RUBY AMP CIRCUIT (not turning on)

[bzblues]

Hi guys! its me again. The amp is awesome! sounds amazing for beeing such a small thing. I have a couple of questions:

1) I want to add a speaker out jack. I'd built a kit (picture attached) that has a speaker out and I added it to the ruby amp, but I only took the out wires that went to the speaker, solder them into the jack, and from the jack, another two wires to the speaker of the ruby but it didn't work. So, I know that I didn't solder the wire from the volume pot to the jack as the picture shows (I'll try that of course)

But what I don't understand is: if the signal "travels" from the circuit board to the speaker thru those two wires, why it doesn't work if the signal goes to the speaker out jack, and then I plug a guitar cable to another speaker cabinet with a 1/4 inch jack aswell?

2) Is there any way to increase the power of the amp ? it delivers 1/2 watt, but maybe there is a way. I've been researching, there are some cool mods, but only to modify the sound of the amp.

(Sorry about the messy drawings!)

Thanks!

 

[dr pepper]

I think you have something wired wrong, the circuit should be able to power an external speaker, so long as its impedance is suitable, ie no less than 4 ohms, however if you plugged a 1w amp into a big pa stack it might not do much, very long leads might also cause issues.
If you want more power then you'll probably need a different amp chip, maybe a tda2030 if you can still get them.
You can put outboard trannies on the Lm386 but its an indepth project, not reccomended.
But you'll need something other than a pp3 battery as it couldnt power a larger amp, maybe some 18650's or a drill battery.

 

[bzblues]

I think you have something wired wrong, the circuit should be able to power an external speaker, so long as its impedance is suitable, ie no less than 4 ohms, however if you plugged a 1w amp into a big pa stack it might not do much, very long leads might also cause issues.
If you want more power then you'll probably need a different amp chip, maybe a tda2030 if you can still get them.
But you'll need something other than a pp3 battery as it couldnt power a larger amp, maybe some 18650's or a drill battery.

Hello! Yes, I tried with a 6 ohm speaker and no sound came out of it. Maybe I need to wire something differente for it to work out.

I'll look up about different chips, and if I need more powerfull power supply.

 

[betwixt]

With a 6 Ohm speaker it would just be a little quieter but it would still work. I think you have the wiring to the loudspeaker socket wrong. When shown as a layout plan it isn't easy to see which pins on the socket are which. You should connect one side of the loudspeaker (black on the diagram) permanently to ground and only interrupt the red wire with the output socket. If you look closely at the socket as you insert a plug you will see the contacts bend back slightly, the ones that are in contact with the plug are the ones to go to the external loudspeaker and the red one to the internal speaker should be visibly disconnected as the contact to it opens.

Again, make sure you use a mono socket and a mono plug.

The small 9V battery will barely be able to supply enough to produce full output power, remember that to get power to the loudspeaker it has to come from somewhere so if you get 0.5W out you are drawing more than 0.5W in as some power is lost in the internal circuitry. I note you also have '100 Ohm' as the resistor value in series with the LED. This wastes quite a lot of battery power, about 70mA which is more than the LM386 consumes! I would increase its value to 1K ohms, it won't be quite as bright but it will make the battery last much longer and probably help to make the amp louder.

Brian.

 

[bzblues]

With a 6 Ohm speaker it would just be a little quieter but it would still work. I think you have the wiring to the loudspeaker socket wrong. When shown as a layout plan it isn't easy to see which pins on the socket are which. You should connect one side of the loudspeaker (black on the diagram) permanently to ground and only interrupt the red wire with the output socket. If you look closely at the socket as you insert a plug you will see the contacts bend back slightly, the ones that are in contact with the plug are the ones to go to the external loudspeaker and the red one to the internal speaker should be visibly disconnected as the contact to it opens.

Again, make sure you use a mono socket and a mono plug.

The small 9V battery will barely be able to supply enough to produce full output power, remember that to get power to the loudspeaker it has to come from somewhere so if you get 0.5W out you are drawing more than 0.5W in as some power is lost in the internal circuitry. I note you also have '100 Ohm' as the resistor value in series with the LED. This wastes quite a lot of battery power, about 70mA which is more than the LM386 consumes! I would increase its value to 1K ohms, it won't be quite as bright but it will make the battery last much longer and probably help to make the amp louder.

