Quote from: J M Fahey on May 06, 2009, 10:05:18 AM
Hi Zappacat.
To begin with, I fully agree with all of Teemu´s suggestions.
I told you to search for the "zillion" Gainclone projects, or LM3886 projects, which of course use a PCB and all necessary components, to save you the chore of designing your own PCB.
I pointed to the "minimalistic" one for you to see just how simple it might become, compared to the LM4780 and its close spaced pins, but of course I agree that a guitar amp, specially a "combo" type , mounted inside the very speaker box, gets handled roughly and should be built sturdily.
You can use the GGG project as a guide.
http://www.generalguitargadgets.com/pdf/ggg_lm3886_amp.pdf
Not the best in the world, but, hey!, it´s free!
It follows exactly the manufacturer´s recommendations, http://www.national.com/mpf/LM/LM3886.html  including the non-use of a Zobel network.
Personally, that makes me nervous; I´d add a .1 ceramic in series with a 4,7 ohm 1/4W resistor from pin 3 (output) to speaker ground.
I´ve searched a lot,it seems that everybody and his brother is offering 3886 kits, but of course nobody posts the PCB design.
If you dare to design your own, go for it.
Yes, I suggest you build two 3886 amps instead of one 4870.
I think it will be easier to get 8 ohm speakers.
Yes, most (¿all?) the stuff published refers to Hi Fi amps, and minimalistic by the way, not guitar amps which get a rougher treatment.
I´m not at home now, later I´ll draw and post a rough sketch of a "guitar version" 3886, including all of Teemu´s suggestions.
Bye.

Can I power two 3886 chips from a single transformer or will I need two transformers?  I'm really looking forward to your sketch.  Thanks for the help.

Quote from: J M Fahey on May 05, 2009, 04:57:39 AM
Hi Zappacat. Keep it simple building *two* LM3886 instead of LM4780, since:
"LM4780 is a dual LM3886 The LM4780 package contains two LMP3886AT silicon dice. This is the same die as used in the LM3886. "

So I should use 2 LM3886's ?  I'm not sure what you are saying here.

QuoteBesides there´s a zillion Gainclone pages out there, including some that use no board at all. It can´t get easier than that.
As for speakers, besides the obvious solution of using the 70-80 , I remember that searching both Celestion and Eminence sites, they had some speaker that was described by them as "flat, to be used in amp modelling setups" or something like that.

Should I be looking for 8ohm speakers for this project?  It's just a stereo cabinet with 2x12's.  I'm not real sure about the advantages of 4 ohm speakers vs. 8 vs. 16.

QuoteI agree with you that building some powered box and driving it with some external preamp , commercial or DIY , is a good solution. Besides, if you don´t like the sound, it´s easy to change the "front end" , keeping the power section.

Yeah, it's the front end stuff I'm worried about.  Still trying to piece together a plan concerning getting the guitar input signal into the power am section with as little noise as possible.  All of these LM series audio plans I've seen so far are for home audio listening and not for guitar.

Quote from: phatt on May 04, 2009, 08:34:37 AM
Hi Zappacat,
         Try this one instead http://sound.westhost.com/project101.htm

Probably eaiser to build,, a Ton more grunt (depending on PSu Voltage used)

The hidden bonus for this one is it will run on just about any voltage all the way up to 70/0/70 VDC rails where it will output over 200watts into 8ohms.
I have not built one but it certainly looks like it would deliver the super clean flat response,, if that's what you want?

Also as you want stereo the price may climb quickly so have you considered some old HiFi poweramp sections they might be worth a look you may even be able to use some of the line inputs and save yourself a lot of work.
You can pick up old 70's hifi amps cheap where I live.
Cheers, Phil.

So, optimally I need to be looking for a good transformer that puts out 70/0/70 VDC.  Any other requirements on the power supply?

Since I'll be running 2 speakers, what ohm rating should I be looking for right now.  I was thinking about getting celestion seventy eighties since that's what they are putting in the power engines.  Any better ideas?

I'm going to build a 2x12 speaker cabinet to house the amplifier and speakers.  This lm4780 allow me to run in stereo right?  I want to send my Line6 POD signal to this box for playing live and practicing.  How big of a deal would it be for me to add a pair of balanced outputs so I can send my stereo signal to the sound board? 

I've seen serveral PCB board renditions on the net for sale but they are all designed for home stereo use.  I was tempted to build this whole thing on a breadboard at first but I've heard that the connections on the lm4780 are so small that you almost need a PCB for it to be able to access the indiviual circuit pins more easily.  I'd like for the amp to drive a pair of Celestion Seventy80's.  Would I need to be using two lm4780s to effectively drive them?  What kind of speakers do you guys suggest for this application?  What ohm ratings and wattages?  Any help greatly appreciated.

While constructing the speaker cabinet should I angle them out from the center a little bit to get more stereo separation?  I've seen that idea employed in some stereo cabinets and not in others.  What are your opinions on this?

Thanks for the help guys!

QuoteYeah, that shouldn't be too hard.  60wRMS power output is easy.  The LM3886 has 50wRMS at 8 ohms and 68wRMS at 4 ohms.  So run a 4 ohm speaker (or two 8 ohm speakers) and you'd get the power quivelent.  After that it's just finding the right speakers to make it sound right.

I'd like to use a lm4780http://home.mira.net/~gnb/audio/lm4780.html for the amplifier.  I'm going to build a 2x12 speaker cabinet to house the amplifier and speakers.  This lm4780 allow me to run in stereo right?  I want to send my Line6 POD signal to this box for playing live and practicing.  How big of a deal would it be for me to add a pair of balanced outputs so I can send my stereo signal to the sound board?  I've seen serveral PCB board renditions on the net for sale but they are all designed for home stereo use.  I was tempted to build this whole thing on a breadboard at first but I've heard that the connections on the lm4780 are so small that you almost need a PCB for it to be able to access the indiviual circuit pins more easily.  I'd like for the amp to drive a pair of Celestion Seventy80's.  Would I need to be using two lm4780s to effectively drive them?  What kind of speakers do you guys suggest for this application?  What ohm ratings and wattages?  Any help greatly appreciated.

While constructing the speaker cabinet should I angle them out from the center a little bit to get more stereo separation?  I've seen that idea employed in some stereo cabinets and not in others.  What are your opinions on this?

Quote from: jmdfd415 on February 22, 2007, 07:19:37 PM
I have a sansamp gt2 and I wanted to run it through a poweramp like the Power Engine by tech 21.  Does anybody know of a poweramp I could make that is similar to that?  I am new to amp building but I have built alot of pedals so I really dont know much about amps.  Thanks for any advice!

Did you ever build an amp?  I posted a similar question here recently and stumbled across your posting while searching for information.  Let me know what you ended up doing if you get the chance.  Thanks!

I'd like to build a combo 2x12 stereo amp that has balanced stereo sends(to send to the PA).  It doesn't need much(if anything) on it for a tone stack.  The more power the better.  It just needs to be uncolored sound.  I guess what I'm looking to build is very similar to a stereo Tech 21 power engine.  Could any of you point me in the right direction.  I'd really appreciate it.

I'm seriously considering trying this amplifier http://sound.westhost.com/project27.htm 100W Guitar Amplifier Mk II.  Have any of you built this amp?  The only thing I see that it lacks is stereo.  Outside of that it seems to be well documented and I like the way he explained it.