Walt Jung biasing opamps in class A

[pucho812]

I read a comment referencing Walt Jung and how he had an article about biasing opamps( example 5532) to be class A operation.
That all you had to do was add a resistor to the opamp output going to the negative rail.

Does anyone have any details on this or the article the reference in the comment?

I would be curious as to what it achieves outside of heat increase?

 

[JohnRoberts]

I read a comment referencing Walt Jung and how he had an article about biasing opamps( example 5532) to be class A operation.
That all you had to do was add a resistor to the opamp output going to the negative rail.

Does anyone have any details on this or the article the reference in the comment?

I would be curious as to what it achieves outside of heat increase?

That was a popular audiophool tweak back in the 70s/80s trying to get something for almost nothing.

In theory forcing the output stage to operate class A at low level by sucking a bunch of current out of it sounds good in theory (to reduce crossover distortion), but if there was any real benefit to that, the IC makers could do it better and cheaper in silicon.

JR

PS; It has probably been discussed on this forum before (years ago), not necessarily as a Walt Jung thing, but general audio phoolishness.

 

[pucho812]

That was a popular audiophool tweak back in the 70s/80s trying to get something for almost nothing.

In theory forcing the output stage to operate class A at low level by sucking a bunch of current out of it sounds good in theory (to reduce crossover distortion), but if there was any real benefit to that, the IC makers could do it better and cheaper in silicon.

JR

PS; It has probably been discussed on this forum before (years ago), not necessarily as a Walt Jung thing, but general audio phoolishness.

So in your opinion, not worth it?

 

[JohnRoberts]

So in your opinion, not worth it?

Not as a general fix for every op amp in every circuit. Probably not for any.

I never took it seriously enough to do my own bench testing for the reasons given. The guys who design op amps are not slackers.

Managing crossover distortion is a well investigated topic by power amp designers too.

JR

 

[JohnRoberts]

I suspect one or more people have performed some bench testing wrt this. I'm too lazy to do a search.

JR

 

[pucho812]

I suspect one or more people have performed some bench testing wrt this. I'm too lazy to do a search.

JR

My thoughts as well but I must be using the wrong search phrase or terms because I can’t find that information

 

[JohnRoberts]

My thoughts as well but I must be using the wrong search phrase or terms because I can’t find that information

https://tangentsoft.com/audio/opamp-bias.html
and here's one from Jon Risch a guy I worked with at Peavey https://www.audioasylum.com/audio/tweaks/messages/31186.html

I didn't see any hard numbers from bench testing.

JR

 

[pucho812]

https://tangentsoft.com/audio/opamp-bias.html
and here's one from Jon Risch a guy I worked with at Peavey https://www.audioasylum.com/audio/tweaks/messages/31186.html

I didn't see any hard numbers from bench testing.

JR

Thanks jr, you are a delight.

 

[Mr. Moscode]

That was a popular audiophool tweak back in the 70s/80s trying to get something for almost nothing.

In theory forcing the output stage to operate class A at low level by sucking a bunch of current out of it sounds good in theory (to reduce crossover distortion), but if there was any real benefit to that, the IC makers could do it better and cheaper in silicon.

JR

PS; It has probably been discussed on this forum before (years ago), not necessarily as a Walt Jung thing, but general audio phoolishness.

Any data on this to support your phoolishness opinion? Don't be so quick to judge.
In the 70-80s opamps weren't what they are today. 741s were still used.

 

[ruffrecords]

Any data on this to support your phoolishness opinion?

You mean like the complete lack of objective measurements?

Cheers

Ian

 

[JohnRoberts]

Any data on this to support your phoolishness opinion? Don't be so quick to judge.
In the 70-80s opamps weren't what they are today. 741s were still used.

As Grace Slick said if you can remember the 60s you weren't really there.

I can remember the 70-80s (mostly), and that was when off the shelf op amps that were well faster than audio, selling for affordable prices, finally became widely available. The 553x and TL07x made circuit design a lot easier. Speaking about the 741 there was even a IEEE paper on the subject. The 741 was a milestone IC because it was the first unity gain stable op amp, thanks to internal compensation. This free'd up circuit designers to apply negative feedback to circuit design with even less understanding , using just simple math.

