diyAB Amp The "Honey Badger" build thread

outtek · 2017-05-15 4:48 pm

Hi to all, just a small question regarding the zener diode in the amp, at the moment of my purchase for parts the 1n4744A was not available so I choose another type, BZX85C15-TAP, I have read a bit today and because of the different current that these have it might not work ok in some circuits, is this the case for the HB? The was in the BOM is now available, should I remove it and order the 4744A and resolder?
Thanks,
Florin

mbrennwa · 2017-05-15 6:38 pm

outtek said:
Hi to all, just a small question regarding the zener diode in the amp, at the moment of my purchase for parts the 1n4744A was not available so I choose another type, BZX85C15-TAP, I have read a bit today and because of the different current that these have it might not work ok in some circuits, is this the case for the HB? The was in the BOM is now available, should I remove it and order the 4744A and resolder?
Thanks,
Florin

Just omit the Zener. It is only useful at clipping. And I think the best choice is BAV21, not 1N4744A.

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outtek · 2017-05-15 7:42 pm

Hi, if I omit that what will be used for the cascode reference? According to the build guide this design provides the best solution. Maybe I wasn't very precise about what diode I was talking, it's the one one in Cascode / Current Mirror Q3 and Q4. Thanks

mbrennwa · 2017-05-16 7:05 am

outtek said:
Hi, if I omit that what will be used for the cascode reference? According to the build guide this design provides the best solution. Maybe I wasn't very precise about what diode I was talking, it's the one one in Cascode / Current Mirror Q3 and Q4. Thanks

Oooops, sorry, my bad. I thought it was the Baker clamp.

I guess the voltage reference should work with most Zeners as long the voltage is right.

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audiofan · 2017-05-19 4:12 pm

beware of zeners .... some have weird bumps aroud the knee region ... in a low current application it may have a strange effect .. .. in these application all zeners should be check on an oscilloscope with a X-Y display .... to see V/I curves ...

RCruz · 2017-05-19 7:40 pm

audiofan said:
beware of zeners .... some have weird bumps aroud the knee region ... in a low current application it may have a strange effect .. .. in these application all zeners should be check on an oscilloscope with a X-Y display .... to see V/I curves ...

Can you post an example please ?

audiofan · 2017-05-20 11:52 am

RCruz said:
Can you post an example please ?

sorry I cannot post example ... about 8 years ago I build a pair of Leach ... and I had many types of 20 V zener ... I did basic curve tracer with a low voltage power transformer, a scope in X-Y display and a resistor ... but I did not make any pictures ...

AndrewT · 2017-05-20 12:22 pm

Hoe did you wire up the test circuit?
How did you wire in the scope to read the Curve?

audiofan · 2017-05-20 1:29 pm

Here is the basic circuit ... only have to select transformer .. resistor & scope scale....

audiofan · 2017-05-20 1:33 pm

I forgot ...beware of display inversion ...may have to use polarity inversionon chanel 2 !

I did use this setup for the last time many years ago .. memory fades sometimes ...

Kay Pirinha · 2017-05-20 6:37 pm

Where's the bump you've been speaking of?

Best regards!

audiofan · 2017-05-20 7:34 pm

Kay Pirinha said:
Where's the bump you've been speaking of?

Best regards!

A zener is suppose to have a sharp bend in the curve at nominal voltage ... I remember having test several zener and at the bend there was a small curve in ''' S '' shape ...

AndrewT · 2017-05-21 7:04 am

there is always a curve.
It start with a steep slope. Then curves around to be come a much flatter slope.
The flatter slope can be used to determine the dynamic impedance.
The higher the current the lower (flatter slope) the impedance.

beware of zeners .... some have weird bumps aroud the knee region ... in a low current application it may have a strange effect

where is the evidence for these statements?

audiofan · 2017-05-21 12:29 pm

AndrewT said:
there is always a curve.
It start with a steep slope. Then curves around to be come a much flatter slope.
The flatter slope can be used to determine the dynamic impedance.
The higher the current the lower (flatter slope) the impedance.where is the evidence for these statements?

There is no proof ... only my words ... at the time I did not take pictures .. but I did see .. I made a sketch .. see it below ... the difference betwen 2 ... 20 Volts zener from different company ..

AndrewT · 2017-05-21 12:58 pm

I have not curve traced. I have measured quite a few/not many.
I have not seen Zener behaviour as shown on the right.
Has any Member seen similar for some/any Zeners?

anatech · 2017-05-21 2:43 pm

Hi Andrew,
I've used curve tracers to characterise zener diodes. Unless you dynamically sweep the component, you would never see the anomaly. I haven't noticed the kink in the curve, but that doesn't mean that the kink doesn't exist. I have seen some really soft knees and running a zener at low current (for the voltage). This is undesirable for obvious reasons.

I try to reach a happy spot where power dissipation is minimised, but high enough so that I'm away from the knee. It's a balancing act with high voltage regulators.

-Chris

mbrennwa · 2017-05-21 5:15 pm

audiofan said:
There is no proof ... only my words ... at the time I did not take pictures .. but I did see .. I made a sketch .. see it below ... the difference betwen 2 ... 20 Volts zener from different company ..

Is your "bump" related to ringing / resonance / overshoot with the transformer in your test setup? A bit like rectifier diodes switching on/off the current, which triggers oscillation in the transformer.

audiofan · 2017-05-21 9:35 pm

Basic curve tracer ... at mains frequency ... same setup ... only different zener from different company ... and not only a specific component .. all component from the same lot tested the same way ! ... ??

stuartmp · 2017-05-23 6:09 am

Hi All. I am a little confused when it comes to the inductor for this board. The schematic and build guild calls for a 1.5uH inductor made from 18 Gauge wire 12.5-15mm Diameter 14-16 Turns.

The thing is I made this then tested / measured it inductance using my oscilloscope.

I followed a YouTube guide from a reputable guy that shows how to measures inductance. I tested out his method on a small inductor that I had at home. The testing method and my calculations yielded the correct resulting inductance.

I am however not able to get anywhere close to 1.5uH with the numbers shown in the guide for the inductor.

I was about to get a inductance of 1.5uh but with only about 4-5 turns

The Youtube guide that I followed was
https://www.youtube.com/watch?v=74fz9iwZ_sM

L = 1 / ((2 x Pi x F ) x C)

F = 4.115Mhz
C = 1nF

Any help or advice on this would be appreciated.

Attached are some photos.

AndrewT · 2017-05-23 9:16 am

That coil looks like ~5.7Turns.
Then add on the loop inductance of the widely separated connections.

1.5uH wound around an AA battery is about 10Turns.

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