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Old 17th August 2014, 06:37 AM   #81
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by owdeo View Post
I connected a CCS consisting of an LED and a BC547 to the +ve rail on each opamp output. The difference in sound shocked me, as I wasn't expecting it to be so huge.
So quite an improvement... obviously audible.

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Originally Posted by owdeo View Post
I'd like to try biasing the LM49710 but don't have the means to measure distortion at present, so would not know which rail will work best. If anyone has tried this and worked it out, please let me know!
So trust your ears and try both configurations and report back with which you feel is the best audibly. That way you are not taking anything on trust but determining the result yourself.
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Old 17th August 2014, 09:17 AM   #82
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by KSTR View Post
5534 ops isn't quasi. It's a single common-emitter NPN (on pin 5). Its collector is both the output (via a diode and limiting R) and level-shifted with a vbe mult which feeds an NPN EF to allow sourcing current from the output higher than the standing current, again with limiting R plus associated transistor.

With the 5534 you don't need an external current source, just connect a resistor from output to pin 5 to increase standing current. Pretty close to a current source because the voltage is (almost) constant. Tektronix did that trick alle the time.
The output from the middle stage (ltp with mirror load) drives a Q. That Q drives an NPN output device attached to it's collector. The same Q drives another NPN output device from it's emitter.

These two output devices are connected by a the pair of output resistors and a diode, (as you have stated above).
That looks like a quasi using a pair of NPN output devices in push pull.

Could you explain your viewpoint in more detail?

It would be easier if the Qs were labeled.
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Old 17th August 2014, 11:19 AM   #83
KSTR is offline KSTR  Germany
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It's maybe semantics but I've always seen a Quasi-Complementary Output as a EF2 on top and a CFP on bottom biased 3 Vbe's apart (one for the CFP PNP and two for the EF2), in order to avoid a power PNP and use a small signal PNP instead (which is the one you wanted to avoid).

I don't see any of this in the 5534, actually there is no PNP involved in the output stage (apart from auxiliary stuff like clamps and protection). Rather there's an EF2 on the bottom (thus common emitter stage) and that "helper circuit" on top of it, but it's tied to the ouput side of the EF.
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Last edited by KSTR; 17th August 2014 at 11:24 AM.
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Old 17th August 2014, 11:23 AM   #84
AndrewT is offline AndrewT  Scotland
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Is the Output (sink) allowing operation as a single ended amplifier using the Output (source) as the single active device?

To me it looks like the Driver is using the upper and lower devices in push pull, but I am doing no better than guessing.
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Old 17th August 2014, 11:26 AM   #85
AndrewT is offline AndrewT  Scotland
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Quote:
Quasi-Complementary Output as a EF2 on top and a CFP on bottom
agreed. two complementary drivers and a pair of push pull NPN outputs.
Here we have only one driver but the same two NPN outputs.
what do we call it?
How does it operate?
Is there some kind of sliding bias?
or is it actually push pull?
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Old 17th August 2014, 11:38 AM   #86
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by AndrewT View Post
Is the Output (sink) allowing operation as a single ended amplifier using the Output (source) as the single active device?
Yes, that's when the diode comes into the picture. Assume a high output current to be sourced. Drive to the sinking NPN is reduced until it's collector (plus shifter on top) has raised enough to turn on the sourcing NPN.
Hence, when you bias it to class-A neg.rail there is one more transistor (the EF) in the chain as compared to pos.rail.

Quote:
To me it looks like the Driver is using the upper and lower devices in push pull, but I am doing no better than guessing.
The attachment of the driver collector seems confusing but I think (guessing here, too) the base of the source NPN is mainly moved by the collector of the sink NPN, not its driver (whose current is much lower). Sim is needed to check that... but the 5534 has been disassembled many times, I think there's a paragraph on it in D.Self's "Small Signal Design" (don't have it handy right now).
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Old 17th August 2014, 11:54 AM   #87
AndrewT is offline AndrewT  Scotland
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The 5534 has access to the three pins, 1, 5 & 8
That makes it almost unique in opamps.
There are many "tweaks" described that make the opamp do the next to impossible (for other opamps).
The 5532 cannot be tweaked like this.

Now to D.Self's tweak: pulling pin6 to +ve.
Pulling pin5 to +ve effectively disables the Vbe and disables the upper NPN.
That leaves the lower NPN as the sole output device. It is driven by the Driver (in your pic).
Can you describe exactly what happens here?

It would explain why the 5534 breaks the usual "rule" for quasi NPN output stages needing a sink to -ve.
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Old 17th August 2014, 11:11 PM   #88
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Still no answer what value that resistor from pin 6 to pin 5 should be.
I thought i knew every trick that can be done with the NE5534.
I use it since it came out in the 70th.
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Old 18th August 2014, 01:26 AM   #89
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Mooly View Post
So quite an improvement... obviously audible.



So trust your ears and try both configurations and report back with which you feel is the best audibly. That way you are not taking anything on trust but determining the result yourself.
It would be nice to know the before and after THD results and link it to perception thresholds.

THx-RNMarsh
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Old 18th August 2014, 01:37 AM   #90
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D. Self has that measurement in his book about analog crossovers.
It really improves the treble to a point where he got the residual of the Audio Precission.
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