diyAB Amp The "Honey Badger" build thread - Page 62 - 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 18th September 2013, 03:06 PM   #611
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Albany , NY (smallbany)
Quote:
Originally Posted by still4given View Post
Does the PS for the front end have to be regulated?
Nope. mine isn't.

OS
__________________
Mongrel website , always current and updated :
http://www.fidelityforce.com/ostripper
  Reply With Quote
Old 18th September 2013, 06:24 PM   #612
diyAudio Member
 
Join Date: Mar 2004
Location: Surrey, UK.
I haven't followed this thread for a while.
Is there a HB kit, with pcb and components ?
Are there any other sources for the pcb ?
Thanks
fs
  Reply With Quote
Old 18th September 2013, 10:17 PM   #613
redjr is offline redjr  United States
diyAudio Member
 
Join Date: May 2011
Location: Danbury, CT
Quote:
Originally Posted by firestorm View Post
I haven't followed this thread for a while.
Is there a HB kit, with pcb and components ?
Are there any other sources for the pcb ?
Thanks
fs
There are no complete kits for the HB that I'm aware. There are a couple of BOMs in this or another thread. Also PCBs are available from the DIY store. I'm going to start building mine as soon as my basement and workshop are done. Just moved into a new home. Too much else to do....

Rick
__________________
redjr
  Reply With Quote
Old 18th September 2013, 11:05 PM   #614
diyAudio Member
 
Join Date: Mar 2004
Location: Surrey, UK.
Rick - thanks
Its not easy buying things from USA, nearly always gets taxed and a huge handling fee from the courier/postal services. A 40USD item will get taxed 8USD (which I don't mind) but the handling is around 20USD. Whereas items from asia don't seem get charged at all, as they seem to report a nominal value without asking, where many of your compatriots prefer to report the full value.
  Reply With Quote
Old 20th September 2013, 11:06 PM   #615
cammy is offline cammy  New Zealand
diyAudio Member
 
cammy's Avatar
 
Join Date: Dec 2011
Location: Wellington
Question Instability upon bias change

Greetings all,
I have been lurking here for a while, but this is my first post. I have built up a HoneyBadger system, pretty similar to JoJo's: Soft-start, Antek AN-8445, 2xUniversal PSU (1 per channel). This is my first amp build, but please don't hold that against me

Upon firing up my first channel (with the bias, offset and ccs resistors set as per the build guide) all seems well... no smoke escaping, led's nicely lit. My offset was a couple of mV. The TP1/TP2 bias measurement was sitting around 0.1 mV. I measure around 7.90 V across R14 (ca. 3.6 mA). I have noticed the heatsink for Q10/11/12 is a little warm, but the output stage transistors are cool. I notice R50 is ever so slightly warm. I have nothing attached at the outputs, apart from a DMM if I'm measuring offset.

Anyway, as I slowly increase the bias all seems well until I hit around 8.2 mV at which point it sky-rockets to closer to 100 mV (and I proceed to turn the unit off). Less than a quarter turn back, and with the unit switched back on and it seems happy again at around 8 mV. If I don't turn the unit off after it has sky-rocketed (and instead try to wind down the bias) even at max resistance of R30 (500R) the bias voltage remains at around 30 mV, until I switch it off and on again, at which point it's back to 0 mV. Sorry about all the information... I figure more is better.

Where can I look to diagnose this instability? I have recently acquired a tired old D61a scope, but that needs some love before it can be of much use. Perhaps this should be my first priority?

Regards
Scott
  Reply With Quote
Old 21st September 2013, 12:05 AM   #616
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Albany , NY (smallbany)
R50 slightly warm = possible instability (oscillation). It should be cold.

I had this happen once when I forgot to set the cascode. Check to make sure you have the C-R or C-Z jumper in (or test the bases Q3/Q4 for a steady voltage,whether it is the Zener or resistive divider).

Also, what input devices are you using. Some ultra high gain Zetex models (simulated) have required extra degeneration (R15/16 higher value) for normal
operation.

Ground the heatsinks ! Check the Q9/Q10 - C7/C8 area, make sure it is right. Also ... you might try
increasing R24 (TMC feedback) from 820R to 1-1.5K.

fire up the second channel , this will determine if it is a mistake or not.

Show some detailed photo(s).

OS
__________________
Mongrel website , always current and updated :
http://www.fidelityforce.com/ostripper

Last edited by ostripper; 21st September 2013 at 12:10 AM.
  Reply With Quote
Old 21st September 2013, 12:18 AM   #617
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Albany , NY (smallbany)
R50 slightly warm = possible instability (oscillation). It should be cold.

I had this happen once when I forgot to set the cascode. Check to make sure you have the C-R or C-Z jumper in (or test the bases Q3/Q4 for a steady voltage,whether it is the Zener or resistive divider).

