• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Op amp supply Quiz - what sounds best ?

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#1
A popular technique used in CD players is the provision of series resistance inward to the I/V stage op amps power supply connections , typical values are 47 ohms in marantz players and 100 ohms in pioneers as example. You would as example find a 100 ohm resistor connecting to Pin 4 and a 100 ohm connecting to Pin 7 ( single ) or Pin 8 (dual )

Can we do better and still keep it fairly simple ? and What actually sounds best ? - lets see any ideas you might have.
 

DonH56

Technical Expert
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
3,808
Likes
5,454
Location
Monument, CO
#2
Should be a capacitor on the pin, the RC is typically used to provide higher PSRR (greater rejection of power supply noise).

Got me on audibility, but it helps keep HF noise off the op-amp's rails (PSRR falls with frequency so they get more sensitive to noise at HF).
 

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#3
Should be a capacitor on the pin, the RC is typically used to provide higher PSRR (greater rejection of power supply noise).

Got me on audibility, but it helps keep HF noise off the op-amp's rails (PSRR falls with frequency so they get more sensitive to noise at HF).
Yes a capacitor is already there 100- 220uf is a typical value. Yes you are on to it, its a great opportunity being presented as you say to keep HF noise off op amp rails. My solution was two semiconductors on each rail replacing the resistors, that also ended up sounding really good too.
 

DonH56

Technical Expert
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
3,808
Likes
5,454
Location
Monument, CO
#4
What sort of semiconductors? Diodes won't do much; a couple of transistors can be set up but then you have to bias them cleanly (unless you just use them as capacitive multipliers?) and worry about their stability. Etc. Anyway, if you can do all that, you don't need my help!
 

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#5
OK lets say the semiconductors are 2x TL431 and 2x MCR100-6 ... Thanks but its more to encourage persons reading, to start seeing imaginative ways of using semiconductors - not necessarily in their published data manner.
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#6
Or just do exactly what all op amp manufacturers recommend, ie low impedance low noise supply to start with, plus low esr bypass caps as close to the supply pins as possible.

Not sure where you are going with this.

First thing you need to do is quantify, ie measure, if you have an issue when doing what the manufacturers recommend followed by comparing it to adding these resistors. I'm not sure I see the benefit. Just seems like a good way to modulate the supply voltage with the dynamic current draw.
 
Last edited:

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#7
Or just do exactly what all op amp manufacturers recommend, ie low impedance low noise supply to start with, plus low esr bypass caps as close to the supply pins as possible.

Not sure where you are going with this.

First thing you need to do is quantify, ie measure, if you have an issue when doing what the manufacturers recommend followed by comparing it to adding these resistors. I'm not sure I see the benefit. Just seems like a good way to modulate the supply voltage with the dynamic current draw.
Low impedance is not required, (but as we see is wrongly planned for in most implementations ) because current draw by op amps is ?( in my experience very low ) Rather if we plan to use a higher impedance will this improve perceived sound quality ?

Where I am going with this is to question electronics ( bad ) habits, such as exampled by what we just discussed, your presumption that low impedance supplies are needed for op amps - when IMO the opposite, namely high impedance supplies suggests as being totally applicable, due to very low current draw by the device. Would you agree ?
 
Last edited:

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#8
It wasnt a presumption.

Low impedance is a relative term. No we are not talking about having to dump 10 amps into a speaker load, but why do you want a load modulated supply?

Putting a resistance in the supply will make its voltage modulate with current flow. It may well be small, and the op amp may well have good PSRR, but none the less you have to have a good reason to do it.

What is your theory behind it possibly "sounding" better? What technical improvement does it provide and what is that effect? Why is it not shown in any manufacturers data sheet?

I think you have asked fundamentally the wrong question with "what sounds best". Trying to tackle this from a subjective POV will not lead you to the answers, just more confusion. If there is a technical justification for this then fine, but Im struggling to see it.
 
Last edited:

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#9
It wasnt a presumption.

Low impedance is a relative term. No we are not talking about having to dump 10 amps into a speaker load, but why do you want a load modulated supply?

Putting a resistance in the supply will make its voltage modulate with current flow. It may well be small, and the op amp may well have good PSRR, but none the less you have to have a good reason to do it.

What is your theory behind it possibly "sounding" better? What technical improvement does it provide and what is that effect? Why is it not shown in any manufacturers data sheet?
Quite the opposite actually, Manufacturers have seemingly found reason of placing resistors in line to op amp supplies I/V stages. A Pioneer PDS 507 as example has R452 R451 as 100 ohm , What I am suggesting is we can do much better. But I am really glad you are now critical of their bad habits.

Armed with 4 semiconductors to keep it comparatively simple , replacing such use of resistance. Can you suggest improvement , as you have now identified their bad habit, of making voltage modulate with current flow. I used 2x TL431 and 2x MCR100-6 Can you do any better with similarly 4 components ?
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#10
Quite the opposite actually, Manufacturers have seemingly found reason of placing resistors in line to i/V stages. A Pioneer PDS 507 as example has R452 R451 as 100 ohm , What I am suggesting is we can do much better. But I am glad you are now critical of their bad habits.

