U-Turn Pluto 2 Review (Phono Preamp)

[B4ICU]

Why Is it a shame? If it doesn’t interest you fair enough but the added negativity just seems pointless considering that this is a phono stage review….

You might remember, why the CD was invented by PHILIPS and SONY? The major objectives were to overcome the LP problems:

Nor to turn sides after 20-25 min.
To play longer than 45 min. (80 min, for Beethoven 9th from start to end)
To have a no wow and flutter!
To have a flat Fr. over the entire disc (constant linear velocity, and not angular velocity).
To lower THD (LP with the MM or MC go way above 1%),
No tracking error (linear rather than a pivot)
No needle wear out.
No LP wear out.
No mechanical alignments of the tone aem.
Size of LP vs CD and storage.
No nylon sleeve wit electrostatics.
No need for constant cleaning from dust and dirt.
And the list goes on and on.
Up's it just returned.

I enjoyed the return of the Jedi, The return of Rocky 75, and many more.
I don't enjoy the return of the LP. It's so wrong...

 

[kyllwtr]

Perhaps it could actually run off a DC supply. The number of diodes makes it look like a full bridge rectifier, not a split voltage supply from an AC source.

My guess is that U3 is a charge pump, generating a -10 V supply from the +12V supply. It could be a TC1044S from Microchip. The pin-out fits with C33 as the charge pump capacitor.

I agree, but it could be, instead, a TC7662A or something like that as pointed by JROSSER

I suspect that it is a switched capacitor negative rail - the traces would make sense for this part http://ww1.microchip.com/downloads/en/devicedoc/21468b.pdf, and you can see the Microchip logo on the SO8 device.

Still I find crazy using a 78M12 supplied with a 9 Vac and a full-bridge rectifier.
Yes, it is possible to get a quite low-ripple (positive) output but at two conditions: low consumption and (relative) high filter capacitor value and regulator acting only to clip voltage at 12V.
But poor line and load regulation (maybe these are of less importance here).

At the end, if so, it should be possible to supply the unit with 12V dc.

 

[silentt29]

Nice to see this review. I have an internal Pluto 2 in my Orbit turntable. I'm guessing the internal model would be similar quantitatively to the external model measured here?

 

[JensH]

I agree, but it could be, instead, a TC7662A or something like that as pointed by JROSSER



Still I find crazy using a 78M12 supplied with a 9 Vac and a full-bridge rectifier.
Yes, it is possible to get a quite low-ripple (positive) output but at two conditions: low consumption and (relative) high filter capacitor value and regulator acting only to clip voltage at 12V.
But poor line and load regulation (maybe these are of less importance here).

At the end, if so, it should be possible to supply the unit with 12V dc.

I agree, it could just as well be the TC7662A, which is very similar.
I found a better picture, which, as far as I can see, shows a TC7660HE, which is surprising, since it can only handle up to 10 V input.

The 9 V AC (most likely at full load) transformer may give sufficient voltage for two reasons:
1. The peak value of the sine wave will be 1.41 x the AC voltage.
2. The AC voltage at low load will be higher than at full load.

12 V DC will probably not be enough to get regulation from 12 V regulator. You may need at least 12 V + 1.5 V (dropout) + 2 x 0.7 V (diodes) = 14.9 V. So a 15 V or 18 V supply might be OK.
The op-amp only consumes around 10 mA, so the total load is rather low.

 

[Helicopter]

Nice to see this review. I have an internal Pluto 2 in my Orbit turntable. I'm guessing the internal model would be similar quantitatively to the external model measured here?

I agree. I can't imagine why they would change anything but the box.

 

[kyllwtr]

I agree, it could just as well be the TC7662A, which is very similar.
I found a better picture, which, as far as I can see, shows a TC7660HE, which is surprising, since it can only handle up to 10 V input.

The 9 V AC (most likely at full load) transformer may give sufficient voltage for two reasons:
1. The peak value of the sine wave will be 1.41 x the AC voltage.
2. The AC voltage at low load will be higher than at full load.

12 V DC will probably not be enough to get regulation from 12 V regulator. You may need at least 12 V + 1.5 V (dropout) + 2 x 0.7 V (diodes) = 14.9 V. So a 15 V or 18 V supply might be OK.
The op-amp only consumes around 10 mA, so the total load is rather low.

(9Vac x 1.41) - 1.4 = 11.29V

I agree, with 12V you rely on the external regulation (since 7812 doesn't regulate) to which diodes and regulator drop must be subtract, but in any case better than AC. If load is only 10 mA, you can supply also up to 15V and get full regulation with a further reduction of residual ripple of minimum 55dB and typical 80dB.

