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Having trouble with Audioguru's electret mic preamp

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TheGuy

New Member
Hi all! I'm in a spot of bother...

Continuing from this thread, I had decided to have a go at building Audioguru's mic preamp.

I planned to build two of them on one board to have stereo. However, I'm having trouble with both of them, so I must be doing something fundamentally wrong.

I've attached both of my attempts. I've gone over them several times and can't see any errors. They both respond in exactly the same manner, giving only a slight 'click' when the mic is connected, after which there's absolutely nothing, not even any noise. Putting an already amplified signal through it results in just the high frequency sounds coming through very quietly (I've attached it directly to a loudspeaker for testing).

The only ideas I have are...
Heat damage (but not to the chip; I used sockets).
The TL071CN chip (which is the one I'm using) is majorly different from the TL071.
I've done something wrong in both (which wouldn't surprise me!).

Being no expert I don't know how to proceed, and any help would be very much appreciated. :)
 

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ericgibbs

Well-Known Member
Most Helpful Member
hi,
Following your coloured lines you show pin4 linked to pin2.???
 

TheGuy

New Member
That green line? Green represents a split in the copper. :) I should have made a key.


The dark green/red lines, and yellow lines on the first image, represent cross-overs. I don't know if 'cross-over' is the correct term, but basically it's connecting a to b across the board using a wire.

Bright green lines on the second image represent splits (I didn't bother marking these on the first).
 

ericgibbs

Well-Known Member
Most Helpful Member
That green line? Green represents a split in the copper. :) I should have made a key.


The dark green/red lines, and yellow lines on the first image, represent cross-overs. I don't know if 'cross-over' is the correct term, but basically it's connecting a to b across the board using a wire.

Bright green lines on the second image represent splits (I didn't bother marking these on the first).

hi,
Post a clear pic of the copper side of the left pcb image you posted.
 

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TheGuy

New Member
I was actually hoping that my appalling soldering skills would go unnoticed, haha. It was my very first try, so please forgive the mess!

I've flipped it and aligned it up with the left diagram to make it a bit easier to see where everything is.
 

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ericgibbs

Well-Known Member
Most Helpful Member
I was actually hoping that my appalling soldering skills would go unnoticed, haha. It was my very first try, so please forgive the mess!

I've flipped it and aligned it up with the left diagram to make it a bit easier to see where everything is.

hi,
Ref the image I posted back, according to your link wire colours, pin 2 is joined to pin 4, which it should not be.
Can you check the image and your pcb.?
The copper image you have posted, the back of the 8pin IC is obscured, thats the bit I am interested in.:)
 

audioguru

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Most Helpful Member
The first photo shows pin 2 wired to pin 4.
The second photo shows pin 2 wired to pin 5.
Stripboard usually has its tracks cut with a drill bit at a hole without any wire in it, not with your teeth.
A few jumper wires are usually used on the component side of stripboard (not on the solder side) to join tracks and parts are also connected between tracks.
 
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TheGuy

New Member
Ref the image I posted back, according to your link wire colours, pin 2 is joined to pin 4, which it should not be.

Oh yeah, I didn't see that you'd posted that edited image. :)

I can't actually see how pin 2 is connected to pin 4, though. As far as I can see, pin 2 is connected to the VR, and then pin 4 to ground. Although, I guess pin 2 is connected to pin 4 through the 2.2k resistor and 22 uF capacitor. Is this what both you and audioguru are referring to?


The copper image you have posted, the back of the 8pin IC is obscured, thats the bit I am interested in.:)

Pin 8 doesn't actually exist because I removed it from the IC socket. :D Judging from the circuit diagram, pin 1, 5, & 8 aren't needed, so I removed them to avoid shorts. I shall take a less obscured photo after my camera has finished charging if it's still required though. :)


audioguru said:
The second photo shows pin 2 wired to pin 5.
Pin 5 has been removed from the socket, along with pin 1 and 8.
 

audioguru

Well-Known Member
Most Helpful Member
I think you have the strips shorting together most pins of the IC because the strips are 90 degrees in the wrong direction.
I think you don't understand that the bottom is a mirror image of the top.

