phono cartridge loading question

2gumby2 · 9145

0 Members and 1 Guest are viewing this topic.

Offline 2gumby2

  • Newbie
  • *
    • Posts: 4
on: November 16, 2009, 12:38:11 AM
The recommended capacitance loading for my cartridge is 0 pf, but my current phono preamp has a set 150 pf capacitance and no adjustment. I was just wondering what the audible deleterious effect might be if any.



Offline Len

  • Full Member
  • ***
    • Posts: 130
Reply #1 on: November 16, 2009, 01:32:26 AM
The recommended capacitance loading for my cartridge is 0 pf, but my current phono preamp has a set 150 pf capacitance and no adjustment. I was just wondering what the audible deleterious effect might be if any.

Hi. This is not an answer to this post, but a question for the administrators:

One advantage of the format of this new board is the ability to place posts in categories. We have some very good information accumulating about SUT's in three other threads:

http://www.bottlehead.com/smf/index.php/topic,73.msg236.html
http://www.bottlehead.com/smf/index.php/topic,86.0.html
http://www.bottlehead.com/smf/index.php/topic,116.msg520.htm

Is there any way we can put this present post and the other three threads into one category?


Paramours
Paraglows
Excites
Heavily modded Soul Sister and Groove Thang
Quickie modded to active low pass filter
Quickie modded to headphone amp
Lots of Bottlehead parts used for building other stuff


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #2 on: November 16, 2009, 02:13:24 AM
The recommended capacitance loading for my cartridge is 0 pf, but my current phono preamp has a set 150 pf capacitance and no adjustment. I was just wondering what the audible deleterious effect might be if any.

The way to achieve proper high frequency response it to "Lift" (or clip) one lead of each of those capacitors in your preamp.  That leaves them in place and allows them to be put back in easily.  

My cartridge is the same, the Seduction has no loading capacitor.  I lucked out.

Excellent suggestion Len!



Online Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 5768
Reply #3 on: November 16, 2009, 11:35:38 AM
The recommended capacitance loading for my cartridge is 0 pf, but my current phono preamp has a set 150 pf capacitance and no adjustment. I was just wondering what the audible deleterious effect might be if any.
It depends on the cartridge. The best source of such information is the cartridge manufacturer. For what it's worth, many phono preamps have 50-100pF input capacitance even without an extra cap installed, and most cables will run around 100pF for a typical 1-m run from turntable to preamp.

Seduction is around 60pF; Eros is unusually low at around 10pF due to the pentode input stage.

Paul Joppa


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #4 on: March 01, 2011, 02:11:04 PM
That seems like pretty high capacitance for 3' of cable (33.33pF/Ft.).  My cable is 20pF/Ft. and I have a lot of Belden 89259 that is 17pF/Ft.



Online Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 5768
Reply #5 on: March 01, 2011, 03:57:50 PM
Here's a table of RF coax:

http://www.rfcafe.com/references/electrical/coax-chart.htm

Capacitances run from 6.5pF/foot (RG-114/A) to 50pF/foot (RG-88) with most of them being 20-30pF/foot.

RG-58 is the most common 50-ohm coax, and runs about 100pF/meter. I suppose that's where I remember this from, since 50 ohms is the standard for most lab gear. (Most BNC connectors are 50 ohms, you have to look around to find 75 ohms which is standard for digital coax.)

RG-59 is about 70pF/meter and at 75 ohms is more common in audio and video applications.

Paul Joppa


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #6 on: March 01, 2011, 04:08:22 PM
The Belden I mention, 89259/17pF/Ft., is a good, center stranded RG59.  I guess I started out on the low range of capacitance.  I had used the 89259 for so long I had thought most others were in that range.