Switched capacitor converter seems supplied from regulated output of 7812. TC7662A can be supplied up to 18V and TC1044S up to 13V

 

[levimax]

(9Vac x 1.41) - 1.4 = 11.29V

I agree, with 12V you rely on the external regulation (since 7812 doesn't regulate) to which diodes and regulator drop must be subtract, but in any case better than AC. If load is only 10 mA, you can supply also up to 15V and get full regulation with a further reduction of residual ripple of minimum 55dB and typical 80dB.

Switched capacitor converter seems supplied from regulated output of 7812. TC7662A can be supplied up to 18V and TC1044S up to 13V

I think the diodes 1-4 are a "full wave voltage doubler" in which case it all makes sense. As far a ripple goes it looks like filter caps were kept to a minimum to save money.

 

[DSJR]

Sure, the overload margin is poor. But as long as it doesn't lock-up to a rail or burst into oscillation, it really doesn't matter that much. After all, who wants perfect fidelity when reproducing a pop or a tick? You could make an argument that a lower overload would make such aberrations not so annoying...

A 55mV overload would have been laughed out of the room in the 70s and 80s. Not even a single stage opamp RIAA in a low end receiver would have less than 120mV. I have preamps with >300mV overloads on MM with 20VRMS output swings.

I think my concern was more for the 'effects' of the surface noise, as some phono stages seem to 'take off' audibly when a click or tick is reproduced. My own preamps have the kind of high overload (and adjustable gain) you describe, so no issue to me, but I was alarmed at say, the Schiit Mani, as overload seemed very low indeed.

 

[B4ICU]

Why Is it a shame? If it doesn’t interest you fair enough but the added negativity just seems pointless considering that this is a phono stage review….

Do you remember the guidelines to develop the CD, by PHILIPS and SONY?
The incentive was to solve all CD problems. There were so many:

Playing time, and the need to turn the LP (side A and B). each 22-25 min only.
The total length of playing time was short. A CD can play 80 min. equals to beethoven 9th symphony from start to end.
The constant angular velocity (RPM) with one FR. at the beginning and a whole other at the end.
The surface noise, so called pops and clicks (sound like a deep fryer is cooking some potato or fish).
The wow and flutter so common with analog sources , but not existing with digital.
Bad SNR of 45-55 dB and so the dynamic range, increased to 96dB.
Tone arm alignments.
THD was 3-5% to include the cartridge and stylus contribution.
Size and cover with nylon sleeve that had a lot of static electricity.
The LP need a constant clean.
The wear and tear of the record on every play, as so the stylus.
Records of their lot No. sounded different. The mold produced them different after 2000 LP's and after 20,000...
A good record player with a separate arm and cartridge would cost so much more than a CDP. OEM CDP's cost almost nothing.
There most likely a few I missed.

Why going back to that? I must have missed something, especially the sense to do so.
Why not going back to medieval medicine? it worked well for a while, not to mention the poor results and the patients suffering.

 

[levimax]

Do you remember the guidelines to develop the CD, by PHILIPS and SONY?
The incentive was to solve all CD problems. There were so many:

Playing time, and the need to turn the LP (side A and B). each 22-25 min only.
The total length of playing time was short. A CD can play 80 min. equals to beethoven 9th symphony from start to end.
The constant angular velocity (RPM) with one FR. at the beginning and a whole other at the end.
The surface noise, so called pops and clicks (sound like a deep fryer is cooking some potato or fish).
The wow and flutter so common with analog sources , but not existing with digital.
Bad SNR of 45-55 dB and so the dynamic range, increased to 96dB.
Tone arm alignments.
THD was 3-5% to include the cartridge and stylus contribution.
Size and cover with nylon sleeve that had a lot of static electricity.
The LP need a constant clean.
The wear and tear of the record on every play, as so the stylus.
Records of their lot No. sounded different. The mold produced them different after 2000 LP's and after 20,000...
A good record player with a separate arm and cartridge would cost so much more than a CDP. OEM CDP's cost almost nothing.
There most likely a few I missed.

Why going back to that? I must have missed something, especially the sense to do so.
Why not going back to medieval medicine? it worked well for a while, not to mention the poor results and the patients suffering.

While LP's technically are not close to digital they can sound very good and for many older titles a clean LP will sound just as good if not better than the latest "digital remastered version". In addition some people enjoy the large format artwork and collecting original versions of their favorite music and playing around with physical media and physical players. If LP's are not for you that is great but why try to convince people that their hobby is foolish on a phono stage review? Enjoying recorded music can take many forms.

 

[JensH]

I think the diodes 1-4 are a "full wave voltage doubler" in which case it all makes sense. As far a ripple goes it looks like filter caps were kept to a minimum to save money.

