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Old 25th January 2013, 05:46 PM   #2631
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Quote:
Originally Posted by myhrrhleine View Post
I thought one of the objectives was access inside?
Otherwise we could use an off the shelf op amp.
With the tight spacing of the parts as described, how will DIYer be able to access internal points to experiment?
Yes, already showed simply 50k to ground on the gain node and you get ~60db OLG out to over 20kHz vs ~120dB OLG at a few 10's of Hz. This being one common hobby horse around some parts.
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Old 26th January 2013, 02:36 AM   #2632
qusp is offline qusp  Australia
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Originally Posted by bcarso View Post
There are a few circuit positions where thick film noise probably wouldn't be noticed, close to the output for example, but only a few. That noise source bit me badly on a front end of a subwoofer amp once and I did a fair amount of study resolving the issue, and "published" the results on the old prodigy-pro forum some years back. As I recall Panasonic parts were better than some. Susumu seems to be the go-to brand for thin film in readily-accessible distribution.

Although you need current in this case to produce the excess over thermal noise, it's also important to realize that can be signal current, not just "standing" bias current. So your results for dynamic range based on peak signal versus zero signal noise can get quite overly optimistic with excess noise a function of signal.
hey thats a nice little reminder, cheers! and yes susumu RG are excellent parts that we could push the price down on pretty dramatically with a GB

the parts spacing isnt THAT tight, plus a few via test points can make things pretty accessible
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Old 26th January 2013, 11:59 AM   #2633
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Quote:
Originally Posted by dchisholm View Post
The attached files describe one possible implementation of the SW-OPA topology.
...
- The PWB's electrical interface uses seven swaged-in-place contact pins. With attention to details and a little practice, a home constructor can successfully install these pins. Videos and written documents showing the process are available on the net.
...
- The physical size is 1.325" by 1.325". This is larger than the "standard" module size (1.125" by 1.125") of the API 2520 et al mentioned above.
Bravo! I haven't looked at the layout yet, but this is a great start.

Comments:

1) Perhaps if dual-transistor BJTs in SOT23-6, SOT363 or SMD6 were used, the outline could be shrunk to the API-2520 form-factor.

2) Similarly, dual-sided SMD layout with the gain stages on one side, and the diamond buffer on the other side, could also help shrink the layout.

3) Apart from the Mill-max gold-plate swage pins suggested elsewhere, Vector K31C/M tin-plated pins of 0.042" diameter, may be a lower-cost and/or more easily available alternative.
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Old 26th January 2013, 07:58 PM   #2634
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Originally Posted by bcarso View Post
... resolving the issue, and "published" the results on the old prodigy-pro forum .... As I recall Panasonic parts were better than some. Susumu seems to be the go-to brand for thin film in readily-accessible distribution.

Although you need current in this case to produce the excess over thermal noise, it's also important to realize that can be signal current, not just "standing" bias current. So your results for dynamic range based on peak signal versus zero signal noise can get quite overly optimistic with excess noise a function of signal.
Brad, this would be Noise Modulation and hence more evil than benign Gaussian random noise of fixed level. One could consider Quantization Noise/Distortion a form of Noise Modulation and even small levels were detectable in my 1990's Double Blind Tests even on pop.

Got a link or even a title to the thread on prodigy-pro?

BTW, prodigy-pro.com is now groupdiy.com
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Old 26th January 2013, 08:05 PM   #2635
dimitri is offline dimitri  United States
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GroupDIY » General Discussions » Drawing Board » High 1/f noise in SM resistors

Last edited by dimitri; 26th January 2013 at 08:11 PM.
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Old 26th January 2013, 09:32 PM   #2636
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Default Proposed Implementation: Comments Requested

Quote:
Originally Posted by dchisholm View Post
The attached files describe one possible implementation of the SW-OPA topology. ... I would appreciate helpful comments on the design, PWB layout, and documentation.
Thanks for this Dale. I hope Guru Wurcer will chip in but here are some of my thoughts ..

Quote:
- The input stage includes a balance adjustment potentiometer (R27). In a traditional opamp architecture this would probably be labeled as "offset adjustment".
Your R27 source resistor will be VERY twitchy. Scott recommended tweaking R9 instead and sims confirm this is less critical.

Quote:
- Both the primary and secondary compensation networks are implemented as pole-zero (i.e., series R-C) networks as shown in Post #1568.
Q15-17, 20 are just CCS so there is no need for R13 C3

Quote:
- The primary compensation node is brought out to an external connection. This may or may not be a desirable feature.
DESIRABLE. You may want C1 off board so you can tweak performance and select where it's earthed. Gets rid of an evil earth pin.

Quote:
- There is provision to connect the secondary compensation networks to either side of the input differential pair. See my comments at Post #2405 et seq.
Scott actually uses that to add a zero to OL. But this is a tricky tweak. Your method is more conventional and safer.

Quote:
- There is provision for on-board power supply decoupling (FB1/C4, and FB2/C5).
This is truly EVIL. For something with supersonic response like this, you MUST use VERY careful earthing. It's probably the biggest fault in the original 990.

See AD797 datasheet for some of what needs doing. You have to differentiate very carefully between clean (feedback/compensation) and dirty (decoupling/other crud) earths.

That means get rid of FB1/2 C4/5.

Quote:
- Most of the PWB bottom side is devoted to a ground plane.
I don't like ground planes for LN audio. But at least make sure there is none under the +ve & -ve i/p tracks to minimize evil capacitance to earth.
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Old 27th January 2013, 12:07 AM   #2637
tvi is offline tvi  Australia
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From
Resistor Current Noise Measurements pdf
Attached Images
File Type: png res noise.png (217.1 KB, 325 views)
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Old 27th January 2013, 04:34 PM   #2638
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by tvi View Post
Good stuff. Source please?
And can you check off the top 7 worse makes/models?

-RNMarsh
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Old 27th January 2013, 04:46 PM   #2639
bcarso is offline bcarso  United States
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Originally Posted by RNMarsh View Post
Good stuff. Source please?
And can you check off the top 7 worse makes/models?

-RNMarsh
check out LSC - LIGO Scientific Collaboration
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Old 27th January 2013, 04:53 PM   #2640
RNMarsh is offline RNMarsh  United States
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Originally Posted by RNMarsh View Post
Good stuff. Source please?
And can you check off the top 7 worse makes/models?

-RNMarsh
never mind. its from www.dcc.ligo.org/public/0002/T0900200/001/current_noise.pdf

-RNM
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