Discrete sounds better than integrated? a possible reason

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ruffrecords

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JohnRoberts said:
Open loop gain that tracks with closed loop gain is a well explored characteristic of the "cohen" topology (also used inside modern mic preamp ICs).
You gotta spill the beans on which modern mic preamp ICs use this technology.
I mentioned this in passing in my 1980 console performance article (when describing Transamp used in a summing amp).

JR
Yes, the Transamp I think was the first 'op amp' to employ this technique but I was not aware it was now embedded in ICs.

Cheers

Ian
 

JohnRoberts

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ruffrecords said:
You gotta spill the beans on which modern mic preamp ICs use this technology.Yes, the Transamp I think was the first 'op amp' to employ this technique but I was not aware it was now embedded in ICs.

Cheers

Ian
The transamp is not an op amp but hybrid combination of discreet bipolar transistors and IIRC a TL072 IC op amp, all inside a potted module.

I don't feel like making a list but pretty much any high performance IC mic preamp uses that topology (Cohen), for the obvious benefit.

Not a secret...

JR 
 

clintrubber

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ruffrecords said:
Here is a link to the three transistor Neve input stage.

...

Here is a link to the Helios three transistor mic pre scehmatic:

...

Cheers

Ian

Hi Ian,

Thanks for those links, hadn't realized before there's indeed a pretty elegant 'tandem action' going on in those topologies.

If this is indeed the main reason for things 'sounding better' then that'd be a nice (re-)discovery, begging to implement it 'for integrated' as well (saw the Cohen example mentioned, need to dig it up & have a look again).

How do DOAs fit in here? They'd be suffering from the non-tracking open loop gain consequences as well, although I expect DOAs don't reach the same open loop gain levels as integrated opamps do.

Bye
 

abbey road d enfer

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clintrubber said:
If this is indeed the main reason for things 'sounding better' then that'd be a nice (re-)discovery, begging to implement it 'for integrated' as well (saw the Cohen example mentioned, need to dig it up & have a look again).
This topology is in use since ages (1980's) in most british mixers (Soundcraft, Amek...) and many others, where it makes a difference, i.e. in stages with a high noise gain, that is, typically, mic preamps and summing amps. Do they "sound better"?

How do DOAs fit in here? They'd be suffering from the non-tracking open loop gain consequences as well, although I expect DOAs don't reach the same open loop gain levels as integrated opamps do.
DOA's have their own raison d'être, but in this respect tend to perform less well than recent opamps with GHz response. They can be used in a transamp topology, though.
 

abbey road d enfer

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Not exactly the same, but offering the same advantages, Current Feedback Amplifiers.
Not easily applicable for audio, since they require low Z design (<100r).
 

volker

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abbey road d enfer said:
Not exactly the same, but offering the same advantages, Current Feedback Amplifiers.
Not easily applicable for audio, since they require low Z design (<100r).
Not necessarily, look at the LT1364 for example, page 11. The negative input is buffered high-impedance as well. I've designed a DOA using this same topology already couple years ago, but alas where is all the time to build stuff...
 

abbey road d enfer

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volker said:
Not necessarily, look at the LT1364 for example, page 11. The negative input is buffered high-impedance as well. I've designed a DOA using this same topology already couple years ago, but alas where is all the time to build stuff...
Well, teh big advantage of CFA's is the possibility to achieve very low noise and high gain margin. It seems this one does not provide the utmost in terms of noise. 9nV/sqrtHz is 6dB more than a 5532.
 

ruffrecords

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clintrubber said:
Hi Ian,

Thanks for those links, hadn't realized before there's indeed a pretty elegant 'tandem action' going on in those topologies.

If this is indeed the main reason for things 'sounding better' then that'd be a nice (re-)discovery, begging to implement it 'for integrated' as well (saw the Cohen example mentioned, need to dig it up & have a look again).
I am suggesting it may be an important factor compared to regular op amps with dominant poles around a few Hz. The other factor is that all the three transistor versions were 100% class A whereas all op amps have class B output stages.

Other discreet designs like the Calrec B series amps used more transistors and had a push pull output stage but it was still run in class A. (schematic attached)

Cheers

Ian
 

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MaxDM

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I just want to say that I found this thread very interesting.

I have never had a great love for all boards that use the typical 80's op amps, although, for dance music, where the bottom has to be tight but the top is often not great, they did serve a purpose, IMO

I remember the first time I heard a 909 open high hat on a good hi fi, and how ugly it sounded
 
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MaxDM

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The opamps are not responsible for the ugly sound. It's the lousy converters.
Yes, but the op amps in 80’s style budget mixers covered that ugliness with distortion, while keeping the bottom end reasonably tight, all things considered

The hi fi showed the warts and all of the actual 909 OH sound
 

JohnRoberts

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Above my paygrade and and somewhat off topic, but nonlinearity simulations look interesting:

I didn't read (understand) every word but they don't appear to address overload and recovery time. My sense of the solid state vacuum tube emulators it was not about normal operation, but how they behave during overload and recovery from overload.

JR
 

Matt Syson

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You guys are ignoring the incestuous* nature of the audio industry, from probably mid '1970's onwards where engineers would do the 'hokey cokey' every few years and mix or merge with others.
I spent a while at Audix (not the American upstarts with microphones) and my boss and several others had 'defected' from Neve and every now and again some others would leave to join Neve.

Only by moving to Yorkshire did I break free from the Essex/Cambridgeshire/Hertfordshire 'effect' and there other circuit concepts became apparent. LF distortion cancelling on output transformers being a notable one.
Going back to Ian's original statements and my other thoughts which have been mentioned by others, it is how a given circuit misbehaves when overdriven which causes some of the perceived 'goodness' of any design. Preventing amplifiers from crashing into the power rails to give flat topped or even 'folding back' nastiness often seen with high feedback 'op amps' and whether they recover symmetrically or other effects for the more typical class A discrete designs.
the SSM2015 as was almost mentioned earlier had an interesting 'quirk' that if hit with a significant peak oversignal it would 'hang' at it's positive rail for a moment but also oscillate wildly for that moment before it would recover. This was in the 'datasheet suggested configuration' but I note that some people diverted from that simplicity which may not have then suffered this issue. The SSM2016 did not have this quirk.

* Incestuous that has nothing to do with removing clothes AT ALL!

Incidentally some of the 'differences or precieved 'niceness may well be down to the interaction of circuit blocks in more complicated systems where 'crosstalk' of it's own signal path either in phase or out of phase can influence the 'sound'. Yet another influence will be differences in 'loading' of particularly output stages and how they handle long cables, other transformers etc.
If you are putting an unbuffered VU meter across an output you can 'just about' get away with it if the output impedance is 30 Ohms or less, but if it is above that then it will distort, about 0.3% at 0dBu (600 Ohm output impedance) if I remember correctly.
 

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