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Thread: New toy - TCC TC-750 phono stage

  1. #11
    Join Date: Feb 2008

    Location: http://www.homehifi.co.uk

    Posts: 6,288

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    Quote Originally Posted by helma View Post
    Btw. sorry to hear of the passing of the designer. You said you had proposed some changes, out of curiosity, what were those?
    I didn't keep a copy of those emails. But a few that I do remember is the non existing power supply decoupling inside the unit. If you use the TC-750 with a 12V battery there is no RF interference that I could hear. The other thing is with the dynamic range that sounds squashed on the TC-750LC after he added a variable resistor at the output, with no buffering. That volume control is affecting the input impedance of the following pre-amp the TC-750 is plugged into, and with that, the frequency response.
    Out of interest, the TC-750 designer used to build me one off samples of my prototype designs, as he owned a small scale PCB factory.

  2. #12
    Join Date: Jan 2008

    Location: Wrexham, North Wales, UK

    Posts: 110,012
    I'm AudioAl'sArbiterForPISHANTO.

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    Got any pics of the unit in question, Kai? I always find when reviewing equipment, and posts become word-heavy, a few nice pics help 'break up the boredom', as it were!

    Not that what you wrote was boring, but most people's attention span is limited, and so often lengthy posts, with reams of text, will put them off reading. Whereas when a few pics are posted, along with it, it helps break things up a bit.

    Anyway, just a small tip for future, and thanks for sharing this with us

    Marco.
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  3. #13
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Quote Originally Posted by Marco View Post
    Got any pics of the unit in question, Kai? I always find when reviewing equipment, and posts become word-heavy, a few nice pics help 'break up the boredom', as it were!

    Not that what you wrote was boring, but most people's attention span is limited, and so often lengthy posts, with reams of text, will put them off reading. Whereas when a few pics are posted, along with it, it helps break things up a bit.

    Anyway, just a small tip for future, and thanks for sharing this with us

    Marco.
    Yeah I certainly get that, and to be honest for the casual reader just browsing through topics I doubt this one will hold much interest, with or without pictures But posting about tweaks like this and just going through presenting my thoughts in a way that might make sense to someone else helps me understand things a bit better myself. If it all might interest someone else, then that's great. Anyway speaking of pictures, here's a shot I snapped after I changed the coupling caps:

    tc-750-newcaps.jpg

    Guess which caps are new.... the large bright red ones are the Audyn Q4 and like you can see they are installed really ugly, with excess length to both the legs and the wire. I did things in wrong order and didn't think them through before starting to poke things with the hot iron. No biggie but doesn't look very nice. The position is pretty much the only place I can have them and still be able to close the case. The mars red film caps are the Panasonic ECW. I just about managed to install them pretty neatly on the board, though it did require a bit of fiddling with orientation and twisting the legs just right. Sadly the Panasonic might have to go, I'm not sure I like how they sound. The Audyns I know I have no objections about, I also used them in my power amp and at least there they sound very good and transparent. The TC-750 has a bit of a hardness/coldness going on, which listening back to the file of the original caps wasn't there - still, it sounds miles better with this cap configuration than the originals, it's really night and day in terms of clarity, detail and transparency, all over the frequency range. Still, a bit warmer sounding caps in place of the Panasonic might be just the ticket.

    I'll be leaving it alone for now, but I think I will revisit those output coupling caps in the future. Also I'd like to possibly adjust the RIAA curve just a bit and get it more accurate, as it stands it sounds a bit lean in lower midrange and slightly hot in the upper mids and treble. As a result basically the warmer the record the better it sounds. The upside is it never really gets too thick or muddy, which has been a problem with my system in the past with some material, partly because of my room. But starting to tweak the RIAA network etc. gets a bit over my head, I'd probably need to take this over to diyaudio.com or something to get some input.

    Clarity, dynamics, imaging etc. are really nice, the treble is a bit sandy or grainy sounding compared to some other gear, not in a deal breaker way but it's there. I think that is not something that can be cured with simple cap changes, I associate the sound signature with simple/cheap BJT transistor gear, so my guess is that's where that's coming from.

  4. #14
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Came upon this so I guess I should update - I was wrong about the treble thing and actually it could be remedied with cap changes. I updated the RIAA network to Russian teflon caps and it fixed the treble and also took care of the slight 'plasticky' sound there was sometimes. I upgraded the caps already a long time ago, sometime last year and ever since that I've had absolutely zero interest in phono preamps, this one is just so natural and right. At the same time I built a CNC / Muffsy phono stage, also using similar Russian teflon caps for RIAA network. The CNC/Muffsy got OPA2134 and LME49720 op amps if I recall correctly. It was a very good sounding little preamp but the modified TC-750 was still better. It's the best phono preamp I've had by a country mile, though to be fair I haven't owned anything fancy, but it's leagues above commercial offerings you can get for I dunno... 200-500 moneys or so these days, with the caveat emptor that of course I haven't heard everything that's at offer at those prices.

    It took quite a lot of work but it was totally worth it. I think what I've done is upgrade components to be able to handle 36V power supply (using 3 series connected SLA batteries for that), recalculate RIAA network for better accuracy and upgrade RIAA caps to teflon, upgrade coupling caps to PP as opposed to the stock electrolytics. That's pretty much it, at least the most important bits. I still managed to fit it all into the stock casing, though only just. Except for the 3 SLA batteries of course!

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