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Beginner building the Ruby amp...
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Uncle Krunkus
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PostPosted: Wed May 28, 2008 5:10 am    Post subject: Reply with quote  Mark this post and the followings unread

You do have the cut at b4?
Your 386 is the right way around?
The MPF102 is around the other way to what is shown on that stripboard layout?

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LetterBeacon



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PostPosted: Wed May 28, 2008 5:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I've double checked all three of those.

Is it significant that on both builds I seem to have too much voltage going to the Source pin on the FET? All the other values seem to be in the correct ball park. On the last build I had some buzzing coming from the speaker, on this one I have nothing so maybe I have made an additional error to the one I made on the last build?

I'll double check for cold solder joints when I get home as, for some reason, I found it hard to get the solder to stick to the copper rails than on the previous build.
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LetterBeacon



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PostPosted: Wed May 28, 2008 1:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, here are the pictures:

I'm afraid I don't have time tonight to desolder all the wires, so it looks a bit of a mess from the component side. If you need me to I can desolder the wires tomorrow evening.

Last edited by LetterBeacon on Fri May 30, 2008 12:48 am; edited 1 time in total
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Blue Hell
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PostPosted: Wed May 28, 2008 2:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks like C5 is soldered in wrong?

I don't see it go to k9 (at the dot of the question mark)

And here is an image that made it easier for me to search ...


all-2.jpg
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all-2.jpg



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Jan
also .. could someone please turn down the thermostat a bit.
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LetterBeacon



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PostPosted: Wed May 28, 2008 3:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow, what an incredibly useful picture - thanks for taking the time to do that!

Fixed the C5 cap. Looks like that was an oversight on this build as I had it in the right place on the previous build. I had to take the cap from the previous build as I had cut the legs too short on this one. Unfortunately I've now got the same result as I had on the previous build - I get a buzzing sound when I turn both pots right up and clicks when I tap anything metal like the on/ off switch; the jack; or the guitar strings when I plug the guitar in.

One thing I've realised is that the C5 from the previous build (that is now in this build) was put in the wrong way originally, i.e. I had the polarity round the wrong way. Could this have damaged it significantly? Maybe I should buy a brand new one and try that tomorrow (eesh, this amp is becoming expensive!!).
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LetterBeacon



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PostPosted: Wed May 28, 2008 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've just managed to put the C5 cap that was in the current build in the right holes - i.e. I'm using a cap that I know hasn't been put in the wrong way at any point in its life, so should be working correctly. Unfortunately I still have the same buzzing results.
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Blue Hell
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PostPosted: Wed May 28, 2008 3:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

C5 will not be damaged, anyway you are getting hum and crackle, so you do have low and high frequencies and amplification ... what happens when you take a small metal pin and touch pin 2 of the 386 chip with it (maybe disconnect the wire that goes from there to the volume pot temporarily). When you get increased hum the 386 part seems to be working, it already does seem so IMO, but just to be sure.

The pic saved me time in searching, and I wanted to do that anyway, so it just saved me time Wink

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Jan
also .. could someone please turn down the thermostat a bit.
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LetterBeacon



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PostPosted: Wed May 28, 2008 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Unfortunately I've had to pack my soldering stuff away for the night (got to get up early for work!) so I won't be able to do as you suggest tonight with the small metal pin. Just out of interest, what do you expect will happen when I touch pin 2 of the 386?
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Blue Hell
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PostPosted: Wed May 28, 2008 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I expect hum. See you around, sleep well!
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Jan
also .. could someone please turn down the thermostat a bit.
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Uncle Krunkus
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PostPosted: Wed May 28, 2008 6:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

The buzzing and clicking all sound very good for this circuit when there is no input connected. So I'd be checking the front end. Check that your guitar cable is okay and that it works when plugged into another amp.

I'm suspicious about the point where your input is soldered to track C. The solder blob looks very close to shorting with track B. I also don't like the look of some of the track cuts. Make sure none are connecting to anything they shouldn't be. Especially that track C is not shorting to either of the track B parts or track D.

