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MiniMax DAC - best opamps to replace stock ones?
MiniMax DAC - best opamps to replace stock ones?
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Old 20th October 2011, 01:11 AM   #21
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by SoNic_real_one View Post
LM4562 has a special input stage, is not a plain jfet.
Right, its not any kind of jfet, its bipolar.
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Old 20th October 2011, 01:42 AM   #22
vdi_nenna is offline vdi_nenna  United States
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Quote:
its bipolar
I couldn't find this in any of the spec sheets. Thanks.
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Old 20th October 2011, 01:50 AM   #23
abraxalito is offline abraxalito  United Kingdom
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The 'giveaway' in a datasheet to distinguish bipolar from FET is the spec for input noise current. LM4562 shows this as 1.6pA/rtHz. A JFET opamp's figure for this is orders of magnitude lower. Take the OPA627 as a comparison, its 1.6fA/rtHz.
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Old 20th October 2011, 04:50 AM   #24
Audio Maniac is offline Audio Maniac  Brazil
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Based on Diyaudio's comments, ESS Technology's "Sabre Aplication Note" and Douglas Schrodeder's articles, I have decided to try the following op-amps:

OPA2604 (I/V conversion and LPF filter) + AD797 (output)
LME49720 ou LM4562 (I/V and LPF) + LME49710 (output)
dual mono OPA627 (I/V and LPF) + OPA627 (output)

I would like to thank all of you who made those helpful contributions in this thread.

Greatings!

http://www.esstech.com/PDF/Applicati...PCB_Layout.pdf
UPDATE 1/18/2011: Eastern Electric Minimax DAC - upgrading op-amps Review - Equipment Reviews - Dagogo
Audio Blast: Eastern Electric Minimax DAC Opamp Rolling - The Columns - Dagogo
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Old 20th October 2011, 07:24 AM   #25
qusp is offline qusp  Australia
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I suggest also trying the lme49990 (output) and opa827 (input), these weren't around when the sabre app note was generated, well perhaps the opa827 was. 827 is jfet input, lme is bipolar
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Old 20th October 2011, 07:40 AM   #26
Mooly is offline Mooly  United Kingdom
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MiniMax DAC - best opamps to replace stock ones?
The AD797 is one that needs care... it might have stability issues as a drop in replacement.

Keep it simple... the OPA2604 and LM4562 should be fine. For a single opamp for the output I would have an OPA604 to hand.

I have also used the AD845 with excellent results.

If the original is an NE5534 you need to check if an external compensation network (cap) is fitted between pins 5 and 8 and remove it.
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Old 20th October 2011, 01:31 PM   #27
Audio Maniac is offline Audio Maniac  Brazil
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Hi Mooly! Thank you again!

I'll do it then. Taking into account it's not cheap and your warning, I'll avoid it.

Qusq, I'll study about the LME49990. In Schrodeder's article, it was used on MiniMax DAC. Thx!
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Old 21st October 2011, 12:12 AM   #28
SoNic_real_one is offline SoNic_real_one  United States
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Quote:
Originally Posted by abraxalito View Post
Right, its not any kind of jfet, its bipolar.
But is not plain bipolar either
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Old 21st October 2011, 12:46 AM   #29
SoNic_real_one is offline SoNic_real_one  United States
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Hint: emitter degeneration
Book.

Last edited by SoNic_real_one; 21st October 2011 at 01:08 AM.
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Old 21st October 2011, 01:20 AM   #30
Michael Bean is offline Michael Bean  United States
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I've used the AD827 for I/V conversion with great results, only caveat is power supply bypassing and circuit layout are very important with this chip. Get it right and nothing, not even discretes sound better.

Mike
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