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Thread: New toy - TCC TC-750 phono stage

  1. #1
    Join Date: Mar 2015

    Location: Finland

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    I'm Kai.

    Default New toy - TCC TC-750 phono stage

    I wanted something to fiddle with, so got one of these cheap phono stages to mess with. It seems generally pretty well regarded for a bottom of the barrel unit, and some people seem to wax lyrical about them with better power supplies and some component changes. On one forum some guy was spending in the excess of $100 on new caps... though I have to say if you want to burn that money on caps, there might be better places to put them in than a $50 phono stage. Being of the skeptical sort, I didn't have any high hopes though. Here's a bit of a journal I wrote yesterday as I was going over it.

    ----

    Unboxing new things is always fun, but man is the 12VDC wallwart the saddest little thing you've ever seen. Of course a switch mode supply for such small power requirement doesn't need to be large, but everything about it yells cheapest you could ever get, most phone chargers seem like substantial pieces of quality kit in comparison. Anyway, the unit itself is nicely made, nothing fancy but it's a kind of endearing small black box with enough weight to it to not feel like a complete toy.

    The unit seems quite sensitive to EMI, a bit of fiddling with positioning fixed that. Right out the gate, it sounds ok, certainly nothing spectacular but as a starter phono stage I'm sure you could do worse, though probably not an upgrade over most inbuilt units if you happen to have one. It's reasonably balanced and dynamic, but the bass is a bit loose and while it hints at pretty good and 3-dimensional imaging and detail, everything seems to be covered with a kind of haze. I suspect and hope that's the effect of the supplied PSU.

    As it is, it's certainly no giant killer but shows some promise. Also worth noting it's had about 30 minutes use and has many electrolytic caps, including for coupling, so there could be considerable burn in over some more use. I was going to record before and after samples, but I think it's not worth the trouble, if this doesn't improve in a "night and day" way after what I have planned for it.

    ----

    So next step, improved power supply. I thought I had at least 3 suitable canditates, but I couldn't find my 12V switch mode supply. Oh well, let's try a simple regulated wall wart. Except my memory was wrong on this one - it isn't regulated. On to the next (and last one), a mystrious fairly large box I got from my dad. If I recall correctly it was made to him by his electrical technician friend, not sure what it was used for, maybe CB-radio. Anyway, it's a fairly substantial affair with 10,000uF cap after rectification and additional 2200uF filtering at the output (I presume), regulation seems to be handled by two to-3 cased 2N3055 transistors. The way it was put together I didn't have a good look at all the parts and have no idea of the actual schematic or way of operation. I'd say it can deliver some serious juju but no idea of ripple etc. and how good it is for the application at hand. I'd like to have a look at the output with a scope... anyway, it gets plugged in and the improvement on the stock supply is substantial. That mysterious haze seems to be mostly gone and the bass player has discovered more notes. This is somewhat encouraging. The sound is still lacking a bit of clarity, best way to describe it is the bass is still a bit unfocused, mids are a tad veiled and there seems to be a bit of an extra splash in the highs. But this is not bad, competition is slightly improved Yamaha A-700 stage and a Pro-Ject Phono Box SEII. I'd say it's probably my least favourite of the bunch overall, though perhaps more cohesive than the Pro-Ject. The Pro-Ject is impressive in some ways, but it's a bit overly thick in the upper bass / lower mids. Sometimes it sounds like it was built to impress in a quick demo. As I plan to do some A/B listening later, I record a quick sample.

    ----

    It's time to get inside the case, I notice all the transistors are STC945, they also have G309 marking on them but no idea what that means if anything. I hope it's some designation for low noise and audiophile pixie dust... From the datasheet the plain STC945 looks like a pretty much 1:1 replacement for the BC549 (or actually BC546 or something, because of the worse noise figure) ... it's described as a general small signal amplifier. From the looks of it (though I didn't go through the board part by part) the rest of the circuit is exactly the same, so I imagine BC549 or 550 would be a drop in fit. Whether it would make any difference I have no idea.

    While I'm at it I remove the 220pF input ceramic input caps (the right channel actually had a wrong part, the markings evaporated into thin air as I grabbed it with my fingers to remove it, but it measured over 400pF) and replace with 33pF film. This should be way better for Audio-Technica cartridges which generally perform their best into low capacitance loads - though I'm using a MC with a SUT at the moment. What I'm really after are the electrolytic coupling caps, 10uF at the input and 2.2uF at the output. My plan was to replace both with 4.7uF PP film caps, but they were so large I wouldn't have been able to fit 4 inside the case. So a slight change of plans, I use 4.7uF polypropylenes at the inputs and 2.2uF polyesters for the outputs, because those I just about managed to squeeze in there and they happened to be available.

