• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Op Amp upgrade

#101
lowfreqgeek said:
Resistors, opamps, caps... All can make a difference, but the trick is knowing when and where to use what and how the specific part used will make the difference. Metal-film resistors (the blue ones) have tighter tolerance and less Johnson noise (up to 40dB less!!) than carbon resistors (usually tan), but blindly replacing ALL the carbon with metal-film won't necessarily buy you much. Same for caps - the signal-path coupling caps in the SWR amps are all WIMA audio-grade Polyester. At least they used to be. While you may get better (at a price), not every cap needs to be audio-grade.

But it sounds like your tech is pretty good, so I'm sure he's familiar with what makes sense and what doesn't. The main thing is that you don't go to the expense of changing every component without understanding why/what/how it behaves.

I may try some TLEx072s in my Line6 UX2. The TL072s are very noisy with high gain (like the gain required to run a Jensen xfmr-equipped DI) and the power supply is already taxed. The 5V supply means I really need rail-to-rail to have any headroom (OP275 is out...) on the instrument input, and the supply can't give any more juice. I've already done major (really major) upgrades, but it's not there yet.

Doesn't really matter, though, as I have an RME for the "real" work...
Click to expand...

My tech was very specific and intentional in the placement of the metal-film resistors...not all resistors got replaced (which until now did not make much sense to me, but obviously he new what he was doing :-D). Those 10000 uF caps are awesome! I've never had the "thermal meltdown" problems associated with the SM+900's to begin with, but the caps help the amp to stay at a "normal" operating temperature even in my skb rack case. Like I said this guy is a genius...he's just released a line of fully hand made preamps and effects pedals! (who's prototypes were built on raw computer chassies and still sounded INSANE)
 
#102
Another explanation for those who are interested: [Invalid or Expired Link Removed]

This one makes a little more sense as it describes the "contact noise", or the noise generated between the resistor leads and the resistor medium. That's where the difference lies between the various types of resistors.

Fun stuff. Way more interesting to me than coding a microcontroller... (what I *should* be doing right now).
 
#103
rumblinbass said:
resistors...quieter?
from the description (tan and blue) you went from carbon to metal film. The metal film resistors are a tighter tolerance (probably 1%) and are better suited for audio...but quieter? first I've heard.
Click to expand...

Yep, quieter.

Resistors generate noise - thermal, contact, and shot noise.

...and contact noise in particular is related to resistor composition.
 
#104
I love reading these posts about swapping opamps to get a phatter/brighter/darker/wibblyer/whatever tone.

Anyone who has done even basic opamp theory will know that the frequency response curve (let's call it tone) comes from what you put round them not from the opamp itself. They are a pretty sterile and predictable device (as long as you operate them within their design specification).

Output offset - almost every stage is AC coupled so a few mV offset means nothing, you don't hear offset unless it is large enough for the output to hit one of the supplies (clip).

The only thing you will improve is the noise that the opamp is responsible for, but as has already been pointed out the other components probably contribute far more noise than the opamp.
 
  • Like
Reactions: MrSidecar
#105
delta7fred said:
Anyone who has done even basic opamp theory will know that the frequency response curve (let's call it tone) comes from what you put round them not from the opamp itself. They are a pretty sterile and predictable device (as long as you operate them within their design specification).
Click to expand...

As someone who spent more money than I care to remember earning my Computer/Electrical Engineering degree - I'd say it's a bit more complicated than that.

Generally - a well designed circuit using an op-amp well within its design envelope will not see much change when swapped for another op-amp operating within it's design window... but things like slew rate, clipping behavior, etc. do matter.
 
#106
Op amp differences amount to more than just noise. As mentioned in my Eden mod thread, I've gone through a lot of op amps, and they all sound a little different. The quality of the rest of the signal path may impact the audibility of those differences, however. Also, sometimes new parts which I had hoped to be "better" didn't sound better to me. Some sound clearer or bassier or thinner or fuzzier....
 
#107
delta7fred said:
I love reading these posts about swapping opamps to get a phatter/brighter/darker/wibblyer/whatever tone.

Anyone who has done even basic opamp theory will know that the frequency response curve (let's call it tone) comes from what you put round them not from the opamp itself. They are a pretty sterile and predictable device (as long as you operate them within their design specification).

Output offset - almost every stage is AC coupled so a few mV offset means nothing, you don't hear offset unless it is large enough for the output to hit one of the supplies (clip).

The only thing you will improve is the noise that the opamp is responsible for, but as has already been pointed out the other components probably contribute far more noise than the opamp.
Click to expand...

In an earlier post I explained that I used 3 different op amps in the same circuit and there was a difference. Subtle...but there was a difference.

If you have DC on a pot you will hear it. If you have DC on a switch, you will hear it. Generally, you do not want dc (even mV's) going from one stage to another.
 
#108
aborgman said:
As someone who spent more money than I care to remember earning my Computer/Electrical Engineering degree - I'd say it's a bit more complicated than that.

Generally - a well designed circuit using an op-amp well within its design envelope will not see much change when swapped for another op-amp operating within it's design window... but things like slew rate, clipping behavior, etc. do matter.
Click to expand...

I totally agree, it is more complicated than that, I was just trying to point out without going into too much technical detail that different opamps do not have their own characteristic sounds - bright, fat, etc as some seem to think.

