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Another newbie with problems with his Ruby :(

Started by Jimmy_, October 01, 2011, 07:02:18 PM

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Jimmy_

October 01, 2011, 07:02:18 PM Last Edit: October 01, 2011, 07:04:24 PM by Jimmy_
Hi!

Yesterday I tried to make myself a Ruby amp so I could still practise the bass while I'm at uni. I thought the soldering went quite well, after a full night, and a large part of a day, I have been unable to get it to work correctly...

I've just read through the debugging sticky, so I'll try to include all the relevant information below  :P

To re-iterate, the project is a Ruby amp, but with several modifications. Since I have a bass guitar, I added the Bassman mods specified on the RunoffGroove website. I used a larger, 470nF capacitor connected to the source pin of my FET to improve the bass, apparently. I used a 2N5457 instead of an MPF102 because that's all the website I ordered my parts from had, and they seem to be interchangeable, looking at the pinouts. This amp does not have a speaker, only a headphone jack. I saw a modified schematic where a second input had been added for an iPod, so I copied it exactly.  :icon_razz: I added another input so I could listen to my phone as well as my bass. I added a switch, an LED and a resistor, too!  ;D

I used VeeCAD to make a stripboard layout based on the modified schematic (knowing me, I've made a big mistake somewhere), and using that I soldered everything to the stripboard.

But what's wrong with it?! - When I turn on the amp, I get the familiar hum of an amp, this is expected. (Aside: When I connect my phone to the second input, I can hear it through my headphones, but it's quite quiet, even with the phone volume on max. I imagine it's to do with the resistors but I don't want to fiddle with that yet). I cannot hear my bass (or my electric guitar, for that matter), unless I connect the tip wire to pin 1 of the LM386(N-1). I tried connecting it to where it's supposed to go, to various points beyond the FET's source pin, all the way to directly touching pin 2 of the IC, to no avail. But when I touch the tip wire to pin 1, I can hear the bass beautifully, and I have no idea why!

Schematic:


Adding another jack for an iPod (I can't remember where I found this picture, unfortunately!):


Stripboard layout:


Everything soldered:
http://i.imgur.com/zRK6o.jpg
Sorry for the blurriness!

The copper side:

Right hand side is the left hand side of the stripboard layout image :-\ I know it looks pretty messy near the top, but I've tried to make sure there's nothing bridging the tracks there!

All images in one album

Multimeter readings:
+: 9.16V
-: 0V

2N5457:

  • D: 9.16V
  • S: 1.16V
  • G: 0V

LM386N-1

  • 1: 1.32V
  • 2: 0V
  • 3: 0V
  • 4: 0V
  • 5: 4.55V
  • 6: 9.16V
  • 7: 4.58V
  • 8: 1.32V

I would really, really appreciate any help with this, as I'd love to have an amp to practise with, and I'd like to actually complete a project of mine, for once! I'm moving back in tomorrow, but I'm going to take all my parts and the board with me, so I can work on it during the week.

Thanks in advance,
Jimmy_

P.S.  :icon_cry:

Jimmy_

#1
October 01, 2011, 09:05:50 PM
I flipped the VeeCAD drawing and laid it over the scan of the copper side of my board  :icon_cool:

PRR

#2
October 01, 2011, 11:46:12 PM
Disconnect everything from Pin 2, get that working, and add-back frills one by one.
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Jimmy_

#3
October 03, 2011, 05:16:16 PM Last Edit: October 03, 2011, 05:49:51 PM by Jimmy_
Quote from: PRR on October 01, 2011, 11:46:12 PM
Disconnect everything from Pin 2, get that working, and add-back frills one by one.
Good evening, PRR!  ;D

I have just disconnected the links that connect the second input to pin 2. I also unplugged the LED. After putting a jumper between the 1st and 2nd sockets where the volume pot would go, and turning the amp on, it worked! It totally worked!  ;D I then plugged the LED back in, everything was fine.

