HighDynamicsOpamp. Link,?'s.

[jeth]

Here is a circuit for a discreet/opamp hybrid circuit I came across..It may be of interest to some of you, I hope so anyway. I ran a search and there doesn't seem to be a link on the forum, apologies if it's nothing new...


www.tnt-audio.com/clinica/dynamicopamp_e.html

Looking at this circuit left me wondering a couple of things..

The increased headroom, and therefore dynamic range, of such a circuit is said to reduce compression of the signal. Surely this benefit would be of no consequence if the signal were to pass through stages before or after this one that were restricted to the standard dynamic range of opamps on a +/-15V supply. OR, is it possible to restore the dynamic range after it has been lost? It seems that any system design would involve stages, any buffer stage in eq/filter sections for example, which could not be built around such an opamp. Would there be any point in the extra headroom if the signal had to stay within the limits of other stages in the system?
I am slightly confused by the whole concept of signals being compressed by stages with limited dynamic range. I thought that signals amplified beyond the available output swing simply distort?
Maybe I'm missing the point... :roll:

 

[Kev]

take a look at the JLM Hybrid or even the Jaycar Headphone amp kit ... or even one of the Neve trasistor assisted opamp drivers.

What you say about headroom and the susequent stages
and
restoring lost headroom is well ... ?

yep
when it's clipped .. it's clipped.
There is an arguement that there is some effect just before it clips OR the effects of lack of SLEW in iether voltage OR current.

As with all these ideas it may be more important to look at the rpoblem that is being solved rather than the circuit being used to solve it.

IN other words
What is the original problem ?
that warrant this circuit over a simple opamp with good power rails.

side note
why do some people still use small power amps to drive headphones ?
surely it has nothing to do with the 40W to 100W

second side note
has anyone studied those Gain Structure diagrams that Yamaha like to publish ?
I actually think they tend to say much more about the equipment than the spec sheet does.

 

[jeth]

Thanks for the reply Kev...

It stands to reason that clipping distortion cannot be removed by further stages. The main thing that confused me was the talk of compression in stages lacking dynamic range. Does it really exist?

 

[Kev]

This is where people have to make clear exactly what they are talking about

opamps do sound different and it can be hard to compare when the tests are varied and people's adgenders are different

I feel that interfacing between stages and equipment is where most of these problems surface.

The main thing that confused me was the talk of compression in stages lacking dynamic range. Does it really exist?

Can a simple opamp working within it's spec and in an adequate circuit configuration cause a loss of dynamic range in a real and typical signal ....
...
ie not just a special case test situation.
???

then there is the second question
Can/Does it send the signal to the second stage or piece of equipment and still retain the dynamic range ?

Replaying a Madona CD or recording an orchestra at 100 feet are completely different problems.

 

[Kev]

What might set this one apart from many of the the other circuits could be the ability to run the very high power rails
+/- 30 volt or more

as I said

what is the original problem being solved by the increase in rail and or the increase in current capability

I like what I see
... it's just that sometimes the cure can cause new problems

 

[Kit]

apologies if it's nothing new

No need to apologies.
This is a variation on the famous "current dumping amp" patented by ARC way back.
Its a neat topology.

Edit: I spoke to soon. This is a little different, i didnt see that the collectors were tied to the output.

 

[bcarso]

One of the drawbacks to the first design posted is evident from the comments they make about setting output current. You have no direct temp compensation on that output current and could easily get into thermal runaway. As well, if you were to try to make these as a production item, you have a very broad spec on opamp quiescent current that you must accommodate. Fine for onesey-twosey DIY, where you have all day to play and set resistor values, but hell on wheels for production where batch-to-batch may vary by a factor of two or more.

True, usually it will be more consistent than that. But if it's not, it's your problem, not the opamp manufacturer's.