Amp Guts Photos - Official Thread - Lets see those pics

[agedhorse]

I don't recommend changing op-amps. There are specific reasons for choosing the op-amps that are in these products.

 

[rufus.K]

Fender Concert Reverb from their 2001 Pro Tube series.
(Gnarly crackling at Full Power, fine at 1/4 power)

 

[Mr. Foxen]

Did a comparison shot of a Status Quo sig Burman 502 compared to standard one.
Link Removed

 

[12bass]

I don't recommend changing op-amps. There are specific reasons for choosing the op-amps that are in these products.

From what I've seen, those reasons tend toward cost reduction more so than sound quality, though I'm unfamiliar with the specific components used in the D-800. A pair of ADA4627-1s will almost certainly sound better than a TL072 or JRC072, as well as outperform them in measurements. Of course, the cost is much higher, as is the quiescent current.

How often do op amps require warranty/service replacement in something like a D-800? Is it often enough to justify using socketed DIPs?

 

[fdeck]

Granted it's a different industry, and a long time ago, but when IBM came out with the original PC, it had most of its ICs soldered to the motherboard. People were horrified, but IBM had a lot of research on their products, which showed that ICs were more reliable than sockets. I worked for an Apple repair facility at the time, and the main repair method for the Apple ][ was to just push all of the ICs on the main board back into their sockets. Next was rubbing the edge connector on the disc controller board with a pencil eraser. I don't think we ever had to replace a defective IC.

There may have been a point in time when sockets served to protect IC's from heat, by soldering the boards before installing the chips, but temperature tolerance of ICs has improved. Some extremely sensitive parts such as infrared sensors are still socketed for this reason. Also, if a board fails, you can pull the expensive sensor and put it on a new board.

Since that time period, IC reliability has increased, partly due to improvements in the purity of the materials being used. I would expect small signal IC's to be insanely reliable, to the point where the main reason for socketed chips would be to replace bad sockets.

 

[seamonkey]

I suppose, if you can pull the IC's is can make it easier to troubleshoot other circuitry on a board.
Or do a bed of nails test without the IC's in the way.

 

[agedhorse]

I suppose, if you can pull the IC's is can make it easier to troubleshoot other circuitry on a board.
Or do a bed of nails test without the IC's in the way.

Yes, this is a big part of it because of the way the circuit is designed. It can be easily troubleshot at the component level by a qualified tech who understands electronics. Generally, only 1 IC will need to be removed which can isolate major sections of the circuitry.

 

[agedhorse]

From what I've seen, those reasons tend toward cost reduction more so than sound quality, though I'm unfamiliar with the specific components used in the D-800. A pair of ADA4627-1s will almost certainly sound better than a TL072 or JRC072, as well as outperform them in measurements. Of course, the cost is much higher, as is the quiescent current.

How often do op amps require warranty/service replacement in something like a D-800? Is it often enough to justify using socketed DIPs?

First of all, different op amps have different strengths and weaknesses as I'm sure you are aware of. In MI amplifiers, one of the most sought after strengths is robustness and reliability in the face of potentially gross overloads. The TL072 is very tolerant of the sometimes absurd operating conditions that an MI amp will see in its lifetime, specifically in how they handle common mode voltage. They are an easy part to design with to insure that the part is not damaged under "almost unrealistic" conditions, and in fact there is a specific warning of device damage from this particular condition on the ADA4627-1 data sheet.

Second, when you consider that an amp with the feature set of these amps might use 10 dual op-amps, and the part may cost $6 each in quantity, it drives the cost of the amp up significantly and IMO does not improve the "sound quality" of the amp in this application.

Third, these parts are only available in surface mount packages, are not stocked deeply by distributors, have long lead times, and are a sole source part, it's just not a practical to consider them for this application. There are not enough benefits to outweigh the drawbacks, and since I'm the designer I get to make this choice!

The reasons for using sockets in these amps is to allow for pre-assembly testing, post-assembly testing and for troubleshooting in the field if ever needed. Occasionally a device will be defective, or damaged from something catastrophic, but it is rare indeed.

 

[disssa]

Here is something old: Invalid Link Removed

 

[12bass]

... Second, when you consider that an amp with the feature set of these amps might use 10 dual op-amps, and the part may cost $6 each in quantity, it drives the cost of the amp up significantly and IMO does not improve the "sound quality" of the amp in this application.

Using the ADA4627-1 would not be an economic choice for most bass amps... however, I am using them in place of the JRC072s in my Eden WT-500, along with the OPA827 and LME49990. I've done enough A/B testing to know that they do indeed improve the sound quality of the amp (and my bass tone). The venerable TL072 sounds "low-fi" in comparison. I've also made RMAA loopback measurements showing improvements with better op amps, so I know that the differences are not just placebo. I was surprised a while back by the improvement when I swapped out the single TL072 in my SVP-PRO preamp for a pair of OPA827s, as I was not expecting much, if any, change in the tone. That said, discussing the differences between various op amps goes beyond the intention of this thread....

