my AV400 is back

bigpanda · 12th May 2005, 03:27 PM

Hi

AV400 :

http://www.aussieamplifiers.com/download.htm

This is the second AV400 that I have built. 1st one is for a subwoofer which is still working quite alright and nothing nasty come out during construction but this one....

I have use 220u instead of 100u for the power rail decoupling caps. (I had the name right?). I found that my pot is just 3k8 instead of 5k as specified. The pre-freight test comes out fine except the voltage across R3 was a bit off.

When I tried to adjust the pot, the voltage across the source resistors give me null reading. No matter how I adjust the pot, there is no reading whatsoever. No q. current?

Can anyone give me some idea what might went wrong. I've checked all transistors before soldering in.

Thanks in advance for your information.

Mattyo5 · 12th May 2005, 04:50 PM

My symmetrical 400 amps wouldn't bias up b/c i had the bias transistor backwards. If you look on the actual pcb for the symmetrical 400, the base, collector and emmitters are marked correctly, though they are marked in a different order than the actual pinout of the transistor. transistor was BCE, order on the pcb is BEC or something like that. just fyi

-Matthew K. Olson

bigpanda · 12th May 2005, 05:38 PM

Tks Mathew,

When you say the bias transistor, you mean Q10--BD139 (just to make sure first). If you look at it in the front, it should be ECB from left to right. I did not use Holton's board, I had mine self-brewed. I did check that (which Holton had specifically warn ) polarity of Q10. I don't think that is the problem.

Mattyo5 · 12th May 2005, 07:24 PM

I don't have the amp anymore, so i don't remember the config. I missed holton's warning...i think it should have been in bigger letters. hehe. Anyway, if i remember right, yes it was bd139. Anyway, good luck w/ the problem...wish i could help more.

-Matthew K. Olson

jleaman · 13th May 2005, 12:02 AM

Do you guys still need help i have my nchannel at my finger tips to help out.

mastertech · 13th May 2005, 12:20 AM

just 3k8 instead of 5k as specified. The pre-freight test comes out fine except the voltage across R3 was a bit off.

When I tried to adjust the pot, the voltage across the source resistors give me null reading. No matter how I adjust the pot, there is no reading whatsoever. No q. current?

-------------------------------------------
i think the substituton of 3k8 could be causing the problem and the bias generator if there is one then again the substitution has rendered it inoperative

bigpanda · 13th May 2005, 01:29 AM

Tks for the tip mastertech, actually I didn't put the 3k8 on purpose. The pot had 502 written on it so it's a 5k, but since it is not working for no reason, that is the time I go snooping around for possible error and I found that this damned thing is only 3k8. I guess all I can do is to put another 1k2 on one side to make it 5k and see if makes the Q10 operative and then I will find a real 5k for it. D***, I was framed if that's what cause the trouble.

BTW, could it be possible that the bd139 is having a hfe that is too low to make the circuit nonfunctioning?

Mattyo5 · 13th May 2005, 01:33 AM

If you take the pot out and check it...does it actually adjust? or does it just sit at 3.8k? i dunno what i'm talking about, but i still suspect bd139

-Matthew K. Olson

BobEllis · 13th May 2005, 03:13 AM

the usual term for this type of "bias generator" is Vbe multiplier. It will work with a range of values but you may find yourself at one extreme of the pot's range. I second Matt's suggestion to check that the pot adjusts and add check the solder joints from wiper to Q10.

What is the voltage emitter to collector on Q10? You should be able to adjust it to greater than 8 volts (output stage disconnected) Maybe Zd3 and Zd4 are in backwards, limiting your bias voltage.

What is the voltage across R37? Any voltage across R34?Basically looking for some current in both places.

Is Q10 electrically isolated from the heat sink? Grounding it will make a mess of things.

how far off was the R3 voltage?

did you remove the temporary 10 ohm resistor?

bigpanda · 13th May 2005, 07:44 AM

I got no reading across R34 and about 5.6mV across R37
Q10 was not s/c to the heatsink.
I had 1.36V across R3

I've got about .56V across ZD1, ZD2. Does it mean they are trashed?

I have the 10 ohm temporal resistor removed.

About voltage emitter to collector on Q10, do I have to desolder all the outputs first to measure it. I can still measure a hfe on it.