Also, what input devices are you using. Some ultra high gain Zetex models (simulated) have required extra degeneration (R15/16 higher value) for normal
operation.

Ground the heatsinks ! Check the Q9/Q10 - C7/C8 area. Also ... you might try
increasing R24 (TMC feedback) to 1-1.5K.

Show some detailed photo(s).

OS
__________________
Mongrel website , always current and updated :
http://www.fidelityforce.com/ostripper
  Reply With Quote
Old 21st September 2013, 06:25 AM   #618
cammy is offline cammy  New Zealand
diyAudio Member
 
cammy's Avatar
 
Join Date: Dec 2011
Location: Wellington
Thanks for the quick reply!

The cascode is set using a Zener reference (C-Z jumper). The voltage across the Zener is 14.34 V.

My chassis heatsink is connected to ground, but the aluminium plate at Q10 to Q12 is not. Should it be?

Everything seems in order in the Q9/Q10 - C7/C8 area and I can't find any shorts. I have tried increasing the TMC feedback resistor to 1k. This has the same effect as before, except I can get to very slightly higher bias voltage before the instability, around 8.8 mV.

I have used MPSA18 transistors for Q1 and Q2. Would you suggest increasing R14/15 in this case? If so, how much higher? 150R? 200R? 1K? Would it be easier to swap these transistors out?

I fired up the second channel and I think it's the same story, but I'm not too sure as I left it on a little longer (at higher bias) and it fried my fuses and "safety" resistors (both R53 and R54). These flameproof 22R resistors just got flamed and now measure around 23k! It seemed happy for several minutes before I touched the bias. I guess I'll try and get the first one going properly before I come back to the second one.

Thanks, I really appreciate the help.
Scott
  Reply With Quote
Old 22nd September 2013, 12:19 AM   #619
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Albany , NY (smallbany)
MPSA18= Hfe min 500 and max 1500.
Too bad that they do not have gain groups - no way to tell if you have 500 or 1500+ ..
KSC1845(f) = Hfe 300/600


I plugged in a Zetex 1048a (below-) , the highest gain model I had (Hfe 1200+).

Yes , the phase margin was "on the edge" (possible instability).

If you have Hfe 1200 (or even 1500) MPSA18 , increase R14-R15 to 220R.

This brings the phase margin back to 78deg - stable , (see below.. 180-102deg.=78).

Also shown below is the high gain zetex models with the resistor changes.
I ran this with the global feedback resistor (R6/R3 - gain) at 22k/27K/and 33K - good.

I tried to get my amp to oscillate when I first built it. Lowered the Q10 miller cap to 47p (nope-all was good). When I lowered R14/15 to 10R (misread the resistors) , I really oscillated and could not set the bias.
Totally SMOKED the zoble resistor !! This was with standard KSC1845(F-Hfe300-600).

PS - you might want to consider using the ksc1845(f) or BC546 BC547(a-b) as LTP.
Also , if the current mirror (Q5-Q6) has uber high gain ... this will have the same effect - something to consider.
OS
Attached Images
File Type: jpg badger margin.jpg (63.3 KB, 290 views)
File Type: jpg badgerZetex.jpg (104.0 KB, 289 views)
__________________
Mongrel website , always current and updated :
http://www.fidelityforce.com/ostripper

Last edited by ostripper; 22nd September 2013 at 12:33 AM.
  Reply With Quote
Old 22nd September 2013, 03:06 AM   #620
janusz is offline janusz  Australia
diyAudio Member
 
Join Date: Oct 2004
This kind of oscillations is one of the worst things to happen as it is difficult to locate its source and the source may be in the quality of some parts including output transistors. I encountered the same problem with "diamond" amp. By the time we got a clue (a friend of mine assisted me) board was almost ruined from desoldering and soldering so I gve up before checking the most recent solution (worked in simulations).

I know very little about TMC but I noticed that in some amps a small antioscillation resistor is added. In HB it would go from C7/base Q9 to R5/R6 joint - C7-additional R are parallel to R6.

In LTP one can also try 100pF plus 1k between collectors of Q3-Q4 if problem is there. Then driver transistors (q14-15) and their caps.

cheers,
  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
diyAB Amp - The "Honey Badger" Variac Solid State 1276 3rd July 2014 11:14 AM
My LM3886 build thread CanAm Man Chip Amps 22 13th July 2012 07:48 AM
Ricci's dual B&C 21SW152 build thread. Josh Ricci Subwoofers 22 12th April 2010 09:39 PM
New Project Build Thread ryoung Multi-Way 5 19th April 2008 01:15 AM
Badger Badger Badger..... Mushroom !! 5th element Everything Else 15 20th September 2003 03:16 PM


New To Site? Need Help?

All times are GMT. The time now is 09:46 PM.


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