diode bridge rectifier as a clipper?

DrNomis · Post by **DrNomis** » 18 Nov 2010, 03:26

Okay,I have figured out a way around this,I happen to have some Ge transistors,the B-E junction of a transistor is basically a diode,so I will implement the circuit using the B-E junction of Ge transistors,the characteristics should be...C.E.F.G.W. (Close Enough For Government Work)....

mictester · Post by **mictester** » 18 Nov 2010, 06:26

DrNomis wrote:C.E.F.G.W. (Close Enough For Government Work)....

Around here we say "Tuned enough for Jazz!"

DrNomis · Post by **DrNomis** » 18 Nov 2010, 06:54

mictester wrote:
DrNomis wrote:C.E.F.G.W. (Close Enough For Government Work)....
Around here we say "Tuned enough for Jazz!"

When I was doing my Basic Electronics Certificate at Uni,we had a guy called John Doyle as one of our lecturers,he was like an ex-army seargeant,funny one minute,cranky the next,he wanted us to do our assignments...in triplicate,anyway,one of his idiosyncrasies was that he would write an electronics equation on the whiteboard,work the equation,then when he'd gotten the answer,he would write C.E.F.G.W. below the answer...

One day,he wrote on the whiteboard,realized that he'd made a mistake,went to wipe it off,then found he'd used a permanent marker by mistake....

HydrozeenElectronics · Post by **HydrozeenElectronics** » 18 Nov 2010, 08:34

Sounds like a solid plan to me.

Thnanks

DrNomis wrote:Okay,I have figured out a way around this,I happen to have some Ge transistors,the B-E junction of a transistor is basically a diode,so I will implement the circuit using the B-E junction of Ge transistors,the characteristics should be...C.E.F.G.W. (Close Enough For Government Work)....

DrNomis · Post by **DrNomis** » 18 Nov 2010, 09:58

Okay,finaly we have a screenshot for a bridge rectifier clipper implemented with Germanium transistors connected as Ge diodes....

DrNomis · Post by **DrNomis** » 18 Nov 2010, 10:24

bajaman wrote:I wonder what a similar configuration of LEDs would sound like
bajaman

Probably a bit louder than the Si diode bridge rectifier version,with maybe a bit softer clipping,check out my screenshots that I posted,I did one with 5 red 5mm leds,i'm not sure if my screenshots were valid results though,but I posted them anyway....

DrNomis · Post by **DrNomis** » 19 Nov 2010, 06:42

So,if you have a handful of unusably low gain Ge transistors,or some Ge transistors lying around,and you're thinking of what to do with them,why not try using them as diodes in clipping circuits.....

DrNomis · Post by **DrNomis** » 22 Nov 2010, 09:18

if anyone is interested in seeing the effect that each type of bridge rectifier has on waveform clipping,here's some pics of what the clipping actually looks like,test signal was a sinewave at about 1Khz....

HydrozeenElectronics · Post by **HydrozeenElectronics** » 23 Nov 2010, 09:29

Very cool, Thanks you can totally see what a difference there is. The GE's look really smooth. and from the sounds I have been getting that is right on the money.

Thanks, I need to try an LED one next only problem is getting enough voltage to get them to clip as hard as the GE's with out resorting to 18Volts but I'm thinking there might be some benefit of going to 18Volts anyway.

DrNomis wrote:if anyone is interested in seeing the effect that each type of bridge rectifier has on waveform clipping,here's some pics of what the clipping actually looks like,test signal was a sinewave at about 1Khz....

DrNomis · Post by **DrNomis** » 23 Nov 2010, 10:09

HydrozeenElectronics wrote:Very cool, Thanks you can totally see what a difference there is. The GE's look really smooth. and from the sounds I have been getting that is right on the money.

Thanks, I need to try an LED one next only problem is getting enough voltage to get them to clip as hard as the GE's with out resorting to 18Volts but I'm thinking there might be some benefit of going to 18Volts anyway.

