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

[Urubamba]

This thread started here:

Pro-Ject Tube Box S2 Phono Preamp Review

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"...

www.audiosciencereview.com

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 with blue LEDs.
The selection of impedances and capacitances of the cartridges is selected from the base with mechanical switches (Dip's).
If we want to use two cartridges of different configuration, such as an MM and an MC, we must lift the PJ, and select the corresponding settings, but the switches look very delicate and honestly, I do not think they can support continuous use. So, I thought about using two turntables. (The same would be if I only had one with two headshell´s, only this way I avoid having to balanced the tone arm, adjust AS, etc.)
A box with the corresponding connections and a selector key would make the change between the two TTs.
To adjust the impedance of the MC cartridge, a resistor in parallel could be added to the 47 KOhms - by default - of the MM circuit to lower said value to that required for an MC cartridge.
Do you see it possible? Do you see that there could be a risk of damaging the ProJect ? If so, what would it be ?


Photos and diagram in the next post, thank you !

 

[Urubamba]

The diagram I thought of, yeah, it's not rocket science, and I have some electronics studies, but you know what?
That is not much use if you do not have the PJ circuit to analyze how the internal wiring is, and unfortunately, currently all manufacturers no longer provide them .....

 

[Urubamba]

Pics

 

[LTig]

Should work. For MM you set the switch of your selector to MM and the gain of the preamp to 40 dB. For MC set the switch to MC and the gain to 60 dB.

Use low capacitance cables as short as possible between selector and preamp, and reduce the capacitive load accordingly with the DIP switch of the preamp.

 

[SIY]

I don't know about your cartridge, but the DL103R works perfectly well into 47k loads with typical capacitances. That's true of nearly all low DCR low inductance cartridges.

So don't make your design more difficult for the same of something carrying questionable benefit.

 

[Urubamba]

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The box is available for testing, I built it a few years ago when using my two turntables with different cartridges, although they were all MM.
I used low capacitance teflon insulation wires.
I will try adding to it the resistance of 470 Ohms, I have read that there are people who claim to use DL-103 with 47 KOhms of load, I will also test that, although it seems to me that so much difference with the manufacturer's recommendation (100 Ohms) will affect in a way significant the SQ. (sound quality)
Before proceeding, I will write to Pro
Ject, I'm interested to know what you think about it, although they will most likely suggest I buy the top model DS2 that comes with two TT inputs and all selectable settings on the front panel. That's easy ...


[URL despliegue = "true"] https://www.project-audio.com/en/product/tube-box-ds2/ [/ URL]

 

[Urubamba]

For LTig and Siy !!!

 

[SIY]

​

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The box is available for testing, I built it a few years ago when using my two turntables with different cartridges, although they were all MM.
I used low capacitance teflon insulation wires.
I will try adding to it the resistance of 470 Ohms, I have read that there are people who claim to use DL-103 with 47 KOhms of load, I will also test that, although it seems to me that so much difference with the manufacturer's recommendation (100 Ohms) will affect in a way significant the SQ. (sound quality)
Before proceeding, I will write to Pro
Ject, I'm interested to know what you think about it, although they will most likely suggest I buy the top model DS2 that comes with two TT inputs and all selectable settings on the front panel. That's easy ...


[URL despliegue = "true"] https://www.project-audio.com/en/product/tube-box-ds2/ [/ URL]

A couple things: Teflon/silver is a particularly poor choice for MM because of triboelectricity. And any Teflon-insulated wire will at least be silver plated.

The 103R has a source impedance of 14 ohms, almost purely resistive. The only difference between loading with 100R and 47k will be a little bit of level, with the 47k being higher (a good thing for signal-to-noise).

 

[Urubamba]

Point 1:
Well I guess there won't be much friction or chafing inside these conductors. When I built and used this box, they were considered the best cables for phono. Back then, my ears were young and I think now any loss from that effect will be absolutely irrelevant.
Point 2:
My cartridge is the DL 103, and it has an impedance of 40 Ohms, but I guess it doesn't change things, I'll test MC at 47 KOhms.
Thanks for the info !

​

 

[Urubamba]

The only difference between loading with 100R and 47k will be a little bit of level, with the 47k being higher (a good thing for signal-to-noise).

