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Beginner building the Ruby amp...
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Thu May 01, 2008 10:27 am    Post subject: Beginner building the Ruby amp...
Subject description: Warning: very basic questions asked inside!
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After nearly completing the MFOS WSG (just waiting on a front panel to be made) I was recommended in another thread to attempt the Ruby. Pretty much the only thing I remember from school is how to solder, so I have some basic questions about it that I hope someone will be able to answer.

I'm hoping to make a stripboard version of this over the weekend. I've found these components on Maplin's website - are these the ones I need?
For the MPF102 FET I have this: QR36P
and for the JRC386D I have this: UJ37S

For the non electrolytic capacitors, does it matter if I use ceramic or polypropylene etc.?

What kind of speaker can I use? Does it have to have certain specification to work with the circuit?

And finally, does everything with a ground symbol in the circuit diagram have to be connected to the 0v rail on my stripboard?

Thanks a lot!
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factus10



Joined: Jun 20, 2007
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PostPosted: Thu May 01, 2008 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Looks pretty straightforward to me. I'd copy the recommended layout instead of trying to interpret it to stripboard, but that's me. The 386 you have should do the trick. Don't have any clue about the FET but it can't hurt to try.

No, it won't matter if you use ceramic. The 386 is not exactly the quietest power op-amp out there.

Use an 8 ohm speaker. Get a 16 ohm for kicks and stick that in to see what it does. The 386 doesn't really drive anything over 5" very well. It's designed for smaller speakers.

Yes, everything with the ground symbol connects together. In that design, it ultimately connects to the - side of your power supply.

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LetterBeacon



Joined: Mar 18, 2008
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PostPosted: Thu May 01, 2008 3:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool, thanks for the help!

The reason I was attempting to stripboard it myself was because I can't quite work out what is going on the underside of their layout! Perhaps I'll try and recreate their layout on a stripboard. Instead of solder wires like they have.

So are ceramic capacitors noiser than other types of capacitors then?

If I wanted to put an on/ off switch in there, I could just put an SPST after the battery before anything else and it would work right?

Thanks again!
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Joel



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PostPosted: Thu May 01, 2008 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

stripboard layout attached, taken from this site. Not checked it myself so worth going through and understanding what's going on before commencing! The red squares on the layout (beneath the IC and at the top) are where you need to cut the copper strips on the underside of the board. Blue lines are linkers between rows - just use bits of wire or legs cut off resistors etc. There's threads around on how to use stripboard, or post back if you have any probs. The labels on the side indicate where to attach wires to the various off board components (jacks etc. - note the input jack should also be grounded although not shown on the schematic; just connect another wire to the gnd row, row g). And yes, just pop a switch between the +ve terminal and the board for on/off control.

Good luck! Joel


ruby.GIF
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ruby stripboard layout
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ruby.GIF


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crashlander42



Joined: Oct 21, 2006
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PostPosted: Thu May 01, 2008 7:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Funny you should mention that. I just built one of these little amps last night and I love it. Even hooked it up to my WSG. I'm using an 8Ohm 1/2 watt speaker.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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Coriolis



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PostPosted: Fri May 02, 2008 12:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Have you been to:
http://www.runoffgroove.com?
I believe they are the originators of the Ruby amp, and should have lots of info on it...

C
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LetterBeacon



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PostPosted: Fri May 02, 2008 6:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Just got back from Maplin and they only had a 6Ohm 60W speaker - before I blow anything up by using it - will it work?

I've got an aluminium box for the container, if I mount the pots on the container will that short anything?
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LetterBeacon



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PostPosted: Sat May 03, 2008 2:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, I forgot to mention - thanks Joel for posting that stripboard layout! I've pretty much built the thing from that, although I've just got to add the speaker and wire the pots in.

Having a really hard time finding an appropriate speaker - The only 8Ohm speakers I can find are 100w - that can't be right, surely?
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Joel



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PostPosted: Sat May 03, 2008 3:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I found an 8ohm 0.5W speaker in a broken answerphone machine - get a little bit creative and you'll usually have some luck Wink

As Coriolis mentioned, it's also worth looking at the runoffgroove site for more info on what this amp can drive etc...