DrNomis wrote:if anyone is interested in seeing the effect that each type of bridge rectifier has on waveform clipping,here's some pics of what the clipping actually looks like,test signal was a sinewave at about 1Khz....

I have been able to get a back-to-back Led clipper to give enough clipping in a 9V circuit,they were placed in the negative feedback network of an Op-Amp,you could try that arrangement for a bridge-rectifier implemented with leds,actually,I might even give that a try and see what happens....

Will post some more screenshots here after I try it....

RnFR · Post by **RnFR** » 23 Nov 2010, 14:02

thanks for posting the shots. they are always interesting to check out.

DrNomis · Post by **DrNomis** » 24 Nov 2010, 02:16

RnFR wrote:thanks for posting the shots. they are always interesting to check out.

You're welcome,I had alot of fun building the three bridge rectifier circuits,taking the pics and uploading them here,it was a bit of a learning experience for me,and I do hope that my fellow stompboxers get something out of it too....

At the very least,it will help clear up any misunderstandings....

HydrozeenElectronics · Post by **HydrozeenElectronics** » 26 Nov 2010, 05:16

DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Greg · Post by **Greg** » 26 Nov 2010, 06:09

DrNomis wrote:if anyone is interested in seeing the effect that each type of bridge rectifier has on waveform clipping,here's some pics of what the clipping actually looks like,test signal was a sinewave at about 1Khz....

What level signal did you use, and was it the same for all tests ?

DrNomis · Post by **DrNomis** » 26 Nov 2010, 06:46

HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Can do,I'm at work at the moment,but I'll get that sorted out this evening when I get home,I'm curious about it too...

Greg_G,I kept the frequency constant at about 1kHz,but I had to vary the signal level quite a bit just to get a clear enough example of what the clipping looked like in each case,my Hameg Function Generator is capable of a maximum signal output level of 20 Volts Peak-To-Peak into a load of 50 Ohms....

I didn't actually keep a record of the signal level going into each circuit,my Hameg Function Generator has two -20dB attenuator buttons for a total possible attenuation of -40dB,I had to switch out both attenuators just to get enough signal level to drive the Led Bridge-Rectifier circuit until it just started to clip,that's why the clipping looks like it does,I had the variable output level control on my Hameg FG set to maximum....

Greg · Post by **Greg** » 26 Nov 2010, 06:50

DrNomis wrote:
HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Can do,I'm at work at the moment,but I'll get that sorted out this evening when I get home,I'm curious about it too...

Greg_G,I kept the frequency constant at about 1kHz,but I had to vary the signal level quite a bit just to get a clear enough example of what the clipping looked like in each case,my Hameg Function Generator is capable of a maximum signal output level of 20 Volts Peak-To-Peak into a load of 50 Ohms....

The Led bridge-rectifier circuit needed quite alot of signal level just to get it looking how it does in the screenshot...

That's what I suspected.. so people need to realise that their results will vary from these for a given circuit and output.

DrNomis · Post by **DrNomis** » 26 Nov 2010, 07:02

Greg_G wrote:
DrNomis wrote:
HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Can do,I'm at work at the moment,but I'll get that sorted out this evening when I get home,I'm curious about it too...

Greg_G,I kept the frequency constant at about 1kHz,but I had to vary the signal level quite a bit just to get a clear enough example of what the clipping looked like in each case,my Hameg Function Generator is capable of a maximum signal output level of 20 Volts Peak-To-Peak into a load of 50 Ohms....

The Led bridge-rectifier circuit needed quite alot of signal level just to get it looking how it does in the screenshot...
That's what I suspected.. so people need to realise that their results will vary from these for a given circuit and output.

That's true,and I think the reason for that is probably due to the forward voltage drop across the Leds,plus also the softness of the knee in the Led's transfer curve...

Leds typically have a voltage drop of about 1.5V,but it does vary depending on what colour the Led is,Blue Leds have a voltage drop of about 3.4 Volts,I think,I may be wrong though...

