Hi guys 
As promised some time ago when I played with RelaiXedSMD that I'll try to find the best OP amp to directly drive First One.
My source was fully differential Wolfson DAC, of course one Wolfson DAC chip per channel. Fully differential DAC voltage output low pass filtered in two stages, filter impedance normally matched to an output impedance of DAC chip. After this differential passive network single sum OP amp follows, which also has to serve as an output low Z driver, all in one. This request is nothing too demanding or strange for modern OP amps to fulfill since most of them can drive full signal swing on 600 Ohms load through extended audio power bandwidth. Signal than followed to low impedance shunt volume regulator exactly matched with input impedance of the First One amplifier.
Most care was taken to power supply decoupling, direct to PCB IC soldering, etc. The candidates were these, also tested in this sequence:
OPA134
LME49713 (specially compensated)
LME49710
OPA1641
LME49990
ADA4627-1
Interestingly each and everyone has its specific sound signature easily recognized through the First One amplifier and Zu Soul Supremes.
Well as there's nothing ideal in this world, the same here, but one has to choose best compromise to match its personal taste. I have not enought time at the moment to put explanation for each of them, maybe sometimes later, I can only say who's my best preferred choice: ADA4627-1
More to come, stay tuned.
As promised some time ago when I played with RelaiXedSMD that I'll try to find the best OP amp to directly drive First One.
My source was fully differential Wolfson DAC, of course one Wolfson DAC chip per channel. Fully differential DAC voltage output low pass filtered in two stages, filter impedance normally matched to an output impedance of DAC chip. After this differential passive network single sum OP amp follows, which also has to serve as an output low Z driver, all in one. This request is nothing too demanding or strange for modern OP amps to fulfill since most of them can drive full signal swing on 600 Ohms load through extended audio power bandwidth. Signal than followed to low impedance shunt volume regulator exactly matched with input impedance of the First One amplifier.
Most care was taken to power supply decoupling, direct to PCB IC soldering, etc. The candidates were these, also tested in this sequence:
OPA134
LME49713 (specially compensated)
LME49710
OPA1641
LME49990
ADA4627-1
Interestingly each and everyone has its specific sound signature easily recognized through the First One amplifier and Zu Soul Supremes.
Well as there's nothing ideal in this world, the same here, but one has to choose best compromise to match its personal taste. I have not enought time at the moment to put explanation for each of them, maybe sometimes later, I can only say who's my best preferred choice: ADA4627-1
More to come, stay tuned.
Hi, L.C !
What do you mean "specially compensated ?" (I wonder, because it is a CFA).
Well, the good feedback resistance value to get no overshoot on pulse ?
Have-you tried to increase this resistance to get-it over compensated (it is better in time domain) ?
Did-you tried-it in inverting mode (haha) or how did -you managed the "fully differential ?
Did-you tried the metal case one ?
(Just my nose is smelling a good perfume around this one, but for asymmetrical input ;-(
nb: Shame on those IC manufacturers who never show anymore schematics of their OPA !
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chip roll'n fun
For that specific application, you really should audition the OPA211/OPA1611 (datasheet comparison is an interesting adventure
).
Cheers
Hi guys
As promised some time ago when I played with RelaiXedSMD that I'll try to find the best OP amp to directly drive First One.
<snip>
Most care was taken to power supply decoupling, direct to PCB IC soldering, etc. The candidates were these, also tested in this sequence:
OPA134
LME49713 (specially compensated)
LME49710
OPA1641
LME49990
ADA4627-1
Interestingly each and everyone has its specific sound signature easily recognized through the First One amplifier and Zu Soul Supremes.
Well as there's nothing ideal in this world, the same here, but one has to choose best compromise to match its personal taste. I have not enought time at the moment to put explanation for each of them, maybe sometimes later, I can only say who's my best preferred choice: ADA4627-1
More to come, stay tuned.
For that specific application, you really should audition the OPA211/OPA1611 (datasheet comparison is an interesting adventure
).Cheers
Hi Christophe
It is fully differential 2 stage filter, so I had to adopt filter components as well as compensation to stabilize it and linearize HF gain response. Still not good since filter would have to be even lower Z, but that would not be acceptable for Wolfson DAC output, one per channel.
Two opamps in series I don't like for such a task, so I use fet input OP amp ADA4627-1 and it works perfectly.
For that specific application, you really should audition the OPA211/OPA1611 (datasheet comparison is an interesting adventure
Cheers
Too high input bias current for my purpose. 🙂
Regards, L.C.
Ufff battery supplied cables, unknown schematic, impedances, resonant circuits, God knows what's inside. 😱
Extra serial LR helped? 🙂
First One chassis C1 ready made amplifier
What's inside:
- 2 First One modules
- 2 SMPS1200A400
- 2 DC sense modules
- C1 Chassis silver
- Acrolink FP-804R speaker binding posts
Regards, L.C.
As promised, First One for my friend finished, tested, already delivered. 🙂Started an assembly of a new First One amplifier for a friend. It's a generic dual mono version with two SMPS1200A400 and DC Sense protection. Pics will follow soon.
What's inside:
- 2 First One modules
- 2 SMPS1200A400
- 2 DC sense modules
- C1 Chassis silver
- Acrolink FP-804R speaker binding posts
Regards, L.C.
Attachments
Opamp roll'n fun
Then give an ear to AD8065, FET input, high SR, okay current drive... kind of a unique opamp with a likeable sound.
<snip>
Too high input bias current for my purpose. 🙂
Regards, L.C.
Then give an ear to AD8065, FET input, high SR, okay current drive... kind of a unique opamp with a likeable sound.
I have a question.
How do you power on and off the amp?
How do you power on and off the amp?
As promised, First One for my friend finished, tested, already delivered. 🙂
What's inside:
- 2 First One modules
- 2 SMPS1200A400
- 2 DC sense modules
- C1 Chassis silver
- Acrolink FP-804R speaker binding posts
Regards, L.C.
