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Topic: Confused by different results on breadboard vs pcb testing (audio/filter values) (Read 6301 times) previous topic - next topic

Wawa

With the probe on R4, you get the frequency response at the end of your filter.
The final result that goes into the power IC.
On the graph, you can see the attenuation on the left, plotted against the frequencies at the bottom.
You can fullscreen the black window to see it better.
You see that your filter attenuates everything ~20db. That's ok, because the LM386 amplifies it again (+26db).
100hz area is bass, 1khz area is midrange, 10khz area is highs.
You can see that the response, with 10n, sags above 3khz.
A 6db drop is clearly audible.
Leo.. 

xl97

some things are still confusing..

1.) I see the 'probe' icon when I hover certain places (kind of hard to get it.. usually its an 'x'..)..

sometimes is some other type of image..  some kind of 'tooth' or 'monkey' looking things with a circle under it with red arrow through it?

2.) when I use/click the probe on R4  (it this supposed to be above it? or on the actual resistor symbol?)
I sometimes get several lines.. other times I get a single (red) line displayed?  Am I supposed to be lookig for/seeing all lines? (ie: the C1 line should be there as well?)


3.) What are all the V(n00X stuff?)  as in V(n002)  V(n004)...etc?


4.) I am trying to post a screenshot.. but when I paste it into photoshop not all the lines displayed are showing up..  only the V(n002) shows up on any screencap?


5.) When I click on the C1 (my C18 equivalent)..  I see MANY lines above..  shows my I(C1) in pink..  but then has 2 pink lines?  one solid..one dotted/dashed?  which do I look at?  and does it matter if my probe is NOT on R4?

If on R4.. the I(C1) doesnt display?

I right clicked on C1, and changed it to 100n.. then re-ran simulator.. the pink lines didnt 'dip' as much? at the 3khz mark...  seems to be 'flat' (straight) to the rest of the right...

if I use one of the suggested values of 2.2n or 4.7n.. .. the lines are like so:



xl97

I swapped out C18 cap for a 102 (1.0nF) value cap.. and I can definitely hear the difference.  (going to a 101, I couldnt really tell much/any difference)..

I have also tried a 2.2n, 4.7n, 6.8n.. all of which sound 'about' the same to my ear...  but much better compared to the original 103 cap used.. (so thanks for that!)

So I have now tweaked my current pcb in breadboard to be a bit better sounding.. but still and not clear as to why the other board wont give same results.. (when using the same values)..

I can only attribute this to me having fat fingered a cap somewhere?  mixing up a value?


I think I'll try to make/bake another board and see if I have better luck on being the same as the pcb in breadboard' sound..


Wawa

Haha, the "monkey" is a current clamp.
You can see the current THROUGH that part.
Not usefull for this schematic.
You should only measure/click the wire/top of R3/R4.
Doubleclick, and it removes previous test lines and only shows the last one.
V(n004) etc. Clicking on it selects the measurement you did on a node.
You can enlarge, cut, zoom, etc. to see fine details, like spikes.
Not usefull in your simple schematic.
Leo..

dshay

This has already been explained to you, but I will repeat for emphasis.

If you insist on prototyping by ear with an analog circuit, cease and desist with the solderless breadboard, especially if you do not have a decent fluke meter ($200) with accurate capacitance readings.

In a solderless breadboard every common bus are plates in parallel, especially the ground/power busses which are long plates in parallel.

See below:



Plates in parallel is the definition of a capacitor.

Design a prototyping board with socket terminals (see harwin/mill max) Swap to your hearts content.

See here for Socket Terminals

Analog circuits is an art form and right now you're being a masochist, your circuits will never be repeatable.

xl97

hmm...  nice opening statement.  (nobody makes you post by the way)  8)   (nothing to be angry over)



anyways..