12th May 2005, 03:27 PM	#1
bigpanda diyAudio Member Join Date: Jun 2004 Location: HKSAR	my AV400 is back Hi AV400 : http://www.aussieamplifiers.com/download.htm This is the second AV400 that I have built. 1st one is for a subwoofer which is still working quite alright and nothing nasty come out during construction but this one.... I have use 220u instead of 100u for the power rail decoupling caps. (I had the name right?). I found that my pot is just 3k8 instead of 5k as specified. The pre-freight test comes out fine except the voltage across R3 was a bit off. When I tried to adjust the pot, the voltage across the source resistors give me null reading. No matter how I adjust the pot, there is no reading whatsoever. No q. current? Can anyone give me some idea what might went wrong. I've checked all transistors before soldering in. Thanks in advance for your information.

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12th May 2005, 04:50 PM	#2
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	My symmetrical 400 amps wouldn't bias up b/c i had the bias transistor backwards. If you look on the actual pcb for the symmetrical 400, the base, collector and emmitters are marked correctly, though they are marked in a different order than the actual pinout of the transistor. transistor was BCE, order on the pcb is BEC or something like that. just fyi -Matthew K. Olson

12th May 2005, 05:38 PM	#3
bigpanda diyAudio Member Join Date: Jun 2004 Location: HKSAR	Tks Mathew, When you say the bias transistor, you mean Q10--BD139 (just to make sure first). If you look at it in the front, it should be ECB from left to right. I did not use Holton's board, I had mine self-brewed. I did check that (which Holton had specifically warn ) polarity of Q10. I don't think that is the problem.

12th May 2005, 07:24 PM	#4
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	I don't have the amp anymore, so i don't remember the config. I missed holton's warning...i think it should have been in bigger letters. hehe. Anyway, if i remember right, yes it was bd139. Anyway, good luck w/ the problem...wish i could help more. -Matthew K. Olson

13th May 2005, 12:02 AM	#5
jleaman Banned Join Date: Apr 2002	Do you guys still need help i have my nchannel at my finger tips to help out.

13th May 2005, 12:20 AM	#6
mastertech Banned Join Date: Mar 2005 Location: Australia	just 3k8 instead of 5k as specified. The pre-freight test comes out fine except the voltage across R3 was a bit off. When I tried to adjust the pot, the voltage across the source resistors give me null reading. No matter how I adjust the pot, there is no reading whatsoever. No q. current? ------------------------------------------- i think the substituton of 3k8 could be causing the problem and the bias generator if there is one then again the substitution has rendered it inoperative

13th May 2005, 01:29 AM	#7
bigpanda diyAudio Member Join Date: Jun 2004 Location: HKSAR	Tks for the tip mastertech, actually I didn't put the 3k8 on purpose. The pot had 502 written on it so it's a 5k, but since it is not working for no reason, that is the time I go snooping around for possible error and I found that this damned thing is only 3k8. I guess all I can do is to put another 1k2 on one side to make it 5k and see if makes the Q10 operative and then I will find a real 5k for it. D***, I was framed if that's what cause the trouble. BTW, could it be possible that the bd139 is having a hfe that is too low to make the circuit nonfunctioning?

13th May 2005, 01:33 AM	#8
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	If you take the pot out and check it...does it actually adjust? or does it just sit at 3.8k? i dunno what i'm talking about, but i still suspect bd139 -Matthew K. Olson

13th May 2005, 03:13 AM	#9
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	the usual term for this type of "bias generator" is Vbe multiplier. It will work with a range of values but you may find yourself at one extreme of the pot's range. I second Matt's suggestion to check that the pot adjusts and add check the solder joints from wiper to Q10. What is the voltage emitter to collector on Q10? You should be able to adjust it to greater than 8 volts (output stage disconnected) Maybe Zd3 and Zd4 are in backwards, limiting your bias voltage. What is the voltage across R37? Any voltage across R34?Basically looking for some current in both places. Is Q10 electrically isolated from the heat sink? Grounding it will make a mess of things. how far off was the R3 voltage? did you remove the temporary 10 ohm resistor?

13th May 2005, 07:44 AM	#10
bigpanda diyAudio Member Join Date: Jun 2004 Location: HKSAR	I got no reading across R34 and about 5.6mV across R37 Q10 was not s/c to the heatsink. I had 1.36V across R3 I've got about .56V across ZD1, ZD2. Does it mean they are trashed? I have the 10 ohm temporal resistor removed. About voltage emitter to collector on Q10, do I have to desolder all the outputs first to measure it. I can still measure a hfe on it.

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