Bob Cordell Interview: Negative Feedback

[mikeks]

Re: Re: Re: Re: Re: Re: Perspective on Open Loop Bandwidth Comparisons

The extent of the common-mode effects in the sim really surprised me a lot.

Your sim. failed to run.

 

[andy_c]

Re: Re: Re: Re: Re: Re: Re: Perspective on Open Loop Bandwidth Comparisons

Your sim. failed to run.

What's the error message?

 

[mikeks]

''time step too small''

increased it, and obtained the same result

 

[andy_c]

''time step too small''

increased it, and obtained the same result

If you look at the error log after the transient sim failure, does it indicate a failure to find the operating point?

 

[Bob Cordell]

Bob, as Matti defined it to me, 30 years ago: TIM is a subset of distortions included in DIM. DIM means: 'Dynamic Intermodulation distortion' and includes TIM as well as any other 'dynamically' manifested distortion, such as PIM, etc.
DIM 30 could just as well have been named TIM 30, but I suspect that Matti was trying to create a more inclusive distortion picture than just TIM, which had been pretty well researched by this time, but did not appear to explain 'everything' that appears to be important in amp performance with dynamic signals.

Thanks for the claification, John. That seems reasonable. It coincides with what I measure when I do a DIM measurement.

Bob

 

[PB2]

If you look at the error log after the transient sim, does it indicate a failure to find the operating point?

Yes, I got: "Use ".option noopiter" to skip."

Is it safe to skip, I've not used this option?

Yes, I remember when we discussed this some time ago.

I'm off for the night, thanks for this latest work.

Pete B.

 

[andy_c]

Yes, I got: "Use ".option noopiter" to skip."

Is it safe to skip, I've not used this option?

Yes, it's safe to skip. My sim does that also. After it fails with this strategy, it should go into the source stepping strategy with a bunch of entries that look like this at the end:

Source Step = 86.9243%
Source Step = 90.2149%
Source Step = 93.5056%
Source Step = 96.7963%
Source Step = 100%
Source stepping succeeded in finding the operating point.

If the source stepping fails, then it starts the sim from an arbitrary set of initial conditions. Sometimes these conditions are so far off that they can cause high frequency ringing such that the time step required to track them becomes too small compared to the time span. That's when you get the "time step too small" message.

Sorry about this guys. Further discussion on this should probably be in email, as it's getting off-topic.

 

[mikeks]

Hi Andy,

Actually, this ground was covered by Cherry and Stochino in EW.

 

[andy_c]

Actually, this ground was covered by Cherry and Stochino in EW.

Sounds like I may need to look into getting CDs of some of their back issues. Right now their site is under construction though.

 

[Nixie]

MLL3281

I can't find such a device. Did you mean MJL?

 

[mikeks]

Actually, this was in the letters section in the case of stochino.

I'll hump this 2 meter-high pile of papers around see if i can scan you a copy.

 

[mikeks]

Folks, guess what, Douglas Self is on-line!!

Welcome to diyaudio, Mr Self!

 

[powerbecker]

Re: Re: Re: Re: Re: Re: Perspective on Open Loop Bandwidth Comparisons

The extent of the common-mode effects in the sim really surprised me a lot.

Andy ,

thank you for the examples!

This is the reason why I prefer the inverting circuit!

If you try your simple stage in inverting mode you will see that the distortion is even a bit less.

Regards
Heinz!

 

[andy_c]

I'll hump this 2 meter-high pile of papers around see if i can scan you a copy.

Thanks very much Mike.

Folks, guess what, Douglas Self is on-line!!

Do you mean he is a member of this forum?

 

[mikeks]

Do you mean he is a member of this forum?

Yup!!

 

[mikeks]

Re: Re: Re: Re: Re: Re: Re: Perspective on Open Loop Bandwidth Comparisons

Andy ,

thank you for the examples!

This is the reason why I prefer the inverting circuit!

If you try your simple stage in inverting mode you will see that the distortion is even a bit less.

Regards
Heinz!

Actually, using a bootstrapped cascode solves that problem; no need to revert to the necessarily noisier inverting configuration.

 

[moamps]

Folks, guess what, Douglas Self is on-line!!

I'm afraid it's a false alarm folks! Just this week we've had about 20 Nelson Passes. Please carry on and don't let that distract you.

Regards,
Milan

 

[powerbecker]

"....no need to revert to the necessarily noisier inverting configuration."

This and parasitic capacities is the reason i prefer also small values for the resistors!
Also if one like to use a opamp one cannot alter its circuit!

 

[andy_c]

Re: Re: Re: Re: Re: Re: Re: Perspective on Open Loop Bandwidth Comparisons

This is the reason why I prefer the inverting circuit!

If you try your simple stage in inverting mode you will see that the distortion is even a bit less.

Hi Heinz,

Good to see you back!

I suspected that an inverting configuration would also have the same effect. One thing that concerns me about inverting mode is that if the input is open for whatever reason, there's a feedback factor of 1, which could lead to oscillations. This worries me, so I figure non-inverting is a safe solution.

BTW, thanks again for your circuit for biasing the diodes for clipping. You probably noticed it in my file from the other forum.

 

[lumanauw]

AD829, for example, has OLG F-3dB corner at some 10kHz, and quite high OLG of 100dB.

In my experience, the amplifiers with high OLG frequency corner and reasonable high OLG gain do sound better than those with corner at some 10Hz

Check out opamp of type CA3100. This opamp has 3dB corner frequency at 110khz. Will it be good for audio?