Amp Guts Photos - Official Thread - Lets see those pics

[agedhorse]

I've done an spl/frequency (20-20khz less than .25db deviation) matched comparison between a Presonus RC500 and GK MB500. GK full of TL072, Presonus full of LME49860/49720.

While they sounded similar, the GK was always a little grungier regardless of gain settings. The RC500 pre could get into the same territory at high gain but also has the ability to be very neutral. I did the comparsion through relatively high distortion speakers and amps. Headphones would have been more telling.

The noise levels were much higher on the GK and very annoying with lighter playing. RC500 is nearly silent even with a slight treble boost.

In a live setting the tonal differences would be inaudible for most.

Such completely different designs that such a conclusion is highly misleading.

Take exactly the same amp, build one with one IC and the other with a different IC and do a true double-blind test. The results are more like comparing apples to apples. This is the sort of thing that amp designers tend to do more often than you might think.

Because of the potential operation into non-linear regions, liner region specs don't apply, otherwise the industry would have run away from tubes (which are grossly inferior in every linear spec) decades ago.

 

[delta7fred]

If you believe that op-amp rolling makes a difference then it does (but only to you).

To the rest of the world it doesn't, especially to engineers who understand how op-amps work.

 

[rufus.K]

Fender. Super Twin

 

[12bass]

Then again, the audiophile hi-fi audio world that's so fond of digging into the minutiae also claims big differences in power cables and will spend hundreds or thousands of dollars for something that no double-blind test has ever shown a difference.

When designing a bass amp, parts are chosen for their particular behaviors and characteristics. Cost is an important characteristics, as is performance, reliability, stability.

This is the same type of argument used in point to point parts placement & wiring, turret boards, tag boards, etc. I use PCBs because it's the best, most repeatable, most consistent, most reliable method for my designs. The parts go exactly where I want them each time, the wiring is routed exactly where it needs to be each time, and it's easily repaired by a qualified service tech.

Doesn't apply to me... never made any claims about magic power cables or point-to-point.... plus, I've made before and after measurements after replacing op amps showing clear improvements, notably lower noise and distortion as well as improved channel separation.

If you believe that op-amp rolling makes a difference then it does (but only to you).

To the rest of the world it doesn't, especially to engineers who understand how op-amps work.

Straw man. I'm not a proponent of such a subjectivist view. I care very much about truth and objectivity, as much as it is possible in audio. I've stated previously that the differences observed have also been measured and quantified to a degree. And engineers do not know everything (they tend to work with idealized models), nor do the technical documents adequately convey characteristics like sound quality. On various occasions I've replaced op amps expecting an improvement only to find that the circuit sounded worse... the OPA275 for example.

I suggest reading the Groner paper lined above.

 

[agedhorse]

I'm familiar with Samuel's paper.

Engineers like me do not work mostly with idealized models because we are keenly aware that devices often do nt behave this way. That's exactly the reason I mentioned the non-linear aspects of a device and the real world implications they bring to the real world performance of a bass amp.

Double-blind testing is very often considered offensive in the audiophile industry, I lost me job over a blind test (not even double-blind) that I rigged specifically to show how foolish people could be in their confidence over which was which. Fortunately I was planning on leaving anyway due to the nature of product misrepresentation, but when everybody had a clear opinion on which of the 2 choices were better, claiming that one was obviously night and day different from the other (they thought they were listening to 2 different amps, one very expensive and one very inexpensive), and that only somebody with a tin ear couldn't hear the difference, it was shown that they had been listening to exactly the same amp, switching between the same outputs. Needless to say this was an uncomfortable event since it was a bunch of socialite audiophile customers stroking each other's egos (and consuming massive quantities of various "tonics and elixirs" until the reveal proved them all to be playing the fool. There was another very respectable engineer from the audiophile community who was in on it with me, but I took the fall (I was already leaving so it didn't matter to me) since he still has quite a career separating those from their money.

The guy who owned this amplifier company used to re-mark conventional parts as esoteric components, couldn't build an amp that was reliable, and ultimately lost his house, his boat and everything else when his lifestyle couldn't live up to his company's income.

 

[12bass]

Sure... the semis in a lot of MI stuff tend to be used in a non-linear fashion; I get that. I also think that the TL072 can sound subjectively "good" in many circuits. Further, I also recognize that the demands of high fidelity applications tend to be different than say a guitar or bass amplifier. I just happen to like a very clean/transparent sound in my bass amplification (unless deliberately distorting via a pedal or tube preamp), and the modern, high performance, op amps help in that goal. I am also skeptical about many audiophile claims and am a proponent of ABX testing and would gladly participate in such testing if someone wanted to set something up.

IMO, there is a lot of gray area in audio, whilst many seem to want to frame things as black and white. Take DACs or CD players for example... some claim they all sound the same... but they surely don't.

Personally, I'd be very curious to see a D-800 or WD-800 with an option to bypass all the extra op amps in the circuit if not using tone controls, HPF, etc... just to hear the difference it makes. I mention this in part because I've always heard an improvement in sound quality when extra circuits are bypassed in high fidelity gear, usually with the "CD Direct", "Pure Direct", or similar switch.

 

[agedhorse]

That's not the designer's intent, the amp (and any amp for that matter) should be taken as a whole. Either it works for you or it doesn't.

There's always the option of designing and building your own if you are up to the task.

 

[fdeck]

Personally, I'd be very curious to see a D-800 or WD-800 with an option to bypass all the extra op amps in the circuit if not using tone controls, HPF, etc... just to hear the difference it makes. I mention this in part because I've always heard an improvement in sound quality when extra circuits are bypassed in high fidelity gear, usually with the "CD Direct", "Pure Direct", or similar switch.

