FrankenPlateAmp- has it already been done ?

max2tall · 10th October 2009, 09:52 AM

Hi,

I'm contemplating stitching together the following:

3 way LR crossover

variable BSC & notch filter on mid

LRT & balanced drive on the bass

with 3x LM4780 output, 1 for tweeter & mid, 2 in bpa for woofer / subs.

Have attached a block diagram & stitched together a few ubiquitous circuits in fig 2.

Before I go any further, has it already been done in a similar enough manner to avoid a waste of time, or is their an available comparable design I could use.

Failing that, anybody interested in getting involved in the design process, or any input / suggestions for circuit improvement before going to board layout.

Cheers.

MJL21193 · 10th October 2009, 04:53 PM

Hi,
I did a similar thing here. It's lack of adjustability was it's downfall.
I reassigned the individual active amp boards to another pair of 3-ways for use in my workshop.
One of the "plate amps":

Picture 053.jpg

The speakers they are powering:

350.JPG

They sound great.

max2tall · 11th October 2009, 04:12 AM

Hi John,

Thanks for your comments. I had a read through that long thread & picked up a few pointers, thanks.

It surprises me that there's not more of this been done, I think I've looked everywhere. What seems to me to be the 'proper' way to do it these days would be some DSP chip sitting there, but I cant see any complete design thats implemented it & it's too much for this old dog to learn about fcpga's now unfortunately

For my own needs I plan to make an all-in-one pair of plate-amps for forthcoming 3way speakers. Everything I need seems to be in those circuits stitched together.

The notch is a problem- I do need a 3db or so 1khz notch to tame the mids, but I think the cct included is a very deep one, I'll look further for something gentler.

There have been other balanced BPA drive options touted, including line drivers and audio transformers, have you thoughts on which is superior? I've got 4 quad opamps fully utilised at the moment, but could lose one perhaps.

I've seen other comments about including filtering around the LM4780's themselves, reducing the cct a lot, but haven't seen any working examples, have you ?

I'll have a look at the plugable filter component concept brought up in your earlier build & see if I can include it. I was already on the path of those dip package header thingies to plug in & out for that.

As a relative veteran here, do you think I should post this in the 'analog line level' or the 'chip amp' area ?

Best Wishes, Max.

MJL21193 · 11th October 2009, 12:35 PM

Hi Max,
To do it over again, I would use the DIP headers as suggested to make it easily adjustable. Another mistake I made was having the boards too small - very difficult to fix or change anything.
In this application, I wouldn't be afraid of using opamps, as many as needed to build the filters. I think it's not a great idea to use the power amp as a filter element.

About BSC: increasing the output to the woofer will effectively do this, unless the crossover point is much different from the baffle step frequency. I now use a DCX2496 and the output to the woofer amp is crossed at 384Hz (coincides with the baffle step) and is boosted 5db. This approach requires the selection of the speaker drivers and baffle width to work but does simplify the circuit.

I would leave the thread here, it will get more attention

max2tall · 12th October 2009, 01:56 AM

You are right.

I was looking at the speakers more as 2 ways plus subs, but if I raise the lower crossover frequency to around that 380hz for 300mm baffle width I can dispense with bsc adjustment.

Should be no problem, the bass/sub drivers are 10" hivi sp10 (hence the need for the bpa amp there)

Mids (4 x hivi m3n) - now looking at a shelving lowpass rather than a notch filter.

Leaning now towards separating the filter and amp boards as suggested earlier also.

There is, after all, only 4 connections from filter /eq section to chipamps & this saves a lot of rebuilding throughout board iterations.

Regards

MJL21193 · 01:20 PM

(For me) I would try to get as much as possible on the same board, but that's me, I don't like wires snaking all over the place. This would really increase the complexity - having the filters, power supply components and amps on one board but would reduce the wiring considerably. Each sub circuit (amps, filter sections, etc.) could be worked on individually and placed on the main board, making the process more manageable.

