Whats wrong with large filter caps for Gainclone?

[Peter Daniel]

I never tried to indicate that this is how manufacturers or others measure high-end. This is how I measure high-end.

And high-end and good sound are two different things.

But you said that those chips are not used in high-end equipment, and Jeff Rowland definitely is high end. So what has thickness of aluminum to do with that?

[planet10]

Originally posted by millwood
I never thought "high-end" is measured in plate thickness

It is unfortunate that in many ways a significant part of the hi-end has gone down this road -- one of the reasons there is such a growing backlash against hi eye-candy products that don't deliever -- unfortuneatly many of the ones that do get swept out along with.

I've got some 2" cedar slabs, if i use some of that as a front plate maybe i'll have a sota piece of gear :^) (tongue firmly in cheek)

dave

[Pedja]

Originally posted by millwood
I certainly don't have a crystal ball for a claim that I didn't make. where did I state that the chip was designed for the low end applications?

C’mon man…
http://www.diyaudio.com/forums/showt...191#post247191

I trust that those engineers at JBL know better about those chips than you and I.

This is not a problem of “who can you trust?” kind (and even if it would be, I probably might choose better).

Pedja

[millwood]

Originally posted by Pedja
I referred to your claim that this chip was designed for the low end applications. Do you have a crystal ball that is telling you these things?

Pedja

the exact "claim" I have made is "The chip was probably designed for low-end applications "

Under no circumstance, I have stated that the chip was designed for the low end applications. I didn't know which part of the market National wanted to target with the chip. I ventured a guess (thus the word "probably") that they were targeting the low-end. But I never would state this as a matter of fact because I just don't know.

Please read a little bit more careful. I don't want to be accused of crimes I didn't commit.

[Pedja]

Yeah, you did not… yup… someone else said somewhere it was intended to be a car amp chip … who knows who was that... it was someone, somewhere… it happens now and then … probably.

Pedja

[vic2]

"Whats wrong with large filter caps for Gainclone? Post #1


When ever i have built power amps, ive always used large filter caps. How come the gainclone only has 1000uF per channel?

What happens if you use lots of uF's in a gainclone"

When I read the 47 Labs information, my inference was that the use of small capacitors allowed for a freer flow of current which fits in with the faster charge/discharge rate. I also thought that this minimalistic thinking applied to the power transformer as well. I think that the whole idea is to have a minimal amount of componentry contributing the the flow of sound through the amp. A kind of feng shui for audio type of thing, I suppose.

PS: don't bash me, I'm not an EE. I started out making speakers for myself and have recently got into the amp department. However, I do believe in minimalism for the audio path when possible.

[jcarr]

Millwood:

>the exact "claim" I have made is "The chip was probably designed for low-end applications"<

My design partner, Petr Mares, was an engineer at the audio division of National Semiconductor. Succinctly stated, the Overture series was designed to be a high-performance amplifier that was targeted at mass-market commercial audio applications. Due to the mass-market target, the project goal was to offer high performance in an affordable monolithic solution (hybrid circuitry along the lines of National's LH-101 would offer better performance but at considerably higher cost), and make it as easy and trouble-free to use as possible.

The design team also came to the conclusion that short-circuit and thermal overload measures tend to give customer manufacturers problems (and eat up valuable pcb real estate). So the Overture chips integrate "Spike" circuitry so the customer manufacturer doesn't have to deal with these issues.

The Overtures are definitely upscale products by National's perspective, but no one in the audio division seemed to have any delusions that these would compete with the Krells or Spectrals of the world (although the guys seemed to be tickled pink that someone like Jeff Rowland would use their ICs in his products). Actually, Petr used to work at Spectral, and there was at least one other fellow (name slipped my mind) who designed high-end audio products as a side-business in addition to his duties at National's audio division.

hth, jonathan carr

[Jocko Homo]

Is the power transformer.

The VA rating of it, its series resistance, and the current demands of the load all enter into chosing filter caps. Without knowing all of these parameters, it is hard to give an absolute answer.

Yes, it is possible to make the caps too big, depending on the application.

And finding the answer, and implementing, it is what separates the winners from the also-rans.

Sorry there is no easy answer. Do what the "big boys" do:

Try every combination that you can. You will learn lots in the process.

But please........don't come up with new theories as to what works, and why. We have too much of that now. Just state what, and forget the why.

Jocko

[millwood]

Originally posted by janneman
Since I happen to know that the xformer is disconnected from the amp for about 85-90% of the time, I find it difficult to believe this would make for a huge improvement.

Jan Didden

I agree with the general view and think it is intuitive. However, I am not sure if the 85-90% figure is that accurate.

You would think that in a typical set-up, the RC constant for the whole amp is quite low: 3300uf x 10ohm =33ms. so I did a little simulation

here are some results:

1) for 1000ufx10ohm, the diode conducts about 50% per half cycle.
2) for 3300ufx10ohm, the diode conducts about 1/3 of the time.
3) for 10,000ufx10ohm, the diode conducts 1/4 - 1/5 of the time.

so 85% - 90% may be too aggressive of a figure for an average PS.

Would be interesting is one simulates ESR in the cap.

One very interesting I have found is that when the diodes are conducting, they don't conduct contineously. Rather, they go through conduct very briefly, then shut down, then conduct briefly again. This is more apparent when the RC constant is smaller.

the situation is likely worse if the PS is used to power an amp that is dirving audio signals into a speaker (the R).

To me, that means using small capacitors in a PS may cause excessive RF noise.

PS: I simulated the case where the capacitor has an esr of 0.1ohm, 1ohm to 10ohm (I have no ideal how realistic the values are). under all cases, the diode conducts at roughly the same time it would have conducted for a perfect cap (ESR=0).

However, with ESR, the conduct-shut down-conduct-shut down cycle mentioned above is gone.

With 0.1ohm and 1ohm ESR, the output voltage is about the same as those under the perfect cap. for 10ohm ESR, the output waveform is simply half wave. ie. the output voltage can never hold.

The above is done for C=10,000uf.

[millwood]

Originally posted by jcarr
The Overtures are definitely upscale products by National's perspective, but no one in the audio division seemed to have any delusions that these would compete with the Krells or Spectrals of the world (although the guys seemed to be tickled pink that someone like Jeff Rowland would use their ICs in his products).

hth, jonathan carr

Thanks jonathan for sharing the inside.

Looks like some of us are trying to push the chip where its designers didn't intend it to be.

Not that it wouldn't be successful there.