helma
24-01-2018, 08:11
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.
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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.
----
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.