Ruby Amp problems

[Govmnt_Lacky]

I built a rather nice little Ruby Amp and I am experiencing two issues with it that I need help with:

Link: http://www.generalguitargadgets.com/projects/13-amps/61-ruby-amp

I am using an LM386N-4 IC and I installed the Heaphone jack mod w/ Zobel network. Also, I used a 1K trim pot on the PCB for the Gain.

1) I have a wall wart for it that puts out 17VDC. I want ot use THIS wall wart with the amp BUT.... it hums like nobody's buisness. Is there a way to get rid of the hum with a simple filter across the DC jack? If so, how would I go about it and what values should I use?

2) I wired the project so that V+ is constantly on the circuit BUT, the ground from the DC jack is fed to a DPDT in order to be able to control power on/off to the Ruby AND a power lamp (12V Gem lamp). When the wall wart is installed and power is OFF of the circuit, I get a "motor boating rattle" out of the speaker & headphone jack when the Volume pot is turned DOWN. Once I turn the Volume pot above 10 o'clock, the rattling stops. Any ideas?

Thanks for the help 

[thedefog]

Sounds like a ground loop or grounding issue. If it isn't already set up with a star ground, I 'd redo it that way. That'll probably get rid of your hum issue as well. What sort of an enclosure are you using for it?

[Gurner]

I'd hazard a guess your 17V is unregulated & has a lot of ripple....ripple feeds into your signal chain....ending up as amplified hum.

To grt rid of the hum, you need to look at the power rail - preferably get a decent supply in the first place, or add a regulator & a good bit of capacitance to your existing one ....consider a low pass filter between the LM386 power pin & your fet supply rail.

[Govmnt_Lacky]

I'd hazard a guess your 17V is unregulated & has a lot of ripple....ripple feeds into your signal chain....ending up as amplified hum.

I pretty much figured that the PS was unregulated and was causing, if not contributing to, the hum. I was just wondering if I could save the money and install a cap or cap + resistor to try to get rid of it.

Does anyone know if the 12V wall wart at Small Bear is regulated?

http://www.smallbearelec.com/Detail.bok?no=1006

Does anyone have any ideas on the motorboating sound through the speaker/headphone jack when the Volume pot is turned down between 0 and 20%??

[Govmnt_Lacky]

OK. I fixed the hum problem by testing with a 12V and 9V DC regulated PS.

I fried my 386 chip due to an improper setup of the DC PS  however, after replacing the MPF102 and 386 chip, it produced sound again.

I am STILL getting the motorboat clicking when the Volume pot is turned down. According to the DC PS, when the pot is turned down, there is an amperage reading of 0.003 to 0.010 alternating with the clicking.

Is this inherant with the Ruby? Should I just insert a 1K resistor between Ground and Lug 1 of the pot so it never gets to absolute 0 ohms?

I am stumped on this one 

[Tony Forestiere]

Cobble two 9 volt batteries in series for 18 volts for testing purposes?

[Govmnt_Lacky]

OK.... now I am getting preturbed!!! 

I checked the amp at my work with a regulated 9V input, and I injected a 440Hz sine at 80mV and it was working NO PROBLEM.

I got the amp home and plugged in my 9V unregulated wall wart (output = about 14V) and I got NOTHING!

I then used my regulated 9V pedal board PS and I got NOTHING!

I don't know WHAT happened but, something caused this amp not to work between work and home.The ONLY thing I can think of is either 1) using the unreg PS did something OR 2) I fried yet another 386 chip and it was a bad batch (see earlier post)

I built off of the GGG Ruby Amp layout with Gain trim pot:

http://www.generalguitargadgets.com/projects/13-amps/61-ruby-amp

I built the circuit to the layout with the Headphone jack and Zobel network with the following changes:

I ran input power DIRECTLY to the circuit board and on/off lamp. I then ran ground from the DC jack to a DPDT switch in order to control the ground line going to both the power lamp AND the circuit. I also ran the output audio to a DPDT switch and ran one side to the speaker and the other to the headphone jack to switch between the two.

Here are my voltages on the non-working unit. Input voltage is regulated 9.0V

MPF102:
D - 9.0V
S - 2.7V
G - 2.9V

386:
1 - 2.7V
2 - 2.6V
3 - 0V
4 - 0V
5 - 8.8V
6 - 9.0V
7 - Goes down from 5V to 1V as I let the meter stay on it to stabalize
8 - 2.7V

These were taken with the volume knob at MAX and the Gain trimmer set to the previous WORKING setting.

Any help is appreciated.

Thanks 

[Govmnt_Lacky]

Fresh, morning eyed BUMP! 

