Ruby 1/2W Amp and External Music Source

[texstrat]

Reading back on some of the ROG Ruby Amp threads, has anyone come up with a way to plug-in an Ipod/MP3/CD player so that you have background music to play over while using headphones or a speaker without going through a mixer?

If possible, I would like to fit all of this in an enclosure, including battery, so that it is portable and would fit in a Hammond 125B enclosure.

[davent]

Knew exactly what i was looking for but still took a lot of searching to find this thread again.

http://www.diystompboxes.com/smfforum/index.php?topic=85055.0

[deadastronaut]

i knocked up a layout incorporating the (linked) mp3 in, and GGG headphone/speaker out

does this look ok?...(didn't have a symbol for jacks.. ...if it looks fine, i'll upload the layout/pcb pdf's if anyone wants those..

[texstrat]

Very cool guys.

Correct me if I am wrong, but isn't the source, Ipod/CD, a line level source? How would you control the volume so that the source doesn't bury your guitar playing?

Thanks.

[davent]

Very cool guys.

Correct me if I am wrong, but isn't the source, Ipod/CD, a line level source? How would you control the volume so that the source doesn't bury your guitar playing?

Thanks.

Use the headphone rather then line output of your ipod, that should give you the control you need.

[texstrat]

Very cool guys.

Correct me if I am wrong, but isn't the source, Ipod/CD, a line level source? How would you control the volume so that the source doesn't bury your guitar playing?

Thanks.

Use the headphone rather then line output of your ipod, that should give you the control you need.

Dave:

Maybe I missed your point about the headphone, my Ipod has one 1/8" jack. After I posted my second reply, I figured that I could control the volume via the Ipod volume control.

Thanks.

[davent]

You can get an adapter that plugs into your ipod's docking port(?) that gives you a lineout, better fidelity available then the headphone output but, it's not affected by the volume control. I bought a couple on ebay for around $5.

http://beavishifi.com/articles/headphonejack/

[texstrat]

Man, I love Dano's site, of course this site as well

One other issue that I have not been able to run down, is when the amp is used as a pre-amp, I pick up a faint radio station. The amp is housed in a plastic case and I was wondering if the aluminized tape, used for duct work, would resolve the radio station issue. Or I thought I read that a R/C combo would rid the amp from picking up strange radio stations.

[texstrat]

i knocked up a layout incorporating the (linked) mp3 in, and GGG headphone/speaker out

does this look ok?...(didn't have a symbol for jacks.. ...if it looks fine, i'll upload the layout/pcb pdf's if anyone wants those..

I am using runoffgrooves pcb and it differs slightly from the above schematic to include the Ipod/MP3 input. Looking at the PCB layout, http://www.runoffgroove.com/ruby-pcb.pdf, do I solder the 22K resistors on the trace between IC pin 2 and Volume lug 2?

I just want to verify before I start messing with the PCB.

Thanks.

[davent]

i knocked up a layout incorporating the (linked) mp3 in, and GGG headphone/speaker out

does this look ok?...(didn't have a symbol for jacks.. ...if it looks fine, i'll upload the layout/pcb pdf's if anyone wants those..

I am using runoffgrooves pcb and it differs slightly from the above schematic to include the Ipod/MP3 input. Looking at the PCB layout, http://www.runoffgroove.com/ruby-pcb.pdf, do I solder the 22K resistors on the trace between IC pin 2 and Volume lug 2?

I just want to verify before I start messing with the PCB.

Thanks.

Yes!... but also according to Paul's schematic you need to add a 3k9 resistor between the wiper of the pot and pin2 of the LM386 so you end up with the three resistors attached to that trace on the ROG pcb.

dave

[teemuk]

If you are relying on overdriving the LM386 chip then you most definitely do not want to have the auxiliary input feeding that amp too.

You need to mix the auxiliary input post LM386, which practically goes down to ...yes.. using a "mixer" for the LM386 output and auxiliary input and then feeding the mixer's output to another amp for headphones/speakers.

How to integrate a mixer to Ruby has been more or less covered already and it practically involves building the mixer stage + another LM386 power amp (and possibly a third LM386 power amp if you want to enjoy stereo sounds) but is it really worth the bother? Rather than building two back-to-back amps I'd rather get a cheap mixer with headphone output and plug the Ruby straight to that. There's far more usage for a simple mixer than for a Ruby with an auxiliary input.

[texstrat]

If you are relying on overdriving the LM386 chip then you most definitely do not want to have the auxiliary input feeding that amp too.

You need to mix the auxiliary input post LM386, which practically goes down to ...yes.. using a "mixer" for the LM386 output and auxiliary input and then feeding the mixer's output to another amp for headphones/speakers.

How to integrate a mixer to Ruby has been more or less covered already and it practically involves building the mixer stage + another LM386 power amp (and possibly a third LM386 power amp if you want to enjoy stereo sounds) but is it really worth the bother? Rather than building two back-to-back amps I'd rather get a cheap mixer with headphone output and plug the Ruby straight to that. There's far more usage for a simple mixer than for a Ruby with an auxiliary input.

Teemuk, I wanted to see if there was a simpler way to achieve incorporating an external source into the Ruby circuit without a mixer or additional LM386's, etc. I see your point, but then again, the whole purpose of DIY is to think, create, fail, rethink, succeed. 

[texstrat]

Ok, I used this layout from PRR, http://www.diystompboxes.com/smfforum/index.php?topic=85055.0

and I get music through the 1/8" stereo input jack. The only problem is that I can barely hear the guitar in the background, the volume on the Ipod has no effect, just the volume on the amp.

So what do I need to do to decrease the volume level of the input source so that it does not drown out the guitar?

[texstrat]

Ok, I used this layout from PRR, http://www.diystompboxes.com/smfforum/index.php?topic=85055.0

and I get music through the 1/8" stereo input jack. The only problem is that I can barely hear the guitar in the background, the volume on the Ipod has no effect, just the volume on the amp.

So what do I need to do to decrease the volume level of the input source so that it does not drown out the guitar?

Anyone have an idea?

[teemuk]

Well, I'm thinking of a passive two-terminal electrical circuit element that resists current flow.... maybe if you hook two of such devices back-to-back it could form a voltage divider that could attenuate the signal... yeah, I know it sounds sounds silly but it's so far-fetched idea it might actually work.   

[texstrat]

Well, I'm thinking of a passive two-terminal electrical circuit element that resists current flow.... maybe if you hook two of such devices back-to-back it could form a voltage divider that could attenuate the signal... yeah, I know it sounds sounds silly but it's so far-fetched idea it might actually work.   

teemuk I am not following you on this thought.

[teemuk]

[texstrat]

Got it, a resistor(s). But how does that differ from this?

[teemuk]

Obviously you have too little attenuation for the auxiliary input. A typical line level input is in between 500 mV - 2V average, depending on source, guitar signal is likely 20 mV - 200 mV average and in the depicted scheme it's attenuated even further with a potentiometer.

No wonder the aux input is drowning the guitar.

Output impedance of LM386 is 56K... you do the math.

[texstrat]

Obviously you have too little attenuation for the auxiliary input. A typical line level input is in between 500 mV - 2V average, depending on source, guitar signal is likely 20 mV - 200 mV average and in the depicted scheme it's attenuated even further with a potentiometer.

No wonder the aux input is drowning the guitar.

Output impedance of LM386 is 56K... you do the math.

Teemuk, this is new information to me, so where would I look to read and get a better understanding of attenuating an electrical source?

Thanks.