Pro-Ject Tube Box S2 Phono Preamp Review

[Urubamba]

My first participation here. I bought the PJ Tube Box S2.
I am very satisfied with the sound.
I use it with Denon DL 103 Moving Coil for the "mint" vinyls and with Ortofón 2M Red for the rest.
Just add that apart from a very wise comment here (post 8,9 and 14) I have not noticed in any "serious" review a detail that seems important to me:
It gets too hot!
Being a design with the 12AX7 tubes submerged inside the casing up to 1/3 of its height, the part corresponding to the filaments is located inside the cabinet. And they are the ones that heat the tubes at the bottom.
The valve holes are approx 2mm. with a diameter greater than them, it is insufficient, the heat that remains trapped inside the cabinet is greater than that which is dissipated from above.
There should be a number of extra holes around it, much like the power tubes on many vacuum tube amps.
One of the risks - apart from the longevity of all the components -, which I see as the main drawback due to this excess temperature, is that there are two polystyrene capacitors very close to the tubes, as they have already mentioned in posts 8,9 and 14.
These types of capacitors are very prone to change in value when they exceed the limit of 75 degrees Centígrados, and do not return to their original value when cooling ...
My unit came from the factory with both caps sloped, away from the tubes. I guess it must be for something. I have already decided to use it "without any clothes", (it is spring and summer is approaching here) although it is not very aesthetic. A flannel ensures that it does not get dust .....
WAF from Project Tube Box S2 is very poor when "clothed", so unclothed is a NO NO NO. But in my case, luckily, they let me do it. It's just that my wife and I are old enough to worry about the impression the visitors get.
Greetings

P.S:
I don't speak English, so Google Translate is my great friend.

 

[Urubamba]

This is my Project S2, you can see the capacitors as they came from the factory.
Resist the urge to straighten them!
By the way, I forgot to mention another "detail" of this phono preamplifier that I see somewhat problematic.
I don't know if the pre-S2 models had the same DIP switches, but these certainly leave a lot to be desired.
They are extremely hard to move - given their tiny size - and it is really scary that they will deteriorate after various adjustments, because they are made of plastic.
So I have decided to use a selector-inverter box between MC and MM, which I had built some time ago to select between two TTs with different cartridges, but both were MM.
Now I must put a load in parallel to compensate the impedance from MM (typical 47 KOhms) to MC (100 Ohms is what Denon recommends for the DL103 cartridge, although I have preferred to use 10 times the value of the cartridge impedance (40 Ohms) to ensure an optimal voltage drop at the input of the Project.
So the idea is to parallel a typical 470 Ohm resistor with the 47 KOhms MM input. It will give 465.34 Ohms of resultant impedance.
I think it will work, comments are welcome and appreciated.

 

[Urubamba]

" WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details."


??????????????


I think this sentence does not make much sense, judging by the reception I have received. Thank you anyway. The forum is very nice.

 

[BDWoody]

" WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details."


??????????????


I think this sentence does not make much sense, judging by the reception I have received. Thank you anyway. The forum is very nice.

Looks like it got buried a few times!!

Welcome to the forum! I hope you don't take it personally. Some threads aren't that active and disappear off the radar quickly...

 

[Urubamba]

I'm an audio enthusiast and thought about developing various tracks here, but it hasn't been a good start.
Putting in parallel an extra load in the input of the Project is not interesting? There can be dire consequences?
What about the impedance selector chip? It is not the same as a mechanical input selector on a "vintage" amp!
Can there be some interaction there, (there are no circuits in sight on the web)?
If this is not arousing any interest here, I think I will return to my usual forum.
Sometimes it is good to alternate, (as with women), sometimes it gets complicated and you have to divorce. In this case, it was just a fruitless approach, the lady is not predisposed......

There are no emoticons here? I have not been able to find them.

 

[BDWoody]

I would suggest starting a new thread. The end of old threads often gets lost. Try the DIY section.

 

[Urubamba]

Um, I see, I had thought about it, but I discarded the idea.
I do not want you to misunderstand me, my English is bad and each contribution I make in the forums takes me a previous step before writing, as I already said, I use GT. , and I have to check the translations because there are always gross errors that I have to correct - if I realize it myself -, or edit when I read the translated page. There are insurmountable twists and turns sometimes.
When I made my DIY cabinets, I documented the entire construction on two simultaneous forums. It took about two years and hundreds of photos and explanations provided! These two forums are English-speaking like yours, one was from the USA, the other from Australia, I don't know in which country the "base" of ASR is located, UK perhaps? At one point I doubted if it was worth so much work that it will be forgotten, but the "prize" during that time was to see that there was interest and I had answers.
A forum member from Australia (https://www.stereonet.com/au/) encouraged me to continue and told me not to be discouraged, that my English was perfectly understood. I did this until I finished my build thread (DTQWTII by Troels Gravesen), although I also participated in other threads, obviously. I emigrated to another forum and currently a sensation similar to the one I report invades me.
It is still a karma for me, and many times I think that I do not receive answers to my threads because my redaction shows that I am "toad from another well" (a saying from here, from Argentina) and that feeling invades me again. There are prejudices around the world and more in these times .....
Although this does not warrant a consultation with a psi, I do not have much time either, so I will leave it to the discretion of the ASR forum members ... you know ... you are an interested party in adding new members, and the "notice" encouraged me to try to participate, but forum subscribers usually don't care about these trifles ...

