A 6-channel A/V amp using BrianGT LM3875 boards

[saabie22]

Attached are some pics from a 6 channel amp that I built using Brian's board kits, and a regulated power supply that I built using Carlo's ideas.

Thanks to all that contribute here.

Mike

[saabie22]

Here are the guts of the thing while in progress.

That's a 330 VA Avel transformer. I have another just in case I feel supply limited but I thought I'd try it in this configuration first.

I decided to segregate the PS from the amplifiers on this project. My first amp was pretty compact and I found it hard to route things in a confined space.

[saabie22]

Part of the back panel (waiting on DigiKey to deliver a pair of jacks!)

[saabie22]

Happiness is listening and not spending another minute at the work bench!

Thanks again everyone!

[Nordic]

Is that 1 transformer with 6 secondaries?

[karma]

seeing so many people playing guitar on this forum makes me want to start playing again

time to hit the pawn shop nice amp

[saabie22]

The transformer 2 secondaries. All 6 amps are run in parallel.

My rails are at +/- 30V. I chose this as my speakers are a nominal 6 ohm and it seemed to provide a nice safe operating condition, if I understand National's data correctly. (roughly 53W at .1 max THD+N, and around 25W peak dissipation). The chips are bonded to a 1 kg chunk of 360 brass which is connected to an aluminum extrusion. I have a small, relatively quiet fan, on hand in case I find that my thermal management is inadequate and I need to go to forced convection.

My thinking is that in the application I will use this, one pair will be providing amplification for L and R and one will be center channel information. Another pair will be rear surround L+R.

The DVD that I'm using provides Dolby 5.1 outputs. My subwoofer has its own amp so in the end I actually will use 5 of the 6 channels.

I thought long and hard about how to power this thing. I started out with dual transformers in mind but when I started to consider how I will use it 330 VA seemed sufficient. My power supply can provide 5A, theoretically, and I currently have roughly 9400 mfd between the trafo and the regulators. With 2000 mfd on each module I think there should be enough 'oomph'.

I am, however, way more mechanical than electrical so I may change my tune and beef up the power supply section if I find it to be limiting.

[maf_au]

Hi.

Nice implementation saabie22!

That's similar to what I've been ruminating over for a 5 channel Stereo/HT amp.

Because of all the DTS/Dolby HT Complications, I think I will have to run a commercial HT Processor, and create a hybrid box for stereo/HT amplification:

* 2 or maybe 3 Transformers depending on whether I dual-mono the FR/FL:

* 1 transformer (or 2 for dual-mono) running the front stereo channels.

* 1 transformer running the centre and surrounds.

A built-in, switchable, minimalist preamp for the front L/R channels, Maybe also an internal DAC.

So, when running in Stereo mode, the transformer powering the center/surrounds will be off, and the single input will be active through the preamp to the front speakers.

When running as a HT power amp, all transformers will be powered up, and the local source, preamp and volume control wil be out of circuit - all channels will be running directly from the 5 channel outputs from a HT Processor.

I imagine I should be able to accomplish this with a 3 way switch on the front Panel: Off/Stereo/HT. Or perhaps an on switch that starts the amp in Stereo mode, with an extra switch that brings up the extra HT channels.

That should be a bit of fun to configure, but it solves many of the SQ and heat issues I have with HT Receivers as stereo amps, and save enough electricity to run a small town in the process

Michael

[saabie22]

Michael,

Its a bit of a problem to figure out how to drive an HT and stereo setup, isn't it?

I've thought of a similar solution to what you describe but from the power amp end. All this gain clone business started out for me during my Leach amp project. My Leach 2-channel is complete except for the chassis and heat sinks. The boards are done and tested and the power supply works great. I just need the time to bundle it together.

I eventually plan to build a hybrid switch box that selects either amp to drive my main speakers (Leach for stereo) and also selects a line level source for the powered sub. I think a 'break before make' condition is probably required so I don't have one amp blowing the other one up.

As far as power consumed by the non active amps in your configuration it may not be too bad. If I interpret the graphs on pg. 10 of the data sheet correctly, dissipation at 0W output power is darn close to zero (maybe 1-2W).

Anyway, best of luck on your project.

Mike

[maf_au]

Thanks Mike,

I understand what you mean regarding power consumption.

My amps will be monobloc Mauro's from this monster thread

There's a few more components running and idling in those than I'd be happy with compared with a standard GainClone. Considering that 99% of the use will be stereo, I can't see the point in leaving it all running, even at idle. Must be some Scottish in me...

Building it all in the one box and using the same amps for the front channels regardless of Stereo or HT mode, avoids some potential problems with switching between amp in the same scenario, especially with the speaker cabling...

Of course, the whole issue can be avoided by listening to Stero in a different room, that way you get to leave it set up just as you like, with no switches on source or outputs

Michael