Let us know how it turns out! Joel
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LetterBeacon



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PostPosted: Sat May 03, 2008 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm having a bit of a hard time understanding the different specs when it comes to speakers though. The Runoffgroove site says that Little Gem MkII (which the Ruby is based on) delivers about 1w. It also says that they had no problem using the Little Gem to drive a Marshall 2x12 cab that, when I looked at the specs, says it can handle 150w! I'm so confused!!

Maplin have got an 8 Ohm 6w speaker, I don't really want to put it in the circuit unless it a) blows up my amp, b) just doesn't work but I can't take it back because it has solder on the terminals, c) all of the above!
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Blue Hell
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PostPosted: Sat May 03, 2008 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Assuming you will drive the circuit from a 9 .. 12 V supply.

It does not matter how many Watt's the speaker is as long as it is more than the amplifier is able to deliver. According the data sheet of of the LM386 it is not able to deliver more than 1 W, so any speaker > 1 W is fine.

The more power a speaker can handle the more expensive it will be and the less efficient it will be, in general of course.

What does matter is the impedance of the speaker, but it is not very critical in this circuit 4 .. 16 Ohm would be fine. A higher value (say 16 Ohm) will result in less volume and less distortion.

When you really want an 8 Ohm speaker but you can only find 4 Ohm you could consider to put two in series.

This is not high power circuitry, so it's not very critical.

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LetterBeacon



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PostPosted: Mon May 05, 2008 1:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent, thank you! I don't quite understand why the impedence of the speaker has to be with 4, 8 or 16 Ohms though.

On the stripboard posted above, it doesn't have the input grounded at all. I'm going to be using a 1/4" jack, should I wire the ground lug on that to the 0v rail?
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Uncle Krunkus
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PostPosted: Mon May 05, 2008 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
Excellent, thank you! I don't quite understand why the impedence of the speaker has to be with 4, 8 or 16 Ohms though.

On the stripboard posted above, it doesn't have the input grounded at all. I'm going to be using a 1/4" jack, should I wire the ground lug on that to the 0v rail?


Yeah, that's fine.

Impedance is basically AC resistance. In this case the AC is the signal which is driving the speaker. If the designer of the circuit has specified 8 Ohms, then that impedance will limit the current going through the speaker to an amount which the 386 can safely deliver without burning out. Remember that the current going through the speaker (and therefore the amount of power (watts) which it will dissipate (and needs to be supplied by the 386)) is inversely proportional to it's impedance. So if 8 Ohms is optimal, 16 Ohms will only let half the current (wattage) through the speaker, and therefore, less volume. 4 Ohms will allow twice as much current (wattage (volume)) to be generated by the speaker, but that power has to be delivered by the 386. So, if you go beyond the 1W which the 386 is rated at, it will get really hot, and eventually will release it's special magic smoke. Without this smoke it will die! Laughing So we want to keep the smoke inside! Laughing

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LetterBeacon



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PostPosted: Tue May 06, 2008 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Right, so 8 Ohms will only let the 386 deliver its optimum current? The fact that my speakers says 6w on it means that that is the highest wattage the speaker can take, not how many watts it needs to work, right?

Thanks again for all your help!
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Blue Hell
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PostPosted: Tue May 06, 2008 12:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
The fact that my speakers says 6w on it means that that is the highest wattage the speaker can take, not how many watts it needs to work, right?


That's right.

To answer the question what impedance would deliver the highest possible output power would require some knowledge about the output impedance of the amplifier, you get best energy transfer when that value is equal to the impedance of the speaker.

