Groner's Low noise measurement amp from Linear Audio vol 3 - spare boards?

SGK

Member
2012-12-17 9:40 am
Miami, USA
I'm thinking of building this measurement amplifier having seen the reference to it in Self's Small Signal Audio Design.

I note that Samuel has kindly made gerber files available on his website but I was wondering if anyone had already ordered some boards and had any spare.

Thanks

Steve
 

SGK

Member
2012-12-17 9:40 am
Miami, USA
Hi Frex - you can download Samuel's full article here Linear Audio | your tech audio resource It's well worth the €3.49. Perhaps you can summarise your design's specs but Samuel's design is certainly compelling. If there are better ones out there I'm all ears.

Hi, Samuel. First, thanks for the article and making your design and PCBs public. I read the article yesterday, having made note to find it while reading Self's SSAD 2nd Ed. I need to read it again today. I don't mind getting some PCBs done, but I thought I would ask the question before I did. Thanks for your response.


Just out of interest, what software did you use to produce the Gerber files? I don't recognise some of the file extensions in the zip folder (e.g. .apr, .DDR) but then I use Cadsoft Eagle and haven't used other software. (BTW shame it slips ever so slightly over the 100mm length which pops it into another price bucket with many board houses. ;) )
 
Yes, recently someone else pointed out that a lenght of 100 mm would have been better. The design is back from the old days where I still used imperial units. My PCB suppliers don't have price steps (just a smooth progression as function of area) and my implementation included 4x9 V cells which required a large case anyway, so I just rounded up to the next nice number.

The Gerbers were done in Protel 95. It could be that there's too much data in it.

Samuel
 
Hi Steve,

I have a couple of boards left, I had them made by pcbways.com (in fancy white), but so far did not come around to build one.... I attached some pictures, the general impression of the boards is good, some minor glitches on the surface finishing around the mounting holes, but nothing on the solder pads themselves.

Since I never built one, of course I cannot garantuee that the boards were fabricated 100% correct. If you bear the shipping costs, you can have one for free, and I have a betatester for the batch of boards as well as some motivation to get mine done, OK?

Best regards,

hallodeletue
 

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SGK

Member
2012-12-17 9:40 am
Miami, USA
Hi Hallodeletue

That would be great! I was wondering what was meant by"an overlay print is not included in the Gerber files" - I now see there's no silkscreen. Not a problem.

I've had good experience with PCBWay recently, although they are currently building my first 4-layer board with them which will be the most significant test so far.

I will PM you my address in London and let me know the cost of postage.

The Gerbers were done in Protel 95.

Hi Samuel

Ok. I was going to ask if you still had the original pre-Gerber file so I could have a nosey as to whether the board length could be shortened easily. But I have no idea whether Protel files can even be imported into Eagle.

I noted your comments in the text regarding batteries: "only true for certain types". Do you have any recommendations in this regard?

Thanks again for taking the time to provide the background/evolutionary material in your text. I'm relatively new to all this and I found it extremely helpful.

Regards

Steve

EDIT: it seems Protel boards can be imported into Eagle once they have been exported from Protel in ACCEL ASCII format.
 
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I noted your comments in the text regarding batteries: "only true for certain types". Do you have any recommendations in this regard?

As far as I recall, my mentioning of battery noise was an argument against them being a "fix it all" for poor PSRR. Again as far as I recall, the literature shows that lead acid cells are among those with lowest noise. But please don't bother--one of the main design goals of my low noise preamp was to get PSRR so high that any reasonable power supply would not interfere with noise performance. So any battery type will do.

Samuel
 

SGK

Member
2012-12-17 9:40 am
Miami, USA
Hi. R117 is specified as 91 Ohms. Mouser stock all the required resistors except 91R. They do, however, stock 90.9R It would seem this is a useful substitute given the function of R117. Am I mistaken?

EDIT: although just as luck would have it Mouser are out of stock on the 90.9R until 25 April...
 
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1000Ω||100Ω=91Ω

True but stacking two cylindrical components onto the same footprint is a finicky thing I'd prefer to avoid if possible. The 91R is there, I understand, to "tune" the gain to 60dB (while "measuring gain to an accuracy of much less than 1% is difficult"). 90.9R is within the 1% component tolerance of the 90R anyway. Maybe I am missing something...
 
TBH not really. Only if one were buying parts for, say, 10 or more boards would there be material savings. I have a Project set up on Mouser UK which I think I can share with you if you send me your email address. You can then "order project" android up counts or delete line items as suits. Buying just the parts needed costs about £35 so you get free delivery (vs paying £12). Of course in some instances it will make sense to round up the part count to, for example, 10 and add the spares to your parts box.