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Old 23rd December 2005, 12:00 AM   #1
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Default Simple Volume/Buffer!

Requiring a quality buffer and volume control between a CD player and power amplifier, and having a small amount of otherwise waste space when panellising my current run of PCBs,
I decided to do a small board for a volume control and OPA2134 dual FET cascode chip to run from an external +/- DC supply of up to +/- 25V with onboard zener reduction and secondary filtering. Once again fully ground planed top layer with through hole plate and teflon solder mask/component overlay.

Unpretentious but fully functional.

Cheers,
Greg
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Old 23rd December 2005, 12:27 AM   #2
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Nice moment, but what is the point?
You are not a type of person who just like to show up, so where is the catch?
Schematic will be…?

P.S.: I will prefer short interconnects and passive attenuator
All the best,

Chicco
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Old 23rd December 2005, 12:36 AM   #3
lineup is offline lineup  Sweden
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Nice little circuit.

amplifierguru
Can you send me 2 of them, thank you!

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Old 23rd December 2005, 01:03 AM   #4
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Well Chicco,

I, and others, have a primary or maybe single source, say a CD or DVD player that they wish, as I do, to keep a simple signal path. The CD won't like loading lower than about 10K and the power amplifiers don't want more than 100R source impedances or their HF rolloff comes early. The output of the CD player is too high to run directly and very few have a volume control built in (or remote) so this simple cct provides a 10K or 25K (pot value) load to the CD player while buffering it and providing a 47R output Z to drive the power amps. It's stereo and only puts one op amp in the signal path so is minimalist. The PS can even be configured to split a DC walwart supply.

There's not too much a unity gain OPA puts in the way of the music.

You have a passive alternative?

Cheers,
Greg
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Old 23rd December 2005, 01:13 AM   #5
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One more opinion about passive variant, without desire to offend anyone, at least Greg.
Any modern source has enough gain to drive anything. Why we will need one more stage of amplification/buffering?
Chicco
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File Type: zip passive.zip (37.5 KB, 378 views)
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Old 23rd December 2005, 01:38 AM   #6
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Greg,
You remember the time when modern world promote electric hair dryers?
I never used one of them…
If I go active in preamp variety I will go with OPA627/BUF634, probably. IMHO
I use 24-position attenuator with Dale resistors and when I take that route I forget about active preamps.
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Old 23rd December 2005, 01:39 AM   #7
Stocker is offline Stocker  United States
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I notice a theme:

Here is my fabulous new product. That is, here is a *photograph* of my fabulous new product.

Seriously, why don't you ever post a schematic with the photo? Nice work and good idea, but come on now.
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Old 23rd December 2005, 01:57 AM   #8
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One more opinion on “my side”:

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Old 23rd December 2005, 02:04 AM   #9
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Passive???
Once more...
Chicco
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File Type: zip how the passive preamps work.zip (5.0 KB, 250 views)
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Old 23rd December 2005, 02:05 AM   #10
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Hi Chico,

i appreciate your material, but none seems to fit with the need.

Conside a CD player

Z out 100R ; Vout max 2V ; load needs >10K


Power amp input

Z in > 10K ; Vin max (say) 2V ; source Z needed << 1K to not upset input HF filter.

So your passive divider could be 9K series 1K ( 10% of the way on a 10K pot) and I would halve the HF response and get 10% of the voltage signal so max 1/100 of the power.

Turn it up, I can't hear it! But you can't, as loading will get worse and HF will get worse. Your zip article refers to both having equal output and drive needs but that's not reality. It means they both clip at the same level.

You just can't load the CD with 10K min and provide the power amp with volume control ( to more than 10%) with < 1K source Z.

That's the nub of the need.

Hi Stocker,

Would you rather I didn't post simple little solutions to a need - such as this. I wasn't gushing about it just showing how it can be implemented/solved. The circuit is so simple I didn't think there'd be any point. I'll do the schema...

Cheers,
greg
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