my AV400 is back - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th May 2005, 04:27 PM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: HKSAR
Default 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.
  Reply With Quote
Old 12th May 2005, 05:50 PM   #2
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
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
  Reply With Quote
Old 12th May 2005, 06:38 PM   #3
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.
  Reply With Quote
Old 12th May 2005, 08:24 PM   #4
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
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
  Reply With Quote
Old 13th May 2005, 01:02 AM   #5
jleaman is offline jleaman  Belgium
Banned
 
Join Date: Apr 2002
Send a message via AIM to jleaman
Do you guys still need help i have my nchannel at my finger tips to help out.
  Reply With Quote
Old 13th May 2005, 01:20 AM   #6
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
  Reply With Quote
Old 13th May 2005, 02:29 AM   #7
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?
  Reply With Quote
Old 13th May 2005, 02:33 AM   #8
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
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
  Reply With Quote
Old 13th May 2005, 04:13 AM   #9
diyAudio Member
 
BobEllis's Avatar
 
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?
  Reply With Quote
Old 13th May 2005, 08:44 AM   #10
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.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Back to Back transformers and safety ground dsavitsk Tubes / Valves 1 9th February 2009 11:10 PM
Back to Back transformers to get +B of 200V ?? Shoog Tubes / Valves 5 23rd September 2005 04:58 AM
(Attn Planet 10!) active xo & 2.5 way back to back Vifa P13 mids - questions paulspencer Multi-Way 9 15th August 2004 06:34 AM
Back to Back Polarized Electro's EchoWars Solid State 11 15th November 2003 10:30 PM
Back to Back input diodes Kevin McCready Solid State 0 10th September 2002 12:56 AM


New To Site? Need Help?

All times are GMT. The time now is 04:42 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2