Why did you post two completely different circuit boards?

How high did you drip the solder from? Solder is not supposed to be dripped on.
The copper trace and wire are both supposed to be heated with the clean tip of a temperature-regulated soldering iron (not a soldering gun) then rosin-core solder is touched to the hot trace and wire. Solder will melt and flow and join the two together. It takes one second.
 

Boncuk

New Member
Building a circuit mirrored may be hard for the first few times.

Here is audiuguru's mic preamp unmirrorred which should work like a charm right from the start.

Do the layout similar to the one pictured here and you're done.

For Eagle files PM me.

Boncuk
 

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TheGuy

New Member
I think you have the strips shorting together most pins of the IC because the strips are 90 degrees in the wrong direction. I think you don't understand that the bottom is a mirror image of the top.

Yeah, on my first attempt I rather dumbly had the IC going along the copper. :rolleyes: I had split the copper (using a knife, not my teeth btw ;) ) beforehand though, and I can confirm that they're not shorting out, as I've tested thoroughly with a multimetre. My surety is backed up by my second attempt with the IC socket in the correct orientation still reacting in the same way and not working.

Although you're right, I don't understand that the bottom is a mirror image of the top. :( Do you mean the bottom/top of the IC?


Why did you post two completely different circuit boards?

I'm making a stereo preamp, so I decided to make two circuits of your design on the same board. When I found that my first attempt (the left picture in the first post) didn't work, I decided to have a go at building the second one. I learned from my mistakes, and used the copper strips to my advantage, requiring only five cut tracks (three of which are under the IC).

When I found that this second layout didn't work, I decided that I must be doing something wrong elsewhere, or had selected the wrong components or something. I've tested over and over for shorts, and checked my layout over and over as well; I can't see anything wrong. :(

How high did you drip the solder from? Solder is not supposed to be dripped on.
The copper trace and wire are both supposed to be heated with the clean tip of a temperature-regulated soldering iron (not a soldering gun) then rosin-core solder is touched to the hot trace and wire. Solder will melt and flow and join the two together. It takes one second.

Do you literally mean dripping the solder from a height? I'm new to this, but I'm not a buffoon, haha. ;) I pretty much did the steps that you just outlined. Although, I'm not sure what you mean by "temperature-regulated soldering iron". I just used a 25w one with a small tip.

I've tested all of the joints, and none of them are dry. :)



So, as you can probably see I'm rather confused at what's wrong, as there's nothing very obvious (to me anyway). Heat damage perhaps? I did try and minimise heat on the components, but I didn't think that capacitors or resistors were particularly heat sensitive.


Building a circuit mirrored may be hard for the first few times.

Here is audiuguru's mic preamp unmirrorred which should work like a charm right from the start.

I was originally going to build it using your layout there, but my dad told me to do it from the diagram to work with this copper track stuff so that I wouldn't have to get a print. I think I'll probably have to try yours now though. But, do tell me, what's the difference between mirrored and unmirrored?
 

ericgibbs

Well-Known Member
Most Helpful Member
hi
Look at this image...:)
But, do tell me, what's the difference between mirrored and unmirrored?
 

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audioguru

Well-Known Member
Most Helpful Member
My temperature-regulated soldering iron has a tip that is clean and is always the correct temperature.
An temperature-unregulated soldering iron has a tip that is covered in burnt stuff and is way too hot. It vapourizes the rosin in the solder that is supposed to clean the copper trace and wire that you are soldering.

Planning an IC on stripboard, pins 1 and 8 use one copper trace, pins 2 and 7 use a second trace, pins 3 and 6 use a third trace and pins 4 and 5 use a fourth trace. The four traces are cut under the IC with a drill bit spinned in your fingers or on a drill press. Most parts and a few jumper wires connect traces and very few parts run along one trace with a cut under them. Diagonal jumpers are rarely used. One wire is in each hole. No jumpers are on the solder side.

