Discrete sounds better than integrated? a possible reason

[JohnRoberts]

This is a very old debate often from marketers pimping some new design.

Test equipment has progressed measurement resolution way beyond what I can hear, and I suspect everyone else here, but I try not to argue with people on the internet about that they say they can hear.

I am a fan of null testing. If you suspect an audible difference between IC and solid state designs, the first step is objective test bench measurements. If this doesn't reveal an obvious difference, a null test will isolate and reveal differences, while it won't tell you which one is causing the difference. 

If this is an old argument does that make it better.

JR

 

[JohnRoberts]

I put it in the same category as Matti Otala's Transient InterModulation, which as long since rejoined Zenon of Elea's paradox, where the arrow can never attain the turtle.

I remember TIM and the alphabet soup of "new" distortions, pretty much all variants on slew limiting phenomena. I don't know what it is about about audio electronics that makes people think it is not a mature technology, rich for new discoveries.

JR

 

[living sounds]

Could it be the case that many monolytic op amps are just more demanding when it comes to implementation?


I have noticed very audible differences with correct vs. incorrect (chassis) grounding (cable shield only connected to chassis at the in-/outlets and audio ground only connected to chassis via the PSU ground input vs. other schemes). Let RF into the circuit and the op amps won't perform as good as they can.

Same with decoupling, for instance there are many ways to create resonances in the impedance response with the wrong combination of PSU decoupling caps.

 

[Matador]

Would this not be easy (at least in concept) to test by using an uncompensated op-amp in a given circuit?  Test A would be compensated with a dominate pole down around 10Hz (as per normal), and test B would be uncompensated, with feed-forward capacitance with a roll-off at 75 kHz?

 

[abbey road d enfer]

Would this not be easy (at least in concept) to test by using an uncompensated op-amp in a given circuit?  Test A would be compensated with a dominate pole down around 10Hz (as per normal), and test B would be uncompensated, with feed-forward capacitance with a roll-off at 75 kHz?

One wonders why it's not been done before...

 

[Matador]

One wonders why it's not been done before...

I'm trying to learn as much as anyone else here...if you think it's a dumb idea, you can just say it's dumb, and I promise I won't be offended.  Ian seemed to be postulating a reason why two supposedly equivalent topologies might sound different, and I offered what I thought might be a (hopefully simple) way to answer his question, but it's also possible I just swung and missed.

 

[JohnRoberts]

I encourage honest inquiry but am repeating myself, this is mature technology.

There are no dumb questions, but unfortunately lots of ASSumptions that live up to the shorter spelling.

JR

PS: Test what exactly..? Dominant pole capacitor compensation is just one of multiple factors affecting a given circuit/s transfer function.

 

[ruffrecords]

I think this should be required reading for anyone designing with op amps like the TL072:

https://www.ti.com/lit/an/sloa020a/sloa020a.pdf

Cheers

Ian

 

[Tubetec]

I suppose really what we want to test is how long is the recovery time of your circuit after a transient event .
Maybe an initial pulse just to get your circuit into 'tail wags dog' territory followed shortly after by a more nominal level steady state signal , not really sure if REW can be set up for that kind of measurement ,maybe more of a job for a Digital storage scope .

 

[JohnRoberts]

I think this should be required reading for anyone designing with op amps like the TL072:

https://www.ti.com/lit/an/sloa020a/sloa020a.pdf

Cheers

Ian

That was not published until decades after I started designing with TL07x op amps (in the 1970s).

I did discuss amplifier stability concerns in my 1980 article about console design.

Again not exactly breaking news to those skilled in the art.

JR 

PS: The TL07x was hot stuff back in the 70s, now we have better devices available. But properly applied the TL07x still does not suck today.

[edit= sorry this sounds a little dismissive.  Tomorrow I'll share a story about NF /edit]

 

[Bo Deadly]

I suppose really what we want to test is how long is the recovery time of your circuit after a transient event .
Maybe an initial pulse just to get your circuit into 'tail wags dog' territory followed shortly after by a more nominal level steady state signal , not really sure if REW can be set up for that kind of measurement ,maybe more of a job for a Digital storage scope .

Just run two circuits in parallel, feed them signals of opposite polarity, then mix the output and trim the levels to minimize the output. What's left is the difference. AKA null testing as JR has already said.

Note that the LF transient / modulation I mentioned before was not in reference to individual amplifiers like op amps or the discrete equivalent. I personally do not believe in that sort of thing at all (how op amps "sound" and such). But when you consider the entire circuit that the amplifiers are in, with filter networks, asymmetric and / or rectifying elements, there could be transient behavior that gets overlooked by folks doing simple THD measurements with a 1kHz tone.

 

[Whoops]

i do not know if it was deliberate or not, but this technique of varying open loop gain at the same time as closed loop gain was used in all Rupert Neve's three transistor class A designs of the late 1960s and in the Helios and Cadac three transistor and Calrec four transistor designs of the same era.

Thank you so much for this thread Ian, and for your explanations, what you wrote in the first post makes sense and I actually think you might be right there.

Just wanted to add up that as far as the Helios goes, I really think besides the electronic circuit, Helios achieved a cult status also because of all the amazing records from the 70s that were recorded or mixed in Helios.
Led Zeppelin, Rolling Stones, Deep Purple, Bob Marley, Jimi Hendrix, Joy Division, Black Sabbath, Eagles, Eric Clapton, The Who....

I love Helios stuff, but I ask myself sometimes it's the fact that it was used in so iconic albums or the circuit that makes the cult...
Could an inferior circuit with the same credits achieve a cult status also?

