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The Opamp thread - Page 269

post #4021 of 4406
6/19/12 at 1:27pm

OPA827 has slightly less colour in my impartial analysis and I couple others I've seen online.

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post #4022 of 4406
6/21/12 at 12:02am

Hiya! Newbie question (sorry to bother all of you experts, but I'm just starting to get interested in this). 

 

A lot of the designs have only a couple op-amps. When I took a look at my Meier Corda Opera, it had 12 (!) LM6171's (socketed, which is awesome given my soldering skills, which I wouldn't trust with a $1300 unit). It is unbalanced, but has a shared active ground (if that makes any difference). 

 

Just wondering, what sort of benefit would having so many op-amps have? Why might it have been designed with so many? Just curious. beerchug.gif


Edited by Chromako - 6/21/12 at 12:04am
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post #4023 of 4406
6/21/12 at 12:08am
Quote:
Originally Posted by Chromako View Post

Hiya! Newbie question (sorry to bother all of you experts, but I'm just starting to get interested in this). 

 

A lot of the designs have only a couple op-amps. When I took a look at my Meier Corda Opera, it had 12 (!) LM6171's (socketed, which is awesome given my soldering skills, which I wouldn't trust with a $1300 unit). It is unbalanced, but has a shared active ground (if that makes any difference). 

 

Just wondering, what sort of benefit would having so many op-amps have? Why might it have been designed with so many? Just curious. beerchug.gif

 



honestly, I dont think you should touch it, socketed or not, his arrangement there will be to enable the psuedo balanced operation and also his crossfeed filter/effect. in these type of circuits the parameters of the opamps will have an effect on the frequency response due to differing input impedance etc. I suggest you leave well enough alone with that one.

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post #4024 of 4406
6/21/12 at 4:07am
Quote:
Originally Posted by qusp View Post

 



honestly, I dont think you should touch it, socketed or not, his arrangement there will be to enable the psuedo balanced operation and also his crossfeed filter/effect. in these type of circuits the parameters of the opamps will have an effect on the frequency response due to differing input impedance etc. I suggest you leave well enough alone with that one.

Huh. Interesting. So having so many helps enable all those cool goodies? I learned something new today! biggrin.gif

 

Mr. Meier (or Dr?) really went all out with the design of this! Coolness.


Edited by Chromako - 6/21/12 at 4:09am
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post #4025 of 4406
6/21/12 at 9:37am

yep, well if you ask Jan, he might be able to point out some opamps that are not part of the filter that you can toy with and maybe suggest some suitable alternatives, or he might be scathing =) dunno.

 

I presume he socketed them for a reason, but its not going to be as straight forward as blind rolling and you may have to change 4 at a time

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post #4026 of 4406
6/24/12 at 9:42am

For the op amp rollers...

 

Why op amps oscillate.

Taming the Oscillating Op Amp part 1.

Taming the Oscillating Op Amp part 2.

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post #4027 of 4406
6/24/12 at 10:09am

Thanks for the links!

 

Mike

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post #4028 of 4406
6/25/12 at 7:28am
Quote:
Originally Posted by Avro_Arrow View Post

For the op amp rollers...

 

Why op amps oscillate.

Taming the Oscillating Op Amp part 1.

Taming the Oscillating Op Amp part 2.

Awesum awesum stuff

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post #4029 of 4406
6/25/12 at 3:27pm

nice one avro arrow, I just came here to link those new Ti articles, very comprehensive

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post #4030 of 4406
6/27/12 at 5:34am

I subscribe to AD's news letter and they sent me this info today http://www.analog.com/en/all-operational-amplifiers-op-amps/operational-amplifiers-op-amps/ad823a/products/product.html

 

I thought the AD823 was an old design? I remember Graham Slee using it in the SOLO. Yet AD are saying this is a new chip, what gives??

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post #4031 of 4406
6/27/12 at 6:52am
Quote:
Originally Posted by SpudHarris View Post

I subscribe to AD's news letter and they sent me this info today http://www.analog.com/en/all-operational-amplifiers-op-amps/operational-amplifiers-op-amps/ad823a/products/product.html

 

I thought the AD823 was an old design? I remember Graham Slee using it in the SOLO. Yet AD are saying this is a new chip, what gives??

New revision, Rev B

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post #4032 of 4406
6/27/12 at 5:06pm

I've just replaced the OPA2604 by an LME49860.

 

I'm actually listening to it with a DT990-250ohms.

 

First feelings :

 

Sounds good indeed ! Less on the dark side... I can hear many things... Music seems closer... Bass seems stronger... Or maybe it's the dynamic... Stereo separation is really there... Fact or fiction, I don't know yet...

 

Next step : more listening, also with the D2000, and comparing against the NAD, wich is my reference...

 

See ya tomorrow guys !

 

Quote:
Originally Posted by Headdie View Post

Hi,
 
I'm looking for advice or suggestions.
 
My new desktop headamp is the Firestone Cute Curve,
 
 
The PSU is 24V and could be raised to 30V.
 
From the specs :
 
Main OPAmp : TI – OPA2604
Servo OPAmp : TI – TL072
 
Both are in sockets.
 
Do you think I could improve it a little with new OPAmp ?
 
