Zen clipping indicator

[Vix]

Hi

In most cases of ¡§normal¡¨ listening Zen¡¦s 20 watt or so are quite enough. But from time to time I get enthusiastic and turn the volume knob more than it is supposed to. Then, Zen just clips. To avoid this, I was thinking that adding a simple (Zen-ish) clipping indicator would provide a good warning¡K

I searched through the forum and eventually found nice and simple schematics, posted by ¡§Cobra2¡¨ in the Solid State forum. To make it easier, I am re-posting the link:

http://users.ece.gatech.edu/~mleach...aphics/clip.pdf

The problem with the schematic provided is that it is supposed to work with dual supply. How should I modify it so I can work for Zen amp? I believe that this is a trivial question for the more experienced, but I do need some help here¡K

BTW, I was experimenting with my Zen V3. Once I tried to modify it into a transconductance amp, then returned to the original¡K. (I decided to wait until Nelson published the F1 schematicsƒº).

Then, playing with the original V3, I disconnected the Aleph current source. Guess what: I liked the sound of constant current source! (I disconnected R19 and R25)
The sound was softer and more pleasant¡K
Any comment?

Vix

[wuffwaff]

Hi Vix,

the link doesn´t seem to work.

william

[Vix]

I downloaded the PDF document from that location. I'll try to attach it here:

[Frank Berry]

It seems to me that the only way you can accurately show that the amplifier is clipping is to compare the amplifier's output waveform to the input waveform. You could use an opamp to subtract the output signal from the input signal. Any difference in the shape of the audio signal could be used to drive an LED.
I've seen this method used in mixing consoles.

[wuffwaff]

Hi Vix,

I think this one compares output voltage with power supply voltage. This is not suitable for a ZEN / ALEPH or X amp cause here clipping will often occur when the current reaches it`s peak value.
In this case the voltage can be much lower than the supply voltage and the led won´t show anything.

William

[Vix]

Thanks a lot. Then, can someone suggest a suitable schematic?

Best regards

[wuffwaff]

Hi,

I did a search for clipping indicator and found something were the in and output are compared with an opamp. This way you can light a led if distortion becomes too big.
I think it was the bottom search result.

William

[Nelson Pass]

Originally posted by Frank Berry
It seems to me that the only way you can accurately show that the amplifier is clipping is to compare the amplifier's output waveform to the input waveform. You could use an opamp to subtract the output signal from the input signal. Any difference in the shape of the audio signal could be used to drive an LED.
I've seen this method used in mixing consoles.

Actually, you can simply look at the Gate voltage which is held
near virtual AC ground. When the amp clips, a lot more AC
voltage appears at the Gate, and you can amplify that and
give it to a comparator which drives a LED.

[Gaucho]

Then, playing with the original V3, I disconnected the Aleph current source. Guess what: I liked the sound of constant current source! (I disconnected R19 and R25)

I did this on my Aleph and I like the effect, however the bass control was slightly compromised. I increased the bias on the input and output stages and seemed to gain some of the bass control back. Before increasing the bias the sound was very sweet but just a little to soft and diffused for my taste.

[GRollins]

Another possibility that no one ever seems to mention as a mod is to use a bipolar supply to run the Zen.
Coupling caps? We don't need no stinking coupling caps. Your choice: Get rid of input or output caps.
Input caps are easy. Nail the Gate to ground and tidy up that pesky bias circuit in addition to getting rid of the cap. Or, conversely, you can drop the output caps and fiddle the input for 0V DC offset at the output. Just be prepared for some drift at the output. All in all, the first mod is easier and more reliable.
Now that you've got a Zen suffering from bipolar disorder, you can add your clipping indicator circuit. That way you can have your cake and eat it, too. Bon appetit!

Grey