But then I took out the jumper wire that replaced the pot, and I could still hear my bass. This suggests to me that signal is still getting to pin 2, either via the 1M5 resistor, or the 3K9, i.e. one of the breaks isn't working  :-\ - I will check them now.

Thanks for your help!

Jimmy_

#4
October 03, 2011, 05:48:59 PM
Actually, I think I can hear it with no pot because the signal gets to pin 2 via the transistor, C3, then R4

Jimmy_

#5
October 03, 2011, 06:23:42 PM
When I reconnect even one of the links (for the second input), I can no longer hear the bass. Strange.

Would they need to be replaced with... diodes perhaps? I don't know.  :-[

Gurner

#6
October 03, 2011, 06:59:05 PM Last Edit: October 03, 2011, 07:05:41 PM by Gurner
C2 & VR1 form a  high pass filter with the corner frequency being 338.8Hz (meaning - if you're playing bass - there ain't much signal gonna get through to your LM386 pin2)

Change the value of C2 to 10uf...that takes HPF filter corner frequency down to 15.2Hz (while you're doing this, I'd be inclined to disconnect C3 totally too)

edit ...oops my bad, your corner frequency with your actual components shown is 33.9Hz - (ahem, dodgy finger on my calculator!).... this would be the point where an audio probe would be useful, but failing that some DC levels in and around Q1.

Jimmy_

#7
October 03, 2011, 08:24:56 PM
Quote from: Gurner on October 03, 2011, 06:59:05 PM
C2 & VR1 form a  high pass filter with the corner frequency being 338.8Hz (meaning - if you're playing bass - there ain't much signal gonna get through to your LM386 pin2)

Change the value of C2 to 10uf...that takes HPF filter corner frequency down to 15.2Hz (while you're doing this, I'd be inclined to disconnect C3 totally too)

edit ...oops my bad, your corner frequency with your actual components shown is 33.9Hz - (ahem, dodgy finger on my calculator!).... this would be the point where an audio probe would be useful, but failing that some DC levels in and around Q1.
Hi, I forgot to mention that I'm using a 22K VR now, this should give me a corner frequency of 15.4 Hz, which should be low enough for even a B string, shouldn't it?  :icon_redface:

And the amp actually works now, but only when I disconnect the links from R5 and R6. I'm going to check my stripboard *again* for any shorts, because I don't understand why these links stop the sound  ???

iccaros

#8
October 03, 2011, 10:22:47 PM
is tip and ring shorted on your jack?

Jimmy_

#9
October 03, 2011, 10:36:17 PM
An update: I ran a scissor blade between the tracks around R5/6, then reconnected the problematic links. Everything's working beautifully now  ;D

I can listen to Learning To Live and play along  :icon_smile:

Thanks for your help guys  :icon_wink:

P.S. Just need to get a nice box for it now  :icon_razz:

Jimmy_

#10
October 03, 2011, 11:23:02 PM
Quote from: Gurner on October 03, 2011, 06:59:05 PM
...(while you're doing this, I'd be inclined to disconnect C3 totally too)
Before I go to bed, I was wondering what C3 actually did? It was mentioned in the Bassman mod on the RunoffGroove website.

PRR

#11
October 03, 2011, 11:45:41 PM
> I was wondering what C3 actually did?

In this case: nothing. 220pFd against a 10K pot (2.5K mid-point) only "does something" above 303KHz, 4 octaves above human hearing.

The cap-value is taken from pots of 1Meg value where 220pFd makes a difference at 3KHz.
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Jimmy_

#12
October 04, 2011, 06:34:39 PM
Quote from: PRR on October 03, 2011, 11:45:41 PM
> I was wondering what C3 actually did?

In this case: nothing. 220pFd against a 10K pot (2.5K mid-point) only "does something" above 303KHz, 4 octaves above human hearing.

The cap-value is taken from pots of 1Meg value where 220pFd makes a difference at 3KHz.
I see... would you advise I remove it from my board , or just leave it there?  :icon_redface:
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