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Chip Amps Amplifiers based on integrated circuits

Another LM4780 for Bi amping
Another LM4780 for Bi amping
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Old 2nd April 2017, 02:10 PM   #1
dipolar is offline dipolar  India
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Default Another LM4780 for Bi amping

Hi Fellow Diyers,

Here is a Diyable single sided LM4780 PCB if you are interested.

Nothing exotic or Fancy about the schematic ,it is from manufacturers Datasheet.

I have built this Amp recently a month ago for my Dipole speakers driven by miniDSP.

Good things as in manufacturers datasheet
1.Approximately 50watt X 4 channels
2.Onboard AC rectifier (directly connect the 25-0-25 AC transformer)
3.No output clicks and pops while startup to blow out tweeters (mute function used) .
5.Tested and working since last 30 days.
6.No ground loop or Hum issues faced so far.
7.Single layer diyfriendly PCB
Bad things
1. Would need a massive Heatsink
2.Fixing the chip on Heatsink can be tricky which plays crucial part in performance and life of this chip.
3.Sometimes LM4780 might be unobtainable.
Attached Images
File Type: png Lm4780.png (191.5 KB, 292 views)
File Type: jpg Lm4780 Schema.jpg (244.7 KB, 300 views)
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Old 4th April 2017, 07:48 AM   #2
AndrewT is offline AndrewT  Scotland
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Quote:
5.Tested and working since last 30 days.
not with the asch you have posted.
The gain looks like it is virtually 1x (+0dB) and the manufacturer tells us all to use >10x (+20dB)
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Old 4th April 2017, 09:24 AM   #3
dipolar is offline dipolar  India
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Quote:
Originally Posted by AndrewT View Post
not with the asch you have posted.
The gain looks like it is virtually 1x (+0dB) and the manufacturer tells us all to use >10x (+20dB)
Gv= 1+(22k /680ohms )
=33

Did we miss something?
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Old 4th April 2017, 09:37 AM   #4
AndrewT is offline AndrewT  Scotland
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I mis-read your sch. You're OK.
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Old 4th April 2017, 09:45 AM   #5
dipolar is offline dipolar  India
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I had to contain 4 amplifiers with 200Va trafo into 30cmx20cmX10cm cabinet.
So tradeoff was small heatsink.
Lm4780 is dual Lm3886 in one package hence double the heat,I ended up forced cooling with a Fan which is triggered by a thermistor above 80dgreeC.

LM4780 is far better than any 50 w Class D amp I have heard,Initially my plan was to use class D amps for the available space but Dipoles speakers were not forgiving with class D amps Then I went back to LM3886 and TDA7293.
I preferred LM3886 as whatever TDA7293 chip I got my hands on were all counterfeits (from UTstar and ebay) .

After fiddling with LM3886 I finally decided upon 2 in 1 LM4780 .It did not dissapoint except for super heat.
In order to further reduce the the thermal resistance I discarded the heatsink Insulator and bolted the Chip directly on the heatsink which makes heatsink active negative.whole PCB and heatsink has been isolated from cabinet using spacers.
Rgds.
Attached Images
File Type: jpg 60999132-9638-45ed-8a4d-14d6ad354613.jpg (123.8 KB, 254 views)
File Type: jpg fba9a303-b85c-4fb2-b59b-7eae65d8c74b.jpg (123.9 KB, 244 views)
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Last edited by dipolar; 4th April 2017 at 09:48 AM.
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Old 4th July 2018, 09:33 AM   #6
The Prof is offline The Prof  United Kingdom
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I hope it is still working nicely in your system now. How will you sum up your impressions after living with it for more than a year?
I am more interested in your dipoles. You may kindly pm me to avoid cluttering the thread.

Warm regards.
--UKP
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Old 6th July 2018, 02:15 AM   #7
MikeWhy is offline MikeWhy  United States
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Actually, I'm interested in the dipole and dual bridged amps, too. I have a similar use in mind. Would love to hear details and impressions. Thanks.
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Old 6th July 2018, 02:25 PM   #8
tomchr is offline tomchr  Canada
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Before diving head first into bridged amps, I suggest reading my Taming the LM3886 - Output Power page. While some of the info there is specific to the LM3886, most of it applies across all amplifiers.

Tom
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Old 7th July 2018, 12:10 AM   #9
MikeWhy is offline MikeWhy  United States
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Hi Tom. I have read your LM3886 site. Thanks for sharing those thoughts.

My interest is speculative at this point. I unearthed a pair of long forgotten 4780's from my parts box, and now am looking for mischief to create. It was the dipole remark earlier that caught my interest more so than bridging.

Bridging always seemed a bad idea, although I've never seen any words written on what seems to me is a guaranteed DC offset. Any -- seemingly unavoidable, actually-- slight mismatch between the two amps or just a variance in gain puts a DC component across the speaker.

Anyway... the two thoughts are related. I'm out of DSP channels and am in possession of some spare parts that are compatible with the excess volt amps of my newly larger toroid.
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Old 7th July 2018, 12:17 AM   #10
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by MikeWhy View Post
My interest is speculative at this point. I unearthed a pair of long forgotten 4780's from my parts box, and now am looking for mischief to create.
Fair enough.

Quote:
Originally Posted by MikeWhy View Post
Bridging always seemed a bad idea, although I've never seen any words written on what seems to me is a guaranteed DC offset. Any -- seemingly unavoidable, actually-- slight mismatch between the two amps or just a variance in gain puts a DC component across the speaker.
Not necessarily. You can put a DC servo on a bridged amp and drive the DC offset to (near) zero if you wish.

The gain mismatch can also be dealt with by using 0.1% tolerance resistors, which are now available for really not that much money. That doesn't eliminate the mismatch, obviously. It only makes it smaller.

If you're stuck at a lower supply voltage, bridging can be the ticket to getting the output power you want. As you've noted, it does come with a set of drawbacks, however.

Tom
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