OPENAMP1 - MM phono preamp open project

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#181
PMA said:
For those who might be interested, I have prepared an open project of the phono preamplifier for MM cartridge. It has very low noise and very low distortion. Gain is 40dB/1kHz. Output is capable to drive 50 ohm load, so one may directly connect headphones via 100 - 220 ohm pot. Please feel free to download documenation from



Preamplifier for MM cartridge
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Link is dead in OP. Can you update to the new link here: Preamplifier for MM cartridge

(would be nice to have in the OP)

Are there Gerbers available for JG’s MC head amp? Perhaps PSU?
 
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#186
chat72 said:
I have no problem using 470uf with Salas shunt.
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Agreed I used a Salas BiB shunt regulator for my Openamp-1 with no issues and no modifications of the circuit. I connected the regulator to the phono board with a short length of shielded twisted pair, about 6 inches as I recall. (and yes I mean 2 regulators, one positive one negative. The voltages were rock solid.)
 
#189
I just built one of these on my own PCB. The sound is very detailed ... best bass I have heard on any phono stage to date! I would describe it as very transparent with no coloration of the sound at all. It is VERY sensitive to proximity of the power supply however. The current PCB has a 3-pin DC power jack so I can use a remote chassis which will be necessary.
 

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#191
PMA said:
It should not be. With the original double-side PCB with top ground plane it is pretty immune to power supply proximity.
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I had it sitting on top of an HP dual lab supply with just a silicone pad and it hummed pretty bad! I moved the HP supply below the wooden shelf from the preamp and it got much quieter! It is not in any enclosure yet either, just a PCB with some leads hanging off of it with jumpers to the PS.
 
#193
OPENAMP1 is a great design

Hello krca45,
Nice work. You made a wise choice in making this phono amp your first project. Can you describe your power supply? I am not familiar with it. I assume it is a shunt regulator.
This phono amp design, in my opinion, is outstanding. As others have stated, the low frequency “weight” is excellent and it easily powers (in my case, 32 ohm) headphones.
 
#194
Hello


Thanks


PSU is shunt regulator with mosfet IRF9510 / 510 as shunt element on the output. Uses BC546 / 556 & BD139 / 140 transistors & MMBF5486 smd jefts ( on the downside ).


Good Gemini by Zen Mod, You should be able to find him on various Pass amplifier builds.


Schematic can be found in Iron Pre preamplifier, it is a part of it, Pass section.


Regards, Krca
 
#195
Some pics of phono & regulator pcbs ( did not twist in-out wires, eventually will do ) - after Gemini regulator, on the phono DC inputs - are resistors ( hidden ), to make RC filter ( with existing C 470uF/50V element ).
 

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#198
mlloyd1,

Thanks for your feedback. While working on the complicated Non-Plus Ultra phono (by H. Polak) I began to fantasize about a more compact, simple MM phono. This and the bugle were my picks.

This may sound strange but here goes? Can the LT1010CT be replaced with a tube buffer? To get some of the "tube" sound in a phono
 
#199
you can do anything if you know what you are doing.
but first some questions:
1. do you have the expertise to make the change while maintaining the design performance?
2. what is your objective in replacing the buffer with a tube and how will you know that you have succeeded (or not)?

I'd recommend building as PMA designed first.
Get a baseline of how it sounds.
Then, make you changes and see what you think.
Just a sugggestion - you do your own thing!
 
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