B.]

Hmm, if you want to get really fussy you could maybe go back to 100K on the input load at the Eros to optimize it for the 1/4 track head, and put another 100K across the 1/2 track head to load it back down to 50K when switched in.

[Grainger49]

Alex,

Just to answer your cable capacitance question, good cable is under 25pF or 30pF per foot.  A 200pF meter cable would probably be a poorly made cable.

[ALEXZ]

Aaaaaaaahhhhh..... It was the cable ....why I did not try it before  Well...I guess  I forgot the    rule " DON'T PANIC!"
Van den hul Thunder ... Core to core 130pf/m ; core/shield 210 pf/m. I decided to use better cable when head block was traveling to and from JRF.
Now I put Eros right behind technics  with 1/2 ' some junk jumpers ... + 2db at 30Hz 0 at 10k, 0 at 15k and maybe some insignificant rase above 16 kh
All the above with the original 100k input.
Looking for low capacitance cable for internal wiring and interconnects. Any recommendations ?
and thank you everyone for your help !

[ALEXZ]

Grainger, sorry have not seen you post - was typing my reply.
I whould not call van den hul cables  poorly made, just my implementation was brainless... But, yes, you're right 30pf per foot whould prevent this painful exercise. Well... Negative experience is also experience never the less.

[Grainger49]

Belden 89259 is an RG59U with 17pF/Ft.  My Cardas Neutral Reference are 20pF/Ft.  There are many, many out there like that VdH is unique and a very good cable but maybe not for this specific use.

[ALEXZ]

Flux/Eros part2.
This time I am 100% sure I'm not measuring my scope bandwidth. I tested scope with audio oscillator with calibrated output and freshly calibrated fluke 87. No issues at list up 50khz.
Tape is MRL 21J203 medium hot (250nW/m) IEC test tape.
Cables are replaced with the shrt jumpers from technics to Eros.
Everything perfectly flat from 125 hz upto 12,500.  16khz +2dB,  20khz +4.5 dB
Not that it is bugging my in any miningfull way. I just want to know, where is this coming from ?
Thank you,
Alex

PS. Could it be a crosstalk? On the higher frequencies coil reads its own signal plus a bit of neighbor's. Can stereo head acts like a transformer  in a way ?

[Doc B.]

Have you readjusted the input resistance of the preamp since you changed cables? If not, try lowering it a bit.

[ALEXZ]

Aha. I did not re-adjust input resisters with the new cables. Ill try, that's probably it.
I guess my crosstalk theory is not a moment of enlightment... Oh well...next time.

[ALEXZ]

Thank you, Dan. Got it right this time, everything above 125 hz nicely flat and a bit of low end bump as expected.   BTW my readings of 30hz from MRL tape and TP tape are a bit more then 2dB apart, TP is lower one.  Everything else is identical.

[Paul Joppa]

Just a guess here - is the TP dual track and the MRI full-track? Fringing effect should go that direction ...

[Doc B.]

Yup TP is two track and MRL is mono.

[ALEXZ]

TP tape is two track.  MRL - I don't know, but will find out. MRL documentation stated that tape is not fringing compensated.
On another topic: what are the recommendations to calibrate NAB with IEC tape ? I've printed "translation" table from MRL site. Are there any gatchas ?
Thank you,
Alex