Pete Millet "LR" Phono pre amp

Discussion in 'Vinyl Nutjob World: Turntable and Related Gear' started by JoshMorr, Apr 23, 2016.

  1. TheloniuSnoop

    TheloniuSnoop Friend

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    BTW, your PS voltages are pretty close to spot on with mine.
     
    Last edited: Jul 10, 2016
  2. TomB

    TomB MOT: Beezar

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    Thanks for that! As you say, the tolerance for a less-than-perfect AD797 must be quite low. I'm excited to see if replacement opamps improve the LR even more.
     
  3. TomB

    TomB MOT: Beezar

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    Here's some acceptable quality pics of my Millett LR Phono Preamp:
    [​IMG]
    [​IMG]
    [​IMG]

    You'll note all the grinding marks around the casework screw points and backplate connectors. Since I had Landfall anodize my case, that meant all the assembly points and mounting holes were insulated. So, I got my Moto-Tool out and sanded down to the bare metal around all the assembly points. Plus, I ran separate ground wires for all of the ground connections on the PCB. I also used Pete's "EMI Feedthrough Filters" to run the power wiring through the case separator plate.

    As also mentioned before, I used a DPDT switch to change the R5 and R7 resistors for different gains - MM and MC. I have no MC cartridges (yet!), but it seems to work OK.

    As I noted up there, I thought maybe it had more noise than it should (NOTE: only when I rack the volume on my Torpedo III), until I compared it to my brand-new Hagtech Bugle. It blows it away in both low-noise and detail. It's the best I've ever heard phono and is superior to many DACs I've heard (and built).

    Thanks, Pete!
     
  4. TheloniuSnoop

    TheloniuSnoop Friend

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    Excellent work. Have you gotten the new 797's in? I'm wondering if the inductors on the amp board pick up any stray
    field from the PS tranny? That's why I put my PS in a separate case.
     
  5. TomB

    TomB MOT: Beezar

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    No, I haven't received new opamps, yet. There may be some things I can do to improve the noise. Honestly, though - after finding out the noise comes later in my volume knob travel than the Hagtech Bugle2 and is less noisy when it comes, I think it's doing very well. I have a pair of relatively high-gain tubes (12AZ7's) in my T3 headphone amp. Normal listening with a DAC and HD800 headphones is about 9 o'clock. Strong listening with the LR is about 11 o'clock. I'd say real noise occurs about 2 o'clock, with the peak around 3 o'clock and beyond. My volume knob goes from 7 o'clock to 5 o'clock in travel.

    Noise with the Bugle2 starts at about 12:30-1 o'clock. At 3 o'clock, it's probably twice as loud as the LR at the same position.

    This is somewhat relative, of course. My headphone amp has a certain gain with those tubes, the Bugle2 has a certain gain, and the LR has its gain, too. However, the Bugle2 and LR are supposed to be the same gain (with MM cartridges) - 40dB. So I think it's a good comparison between the two: the LR is superior when it comes to noise.
     
  6. TomB

    TomB MOT: Beezar

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    Well, new AD797s were a bust. I got a pair of samples directly from Analog Devices that came in yesterday evening. I swapped them out with the first stage opamps today. As a result, I couldn't get the offset to zero out in either channel, no matter what I did - and it was much higher than the trouble I had the first time.

    I pulled the opamps in the second stage and put the new ones in there. Then I put back the two original opamps that allowed me to zero the offset before. Everything worked fine.

    Moral to the story: TheloniuSnoop is correct. Order at least a couple of opamps as spares (or more). Be prepared to swap them in and out of the first stage until you are able to zero the offset. If an opamp doesn't work, it doesn't mean it's bad - just that the LR preamp doesn't like it in the first stage. Feel free to plug any AD797 into the second stage, even if it doesn't work in the first stage. That should save some money and it doesn't appear to have any ill effects.
     
  7. therobbstory

    therobbstory New

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    Boy, wish I'd seen this thread a few weeks ago.

    I was just going back and forth with @TomB this evening over email about another project and realized we've both had similar experiences with the 797s in this circuit. In my case, I was getting just shy of PSU voltage on one channel no matter the trimpot setting, while the other channel was fairly quick to get to to zero. The DC offset followed the opamps when switching channels.

