The Opamp thread - Page 288

Nigel,

 

 

I've benefited greatly from your advice, despite your lack of education.  Please continue your malpractice with my blessings, but by all means, pursue a better understanding, as your passion for knowledge moves you.

 

 

Mike

Quite honestly, zilch0md, I think your response is disappointing.

 

I'm not surprised by it, you want to continue swapping opamps and talking about it. If you really paid attention to what jcx wrote, and the stuff in the Sound Science forum, you'd have to give that up almost in its entirety.

 

Sometimes our illusions matter more to us than the truth, when we have a big emotional investment in them.

 

I want to continue designing bits of electronics and talking about them, and electronic design, and sharing what I know. So I try to avoid getting into these arguments, because they rarely have a positive outcome. I'm not always successful, though, and anyway, you never know your luck. 

 

I have external confirmation of my ideas, there's certainly no way that many of the things I build would work at all if I didn't have a good grasp of how they work. That's how I get satisfaction from what I do, I build things, they work, it reinforces my world picture. What they call a vicious circle .

 

Of course sometimes they don't work, the universe spits them back at me, and I'm forced to change my ideas. Or at least acknowledge that I made a mistake. They do happen. As they say, the man who never made a mistake never made anything.

 

I recommend this activity to you, or some other truly constructive activity. I don't recommend carrying on the way you are going, it's pointless and unrewarding by comparison. Opamp rolling isn't even a hobby, it's just a habit.

 

Again, I don't expect you to be very happy when I say this, I probably wouldn't take too kindly to being told that what I do is pointless and unrewarding, but there's no point in dissembling. Just try and accept that it's said with the best of intentions. I know you believe in it, but I don't have to believe in what I do, I have the proof in my hands.

 

You say that you don't have any choice. I can see how you might feel that, but I know that you do have a choice, uncomfortable as it might be on occasion to acknowledge it. If you live forever within your comfort zone, you look forward to a life without progress.

 

So, all you opamp rollers, get out there, grasp the nettle, get out of the paddling pool and learn to swim. Or whichever mixture of metaphors takes your fancy. You know it makes sense.

 

w

I hear you loud and clear:  I shouldn't do any rolling until I've mastered the subject matter, even though it can take years to actually do so.

 

Thank you for caring, and Merry Christmas!

 

Mike

It frustrates me sometimes when it comes to learning this stuff. I sit on the edge wondering how deep am I really going to sink myself into this. I'm capable, but time and resources are the limiting factor. Sure, I can design a rudimentary circuit, and I've built the odd one here and there as proof of concept that yeah I can actually get it to work. But then I look at the mountain of possibilities beyond that, all that stuff beyond following the sample diagram in the spec sheet, and I start to read, then read some more, then realize oh crap if I really want to get into this, and I mean *really* get into this, it's going to cut even more heavily into my time. Then I'll need more tools, more equipment, more *toys*... 

 

So with a bit of sanity/sadness, I pull back. "This way lies madness" I tell myself. I can only support so many vices at one time. Well, unless I can make money doing so. Man, I spent all these years doing my PhD in a decidedly non-audio related fields (unless you want to discuss metallurgy and cables... but I gave up on sound science a long time ago already). If only I wanted to be an audio guy instead of a blacksmith when I was a teenager, perhaps I would have gone down a different path eh?

 

Armaegis, I think you have summed up the thoughts of the majority on this thread, nicely put.....

 

Me? I'm going to carry on regardless.

I didn't read this, I didn't read this, I DID NOT read this - damn, I did !

 

That pulling back hurts sometimes - well, not only sometimes, it keeps reoccuring - at the oddest of times.

 

We have a saying, that goes, roughly translated, like this: Where went the bull, the rope should follow ...

 

It was way past the age people normally decide what path to take in their lives that I realized audio , one way or another, IS my thing - or I would end up forever yearning "what if". 

 

Better to fail than the above - therefore I soldier on. But sometimes it is hard.

 

Yes and yes.

 

Thus far, for me, the rewards have outperformed the undeniable but reasonably affordable risks. I've not yet destroyed anything, but my ears are very happy, having blindly rolled the dice, again and again, ignorantly blundering my way to an obviously superior audio experience.

 

In short, I've been touching the hot stove without getting burned - and I'm rewarded for doing so.

 

Mike

March on, brother, march on!

