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Old 17th October 2010, 12:45 PM   #1
Bonsai is online now Bonsai  Taiwan
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Default X-Altra Mini One

Hello. I have posted up my X-Altra Mini One preamp write up here

HiFiSonix

The .pdf is near the bottom of the page.

Please feel free to tale a look. Any questions, I'll be happy to answer.

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Last edited by Bonsai; 17th October 2010 at 12:48 PM.
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Old 17th October 2010, 01:32 PM   #2
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Some Pictures
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File Type: bmp X-Altra_photos.bmp (180.0 KB, 72 views)
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Old 19th October 2010, 09:17 PM   #3
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Thanks for sharing, Bonsai!
That's as fine and professional a presentation as I have seen for a line-pre project or even retail product. I get the impression, however, that the all-up cost to duplicate your "quick and dirty" build would be well over $300 US. That's no great concern really, since any DIY pre. to this standard, regardless of electronic design, is going to be quite expensive.

I have been using LM4562 preamps in lesser (integrated) kit built implementations for Self type class A and AB amps for a couple of years now and concur with your comments on the relative sound qualities with similar program to that you describe on your site. While they have other good qualities, two discrete design clone preamps I have built recently just don't match them for "Live sound" and spatial definition.

The down side is that unless you have equally highly specd amps and line sources, the benefit goes unnoticed (well, to me at least). When you really get low noise class A going with overall noise and distortion in the order of the preamp, then these little wonders and indeed lots of other high quality gear really begins to shine.

Did I miss your comment on the headphone amp performance?

Thanks again
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Old 20th October 2010, 05:07 AM   #4
Bonsai is online now Bonsai  Taiwan
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Hello Ian.

I have been hugely impressed with the LM4562 and commented in the write up that I doubt this kind of performance (i.e. the op-amp's) could be had with a discrete small signal design for anywhere near the same money (I paid about $4.5 US each from Digi-key). It measures well and sounds wonderful.

I guess I did 'overspend' on the case, knobs etc, but if one is willing to dispense with these and make something at home, or do some drilling and filing on a stock chassis, then you can build it for a much lower figure than you mention. the PCB of course is a big expense if you do not etch it yourself at home.

My plan is at a later date to use the existing chassis and take things up a notch or two in terms of the spec and facilities.

Re the headphone amp, I'll be posting some stuff up in a few weeks after I've uploaded the write up on my power amp.

Thanks for visiting and your comments!
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Old 21st October 2010, 08:59 PM   #5
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Hmmm.....there's a challenge; beat the LM4562 with discrete BJTs (no NOS or unobtanium). Naturally, submissions would have to sport comparable features to commercial products to get a cigar.

Any takers?......Oh, sorry - O/T!

'looking forward to seeking the further developments anyway, thanks
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Old 22nd October 2010, 03:32 PM   #6
Bonsai is online now Bonsai  Taiwan
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I have uploaded the Gerber files onto the website - these include the top, bottom, silkscreen and drill files.

Does anyone know how to convert Gerbers into PDF's? If you are going to etch these PCB's yourself, PDF's that can be printed out are probably a lot more useful.
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Old 24th October 2010, 11:50 AM   #7
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Gerbv can export PDFs? never tried it though.

I don't know if it only happened in the PDF transfer but the schematic is a touch confusing as there appears to be no distinguishing between connections and jumps.

The article's been quite nicely authored though, thanks for sharing
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Old 24th October 2010, 01:01 PM   #8
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Bonsai,

Very interesting article, well written and presented, and I love the attention you've paid to the build.

A couple of things that you might be interested in. I built a kit headphone amplifier, that after modification, is similar to the stage in yours. Replacing the original op-amp used with the kit to a LM4562 did improve the SQ considerably, but by improving the quality of the supply to the amp (originally a 317/337 based supply) the SQ took a huge jump forward. It really shows that LM4562 needs a clean, low impedance powers supply for best results. A current GB has the the board we used to improve the supply (look for the John Linsley Hood ripple eater GB)

A considerable amount of people built this amp, and used the JLH ripple eaters, and all found it brought an improvement in SQ.

The other point is that some of us (the people who used this amp) replaced the standard LM4562 with the to-99 variant. Again, many found a further improvement in SQ. The LME49720HA is the same as the to-99 cased LM4562.
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Old 24th October 2010, 10:32 PM   #9
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Thanks for the feedback Woodenhead. I heard the TO-99 version is better and hope to try it sometime in the near future. On the power supplies, I ended up as you will note using heavy filtering at the op-amp supplies - theres a lot of attentuation of HF garbage as a result. Yes, ripple eater is a good way to go - something for next time I guess.
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