LME49720 & 49720 improvement

[Emmathom]

Hi Gentlemen

I need your knowledge & advice please

I recently opened my DAC (ES9018 + Xmos) and noticed LM49710 & 49720 at output. I must say that I don't have the DAC schematic.
My questions are :

- are they "good OPAs" ? where would you classify them in a "good sounding" scale ?

- if they can (must ?) be replaced which ref. do you advise to possibly improve the sound ?

Thanks for your answers !
Best Regards

 

[ccaudle]

are they "good OPAs" ?

Some of the lowest distortion op-amps ever made. There is no technical improvement to be made by replacing them unless there is some other design fault which uses them in a non-optimal manner.

 

[Emmathom]

Thank you @ccaudle !
Happy to notice that some chineese manufacturers work for quality.
I use this DAC since 2010 (my first and only) and the sound is really good. Even the board is well built...

 

[elskardio]

Thank you @ccaudle !
Happy to notice that some chineese manufacturers work for quality.
I use this DAC since 2010 (my first and only) and the sound is really good. Even the board is well built...

I wouldn't change a thing! Those are all high quality components. You even have Nichicon Muse Capacitors.

 

[Emmathom]

I wouldn't change a thing! Those are all high quality components. You even have Nichicon Muse Capacitors.

Yeah and Wima FKP2 too ! Great

 

[ruffrecords]

The only downside I can see is some of the soldering looks like it has been done by a 5 year old

Cheers

Ian

 

[Emmathom]

The only downside I can see is some of the soldering looks like it has been done by a 5 year old

Cheers

Ian

Yes I must refresh/resold that with silver solder one of these days...

 

[living sounds]

Thank you @ccaudle !
Happy to notice that some chineese manufacturers work for quality.
I use this DAC since 2010 (my first and only) and the sound is really good. Even the board is well built...

Nichicon Muse (the green ones) are my favourite electrolytics in the signal path. The violet ones at the bottom look like Os-Cons - good choice for digital decoupling. It looks a little bit like they are using 0.1uf film caps and low ESR caps for audio PSU line decoupling, that I am not a fan of. The big square WIMAs could be for S/H duties, where polypropylene is a good choice.

If they made LME497XX work as they should I wouldn't change a thing.

 

[Emmathom]

Nichicon Muse (the green ones) are my favourite electrolytics in the signal path. The violet ones at the bottom look like Os-Cons - good choice for digital decoupling. It looks a little bit like they are using 0.1uf film caps and low ESR caps for audio PSU line decoupling, that I am not a fan of. The big square WIMAs could be for S/H duties, where polypropylene is a good choice.

If they made LME497XX work as they should I wouldn't change a thing.

The 10nF (red cubes) must be FKP2 which are my best cap espescially close to OPA for last PSU filtering.
What means S/H duties ?

 

[living sounds]

The 10nF (red cubes) must be FKP2 which are my best cap espescially close to OPA for last PSU filtering.
What means S/H duties ?

I would be surprised if FKP2 were used for PSU filtering here. Doesn't make sense. S/H = Sample & Hold. That's a common element of a DAC output stage.

 

[Emil C]

Hi,
years ago I've tested some op amps on a chinese DAC, in the I/V conversion stage. It was a simple design with a single OA per channel, galvanic coupled to RCA output. Originally it was equipped with 5532 on socket. I found OPA1612 (bought mounted on adapter, from Aliexpress) to be clearly better than LME49720 (from Mouser). Subjectively the high frequency sounds were more "silky". One explanation may be that OPA1612 open loop gain at 10kHz is 80dB, vs less than 60dB for 49720 so negative feedback is stronger and distortion lower.

 

[Emmathom]

Hi,
years ago I've tested some op amps on a chinese DAC, in the I/V conversion stage. It was a simple design with a single OA per channel, galvanic coupled to RCA output. Originally it was equipped with 5532 on socket. I found OPA1612 (bought mounted on adapter, from Aliexpress) to be clearly better than LME49720 (from Mouser). Subjectively the high frequency sounds were more "silky". One explanation may be that OPA1612 open loop gain at 10kHz is 80dB, vs less than 60dB for 49720 so negative feedback is stronger and distortion lower.

Hi @Emil C
Interesting... You mean you exchanged NE5532 to LME49720 and then to OPA1612 ?
Since these OPA1612 are still available and qiet cheap @ Ali Express why not give a try ?

So for LME49710 you must get OPA1611 ? one channel...

 

[ccaudle]

I found OPA1612 (bought mounted on adapter, from Aliexpress) to be clearly better than LME49720 (from Mouser). Subjectively the high frequency sounds were more "silky".

LME49720 has been reported to be somewhat RFI sensitive, and an I/V converter is subjected to very high frequency noise from the DAC output images (assuming that no passive filtering is implemented between the current output and the I/V converter, which seems rare).

 

[Emil C]

Yes, exactly. But you must find OPA1611 mounted on adapter, also.

 

[Cqwet Dbdfte]

Yes, exactly. But you must find OPA1611 mounted on adapter, also.

SO8 to DIP8 adapters should be easy to find. Or let JLC PCB make a lifetime supply for $5.
AD846 used to be the go-to trans impedance amplifier.
The input is grounded base, emitter input device, ideally suited to I-V converter. Any voltage appearing on the input is an error.

 

[Emmathom]

Thanks you all for these infos.

What is the appropriate load for these LME ? I mean which pot value should I use for volume in the following amplifier ?

 

[Cqwet Dbdfte]

"Easily Drives 600Ω Loads"
Depending on the load, but 1k should work. Or use a second one as a buffer like the data sheet.

 

[Emmathom]

I opened my amplifier (Mosfet 2x50w) and I found a ALPS KA 2x50KΩ : I think 2x10KΩ log should be better > even for other sources like Bluray player / Tv decoder / etc

 

[Emil C]

It also depends on amplifier input impedance which is in parallel at max volume. Low load impedances stresses the OA, at high resistances potentiometer noise increases (at median volume). Also, at high potentiometer resistances volume variation curve is modified by the amp input impedance. I would go for 2k to 10k for potentiometer.

 

[Emmathom]

It also depends on amplifier input impedance which is in parallel at max volume. Low load impedances stresses the OA, at high resistances potentiometer noise increases (at median volume). Also, at high potentiometer resistances volume variation curve is modified by the amp input impedance. I would go for 2k to 10k for potentiometer.

The input is by K170 with 100KΩ to ground : here is the schem. So with a 2*10KΩ pot = 100KΩ//10KΩ = 9KΩ per channel