    Two 'burned in' opamps from eBay (Mouser was out of stock and I got a baaaad vinyl habit) later, and I was able to get both channels happily around 0vdc. That was about 20 hours of playback ago, though, so I should probably get the DMM out again.

    I get a low-level 60hz hum, more so when my refrigerator kicks on. I should note that both PSU and LR pre are sitting naked on top of a bookshelf at present. FPE panels shipped yesterday and should be here by Monday. Hopefully that kills the noise. I hear a little of the seashore noise, though I assumed that was from the Millett Max preamp driving my Grado RS1.

    Overall, MASSIVE improvement over the Bellari VP129 I've been rocking the last 10+ years before I came to the light and heard a real phono pre for the first time.

    Will get some photos up next week once it's all cased up!
     
  8. TomB

    TomB MOT: Beezar

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    The sea shore noise will go away with a case. Even Dave at Landfall cases (he built the one on Pete's site with the battery power) noted that he gets ocean noise when the lid is off the case side that has the preamp board.

    As for the 60Hz hum, that's a bit more discouraging. I get that in mine when the volume is turned up to ear-splitting, so it's silent otherwise. I assumed that the closeness between the boards was the issue because even Dave's Landfall cases have only aluminum as the separator. It usually takes steel to shield off transformer hum. However, if your boards are separate and even uncased, you should be able to separate them far enough apart so that the hum goes away. If that doesn't make it go away, then there may be something in the power supply board or the design that's causing this.
     
  9. TheloniuSnoop

    TheloniuSnoop Friend

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    My build uses separate cases for amp and PS, and I still get hum, but only at very high levels as tomb mentioned. Dead silent at human levels.
     
  10. therobbstory

    therobbstory New

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    I'm fairly certain the hum I'm hearing is from lack of shielding. There are also a number of other places where hum could be creeping in as my system is by no means finalized at the moment. At human levels, it's only audible when the fridge (about thirty feet away) kicks on. FPE goodies are being delivered tomorrow. It'll look similar to the landfall split cases, with a third Galaxy Hi-Fi 'side' bolted to the base, front and rear panels. I should have done some homework on the EMI shielding properties of aluminum, but...didn't. I suppose I can always replace it with copper or steel later on.

    Here are some design images of what I'm expecting to recieve tomorrow. I don't have a MC cart, but I future-proofed my design with provisions for Sowter MC step-up trafos. I don't have them, and don't intend to add them until my system demands it.

    Front
    [​IMG]

    Rear
    [​IMG]

    Base plate
    [​IMG]
     
  11. therobbstory

    therobbstory New

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    FPE delivers!

    [​IMG]

    The panels mount to the case just fine. No matter how many times I comb over my FPE files, there's always something wrong when my plates arrive. This time the cutout for the IEC inlet is slightly too small to flush mount the socket from the rear. I can mount it to the front of the rear panel however. Not pretty, but it'll function.

    Also failed to allow enough room for the grounding posts securing nut. Grr.

    I'll try to get it wired up tonight and get some better photos along with a listening impression.
     
  12. lehmanhill

    lehmanhill Almost "Made"

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    If you will indulge me, I would like to breathe life back into this old, dead, and rotting thread.

    I have recently become aware of the Millett LR phono and am intrigued by its design. I was going to spring for the Holo LCR-1, but a major price hike put me off. Complicating things is that I need MC levels of gain, but my low output cartridge is a Soundsmith Zephyr Star that I have been told on the highest authority (David Slagle) is fussy about step up transformers due to the Star's higher inductance. So I need to provide the first gain stage without trannies.

    Obviously, the Millett LR is a MM gain phono, so I would need my own active first stage, but I wondered how the Millett has stood up over time. For those of you who built it, are you still using it? How does it compare to something more modern that we may have heard of?

    Thanks in advance for any input you can give me.

    Jac
     
  13. Cspirou

    Cspirou They call me Sparky

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    old post but did you happen to catch this?

    https://www.superbestaudiofriends.org/index.php?threads/mid-fi-headamp-shootout.11073/#post-350143
     

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