Carl_Huff

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« Reply #40 on: May 28, 2006, 11:13:59 PM »
R9 & R10 are 2.7 ohm 1% metal film 1/2 watt resistors.  I am having a problem finding a source for those buggers.  Anybody have a suggestion where I might find them?  I am near Los Angeles, USA

The usual suspects (Newark, Digikey and Mouser) don't carry them.
Best Regards,
Carl Huff


Samuel Groner

    Zürich, Switzerland
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« Reply #41 on: May 29, 2006, 02:15:10 AM »
You might check if you find a 0.6 W. I use Farnell 946-7068.

If you are sure that you'll never short the output, a 0.25 W well be fine as well.

Samuel

AnalogPackrat

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« Reply #42 on: May 29, 2006, 12:09:10 PM »
Carl,

On page 485 of the current Mouser catalog you'll find Vishay BC 5% 1W metal film resistors which are quite small for 1W and come in 2.7ohm.  Buy more than you need and match them by hand--you should be able to find, say, 2 or 3 good pairs in a set of 10.  You'll need a decent meter to read better than ~0.2ohms or precision at the low end, though.

A P
If it is to be, it is up to me.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #43 on: July 30, 2006, 01:16:15 PM »
Latest revision of the documentation: [removed]

Includes the summing amplifier schematic and description as well as a few minor changes in the mic pre.

Samuel

Bo Hansen

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« Reply #44 on: July 31, 2006, 07:17:15 AM »
Samuel,

First time I see your op-amp design/documention, very nice work and description.

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

gyraf

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« Reply #45 on: July 31, 2006, 07:47:08 AM »
That is a really, really nice paper..!!

Thanks, Samuel..!

Jakob E.
..note to self: don't let Harman run your company..

bcarso

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« Reply #46 on: July 31, 2006, 06:19:16 PM »
Quote from: "Samuel Groner"
Latest revision of the documentation: SGA-SOA-1_documentation.pdf

Includes the summing amplifier schematic and description as well as a few minor changes in the mic pre.

Samuel


Nice job.  Looks like the numbers on input bias current are wrong though---I should think you meant 1 uA, not 1 nA.  Those would be some high-beta devices indeed otherwise!

kiira

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« Reply #47 on: July 31, 2006, 07:16:34 PM »
That is really terrific documentation... makes me wish I had bought a few SGA-SAO1 boards!  :razz: It would be great to see the headphone amp schemo sometime... I'd like to build a discrete RIAA/phones/line amp sometime.

Kiira

Dan Kennedy

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« Reply #48 on: July 31, 2006, 08:46:42 PM »
Hey Kiira,

Good to see you are still out there and still building!

Nice work Samuel.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #49 on: August 01, 2006, 12:31:34 AM »
Quote
Looks like the numbers on input bias current are wrong though--I should think you meant 1 uA, not 1 nA.

Oh yes--thanks for pointing that out!

Samuel


Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #50 on: August 06, 2006, 02:19:11 PM »
Finally added the headphone amplifier schematic and description as well as the input bias value correction from -1 nA to -1 uA: [removed]

Samuel

ruairioflaherty

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« Reply #51 on: August 06, 2006, 07:37:51 PM »
Hi Samuel,

I just wanted to thank you for the superb documentation you've written for this project.  It's detailed yet totally readable for an electronics beginner like me.  Speaking of which I just got a copy of the Radio Designer's Handbook 4th ed which is some seriously intense sh*t - it takes all my meagre brain power and a strong cup of coffee to digest a few pages of that mo-fo.

I hope I can build some of your SOA when I'm schooled,

cheers,
Ruairi

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #52 on: August 17, 2006, 01:27:06 PM »
Thanks for your comments--I hope you'll like the amp as much as its documentation!

Fabio asked me if it is possible to fit BC550/BC560/BD139/BD140 instead of the suggested transistors and I thought I'd post my answer here so that all interested can read it:

It is if you accept that:
* voltage noise is higher (didn't calculate how much, but it's more than just half a dB)
* distortion gets a tad higher because beta of Q4 and hence open-loop gain is lower
* it is likely a pain to fit the transistors because Q1-Q5 have a different pinout

In order to maintain correct bias of the input stage I suggest the following two changes:
* R3 = 1k69
* R4 = 720

For Q1, Q2 and Q4 it is important to fit the highest beta rating with the suffix "C".

