Some LM4780 Love

Kevin P · « **on:** 27 Jan 2005, 01:17 am »

These are going to be the heart of our new Exodus Active Amplifier (EAA Series)platform. The goal is to offer some affordable active amplifier projects combining some of the new Adire XBL^2 enabled drivers. I've very pleased with their performance driving traditional speaker loads. Used into a driver without a crossover they are exceptional.

Cost? We are estimating the amplifier board populated with heatsink for a complete 2 channel amplifier under $95. It will be very easy to have complete active amplifier projects with the Exodus Chassis for around the $500-$600 price point using these modules.

http://www.diycable.com/main/images/LM4780.jpg" >

http://www.diycable.com/main/images/LM4780-2.jpg">

And here is a complete working prototype. The transformer & bridge rectifier are about $40 and the other board on the AC input is our DC Filter + RFI Filter unit ($50). The chassis is about $150 so the complete amp as shown would cost just over $325 complete. It is about 50-60W/Ch into 8 Ohms and drives the new CS125 based kit with aplomb.

http://www.diycable.com/main/images/New-amp.jpg">

Kevin P · « **Reply #1 on:** 27 Jan 2005, 02:22 am »

Oh.... for those who are asking why they should be interested in active speaker designs.

#1. Because I'm selling it.

#2. It really allows us MUCH more flexibility in crossover design.

#3. It effectively allows us to ignore driver efficiency in matching different drivers together.

#4. It allows us to EQ the bass (LT circuit) and provide other room specific EQ circuits for better overall system design not achievable with a passive crossover network.

#5 It uses amplifier power more efficiently.

#6 It provides much tighter tolerances in crossovers. It also allows us to use low crossover points without the expense of large inductors & caps.

#7. The crossover is much more precise under power. Passive units are somewhat dynamic due to VC heating and the change in DCR of the VC. Passive componets typically have 5-10% tolerances and active parts are often less than 1%.

Many more good reasons that don't have anything to do with voodoo. The only negative to active designs has always been cost. We are going to solve that little problem.

http://sound.westhost.com/biamp-vs-passive.htm

http://sound.westhost.com/bi-amp.htm

http://www.linkwitzlab.com

thayerg · « **Reply #2 on:** 14 Mar 2005, 05:44 pm »

What is the ETA on these things?

Kevin P · « **Reply #3 on:** 15 Mar 2005, 04:14 am »

The amplifier modules will come first. We will have a kit version with the unpopulated boards available once we get documentation done. ETA for just the amplfier modules is 2-4 weeks.

The active amplifier kits are going to be based upon all of our new speaker kits arriving soon. We will also have a board providing a couple bands of PEQ to help people to tune their speakers to their room. Expect these to start arriving late summer.

Often our release schedule depends upon our available cash flow which is hard to predict.

Russtafarian · « **Reply #4 on:** 15 Mar 2005, 07:06 am »

Kevin,

Help! Your pictures confused me. Are you using one LM4780 chip in stereo to get 50-60 wpc or two chips in a bridged or parallel configuration to get 50-60 wpc?

Also, what +/- VDC are you sending to the chip and what sort of capacitor scheme are you using for filtering?

Thanks. I'm definitely interested in this one!

Kevin P · « **Reply #5 on:** 15 Mar 2005, 11:13 pm »

All of the modules shown are hooked up as stereo LM4780s. There are very few changes that need to be made to implement the parallel or bridged mode.

For the board shown I was using 31V on the rails, which requires about a 22VAC on the secondary. If you were going to run either bridged or parallel you will most likely want to choose different rail voltages. If you know your load you can also dial in the best rail voltage by looking at the National Semiconductor tech notes.

The power supply is just your standard bypassed supply as per the National Semiconductor tech notes. We bypassed on the chip with an MKP 0.1uF & 10uF Electrolytic. The rest of the capacitor bank is all in parallel with capacitors mounted on both sides of the board (too keep them as close as possible to the chip). I've been using 6,000uF per rail using very good quality FM Series Panasonic caps. All critical traces are doubled up on both sides of the board.