zener-phobe

[PhaseLockLoopy]

Hi guys

I just started a new discrete transisitor Pre-amplifier inspired by a Mark levinson

Great until i finished regulating for 15volt rails

Got the thing slung together and I have been chasing my tail on noise ever since
only to now find it's coming from Zeners............. ooooh yes what fun

Typically my regulator circuits follow the pic -- (see pic)

Interesting is the spectral density of the noise
If i get my soldering iron close to them the density and type of noise changes - suggesting thermal fluctuations linked to electron avalanche effect as per Boltzmans constant
The problem is I have swapped Zener after Zener after Zener with no improvment

Has anyone else had a tearing of hair moment with Zeners


i love noise -- dont you ? ....ooooooooooh joy

[Samuel Groner]

That design must have super poor PSRR if that regulator ain't low enough noise... Anyway, the zener should be running at > 1 mA for reasonably low noise--at low currents multi-state noise (random changes between two potentials, similar to popcorn noise) appears and also the white noise content increases. Too lazy to calculate the zener current, but intuition suggests that it might be pretty low at low output currents. I'd go for a topology where zener current is well defined and independent of output current.

Further enhancements include the use of lower voltage diodes (3x 5.1 V will give *much* lower noise) and increased filtering.

Samuel

[Tekko]

Don't u need resistors to feed the 2955 and 3055 bases from the unput supply in order for the thing to work ?

[AndrewT]

Hi,
are Q1 & Q4 wired correctly?
What is the purpose of R2 & R5?
What is the purpose of the two Vr?

[DF96]

All zeners are noisy, it is just that some are noisier than others. That is why they are used as noise sources. If you want low noise then bypass with a fat capacitor.

I don't understand your circuit. It seems to rely on the output transistors having large c-b leakage. Are there components missing or in the wrong place? Why have you inserted a noisy 'regulator' between big capacitors?

[CBS240]

Zeners, noisy? Hmmmm Yep, they are. This is why I don't use Zeners as voltage references in regulators where noise is an issue. I prefer to use a lower conductance low noise J-fet at Idss and cascode with another of higher Vgs at Idss of the lower conductance one. Then the constant current through a constant resistor, metal film of course, gives a constant voltage. Place a few nf cap across the resistor to diminish Johnson noise. Now you have a much better voltage reference.

[Rodeodave]

Once again I'd like to thank Christer for sharing his measurements: Some noise measurements for LEDs and zener diodes
He shares a summary of his findings in post #65: Some noise measurements for LEDs and zener diodes

[SY]

The answer is LM329.

[janneman]

Originally Posted by PhaseLockLoopy

Hi guys

I just started a new discrete transisitor Pre-amplifier inspired by a Mark levinson

Great until i finished regulating for 15volt rails

Got the thing slung together and I have been chasing my tail on noise ever since
only to now find it's coming from Zeners............. ooooh yes what fun

Typically my regulator circuits follow the pic -- (see pic)

Interesting is the spectral density of the noise
If i get my soldering iron close to them the density and type of noise changes - suggesting thermal fluctuations linked to electron avalanche effect as per Boltzmans constant
The problem is I have swapped Zener after Zener after Zener with no improvment

Has anyone else had a tearing of hair moment with Zeners


i love noise -- dont you ? ....ooooooooooh joy

I think you have a basic issue with this circuit. You need a resistor to feed current into the base of the pass transistor. Next you can use a regulation transistor to siphon off excess base current to make it regulate to the set output. I wonder if this works at all, unless you have a very leaky pass transistor? The zener noise is about 6 steps down on the issue list ;-)

jan didden

[cbdb]

Will this cct work? Q2 is trying to pull current out of the base of Q1 instead of feeding it into the base. EDIT: Sorry just read last post: What janneman says.