 

[Roxbororob]

Here is something old: Invalid Link Removed
View attachment 3541079

Can we see the other side? Please?

 

[disssa]

Can we see the other side? Please?

This one?

 

[Roxbororob]

This one?
View attachment 3541248

Ahh...beauty is in the eye of the beholder. Love it! Thx

 

[tubedude]

The contrast between the chassis and transformer appearance make it look like a photoshop job.

 

[disssa]

Yes, the photo was edited using Photoshop. Here is the "original" out of the camera, only resized and tagged with "disssa.de".
I dont like power cords on pics. And I am not a good photoshoper...

 

[BoogieZK]

Using the ADA4627-1 would not be an economic choice for most bass amps... however, I am using them in place of the JRC072s in my Eden WT-500, along with the OPA827 and LME49990. I've done enough A/B testing to know that they do indeed improve the sound quality of the amp (and my bass tone). The venerable TL072 sounds "low-fi" in comparison. I've also made RMAA loopback measurements showing improvements with better op amps, so I know that the differences are not just placebo. I was surprised a while back by the improvement when I swapped out the single TL072 in my SVP-PRO preamp for a pair of OPA827s, as I was not expecting much, if any, change in the tone. That said, discussing the differences between various op amps goes beyond the intention of this thread....

As said AgedHorse, it can do more "damage" to an amp to swap Opamp with said "better" choice.
The main reason for swapping Opamps is noise floor and slewrate IMO.
But some OPA are subject to self-oscillation and instability.

Frequency response and "tone" is not a real fact inside OPA because all OPA are capable of having a perfectly flat frequency response with the human hearing range.
Most of the time, the design of a preamp or amp is limiting the frequency response to avoid ringing or instability.

 

[12bass]

As said AgedHorse, it can do more "damage" to an amp to swap Opamp with said "better" choice.
The main reason for swapping Opamps is noise floor and slewrate IMO.
But some OPA are subject to self-oscillation and instability.

Frequency response and "tone" is not a real fact inside OPA because all OPA are capable of having a perfectly flat frequency response with the human hearing range.
Most of the time, the design of a preamp or amp is limiting the frequency response to avoid ringing or instability.

FWIW, I totally disagree about the supposed universal transparency of op amps (i.e. they have no sound). They all sound different in my experience... though the differences are sometimes subtle and may require a trained ear. I just swapped out the TL082 in the output section of my newly acquired Sony CDP-X111ES CD player for a pair of ADA4627-1s and the difference is clearly audible... more open sounding... less distortion. Just swapped in a TL072 for comparison and I'd be more than willing to do an ABX test to see if I could identify each. The small capacitors are soldered directly across the rails to prevent oscillation. At the top of the photo is a pair of OPA211s operating as the output buffer.

More interesting reading here: Analog Circuit Design · Samuel Groner · Resources · IC OpAmps

 

[BoogieZK]

View attachment 3542049
FWIW, I totally disagree about the supposed universal transparency of op amps (i.e. they have no sound). They all sound different in my experience... though the differences are sometimes subtle and may require a trained ear. I just swapped out the TL082 in the output section of my newly acquired Sony CDP-X111ES CD player for a pair of ADA4627-1s and the difference is clearly audible... more open sounding... less distortion. Just swapped in a TL072 for comparison and I'd be more than willing to do an ABX test to see if I could identify each. The small capacitors are soldered directly across the rails to prevent oscillation. At the top of the photo is a pair of OPA211s operating as the output buffer.

More interesting reading here: Analog Circuit Design · Samuel Groner · Resources · IC OpAmps

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...

 

[agedhorse]

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...

Agreed in general. In particular, many designs in MI capitalize on the selective addition or generation or manipulation of harmonics, and how the op-amp behaves under these conditions is something that is considered an "off-sheet" application in the hi-fi audio world.

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.

 

[fast slapper]

View attachment 3542049
FWIW, I totally disagree about the supposed universal transparency of op amps (i.e. they have no sound). They all sound different in my experience... though the differences are sometimes subtle and may require a trained ear. I just swapped out the TL082 in the output section of my newly acquired Sony CDP-X111ES CD player for a pair of ADA4627-1s and the difference is clearly audible... more open sounding... less distortion. Just swapped in a TL072 for comparison and I'd be more than willing to do an ABX test to see if I could identify each. The small capacitors are soldered directly across the rails to prevent oscillation. At the top of the photo is a pair of OPA211s operating as the output buffer.

More interesting reading here: Analog Circuit Design · Samuel Groner · Resources · IC OpAmps

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.