    ----

    First listening is without the outer case, but man this thing really likes to pick up interference. It's not overpowering, but it's there underneath the music. I want to do the new parts justice and put the case on, much better. I spin a disc, sounds like marked improvement, the mids have a new sense of depth and clarity and the bass is cleaned up further. The highs, while perhaps a tad better behaved still seem to be a bit too eager to make their presence known. I'd say they are probably cleaner, the overly splashy quality seems mostly gone, but hi-hats for example still have a bit more zing than the other two phono stages. I think at this point it's mostly RIAA curve issue, if the one printed on the cover is accurate (I suppose it's the circuit with zero tolerance parts...) the response gradually rises from 0 to +0.5 from 2k to 20k. I'd say this sounds inline with my observations, though I'm suspecting the rise might be a bit (though not much) more than that. Anyway, I'm quite liking it with new caps, there's more presence and depth to instruments. I wouldn't say it's spectacular, but I wouldn't hesitate to put it against phono stages retailing in the 150-300 price bracket - I'm pretty certain there would be better ones in that group but this one wouldn't be shamed at all. I record the same song again to do a little reality check and what do you know, I wasn't fooling myself, it really does sound better. The superduper holographic soundstaging the unit hinted at remains elusive quality, it's not really there. I'm thinking it could perhaps be squeezed out but not sure how. Still, I have heard far more highly regarded phono stages that didn't image any better or did worse, so I'd say it's more of a strength than weakness of this unit.

    Interestingly, the last fully discrete phono stage I had also excelled in depth of the sound field. It was a far more elaborate design and I would've really loved to rebuild it using modern high quality parts (it was in a 70s JVC receiver...) but that thing would've been a pain to work on and it was pushing 40 so I sold it on. The buyer seemed ecstatic enough after he got home and hooked it up he sent me a message how he was hearing his speakers to their true capability for the first time. It was a really nice receiver with monstrous power (JVC JR-S600) and the power amp and phono stage I liked especially well. I feel the line stage wasn't quite up to the rest of it, though not bad. Anyway the thing was full of 40 year old electrolytics and carbon comp + carbon film resistors. Even transistors get a bit iffy at that age. I think it was a really good design and if it was badged Pioneer and had a more classic look to it, people would probably pay $1000 for one today. Lookwise wouldn't trade it for a Pioneer or similar though, I really came to love the look the couple years I had it.

    ----

    Now it's just about the chore of listening to more records and see if the sound develops further. And speaking of that, I'm listening as I'm typing this last part and had a bit of an "holy crap" moment spinning a familiar disc. This thing has really nice musicality about it, and the soundstaging is actually really good. The tonal balance seems to highlight the presence region just a tad though, I'm thinking if this doesn't change with more hours it might be worth it down the line to see if that can be corrected. Makes me also wonder if different transistors might be the ticket, no experience with that...

    I congratulate you if you got this far, and thank you for reading, I realize this got a bit wordy. I'll probably upgrade with some comparisons to the aforementioned phono stages in the future.

  2. #2
    Join Date: Oct 2012

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    My goodness what a long post. Interesting reading though and good result.

  3. #3
    Join Date: Mar 2015

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    Posts: 237
    I'm Kai.

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    Yeah I realized it got really long... it's because I didn't write it all on one setting but kept adding to it as the day went on. Probably would've been an easier read if I just posted it bit by bit Btw. a little correction, the 2.2uF caps I used as output coupling caps were metallized PP instead of polyester, my memory was off. Panasonic ECW-FD series to be exact.

  4. #4
    Join Date: Mar 2015

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    Well it's been a few days and I've spun quite a bit of vinyl with the TC-750 in the chain. I've been using Ortofon MC10 Supreme with a 1:10 DIY SUT. My opinion on the TC-750 has been fluctuating quite a bit, yesterday I though about updating this thread, I was pretty taken with it at that time. Today I seem to think less of it. I've noticed some break in which has cleaned up the high range somewhat, so it might be both the user and phono stage need some more hours

