TC-750 Phono Pre-Amp (Continued)

Discussion in 'Vinyl Nutjob World: Turntable and Related Gear' started by purr1n, Oct 6, 2015.

  1. JK47

    JK47 Guest

    @purrin

    If you decide to go the MC cartridge route (saw you considering it, in another thread), will you get the TC-760LC phone preamp and do the same mods?
     
  2. purr1n

    purr1n Desire for betterer is endless.

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    Probably not because the TC-760 isn't a totally discrete design. There is an opamp somewhere in there, and even then there might be not enough gain. The beauty of the TC-750 is that it is totally discrete with only three transistors.

    I bypassed the 10uF Solens with 1uF film caps (no-names that we use in the ZDS). Sounds wonderful now. These caps can be eliminated if I use the Jensen step-up transformers with MC.
     
  3. JK47

    JK47 Guest

    Got the TC-750 and Sola PS today. Tried the TC-750 with stock PS, and it hummed and faintly picked up a country radio station. Soldered the power cables to the Sola and let her rip... Humm cut down, but that pesky country radio is still there (tried re-positioning cables, TC-750, and PS to no avail). Tried the old tinfoil trick for shielding...better, but not quite gone. I'll try layering some foil inside the case when I take the TC-750 apart for mods.

    Definitely more resolving and detailed compared to my Pro-Ject Tube Box S phono preamp.
     

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  4. Dr. Higgs

    Dr. Higgs Boson - Member

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    I had the same interference issue with mine (except it was some christian broadcasting station). I thought the TC-750 sounded a bit better than my Mani with the stock wallwart, but I ended up switching back to the Mani to cut down on the interference. I'll probably end up picking up a Sola PS and modding it, so I'm interested to hear if anyone can figure out how to improve the shielding.
     
  5. purr1n

    purr1n Desire for betterer is endless.

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    With the exposed mess of caps, I'm getting minor noise (buzzing) which is just a bit louder than groove noise. Have you guys tried changing interconnects? I will remove the inline 1k resistor as suggested by OJ and see what happens.
     
  6. JK47

    JK47 Guest

    I had a Mani before I had the Tube Box S, and it picked up 2 radio stations and had a more wicked hummm (in the right channel) than the TC-750 (with stock PS, humm was in Left channel). With my Mani, I had it wrapped up in a ton of tin foil and that helped with the radio stations, but looked ridiculous. The Tube Box S eliminated the radio stations and brought down the hummm. The LPS for my Project Carbon DC all but eliminated the hummm problem. I'm going to layer the foil nicely inside the TC-750 case later today when I take it apart. Will report back tonight.

    Originally with my Mani, I tried the stock Project interconnects = fail, Monster interconnects = fail, and Blue Jeans interconnects = better. With the TC-750 I've only tried the Blue Jeans and stock Projects, and the Blue Jeans are noticeably quieter.
     
  7. Dr. Higgs

    Dr. Higgs Boson - Member

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    I have an original Debut Carbon with speedbox too, so I might do a little experiment to swap turntables, interconnects, and preamps to see if it has an impact on the interference. I currently use Blue Jeans interconnects, but I have some no-name interconnects that I could try out.
     
  8. JK47

    JK47 Guest

    Oh man, o' man. Double layer of foil on top and bottom (removed PCB to cover the bottom). Almost completely dead silent, no radio, no humm, just a subtle hiss when the amp volume is maxed out, very black background when amp is at listening levels. This is very very nice, much better than the Tube Box S background noise wise, and when it comes to detail retrieval. I can't wait to start playing with the caps.
     

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  9. Dr. Higgs

    Dr. Higgs Boson - Member

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    Wow great work, I'm going to have to try that out now.
     
  10. JoshMorr

    JoshMorr Friend

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    Looks like the old Changstar post on this subject is at http://static.changstar.com/www.changstar.com/index.php/topic,2778.0.html

    I am currently gathering parts for this mod. I have the TC-750, Sola power supply in route, but had a couple of questions on the caps.

    Marv said the Solen's aren't good, or need a bunch of burn in time. Any update or recommendations? Is the Audiocap brand from Parts Express worth the money? DO I just buy a bunch of cheaper options and roll until I find something I like? Find a decent poly or just suck it up and spend of the film/oil's?

    Second - what size inputs / outputs. Initally I saw 4 uf's for in outputs and 10 uf's for the input, but later Marv said he tried out some 1uf films that sounded better. Does the size of these caps differ from table to table or cartridge to cartridge?

    Sorry for all the new guy questions- looking to see if I can beat my Project phono box ds.
     
  11. purr1n

    purr1n Desire for betterer is endless.

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    Jantzen superior 10uF and 4uF. Or Audyn caps for bang for buck.

    I overlaid a good quality 1uF (parallel) over the crappy Solens, but best to use a single cap.
     
