Bonsai’s X-Altra MC/MM Phono Preamp

[Bonsai]

Very good. Looks like you are good to go

🙂👍

 

[Chrisr3521]

Chris,

Important note: if the preamp is picking up noise, the readings will be all over the place. For your measurements, leave the MC input OPEN and SHORT the MM inputs right at the input connector. This will ensure the preamp willbe quiet enough for good DC readings.

For shorting plugs what you you recommend? Shorting with just wire or a 470 ohm resistor between signal I put and ground in the plug

 

[Mark Tillotson]

There's no ambiguity about the word "SHORT". You want to prevent the internal load resistor from putting its Johnson noise on the signal, 0 ohms is good for that! Keep the wire short as possible so it won't pick up much RF too...

 

[Bonsai]

For MM, short the inputs, but for MC leave them open or, connect a 47 Ohm resistor across the inputs under the connector. If you dont want to use a short wire, you can use shorting plugs like this from Amazon

https://www.amazon.co.uk/Tertullus-...ords=RCA+shorting+plugs&qid=1688571113&sr=8-3

Reason is on MC, because its a current input common base circuit, if you short them the gain will be very high (gain is dependent upon cart resistance).

 

[Bonsai]

Mouser has stock of the ZTX 851 here: Mouser Pt# 522-ZTX851STZ and the ZTX951 here: Mouser Pt# 522-ZTX951

If you've been stalled on your preamp builds, suggest you hurry up and order the devices above (you will need 2 off each to build an X-Altra MC/MM) - they only have c. 300 of the one type.

 

[al2002]

Mouser shows a ztx851 and also an ztx851stz. The data sheet is the same for both. Anyone know the difference?

 

[geoffw1]

They appear to be exactly the same parts and case type/spec. One in in "ammo pack" and the other is "bulk" There's a slight price difference and they currently have 3,100 of one and 323 of the other.

 

[geoffw1]

C

they currently have 3,100 of one and 323 of the other.

Correction- they currently have 3100 on order for one and 323 in stock of the other. Get ordering!

 

[al2002]

Thanks for the responses.

 

[Bonsai]

Just checked again today and they are now showing 323 of the 851 and 7800 of the 951. I ordered 25 of each yesterday.

They also do SOT23 SMD versions, but I am checking to see if these can be directly mounted on the board (underside). I suspect these will generally be easier to get in the future. I’ll come back with an update in the next few days.

If you are after really good MC noise performance there isn’t much out there other than the 851 and 951 devices.

 

[al2002]

Looks like the quantity in stock is not being updated. They still show 323.

 

[Pendergast]

I purchased those missing parts a few weeks ago and was able to match them at 100%. Now I need a good MC cart!

 

[Bonsai]

For those who placed orders over the last two weeks and have had top wait, PCB sets are back in stock again - pending orders will be shipped out tomorrow. Thank you for your support

 

[Nick Sukhov]

Quick update re the LSK389B devices. Some builders have struggled to secure these as they have not been generally avaiablle at the major distributors.

TI recently introduced the JFE2140 dual JFET which has been positioned as an alternative to the LSK389/489 devices.

Yes, I see JFE2140 has slightly less noise than LSK389 and is much cheaper - https://www.patreon.com/posts/84327298

 

[Mnk21]

Hello there,
I received my board (V1.0 July 2020 green pcb) a few weeks ago and started soldering resistors and capacitors.
I noticed some discrepancies between the BOM and the silkscreen on the board.
Can any of you confirm that the following values which are from the silkscreen are right ?
If so I‘ll need to order these parts since they are not in the latest BOM.

R61-26-25-10-9 1k ohm
R7-28 120 ohm
R81-85 110k ohm
R79-84 150 k ohm.

C79-86 220 pf
Thank you guys !

 

[Bonsai]

Hi did you download the latest BOM from the audioXpress website? It was updated about 3 months ago based on builders feedback.

(I’ll come back to you later today - I’m out at the minute)

 

[Bonsai]

I've just been on Mouser, and they have large stocks of the LSK389B in SMD8A and TO-71.

You can also use TI JFE2140 Mouser Pt# 595-JFE2140DR

Mouser has Stock of the ZTX951 (few thousand) and RS has some small stock of ZTX851

 

[hbtaudio]

Hello Bonsai,
I've just had a look at your PreAmp - amazing, a fantastic design.

Congratulations and thank you for sharing the articles on your website.


Regards,
HBt.

 

[Bonsai]

Thank you HBt! Appreciate it 👍

 

[Zephyrin]

Hello, i will build the Preamp too.

The component MUR820G is not available on mouser , is it possible to replace it by an other rectifier ?

It seems that it is not possible in Switzerland to place an order with RS as private, it is reserved for businesses. How did you do for order components from them?
He asks me for proof that I am a professional!