 

[abbey road d enfer]

I suppose really what we want to test is how long is the recovery time of your circuit after a transient event .
Maybe an initial pulse just to get your circuit into 'tail wags dog' territory followed shortly after by a more nominal level steady state signal , not really sure if REW can be set up for that kind of measurement ,maybe more of a job for a Digital storage scope .

Recovery is about how a circuit reacts after it has been submitted to a signal that puts it out of its linear operation, typically after an overload or a slew-rate limitation.
Regarding the former, some discrete circuits have an edge here, if they take advantage of bootstrapping or staggered rails, which maintains normal operation of some elements even when the rails are hit.
About slew-rate limitation, it is long known that it should be avoided by placing a passive LP before the input.
It is what should define the final power BW of the compound.
The consequence is that the actual power BW of the active stage must be higher than that of the passive filter.
Failure to achieve this is what gave some circuits bad rep.
The "tail wags dog" situation you describe became an issue when audiophools tried to make their power amps capable of passing AM radio frequencies. Problems that could be put in evidence in the lab were non-existant in the field, whatever they said at the time.
Indeed, some discrete circuits, using local NFB or degeneration and very little or no global NFB, having a much higher slew-rate, seldom show slew-rate limitation problems.

 

[abbey road d enfer]

I ask myself sometimes it's the fact that it was used in so iconic albums or the circuit that makes the cult...

One could ask if it's the U47/44BX or Sinatra/Elvis' voice...

 

[Whoops]

One could ask if it's the U47/44BX or Sinatra/Elvis' voice...

Yes.
Well I'm pretty sure Sinatra/Elvis would sound good even through an SM57

 

[dbelousov]

The same with the "null tests". If I hear some difference that is not measurable with common metrics that are available to me (FR, THD, etc.) I just make a null test with some real and complicated actual music.

For mics, it is not easy to implement. So I use a different strategy: a reference mic. I put a very decent microphone as the "reference point" and the mic I'm working on is always compared to it with every adjustment.

 

[abbey road d enfer]

Yes.
Well I'm pretty sure Sinatra/Elvis would sound good even through an SM57

that's exactly it. Too much fetichism about gear.

 

[JohnRoberts]

I think this should be required reading for anyone designing with op amps like the TL072:

https://www.ti.com/lit/an/sloa020a/sloa020a.pdf

Cheers

Ian

OK as promised here's today's TMI about TL07x and NF.

Last century I killed way too many brain cells trying to improve phono preamps that were already way better than vinyl. To connect the TL07x dot and NF dot, a preamp kit I designed in the early 1980s used a Cohen topology flat gain front end (JFET for MM and low noise bipolar for MC), followed by a novel RIAA EQ topology.

Without getting too esoteric, but warning what follows is pretty esoteric, as I investigated in my 1980 article about console design the typical op amp input error voltage (effectively 1/loop gain) is phase shifted 90' by the dominant pole stability compensation above that pole frequency.  This means that the input error voltage is phase shifted 90' wrt to input and output signals. This is generally innocuous as long as loop gain margin is large so error voltage is relatively small causing only a tiny net phase shift in practice. Operating such op amps at too high noise gains (like virtual earth sum bus amp with too many stems) can result in measurable phase shift and more. :-( 

Getting back to my RIAA phono preamp, the RIAA EQ involve a pole at 3,180uSec, a zero at 318 uSec, and another pole at 75 uSec. Looking at the bode response, open loop gain plot of TL07x (figure 9 in Ian's link), we observe that the dominant pole compensation in the TL07x begins lower than the 3,180 uSec RIAA pole. This means that the TL07x configured as a LPF integration stage would exhibit input error voltage that would be effectively in phase with the closed loop transfer function. I warned you that this was more than a little esoteric.

Here is a link to that preamp kit article with schematic. http://www.johnhroberts.com/p-10_art.pdf

I make no other claims about this other than it is way too much information about NF and coincidentally about TL07x that I have used truckloads of over the decades...

JR 

 

[Winston OBoogie]

Thing is, discrete circuitry needn't sound like anything. 
Again it's down to how things misbehave.

If you're wanting transparent, you'd have to be pretty good with discretes and know your stuff to better something like the 5532.  It is possible but, there's a lot to consider. 

Where an I.C. fails in certain applications is:

1/ there aren't any that I know of with big beefy BJT or J-Fet  diff. amps that can compete, noise wise, with the sub 1 nv/rt. Hz of the old Rohm & Toshiba's. So you're looking at putting another I.C. of matched low noise BJT's before it for mic amp applications etc.

2/ Put a low F.B load on an I.C. such as the 5532 (again, for noise reasons), and it'll be operating in class B.  Well designed class B but, class B nevertheless. 
I'd rather a properly biased class B than AB,.  But better still is class A.  So we put a class A buffer on the output, usually a discrete, but there are I.C. 's for that too.  Current source the 5532 output to about 2mA class A and run the thing into your high Z buffer of choice.

It's pretty easy to build a discrete that misbehaves in some way that we perceive as nice.  But damn hard to build one that's bullet proof and "blameless". 

Another thing to consider is that discrete allows the circuit to do exactly what we want, and where we want.  In some circumstances, a standard "building block" 5532 or TL072 is too much or not enough.
But again, you'd better be damn good with discrete to better what you can do with the above standards in terms of blamelessness and transparency. 

 

[iampoor1]

It's pretty easy to build a discrete that misbehaves in some way that we perceive as nice.  But damn hard to build one that's bullet proof and "blameless". 

I have often wondered if a big part of the general opinion that discrete = sound better is that dont discrete circuits tend to clip asymmetrically with respect to the Positive and negative rails?