Does the bass amp have an effects loop? Going in via the FX return will bypass most of the guts of the amp. Also, have you measured the effect of bypassing on that hi-fi gear? Mainstream computer audio hardware has gotten so good that setting up a home audio test lab has ceased to be prohibitive, so long as you don't need an anechoic chamber or a calibration certificate. (There are tricks to avoiding the need for one for some kinds of speaker testing). If something is audible, then it's measurable, and you might find out what the controls are actually doing.

Now, some amp circuits will have additional nonlinear components in the signal chain that will remain present if the op amps are swapped out. Any amp worth investigating is worth finding out how it works, either from the schematic or from a close look at the layout. One well known amp has a Class-A JFET gain stage in the signal chain, ensuring a certain amount of residual nonlinearity regardless of the op amp type used.

 

[agedhorse]

The availability of the home audio software test suites have resulted in some of the most absurd claims and conclusions ever imagined. Data is one thing, good data is another, understanding the data is yet another.

 

[12bass]

That's not the designer's intent, the amp (and any amp for that matter) should be taken as a whole. Either it works for you or it doesn't.

There's always the option of designing and building your own if you are up to the task.

The above reads like "my way or the highway"... not sure if that's what was intended... but it is certainly condescending and off-putting. FWIW, I've talked with other amp designers who understand the merits of a more minimalist design philosophy and recognize the differences in sound from using different op amps. Further, countless evidence-based audio manufactures have also recognized the merits of minimizing the number of op amps in their circuits and have used modern high performance op amps in place of more generic 70s designs, so it is not as if I'm suggesting anything "woo" here....

Does the bass amp have an effects loop? Going in via the FX return will bypass most of the guts of the amp. Also, have you measured the effect of bypassing on that hi-fi gear?

Yes, I've made such measurements, as well as listened to amplifiers whilst going in through an effects return (or similar). Fewer op amp stages is almost invariably better from a sound perspective.

 

[agedhorse]

Maybe it comes off as arrogant, but I don't know how to say it honestly any better. I designed the amp line in a way that appeals to practical players. Since the whole line is well regarded by real world players, to me that's all that really matters. I frankly don't care about your "better" way of doing things because my philosophy is different than yours, and it's my design to live and die by.

If you are convinced that you have a better way, there's nothing stopping you from designing and producing a better mouse trap.

I think this discussion gone far enough, it's no longer of any benefit to others on this thread IMO.

 

[fdeck]

The availability of the home audio software test suites have resulted in some of the most absurd claims and conclusions ever imagined. Data is one thing, good data is another, understanding the data is yet another.

Good points. Perhaps I underestimate the challenge because my background is in scientific measurement, not specifically audio, but the place where I work sold one of the earliest commercial Fourier transform analyzers.

 

[agedhorse]

Good points. Perhaps I underestimate the challenge because my background is in scientific measurement, not specifically audio, but the place where I work sold one of the earliest commercial Fourier transform analyzers.

It's worse Francis, even folks who say they know better struggle. Remember the power measurement fiasco where the guys making the measurements had no grasp of line voltage on measurements and when they came up with bad results they still went public because they were convinced that they knew more than they did,. They failed to grasp conceptually that a drop in peak line voltage (the value that matters in a line frequency supply, though they were using average numbers which makes no sense) of 10% does not cause a 10% drop in measured power but a ~20% drop in measured power. This was a gross embarrassment and they had an AP system, which reinforces how bad data is worse than no data at all and can result in incorrect conclusions.

 

[Leo was right]

Yep, we have the opposite opinion on this.
Two different OPA inside a circuit can have two different behavior, yes.
But placebo effect is so massive in audio that besides technical measures, you will not change my opinion on opa sounds.

For exemple AUDIO opa categorie = bad OPA categorie simply because they are not good enough for other application.
And distortion i'll dare you to find the difference by ears between a 0,1%THD vs a 0,0001%THD claim on the OPA211...

In my day job I work in audio and video. Two différents world, in video everything is square and pragmatic, in audio they have a crazy bunch of fools in the gang.

 

[Jeff Scott]

In my day job I work in audio and video. Two différents world, in video everything is square and pragmatic, in audio they have a crazy bunch of fools in the gang.

Which would you rather be, crazy, or square?

 

[BoogieZK]

In my day job I work in audio and video. Two différents world, in video everything is square and pragmatic, in audio they have a crazy bunch of fools in the gang.

Same observation, i work in super high frequency electronics ... and we use for example powercables worth like 2€ with equipements worth more than my house BECAUSE powercables are not important.

HIFI is a massive goose that lays heavy golden eggs.

I would like to see modern amps like GRamps, wayne jones amps or even an EBS Fafner II.

 

[Leo was right]

Which would you rather be, crazy, or square?

Well I must admit, I am certified tech in audio, video and RF, now I am in audio and video fusionned dept, but for 30 years I was in audio.

Here is one of the best I heard, from a guy which is a very good tech: If you plug a speaker cable in a certain between the amp and the loudspeaker, and suddenly reverse it, it will not sound as good....

Or : IEC power cable under 500$ sound like crap.

 

[agedhorse]

The amount of crazy in the high end audiophile world is eye opening. It gives snake oil salesmen a run for their money IME.

 

[fast slapper]

 

[Rockbobmel]

I know I threw this out before, but I have to repost after sniffing all the fumes of snake oil. Reeves C225