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Old 9th July 2005, 08:22 PM   #1
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Default The "Freebird" ultra clean ultra simple preamp design

Ok, so in another (much longer) thread we have been discussing preamp for chip amps.

Well, I have several designs in the works, and here is one of them The preamp is designed for those who just need a clean preamp with enough current to drive a typical chip amp (anything with moderate to high input impedance).

This is a simple stereo preamp with seperate 0V plane for signal ground. The board is designed the the GND plane and the 0V planes can be joined on board by a resistor or a jumper.

The board is compact at 3.3" x 1.575".

I have been aproached by several people about bringing forward a design like this as a group buy. Well this is what I have to offer right now. If there is enough interest I will order some for a group buy.

Keep in mind I know that some of you want a design with a buffer, and I am working on a few of those types as well, but that will be for a different thread.

Please take a look and give me your feedback. Thanks!
Russ

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Old 9th July 2005, 08:35 PM   #2
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So, where are the regulators? They won't work that well if they are not in the immediate vicinity of the opamps. Or are you're going to use sense lines?
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Old 9th July 2005, 08:47 PM   #3
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Quote:
Originally posted by analog_sa
So, where are the regulators?
That is for a different design. This one is intended to be "simple" and compact.


I am listening to it right now with a +/- 15V reglated supply with about 3" wires from the supply to the board. It sounds simply stunning.
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Old 10th July 2005, 12:17 AM   #4
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Here are some pics of my first prototype board efter I etched,drilled, and applied the (sorta)silkscreen.

Cheers!

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Old 10th July 2005, 02:51 AM   #5
maxw is offline maxw  United Kingdom
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Quote:
Originally posted by analog_sa
So, where are the regulators? They won't work that well if they are not in the immediate vicinity of the opamps.
Anybody else agree with this? Would be interesting to get some feedback from people who have tried both. There may be some truth in it, eg RJM's Phonoclone uses 1x reg per opamp rail (4 regs per channel). I'm just curious...
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Old 10th July 2005, 03:39 AM   #6
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Quote:
Originally posted by maxw


Anybody else agree with this? Would be interesting to get some feedback from people who have tried both. There may be some truth in it, eg RJM's Phonoclone uses 1x reg per opamp rail (4 regs per channel). I'm just curious...

Yes there is truth to it, but no it will not be in this design.
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Old 10th July 2005, 04:02 AM   #7
Bare is offline Bare  Canada
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Now I'm a nooby at Chip amps..
But why does one even Need a PreAmp??? I see no phono section in yr Gizmo.
Most Cdp or DVD players output 2 volts (at least)

A simple elegant Stepped attenuator has gotta be a simpler more elegant circuit that a couple of Opamps which will invariably require some excreable Pot for volume control.
IMHO seems this all seems errr ....redundant.
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Old 10th July 2005, 09:08 AM   #8
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Quote:
IMHO seems this all seems errr ....redundant.

All means of controlling the volume sound radically different. If you have compared resistor based passives against transformer based against active line stages you would know that choosing the best presentation to suit your system is not trivial.

The basic criticism against passives is their reluctance to convincingly drive anything. Even when impedances are easy a passive attenuator may suffer at drive, pace and substance as far as musical presentation is concerned.

To build an active line stage which approaches the transparency of a passive attenuator is, otoh, extremely difficult. Can it be done using an opamp? Hmmm.
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Old 10th July 2005, 11:03 AM   #9
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Quote:
IMHO seems this all seems errr ....redundant.
An active preamp is a desirable thing for those who choose to use lower gains in there chipamps, for whatever their reasons or beliefs.

I for one use an OPA549 chipamp, these chips can only really use a gain of 10 at most (IMO) before the sound starts to becomes a little coloured.

However if you are using the National LM chips as they can accept higher gains, an active pre MAY not be needed, but then that depends on the user.

Also people want to try their hand at designing and building other things.
If their designs are succseful and and generate enough interest from other people, why not suggest a group buy?

By no means am I trying to start an argument or rubbish the beleifs of others, I'm meerly tying to state that, you cant please all people all the time, and every one is entitled to their own opinions right or wrong.


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Old 10th July 2005, 01:26 PM   #10
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I have built the BrianGT Lm3886 chipamp kit and have used it with passive and active preamps. There is absolutely no comparison, I know a lot of people do it but these chipamps work on a whole different level with used with some sort of either active or just buffered preamp. With pasive preamp you get a really clean soundng amp, if thats all you want fine. I simply couldnt listen to it, just boring. Even using my Nad c350 as a preamp put the amp into a diffeent league, now with nuuks buffered solution it sounds even better. All the drama goes out of the music when you use just a pot and a source selector, nothing has any impact or drame.

By all means use a passive pre it just your missing all the music.

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