Leach type input for ne5534

donovas

Member
2014-06-22 6:45 am
Recently ive been messing with discrete inputs for ne5534 as per circiut below. It works well, sounds good but i wanna get it to work with a leach type input seen on the other pic.

Would it be as simple as using the collectors of q1 and q3 to the opamp's pins?

Please let me know, thank you.
 

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Interestingly I found conflicting equivalent schematics for the 5534, some with PNP inputs and some with NPN inputs. Tying 2 & 3 to -15V only works for the NPN input schematics, I wonder if there are multiple versions or if your experiments simply invalidate the PNP schematic as nonsense (it has several differences, not just in the input transistors).

Checkout the schematics in these references:

NE5534 Integrated Circuits under Repository-circuits -54440- : Next.gr

http://www.ti.com/lit/ds/slos070d/slos070d.pdf
 
Here's the most simple bootstrapped folded cascode topology I could come up with. This is just meant for illustrative purposes, it might work absolutely terribly for all I know. I haven't checked the currents or anything.
attachment.php


EDIT: OK, now somewhat sane. At least it would probably work like this.
 

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donovas

Member
2014-06-22 6:45 am
Here's the most simple bootstrapped folded cascode topology I could come up with. This is just meant for illustrative purposes, it might work absolutely terribly for all I know. I haven't checked the currents or anything.
822989d1583564837-leach-type-input-ne5534-folded-cascode-1-topology-png


EDIT: OK, now somewhat sane. At least it would probably work like this.

How does it simulate?

I would not mind building this

And how about a singleton ver?
 
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Latest versions. I haven't actually done much in term of simulating, just op points for now. Looks like you want a floating reference current source for things to remain largely supply-independent.

Can't say I'm too happy with the folded cascode yet, aside from the parts count I also don't have much headroom for the whole common-mode bootstrapping thing (the one advantage of this scheme becomes a disadvantage here), and for that to work well I think I'd also have to replace the resistors down there by current sources again (more parts).

I think a regular cascode it is then. I had a singleton cascode in a version of the 3-transistor preamp, so the normal cascode would be sort of a cross between that and the circuit above.

Do you have any particular application and supply voltage range in mind?
 

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PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com

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PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
...PNP is in theory lower noise than NPN, yet few opamps competed with the 5534A for noise for many decades.

The theory is not unbeatable even for "ideal" parts.

The PNPs in older IC technology were crap. A parasite side-bay of a NPN tub. Hans' book gives some ugly details, though he was not too much concerned with hiss.

Are you saying that with 2020 processing, somebody is selling PNP-input '5532s? That would be odd.
 
The NE5534 schematic with PNP input transistors makes no sense at all. Even if you would want to use PNP emitter followers as the input stage, which would be a bad idea if you want low voltage noise, tying together their collectors and connecting them to a current source would not make any sense. Besides, like PRR wrote, 1970's lateral PNPs are indeed quite poor in all respects.