I finally had a few spare hours and got the preamp and amp tied together. I figured I'd throw the schematic up and see if anyone found holes in it before I took to breadboarding it.



The more I look at the preamp circuit, the happier I am with it  :tu:
Baja

Ok, I suppose I walked right into that one. No lemmings around here, but I might be able to scare up a oppossum or something. The last time I attached something to the wife I ended up with another mouth to feed, so hanging in the breeze works well enough for me :duh

As fdor the power feed, I understand what your getting at now, and I'll correct it and repost the schematic tomorrow. Thanks again for the help and the laughs :lmao:

Baja

Quote from: phatt on April 16, 2013, 03:12:42 AM
I'll have a guess,  Maybe try Power feed at other end. 
Phil.

Ok, I'm lost with this one....

On a good note, I found a source for the MPF102's :dbtu:

I'm going to finish up the schematic for the amplifier portion today and get my parts order squared up. I'd love to get this thing runing next week, the weather is starting to get nice out here and we've been having a ball playing outside lately.

@ Roly - Thanks so much for the help on the preamp! I've spent a few hours with the old elctronics book from college and the calculator out trying to figure it all out. I did have one question, is the third leg of the preamp gain pot ok just hanging in the breeze, or should it be attached to something?

Baja

Well I got the schematic all rolled into Eagle this morning, and I thought I'd run it by everyone before I went any further. I stuck in the J201's hoping they will work in the circuit, but I'm going to run this on a protoboard before I PCB it anyways.



Anyone see anything I missed?

Baja

That's cool! I just have one question, do the fets have to be the MPF102 or can they be the J201?

Baja

Quote from: Roly on April 13, 2013, 02:12:43 PM
Now why do I look at that preamp with all those bloody trimpots and have a strange feeling of deja vu?   

Let me guess, something you've worked on?

Yea, the umble circuit is really cool, but the big question is do I run a LM7809 to bring the 12V down to 9VDC, or refigure all of the resistances so I don't feed the J201's more than they can handle? From the protoyping end, I'd be better off using the regulator in case I don't end up using the two togther, but I can't see leaving it that way in the end.

Baja

So I decided to purse the TDA2005 chip in bridged mode, which should give me about 12 watts into an 8ohm load. I found this schematic (which is right out of the datasheet) that looks like it will work. It even has a nifty veroboard layout which should help with the prototyping:


I'm looking to pair it up with the umble schematic from runoffgrove. It should give me a great little preamp with good adjustability and I hope play well with the input impedance of the TDA2005.



I'm not seeing any giant issues, but I'm not a designer by trade. I figured I'd post up the two and see if the designers of the group had any comments before I started running it all together into a single schematic.

Thanks for looking!

Baja

Quote from: J M Fahey on April 11, 2013, 02:45:16 AM

Quotebridged TDA2050 or TDA2030 to get the job done,

If you have only 12V, these are not a good choice, original TDA2003 (or 2005, which is 2 x 2003 in the same chip) or all other "car amps" are better.

You are completely right, sometimes I think that without dislexia I'd have no fun.... :duh

Thanks for the correction, those are the two chips I looked into.

Baja

Quote from: Roly on April 11, 2013, 12:57:02 AM
@Bajaguy - my point, to continue your parallel, is that you need less (average) power if you don't drive around with the handbrake on.  The difference between an 89dB/W speaker and a 98dB/W is the difference between the battery going flat before lunch is over, and going for hours with awesome SPL reserve - using the same battery and chip.

I understand your point completely.

Baja

I look at it like the horsepower rating in your car. You don't NEED 400 horsepower to drive back and forth to work, but you'd be glad to have it if you take your car to the dragstrip :dbtu:

I always have a tendency to overbuild, not saying that I couldn't get the job done with something way smaller. Still, the idea of having a clean 20 Watts through a nice fat 8 in a portable amp that looks like a cigar box would rank right up there high on the cool scale :tu:

I looked through a few amplifier kits online the last few days to see if I could buy the building blocks cheap enough, rather than having to proto them. I'm looking seriously at a bridged TDA2050 or TDA2030 to get the job done, but i'm not sold until I've rocked one in the box to see if it's the right fit.

Baja

I read that thread, your amps are very nice! Are you running the tweetr and 10 on separate controls? It's an interesting concept, and very close indeed to what I'm looking for in this design.

I'm looking at both of those chips now, thanks for the leg up!

Baja

Thanks guys, I'm tickled that I found a forum like this!

That mini marshall is cool, and it one of the ones they play out there alot, along with the mini Orange. They just don't make enough noise is the big problem, but they have tones of cool tones.

I'm thinking more of something in the 10 - 20 watt range that runs a 6" or an 8", with a umble tone control and a clean boost circuit for those days that ya just gotta be clean and loud. It's also got to be able to handle a pedal if they need it. I spent a bunch of hours last night going over some of the chip amps availible, and there's a ton that will run on 12V. I really don't want to build a differential supply if I don't have to, but I'm not afraid of it either. Anyone got a preference or a suggestion?

Baja

Howdy! I'm new here, and found the forum while researching an idea for a bigger portable amp. I have been an electronics tech for a grass roots company for the last 14 years, and I've been fixing pedals and amplifiers for a few of my musicain friends for what seems like forever...

There's a group of guys that I've hung out with for years that have been bitten by the cigar box guitar bug. They have built several 2, 3, and 4 string CBG's that sound awesome! They commonly play in the smoking area at work, which doesn't have access to power. Several have bought small 9V powered mini amps, but most of them have horrible tone and very small output. I built a couple of Noisy Crickets that were converted to cigar box amps, but the tone of those amps is horrible and not what anyone considers usefull. I built a MKII with the bridged LM386 chips and it was a flop with the group as well.

My goal has been to design and build a small portable amp that's battery powered and has clean headroom with enough volume that they can play for at least an hour without recharge. I'd like to add in a SLA battery with a charging circuit that would allow the amp to be played off of the charging circuit without loss from the battery, yet keep the battery charged and ready for any excursion. The ability to charge the battery from a cigarette lighter in a car would also be very usefull.

The enclosure would be similar to a 10" x 10" x 5" cigar box built from 1/4" western red cedar, and I'd like to have the option of using 5", 6", or 8" speakers.

I've been paging through the portable amplifiers that grace the pages here, and I'm sure there's a chip amp that will be perfect for this, but I'd like to get a few opinions on what would be the better route for this set up. I have a umble preamp that I built as a pedal that I'd like to use for the preamp section on this, but it's not a design requirement.

Anyways, nice to meet everyone, and I'm interested in any ideas that may come up.

Thanks,

Baja