HQ Balanced Phono Preamplifier for MC Cartridges using OPA2604 - diyAudio
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Old 8th September 2008, 12:02 PM   #1
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Default HQ Balanced Phono Preamplifier for MC Cartridges using OPA2604

Hello all. This is certainly the most informative DIY audio site I have came across and have been reading various topics for weeks now.

I have an idea for a HQ phono preamplifier with balanced input and SE output. I have read many great reports about balanced phono preamplifiers and this makes me exciting to try it.

Recently studied some op-amps and the Burr-Brown OPA2604 looks like a good candidate.

I am aware that not many enthusiasts are keen on using op-amps but I take a different view. The high PSRR is one of the first attractive features. Dual packages (or even quad) the second, etc.

I would like to toy with a 3 stage balanced setup using passive RIAA networks and maybe round it off with a tube buffer.

Gain of around 60dB is the goal and SNR of 60dB or more would be nice.

Lets embrace this wonderful technology called INTEGRATED CIRCUITS!

I believe Graham Slee uses op-amps in their phono preamplifiers.

Cheers

BIEP BIEP
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Old 8th September 2008, 12:31 PM   #2
Werner is offline Werner  Europe
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"the Burr-Brown OPA2604 looks like a good candidate."

Why? High noise and high distortion (forget the datasheet) make it
less than suitable for a phonostage front-end. About its only interesting feature is its very wide supply voltage range.

"The high PSRR is one of the first attractive features."

I wouldn't call 80dB particularly high.

"Gain of around 60dB is the goal and SNR of 60dB or more would be nice. "

The first 60dB indicates you want to make an MC pre, right? The second 60dB isn't very ambitious. Try to aim at 75-80dB to make life, and the project's result, more interesting.

Consider a low noise instrumentation amplifier like the SSM2019
or INA103.
You'll find these in quite a few commercial microphone and moving coil preamps. They are natively differential-in and have noise performance close to what's attainable with integrated devices.

If you really want to throw standard opamps at a differential input, then have a look at the AD797 and LT1028.

If you want to go discrete, then FETs like the 2SK369 apply. There's a neat example
here.
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Old 10th September 2008, 11:12 AM   #3
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suggestion: tray a simple mad_k mod of PacificRiaa

jfet single ended-openloop no feedback, cheap, very very nice romantic sound ,if you want more detail(lower 2HD) change 2sk170gr idss 5ma for bl +33r on source
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Old 31st October 2008, 07:22 AM   #4
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Default Phono stage; balanced

I own two balanced Phono stages;

one is DIY and uses the DACT Phono board ( Danish Audio Connect ) which is superb; it's only a matter of fabbing a box + power supply; single ended input + balanced output

The DACT board uses surface mount components + is very accurate to the RIAA curve. Easilly adjustable for gain + capacitance with internal dipswitches

The other is the B.A.T. VP10SE; which is not DIY, has the choice of Balanced or single ended input, but only balanced output

Using Balanced cable ( XLR's ) greatly reduces the noise floor compared to SE, in a Phono stage, in my experience

Good luck with your project!

The Electric Gypsy
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Old 31st October 2008, 08:29 AM   #5
h_a is offline h_a  Europe
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Don't forget differential input has 3dB worse noise compared to single ended input,

http://www.diyaudio.com/forums/showt...96#post1354996

If you use nice 100% covered shielded cabling, I don't see much that can be left to be canceled by balanced cabling

Have fun, Hannes
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Old 1st November 2008, 05:27 AM   #6
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Default Balanced vs. Single ended input

Using a balanced input on the B.A.T. , compared to a single-ended input, results in a significant drop in background noise + an increase in detail

This is particularly noticeable with low-output moving coil cartridges

I have 2 Phono cables that are identical but for their RCA/XLR terminations ( ie: same length, type + manufacturer ) and A/B'ing these the XLR setup is immediately noticeable as the better ( and quieter ! ) of the two

GW

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