Samuel

Bauman

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« Reply #53 on: August 17, 2006, 01:39:37 PM »
Thanks Samuel!

Ya know, it was just a WHAT IF in my head... :)
Now waiting for the right transistors to hear this nice opamp :)

Probably I will try the BCs/BDs on one board just for the fun of it :D


many cheers!
Fabio
cheers!
Fabio
_____________________
www.thediypill.com/store

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #54 on: August 18, 2006, 12:40:30 PM »
Quote
I wonder if there will be any issues about that, being symetrical and all.

I suspect that the inherent imbalance from NPN to PNP is much larger than the manufacturer difference--but only a careful measurement would tell us the true story.

Samuel

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #55 on: November 11, 2006, 04:01:04 AM »
I wonder if somebody got his board from Fabios batch running? I just heard from mnats that his boards tend to short to the ground plane, so we'd appreciate your feedback. I did not have this problem on my boards, but I got them from another board house and without silk screen.

Samuel

mnats

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« Reply #56 on: November 23, 2006, 03:04:24 AM »

As Samuel mentioned earlier, I've been having some problems building his design on boards supplied by Fabio. At work, I commonly hand-solder parts with pads spaced three to a millimeter, so I'm fairly confident my soldering skills weren't to blame.

So far, I've built three SGA-SOAs working very meticulously - measuring or testing every component and double checking the location before soldering it in place. Samuel's documentation is very useful and his assembly sequence was extremely helpful. Still, the first one didn't work.

The first module was drawing excessive current. The problem was traced to a short to ground at the base of Q3. No fault was visible even under intense magnification, but measurement showed the pad was definitely shorted to ground. My theory is that the solder is able to make a bridge just under the silk screen layer out of sight just under the white ink. The affected pad had white ink between the pad and the ground plane which formed a neat radius around part of the pad. Here's an image of the pad after I had fixed the short (click for enlargement):


I removed the transistor and used solder wick on the top pad and the short was gone. To ensure that problems didn't recur, I carefully scratched off the ink around the pad.

Number two gave me similar problems, though on a different transistor. When I pulled the transistor and used the same trick with the solder wick, I still had a short. Finally I discovered that while removing the transistor with a heat pen one of the ceramic capacitor pads had gone short as well when the solder reflowed. The same sort of bridge was found with white ink surrounding part of the radius of both pads.

On my third board, I tried deliberately to make a short, but found I was unable to do so. Closer inspection revealed that the ink did not make a complete bridge between the pad and the ground plane. Even so, I removed any ink from between the pads and ground plane before stuffing the whole board. This one worked without any problem first shot.

Hope this helps anyone who is experiencing problems with the batch of boards from Fabio. I believe Samuel is reworking his files to prevent this problem from occurring in the future.

Can anyone else share their experience?
« Last Edit: May 30, 2009, 07:19:20 PM by mnats »

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #57 on: November 23, 2006, 06:40:40 AM »
Thanks for posting--I've been much too busy to do that before.

I marked the pads which seem to be the most imperilled ones here:
SGA-SOA-1_PCB_corrections.pdf

I'm very sorry that this happened. My boardhouse edits the overlay print in case there is an overlapping region, that's why I never noticed that I should change my footprint library. I hope you get the boards running--don't hesitate to contact me with further questions.

Samuel

hitchhiker

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« Reply #58 on: April 11, 2008, 02:06:34 PM »
Hi Samuel,
 
  I bought a pair of SGA-SOA-1 kits fron ptwownkid and built up your mic pre design as drawn in the documentation paper. I like it very much! Thank you!  I only had a 6 pos switch so I used gain setings 3 thru 8 and it covers my needs well. I'll install the pad someday to complete it.  I can't help thinking this would be a nice pcb to offer with the 990 footprint.
Sounds fast, punchy and mid present yet smooth and pleasing. I went with transformerless output and a Lundahl input.
 

Cheers! :guinness:
Lance

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
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« Reply #59 on: April 11, 2008, 03:32:31 PM »
Thanks, Lance, for your feedback; I'm glad you like the result.

Quote
I can't help thinking this would be a nice PCB to offer with the 990 footprint.

In fact I allredy have a slightly more complex implementation (with additional transformer balanced output and some other features) with fully tested PCB ready. I just haven't finishing my homepage on analogue audio electronics (which will host the Gerber files) yet...

Samuel


 

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