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Old 9th September 2003, 02:08 PM   #1
Elkaid is offline Elkaid  Canada
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Default A Buffer ? Why ?

Hello everyone !

In my quest on learning audio electronic basics, here's another question coming to my mind :

What's the purpose of an input buffer ?
The bridgeclone (2 paralled chip) by example is using a buffer and the PA100 circuit in National's AN1192 doesn't use any.

Those two schematics looks very similar... Any advantages in using a buffer ? Is it dangerous when omitting it ?

Thank you in advance for your help !
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Old 9th September 2003, 02:33 PM   #2
Bricolo is offline Bricolo  France
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I don't know for the PA100, but most circuits in application notes are built with the non inverting configuration

the gainclone is inverting, and has 2 disadvantages due to this:
low input impedance
the volume pot is inside the feedback loop, and feedback changes when the pot is turned


using a buffer solves these problems
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Old 9th September 2003, 04:44 PM   #3
Elkaid is offline Elkaid  Canada
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Default Merci :)

Thanks Bricolo,

PA100, as you guessed, isn't inverted.

What about DRV134 ? Is it any good ? I saw several people with OPA627 but ending with little problems...

I was planning a separate power supply for the -15/+15V feeding the DRV134 and another winding feeding my input selector PCB.

Any ideas or comments about those buffers ?

Thanks !
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Old 9th September 2003, 04:45 PM   #4
Elkaid is offline Elkaid  Canada
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Original PA100 schematic from AN1192
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File Type: jpg pa100.jpg (21.0 KB, 1440 views)
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Old 9th September 2003, 05:23 PM   #5
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Default Re: A Buffer ? Why ?

Konnichiwa,

Quote:
Originally posted by Elkaid

What's the purpose of an input buffer ?
To isolate what is behind the buffer from that in front of the buffer and visa versa.

Quote:
Originally posted by Elkaid

The bridgeclone (2 paralled chip) by example is using a buffer and
Actually, according to MY suggestions it does not, it would use a transformer. The Circuit in the original Bridgeclone thread uses a buffer and an inverter to both isolate the input from the low impedance load of the Inverter and the two other Amp's, plus it accomplishes the "phasesplit".

Using a Transformer with some stepdown is a better chocie IMHO....

Quote:
Originally posted by Elkaid

the PA100 circuit in National's AN1192 doesn't use any.
It is a simple parallel circuit, not a bridged circuit, plus it is non-inverting.

Quote:
Originally posted by Elkaid

Those two schematics looks very similar...
Do they? I would say they are about as different as possible while still using the same chip.

Quote:
Originally posted by Elkaid

Any advantages in using a buffer ?
Depends upon the application.

Quote:
Originally posted by Elkaid

Is it dangerous when omitting it ?
Usually not, the worst thing is that the source is loaded too much and starts to distort and sopund bad....

Sayonara
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Old 10th September 2003, 12:08 AM   #6
Elkaid is offline Elkaid  Canada
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Salut,

Using an input transformer is appealing indeed. Is there any suggestion for input transformer cheaper than Jensen ? I'm not sure if the sound difference worth 100$/tx.

I would like to try "standard" input transformer (something like up to 40$) and then if everything's working fine, upgrade to higher quality components.

If anyone has input transformer suggestions, please don't hesitate to share your ideas.

On a side note, just to make sure that I understand a bit the role of a DRV134 buffer by example, would the following works ?

Thank you a lot
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File Type: jpg buffered parallel gainclone small.jpg (20.5 KB, 1371 views)
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Old 10th September 2003, 02:20 AM   #7
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Quote:
Originally posted by Elkaid
Salut,

Using an input transformer is appealing indeed. Is there any suggestion for input transformer cheaper than Jensen ? I'm not sure if the sound difference worth 100$/tx.

I would like to try "standard" input transformer (something like up to 40$) and then if everything's working fine, upgrade to higher quality components.

If anyone has input transformer suggestions, please don't hesitate to share your ideas.
Sowter seems to have some relatively inexpensive input transformers.

And check out this thread started by tiroth.

http://www.diyaudio.com/forums/showt...854#post232854

He's actually using a Talema power transformer as a line level input transformer with apparently decent results.

se
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Old 10th September 2003, 03:11 AM   #8
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Quote:
Originally posted by Elkaid

On a side note, just to make sure that I understand a bit the role of a DRV134 buffer by example, would the following works ?
The DRV134 is only justifiable as a buffer if you are going to use it to invert one phase for a bridge.

If I'm not wrong you shouldn't ground one output direct, but through a resistor.

Carlos
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Old 10th September 2003, 04:09 AM   #9
Elkaid is offline Elkaid  Canada
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Thank you

So finally, it's not very practical to try do build an Buffered Inverted Paralleled GainClone is it ?

I never found such schematic...
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Old 10th September 2003, 04:35 AM   #10
JoeBob is offline JoeBob  Canada
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If you want a buffered amp, that is inverted and as well as paralleled, than build such an amp, regardless of if you've seen a schematic of it.

It's just that the DRV wouldn't be a good buffer to use. I use an OPA627 for gainclone buffering services. You could also easily use a BUF chip or even an Elantec EL200x buffer if you can get ahold of any.

The DRV is a good balanced line driver, that's why you may have seen it in bridge/parallel circuits.

You do only want a parallel amp and not a bridge/parallel amp, right?
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