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Beginner building the Ruby amp...
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Blue Hell
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PostPosted: Wed May 21, 2008 1:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
To do this, should I put one point of the meter on the 9v rail and one on the Gate connection?


Voltage measurements are by convention made relative to the ground level (which then by convention must be zero Volts), having the black lead (-) connected to ground (which in this case is the - terminal of the battery) and poking around with the read lead to measure the various voltages in the circuit.

Reading back and assuming you made your earlier measurements relative to the battery + terminal as well they don't look that odd anymore - it really had me puzzled as to how this could ever be possible Laughing

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also .. please don't march .. we are on a bridge right now.
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Blue Hell
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PostPosted: Wed May 21, 2008 1:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh and when measuring around, please include the battery voltage, or at least check it to be around 9 V, just in case it runs empty for some reason and messes up everything else.
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Peake



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PostPosted: Wed May 21, 2008 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

mpf102 can be found inexpensively on ebay.
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LetterBeacon



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PostPosted: Wed May 21, 2008 1:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Voltage measurements are by convention made relative to the ground level (which then by convention must be zero Volts), having the black lead (-) connected to ground (which in this case is the - terminal of the battery) and poking around with the read lead to measure the various voltages in the circuit.

Right, I see now! Thanks for your patience with me, I do have books on this as well, but I must have missed that vital bit of information when I was reading through!

Quote:
mpf102 can be found inexpensively on ebay.

Wow, can't believe I didn't think of that - thanks a lot!
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Blue Hell
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PostPosted: Wed May 21, 2008 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
Right, I see now!


Well, just to be sure, any other reference system is equally valid, but your readers would not expect it Laughing

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LetterBeacon



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PostPosted: Wed May 21, 2008 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, here are the results of my new tests with the black point on the -v wire coming from the battery (I have to touch it to the solder joint on the stripboard because it's soldered it, but that should be ok, right?), and the red point on the different pins.

Battery = 9.30v

2N3819
Drain = 9.27v
Source = 3.09v
Gate = 0.0v


LM386-N
Pin 1 = 1.33v
Pin 2 = 0.0v
Pin 3 = 0.0v
Pin 4 = 0.0v
Pin 5 = 4.45v
Pin 6 = 9.25v
Pin 7 = 4.63v
Pin 8 = 1.33v

When I re-tested them to make sure I only got 0.0v from pin 8, on the third and forth goes to make sure I got 1.34v.

Other than that it looks pretty close to modman's readings:

2N5457 JFET:
Drain = 9.18V;
Source = 0.84V;
Gate = 0.00V

LM386 opamp:
1 = 1.34V;
2, 3 and 4 = 0.00V;
5 = 4.56V;
6 = 9.18V;
7 = 4.64V;
8 = 1.34V

So it looks like it might be something to do with the FET, I think.
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Blue Hell
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PostPosted: Wed May 21, 2008 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
but that should be ok, right?


Yup!

Looks like most things are soldered and measured right now. The FET is a bit low on the source indeed, but still some signal should get through I'd think ... well you were going to change the FET anyway.

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LetterBeacon



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PostPosted: Wed May 21, 2008 3:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I do get a tiny amount of level, but mostly it just buzzes! What do you think is stopping the source from getting a proper voltage? What things should I look out for on my circuit?
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Blue Hell
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PostPosted: Wed May 21, 2008 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Erm, where I wrote low I meant high, mixed up the tables, but it seems not way out to me ...

What you could try is to temporarily remove the FET and connect your input signal to the connection point between the 3k9 resistor and the 47 n capacitor, to see if you get some signal amplification from the main amplifier, not too much maybe, but some.

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Blue Hell
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PostPosted: Wed May 21, 2008 3:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Buzzes as in mains hum?
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LetterBeacon



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PostPosted: Wed May 21, 2008 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Not sure, I think so - it sounds like an amp does when you have a guitar plugged in but not playing (if that makes sense).
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Uncle Krunkus
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PostPosted: Wed May 21, 2008 3:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Letterbeacon and Jan,
I've just woken up and I think you two are still awake.
I'm gonna breadboard this up right now and see what happens.
Jan - The Source on a FET goes towards the +ve rail yeah?
On a schem, how do you tell the difference between the source and drain?
ie; which one has the Gate "pointing" at it?

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Uncle Krunkus
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PostPosted: Wed May 21, 2008 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay,
I've just powered it up and it worked first go! (Sorry letterbeacon! Embarassed )
Great little amp too! I'd like to hear it through two 4R oval speakers I pulled from an old stereo, and properly mounted in a little cab of some sort. (even a basic bin would do heaps for the bottom end)
Anyway, the main point is, mine works and I'll take some measurements to see if they match up with the other ones.
BTW I'm using an MPF102.
You do have your input across the input AND ground don't you letterbeacon?

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LetterBeacon



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PostPosted: Wed May 21, 2008 4:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Heh, typical!

Yes, I have a wire going from the 1/4" jack socket to the 0v rail as well as the one going to the input hole on the board. Maybe I should buy one of the MPF102s from eBay then?

Oh and thanks very much for taking the time to breadboard it!
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Peake



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PostPosted: Wed May 21, 2008 5:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
Quote:
mpf102 can be found inexpensively on ebay.

Wow, can't believe I didn't think of that - thanks a lot!