Hi Siy :
I listened to the DL 103 with a load of 47 KOhms.
Sorry, it's a no, no, no.
Some time ago I had read this article and it took a while to find it, but I think the reason is in the paragraph that says:

" It is certainly not correct for MC cartridges most MC cartridges perform best with a load of between 20 Ohm and a few hundred Ohm). "

Discussion on MC Cartridge Loading

For my ears, the bass and mid-bass lost force and clarity, and the treble seemed to have increased, but I think it is a consequence of the decrease in the frequencies mentioned above ... I also noticed differences in the tonality of the instruments, it is as if there were missing harmonics that I did notice with the 470 Ohms load in the Project Tube Box S2.

 

[SIY]

Hi Siy :
I listened to the DL 103 with a load of 47 KOhms.
Sorry, it's a no, no, no.
Some time ago I had read this article and it took a while to find it, but I think the reason is in the paragraph that says:

" It is certainly not correct for MC cartridges most MC cartridges perform best with a load of between 20 Ohm and a few hundred Ohm). "

Discussion on MC Cartridge Loading

For my ears, the bass and mid-bass lost force and clarity, and the treble seemed to have increased, but I think it is a consequence of the decrease in the frequencies mentioned above ... I also noticed differences in the tonality of the instruments, it is as if there were missing harmonics that I did notice with the 470 Ohms load in the Project Tube Box S2.

That's a novel claim, but likely a result of sighted evaluation. The low source impedance and negligible inductance of an MC mean there's little dependence of response on loading. The site you linked gave zero detail on how those graphs were derived- they look to me far more like the effect of changing load on the cartridge by changing secondary load on a step-up transformer, a totally different kettle of fish.

 

[Urubamba]

That's a novel claim, but likely a result of sighted evaluation. The low source impedance and negligible inductance of an MC mean there's little dependence of response on loading. The site you linked gave zero detail on how those graphs were derived- they look to me far more like the effect of changing load on the cartridge by changing secondary load on a step-up transformer, a totally different kettle of fish.

My statement is not new or biased, I have read hundreds of articles on the web on this subject, and although there are isolated cases of users who declare to use 47 KOhms, they are the exception, not the rule.
The majority opinions of users of DL-103 oscillate between using the load of the generic specs of 100 Ohms, or 10 +/- the value of the impedance of the cartridge, and also many claim 1000 Ohms.
My cartridge was tested with 1000 Ohms, and you can see the FR that goes down 3 Db around 15 Khz.
It looks like the famous BBC curve! I would have liked more extended there, but this cartridge is like that, somewhat "limited" in the high spectrum, but my ears don't pick up much beyond that anymore, so I'm satisfied and happy.
I am attaching a link (in French) from which I extracted and attached graphics of different cartridges:
The DL103 has the same dropout as my cartridge (the # 2825), but the 103 R with a load of 47000 Ohms, extends the treble FR up to 18 Khz.
I interpret that the author of the phrase quoted by me applies to the load used in all MC cartridges, which includes step-up transformers or preamps, but it does not matter. I may be wrong, you know, my English is limited.
Ultimately, a cartridge is a tiny electromechanical transducer, and in the case of MCs, the voltage generated (which varies with modulated frequencies in vinyl) is so low that it needs to be used to its full potential. And there the "mother of all battles" intervenes, Ohmn's Law. So, I understand what you are saying, there is an impedance matching, and if I remember correctly, a higher voltage will drop on the 47 KOms resistor than on 100 Ohms, but I think the topic does not end there.
Inductance is small, but we can't rule it out, based on how it interacts with resistors and different frequencies. that's why it's impedance, right? And then, it enters the debate of which load is better, that not all of us listen the same. We have to consider the physiological structure of our ears - no two are alike - the listening room, the speakers, among the factors to be evaluated. .
Well, I hope you agree and if not, as you say in the promotional notice, let's take this with humor, (that's why the balloon, I hope you have understood) and I propose to conclude this section Denon DL 103 / R and continue with the motif of the thread. I will write to Pro - Ject - since I continue with my original idea of using the selector box -, I have confirmed that the analog switch is the DG412DY, but what I do not know is if it works only with the capacitance settings or if there are any type of interaction with the mechanical Dip's that adjust the impedances. Without circuits and without practical experience in technical services of audio equipment for many years due to the continuous updating of electronic components that I do not know, for me, this does become rocket science!
I saw a red LED constantly lighting up on the bare PCB of the ProJect and I thought: What does it do if it can't be seen? And reading and reading, I found out that they are used like conventional diodes, but that they have some advantage over them. I don't remember what it was ...
Maybe you or someone from the forum can inform me.

