X-Altra Line Level Preamp

[Bensen]

What material is the back plate made of? Where have you ordered this, looks really nice manufactured. I see you are using female output signal XLR’s, on commercial stuff I always see male output XLR’s. Using female looks more logical to me as wel.

 

[Bonsai]

Will you be supplying a detailed schematic?

Yes, and a BOM, PCB’s and I’m going to ask Gianluca as Modushop to provide a housing kit with milled/printed f/plate so builders can order if they want. But, I still have a few weeks of work and measurements ahead.

😊

 

[Bonsai]

Bensen, the rear panel is made of two 1.6 mm PCB’s stacked together.

 

[Bonsai]

Progress! Making music tonight. The phono board still has to be assembled and tested, but I'll clear the bench tomorrow and set everything up for measurements.

 

[bambadoo]

Wine is well deserved

 

[Carl_Huff]

Kudos Bonsai! I am always amazed how well done smc takes up so little space.

 

[Bonsai]

👍This would be a big box if it was all through hole

 

[poseidonsvoice]

Impressive. I look forward to your final writeup! I always learn quite a few details...the kx2 is particularly excellent. Looking forward to the balanced version of this line stage.

Best,
Anand.

 

[Bonsai]

Thanks Anand. Write up and BOMs etc will take a few weeks yet.

 

[Bonsai]

The beast is boxed up and ready for measurements of everything other than the phono stage. If this goes well the wiring will be secured, knobs washed and polished and then the phono board mounted. I still have to fit the XLR release catches as well.

 

[mlloyd1]

Lookin' good, Andrew!

 

[Bonsai]

Thank you 👍

 

[Bonsai]

Here are some more measurements of the completed, boxed up preamp.

 

[Bonsai]

Some updates and the module circuit diagrams posted here https://hifisonix.com/x-altra-mini-ii-line-preamplifier/

 

[Carl_Huff]

Andrew,

I have been studying your document that you point to. I see your Mini II to be an excellent state of the art design. Kudos to you!

 

[Bonsai]

Thanks Carl. I’m assembling the phono amp at the minute - hopefully I’ll get it tested and installed this weekend to complete the whole thing.

 

[Carl_Huff]

Andrew,

I have a curiosity question. I have studying your LSK386 line amp as described in your downloadable paper that you pointed to in #34.

My question is did you consider using the LSK486 rather than the LSK386? The LSK486 is promoted as an enhancement over their LSK386 part.

 

[Bonsai]

Hello Carl,

the LSK489 offers dramatically lower input capacitance. But the noise IIRC is not any better. I have a stash of 389’s so that’s why I’ve been using them. And have been very impressed with the noise performance. I guess given the bandwidths (ie audio) we are dealing with, the 389 is still a great fit. For more demanding applications, you of course should go for the 489. I have not tried the 489, so cannot comment on whether there would be any issues in the X-Altra discrete line stage as it stands.

(I’ve been otherwise occupied the last week or so, so progress has been a bit slow - hopefully next week I can get back to it. I’ll be ordering a new front panel with printed lettering etc from Modushop as well to finish the whole thing off)

 

[Carl_Huff]

Andrew,

Thank you for the detailed answer

 

[rsavas]

Hello folks

I have been using lsk489 and lsj689 in the Bob Cordell dh-220c design for the input stage.
The lsk389 with its larger die has less noise at the expense of higher capacitance.
The lsk389 is suited for lower impedance sources whereas the 489 is better suited for higher impedance sources such as MM phono