Considering you'd sourced the 2N3819 for 1.09L each in your first post, I thought that you might prefer the original for 20 cents each US.

Last edited by Peake on Thu May 22, 2008 12:06 pm; edited 1 time in total
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Uncle Krunkus
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PostPosted: Wed May 21, 2008 6:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Firstly,
I'm using an almost dead 9V, so I only have 7V6 on the +ve rail. (goes to show it's a nice design, as it still sounds quite good!)
Even so, I have 1V6 at the drain, and 0V at the input.

I've also confirmed that the Source and Drain (on the MPF102) are interchangeable for this design. It sounds great either way.

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LetterBeacon



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PostPosted: Thu May 22, 2008 1:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
What you could try is to temporarily remove the FET and connect your input signal to the connection point between the 3k9 resistor and the 47 n capacitor, to see if you get some signal amplification from the main amplifier, not too much maybe, but some.

Ok, I'll try this when I get home from work tonight.

So do you think using the 2N38219 might be causing the wrong voltage to show up at the source connection, maybe if I use an MPF102 it should fix it?

Peake wrote:
Considering you'd sourced the 2N38219 for 1.09L each in your first post, I thought that you might prefer the original for 20 cents each US.


Just ordered 10 of them. Including shipping it works out to about £2 - bargain, thanks a lot!
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Peake



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PostPosted: Thu May 22, 2008 12:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

My pleasure, hope it works. (Corrected extra numeral in my original post.)
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LetterBeacon



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PostPosted: Thu May 22, 2008 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
It doesn't really matter as long as the middle connection (2) goes to the right place. Swapping the outside two just reverses the effective rotation.


When you say "reverses the effective rotation" do you mean the pot is reversed? i.e. you have to turn the pot counter-clockwise to turn the volume up?
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Blue Hell
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PostPosted: Thu May 22, 2008 4:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
counter-clockwise


That's better Wink

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LetterBeacon



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PostPosted: Tue May 27, 2008 3:31 pm    Post subject:
Subject description: !!
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I got the MPF102s in the post this morning and rebuilt the stripboard from scratch this evening. Unfortunately I don't even get a hum now! Here are the results of my voltmeter testing:

Battery = 9.19v

MPF102
Drain = 9.17v
Source = 2.84v
Gate = 0.0v


LM386-N
Pin 1 = 1.33v
Pin 2 = 0.0v
Pin 3 = 0.0v
Pin 4 = 0.0v
Pin 5 = 4.53v
Pin 6 = 9.16v
Pin 7 = 4.59v
Pin 8 = 1.33v

So, as you can see, I have much the same results as when I had the other FET in. I seem to have too much voltage at the Source. I've checked for short circuits on the rail the Source is connected to and there's nothing suspicious there. There must be something obvious I'm doing if I'm getting the same results with a new build and new FET, but I can't for the life of me figure it out! This is supposed to be an easy project!! Rolling Eyes
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Blue Hell
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PostPosted: Tue May 27, 2008 4:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, a rebuild gives different results ... right ... was the possibility that the amp chip is broken considered already? It does seem to do something, judging the voltages, but what exactly hard to see from here.

Maybe .. could you past some pics again, but they need to be better than las time, take 'm outdoors maybe, the light will be much better there, avoid the flash, both sides of the board please Wink

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Uncle Krunkus
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PostPosted: Tue May 27, 2008 8:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, but don't get too close! Most digital cameras can't get a focus lock if you're under about 2 feet away. (Unless they have a macro setting) An in focus shot under daylight can always be cropped down to something good. No focus lock will always be,.... well,..... out of focus. Sad
I'm starting to wonder about resistor values.
Maybe it's something which, as a new builder, you've misunderstood, and we have taken for granted. A good pic should show these kind of things up.
Especially as you now have MPF102s to play with, I'm very determined to help you get this thing happening.
I'm about to make a little cab for mine.
I might even make a second one for a friend.
They really are very cool.

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LetterBeacon



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PostPosted: Wed May 28, 2008 2:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Hmm, a rebuild gives different results

Well the results of the rebuild are fairly close to the results of the original - my battery is slightly depleted so maybe that could be affecting it?

Quote:
I'm starting to wonder about resistor values.

I posted the colour bands of the resistors earlier in the thread and I think they seemed to be correct:

Earlier, I wrote:
Ok, so I think I have 4 band resistors with a 5th for tolerance. They are:

My 1.5M is brown, green, black, yellow + brown = 150 000 = 1.5M which is correct

My 3.9K is orange, white, black, brown +brown = 3900 = 3.9K which is correct

My 10R is brown, black, black, gold +brown = 10.0 which is correct.


In this build I have used brand new electrolytic capacitors and a new MPF102. I salvaged the resistors and ceramic capacitors from the old build. Two of my capacitors have 473 written on them, which I understand to be 47nf; and the other one has 104 on it, which I think is 100nf.

I'll definitely try and take a picture when I get home from work tonight.

Quote:
I'm very determined to help you get this thing happening.

Thanks - I really appreciate all the help I've had in this thread so far. I've learnt so much about circuits purely from this little project, it would be great if we could get it to work!
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Uncle Krunkus
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PostPosted: Wed May 28, 2008 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
I've learnt so much about circuits purely from this little project, it would be great if we could get it to work!


Oh it will work.
It just doesn't know it yet. Twisted Evil

I assume you've double checked the actual MPF102 pinout.

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