I think we've got this fault on the run. Very Happy

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LetterBeacon



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PostPosted: Thu May 29, 2008 12:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
The buzzing and clicking all sound very good for this circuit when there is no input connected. So I'd be checking the front end. Check that your guitar cable is okay and that it works when plugged into another amp.

I've tried it with two different cables with the same results. The clicks occur when I touch the guitar strings so there must be some signal coming from the guitar. Does the fact that it clicks whenever I touch anything metal (ie. the metal on/ off switch or the input jack) mean that I haven't grounded the circuit properly?
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Uncle Krunkus
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PostPosted: Thu May 29, 2008 1:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd say the buzzing and clicking when touching various metal parts points to the input not being tied down. ie: if the input isn't connected properly there will be no path from the input connection to ground, and therefore the input will act as an antenna. If the input is connected directly to ground you should get ground - nothing. If there is a guitar pickup between the input and ground you'll get the guitar signal. If there is no connection at all between the input and ground, you'll hear a lot of mains hum, static discharges, radio frequencies, Pink Floyd bouncing off the dark side of the moon, various Satanic transmissions from somewhere inside the Vatican, Cliff Richard, etc. etc. etc. (the last two sound very similar actually Shocked )
And it sounds like that is where you are now. Make sense?

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Uncle Krunkus
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PostPosted: Thu May 29, 2008 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

What kind of socket have you got connected to the input for your guitar to plug into, and have you ascertained that the sleeve connection for the socket is the one you've connected the ground wire to? (Multimeter)
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LetterBeacon



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PostPosted: Thu May 29, 2008 2:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, that all makes sense.

This is the socket I've got: BW78K

I thought I'd got the correct bits connected, but reading the FAQ on the site maybe I haven't:
[quote=Maplin's FAQ"]Q) What is the pinout; what ARE the connections? What does it all mean? - Owen Woods
A) It is a standard 1/4" jack socket with 4 connections. One connects to the tip of an inserted plug and one connects to the body (ground) of an inserted plug. The other two connect to these two connections when no plug is inserted. Inserting the plug breaks the connection. This is useful for disconnecting an internal loudspeaker, for instance, if a headphone plug is inserted.
[/quote]

I put one point of my multimeter into the socket and the other on each of the legs in turn. The leg with no resistance is the one that goes to the input on the board right?
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Uncle Krunkus
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PostPosted: Thu May 29, 2008 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Looking at it like it is pictured in that Maplin link, the input goes to the connection on the right, and ground to the connection on the left.
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Blue Hell
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PostPosted: Thu May 29, 2008 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
I put one point of my multimeter into the socket and the other on each of the legs in turn. The leg with no resistance is the one that goes to the input on the board right?


The G spot can be hard to find that way Wink

Either look at the construction and deduce from that what two pins to use, or insert your guitar cable and connect one probe of your ohm meter / continuity tester to the tip of the unplugged jack and find which connector pin corresponds to that by making your connectivity tester go beep or by making the ohm meter go to a low readout value, like a couple of Ohms.

Then do the same thing for the sleeve. The tip connected one goes to the input of your circuit, the sleeve connected one to the ground of your circuit.

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Jan
also .. could someone please turn down the thermostat a bit.
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LetterBeacon



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PostPosted: Thu May 29, 2008 10:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent - I'm off home now so I'll report back shortly!
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LetterBeacon



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PostPosted: Thu May 29, 2008 12:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow, it works!! Can't believe I'm finally hearing my amplifier work! Turns out I did in fact have the wires soldered onto the wrong points on the 1/4" jack socket.

Thank you so much everyone who offered advice in this thread - special thanks to Uncle Krunkus and Blue Hell who persevered with me right to the end!
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Blue Hell
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PostPosted: Thu May 29, 2008 12:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

wave
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LetterBeacon



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PostPosted: Thu May 29, 2008 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just to confirm: The signal is amplified by the MPF102 and the 386 amplifies it further and adds distortion when you turn up the gain pot?