Brian.

Hi Brian, yes, I had the wires the wrong way around. Now its working propperly. I've been reading that, to get more power I should try different Op amp chips. Thank you for the advice on the LED resistor, I'll change it to get more battery life.

Cheers!

 

[Audioguru]

Is the Full Fat stripboard circuit your new kit? It has some differences and errors:
1) Why does it have a 470 ohm rheostat in series with the speaker and speaker jack?
2) Why is there a switch and a 47nF capacitor connected from pin5 to pin7 of the 386 amplifier?
Please post its schematic because some of the parts block where they are connected.

Increase the power? Sure, replace the low power 386 amplifier with a more powerful one and maybe a higher voltage and higher current battery.

 

[bzblues]

Is the Full Fat stripboard circuit your new kit? It has some differences and errors:
1) Why does it have a 470 ohm rheostat in series with the speaker and speaker jack?
2) Why is there a switch and a 47nF capacitor connected from pin5 to pin7 of the 386 amplifier?
Please post its schematic because some of the parts block where they are connected.

Increase the power? Sure, replace the low power 386 amplifier with a more powerful one and maybe a higher voltage and higher current battery.

Hi! The Full Fat is a kit that I bought a few months ago. The problem with that one was that the volume pot (470 ohm) behave strangely. As you start to turn the volume up the signal was really low volume, then in the last quarter turn the volume steep up exponentially. I talked to the seller and he didn't know how to fix that problem, so I shelve it. Any ideas why this happen?

About the switch, its for selecting a more "aggressive" grit distorsion if I'm not wrong. Here is all what I could found, hes website is no longer available:

https://mylkstuff.tumblr.com%2Fpost%2F82193722145

The Ruby amp works perfect!

 

[betwixt]

For example:

3 Watts per channel Stereo (the board, not my finger). The only drawback is you can't operate it in bridge mode to get 9W but you can link the L and R inputs together and drive two separate loudspeakers at 3W each or just ground one input and ignore its output for a single 3W amplifier.

Brian.

 

[Audioguru]

I've been reading that, to get more power I should try different Op amp chips.

No. An opamp produces a very low output power and cannot drive a speaker. You need a power amp chip instead.

The LM386 little amplifier was designed to use a 9V supply and produce an output of 0.5W into an 8 ohm speaker for kids toys and clock radios.
Since the sensitivity of our hearing is logarithmic, not linear then 10 times the power sounds twice as loud.

The volume control is supposed to be at the input of an amplifier, not at the output.
Above I explained that our hearing is logarithmic which is why an input volume control is a log or audio type.
The "volume control" at the output operates strangely because you used the wrong type. It should be a reverse log type but the article wrongly says "audio" type.

--- Updated Nov 16, 2020 ---

3 Watts per channel Stereo (the board, not my finger). The only drawback is you can't operate it in bridge mode to get 9W but you can link the L and R inputs together and drive two separate loudspeakers at 3W each or just ground one input and ignore its output for a single 3W amplifier.

The PAM8403 amplifier IC already has the output of each channel "bridged" which is why it produces 3W per channel into 4 ohms when its supply is only 5V.
3W into 4 ohms which is produced by 3.46V RMS which is 9.79V peak-to peak. Then each half of a bridged amplifier produces half of the 9.79V which is 4.98V and is slightly less than the 5V the supply voltage.
You cannot bridge amplifier channels that are already bridged.

 

[betwixt]

Isn't that what I wrote ?

Brian.

 

[dr pepper]

I wonder if the rheostat is there so you can overdrive the amp into distortion but keep the sound level down so's not to annoy next door.
I have a coupleof those pam switching amps, they are not so bad for what they are/cost, but I suggest you get a 10w or so amplifier if the little '386 isnt loud enough.

 

[bzblues]

I wonder if the rheostat is there so you can overdrive the amp into distortion but keep the sound level down so's not to annoy next door.
I have a coupleof those pam switching amps, they are not so bad for what they are/cost, but I suggest you get a 10w or so amplifier if the little '386 isnt loud enough.

actually I purchased a 10W kit aswell and put it together. On its own it sound veeery low volume, but when you use pedals with it, it rips. I don't understand why that happens.

