Tube Phono Preamps

[Sodacose]

I'm sure that will work a treat! Let us know how it goes.

 

[adam1016]

Mine is still suffering hum issues, I'm convinced I need to regulate my voltage. Pelayostyle, I'm wondering how you're going to configure the boards. What filtering are you gonna do before the millett regulators? What transformer taps are you using?

 

[Sodacose]

Adam1016, are you in Chicago? I'm up in Milwaukee.

Glad to hear you haven't given up on your build.

 

[pelayostyle]

Mine is still suffering hum issues, I'm convinced I need to regulate my voltage. Pelayostyle, I'm wondering how you're going to configure the boards. What filtering are you gonna do before the millett regulators? What transformer taps are you using?

Hi Adam,
I'll be using this Filament Regulator which is basically the same circuit as Pete Millet's but this one uses a low dropout regulator in order to get regulated 6.3V DC from 6.3V AC. Just one board for both tubes in parallel.

I'm also using the Edcor XPWR123 which is essentially a clone of the Allied 6K3VG.

 

[spswmsw]

Tube Phono preamp.
Works with Audio-Technica AT-95E cartridge
EF86 - STR85/10 - 6P14P(EL84)trio - ECC82 (optional)
Two outputs by chioce depending on length of a cable.

 

[stocktrader200]

this preamp looks really good.
I would use SS power supply using 1 tube rectifier to ease in the B+
and DC on the heaters of at least the 1st stage tube

 

[Koifarm]

Below very good schematic is used in my last phono preamp.

 

[Hi_Q]

Death circuit No mains isolation

 

[kevinkr]

I'm pretty sure he has a power transformer, and has just not shown it in this schematic.

Note that there are two supplies shown on the sheet.

I use the LR8N in some of my designs, works well.

 

[kodabmx]

I use one of these in one of my phono amps... Works like a charm!

DC-DC 8-32V to 45-390V Step Up Power Supply Module High Voltage ZVS Boost Module | eBay

 

[Merlinb]

I'm pretty sure he has a power transformer, and has just not shown it in this schematic.

Maybe Hi_Q has 12V mains?

 

[Koifarm]

Death circuit No mains isolation

I use transformer with 230v and 12v secondairies.

 

[pelayostyle]

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.

 

[Sodacose]

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.

 

[adam1016]

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?

 

[kodabmx]

FYI I had a minor ground loop. I fixed it by removing the ground from turntable power.

 

[Bigun]

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 ?

 

[Sodacose]

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.

 

[kodabmx]

A lot of MC carts want a load of like 150R making a grounded grid topology a possibility.

 

[stocktrader200]

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?