simple studio monitor DIY project?

[barret77]

Hello all

I have a 6" all purpose radio shack speaker lying around, and some nice pine wood.
I'm wondering: is there any simple good SS amp project, so I could put it together and use the speaker as a mono monitor?
I'm currently using logitech multimedia speakers in the computer, and they're great for dvds but horrible for listening guitar recording.
The all purpose Radio Shack is really NOT a quality part, but it has a well distributed response (I think it has at least).
If anyone has ideas on taking advantage of this at extremely low cost, let me know...

[mathflan]

Hi,

I can just give you some url:

http://www.speakerbuilder.net/web_files/default.htm

http://home.hetnet.nl/~geenius/

http://yellow.mynethost.com/~bv126368/shop/catalog/index.php?osCsid=e3d1a1f363fa837a99e28593a52346dc

http://www.theloudspeakerkit.com/

http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=209
if you are in USA, partexpress is very good if you want to build our own monitor for less money..


A forum:

http://www.johnlsayers.com/phpBB2/viewforum.php?f=12&sid=7eda3e6cd73b3133b8682e52e735e38d

[barret77]

wow! a lot of nice resources there!
But they are all really good... too good. I'm looking for a low tech PCB SS mono amp to connect between mixer out > speaker... not very loud, like 1 to 5 watts, but transparent...
these sites left me drooling for real monitors, but no $200 in the pocket for now...

[moosapotamus]

LM386
http://www.njr.co.jp/pdf/de/de05001.pdf

~ Charlie

[barret77]

hey, that's great! just what I need.

I just want to bother the forum with 2 more questions:

1) there are 2 versions of this chip at jameco.com: a 250mw and a 500 mw;
can I use any of them with the schematics on page 2 of the datasheet pdf? Does that schematic change when the wattage change or not?

2) I'm about to close an order at mouser; they don't have this chip, but they have "equivalents"... Should I try one of those? Does anyone recommend me a stock part number from Mouser?

[edit] oooops I found that at mouser... nevermind the question 2...

Really thanks!

[octafish]

I built a DI box for a mate and gave it two outputs, then built a "clean" Ruby in an old HiFi speaker enclosure to use as a monitor. Just built the Ruby per spec but add a switch to totally disconnect pins 1 and 8, easy as. Plus if you have vero I think Torchy has done a layout of the Ruby.

[cab42]

but add a switch to totally disconnect pins 1 and 8, easy as.

Sorry if it is a stupid question, but why would you want to do that? What effect does this have on the sound?

BTW I build a stock Ruby and I'm extremely happy with it, but consider using a Fetzer Valve (build it yesterday) or something else as input buffer. How about the new Tone Mender from ROG?

Regards

Carsten

[petemoore]

Ruby uses 386, that chips pins 1 and 8 set gain above internally preset min gain.
 Raise gain= lower freq response/increase distortion
 ...Feel free to correct...check out the Ruby Chip specs and that chips data sheet.

[octafish]

The pin thing?

Sorry if it is a stupid question, but why would you want to do that? What effect does this have on the sound?

Ruby uses 386, that chips pins 1 and 8 set gain above internally preset min gain.
Raise gain= lower freq response/increase distortion

Yeah thats it, if the pins are unconnected then gain is set to 20db IIRC. Also I think the amp I built is running on 12V now to give it some extra headroom. This Ruby was built to be a studio monitor/practice amp so I added the switch rather than just leave out the gain control entirely. It doesn't distort unless you hit it with something really hard, say an Uglyface or something. When its being used as a monitor it is fed by a DI box and sounds close to the tone that the computer is recording. Drape a t-shirt over the front of the 4 inch speaker and the monitor is spot on, well... close enough for jazz.
I tried to build a Ruby with a Fetzer into a tonestack into a fetzer as the buffer but I ended up just rebuilding it as a (Bassman) Ruby. If I want to sound more tubey I just hit it with a Tube Reamer or the Eighteen.

Tim Escobedo and Runoffgroove where would I be without you...


...probably playing more guitar and building less circuits.

[Peter Snowberg]

The best 386 out of all I've tried is the NJM386BD. Hands down the winner.

http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=381293&e_categoryid=257&e_pcodeid=51308

When you connect pins 1 and 8, the gain gets increased by about 10 times, but this should be done by providing an AC path between these two pins and not with a DC path. A DC path will upset the bias of the input stage and cause the negative feedback to clip which is not good for the sound.

Fixing this is just a matter of putting a cap in series with 1 & 8. Any value from 10µF to 100µF will work great. Smaller values work like a trebble boost. Multiple RC combinations across these pins allow for a good bit of tone shaping, but a simple 22µF cap is what I use most of the time.

[barret77]

Great, thanks all for the information.
I didn't know the Ruby project, it seems to be great.

One question: What about the speaker impedance?
My speaker is 8 ohms...
The schematic says nothing about this...

Thanks!

[B Tremblay]

8 ohms is perfect for the Ruby.  4 or 16 ohms would also be fine.

[octafish]

the 386 can handle 4 ohms plus so 8 ohms should be perfect.