How convert Creek OBH-8 to MC cartridges?

[x-pro]

Which parts are determine the line gain factor after remove the RIAA network consist of C5+10/R8+9/C4 ?
One part is the resistor R2 + the forward transfer admittance.

The gain is determined by that and by the dynamic impedance of the load, including Q1-Q4, C2, R1 and R4. For that reason R4 may need to be adjusted for the flattest frequency response at LF as Q1-Q4 parameters may vary from one manufacturer to another.

Cheers

Alex

 

[tiefbassuebertr]

which other available commercial RIAA head amplifiers like Creek's OBH-8 topology resp. the other here mentioned circuit versions was on the market?
Thanks for advices.

 

[tiefbassuebertr]

any news ?

check out post #483 of this thread:
https://www.diyaudio.com/community/threads/cambridge-audio-a3i-repairs-and-mods.122378/page-25
and this threads
https://www.diyaudio.com/community/threads/jfet-srpp-riaa-preamp.64028/
https://www.diyaudio.com/community/threads/discrete-phono-stage-single-supply.255309/
https://www.diyaudio.com/community/threads/simplistic-njfet-riaa.129126/page-256 (#5103)

 

[jah_zoldat]

I built an MC '2010' version phono stage for a friend. It sounds just as good as the MM version, very fast, detailed and effortless. But bypassing R2 results in increase of 4rd and 5th harmonics, so I settled for 55dB gain.

 

[tiefbassuebertr]

Maybe a normal or Sziklai (compound) darlington (i. e. by using an additional BjT) reduce this 4rd and 5th harmonics.
check out the attachment and
https://sound-au.com/articles/cmpd-vs-darl.htm
OTOH - I doubt, that a bit higher values for 4rd and 5th harmonics are audible.

 

[jah_zoldat]

Thanks for the idea. My thought was to take two 2sk170 in parallel with separate source resistors for J1, and to reduce R1 accordingly.

I thought that additional distortion shouldn't be a big deal, but in comparison with a lower gain version it sounded very dull. Bypassing R2 also reduces input overload capability in half to around 2.5mV.
Here are detailed reports.