How do you see the levels of each speaker being adjusted? My original build had slide pots on the outside:

IM000972.JPG

When I reused the amp/filter boards for the workshop 3-ways I put trimpots in place on the boards. This makes it very inconvenient to adjust (I have to take the back off the speaker to access them).
Things to think about.

Neil Davis · 12th October 2009, 04:05 PM

Quote:

Originally Posted by max2tall

Hi,

I'm contemplating stitching together the following:

3 way LR crossover

variable BSC & notch filter on mid

LRT & balanced drive on the bass

with 3x LM4780 output, 1 for tweeter & mid, 2 in bpa for woofer / subs.

If you want to use an analog solution, the 3-way crossover board at the link listed below might be useful (see circuit #2). I've made a number of 3-way active speakers with this board and they have worked out well. I've got pictures, somewhere... It's an old design, but you can update it by downloading the posted ExpressPCB files and changing the design to meet your needs.

As John pointed out, this approach lacks flexibility, and everything I've done recently is using the STA308-series chips. These chips have built-in DSP for designing crossovers and EQ, plus they are digital, which allows using a smaller heatsink and a smaller power supply (less heat), which is good for a plateamp solution.

Right now I've got a number of smaller 2-way TAS3004 and STA328-based plateamp designs, but I've got a "4.2" plateamp that is getting debugged (lots of software). The PCB outline is below. It should be a nice plateamp. Higher-powered versions are next.

Someday I'll get around to updating that old plateamp page.

Plateamp page link: http://home.comcast.net/~neilrdavis/Plate_amps/
BCPA-4_PCB.gif

max2tall · 15th October 2009, 02:35 AM

Hi Guys, sorry I've had to be away from this for a bit, damn work is inconvenient sometimes!

John: Adjustment trimmers are to be available through holes in the plate.

Neil: A usb port on speakers would be great. Just plug in the lapptop, fiddle around with settings, sweet

Wireless setting would be even better ! This will happen I guess, but not from people like me who can't get their head around those DSP chips at all.

I've got the crossovers, mid eq, sub LRT & balanced drive all simmed in ltspice working happily together now. Next step is to layout some boards...

Currently looking like roughly 4"x4" to provide 50w+50w+300w per speaker

Cheers, Max.

star882 · 15th October 2009, 03:46 AM

Quote:

Currently looking like roughly 4"x4" to provide 50w+50w+300w per speaker

What's the third dimension? But regardless of size, pure or hybrid digital is definitely the way to go, especially for the 300w output. Stick to hybrid if you don't want DSP.

max2tall · 15th October 2009, 07:21 AM

"What's the third dimension? "

PS caps would be the highest item around 2" then.

"But regardless of size, pure or hybrid digital is definitely the way to go, especially for the 300w output. Stick to hybrid if you don't want DSP."

Indubitably, such as ? Got one to share ?

Cheers.

12th October 2009, 01:17 PM	#6
MJL21193 Account disabled at member's request Join Date: Mar 2007	(For me) I would try to get as much as possible on the same board, but that's me, I don't like wires snaking all over the place. This would really increase the complexity - having the filters, power supply components and amps on one board but would reduce the wiring considerably. Each sub circuit (amps, filter sections, etc.) could be worked on individually and placed on the main board, making the process more manageable. How do you see the levels of each speaker being adjusted? My original build had slide pots on the outside: IM000972.JPG When I reused the amp/filter boards for the workshop 3-ways I put trimpots in place on the boards. This makes it very inconvenient to adjust (I have to take the back off the speaker to access them). Things to think about. Last edited by MJL21193; 12th October 2009 at 01:20 PM.

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10th October 2009, 04:53 PM	#2
MJL21193 Account disabled at member's request Join Date: Mar 2007	Hi, I did a similar thing here. It's lack of adjustability was it's downfall. I reassigned the individual active amp boards to another pair of 3-ways for use in my workshop. One of the "plate amps": Picture 053.jpg The speakers they are powering: 350.JPG They sound great.