[jefe]

2) I wired the project so that V+ is constantly on the circuit BUT, the ground from the DC jack is fed to a DPDT in order to be able to control power on/off to the Ruby AND a power lamp (12V Gem lamp). When the wall wart is installed and power is OFF of the circuit, I get a "motor boating rattle" out of the speaker & headphone jack when the Volume pot is turned DOWN. Once I turn the Volume pot above 10 o'clock, the rattling stops. Any ideas?

Thanks for the help 

This seems like an odd way to wire the power, but I can't quite put my finger on it at the moment. My morning coffee hasn't fully kicked in yet.

[Gurner]

I'd say your 386 is screwed ....pin 5 should be about 1/2 your power supply (therefore 4.5V)...pin 2 should be virtually sitting at ground potential.

What do you get on pin 2 with the 386 removed?

[Govmnt_Lacky]

I'd say your 386 is screwed ....pin 5 should be about 1/2 your power supply (therefore 4.5V)...pin 2 should be virtually sitting at ground potential.
What do you get on pin 2 with the 386 removed?

I will post back later about voltages with the pins removed however, the voltage on Pin 2 of the 386 changes with the Volume knob. At max volume, the voltage sits at 2.6. At min volume it goes to 0.

This seems like an odd way to wire the power, but I can't quite put my finger on it at the moment. My morning coffee hasn't fully kicked in yet.

I know how you feel. I am useless in the mornings until I get my morning cup of coffee 

The basic layout ay GGG/ROG looks like there is power on the circuit AS SOON AS you insert the battery/DC power plug. So, essentially you are using the DC power jack as a power on/off switch CORRECT?
By wiring it my way, I have moved that on/off switching to a DPDT. One pole sends the ground to the circuit. The other pole sends it to the Gem light.
I do plan on rewiring my grounds (star grounding with the DC jack ground going directly to the DPDT and  the rest going to the circuit board ground rail)

This "would be" the secong LM386-4 chip that I have fried and I have no idea why  The circuit WORKS but it seems like it intermittently fails. I had it running on 9V regulated for 20 minutes yesterday. Then I packed it up and took it home and it QUIT on me!

[jefe]

The basic layout ay GGG/ROG looks like there is power on the circuit AS SOON AS you insert the battery/DC power plug. So, essentially you are using the DC power jack as a power on/off switch CORRECT?
By wiring it my way, I have moved that on/off switching to a DPDT. One pole sends the ground to the circuit. The other pole sends it to the Gem light.
I do plan on rewiring my grounds (star grounding with the DC jack ground going directly to the DPDT and  the rest going to the circuit board ground rail)

I don't think that's how I wired mine. I used a toggle switch, but I didn't wire it so that the board always has power. I'll have to look at it tonight.

[Govmnt_Lacky]

I don't think that's how I wired mine. I used a toggle switch, but I didn't wire it so that the board always has power. I'll have to look at it tonight.

Are you thinking that I should use the DPDT to control the flow of V+.... INSTEAD of V- ??

Basically run the 9V from the DC jack to the DPDT, then just star ground ALL of the grounds (DC jack ground included)??

[thedefog]

I don't think that's how I wired mine. I used a toggle switch, but I didn't wire it so that the board always has power. I'll have to look at it tonight.

Are you thinking that I should use the DPDT to control the flow of V+.... INSTEAD of V- ??

Basically run the 9V from the DC jack to the DPDT, then just star ground ALL of the grounds (DC jack ground included)??

Yep, that should do it.

[Govmnt_Lacky]

I don't think that's how I wired mine. I used a toggle switch, but I didn't wire it so that the board always has power. I'll have to look at it tonight.

Are you thinking that I should use the DPDT to control the flow of V+.... INSTEAD of V- ??

Basically run the 9V from the DC jack to the DPDT, then just star ground ALL of the grounds (DC jack ground included)??

Yep, that should do it.

I will do the rewire tonight and post back on it tomorrow.

Thanks all for the help. Fingers crossed.... hopefully this will do it. 

[jefe]

I don't think that's how I wired mine. I used a toggle switch, but I didn't wire it so that the board always has power. I'll have to look at it tonight.

Are you thinking that I should use the DPDT to control the flow of V+.... INSTEAD of V- ??

Basically run the 9V from the DC jack to the DPDT, then just star ground ALL of the grounds (DC jack ground included)??

I'm 90% sure that's how I did it.

[Govmnt_Lacky]

Any chance that this will solve my ticking issue when the Volume pot is turned down?

[Govmnt_Lacky]

I replaced the 386 and the MPF102.

More importantly, I star grounded to the circuit board AND I switched the DPDT to control V+ instead of V-.

Now, the amp sounds SWEET and the motorboating on the Volume pot is GONE! 

Now, I need to run another power wire from the DC jack to the power DPDT. As it is wired now, I have one wire from the DC jack across BOTH center poles of the switch to feed the circuit AND the Gem lamp (power on/off lamp).

It works BUT.... whenever I strum a note or chord, the Gem light dims due to power drain.