I plan the wiring from the component side on grid paper and use an "X" for each cut of a trace. Then I count the holes on my plan and on my circuit board and use a marker pen on the traces where they must be cut.
 

TheGuy

New Member
Thanks very much for the advice. :)

My soldering iron isn't temperature-regulated, judging from what you've described. I don't know if that's an issue or not really. It seemed to work alright, and my components are all attached nicely.

Actually, "it seemed to work alright" is a bit of a daft statement for it obviously isn't alright. Nobody's answered this yet... Could I have damaged any components by heat, or am I safe to assume that it's something else?


Anyway, let's for now ignore my diabolical first attempt and just take a look at my second attempt, which should be a lot more clear and easy to sort out. I've attached a nice clear diagram, just so that you chaps can see the board and make your judgements.

Thanks everyone for the input so far. :)
 

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audioguru

Well-Known Member
Most Helpful Member
You do not understand that the bottom of the circuit board is supposed to be a mirror image of the top. The left side of the components side is the right side on the solder side and the right side of the components side is the left side on the solder side.
Pins 1 to 4 of the IC are on the left side on the components side of the circuit board but they are on the right side on the solder side.

A cheap soldering iron gets too hot so it is never clean. It is covered in burnt stuff and oxides of the solder which causes a solder joint to take too much time which might burn the parts. My temperature controlled soldering iron is always at the correct temperature so nothing burns, the tip is very clean (I occasionally wipe it on a damp sponge) and a good solder joint takes only 1 second so the parts do not get too hot.
 

TheGuy

New Member
You do not understand that the bottom of the circuit board is supposed to be a mirror image of the top. The left side of the components side is the right side on the solder side and the right side of the components side is the left side on the solder side.

Yeah, I know. I just flipped the image to make it easier to compare the top side to the bottom side. It would be a jolly old mess if I tried soldering without taking the mirroring into account, haha!
 

TheGuy

New Member
Wait... so you're saying that I've been visualising your circuit diagram from the top down, when I should have been visualising it as looking at the bottom of the board?


If that's the case then I guess that's the answer to why it's not working. Ouch. My n00bness is my downfall! Sorry for not believing you from the off, audioguru.

So if this is the case, I'll have to resolder everything, or perhaps bend the pins of my IC back so that I can just have it upside down if it's only the IC that's wired wrong.

Edit: I've just tried the circuit again, and it sort of works with the very high frequencies. Pretty useless still if it's only amplifying 18khz though. Still, it's progress, though I may have just not noiced before (it's rather quiet).
 
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audioguru

Well-Known Member
Most Helpful Member
Edit: I've just tried the circuit again, and it sort of works with the very high frequencies. Pretty useless still if it's only amplifying 18khz though. Still, it's progress, though I may have just not noiced before (it's rather quiet).
What is its load? It is designed for a ten-thousand ohms or more load (then its output drops below 48Hz), not an 8 ohms speaker. The preamp can drive a power amplifier that can drive a speaker.
 

TheGuy

New Member
Oh, I was lead to believe that it was powerful enough to drive a speaker. I guess I merely minunderstood you. :)

TheGuy said:
Also, because the Zen has NO amplifying at all, it requires quite a loud input to be just under clipping. If you'll excuse the non-precise comparison, it requires something similar to an MP3 player on 2/3 volume. So, because your circuit is a pre amp, it'll also need another amplifier afterwards, correct? Or will your circuit amplify the mic quite a bit more than I'm thinking?
My preamp has plenty of adjustable gain. With a 9.0V supply its max output before clipping is 2.3V RMS which is much more than an MP3 player.

Now that I need to use a seperate amplifier, it kind of defeats the point of my project as it was supposed to be as small as possible. Ah well, at least I have a 9v amp board from some PC speakers that will work well.

Anyway, yes, I was using an 8ohm speaker. Attaching the preamp to the previously mentioned secondary amp reveals that it works, thanks!

I've only tried one so far, but I expect the other will work as well.

One thing that really impressed me was the noise levels, or lack thereof. I'll do some more testing soon, but from what I've heared so far it seems to be very high quality. Great circuit design, audioguru!
 
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