11th October 2009, 04:12 AM	#3
max2tall diyAudio Member Join Date: Jul 2009	Hi John, Thanks for your comments. I had a read through that long thread & picked up a few pointers, thanks. It surprises me that there's not more of this been done, I think I've looked everywhere. What seems to me to be the 'proper' way to do it these days would be some DSP chip sitting there, but I cant see any complete design thats implemented it & it's too much for this old dog to learn about fcpga's now unfortunately For my own needs I plan to make an all-in-one pair of plate-amps for forthcoming 3way speakers. Everything I need seems to be in those circuits stitched together. The notch is a problem- I do need a 3db or so 1khz notch to tame the mids, but I think the cct included is a very deep one, I'll look further for something gentler. There have been other balanced BPA drive options touted, including line drivers and audio transformers, have you thoughts on which is superior? I've got 4 quad opamps fully utilised at the moment, but could lose one perhaps. I've seen other comments about including filtering around the LM4780's themselves, reducing the cct a lot, but haven't seen any working examples, have you ? I'll have a look at the plugable filter component concept brought up in your earlier build & see if I can include it. I was already on the path of those dip package header thingies to plug in & out for that. As a relative veteran here, do you think I should post this in the 'analog line level' or the 'chip amp' area ? Best Wishes, Max.

11th October 2009, 12:35 PM	#4
MJL21193 Account disabled at member's request Join Date: Mar 2007	Hi Max, To do it over again, I would use the DIP headers as suggested to make it easily adjustable. Another mistake I made was having the boards too small - very difficult to fix or change anything. In this application, I wouldn't be afraid of using opamps, as many as needed to build the filters. I think it's not a great idea to use the power amp as a filter element. About BSC: increasing the output to the woofer will effectively do this, unless the crossover point is much different from the baffle step frequency. I now use a DCX2496 and the output to the woofer amp is crossed at 384Hz (coincides with the baffle step) and is boosted 5db. This approach requires the selection of the speaker drivers and baffle width to work but does simplify the circuit. I would leave the thread here, it will get more attention

12th October 2009, 01:56 AM	#5
max2tall diyAudio Member Join Date: Jul 2009	You are right. I was looking at the speakers more as 2 ways plus subs, but if I raise the lower crossover frequency to around that 380hz for 300mm baffle width I can dispense with bsc adjustment. Should be no problem, the bass/sub drivers are 10" hivi sp10 (hence the need for the bpa amp there) Mids (4 x hivi m3n) - now looking at a shelving lowpass rather than a notch filter. Leaning now towards separating the filter and amp boards as suggested earlier also. There is, after all, only 4 connections from filter /eq section to chipamps & this saves a lot of rebuilding throughout board iterations. Regards

15th October 2009, 02:35 AM	#8
max2tall diyAudio Member Join Date: Jul 2009	Hi Guys, sorry I've had to be away from this for a bit, damn work is inconvenient sometimes! John: Adjustment trimmers are to be available through holes in the plate. Neil: A usb port on speakers would be great. Just plug in the lapptop, fiddle around with settings, sweet Wireless setting would be even better ! This will happen I guess, but not from people like me who can't get their head around those DSP chips at all. I've got the crossovers, mid eq, sub LRT & balanced drive all simmed in ltspice working happily together now. Next step is to layout some boards... Currently looking like roughly 4"x4" to provide 50w+50w+300w per speaker Cheers, Max.

15th October 2009, 07:21 AM	#10
max2tall diyAudio Member Join Date: Jul 2009	"What's the third dimension? " PS caps would be the highest item around 2" then. "But regardless of size, pure or hybrid digital is definitely the way to go, especially for the 300w output. Stick to hybrid if you don't want DSP." Indubitably, such as ? Got one to share ? Cheers.

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