Bonsai’s X-Altra MC/MM Phono Preamp

[Joel Wesseling]

I went back and opened U28 and U29 - +84mv at right MC input and -14mv on the left input
At turn on they start at a few hundred mv and settle after a minute or so

 

[Joel Wesseling]

"On both those caps, the + must go to 0V"

Let me please get this one straight.. Do all of C9,10,24 and 25 + go to 0V ??

I'm seeing variations in different photos.. example my attachment is from the filter switch wiring attachment and it look wrong

 

[Zephyrin]

Hello and happy new year.
I have a question about components.

I have just order component that I found in the BOM (June 2023) but the Mom not matching with overlay on PCB!

Where is the right value ? On the PCB ?
i have just started with resistors and there are some missing value in the BOM compared to the PCB !
Perhaps I don0t have the good BOM ?

 

[Bonsai]

The ZTX951 and ZTX851 are in stock in Mouser, so you can get these devices again for the X-Altra MC/MM and I still have a few board sets left.

 

[Crazoff]

Good afternoon. Tell me, please, what is the reason for the installation of capacitors C90, C75, C3, C4 (2,2µF/63V FILM) on the underside (bottom) of the PCB? Is it possible to use ZTX753, ZTX653 transistors in place of Q1-Q4 transistors?

 

[Bonsai]

Cazoff, these are the interstage coupling capacitors that are mounted under the board to save space. You can use the Zetex ZTX753 and 653 but the noise performance won’t be quite as good.

 

[Zephyrin]

Hello
some pictures of my build, I just need to drilled the front panel and also make some tests


I'm missing the MC/MM push button cap. I stupidly ordered the model without a hood. This one is currently not available from early June at mouser

I'm thinking of using it with my teac series 300 set.

I am going to make a dedicated front panel at Schaeffer with screen printing and I will put rectangular blue LEDs as in the photo below.
I'm also thinking of making the top out of aluminium.

 

[Bonsai]

Beautiful build! I hope you like the sound 👍.

Will be nice to see the completed preamp in the housing when you are finished. Thanks for posting

😊

(Nice Teac amp BTW!)

 

[Crazoff]

Hello, Bonsai. Check your private messages. Thank you.

 

[Pendergast]

Hi, this may be a stupid question: in a 2 turntable set up, one mm mono and one MC not requiring any changes in the switch board, would it be reasonable to plug 2 turntables simultaneously in the X-Altra?

 

[Bonsai]

Yes - you can plug 2 turntables into the X-Altra MC/MM. You can then select either one with the push button (BUT turn the volume on your preamp or integrated amp down before doing this as you may get some loud plops from the speakers). Unfortunately, I put the input select PB on the rear panel, mainly because I wanted to avoid drilling the front panel other than the 3.1mm LED holes.