LM3886 running inverting only and bridged - for 8 Ohms only - Page 2 - diyAudio
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Old 31st October 2012, 06:09 AM   #11
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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

Last edited by geraldfryjr; 31st October 2012 at 06:22 AM.
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Old 31st October 2012, 10:23 AM   #12
astx is offline astx  Austria
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dear jer,

interesting variant of the inverter stage. Are you sure you are not worsening johnson noise and/or stability? With LM4562 the inverter stage alone works better as my lab equipment can measure. Also 180 degree phase shift is exactly reproduced on my 150MHz OSC ...

Regards, Toni
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Old 31st October 2012, 03:19 PM   #13
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I don't know if it increases any noise.
I do know that the same technique is used to increase the CMRR of a balanced inputs to a preamp stage or a line stage.
I got the idea out of one of Walter Jung's books on opamp applications.
My thought is that it might help keep the propagation delay equal on the two outputs compared to the input signal.

There was a study started a while back in a thread about which has less THD, a Paralleled amp or a Bridged amp.
The TDA7293 was used.
I can find the link if you like.

jer

Last edited by geraldfryjr; 31st October 2012 at 03:39 PM.
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Old 31st October 2012, 03:37 PM   #14
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Here is the link with some interesting results,

TDA7293 single, bridge, parallel

Jer
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Old 31st October 2012, 03:40 PM   #15
astx is offline astx  Austria
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Dear jer,

perhaps somebody is out there which can tell us the pro and contra of the two inverter stage variants.

About paralleled / bridged (op)amp:
Thank you for the link!

Regards, Toni

Last edited by astx; 31st October 2012 at 03:41 PM. Reason: A bit too late ...
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Old 1st November 2012, 11:24 AM   #16
AndrewT is online now AndrewT  Scotland
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I can only see one single ended to differential output stage.
How can we compare?

The one shown is simply a non-inverting stagem followed by an inverting stage.
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Old 1st November 2012, 02:09 PM   #17
astx is offline astx  Austria
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Dear AndrewT,

this is to be compared. See schematic.

Left: high input impedance

Right: needs low input impedance. Input will be attenuated to 50%.

The Question is: does the right variant help to keep the propagation delay equal on the two outputs compared to the input signal?

Regards, Toni
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File Type: png se_to_balanced_driver_variants.png (36.2 KB, 197 views)
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Old 1st November 2012, 02:19 PM   #18
AndrewT is online now AndrewT  Scotland
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the 1k+1k (-6dB) attenuator on the input has absolutely no influence on the propagation delay of the single ended to differential stage.
It simply changes the sensitivity of the whole stage by 6dB. i.e. the My variant needs less input for the same output, if the stage gains are the same.

I'm not so sure about the effects that the changed feedback network have.
The gain of both parts of My are set to 1 (+0dB).
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Last edited by AndrewT; 1st November 2012 at 02:23 PM.
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Old 1st November 2012, 02:42 PM   #19
astx is offline astx  Austria
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If we compare the two topologies, IMHO there could be no significant reduction in propagation delay.

geraldfryjr: perhaps you can post us more about Walter Jungs findings about this?

Cheers,
Toni
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Old 2nd November 2012, 02:32 AM   #20
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Here are a few things,

http://waltjung.org/PDFs/ADI_1993_Se...io_Drivers.pdf

http://waltjung.org/PDFs/Op_Amps_in_...ircuits_P2.pdf

On page 42 of this document is pretty much what was in my book and page 69 is something similar as well but more involved as it is a diagram of a SSM2142 driver chip,Page 113 and 138 is of interest of the cross coupled driver in more detail,page 161 is more like the configuration I came up with only it has a balanced input configuration,

http://www.analog.com/library/analog...h6_final_I.pdf

I don't know off hand were my book is as it is in a few pieces as I have read it so much through the years.
But if I can locate it soon I will scan the pages in it as well and post them.

Here is were I found these links,

Services

Great stuff !!!

jer

Last edited by geraldfryjr; 2nd November 2012 at 02:45 AM.
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