No. D1 - D4 are just a regular bridge rectifier.
But the transformer may output around 11 - 12 V ( x 1.41) at light loads, so perhaps there will be some voltage for regulation. But it looks a bit marginal. With no detailed information abot the transformer it is difficult to know for sure of course.

 

[JRG]

Do you remember the guidelines to develop the CD, by PHILIPS and SONY?
The incentive was to solve all CD problems. There were so many:

Playing time, and the need to turn the LP (side A and B). each 22-25 min only.
The total length of playing time was short. A CD can play 80 min. equals to beethoven 9th symphony from start to end.
The constant angular velocity (RPM) with one FR. at the beginning and a whole other at the end.
The surface noise, so called pops and clicks (sound like a deep fryer is cooking some potato or fish).
The wow and flutter so common with analog sources , but not existing with digital.
Bad SNR of 45-55 dB and so the dynamic range, increased to 96dB.
........

I think using phono sources is not a technical question.

Many people already have large LP collections and they want to play and enjoy them.
Is about collecting more that about searching the best possible technical sound specifications.
Today even the CD is an obsolete format. The easiest way is to use some of the digital streaming services, but this is not que question.

Other issue with modern "digital remastered version" is that they usually are made to sound good in today's common devices... like smartphones, bluetooth battery powered speakers, mini headphones,... and the main objective of the mastering enginner work is to get high and strong sound in that devices applying heavy dinamic compression.

Vintage vinyls were not mastered to sound as strong as possible in a smartphone but to sound good in common hifi devices of they era.
paradoxically, that often means better sound on hifi equipment. Not because the format is better, but because at the time the mixing and mastering was done with other objectives in mind.

 

[levimax]

No. D1 - D4 are just a regular bridge rectifier.
But the transformer may output around 11 - 12 V ( x 1.41) at light loads, so perhaps there will be some voltage for regulation. But it looks a bit marginal. With no detailed information abot the transformer it is difficult to know for sure of course.

Not challenging you just trying to learn. How can you tell how the 4 diodes are wired by looking at the top of the PC? Seems like the 4 diodes could either be a regular bridge or a doubler. Thanks.

 

[Anthony T]

You might remember, why the CD was invented by PHILIPS and SONY? The major objectives were to overcome the LP problems:

Nor to turn sides after 20-25 min.
To play longer than 45 min. (80 min, for Beethoven 9th from start to end)
To have a no wow and flutter!
To have a flat Fr. over the entire disc (constant linear velocity, and not angular velocity).
To lower THD (LP with the MM or MC go way above 1%),
No tracking error (linear rather than a pivot)
No needle wear out.
No LP wear out.
No mechanical alignments of the tone aem.
Size of LP vs CD and storage.
No nylon sleeve wit electrostatics.
No need for constant cleaning from dust and dirt.
And the list goes on and on.
Up's it just returned.

I enjoyed the return of the Jedi, The return of Rocky 75, and many more.
I don't enjoy the return of the LP. It's so wrong...

*Yawn* like I said, it’s a review of a phono stage. You’re just creating a distraction that doesn’t belong on the thread but of course you know that don’t you? Go play elsewhere please, I thought this sort of nonsense was frowned upon in review threads. Sigh….

 

[H-713]

Nice and clean built quality. Wonder why mix manufacturing process: through hole and SMT?
I see that LP returns big time. What a shame.

The use of THT resistors might be an issue of cost. It's trickier to find thin-film SMD resistors for a reasonable price, but metal film THT resistors are easily found for cheap. At least, that's about all I can come up with.

As for Vinyl, who cares if it's technically inferior. Lots of people find the process of collecting LPs, setting up turntables and trying different cartridges to be a fun hobby, and there's nothing wrong with that- it's a hobby, and the whole point is having fun.

As an analogy, there are people who collect and restore Tektronix vacuum tube oscilloscopes. Is a Type 555 technically inferior to a similarly-priced DSO in almost all respects? Yes. Are there a few select areas where they're a little better than a modern scope? Yes. Is it fun to restore, use and tinker with? Absolutely.

 

[B4ICU]

While LP's technically are not close to digital they can sound very good and for many older titles a clean LP will sound just as good if not better than the latest "digital remastered version". In addition some people enjoy the large format artwork and collecting original versions of their favorite music and playing around with physical media and physical players. If LP's are not for you that is great but why try to convince people that their hobby is foolish on a phono stage review? Enjoying recorded music can take many forms.

"they can sound very good and for many older titles a clean LP will sound just as good if not better than the latest "digital remastered version".

