R2-D2 mk2, DAC/MC transformer test results

[Dorin Bodea]

In the year 2015 I have built R2-D2 , an universal MC step up xfmr, but still focused on Denon DL103 cartridge. This transformer had 1:1:22:22 ratios and a max input at 50-100mVrms.

Recently I've decided to unify MC and DAC requirements under the same umbrella, so R2-D2 mk2 came along, with 1:1:10:10 ratios, but with 250-500mVrms input capabilities (above this level will result in increasing THD at lower bass, as in 20Hz-100Hz, nothing more ).

The measurements attached are at 1:20 wiring, 50Ω generator in series with 10Ω resistor, sweeps 10Hz-500kHz at 200mV, 775mV and 1V onto a 47kΩ load, no capacitor compensation involved (aside from unavoidable 30pF of the instrument), as in a Zobel network!
Let me know your thoughts, thanks!

 

[Dorin Bodea]

classic 10Hz-100kHz view at 200mV input, 1:20, just we can understand each other

 

[Lampie519]

It all depends what you are trying to achieve. A natural sound or to get rid of digital harshness. If you have the last the i would suggest to rebuild your converter,

 

[Dorin Bodea]

It all depends what you are trying to achieve. A natural sound or to get rid of digital harshness. If you have the last the i would suggest to rebuild your converter,

I can hardly meet digital harshness in a RIAA preamp but I guess you're right on the second possible app

 

[Lampie519]

Try less step-up like 1:4

 

[Dorin Bodea]

Try less step-up like 1:4

No thanks, that will be too easy...
The whole rationale is to have as much as possible passive voltage amplification, as it will have at least an order of magnitude less THD and/or noise than active amplification, by the means of any known electronic device, like triode, transistor, you name it...

 

[Lampie519]

I am not sure if that is true as transformers need to be shielded very well not to introduce noise.

 

[Dorin Bodea]

I am not sure if that is true as transformers need to be shielded very well not to introduce noise.

Oh, you're not sure, well...

 

[Lampie519]

There are good amps that can do the job with less distortion for sure but again it is what you favor.

 

[Dorin Bodea]

There are good amps that can do the job with less distortion for sure but again it is what you favor.

You have 10 tubes and probably 20 triodes in the preamp above and you're telling me not to worry, it's just a matter of taste?

 

[Lampie519]

Only 2 stages and coupling caps. The rest is power supply and keeping the stage that matters under control. That is how to make an amp with ultra low distortion,
It is inspired by Allen Wright
http://www.vacuumstate.com/

 

[Dorin Bodea]

Only 2 stages and coupling caps. The rest is power supply and keeping the stage that matters under control. That is how to make an amp with ultra low distortion,
It is inspired by Allen Wright

Thank you for your explanation but please be sure we're not comparing apples with oranges here, thanks!

 

[Lampie519]

Do you know his amps ?

 

[Dorin Bodea]

Do you know his amps ?

Of course I know designs that matter in this area but right now I'm more concerned about my projects... if you catch my drift

 

[Dorin Bodea]

Here's a rough depict of the THD behavior, yellow input 344mVrms and blue output 6.43Vrms

 

[Dorin Bodea]

THD N and THD vs frequency measured with a Scarlett 2i2, 100k load, about 0dBu output level

 

[Disco Volante]

Looks like good stuff. I have a Denon DL103R and a Ortofon MCA76 step-up on the "daily runner" home stereo. I'd like to try a set of transformers one day;-) Mainly out of curiosity, though: I've tested a number of (active) step-ups. The Luxman CX1 and the MCA76 sound the best to me (have the least noise).

 

[Dorin Bodea]

Looks like good stuff. I have a Denon DL103R and a Ortofon MCA76 step-up on the "daily runner" home stereo. I'd like to try a set of transformers one day;-) Mainly out of curiosity, though: I've tested a number of (active) step-ups. The Luxman CX1 and the MCA76 sound the best to me (have the least noise).

It is very good stuff, I have designed it to better what's on top in the market today. The whole idea is that amplifying signals under 1mV by the means of active devices isn't quite easy and/or fully transparent, noiseless... The advantage with this (passive solution) transformer resides in its universality, can be put between the MC cartridge and almost any MM RIAA preamp, which are quite spread compared with MC preamps.

Here's a possible fit out, as I used it in 2015 for the original R2-D2 xfmr

 

[volker]

Is this just a show and tell or are you going to share some more details about the winding of your transformers?

 

[Dorin Bodea]

Is this just a show and tell or are you going to share some more details about the winding of your transformers?

Sure, it's made using 0.1 and 0.08mm enamel wire spread on 14 sections summing about 5k turns, all around a permalloy 80 core of about 0.82sqcm. I hope this helps and I'm also glad that someone finds my xfmr interesting enough to copy it.