 

Welcome to head-fi, sorry about the... fingertips?

I recently got a Claro Halo XT for HTPC duties (movies mainly). I'm using a Harman Kardon Signature 2.1 power amplifier and Jamo C80 series speakers.

I want to roll some op-amps in it and I have some questions:

1) What is the output impedance of the headphone jack and the RCA outs? Can I influence this by changing opamps? I'd like an under 2ohm headphone out impedance and under 100ohm RCA out impedance.

2) Which position (I/V, buffer) has the most influence on the sound? I presume I/V, is that right?

3) What's the voltage this card runs it's op-amps at (including XT)?

4) I see there's an I/V and a buffer position on the HALO card and just three dual opamps on the XT daughter board. What do the op-amps on the daughter board do, I/V or Buffer? If the opamps on the XT do I/V, are those outputs buffered with another opamp/buffer on the PCB? I want to run the same opamps/buffers on all channels if possible.

6) If there's a single opamp on the XT, has anybody you know (or yourself) tried the AD8397 high current dual opamp in there?

7) If I want to keep all channels the same, can I leave the buffer sockets empty or do I need some kind of bypass adapter?

8) I was thinking about 2xAD797BR on DIP8 adapters for I/V (seems a popular choice) and for buffers I don't have any idea ... BUF634? What other buffers do you recommend? Do you have a list of opamps that are safe in the Halo XT?

Thanks!
Edited by eugenius - 12/26/12 at 2:10pm

The HT Omega website says the Claro Halo XT uses a TPA6120A2 to drive the HP output. You cannot readily replace this part, as it is SMT with a central heatsink pad on the underside, removing it from the board might be possible with a hot-air desoldering station, but it will not be easy, and anyway what would you replace it with? It is a dual amplifier with independent supply in a 20-pin package with 10 pins N/C. An AD8397 will not fit the footprint, and anyway is probably an inferior part, certainly it has no short-circuit tolerance and will not drive as much current (700mA P/C).

 

The TPA6120A2 can be configured to provide <2ohm output impedance, but the datasheet recommends at least 10 ohm series impedance to obviate oscillation by isolating the amplifier output from any load capacitance. It's possible to replace this resistor with an inductor, but if a ferrite-cored type is chosen it may negatively impact the THD depending on exact type. Of course the device may already be so configured.

 

w 

Wakibaki, thanks for answering, but was thinking of using AD8397 as a buffer not as a TP6120A2 replacement. As I understand it, the AD8397 is an opamp that doesn't need an extra buffer as it can give more than enough current, so by putting AD8397 all around (obviously with the buffer position bypassed on the main card) you can have all channels with the same config.

In the mean time I received some answers from HT Omega (which I might add, seem to threat their customers well and actually respond to questions well and fast). The answers:

- The Zout of the headphone jack is 8ohm.
- The Zout of the rca's is 150ohm. Both acceptable I think, unless you have Grado's and you like super tight bass. Any headphone over 60ohm should be great.
- The card runs it's op-amps at 12V.
- The opamps on the XT are buffers.
- The recommend the LME49790NA and the OPA2132P. They have users reporting success with OPA627 (ha!) and users asking about AD797 but no reports with it.

So, can I use AD797 all around and BUF634 in the buffer position on the main card? What are some safe (tested) opamps for this card?
Edited by eugenius - 12/27/12 at 4:25pm

Can anyone help me recollect wether the OPA627, ADA4627 and LME49860 will become warmer/darker or colder/brighter when biased into class-A with 3.3KOhm resistors?

Edited by kazaakas - 12/28/12 at 1:37pm

Depends on the circuit.  Class-A isn't really worth it with 4627, instead add a 0.02uF ceramic capacitor and two Vishay MKP1837 capacitors across the power supply pins if you intend to use it in the M-Stage.  The two film caps should be combined like this (frontmost, center opamp module).  This will give you far more improvement with 4627 than any sort of class-A biasing.

myself I stick to low inductance ceramic or thin film SMD, perhaps SMD PPS film. completely agreed, high class opamps are already running output stages in Class A or high bias AB for most loads. besides a CCS would be preferred for bias in a case/device that responds to it. indiscriminately biasing into class A is of little benefit IMO

Was actually going to try them out with my soundcard, got a LME49860 in the M-Stage now, which I'm really digging, was wondering what class-A biasing could do