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Tube Phono Preamps
Tube Phono Preamps
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Old 3rd November 2017, 08:15 AM   #231
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by kevinkr View Post
I'm pretty sure he has a power transformer, and has just not shown it in this schematic.
Maybe Hi_Q has 12V mains?
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Old 3rd November 2017, 09:25 AM   #232
Koifarm is offline Koifarm  Netherlands
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Quote:
Originally Posted by Hi_Q View Post
Death circuit No mains isolation
I use transformer with 230v and 12v secondairies.
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Old 10th November 2017, 07:51 PM   #233
pelayostyle is offline pelayostyle  United States
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Tube Phono Preamps
Found some 2.2uf sonicaps in my junk box! Just want to make sure there is no problem in using these in place of the 2uf on the schematic. Thanks.
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Old 10th November 2017, 07:56 PM   #234
Sodacose is offline Sodacose  United States
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That'll work a treat as long as they have sufficient voltage rating.

The critical cap values are between the 12AX7 stages. The output is a little more flexible.
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Old 11th November 2017, 05:15 PM   #235
adam1016 is offline adam1016  United States
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Just bought the filament regulator, hopefully that clears up hum, and otherwise I'm going to completely re-do my grounding. It's been a long journey, but I still have hope that it's all going to pay off in the end. Also, I'm designing a pair of baby hueys, and have access to a CNC machine and tons of HDPE, but no tooling for aluminum. Will HDPE work for the plates while I save up for tooling?
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Old 11th November 2017, 05:30 PM   #236
kodabmx is offline kodabmx  Canada
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FYI I had a minor ground loop. I fixed it by removing the ground from turntable power.
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Old 2nd March 2018, 07:30 PM   #237
Bigun is offline Bigun  Canada
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Tube Phono Preamps
I've read that a 12AX7 is a poor choice for v1 because of miller capacitance. Yet there are many well liked phono stages using it.

Is the miller issue overblown ?
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Old 2nd March 2018, 07:59 PM   #238
Sodacose is offline Sodacose  United States
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A lot of MM carts spec 150pF+ of capacitance loading. That just so happens to be about the Miller Cap of a grounded cathode 12AX7 with a resistor load:

150k load, 66k Rp, Mu 100
100 * 150k / (150k + 66k) = 70x gain
71 gain * 1.7pF Cga + 1.6pF Cgk = 120pF+

OTOH MC carts don't like that large of a capacitive load and so a grounded cathode 12AX7 is not as good of a match. I'm not sure if high output MC carts tend towards MM type loading or MC loading (or if there is any general trend that could be identified).

Cascode input type preamps might be a better match for a MC cart as they sidestep the Miller cap issue.
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Old 2nd March 2018, 08:21 PM   #239
kodabmx is offline kodabmx  Canada
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A lot of MC carts want a load of like 150R making a grounded grid topology a possibility.
Click the image to open in full size.
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Old 2nd March 2018, 08:37 PM   #240
stocktrader200 is offline stocktrader200  Canada
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Is anyone interested in posting MP3 256kps samples of their turntable and preamp sound.
a popular song, as in most people have it, would make comparisons easier

maybe as a new thread?
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