best op amp for C'moy amp

[xrk971]

Thanks, I also found same ones by googling. Simple.lib directive and usual opamp2 symbol works fine. It's rare that off-the-shelf models work this easily.

 

[00940]

I made a lot of copy pasting in the sim file so I don't have the sim of the FR but it's easily reproduced. Here is the .asc for the stability probe.

 

[xrk971]

This could be part of the reason why the OPA1688 sounds so good. The FFT shows dominant H2 and monotonically decreasing higher orders. This is unusual for an opamp, which normally are H3 third order dominant due to use of typical LTP input stages. This is 2vpp into 47ohms:

 

[Dibya]

Should I keep 47pf ?

 

[xrk971]

The adjustment of the feedback cap is a very subjective thing. If you have an Oscope you can reduce until onset of oscillation and then increase by certain value. Without an oscope, I recall a technique described as listening for a “glassy sound” as you reduce the cap value. Once you hear the glassy sound, do not go any smaller in value. Let me double check this - it was mentioned by Aksa. I can go in and drop the value to 16pF by using two 33pF NP0 in series.

I think it sounds quite good at present. But you never know until you try.

 

[xrk971]

I just took it down to 33pF and I think it subjectively sounds better. Also increased the Zobel R from 4.7R to 47R.

 

[Dibya]

I am Dead . People are sound blind. The guy from Mayflower electronic said MP3 and flac don't sound different. God take me to heaven. How he dare to call himself as audiophile. Most of the cases I feel difference . MP3 on my scurlet solo feels like I am listening to a old mp3 player. I am nailed someone save me .

 

[xrk971]

Of course they sound different, and depending on bit rate of mp3 etc. 256k mp3 is not too bad, but 192k 24bit FLAC is definitely better. There is also 768k 32bit - I only have a few songs recorded at this rate and with the proper amp/headphone you hear it for sure.

Focusrite is a nice DAC. The AK4490EN is a bit more resolving - that's on my Cayin N3.

https://www.akm.com/akm/en/file/datasheet/AK4490EN.pdf

 

[Dibya]

Even I see difference between flac and MP3 when I play it on my Nokia 8 .
I love my focusrite scarlet solo . I am amateur singer . I love it to record my stuff's. I want to learn to play guitar too ..... Oh sorry getting bit off topic

 

[Dibya]

I am wondering how to get 768Hz/32-bit from usb as i2s .

 

[Stillhart]

Unless you feel like re-inventing the wheel....

Use two 1688 and just get the nice board from AGDR that handles all the issues of unbalanced rails auto-protect, turn on thump protect relay, etc. 1688 makes a really nice amp. There are just a lot of ancillary supporting components needed to make it a user friendly amp - and might as well make something that sounds better than an O2.

OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs

Sorry to hijack but I am working on a super basic CMoy as my first DIY project using the instructions here and I was wondering if I need to modify the circuit in any way if I want to use the 1688 instead of the recommended OPA2132PA.


EDIT - Oh I see it's SMB only and you need 2. I'll save that for my second go round... Please disregard.

 

[xrk971]

You can get an adapter board that lets it fit on DIP8 socket. The OPA1688 is a dual opamp.

 

[xrk971]

Just an update that I am still using this mostly as a low noise preamp in any situation where I need to break a ground loop hum. But turns out to sound great and be useful as a general purpose Preamp. The rechargeable 9v batteries last about 3-4 days with average use. Very reasonable recharge rate. I will put his in a proper portable case and keep on hand as a tool for on the spot pre duties.

 

[xrk971]

Here is a dual parallel buffer version of the above amp good for 150mA into 32ohms:

More info here:
http://www.diyaudio.com/forums/head...pa1688-low-thd-muscle-amp-10.html#post5494197

 

[xrk971]

This is my current listening rig while the basement audio lab is undergoing repairs due to flooding. The dual OPA1688 buffer amp shown above plus the PSU from this project: a 310mA +/-18v DC-DC plus TPS7Axxxx LDO regulators and MOSFET cap Mx plus CRCRC filter is an awesome combination. Powered by a 1amp 12v Class 2 wall wart transformer, it is absolutely silent no hiss or hum. With OB-1 headphones and Focusrite as DAC, I can't play it past 1/2 volume before too loud. 150mA of drive at +/-18v is a lot of headroom for most headphones.

This is the PSU - hand etched prototype:

 

[Dibya]

I managed somebody to solder OPA1622 to dip8 socket. I want to try OPA1622 . He want stencil for OPA1622 which I can't find anywhere. Please someone help me to find one.

 

[OlegSh]

If it is a one-off adapter then producing a stencil for it is not worth the effort and money. I doubt you'll find one. Some time ago I designed and assembled several of these adapters. I solder OPA1622 successfully without a stencil.

If you are absolutely sure you need a stencil just search for VSON-10 or QFN-10 package stencil, not necessarily OPA1622 since there are many ICs in such packages these days.

 

[xrk971]

OPA1622/VSON10 breakout board layout

You don’t need stencil to solder. Just apply paste with syringe and hypo needle. Then heat over hotplate or airgun (if you have one).

 

[Dibya]

Thanks OlegSh and xrk971.
I don't have any solder paste and hot air gun.
I will try to find solder paste.

 

[OlegSh]

If you plan to continue with this hobby then the sooner you learn to use hot air station and solder paste the easier it will be for you to try different designs in the future since most of new interesting parts are SMD. Even relatively diy-friendly SOIC packages are considered large by the nowadays industry standards.