Denon DL 103 - Page 13 - Vintage Audio Heritage

DG412DY Datasheet(PDF)

Part #: DG412DY. Download. File Size: 342Kbytes. Page: 12 Pages. Description: Improved, Quad, SPST Analog Switches. Manufacturer: Maxim Integrated Products.

www.alldatasheet.com

 

[SIY]

My statement is not new or biased, I have read hundreds of articles on the web on this subject, and although there are isolated cases of users who declare to use 47 KOhms, they are the exception, not the rule.
The majority opinions of users of DL-103 oscillate between using the load of the generic specs of 100 Ohms, or 10 +/- the value of the impedance of the cartridge, and also many claim 1000 Ohms.
My cartridge was tested with 1000 Ohms, and you can see the FR that goes down 3 Db around 15 Khz.
It looks like the famous BBC curve! I would have liked more extended there, but this cartridge is like that, somewhat "limited" in the high spectrum, but my ears don't pick up much beyond that anymore, so I'm satisfied and happy.
I am attaching a link (in French) from which I extracted and attached graphics of different cartridges:
The DL103 has the same dropout as my cartridge (the # 2825), but the 103 R with a load of 47000 Ohms, extends the treble FR up to 18 Khz.
I interpret that the author of the phrase quoted by me applies to the load used in all MC cartridges, which includes step-up transformers or preamps, but it does not matter. I may be wrong, you know, my English is limited.
Ultimately, a cartridge is a tiny electromechanical transducer, and in the case of MCs, the voltage generated (which varies with modulated frequencies in vinyl) is so low that it needs to be used to its full potential. And there the "mother of all battles" intervenes, Ohmn's Law. So, I understand what you are saying, there is an impedance matching, and if I remember correctly, a higher voltage will drop on the 47 KOms resistor than on 100 Ohms, but I think the topic does not end there.
Inductance is small, but we can't rule it out, based on how it interacts with resistors and different frequencies. that's why it's impedance, right? And then, it enters the debate of which load is better, that not all of us listen the same. We have to consider the physiological structure of our ears - no two are alike - the listening room, the speakers, among the factors to be evaluated. .
Well, I hope you agree and if not, as you say in the promotional notice, let's take this with humor, (that's why the balloon, I hope you have understood) and I propose to conclude this section Denon DL 103 / R and continue with the motif of the thread. I will write to Pro - Ject - since I continue with my original idea of using the selector box -, I have confirmed that the analog switch is the DG412DY, but what I do not know is if it works only with the capacitance settings or if there are any type of interaction with the mechanical Dip's that adjust the impedances. Without circuits and without practical experience in technical services of audio equipment for many years due to the continuous updating of electronic components that I do not know, for me, this does become rocket science!
I saw a red LED constantly lighting up on the bare PCB of the ProJect and I thought: What does it do if it can't be seen? And reading and reading, I found out that they are used like conventional diodes, but that they have some advantage over them. I don't remember what it was ...
Maybe you or someone from the forum can inform me.

Denon DL 103 - Page 13 - Vintage Audio Heritage

DG412DY Datasheet(PDF)

Part #: DG412DY. Download. File Size: 342Kbytes. Page: 12 Pages. Description: Improved, Quad, SPST Analog Switches. Manufacturer: Maxim Integrated Products.

www.alldatasheet.com

There is certainly a lot of mystique and bullshit surrounding MC cartridges. The upper midrange dip is very common- Gordon Holt used to complain about it and mostly stuck to MMs for years (he and I used the same Technics MMs).

However, all the tweak magazine articles in the world can't change the basic electrical laws. A low output MC is a nearly pure resistive source. Period. Reducing load resistance changes the level. It does not change the damping or anything else like that.

 

[Urubamba]

I found this article, I did several listens and definitely load in 47 KOhms an MC cartridge is not only bad in graphics and calculations, it is also audible. And it sounds bad.
Just so any unsuspecting reader doesn't jump to the wrong conclusions.

Hagerman Technology LLC: Cartridge Loading