No way.
The technical list of LP downsides are well noticed while listening to one. I'm especially sensitive to the pops and clicks of the LP's surface noise.
Mechanical FB of the low Fr. (especially if you own a good Sub) are inevitable.
I can agree that people may like it, that the THD and IMD may appeal to them, Fr. is not an issue and so on.
If this compare would be done on one of Amir's test, even an EQ on the LP side would not even it out.

 

[B4ICU]

The use of THT resistors might be an issue of cost. It's trickier to find thin-film SMD resistors for a reasonable price, but metal film THT resistors are easily found for cheap. At least, that's about all I can come up with.

As for Vinyl, who cares if it's technically inferior. Lots of people find the process of collecting LPs, setting up turntables and trying different cartridges to be a fun hobby, and there's nothing wrong with that- it's a hobby, and the whole point is having fun.

As an analogy, there are people who collect and restore Tektronix vacuum tube oscilloscopes. Is a Type 555 technically inferior to a similarly-priced DSO in almost all respects? Yes. Are there a few select areas where they're a little better than a modern scope? Yes. Is it fun to restore, use and tinker with? Absolutely.

The resistors are the cheapest components on that board. How cheap that can be? I estimate it might be all, cost less than a $1.-
SMT resistors should cost about 5 cents each, in quantities.

I don't care what people collect. LP's sound is terrible. There is a lot of foreplay, before getting started, and 22 min. later, it repeats all over again.
The LP is so inferior, we were so happy it was gone, so why take it back. It's like knowing all the answers and still fail the test (same was said about
president Bush, when elected for a second time).

 

[levimax]

"they can sound very good and for many older titles a clean LP will sound just as good if not better than the latest "digital remastered version".

No way.
The technical list of LP downsides are well noticed while listening to one. I'm especially sensitive to the pops and clicks of the LP's surface noise.
Mechanical FB of the low Fr. (especially if you own a good Sub) are inevitable.
I can agree that people may like it, that the THD and IMD may appeal to them, Fr. is not an issue and so on.
If this compare would be done on one of Amir's test, even an EQ on the LP side would not even it out.

If an older LP was made from a fresh master tape and mastered by a skilled engineer (like many original pressings are) and the LP is still in good condition and a worn out or copied version of the master tape was "re-mastered" decades later to make a CD it is very possible the LP will sound better than the CD or any later digital version.

 

[Bob from Florida]

The resistors are the cheapest components on that board. How cheap that can be? I estimate it might be all, cost less than a $1.-
SMT resistors should cost about 5 cents each, in quantities.

I don't care what people collect. LP's sound is terrible. There is a lot of foreplay, before getting started, and 22 min. later, it repeats all over again.
The LP is so inferior, we were so happy it was gone, so why take it back. It's like knowing all the answers and still fail the test (same was said about
president Bush, when elected for a second time).

So, this is a nice review of a budget phono stage - thank you Amir. It does well for its price point and will give budget minded folks some "bang for their buck".
Based on your posting it would seem you have no interest in vinyl record playback. If that is true, then why would you even read up on a phono stage review or really anything to do with vinyl records? This all seems very argumentative to no purpose.

 

[kyllwtr]

The use of THT resistors might be an issue of cost. It's trickier to find thin-film SMD resistors for a reasonable price, but metal film THT resistors are easily found for cheap. At least, that's about all I can come up with.

As for Vinyl, who cares if it's technically inferior. Lots of people find the process of collecting LPs, setting up turntables and trying different cartridges to be a fun hobby, and there's nothing wrong with that- it's a hobby, and the whole point is having fun.

As an analogy, there are people who collect and restore Tektronix vacuum tube oscilloscopes. Is a Type 555 technically inferior to a similarly-priced DSO in almost all respects? Yes. Are there a few select areas where they're a little better than a modern scope? Yes. Is it fun to restore, use and tinker with? Absolutely.

It is possible that the choice of THT is due to other reasons, not the cost, since THT today tend to cost more than SMD.
In any case, THT costs more in working phase (consider that IC are SMD and thus 2 different working phases are required).

One possible reason is resistance precision matching, that can be done before mounting by pair selection (you can easily separate resistors in different bins with tighter precision before mounting).
High matching precision allow differential amplifier to have higher CMRR and reduce distortion.
Metal film resistors are quite stable in temperature and have more predictable temperature coefficient TC.
From what I remember, they also have low noise performance.
Using SMD resistors would have required precision from 0.5% to 0.1%, more difficult to find and probably with more noise.
Also TC is higher in standard SMD resistor (high precision thin film are required).

In a similar fashion the choice of the amplifier capacitors, that to me, seem to be high precision, high stability and low loss ones.

In SMD you can find similar component, but, if you do not have big production volume, it can be a nightmare to manage production.