Ruby Guitar Amplifier Old intercom speaker retrofit and revamp

[1FenderGuy]

add one with reverb! so i can do AC/DC at low wattage

[H0LL0WBELLY]

stunning amp.absolutely stunning.

[frankoenburen]

so sweet!

[boagley1]

Sounds just like a pignose! Nice work!!!!!

[IYanoplathizoI]

I am thowing my first one together. I have little electronical knowladge so can I ask a few questions?

1. Will two 8ohm speakers in parallel for 4r? Will that do?

2. Can I use a CA3140EZ as the MPF102 FET?

Cheers,

Yano

[chainduck]

@IYanoplathizoI Two 8 ohm speakers will work fine. I'd test them first though...reason being is that sometimes one speaker will actually sound better on its own than two....not sure about the science. But, I've noticed this before.

I don't know about the transistor. Substitutes are fine. But, check a cross reference table to make sure.

I'm no electronics wiz either. I just solder things together and maybe vary circuits just to see what works. I

[nihilnoise]

@IYanoplathizoI MPF102 aren't hard to find, if i was you id try and stick with whats recommended cause using an unknown transistor could be the one thing that yield an amp that doesnt work, could be for many reasons, different pin out or not even the right type, is this CA transistor a FET?

just google MPF102 for sale and you should find em, very cheap too

i recommended Small Bear Electronics

[chainduck]

@nihilnoise I had trouble finding them, but my local electronics guy gave me an equivalent that works just fine. I'm using them in all these amps.

2N5485 costs about a dollar, I think....

Eric

[isethaitchison]

really, it must be a really good speaker lol

[chainduck]

Well, it was torn. I fixed the tear with rubber cement and a bit of paper. These old speakers are often low wattage...perfect for the little Ruby circuit. It has a heavy steel voice coil over an Alnico magnet. But, the actual winding is minimal. If you look in many pre 70's cheap stereo speakers, you see similar. Most are rated at around 6-8 watts...and midrange heavy. I keep an eye out for those old speakers for just this use.

[isethaitchison]

obviously thats not the origional speaker inside. love the finish. how many watts is it?

[chainduck]

Actually, it is the original speaker. I only added the battery powered amp. The original intercom system must have used separate send and receive components as this speaker had no onboard amp of any kind. I think it was more like an office PA extension.

[huskyd2000]

Beautiful--both in looks and sound! The distortion on that is amazing! It reminds me of the warm overdrive from a "Daddy-O" pedal. I built a Little Gem amp, (although I went back and changed the volume pot location and added the FET buffer so in the end its basically a Ruby now) but when I crank up the gain it doesn't sound nearly as good as yours. Were you using any effects feeding the amp, or does it sound that way because of the speaker or amp module itself?

[chainduck]

Several things account for the sound. 1. the speaker is an old paper cone with Alnico magnet. Nice thing about tiny amps like the Ruby, is that you don't need high watt handling speakers. So, you can use some old, low watt speakers that aren't useful for high powered amps. 2. I like the Ruby sound in a closed cabinet most of the time. However, that changes with the size of the box. I find that some porting is necessary on the smaller boxes to keep them from sounding dull.

[chainduck]

Finally, the guitar is a blade humbucker from Bill Lawrence. It adds a lot of oomph to the sound...particularly in the high end.

Possibly, my components my color the sound. But, I haven't noticed compared to all the other factors.

[huskyd2000]

Makes sense. Drive the amp with a stronger signal to get more distortion and sustain. Also, I noticed that most users recommend the JRC386D op-amp, and that it sounds better than the more common LM386 that you find at radioshack. I've since been tinkering around with different ways to boost distortion. So far, the most viable possibilities appear to be either clipping diodes, feedback, or even changing the FET buffer around to a booster.

[chainduck]

Hmmm...I like the idea of making the buffer into a booster. Let me know how it goes. The opamp in this amplifier is the LM386N. And, it is being run at 12Volts...so a bit louder. That said, I still believe that the speaker and box are making the biggest difference. I build a few of these amps in different boxes and every one of them has just a bit different color.

[mattvl]

Do you know what wattage resistors you used on this project?

[chainduck]

I believe they are all 1/4 or half....whatever the ones that cost me a dime are...LOL The amp draws so little current that you should have no trouble with the small size resistors.

[jks2]

doesn't it get to warm inside the box with hot tubes?

[chainduck]

I consider that, a great compliment!

No tubes at all...just a tiny IC amplifier circuit. :)

Eric

[Scioneer]

Old 8 inch PA drivers are actually very similar to the ones used in lower wattage guitar amps. Probably one reason why it sounds so good.

[chainduck]

Excellent info! Thanks. I'm already on the lookout for more of those old intercoms.

Eric

[faunoram]

beautiful and it roars like a lion

great job!

[chainduck]

Thanks, I was pretty surprised that the old speaker still worked. I had to glue a big tear in the cone. I was originally intending to replace the speaker, and just tried it first as a "nothing to lose" option. I was psyched to find out that it not only worked, but sounded great.

[ddl312]

Could you give me the link to the website you got the amp plans off of. That would be great, i want to try making one of these.

[ddl312]

Wow, Very nice

[hamnhock]

that is one badass sounding little amp!,,,

[chainduck]

Thanks! I think there are two important things to getting a good sound out of these. One is to use a cube type box....wooden preferably, and sealed. Two is to use as large an 8 or 16 ohm speaker as the box will permit. Don't go overboard on the magnet though. The amp can only push so much iron...so no need to use a high watt voice coil. My faves are some small coil Alnico mag 4" 16ohm speakers I get at my local electronics supply.

[DeltaBluesClassics]

Beautiful work...Nice job!

[chainduck]

Thanks, I have a lot of fun with these little amps.

[psychodelicdragon]

looks grreattt!!!!1

[docwilliamson]

What a beautiful amp Eric and you resurrected the cab from the dead.