  12. JK47

    JK47 Guest

    I have 4 10uF WIMA caps on the way that I'll try in both input and ouput spots. A fellow on SteveHoffman forums suggested 10uF on the output as well. I have a pair of 4.7uF WIMA caps enroute as well that I'll try in the output postion to compare to the 10uF.

    http://forums.stevehoffman.tv/threads/phono-stage-modifications.334928/

    The TC-750 w/SOLA PS handily beats my Project Tube Box S (I may order a 15V SOLA and adjust it up to 18V for the Project to compare them again). I'm anxious to try out the caps next...

    EDIT: changed audiokarma to stevehoffman after I found the link. same user on both forums
     
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  13. JoshMorr

    JoshMorr Friend

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    Thanks! Ordered up a mystery project box from china and the Jantzen superior's from parts ex. @JK47 interested to see how your upgrade goes. Have you done any of the other mods or removals?

    I also have a project tt - let me know if the power supply upgrade has a noticeable audible improvement.
     
  14. JK47

    JK47 Guest

    I haven't doen any of the other TC-750 upgrades yet. Will try the input/output caps first then eliminate the diode and power caps. Will also remove the 220pF output caps and try it with nothing and with a pair of 50pF caps I ordered as well.

    My Project Debut Carbon DC benefited with a 15V linear power supply, much quieter than the stock wall wart. Then I tried the TC-750 (interior wrapped in tin foil) and the SOLA PS, and wow a wowee. The background is very black and quiet compared to before, no humm, no radio stations, no nothing, just the sound of the needle riding the grooves once its dropped.

    I'm fairly certain the Tube Box S will go up for sale when I get home from work in a few weeks, and go towards my VPI Classic fund.

    There's one of my pics from another thread, the TT linear power supply is below with the blue 15.0 on the display.
     

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    Last edited by a moderator: Jan 19, 2016
  15. JoshMorr

    JoshMorr Friend

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    Handsome looking setup - jealous of your enhanced table and the Ortofon Blue.

    In the provided link the replaced the cart loading caps where purrin just took them out. Is this simply a preference of what sounds best? If they are just removed is a jumper needed? In the schematic posted by OJ it looks like they can just be bypassed, but I aint that smart.
     
  16. purr1n

    purr1n Desire for betterer is endless.

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    The cart loading caps are a preference of what sounds best (or if you want to measure to get a flat EQ). Some carts have a bump in the high end, so changing capacitance will help. No jumper needed, just pull them. You DO NOT want to close the circuit with wire. We are talking about picoFarads. Your cable will have some capacitance of its own.
     
  17. JoshMorr

    JoshMorr Friend

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    Here we go.... will try to document some of my process
    IMG_20160130_101735.jpg
    Pic of the board with (1) diode removed - jumper added, (2) output caps removed, (3) input caps removed, (4) power filter caps removed, (5) remove cart load caps

    IMG_20160130_102145.jpg
    New parts w/ removed old parts to the right. Now time to figure out how to put new large caps where old small caps used to be

    IMG_20160130_103218.jpg
    This is the case I bought to put everything into. Tried to stay fairly small (6" x 9" case). Due to foresight issues (mainly remembering to look at case inside dimensions, remembering to figure the size of the new caps in, and the metric system) doesn't look like everything is going to fit. I was banking on the power supply being able to be removed from the aluminum enclosure (not easily done) so it currently sticks out roughly 1/2" from where the cover is supposed to be. Also, the metric system confuses simple americans like myself. New case TBD.

    I think I understood the above, but does anything need to be replaced where the power filter caps used to be? Looks like they can just be removed.

    Hope to update on a working set up sooner than later.
     
  18. BioniclePhile

    BioniclePhile The Terminal Man - Friend

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    What about some used Tripp-Lite power supplies? 13.8 Volts good enough?
     
  19. peef

    peef Friend

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    I know it's a dirty word around these parts, but a SMPS with a good linear regulator might make sense. Something like this, into a shunt regulator:

    http://ca.mouser.com/ProductDetail/...H5rwl1hUZB%2bW5a6L9tEtppmehik46ey%2bqQfJz/w==

    They are tiny, and operate at 40kHz, which makes filtering any residual noise very simple. You might be better with a different voltage, if you don't want to increase the rails too much, but some of the lower power units do run at a lower switching frequency. They also make DC-DC converters that work well with wall-warts-- could save you some trouble with grounding and ground loops. I've used the RAC-05 series and got noise down to microvolt levels under load, with a simple regulator and just a high quality 1uF film cap on the output. Shunt is ever better, and won't get too hot here.
     
  20. purr1n

    purr1n Desire for betterer is endless.

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    Just remove them. You will be relying on the caps in the PS instead. Those stock bank caps were for the provided switcher / wall wart.
     

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