FWIW there were many acceptable performance semi-pro bedroom recording SKUs designed using 741-era ICs (0.5v/uSec slew rates). As long as audio path levels were kept modest (like using the lower nominal -10dBV 0VU standard). I even dedicated one of my audio mythology columns back in the 80s to comparing -10dBV paths to +4dBu. The -10dBV paths came out a lot better than expected.

Don't be triggered by the mention of "phoolish", I wasn't referring to you.

You mean like the complete lack of objective measurements?

Cheers

Ian

+1 I was disappointed that I didn't find an objective study revealing what op amps benefited from how much skewed output current loading. Of course the loading and several other factors would also affect this.
======
I mentioned that I worked with Jon Risch at Peavey last century.... He was our resident "golden ear" and I used him successfully on a handful of projects. We would sometimes get into discussions not unlike how many angels can dance on a pin head, related to electron behavior down at the atomic level. He was actually working in transducer engineering so didn't work directly for me. He only assisted my group on a small handful of projects.

I was disappointed that Jon's essay about this didn't include any objective data... I think he said something like adding the current draw sounded "sweeter" . FWIW Jon is a real engineer. As I recall he presented a serious AES paper back then investigating multi-tone (more than two) IMD measurements.

I've shared this story before, I once signed an ECN (engineering change notice) to use a more expensive film capacitor inside a passive loudspeaker crossover. The cost increase was something like only $0.10-$0.20, but his boss was too cheap to approve any cost increase afraid of what our big boss would think (cost increases were generally frowned upon). As a favor to Jon I approved the cost increase even though it was not my direct area of responsibility because I knew that film caps could make a measurable improvement in passive crossovers, and because I could .

JR

 

[living sounds]

There is information about doing this in Douglas Self's book "The Design Of Active Crossovers". He shows (with measurements) that under certain conditions it's possible to markedly lower distortion in 5532/5534 op amps by adding a 3.3 k ohm resistor between output and the positive supply rail.

However, in practise I never found an audible advantage.

 

[JohnRoberts]

There is information about doing this in Douglas Self's book "The Design Of Active Crossovers". He shows (with measurements) that under certain conditions it's possible to markedly lower distortion in 5532/5534 op amps by adding a 3.3 k ohm resistor between output and the positive supply rail.

A book I could have used a couple decades sooner....

JR

However, in practise I never found an audible advantage.

 

[dai h.]

FWIW, there is an old thread on this:

https://groupdiy.com/threads/modifying-existing-op-amp-circuits-to-operate-in-class-a.62082/

 

[ruffrecords]

There is information about doing this in Douglas Self's book "The Design Of Active Crossovers". He shows (with measurements) that under certain conditions it's possible to markedly lower distortion in 5532/5534 op amps by adding a 3.3 k ohm resistor between output and the positive supply rail.

However, in practise I never found an audible advantage.

I wonder why he never mentioned it in any of his other books?

Cheers

Ian

 

[k brown]

Thanks jr, you are a delight.

Who you callin' junior?

 

[JohnRoberts]

FWIW, there is an old thread on this:

https://groupdiy.com/threads/modifying-existing-op-amp-circuits-to-operate-in-class-a.62082/

Thanks... indeed we've been down this rabbit hole before...

JR

 

[Flatpicker]

Ages ago there was an article published by Walt Jung and Richard Markell that used a FET and resistor from the op amp out pin to the -V rail to create a current source for this purpose. Also Paul Stamler published a preamp design (forgot what magazine it was for) using a constant current sink to achieve the same result.

I've not tried either, but I have found that sticking an op amp IC into a hybrid circuit such as CAPI's IC-DOA which basically just adds a discrete output stage makes a night and day difference, at least to my ears. https://capi-gear.com/catalog/index.php?cPath=71_183

 

[squib]

you know that in this thread
https://groupdiy.com/threads/modifying-existing-op-amp-circuits-to-operate-in-class-a.62082/
is the information to take a 5534 and turn it into a true class A opamp with easily selectable idle current to suit the expected load.