Active 3 way center channel /Gainclone amp

Systems

While I'm mostly satisfied with my current center channel which is an active 2 way MTM design,I thought I would go the next step and go with a full 3way active design.The horizonal MTM driver configuration normally used for CC duties can have some off axis dispersion limitations that a 3 way with centrally located midrange with a tweeter directly above does not have.I hope by adding the dedicated mid ,I will gain some improvement in the clarity of movie dialog.

I will be using a SEAS 1" aluminum dome tweeter,5.25" Tang Band mid,and a pair of Vifa 6.5" woofers.
The cabinet is in the works and made of MDF and I use dado joints to help keep things square and make for a very easy assembly.

The pre amp/active crossover (silver box in pic) will have crossover points at 300hz between the mid and woofers and at 2.2k between the mid and tweet all with 24 db slopes..
Because of the 3way config I will need to add another channel of amplifcation.

I will be using my existing Bryston 2B LP one channel each to drive the woofers and mid.For the tweeter I'm building a mono version of the popular LM3875 chip amp or Gainclone.It should do the job nicely driving the very easy tweeter only load. The black chassis in pic shows the beginning stages of this unit.The driver shown is the midrange.

Deadof_knight

GV very nice construction . I like the recessed grooved to lock everything in. looks to be very solid with very very little coloration.

MillerLiteScott

Very nice work. Rock on.

Face

Very cool.

zingo

I can't wait to see that thing finished! Looks great!

Systems

Thanks for the kind comments.

This is a pic of my current CC ,the new one will look very much the same but wider to allow for the woofers to be placed further apart so the midrange can fit between them.
Oh and I'll use flat black paint on the baffle instead of the distracting sparkly stuff I used on the first one.:D

Systems

Its taken a few months but I finally completed work on the enclosure. The veneer is cherry to match match my main speakers.I still have some work to do on the crossover before I can try it out.

ben62670

Sweet. I am working on a similar design to drive my tweeter with a parallel gainclone with a line stage tube buffer, and Op Amp active XO. can't wait to here on your experience. What board did you use for the LM chip, and are you going raw for the PS, or regulated?
Thanks
Ben

Systems

ben62670 wrote: »

What board did you use for the LM chip

I ordered from Audio Sector.http://www.audiosector.com/

are you going raw for the PS, or regulated?

Im just going to use a regular supply but with substantialy more capacitance than the anemic 1500uf that most are recommending for use with these chips (although 1500uf would likely be sufient for use when driving just a tweeter.Im currently using a pair of LM3875's (with about 12000uf on each rail) to drive my 2 way Vifa monitors on my PC rig, with excellent results.Im sure a properly designed regulator would improve their performance but it would also add consisiderable to the complexity.Besides,the promise of good sound from a simple circuit with low parts count is why I chose these for my PC audio and as a tweeter amp.


Good luck on your project it sounds interesting, especially that tube input stage.

ben62670

I always enjoy reading your stuff. I too am going raw. I don't like to add regulators in my PS circuitry. The tubes I am going to be using are the low voltage 6GM8's They are very happy at 24vdc with 5-6.3 heaters. My voltage is going to be slightly high on the LM3886 chips at 34-vdc, and 34+vdc, but I will have large heat sinks, and will have two or three in parallel. I know we'll keep each other posted. If you want to try the tube thing a simple regulator and the 6GM8's work great for the gainclone. If you can't find the tubes, and are interested let me know.
Ben

ShinAce

My sub amp is running two LM3886T's bridged to an 8 ohm load. You guessed it, rail voltages are about +/- 34 VDC (48VCT xfmr).

I don't think it is high at all.

ben62670

ShinAce wrote: »

My sub amp is running two LM3886T's bridged to an 8 ohm load. You guessed it, rail voltages are about +/- 34 VDC (48VCT xfmr).

I don't think it is high at all.

Hey man where are you located. I need friends that aren't afraid to burn there fingers! I was going to parallel them so my 4ohm load would be seen as an 8:cool:
Peter doesn't have 3886 boards, but Brian does over at chaipamp.com
The prices are very low. I like the 3886 chips for their inproved SOA.
Ben

Systems

ben62670 wrote: »

I too am going raw. I don't like to add regulators in my PS circuitry.

Yeah, while the current demands are low enough on these chips that using a regulator would be feasible,just using lots of capacitance can get you most of the advantages that a regulator would provide.(Most power amps only use regulation for the input and driver stages because the current required by the output stage would require a regulator that has as much current capability as the output transistors).

My voltage is going to be slightly high on the LM3886 chips at 34-vdc, and 34+vdc, but I will have large heat sinks

Im running about +-33 DC but I also have lots of heat sink and only driving 6-8 0hm loads.

If you can't find the tubes, and are interested let me know.
Ben

Thanks Ben for the generous offer.This would be something I would like to try sometime but I have a big pile of unfinished projects that I need to clear up first.I will certainly be watching with interest your progress on this one .

Systems

Its finally in its new home above my plasma.:D

Performance wise in direct comparison to the MTM it replaces,the mid -tweeter blending is much smoother and dialog sounds more natural with increaed clarity which was one of mine main goals for building a 3 way.
As well the listening window is somwhat wider, whereas the MTM was limited to a +-20 degree horizontal listening window for best results.
This is an inherant problem with MTM 's, a direct result of their side by side mounted mid -woofers (or is that mid-bass's?:) and the cancelation that occurs.

Of all my projects I think I'm most pleased the way the cherry veneer turned out on this one.

ben62670

You're such a geek:p

Looks good!

Systems

ben62670 wrote: »

You're such a geek:p

Thanx,and yes I iz.:)

Looks good!

Thanx again.