Greg · Post by **Greg** » 26 Nov 2010, 07:49

DrNomis wrote:
Greg_G wrote:
DrNomis wrote:
HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Can do,I'm at work at the moment,but I'll get that sorted out this evening when I get home,I'm curious about it too...

Greg_G,I kept the frequency constant at about 1kHz,but I had to vary the signal level quite a bit just to get a clear enough example of what the clipping looked like in each case,my Hameg Function Generator is capable of a maximum signal output level of 20 Volts Peak-To-Peak into a load of 50 Ohms....

The Led bridge-rectifier circuit needed quite alot of signal level just to get it looking how it does in the screenshot...
That's what I suspected.. so people need to realise that their results will vary from these for a given circuit and output.

That's true,and I think the reason for that is probably due to the forward voltage drop across the Leds,plus also the softness of the knee in the Led's transfer curve...

Leds typically have a voltage drop of about 1.5V,but it does vary depending on what colour the Led is,Blue Leds have a voltage drop of about 3.4 Volts,I think,I may be wrong though...

Yes, proximity to clip is the common term I think (Thanks Mark Hammer).

Vf of LEDs can vary even if the same colour.. depending on manufacturer and spec.

DrNomis · Post by **DrNomis** » 26 Nov 2010, 08:09

Greg_G wrote:
DrNomis wrote:
Greg_G wrote:
DrNomis wrote:
HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

Can do,I'm at work at the moment,but I'll get that sorted out this evening when I get home,I'm curious about it too...

Greg_G,I kept the frequency constant at about 1kHz,but I had to vary the signal level quite a bit just to get a clear enough example of what the clipping looked like in each case,my Hameg Function Generator is capable of a maximum signal output level of 20 Volts Peak-To-Peak into a load of 50 Ohms....

The Led bridge-rectifier circuit needed quite alot of signal level just to get it looking how it does in the screenshot...
That's what I suspected.. so people need to realise that their results will vary from these for a given circuit and output.

That's true,and I think the reason for that is probably due to the forward voltage drop across the Leds,plus also the softness of the knee in the Led's transfer curve...

Leds typically have a voltage drop of about 1.5V,but it does vary depending on what colour the Led is,Blue Leds have a voltage drop of about 3.4 Volts,I think,I may be wrong though...
Yes, proximity to clip is the common term I think (Thanks Mark Hammer).

Vf of LEDs can vary even if the same colour.. depending on manufacturer and spec.

The Vf of Leds are usually within a certain tolerance range,I believe that the slight differences are probably caused by the impurity doping which turns the semiconductor substrate material into a diode,I think that the matching of the Vf for back-to-back diode clippers,isn't really critical,one area where the matching is critical is in circuits which use Transistors in a long-tail-pair,or Differential Amplifier configurations,I built a couple of VCO's (Voltage Controlled Oscillators),and they required a pair of matched transistors,I happened to have a few LM394CH ICs lying around,they are supermatched Transistor pairs(BE Vf matched very closely,probably to within .002Volts),so I used one for each VCO circuit,they worked fine....

That's just an example of where the matching of Vf is critical,but if you're using two back-to-back diodes as clippers,it's not that critical at all and maybe beneficial to have some mismatching,it has an affect on clipping symmetry,with a slight asymmetry causing even harmonics similar to Valves....

I wish I had some kind of spectrum/distortion analyzing equipment at home,it would be interesting to do a plot of the distortion harmonics generated...

I do have construction details for a DIY THD Analyzer somewhere at home,could be a good project to tackle soon...

DrNomis · Post by **DrNomis** » 26 Nov 2010, 10:03

HydrozeenElectronics wrote:DrNomis,

could you do one more test? I'm interested in seeing what three GE diodes in series pared up shunted to ground would look like vs the rectifier set up. In the rectifier the signal travels through three diodes but it might be changing the signal a little. I would like to see the difference.

thanks

I'm assuming this is the circuit configuration you mean,I don't have any Ge diodes so I'll use some Ge Transistors instead,results should be the same...