Armed with 4 semiconductors to keep it comparatively simple , replacing such use of resistance. Can you suggest improvement to, as you have now identified their habit, of making voltage modulate with current flow ?

What is that reason? Someone may point out a blindingly obvious reason that I havent thought of, but I simply dont know what was in the mind of the designer.

Try low noise voltage regulator, ie one that also has good rejection at high frequencies (simple ones dont) and follow the op amp manufacturers recommendations WRT decoupling/bypass caps.

My next question is why are you asking? Are you trying to come up with some kind of mod/improvement to these players you have mentioned?
 
Last edited:

BDWoody

Major Contributor
Forum Donor
Joined
Jan 9, 2019
Messages
1,453
Likes
2,384
Location
Mid-Atlantic, USA. (Maryland)
#11
Armed with 4 semiconductors to keep it comparatively simple , replacing such use of resistance. Can you suggest improvement to, as you have now identified their habit, of making voltage modulate with current flow ?
What problem that leads to a potentially audible issue are we trying to solve? Are we just assuming every box should be messed with and is easily 'improved?' I think I'm missing something...?
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#12
What problem that leads to a potentially audible issue are we trying to solve? Are we just assuming every box should be messed with and is easily 'improved?' I think I'm missing something...?
I think you may have hit the nail on the head.
 

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#13
What problem that leads to a potentially audible issue are we trying to solve? Are we just assuming every box should be messed with and is easily 'improved?' I think I'm missing something...?
To reach consensus that op amp supplies can be improved by using high impedance supplies. And that the use of resistors as @March Audio
identifies leads to "making voltage modulate with current flow"

If we could agree with always using high impedance supplies for op amps, why on earth do we accept the opposite in equipment and indeed op amp manufacturers recommendations ? I agree with them however with the use of capacitors close to pins for bypass.

Or just do exactly what all op amp manufacturers recommend, ie low impedance low noise supply to start with, plus low esr bypass caps as close to the supply pins as possible.
I am certain we would all notice an improvement in sound quality, if ,as we have just discovered - that we firmly disobey what is recommended
as low impedance supplies, and instead cater precisely for the current requirements of the op amp itself.
 

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#14
I think you may have hit the nail on the head.
But you are then awkwardly contradicting yourself by stating @March Audio "Putting a resistance in the supply will make its voltage modulate with current flow" which is very common practice in CD players ( Marantz / Pioneer )

and then seeing no reason to change anything.
 

BDWoody

Major Contributor
Forum Donor
Joined
Jan 9, 2019
Messages
1,453
Likes
2,384
Location
Mid-Atlantic, USA. (Maryland)
#15
I am certain we would all notice an improvement in sound quality.
Why? Back to what audible problem is being solved...?

Some like to tinker, feeling they will always know better...

I'd rather buy something designed and built properly...
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#16
To reach consensus that op amp supplies can be improved by using high impedance supplies. And that the use of resistors as @March Audio
identifies leads to "making voltage modulate with current flow"

If we could agree with always using high impedance supplies for op amps, why on earth do we accept the opposite in equipment and indeed op amp manufacturers recommendations ? I agree with them however with the use of capacitors close to pins for bypass.



I am certain we would all notice an improvement in sound quality, if ,as we have just discovered - that we firmly disobey what is recommended
as low impedance supplies, and instead cater precisely for the current requirements of the op amp itself.
With respect you are coming at this from the wrong angle.

You need to present some technical reasons / benefits of using high impedance supplies. Why are you assuming there are benefits?

I think you are looking for a reason to justify a methodology based on assumptions and reasons that arent there
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#17
I am certain we would all notice an improvement in sound quality, if ,as we have just discovered - that we firmly disobey what is recommended
as low impedance supplies, and instead cater precisely for the current requirements of the op amp itself.

Why? Please technically explain.

Please technically explain what you mean by "cater precisely for the current requirements of the op amp itself".

You are making assumptions.
 
Last edited:

BDWoody

Major Contributor
Forum Donor
Joined
Jan 9, 2019
Messages
1,453
Likes
2,384
Location
Mid-Atlantic, USA. (Maryland)
#18
But you are then awkwardly contradicting yourself by stating @March Audio "Putting a resistance in the supply will make its voltage modulate with current flow" which is very common practice in CD players ( Marantz / Pioneer )
and then seeing no reason to change anything.
If there's no identified audible problem to be solved, I'm still missing the point.
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,730
Likes
5,332
Location
Albany Western Australia
#19
But you are then awkwardly contradicting yourself by stating @March Audio "Putting a resistance in the supply will make its voltage modulate with current flow" which is very common practice in CD players ( Marantz / Pioneer )

and then seeing no reason to change anything.

What contradiction? You are assuming the reasons that those manufacturers have done this is audio quality. I dont know why they have done that or what problem they were trying to solve with it.
 

stereo coffee

Active Member
Manufacturer
Joined
Jan 2, 2019
Messages
139
Likes
42
#20
Why? Back to what audible problem is being solved...?

Some like to tinker, feeling they will always know better...

I'd rather buy something designed and built properly...
The problem being sought as being solved, is in one word , mediocrity
 
Top Bottom