    With the aforementioned combo I occasionally had the feeling the mids were a tad cold and the sound was a bit wimpy to use a highly technical term. This is also highly source material dependant though. I know the Audyn Q4 caps sound fine, after all I also used them in my power amp for coupling and have nothing bad to say about them really. Not that I've tried anything else in there besides the original eletrolytics. Out of curiosity I searched for opinions on the Panasonic ECW which I used at the output of the TC-750. Didn't find much but found the following tidbit about using them for coupling: "These are tolerably good. They are a bit on the bright side, lack some bass, and are slightly hard in the midrange. They do, however, pass a fair amount of detail, and in a dull sounding circuit might be a decent choice if one's budget is tight. Not as good as either the Solens or the BCs, but tolerable." (source http://diy.ecpaudio.com/p/some-notes...apacitors.html)

    Interestingly the above pretty much spot on sums most of the gripes I've been sometimes having about the sound of the TC-750. Makes me wonder if I should try something else in there. I have more of the Audyns, but I would have to do away with the top of the case, which I don't want to do. I also have some 1uF ICELs, which I think I could squeeze in there somewhere. Maybe I'll try those at some later time just out of curiosity. Also the SUT I have tends just a bit on the bright and lean side, though loading the secondaries down a bit helped with both the highs and giving some more meat to the bass at the cost of losing some output. So some synergy issues at play here. I'm currently listening to a Glanz MFG31E which is a nice "moving flux" (type of MI I think) cartridge with better transparency than most MMs but somewhat warmer and thicker sound than most moving coils. Seems a better synergistic match with the TC-750.

    I'll let it be for now, but at some later point changing the output caps might be worth a shot, beyond that I think there are some polyesters in the RIAA circuit, maybe some decent PPs would be an upgrade there. Also searching the net I've noticed the TC-750 has been built at least with 3 different transistors during it's lifetime, including 2SC1815, BC459 & 2SC945. Mine has STC945 which I assume are supposedly identical to the 2SC945. Now I don't know if they have compensated for difference in transistors in the circuit, but if they haven't I can't imagine all 3 types sounding exactly the same despite seemingly being compatible with each other in this application, taking a quick look at the datasheets. I think BC550 should work fine and be an upgrade in noise specs, so I could imagine perhaps trying those if I get fiddly enough. They seem to cost less than 0.10 euros a piece, so 5 euros would buy dozens.

    I know I've focused more on the negatives in this post, but there are a lot of nice things to say about it as well and not just "for the price", so I don't feel messing with it is a waste of time, and a learning experience anyhow.

  5. #5
    Join Date: Mar 2015

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    My little learning experience keeps getting weirder and by weird I mean I learn things I was not set out to learn. I did some side-by-side listening and there was something off about the TC-750, it was really hard to put to words but it was like I was missing pieces of the music, like it was somehow filled with empty gaps. Words don't really cut it. A subtle thing but once I noticed it, it kept bugging me. I recorded some sound files so I could smoothly switch from preamp to preamp and as I was lining the files up in Audacity so that both start at exactly same time, I noticed the TC-750 inverts polarity. Changing polarity of the Pro-Ject file so that it corresponded with the TC-750, that same weird feeling of 'missing pieces' followed, while inverting the polarity on the TC-750 file it started to sound right, it was solid again and had 'all the music'.

    I never thought polarity inversion was audible (or thought that much about it at all) and when I've done multitrack recording I've had no qualms about hitting the polarity invert switch for a certain track to get the phase 'right' for the mix. I never noticed a worthwhile difference for how that single track sounds solo, though obviously it affects the sense of space for the whole mix. So I read what the interwebs have to say on the subject to get some sort of idea if I'm losing my marbles of if I simply noticed something I haven't noticed before. The way someone described the difference sounds exactly like what I was experiencing, though he used different words.

    Seems to be a record specific thing, not every record seem much affected while others it's noticeable. Certainly something to be aware of when comparing two components, one should make sure both have same polarity, unless you want to add comparing how inverted polarity sounds into the mix. Oh man, be wary of the upside down... now I need a serious break from this fiddling, not that I've been doing it 24/7 or anything, but spent a couple hours at it every day, but that's enough for me to get a bit too deep into this stuff

  6. #6
    Join Date: Feb 2008

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    I have sold the TC-750 and TC-750LC at various times. And I did speak to the designer about making some changes, but he never did take up my offer. Unfortunately he passed away the year before last. So I doubt there will ever be any changes.

  7. #7
    Join Date: Mar 2010

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    Is absolute phase audible? That's a really hot topic these days with some decent research being done into the audible difference between its effects on compression and rarifaction of sound waves.

