LM3886 running inverting only and bridged - for 8 Ohms only - Page 3 - diyAudio
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Old 2nd November 2012, 07:58 AM   #21
astx is offline astx  Austria
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Join Date: Jan 2011
Location: Tyrol / Austria
Dear Jer,

thank you for the links. The "cross coupled driver" circuit (page 113 and 138 from PDF Web_Ch6_final_I.pdf) was also one of my favorites. I didn't use it because this configuration needs an extra input buffer to get high input impedance.

... hopefully waiting for scanned pages ...

Cheers, Toni
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Old 5th November 2012, 12:52 PM   #22
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Join Date: Feb 2008
Location: Jackson,michigan
Quote:
Originally Posted by geraldfryjr View Post
I have used that input phase splitting input configurations for many years in simulations and a few projects.
I have been wanting to try it driving some LM4870's that I have five of for a BPA400 or 800 setup or something.
As I was going to get some more when National Semiconductor used to send you some free samples .
I haven't messed with them because I recently got my big power amps back from Florida.
Now I find my requirements are more for a parallel style setup for my ESL's.
But here is the start of my project,

TDA7293 Bridge Parallel Circuit

I wanted to not have to use a transformer or any special opamps.
When I first started using the circuit in the 90's, differential output opamps were scarce and a bit rare to find.

I also used the same method for this bass preamp for a fellow DIYer,

Help needed with direct output (DI) for bass amp

Cheers!!

jer

Oops I meant LM4780's !!

Sorry !!

jer
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Old 24th January 2013, 02:15 PM   #23
astx is offline astx  Austria
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Join Date: Jan 2011
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THD Spectrum at 1kHz
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File Type: png 1024x718-THD+N_1kHz_30VRMS.png (33.3 KB, 99 views)
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Old 24th January 2013, 05:01 PM   #24
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Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)
I've always liked the sound of inverted better--the highs seem cleaner?!?

I also like the idea of a balanced output stage. If you're careful and make everything as symmetrical as possible you can cancel some distortion and other products of the 3886. I also like that it draws on the power supply in a symmetrical way with the same sorts of benefits. I wonder if going with a LM4780 would be even better because you would get better matching between the two 3886s (same die) and better thermal tracking too!

Note that this amp won't drive low loads. Each amp 'sees' half the load so a 6 ohm speaker looks like a 3 ohm load to both of the 3886.

Good luck, it looks like fun .... I have some 4780 boards around here somewhere, I might join you!

Cheers,
Jeff

PS How about one of those single-ended to balanced chips (DRV134, THAT1646) or transformer input (gal iso, single-end to bal, 10k:600 to drive 1k, BW limiting, ...)?

Last edited by AudioLapDance; 24th January 2013 at 05:10 PM.
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Old 24th January 2013, 07:50 PM   #25
astx is offline astx  Austria
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Join Date: Jan 2011
Location: Tyrol / Austria
Dear AudioLapDance,

thank you for "good luck" - the project is finished since sommer 2012 and the power amp is playing like a charm every day.
Of course it is well known, that LM3886 bridged can only serve 8 Ohm speakers - and the cooling must be very good to avoid the built in SPIKE protection.

The reason not to choose LM4780 are:
  • harder for DIY due to smaller pin distance and the need for smaller PCB traces
  • lower total power with higher distortion driving 4 Ohms.
The LM3886 can drive 68W to 4 Ohms - or more as 120W in bridged mode to 8 Ohm speakers. LM4780 does not have the same low distortion level on full power output bridged into 8 Ohms.
Regarding the sound of inverted: you are completely right.Not only THD and IMD graphs are relatively nice - the sound is very clean, clear and transparent.
IMHO input transformers are a no go for me (use them only to galvanically decouple SPDIF or so). I have choosen the LM4562 as they perform very well, neutral and fast to provide a balanced output signal to drive the two LM3886 inverted. But if you have some Ideas I think other users will be very happy to read more about.

Cheers, Toni
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