DC Coupling for MC Cartridges - how much error voltage before coil damaging - Page 2 - diyAudio
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Old 26th November 2009, 09:10 PM   #11
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Quote:
Originally Posted by jcarr View Post
The most extreme of the Matsudaira-designed MCs (MySonic Labs) use 60um wire for an internal impedance of 0.6ohms.
hth, jonathan carr
Very interesting - and new for me.

Do you mean the model "Eminent" ? - describted about the weblinks
http://www.soundscapehifi.com/mysoniclab.htm
http://www.analog-audio-connection.d...inent_Info.pdf
http://www.high-end.ch/p_analog/tonz...onic_Flyer.pdf

By the way - what kind of DC protection solution for the moving coils of cartridges are inside in your RIAA phono preamp models?
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Old 26th November 2009, 09:17 PM   #12
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by tiefbassuebertr View Post
By the way - what kind of DC protection solution for the moving coils of cartridges are inside in your RIAA phono preamp models?
In my current design there is no such protection (it is not required) and there is no input capacitor (it is also not required), as it is a straight FET input with no DC current to speak of.

Alex
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Old 27th November 2009, 04:33 AM   #13
jcarr is offline jcarr  United States
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Quote:
Originally Posted by tiefbassuebertr
Do you mean the model "Eminent"?
No, My Sonic Lab Ultra Eminent BC. Link below:

Ultra Eminent BC

Quote:
Originally Posted by tiefbassuebertr
What kind of DC protection solution for the moving coils of cartridges are inside in your RIAA phono preamp models?
Same as Alex. JFET inputs, no capacitors, DC servo.

hth, jonathan carr
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Old 27th November 2009, 04:59 PM   #14
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Quote:
In MC cartridges, the range of coil wire used will be between 12um and 60um. 12um is very seldom used, as it tends to break too readily in production. 15um was used by some medium-to-high impedance Denon cartridges. For low-impedance MCs, 30~40um wire will be more typical (35~40um in my case). The most extreme of the Matsudaira-designed MCs (MySonic Labs) use 60um wire for an internal impedance of 0.6ohms.
Thank you for that information. That would mean a safe continuous current would be (for 35~40um) about 2ma. Fusing current would be higher. I would think even a poorly designed BP phono stage should have no more than one tenth that amount.
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Old 28th November 2009, 07:07 PM   #15
oshifis is offline oshifis  Hungary
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Right, the Dynavector has 12 um coil (about 56 AWG). I don't know the number of turns, but it is low impedance.
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Old 9th August 2012, 10:23 PM   #16
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Dr. Leach had a neat method of preventing current from flowing in the MC cartridge. See here. Moving Coil Cartridge Head Amps
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Old 9th June 2013, 10:43 AM   #17
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check out also post 17 about
Audio Research MCP 33
and
Allowable DC Current for a Phono Cartridge
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Old 10th June 2013, 01:36 AM   #18
andyr is offline andyr  Australia
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Quote:
Originally Posted by tiefbassuebertr View Post

There are two methods of coupling the moving coil cartridge to the prepre input:
1) AC coupling about a capacitor
2) DC coupling (without a capacitor)
By AC coupling I have lack in quality cause additional capacitor device in series to the moving coils, but by DC coupling I risk a damage of both internal cartridge moving coils in case of an error in the head amp circuit (frontend).
My AKSA 'Paris', JFET-based head amp has no input coupling cap. I've never had any issues with my Benz LP.

I thought DC offset occurred at the output of a gain stage ... not at the input?


Regards,

Andy
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Old 10th June 2013, 05:17 AM   #19
Calvin is offline Calvin  Germany
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Hi,

the input bias current of the input transistor leads to a voltage drop over the input impedances. Since the gate leakage of JFETs is so much smaller than the base currents of bipolar transistors its no issue with JFETs.

jauu
Calvin
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Old 10th June 2013, 07:28 AM   #20
andyr is offline andyr  Australia
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Quote:
Originally Posted by Calvin View Post

Hi,

the input bias current of the input transistor leads to a voltage drop over the input impedances. Since the gate leakage of JFETs is so much smaller than the base currents of bipolar transistors its no issue with JFETs.

jauu
Calvin
Aah, thanks for the explanation, Calvin.


Regards,

Andy
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