 

[dr pepper]

Because of the gain otherwise known as sensitivity, for the '386 to give full wack it might only need 100mv of signal, 'proper' power amps need more in the order of 1v depending whether its classed as domestic or 'pro'.
Effects pedals can give you the required increase in signal.
You could put a pre amp before the amplifier, but if you get what you need with effects doesnt sound like you need to.

 

[Audioguru]

A pedal adds a lot of voltage gain so that the amplifier produces massive full power clipping distortion.

 

[bzblues]

Hello everyone! its me again! Well, I must tell you, I've been practicing and I've built a few of these ruby amps and I'm learning quite a few things!

I'm using an 1980s telephone that comes with a built in speaker that was used as a speaker phone. The problem is that it distorts and rattles weirdly when the volume goes up. I'd checked everything to see if there where parts of the phone chassis that where loose, but everything is held together really tight, so I'm gueessing that the small speaker is the one that is causing all the trouble. Its a 3.5 inch, 2W 8 ohm speaker.

Maybe I should add a component to the circuit that allows the speaker to work better with the signal. Any thoughts?

Thank you!

 

[dr pepper]

I spose the thing to do is find if the noise is something up with the speaker, or the amps just run out of power, a little '386 cant raise the roof.
If the amp is clipping theres not much you can do 'cept go for a bigger amp, you can tell clipping by playing a note without effects, crahnk up the volume at the onset of clipping other notes will appear, 3 octaves higher and above.
The lm384 makes 5w, its a bit like the '386 but has more pins, a pp3 9v battery will not power it though, you'd need a stack of AA's.

 

[bzblues]

I spose the thing to do is find if the noise is something up with the speaker, or the amps just run out of power, a little '386 cant raise the roof.
If the amp is clipping theres not much you can do 'cept go for a bigger amp, you can tell clipping by playing a note without effects, crahnk up the volume at the onset of clipping other notes will appear, 3 octaves higher and above.
The lm384 makes 5w, its a bit like the '386 but has more pins, a pp3 9v battery will not power it though, you'd need a stack of AA's.

It is the speaker. I've built 4 of these amps with the same telephone speaker and the problem is exactly the same, also I've built a ruby amp with a propper guitar amp speaker and works perfect. Maybe if I increase the resistance of the small telephone speaker by adding a resistor, but with 8 ohm it should be enough, right ? Or adding the resistor to the input .

 

[bzblues]

Ok, I'd put FIVE! 1M resistors in series and, it work just a little, but still, the rattleing continues altough a quite less. I guess that I should try another speaker bucause this one doesn't deliver the goods. Do you guys have another alternative?

Thanks!

 

[Audioguru]

A speakerphone is designed to play voices when it is close and directly in front of you. Then its power in the speaker is only 0.1W for the loudest peaks.
So it has a cheap speaker that works poorly above 0.1W which is not much power.
Guess why a guitar speaker is not a cheap one from a phone?

The Ruby amplifier produces almost 0.5W into an 8 ohm speaker when the battery is brand new.
A speaker needs to be mounted in an enclosure designed for it to prevent bad sounds.
Have you tried using a computer desktop speaker? My computer speakers sound pretty good and play about 2W each. They are properly enclosed.

 

[bzblues]

A speakerphone is designed to play voices when it is close and directly in front of you. Then its power in the speaker is only 0.1W for the loudest peaks.
So it has a cheap speaker that works poorly above 0.1W which is not much power.
Guess why a guitar speaker is not a cheap one from a phone?

The Ruby amplifier produces almost 0.5W into an 8 ohm speaker when the battery is brand new.
A speaker needs to be mounted in an enclosure designed for it to prevent bad sounds.
Have you tried using a computer desktop speaker? My computer speakers sound pretty good and play about 2W each. They are properly enclosed.

But this speaker is 2W and 8ohm, so I don't quite understand why its not working good enough if the amp delivers 0.5W at its max...or 2W is an estimate number and the real one is lower?