What is the function of the 100uf capacitor in the circuit?
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Thanks again for all your help - I can't believe it took 4 pages for me to complete it, but we got there in the end!
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Blue Hell
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PostPosted: Thu May 29, 2008 1:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, questions, very good Cool

The FET mainly servers as an impedance converter, it offers a (verty) high impedance input that presents not much load to what you connect to it. It has a low impedance ouptut so a relatively low valued pot can be used for volume control without partly short circuiting the input generator (your guitar here).

Amplification is performed by the 386 chip, but that one also further lowers the impedance such that it's low enough to drive a speaker.

NB impedance lowering can also be seen as current amplification (as opposed to voltage amplification).

The 100 uF cap over the battery is used to have a low AC impedance path there. A battery has a relatively large intrnal resistance, but for a good working circuit it is important that there is no AC present at the positive supply, the 100 uF cap simply short circuits its to ground. A good power supply would have this "short circuit function" (or low output impedance) as well.

The gain pot adjusts the voltage amplification up to a point where the output voltage of the 386 would be larger than the battery voltage or lower than zero. This is physically impossible and the signal will be clipped instead. You'll hear that clipping as distortion, basically it means that too much amplification was requested (which will not destroy anything here).

Normally the output of the 386 is regulated to be halfway between the battery voltage and zero (and you confirmed such by measuring it), so clipping will occur when either the upward or the downward bit of the speaker signal is greater than about 4.5 V.

Hope that helps a bit.

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also .. could someone please turn down the thermostat a bit.
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LetterBeacon



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PostPosted: Thu May 29, 2008 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Ah, questions, very good Cool

The FET mainly servers as an impedance converter, it offers a (verty) high impedance input that presents not much load to what you connect to it. It has a low impedance ouptut so a relatively low valued pot can be used for volume control without partly short circuiting the input generator (your guitar here).


I hate to say it, but I think my brain just exploded as I was reading that paragraph over and over trying to work it out! Is there anyway you can explain that further? Or are there any good resources on the net that I can read that would explain it? Obviously if you haven't got the time, don't worry - you've given up loads of your time to this already!
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Blue Hell
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PostPosted: Thu May 29, 2008 4:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Embarassed yes, I can imagine ... I tried to write a short introduction, but it started to get book like proportions and then I ran out of beer, which is not too bad actually as tomorrow the boss will want things from me Wink

Guess you'll wantto read a good introduction about batteries and wires and voltage and current and resistance first. Stuff like "what is electricity"

or ...

erm firefox is about to crash here, probably it ate all the memory again ... I'll post this now and continue later.

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also .. could someone please turn down the thermostat a bit.
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Blue Hell
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PostPosted: Thu May 29, 2008 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Indeed, it had consumed 1.4 GB of memory, the bastard, but luckily when you just kill the process and then restart it, it will go on as if nothing happened with lots less memory used Very Happy

A good entry seems to be : http://sonic.net/~ax/articles/What.Is.Electricity.html

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also .. could someone please turn down the thermostat a bit.
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Uncle Krunkus
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PostPosted: Thu May 29, 2008 5:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah!!!!
I'm so glad you got it working LetterBeacon. Very Happy
Don't ever be worried about asking questions and learning the basics.
It turned out to be just like I said a few posts ago, "something which, as a new builder, you misunderstood, and Jan and I had taken for granted."
The connections on a 6.5mm socket! Laughing
This is actually really great, as it demonstrates how the "hard" bit can easily cloud the "easy" bit. Which is a very important lesson in troubleshooting. I'm very glad you got the chance to learn it early on. Very Happy

Satisfying knowing that you got to the bottom of it hey?

The actual functioning of the circuit is not one of my strong points either, although I know heaps more than I did 3 years ago when I started hanging out around here. I have people like Jan to that for that. salut

That part will come with time, and be more intuitive as you study more schematics, troubleshoot more problems and read more theory.

When I was young(er) (like 16 or 17) I would build these circuits up which were way beyond my troubleshooting skills. Of course half the time they wouldn't work first go, but I had no Internet, and no one else to bounce ideas off and keep me motivated to track down the fault. The fact that I kept getting inspired to build something else is amazing. The fact that I ended up quite deflated and stopped doing DIY electronics isn't.

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