zen4 adjustement

mermoz · 2nd December 2002, 03:33 PM

hi,

I want to build a Zen4, and in the adjustment chap. a Variac is used.
Where must this device be connected and what caracteristics do it have.

Of course I'm a newbee !

bye

Taco · 2nd December 2002, 03:49 PM

Instead of your powersupply you use a variac, so you can power things up very slowly. And measure if things are right. It's a saver way to test your work. A variac is a variable powersupply.

Nelson Pass · 2nd December 2002, 04:19 PM

I would like to offer up a more refined definition. A Variac (tm)
is a variable AC power source. You plug your amplifier's
power cord into it and turn up the AC from 0 volts to as high
as 20% over the voltage from the wall.

If you turn it up slowly, you can catch amplifier faults often
before the smoke and flames.

miguel2 · 2nd December 2002, 05:21 PM

Hi

Having seen smoke and flames

and not having a variac I came across the idea of using the zeners on the Zen PSU to increase the voltage up. So if you use a single zener the voltage in the regulated rail will be around 4-5 V. Puting another one will increase it a bit to around 14 V. Can this be done? Any change in the resistors of the PSU (or caps)?

vpharris · 2nd December 2002, 05:57 PM

Yes, but....

You are assuming that the regulator portion of the circuit is wired correctly and all its devices are working. Correct?

Also, by doing so, you are making the pass transistor in the regulator stage (Q5) do all the work of reducing the voltage. So if you amplifier is biased with 2 amps of current, the power dissipated across this transistor will be (50-5V) x 2A = 90 watts for your first case, 70W for your second. [I'm not checking your 5V number]. That's a lot! Probably too much for more than a couple of seconds. And.... if something else is wired incorrectly so that it draws more than 2 amps, you could really be in trouble.

So; nice idea. But it has some real limitations.

A variac or similar adjustable transformer is a great investment if you are interested in doing further DIY projects.

miguel2 · 2nd December 2002, 06:11 PM

Hi Vince,

I always check the PSU first and then the rest of the circuit.

The Zen amp has a resistor that controls the bias current, so we can adjust it so to have no problems on the pass transistor. Of course the current cannot be very high but maybe it is sufficient to see if everything looks well.

2nd December 2002, 03:33 PM	#1
mermoz diyAudio Member Join Date: Aug 2002 Location: France	zen4 adjustement hi, I want to build a Zen4, and in the adjustment chap. a Variac is used. Where must this device be connected and what caracteristics do it have. Of course I'm a newbee ! bye

2nd December 2002, 05:57 PM	#5
vpharris diyAudio Member Join Date: Dec 2001 Location: Philadelphia	Yes, but.... You are assuming that the regulator portion of the circuit is wired correctly and all its devices are working. Correct? Also, by doing so, you are making the pass transistor in the regulator stage (Q5) do all the work of reducing the voltage. So if you amplifier is biased with 2 amps of current, the power dissipated across this transistor will be (50-5V) x 2A = 90 watts for your first case, 70W for your second. [I'm not checking your 5V number]. That's a lot! Probably too much for more than a couple of seconds. And.... if something else is wired incorrectly so that it draws more than 2 amps, you could really be in trouble. So; nice idea. But it has some real limitations. A variac or similar adjustable transformer is a great investment if you are interested in doing further DIY projects. __________________ Vince Harris

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2nd December 2002, 03:49 PM	#2
Taco diyAudio Member Join Date: Nov 2002 Location: Place in the Netherlands	Instead of your powersupply you use a variac, so you can power things up very slowly. And measure if things are right. It's a saver way to test your work. A variac is a variable powersupply.

2nd December 2002, 04:19 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	I would like to offer up a more refined definition. A Variac (tm) is a variable AC power source. You plug your amplifier's power cord into it and turn up the AC from 0 volts to as high as 20% over the voltage from the wall. If you turn it up slowly, you can catch amplifier faults often before the smoke and flames.

2nd December 2002, 05:21 PM	#4
miguel2 diyAudio Member Join Date: Jun 2002 Location: Portugal	Hi Having seen smoke and flames and not having a variac I came across the idea of using the zeners on the Zen PSU to increase the voltage up. So if you use a single zener the voltage in the regulated rail will be around 4-5 V. Puting another one will increase it a bit to around 14 V. Can this be done? Any change in the resistors of the PSU (or caps)?

2nd December 2002, 06:11 PM	#6
miguel2 diyAudio Member Join Date: Jun 2002 Location: Portugal	Hi Vince, I always check the PSU first and then the rest of the circuit. The Zen amp has a resistor that controls the bias current, so we can adjust it so to have no problems on the pass transistor. Of course the current cannot be very high but maybe it is sufficient to see if everything looks well.

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