    Do you have any pics of the unit?
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  8. #8
    Join Date: Feb 2008

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    Looking at the circuit, there is no reason to accept that the phase is reversed. Both the left and right channels are exactly the same.

  9. #9
    Join Date: Mar 2015

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    Quote Originally Posted by sq225917 View Post
    Is absolute phase audible? That's a really hot topic these days with some decent research being done into the audible difference between its effects on compression and rarifaction of sound waves.

    Do you have any pics of the unit?
    I took a couple pics of the insides when I was changing out the caps, I'll post them later thought probably not today, about to get busy.

    Re absolute phase - well it's odd, I had some previous files also and checking those, they were in same polarity between the phono stages. I'm not sure what happened with the latest files (or the previous ones). So for now I'm not sure what pieces in my system might invert and what might not. As for absolute phase being audible, I did some experiments and I'd say yes it is, and once you know what you are listening for, to a degree it's hard to imagine what would be so hot about the topic - though the audibility depends on the recording and system and it's one of those things you need to hear it for the first time, before that it doesn't exist. It was more audible with the TC-750 than my other two phono stages and had I not gotten the TC-750 I probably wouldn't have discovered the phenomenom at this point. The upside of that is where there is good space, the TC-750 does a better job describing it, but with some recordings which are jumbled, it also highlights the anomalies, which I now guess is part of the reason why with some recordings I felt like there were pieces of the music missing (the other reason being a tonality issue). Since the other two phono stages weren't as revealing of the subtle spatial information / room cues, they mask them and once my room enters the picture, it masks them further resulting in a more cohesive experience where the oddities aren't heard much.

    Anyway I'd say absolute phase is most audible on spatial information / presence and dynamics. If it matters with the recording, with the right polarity the soundstaging is life like - singer and instruments have presence, they come to perform in your room, or you take a trip to their room, I guess depending on your room acoustics. In any case the music happens in a realistic sounding space. With the polarity inverted, everything is pushed back in a way that sounds unnatural, it's almost like the space implodes upon itself. It's a bit tricky to describe in words, but it's like the performers are doing their thing in an odd bubble of space which is neither here nor there - it doesn't sound realistic, there's something unnatural and wrong about it. Likewise dynamics can get a bit duller, this was most apparent with instruments which have strong leading transients, high freq guitar string attack, some percussive instruments etc.

    It's one of those things if you have never noticed it you never might, but once you notice it, while it is in many ways a subtle effects it can be quite clear. At least for me it was one of those "how come I never noticed that before" type of things and actually made me feel pretty silly I had paid no attention to it at all before. On the other hand many multitracked studio recordings have no natural space to begin with and polarity might be all over the place between tracks if no attention wasn't paid to it, so with that type of material there might be no right or wrong so whatever change you might hear or not would probably be pretty random. With more natural sounding recordings it becomes more important.

    Just for reference, my system as it stands: Lenco L75 w/ FR-54 arm & Ortofon MC10 Supreme -> SUT + TC-750 -> Sherwood AM-8500 power amp -> JBL 120Ti - so nothing overly expensive or 'high end', though those JBLs cost a pretty penny in the 80s when new, but actually precise imaging isn't their strong point, they're not the type of speaker to throw holographic "sound images" at you. The rest is just good quality decent gear. The Lenco I have spent quite a bit of time tweaking and in the case of the TC-750 and Sherwood, electrolytic coupling caps have been changed for PP film types.

  10. #10
    Join Date: Mar 2015

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    Quote Originally Posted by StanleyB View Post
    Looking at the circuit, there is no reason to accept that the phase is reversed. Both the left and right channels are exactly the same.
    Oh of course not, it's not about the channels being out of phase between each other, that would be quite horrible. I was talking about inverting polarity, or absolute phase as it might be called - meaning that a positive signal going in comes out as a negative. A lot of gear does this, but like I said in my previous post, I'm not actually sure at this point which pieces in my system invert (if any) and which keep polarity. Inverting polarity is the equal to swapping + and - leads at the speaker end - signal which used to cause an initial positive movement of the speaker towards the listener, will now do the opposite. In a lot of systems for a lot of people with a lot of music material, this won't mean anything, but I just became convinced yesterday that with certain types of recordings, mostly ones with strong spatial information of space, preserving original polarity of the signal does matter. Actually that I came to notice it at all, is a compliment to the TC-750, that a cheap 50 euro preamp presented this information in such a way it became readily audible, while many way more expensive preamps seem to blur it.

    Btw. sorry to hear of the passing of the designer. You said you had proposed some changes, out of curiosity, what were those?

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