1.) I asked what I am trying to 'get to' (achieve) in the LTSpice simulator (having never used it before.. and explaining I am new/not very experienced in audio stuff!?)...  I changed the values.. and see 'some' line changes as well..  I also explained the results I got, with what values..etc.. but if I am not clear on what RESULTS I am trying to achieve in the top portion, I am just changing values for fun.. hence the change in the values on the board to 'hear' the changes in real life as well.


now, either you didnt read fully,..or you dont understand? ....  "but I will repeat for emphasis."   ;)

2.) If the cap I am changing out is NOT IN THE BREADBOARD, I am failing to make the connection about your 'plate' comments and pics of the internals of a breadboard?.. or how extra capacitance is being added???

instead of soldering the cap (C18) to the board, I have female terminated leads going to the cap instead.  (I guess a flexible 'socket' if you wanna go that route.)

at this point...the only part in the breadboard.. (which I guess could also just be connected to wire/leads directly, although they dont fit very tight, so I used a breadboard to secure my connections.) is the POT for R5/R6  (nothing to do with capacitance)..  so why the condescending tone?  (I'm just looking for guidance from those more experienced then myself)..  so back to what are you talking about for the breadboard/plate point?  You are now talking about the POT? (which is resistance?)

Using a lower value cap for C18 as Wawa suggested/explained to me, did in fact, increase the quality of the audio..(from what I already considered pretty decent for a little hobby board)

the other board (which did not have a switchable/variable cap for C18) was not sounding the same as the original board.. it only had swappable parts for R5/R6 and R8..  which as explained (doesnt have anything to do with audio quality or capacitance, but mostly the volume)..  hence my comments that that board must have a different value cap for C18 that I 'fat fingered'. the SMD value or something..








dshay

To be honest I read the first couple posts in horror and rushed to post, I was on a phone and didn't see your circuit.

The plates you have your potentiometer plugged into would appear in a parallel circuit to your potentiometer making the circuit not just resistant and would react differently at different frequencies.

But the main point of my post was that analog is tricky and it's best to prototype as closely to your finished circuit as possible and you're injecting unknown variables into your circuit.

The size of your board I'd recommend investing in wire wrap or just using two soldering irons to remove components directly from your board.

xl97

I have done 'exactly' that..... used soldering irons to removed the components directly form the board..
and instead of soldering directly back in.  I used female terminated wires to re-connect them. (no breadboard in the mix -at all-)

as for the POT.. if its only used for the volume.. and the volume seems to be correct..... whats the issue?

The cap(s) seemed to be the focus that Wawa was relaying to me (correctly) as part of the sound quality issue/correction.. (and hence the capacitance tip, if things were also in the breadboard)  (they were not, never were)

I think part of the confusion came from that one board had replaceable caps and the other not, only swappable resistors (thinking that my caps were correct on both boards, and why the sound quality wasnt the same)..


pito

The capacitance between the rows of that breadboard is 3.2pF.
So not a big deal when talking audio stuff.

Wawa

Exactly what I think.
The only thing I can think of is audio ICs oscillating.
The only time I had trouble with breadboard capacitance was a few weeks ago when I tried to make an 8-button touch sensor with the 74HC273.
Leo..

pito

Mind the ceramic capacitors are not recommended to have in the audio path.
Especially cheap smd ceramics one and ceramics multilayers one (larger capacities). They may create distortion as they are highly nonlinear.
Also the capacity of ceramics caps heavily depends on the DC bias, ie. 1uF rated for 6V may have 0.2uF at 5V.
So for hifi and precise filters always use quality film polymer capacitors.
If you had used film caps on the breadboard and the cheap smdies on the production board, you may hear a difference, of course.
Good reading:
http://www.murata.com/en-us/support/faqs/products/capacitor/mlcc/char/0005
http://www.murata.com/en-global/products/emiconfun/capacitor/2012/11/28/en-20121128-p1
http://www.eevblog.com/forum/blog/eevblog-626-ceramic-capacitor-voltage-dependency-download/15/
http://www.ee-training.dk/tip/why-you-should-specify-mfg-and-pn-of-bypass-caps.htm
http://www.maximintegrated.com/en/app-notes/index.mvp/id/5527

Wawa

Yes, I knew about the voltage dependency of certain ceramic caps.
But in this application, there is no DC on the caps. And t/t AC is very low.
Leo..

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