(I too have a Electrical Engineering degree. I retired 10 years ago so have forgotten quite a lot of the finer detail now. The last time I did any serious electronic deign was in the 80s, I much preferred the commissioning and fault finding side, it got me out of the office more. :D)
 
#110
delta7fred said:
I totally agree, it is more complicated than that, I was just trying to point out without going into too much technical detail that different opamps do not have their own characteristic sounds - bright, fat, etc as some seem to think.
Click to expand...

Different op-amps in the same circuit may sound distinctly different. That has nothing to do with an op-amps characteristic sound, and everything to do with the op-amps response to surrounding circuitry.
 
#112
aborgman said:
Different op-amps in the same circuit may sound distinctly different. That has nothing to do with an op-amps characteristic sound, and everything to do with the op-amps response to surrounding circuitry.
Click to expand...

Although a factor, dunno if design implementation is the only factor. My op amp testing has used a number of different circuits, and found some similarities/differences in sound across application. I also listen through AKG K702s.

Although a bit of a tangent, sometimes I get the idea that engineers never go beyond the spec sheets and actually listen to the devices in question. This approach tends to lead to the "the specs tell all" sort of attitude. I'd disagree with that, as IMO the specs leave a lot out. That said, I'm a proponent of the scientific method and things like double-blind testing, just in case someone might want to label me as an "audiophool".
 
  • Like
Reactions: AlexanderB
#114
12bass said:
I also listen through AKG K702s.
Click to expand...

I've often wondered about this. I frequent a Headphone enthusiast's forum, and there's not often a debate about whether or not opamp rolling makes a difference over there. I might submit that it's far easier to hear such differences with high-fidelity reproduction equipment and high-quality source material. I wonder if this is why there's so much more debate about this here--so much of the entire signal path of instrument amplification equipment seems designed towards "creating" a sound, as opposed to simply reproducing a source faithfully. Listening to well-mastered classical recordings on a high-end sound card through a pair of Senn. HD580's, opamp changes to a headphone amp seem quite noticable to me. But there's also a lot more information to evaluate in a musical excerpt like this than there is in a single bass or guitar note--and the other parts involved in creating that note (as some here have already intimated in this thread) may play a role in masking apparent differences contrived in the rest of the signal path. ....but here I go waxing all geeky again. ;)

I'm glad the OP's experiments have been fruitful...it reinforces my desire to experiment and flesh out my own designs a little bit better. :D
 
#117
12bass said:
Although a factor, dunno if design implementation is the only factor. My op amp testing has used a number of different circuits, and found some similarities/differences in sound across application. I also listen through AKG K702s.

Although a bit of a tangent, sometimes I get the idea that engineers never go beyond the spec sheets and actually listen to the devices in question. This approach tends to lead to the "the specs tell all" sort of attitude. I'd disagree with that, as IMO the specs leave a lot out. That said, I'm a proponent of the scientific method and things like double-blind testing, just in case someone might want to label me as an "audiophool".
Click to expand...

I always subject my own designs to a listening test. But...

Nobody has the time or money to test every possible combination of components, and it's possible to make reliable educated guesses that don't really need to be confirmed through testing. This process is not just based on "specs," but on a fundamental understanding of how circuits work.

There's a middle ground between specs and listening tests, which is to use measurement instrumentation.

Listening tests certainly make sense when one knows that two designs are likely to sound different, and you want to decide which one you like better.
 
#118
lowfreqgeek said:
Atmel ATXMega in C. Pretty much a staple around here, but I'm a dyed-in-the-wool analog EE, so I much prefer the nuances of current sources and sine generators and transimpedance amps, etc.

End app is particle concentration and biological aerosol collection/detection.
Click to expand...

That's cool. I've done rudimentary PIC and 8051 stuff, and have only recently converted to coding in C. I'm a physicist, but am also interested in electronics. At my day job, I get involved in "physics meets electronics" situations, such as noise analysis of optical detectors.

Are you at a company, or doing academic research? It seems to me that solid knowledge of both the analog and digital domain is a pretty useful combination.
 
#119
lowfreqgeek said:
Another explanation for those who are interested: [Invalid or Expired Link Removed]

This one makes a little more sense as it describes the "contact noise", or the noise generated between the resistor leads and the resistor medium. That's where the difference lies between the various types of resistors.

Fun stuff. Way more interesting to me than coding a microcontroller... (what I *should* be doing right now).
Click to expand...


You can do more with high voltage and carbon composite resistors
http://www.geofex.com/article_folders/carbon_comp/carboncomp.htm

There's the Mojo
 
#120
One way to look at bass amplification is as part reproduction and part tone creation. What I look for in a high fidelity reproduction component may be different than what I seek in a musical instrument amplifier. In sound cards, mixing boards, preamps, and amplifiers, uncolored sound is generally what is preferred (i.e. "straight wire with gain"). However, when choosing parts for my bass amp, I also considered what sounded "best" in terms of tone color, which does not necessarily lead to the same choice in a pure high fidelity scenario. That said, I did end up using two very high quality op amps - OPA827 and OPA211 - as they sounded "better" than others I've tried in this particular application.
 
  • Like
Reactions: AlexanderB

Latest posts

Top Bottom
Back