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Old 9th January 2010, 12:33 AM   #21
gootee is offline gootee  United States
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Yes. DO listen very carefully to everything that GK says, suggests, and implies. He has great knowledge and _much_ useful information.

I forgot to mention that I have sometimes had too many problems when trying to use those white plug-in boards that you have used. It got to the point where it was more time-efficient to simply make printed circuit boards, even just for prototyping. And a PCB can give much better results, even if the protoboard is not having its own problems.

You would need some way to be able to print your PCB layout on a laser printer. And you need some PCB blanks (mouser.com or search for FR4 on ebay.com). But with the method at Easy PCB (Printed Circuit Board) Fabrication, Using Laser Printer Toner Transfer, with a Household Clothes Iron and Glossy Inkjet Photo Paper; DIY at Home; Better AND Cheaper than Press-n-Peel ( PnP / P-n-P )! Making, Cheap , Economical , fastest fas , virtually everything else can be purchased almost anywhere that has civilization. I hate having to wait for something to come in the mail, such as etchant, when I want to fabricate a pcb. So I put together the method described, there. It works well-enough for one-offs and small production runs of one- or two-sided boards. You can go from screen image to finished board in less than an hour.

There are lots of threads, on this site, that descuss the best way to route the traces, etc. I actually used MS Paint to do the artwork, at first. But a dedicated PCB-CAD package is a much better idea. There are threads here that discuss which ones are best, and free ones, etc.

Tom
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Old 10th January 2010, 04:03 PM   #22
Bonsai is offline Bonsai  Taiwan
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"One of the first things I learnt when beginning to play with opamps and pots.
Crappy MSpaint pic:
"

I confess to have made the same errors.

Pause for Thought: an op-amp might have a loop gain of >100dB at 50Hz. Its quite easy to pick up 0.5uV over 6" of pcb trace between the feedback resistor junction and the input. Multiply this by 100dB . . . . say goodbye to high fidelity.

Another few:

Using non-unity gain stable op-amps in buffer or low gain circuits. Wonder why it sounds hard 'n harsh? Or 'veiled'? or noisy?

Another classic. Plugging op amps into DIP sockets . . . .without thinking about the comp cap connections (some place the comp cap across pins 5 and 8 . . . and others across 1 and 8 . . ). Of course, this assumes the user understands why a comp cap is needed in the first place.

Decoupling . . . plenty of opportunity to run into problems . . .

Might be a good idea to make a page in the wiki 'Op-Amps for Everyman'
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Old 10th January 2010, 09:55 PM   #23
gootee is offline gootee  United States
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Quote:
Originally Posted by Bonsai View Post
"One of the first things I learnt when beginning to play with opamps and pots.
Crappy MSpaint pic:
"

I confess to have made the same errors.

Pause for Thought: an op-amp might have a loop gain of >100dB at 50Hz. Its quite easy to pick up 0.5uV over 6" of pcb trace between the feedback resistor junction and the input. Multiply this by 100dB . . . . say goodbye to high fidelity.

<snipped>
That also reminded me about why "star"-type grounding is so necessary, sometimes: Suppose you have a ground-return trace that is carrying a 1 Amp sine at 5 kHz (maybe like a speaker's ground return). Suppose that an opamp's or chipamp's input resistor's ground shares that same ground trace (i.e. it's NOT star grounded). If the trace is only four inches long, it might have 100 nH of inductance and 4 mOhms of resistance. Because of V=L(di/dt) and V=IR for the distributed inductance L and resistance R of the trace (or wire) itself (where di/dt is the rate-of-change of the current), the +/- 1 Amp 5 kHz sine current would induce a +/- 5 mV sine voltage, back at the NON-ground end of that trace, and that +/- 5 mV sinusoidally bouncing ground reference would then be arithmetically SUMMED with the opamp's input voltage!!
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Old 2nd February 2010, 08:05 PM   #24
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How is your project going? I am also going to try the burr brown route for a mic pre. You can also look at Jensen transformer site. They have a schematic showing JT-16 transformer in conjunction with SSM2017 which is precursor to INA217.
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Old 2nd February 2010, 09:05 PM   #25
hags is offline hags  United States
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Quote:
Originally Posted by Bonsai View Post

Another classic. Plugging op amps into DIP sockets . . . .without thinking about the comp cap connections (some place the comp cap across pins 5 and 8 . . . and others across 1 and 8 . . ). Of course, this assumes the user understands why a comp cap is needed in the first place.
That is assuming the op amp in question isn't already internally compensated.
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Old 4th February 2010, 07:08 AM   #26
Bonsai is offline Bonsai  Taiwan
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Of course!
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Old 25th September 2010, 07:46 AM   #27
ettos is offline ettos  Italy
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Default Adding an input transformer

Hi all,
I've resumed my INA217 project after almost one year! I'm going to modify some things on the circuit, that is to replace DC blocking caps with an input transformer particularly to add some color to the sound... I thought to use a transformer with 1:3.5 ratio from Cinemag (CMMI-3.5C) implemented in the way you see on the schematic I attached. With R5 and R6 of 15k the input impedance should be of 2k (differential input impedance seen by the microphone).
Next step is to make a PCB following the guide written by gotee.
I really need your critics and comments!

M.
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Old 25th September 2010, 08:17 AM   #28
PMA is offline PMA  Europe
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Quote:
Originally Posted by ettos View Post
I'm getting a lot of noise (a sort of white noise).
DRV 134 has floating balanced output. In case you take only one output signal, for example OUT+ vs. ground, you will get a lot of noise. You have to use true balanced output, i.e. OUT+ vs. OUT-, then the noise level would be approx. 20dB lower.
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Old 9th October 2011, 05:05 AM   #29
gootee is offline gootee  United States
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Ettos,

I would add a 10 uF electrolytic from each chip power pin to ground.

DC servos are "fun". Not sure these suggestions are needed or applicable (haven't simulated your circuit), but:
- You could add diodes to temporarily greatly speed up the integrator's response when there is a very large DC offset. I'm not sure they would be desirable in this circuit, though.
- You might want a good low-pass filter or two right after the differential integrator.
- You might want a resistive voltage divider, just before the servo output signal goes into the inamp's REF input.
- You will probably want a trimmer or pot, somewhere, to be able to adjust the circuit for zero DC offset at the inamp's output.

Tom

Last edited by gootee; 9th October 2011 at 05:15 AM.
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Old 16th October 2011, 05:54 AM   #30
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Quote:
Originally Posted by GK View Post
One of the first things I learnt when beginning to play with opamps and pots.
Crappy MSpaint pic:
Can-you explain the difference at normal line levels ? They are in serial. Currents are the same in both topologies. Or did-you believe in some magic fighting against the physical laws ? Or Op Amps sympathies to his nearest neighbor ? If it is about noise at very low level can-you provide difference in noise measurement in a well shielded housing and real situation?

The best sounding way to manage variable resistances is ... to not use them: tune, measure their values and replace them with a metallic resistance of the same value.
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