Greetings, friend !


As you can see, I found the emoticons! Thank you as well !

 

[LTig]

I do not want you to misunderstand me, my English is bad and each contribution I make in the forums takes me a previous step before writing, as I already said, I use GT. , and I have to check the translations because there are always gross errors that I have to correct - if I realize it myself -, or edit when I read the translated page. There are insurmountable twists and turns sometimes.

At least I can certify that your hard work to get a proper english translation leads to perfect understanding - even for me as a non native english speaker.

 

[LTig]

This is my Project S2, you can see the capacitors as they came from the factory.
Resist the urge to straighten them!
By the way, I forgot to mention another "detail" of this phono preamplifier that I see somewhat problematic.
I don't know if the pre-S2 models had the same DIP switches, but these certainly leave a lot to be desired.
They are extremely hard to move - given their tiny size - and it is really scary that they will deteriorate after various adjustments, because they are made of plastic.
So I have decided to use a selector-inverter box between MC and MM, which I had built some time ago to select between two TTs with different cartridges, but both were MM.
Now I must put a load in parallel to compensate the impedance from MM (typical 47 KOhms) to MC (100 Ohms is what Denon recommends for the DL103 cartridge, although I have preferred to use 10 times the value of the cartridge impedance (40 Ohms) to ensure an optimal voltage drop at the input of the Project.
So the idea is to parallel a typical 470 Ohm resistor with the 47 KOhms MM input. It will give 465.34 Ohms of resultant impedance.
I think it will work, comments are welcome and appreciated.

I'm not quite sure what a selector-inverter box is. You could add a box with a switch in front of the preamp to switch between different MM or different MC pickups, and you can use resistors in parallel with the 47 kOhm setting for proper termination, but you cannot switch between an MM and an MC system. For this you need to adjust the gain separately for MM and MC which is not possible with such a switch. You could set the preamp gain for the MC pickup and use attenuators for the MM pickup to reduce gain but then you'll loose a lot of signal to noise when using the MM pickup. Not recommended.

 

[Urubamba]

It is good that you confirm me again, this time from a European. Greetings from a South American.
Thanks

PS1: Any comments on my Project? I was almost certain that someone would say:
If you use it without the case, the sound will degrade and / or pick up hum. Neither of those two things happens, luckily.

PS2: Emoticons have disappeared again, is there a choice between "quick reply" or "full editor"?

 

[Urubamba]

I'm not quite sure what a selector-inverter box is. You could add a box with a switch in front of the preamp to switch between different MM or different MC pickups, and you can use resistors in parallel with the 47 kOhm setting for proper termination, but you cannot switch between an MM and an MC system. For this you need to adjust the gain separately for MM and MC which is not possible with such a switch. You could set the preamp gain for the MC pickup and use attenuators for the MM pickup to reduce gain but then you'll loose a lot of signal to noise when using the MM pickup. Not recommended.

That is the point.
The reversing key, it will go back to 47 Kohm when I select the TT with MM cartridge and when I select the TT with MC, it will add the resistor in parallel and I will go down to +/- 470 Ohms.
It is a common practice, but the question is how it could affect the impedance selector of the PJ which is a chip. I wouldn't want to spoil it, obviously.
Do you think measuring the impedance on RCA connectors could give me an idea?
I will make a diagram to make it more clear.

 

[Urubamba]

As suggested by BDWoody, I opened a thread here :

Project Tube Box S2 and two MM / MC turntables, is it possible?

This thread started here: https://www.audiosciencereview.com/forum/index.php?threads/pro-ject-tube-box-s2-phono-preamp-review.12873/page-6#post-1009879 The Project Tube Box S2 has a chip that acts as an electronic switch to select gain (Db), which can be viewed on the front panel illuminated...

www.audiosciencereview.com

 

[johnjames]

I didn't see this mentioned in the thread, the two parts that people are claiming to be op-amps are DG412DY analog switches, they are most likey switching in extra transistors for the gain control.