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Old 18th September 2003, 09:05 PM   #1
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Default PGA2310 buffer question

Now my minimal PGA2310 volume controll is working, i think about a buffer.

From the datasheet: "[...] the capability to drive 600 Ohm loads directly without buffering" -- ok, no output buffe needed.

"[...] It is important to drive the PGA2310 with a low impedance . If a source impedance of greater than 600 Ohm is used, the distortion performace of the PGA2310 will begin to degrade."

ok, my CD player is 3k Ohm. Buffer needed.

Should i use opamp stuff like buf634, or would the simple single mosfet buffer from Zen V4 work also for the PGA?
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Old 18th September 2003, 09:51 PM   #2
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Just curious: why is your CD player 3k? It seems like a better plan to reduce the output impedance of the cd player rather then introduce extra stages. What's the sound like at present?
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Old 19th September 2003, 04:33 PM   #3
cdl is offline cdl  Denmark
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Sounds good that vol-ctrl is working!

Zen stage sounds rather tempting, but on the other hand there's an opamp in the PGA thingy anyway, so another opamp might be a natural starting point...

How about a simple opamp in unity gain...? E.g. Opa627, should work I think.

Those who like it can use a current source / pulldown resistor to bias it class A.

Should be fairly easy to try both Zen and opamp out that way,

/cdl
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Old 19th September 2003, 10:35 PM   #4
soren is offline soren  Denmark
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I have made some measurements of PGA2310 and 2311 with an Audio Presicion equipment. I used both unbuffered or buffered (inverting, noninverting) output. As outputbuffer I tried OPA627 and OPA134 (which should be the same as the one inside the PGA231x).

I could not see any differences in the output spectrum wheter it was buffered or not, I tried both 100k and 600 Ohms of load impedance.

The measurements where made with a rather crappy power supply, but I met the specs in the datasheets. One thing that could be taken into account when choosing between the two is the lower noise from PGA2311, but only if you can live with the lower maximum output.

The results made it clear to me that my next preamp should not have any buffering after the PGA.
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Old 19th September 2003, 10:38 PM   #5
soren is offline soren  Denmark
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Ooouups...

I read a bit too fast.

Till will make an input buffer. My measurements was of an output buffer...
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Old 20th September 2003, 12:57 AM   #6
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sorry, i checked, my CDP and TDA1305 DAC isnīt 3k output impedance, but says minimum Rload = 3k.

Does this mean no buffers needed? What is input impedance of PGAS2310?
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