Ruby amp not working, help needed pls

[hotdiggity]

Haven't been able to get Ruby Amp (http://www.runoffgroove.com/ruby.html) to work using veroboard. I've checked everything numerous times, made corrections to some stupid errors, and have replaced the transistor and IC just to be sure. No short circuits as far as I can tell. Can't see anything further.


(Note, transistor around the wrong way in this diagram, well at least for a TO-92 package)



Turned on, with volume up to max, I can hear a quiet hiss in the speaker with no change in volume when I rotate the pot. When I turn the gain pot there is a difference in volume. No guitar amplification when plugged in.

In terms of voltages:

Main voltage: 8.48V
Speaker: 2W 4 OHM Sammi

MPF102:
1 D - 8.48V
2 S - 1.27V
3 G - 0V

386:
1 - 1.32V
2 - 0V
3 - 0V
4 - 0V
5 - 3.95V
6 - 8.46V
7 - 4.27
8 - 1.31V

The only other option I have now with my limited skills would be to rebuild it from scratch. Any ideas out there please?

[Govmnt_Lacky]

Just a heads up.... current draw with this circuit increases DRAMATICALLY when you increase gain and volume. It can go up to 200 to 225mA 

Try plugging in a wall wart with a 300mA+ current rating and see what you got. 

[deadastronaut]

you have input to ground...and input . pin 3 and ground again....input should be pin 2 as well.....

i'd redesign it..


or


http://media.photobucket.com/image/ruby%20amp%20vero/grievousangelphotos/th_ROGRuby.gif?t=1287992406

[Govmnt_Lacky]

you have input to ground...and input . pin 3 and ground again....input should be pin 2 as well.....

HUH? 

I don't see what you are saying Rob. He has the input (Pin 2 of the 386) going directly to Lug 2 of the Volume pot as required IAW the runoffgroove schemo.

Pin 3 is tied to ground IAW the schemo as well.

HUH? 

[deadastronaut]

ok,.headslap 

sorry i'll slap myself again....just ignore me .

[PRR]

> quiet hiss in the speaker with no change in volume when I rotate the pot. When I turn the gain pot there is a difference in volume.

It's working from volume pot to speaker.

All DC voltages are reasonable.

My dime says your input jack wiring isn't right. Check that again.

Still no go? Disconnect Vol2 wire. Connect gitar jack, tip to stripboard i1, sleeve to j1. Touch the jack's tip-finger. It should BUZZ. Connect guitar. It may be mellow and lame, but you shoud hear guitar.

> current draw with this circuit increases DRAMATICALLY when you increase gain and volume.

Only with big signal and load.

Turning-up the volume, yes, does add "signal", the quiet hiss he reports. But since it IS quiet and thus weak, it is teeny power and teeny current demand.

[hotdiggity]

Thanks guys. After your suggestions didn't work I checked the soldering (again) for short circuits and found a almost invisible splash of solder shorting rows I & J, right at the very end!

deadastronaut - like the compactness of your circuit. What app are you using there the create veroboard circuits?


PS. How great is the sound of this amp?!

[hotdiggity]

PPS My wife just told me the picture on our digital telly breaks up when I'm using the amp (no mains power supply, just battery for testing). Said the effect looks like a rock video clip!

[Govmnt_Lacky]

Thanks guys. After your suggestions didn't work I checked the soldering (again) for short circuits and found a almost invisible splash of solder shorting rows I & J, right at the very end!

deadastronaut - like the compactness of your circuit. What app are you using there the create veroboard circuits?


PS. How great is the sound of this amp?!

Judging by your question.... I am guessing that your repair of the "almost invisible" solder run DID NOT fix the problem  

EDIT: Posted the same time as above.

[deadastronaut]

Thanks guys. After your suggestions didn't work I checked the soldering (again) for short circuits and found a almost invisible splash of solder shorting rows I & J, right at the very end!

deadastronaut - like the compactness of your circuit. What app are you using there the create veroboard circuits?


PS. How great is the sound of this amp?!

its not my layout...but i use version 3 of diylc...its much better...but not compatible with version 1 files...yet!...download it!..

never built it!..but have messed with the 386 a lot!..

[Gurner]

To help establish the source of the problem...inject an audio signal into pin 2 on the LM386 & see what audible results you get.

Most audio equipt has a low output impedance & can be used for the purpose of generating a signal to use here ....an old transistor radio headphone socket, an old walkman, PC soundcard line out etc (your headpnoe socket to circuit ground, the hot wire to pin 2).....sure the end result might sound distorted, but it'll prove whether your LM386 is pumping blood or not (when you don't know where the fault might lay - &/or you've checked the obvious - a 'split half' technique/approach is as good a place to start as any...and that's what I'm advocating here...essentially ruling out the first half of the circuit to see if the second half appears to be working)

[iccaros]

PPS My wife just told me the picture on our digital telly breaks up when I'm using the amp (no mains power supply, just battery for testing). Said the effect looks like a rock video clip!

I would have your TV checked out.. there is no reason a Analog amp connected to battery would mess with a digital television, even as a radio transmitter, unless its putting out UHF sidebands..

If it is transmitting, look at at CAP and resistor on the output.. together they can create an antennae

[Gurner]

I would have your TV checked out.. there is no reason a Analog amp connected to battery would mess with a digital television, even as a radio transmitter, unless its putting out UHF sidebands..

The other option is to sell the present iteration as an effect to a company who makes rock group videos.

[hotdiggity]

If it is transmitting, look at at CAP and resistor on the output.. together they can create an antennae

Wouldn't I need something that didn't create an antenna or cancelled the effects of transmission? If that's what you mean, what CAP and resistor would you recommend?

Could there be something wrong with the guitar, or is it acting like a big antenna?

(Is it possible to edit posts on this forum - can't see a link?)

[iccaros]

If it is transmitting, look at at CAP and resistor on the output.. together they can create an antennae

Wouldn't I need something that didn't create an antenna or cancelled the effects of transmission? If that's what you mean, what CAP and resistor would you recommend?

Could there be something wrong with the guitar, or is it acting like a big antenna?

(Is it possible to edit posts on this forum - can't see a link?)

You are saying that it is transmitting, nothing in the guitar is strong enough to interrupt the TV unless its sitting on the TV
So from the amp is a 220 uf decouple cap, and a resistor to ground, I would check that they are good, no bad joints, and they have good connection to the speaker.. a bad solder joint can cause audio waves to become like radio waves, and if they are at a resident frequency, effect things on a higher band when close enough, like your TV.


or as Gurner said, sell it off as a TV effect.. Make millions and by an amp

[PRR]

> like the compactness of your circuit.
> the picture on our digital telly breaks up when I'm using the amp

The '386, like any high-gain "audio" amplifier, MUST be built tight and neat or it will find ways to oscillate, often outside the audio band, and sometimes well into the radio/TV bands.

'386 should also have 10 ohms and 0.05u (or so) across the output to damp supersonics. See datasheet. Yes, people often omit it, and often have no trouble.

Other signs of oscillation are excess heat and hiss.

Still, an oscillating '386 will usually "play".

There is a "Modify" button on your own posts for only about an hour. This forum does not want you changing the past.