Tech 21 Power Engine

[jmdfd415]

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!

[joecool85]

Could you give me a link to this "Power Engine"?  I've never heard of it.  We can help you on building a power amp though.

[jmdfd415]

Here is the link.  I am looking for something like the 1x12 on here.

http://tech21nyc.com/pe60.html

[joecool85]

Yeah, 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.

[jmdfd415]

Could you point me in the right direction of where I should start?

[joecool85]

First, I would read about Chipamps: http://wiki.ssguitar.com/index.php?title=General_Chipamp_Info

Then, about the LM3886 here: http://wiki.ssguitar.com/index.php?title=LM3886

[Zappacat]

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!

[Dylan]

ME too. i would like DIY.yesterday i built a preamp,it is work,but there lots of noise.
i don't know what happened.
good luck!

[J M Fahey]

Packing together all that was said above :
1)Yes, you can build something that´s practically the same, with power and very good sound.
2)To keep it a 1x12" affair (and for cost reasons), an LM3886 driving a single 12" 8 ohms guitar speaker will provide 50W RMS, practically the same as the original.
3)Try to use a relatively "flat" guitar speaker or at least one similar to the "Seventy80" they use.
If you use a good known chipamp , which by design is clean and flat, and the only equalisation is the speaker´s own frequency response, and a similar box to wrap everything, you´ll duplicate the original commercial product.
Good luck with your project.
Please keep us up to date.
I´ve built *lots* of 100W , 2x12" powered cabinets for guys with JMP1, Peavey Ultra and Rockmaster, SansAmp PSA1 and floorboxes, VTwins (pedal and rack), and even as power boosters for Champs or 2xEL84 amps.
The results have always been excellent.
The only "law" that has to be respected is that you must have available at least *twice* the RMS power you´ll need onstage, adding as many cabinets as necessary, so they *never, ever* clip, muddying the excellent sound that the pedal or preamp supplies.
That means: 100W RMS if you need the equivalent of a 50W RMS tube amp, and so on.

[teemuk]

AFAIK, Trademark 60's use LM3875 in the power amp circuit. I wouldn't be surprised if the Power Engines are about the same circuit-wise.

Edit: Corrected the chip..

[Zappacat]

Yeah, 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?

[J M Fahey]

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. "
Besides 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.
I 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.

[J M Fahey]

Hi. It doesn´t get any easier than this:
http://www.dogbreath.de/Chipamps/ThreeResAmp/ThreeResAmp.html

Good luck.

[teemuk]

Simple, yes. But not neccessarily the best or most sturdy.

I would at minimum:
- AC couple the input
- AC couple the feedback path to ensure unity DC gain
- Add a RC Zobel to the output

Additionally:
- Parallel 20p - 100p cap to Rf, possibly with a series resistor
- Pararallel cap to Rg to reduce RF interference
- Series current limiting resistor to the input, value = Ri
- protection diodes from the output and input to both supply rails (LM3886 might actually include these already)

If you are not building PTP the bypass caps go as close to the chip's power supply pins as possibly. They have lesser effect (if any) at the pins of the smoothing caps.

I would prefer a PC board. Not only do the parts hanging loose in the air look unreliable (especially the big filter caps) they also create a mess that is hard to troubleshoot and repair.

[Zappacat]

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.

Besides 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.

I 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.