OPENAMP1 - MM phono preamp open project

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Nick Sukhov

Member
Joined 2022
patreon.com/nick_sukhov
noviygera said:
Question:
In reference to post#60
"above 1kHz the noise in MM preamp is dominated by the 47k standardized load resistor"
Does this technique reduce the noise caused by the loading resistor? Has anyone tried this?
Click to expand...

I use "passive cooling" 150k/25pF input instead of 47k\150pF for both lowering noise and also widening freq resp with budget MM


Detailed see here https://www.patreon.com/posts/mm-constant-loop-67857060
 
M

MarcelvdG

Member
Joined 2003
noviygera said:
Just finished building Opanamp1 using pcb from craigtone. Using Jung/Didden Superreg for the PS. Will listen for a few days and post my findings.

Question:
In reference to post#60
"above 1kHz the noise in MM preamp is dominated by the 47k standardized load resistor"

The following phono preamp uses what they call "electronic termination" or "“Electronic Cooling” and according to this whitepaper it reduces the input noise by (in the limit) 13.28 dB
whitepaper:
www.akitika.com/documents/ElectronicCooling.pdf
schematic:
www.akitika.com/documents/SchematicPhonoPreampRevB4.pdf


Does this technique reduce the noise caused by the loading resistor? Has anyone tried this?
Click to expand...

Apologies for the late reply... I use it all the time, but that 13.28 dB from the whitepaper is when you only look at the noise contribution of the termination resistor. It's more like 3 dB when you take the cartridge thermal noise into account, including iron losses. It gets even smaller when you account for other noise sources such as amplifier voltage noise and record surface noise, but then again, termination resistor noise and cartridge iron losses thermal noise mainly contribute to high frequency noise that sounds more annoying than lower frequency noise.

See also "Noise and moving-magnet cartridges", Electronics World October 2003, pages 38...43, https://worldradiohistory.com/UK/Wireless-World/00s/Electronics-World-2003-10-S-OCR.pdf Mind you, Electronics World drew one of the sections of the gain switch in the wrong state in figure 5 and I mixed up the terms spectral density and power spectral density. It's a technique from 1939, by the way.

Nick's alternative is very interesting if you don't mind building the amplifier into the turntable and if you don't have a cartridge with a strong mechanical resonance. It improves noise as well as frequency response.
 
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