Maybe someone can tell what the amp's output power is, it's too long ago for me I did such calculations to do it with ease Laughing

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asafnetzer



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PostPosted: Tue May 06, 2008 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't mean to hijack this thread but as people here already talking about Amps I didn't want to open a new one just for this question.
I have some old speakers 8Ohm 50w - 100w and I've thought about transform them into cheap monitors, Is there any way to drive them,
Did any of you build an Amp that can handle more, I have tried the ruby and it's nice but not powerful enough.
Thanks,
Asaf
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LetterBeacon



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PostPosted: Tue May 06, 2008 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right, I have built it and... er, nothing. I plugged a guitar in, whacked the pots up to full (put a battery in) and there's no sound coming from it!

The only thing I have changed from the stripboard posted above is a switch between the battery's + terminal and the board, and I ran a wire from the ground of the input jack to 9G on the board.

If I set my multiometer to 20K Ohms and put a leg into the input jack, and another on the + of the speaker I get a reading of 8.83. This is good right? This means that current can pass through from the input socket to the speaker. How do you recommend troubleshooting in more detail?

I'm still not entirel sure if my FET is the correct one. Would a kind soul be able to check that the one I mentioned in my first post is the correct one? I've read through the datasheet but I can't really tell!

Thanks a lot!
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asafnetzer



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PostPosted: Tue May 06, 2008 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon,
Regarding the FET's , both the 102 and 2N3819 look like right for the job but the pin placement is different according to their tech spec (If I understand it correctly)


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Uncle Krunkus
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PostPosted: Wed May 07, 2008 3:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Yep,
I agree, pinout is different. You'll need to swap the legs around.

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LetterBeacon



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PostPosted: Wed May 07, 2008 10:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for that guys. Hmmm, looks like I'll have to run wires from the board to the different pins. Should be do-able!
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Wild Zebra



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PostPosted: Wed May 07, 2008 10:53 am    Post subject: Reply with quote  Mark this post and the followings unread

These amps are great I've built three and counting great for guitar nice gain, great for my SL on camping trips. I put a line out also have used it with my fisher price record player powering two Kustom monitors for camping vinyl goodness. Enjoy you won't make just one, great project for all those tins laying around the thrift store.
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Wild Zebra



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PostPosted: Wed May 07, 2008 10:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
I found an 8ohm 0.5W speaker in a broken answerphone machine - get a little bit creative and you'll usually have some luck
Yes don't overthink the speaker too much. One of mine has a speaker from an alarm clock one has two from an old boombox radio (think I need to wire in series they might be parallel I get some squeal) and the other is another pish posh speaker I got in a box of electronics. Experiment with enclosures. My wood one sounds diferent from my metal one and different from the tiny tin one. etc, etc.
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LetterBeacon



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PostPosted: Wed May 07, 2008 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right, I've soldered some wires to the pins and put them into the correct holes on the stripboard (thanks for pointing that out!) and.... it's a synthesizer! It seems to be oscillating and, when I turn the volume and gain knobs the frequency it's oscillating at changes! It makes some pretty cool sounds, but it's not really what I want from an amp!

Is this because I have too much current going to the 386?

I'll have a proper investigation tomorrow when I have proper internet access (I'm typing this from my phone at the moment), but any input from you guys here will, as usual, be much appreciated!
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asafnetzer



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PostPosted: Thu May 08, 2008 2:05 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
and.... it's a synthesizer!


You see, after the WSG, what you really wanted was another Synth Very Happy

Have you tried to replace the FET with a new one ?

I took a look again at the tech specs, not really my field of understanding but it seems that some voltage values of the FET's are different.

If it's a problem with the FET and you don't have an access to the 102, I have some spares and can send you one, two, three... but thats it. Very Happy

Best regards,
Asaf
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LetterBeacon



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PostPosted: Thu May 08, 2008 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Heh, it does make some pretty cool noises!

I haven't replaced the FET, I merely soldered wires to the pins and wired them in their correct holes on the stripboard. Here's a picture of it (please ignore the rubbish soldering!):
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Thanks for your offer of sending me a spare FET. I think I'll try sourcing one from here in the UK first - it'll save you the bother of sending one over. That's very kind of you though!
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