I don't know anything about it. I've read enough in this thread and elsewhere to understand that the best I can do is to ask for a little help.
 
My phones range from Denon D2000-25ohms to Beyerdynamic DT990-600ohms. If it's relevant, I'd prefer to optimize it for mid/low impedance... I already have what it takes for high impedance cans.
 
I listen to jazz, classical, progrock and many thing else.
 
I don't listen loud with headphones, if it matters to op amp selection...
 
So what do you think guys : Am I a good candidate for new opamps ? And what would you suggest...
 
Thanks a lot,
 
Headdie
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post #4033 of 4406
6/27/12 at 9:06pm

After some readings, I understand that I could roll the main op-amp (what I've done replacing the opa2604 by an lme49860), but that I should leave alone the servo op-amp (tl072), because it's not in the audible audio path... Am I mistaken ?

 

Also, the servo tl072 is paired with the main opa2604 in the Firestone Cute Curve, but is it compatible with another op-amp like the lme49860 that I've rolled in ?

 

After more listening, the Cute Curve with LME49860 is definitly an improvement with the DT990, but I'm still not sure with the D2000. With the DT990, it is now up to the level of my NAD, maybe even better.

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post #4034 of 4406
6/28/12 at 1:41am
Quote:
Originally Posted by Headdie View Post

After some readings, I understand that I could roll the main op-amp (what I've done replacing the opa2604 by an lme49860), but that I should leave alone the servo op-amp (tl072), because it's not in the audible audio path... Am I mistaken ?

 

Also, the servo tl072 is paired with the main opa2604 in the Firestone Cute Curve, but is it compatible with another op-amp like the lme49860 that I've rolled in ?

 

After more listening, the Cute Curve with LME49860 is definitly an improvement with the DT990, but I'm still not sure with the D2000. With the DT990, it is now up to the level of my NAD, maybe even better.

Arg. Build a faux impedance decreasing adapter for the D2k, it makes a much bigger difference then opamps.

For analytical phones like AKG K240mkII its the opposite. 

 

and try the THS4032 in the I/V, I like it for neutrality, and clarity and having no detracting factors.

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post #4035 of 4406
6/28/12 at 3:39am
Originally Posted by Avro_Arrow View Post

Your chasing a ghost...

Any DAC, whether current out or voltage out, still requires a low pass filter to keep the high frequency "junk" from

making it through to the amp. You might think that the fewer components after the DAC the better, but only to a point.

 

I think the quote from Albert Einstein says it best..."Make things as simple as possible, but not simpler."

 

Even the PCM5102 (which puts the I/V stage on the chip) recommends a low pass filter on the output.

 

Originally Posted by qusp View Post
Originally Posted by kiteki View Post

The common perception is to use LOD to bypass the amplifier, and that the signal is sent directly from the DAC.

 

The TeraDak has "passive I/V" and the Lite-Dac AH uses AD847, one uses op-amps - the other doesn't - so no I still don't get it...

 

the common perception is wrong...

 

the teradak is compromised IMO, it is designed for tweakers, with plenty of space so they can install huge film caps and boutique resistors where a proper output stage should be =) i'm of the opinion that while you can make something half decent if you basically replace everything in it, there is no water into wine. as TDA's go, this chip is entry level only and the PCB layout, particularly the digital and power supply section is ....not ideal.

 

you cannot build that type of thing point to point with patch wires and expect high performance, if you want a decent dac, build or buy a decent dac from the ground up. some designs are basically good designs that could use a bit of a helping hand, but the layout, parts choice and grounding of this simply cannot be undone. sure its a bit of fun and some people have done some interesting things with these dacs, but there is a point where the layout itself hampers efforts.

 

yes i'm opinionated, some will disagree with my view, but dacs, particularly these days of higher speeds are more akin to RF than standard analogue, so are quite sensitive to layout issues /rant

 

I know these posts were over a week ago, I just wanted to note...

 

The 'common perception' is logical.  You can construct a DAC section and amplifier section on the same circuit board, or you can construct a DAC section and amp section on two seperate circuit boards, with two enclosures surrounding them, so what is the difference?  The difference is... if you get a nice rectangular piece of circuit board and connect them again... nothing. ;)  This is also known as a cable, unless cables have some sort of issue.

 

So back to my situation - I'm not looking for the ultimate DAC or a DIY project right now, I just want something that doesn't have hints of colour or tint in the signal path for experimentation purposes and peace of mind.  For example if I want to try the OPA1611 versus OPA827 in my DIY amplifier, I wouldn't feel right with the Lite-DAC with 2x AD847 supplying the signal, let alone the TeraDak if it improves with film caps and fancier resistors.

 

I know NOS sounds pretty weak compared to modern OS chips, and if you scored them in 10 different categories from 1-10 OS would easily win, but NOS does win in at least 1 category I am fairly certain of (via my listening, not specs), which is why it's still used today in various high-end projects.

 

I might be chasing a ghost asking for advice on a 'pure' DAC which is just a lonely chip with nothing around it, but I hope my clarification makes sense that some DAC's are purer than others.  For the end result it may not be very important factor, but for evaluation purposes you need as little colour as possible.

 

In other words a pre-amp might be technically better to have in some situations for the end result, but if you're building or evaluating an amplifer you don't want a weak sounding pre-amp supplying it right...

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