Amp Repair - GAS Son of Ampzilla - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 27th September 2004, 10:15 PM   #1
diyAudio Member
Join Date: Sep 2004
Location: Nevada
Default Amp Repair - GAS Son of Ampzilla

I have a few GAS Son of Ampzilla amps. I love the sound of these amps. One of them recently developed severe distortion in one channel.

I am NOT an electronics tech but I can solder/desolder parts. Anyway, every time I have had one of these amps repaired it was ALWAYS the output transistors that needed replacing.

Since there are 4 power transistors per channel (2 NPN and 2 PNP) I figured I could buy all for parts for around $20. I can easily desolder the old and solder in the new parts.

If this doesn't fix the distortion then I am only out $20 in parts. Like I stated, it has always been these parts that was the source of the amp failures in the past.

On the other hand, I realize that the distortion problem could be caused by the drivers or bias circuits. Does anyone have an educated guess as to whether my DIY repair would be successful or even worth trying?

  Reply With Quote
Old 27th September 2004, 10:42 PM   #2
diyAudio Member
Join Date: Jun 2004
Location: Knoxville
Hi Horizons

Do you have an ammeter to measure current? When you replace the outputs and verify that the speaker output has no DC on it, then connect the collector of each transistor through an ammeter to the appropriate rail voltage. Measure the idle current through each device and make sure they are the same. This being a BJT amp, the idle shoudn't be very large, less than 100mA probably.
I am not familiar with this particular circuit, but judging from the output power it sounds like it is servo biased and probably has a small trim pot in the board someware around the driver stage that controls the amount of idle current in the outputs and can be adjusted. If you turn the idle to low then you will get crossover distortion and if it is too high, then the outputs produce lots of unneeded heat and will draw more ripple noise from the power supply. Measure the current and adjust the pot.
  Reply With Quote
Old 27th September 2004, 10:48 PM   #3
diyAudio Member
Join Date: Nov 2002
I am of the opinion that you don't blindly throw parts at an amp in hopes of fixing it. No, your replacement of the outputs will not solve the problem. The bias IC isn't bad either or the amp would have blown up. It could very well be a driver or another problem.

It is time to go ahead and replace all the transistors and go thru this amp very carefully.

Check the SAE forum, someone should have a schematic for the amp. I have one somewhere. If I can find it I will post it.
  Reply With Quote
Old 28th September 2004, 02:28 PM   #4
diyAudio Member
Join Date: Aug 2001
Location: USA,NorthCarolina
Default GAS Components

Hello Everyone,
I was looking thru the solid state forum and came across this thread. I own a Son of Ampzilla,Thoebe preamp and Goliath phono preamp. The Son of Ampzilla still plays but has some hum
in it now,my Thoebe preamp has started to do the same. I looked at the SAE forum some years back and saw that the designer of these products was offering restorations for them. But the cost of of his services seemed to be a little steep for me at that time. I too, have enjoyed these products very much and would like to see them working again properly. The schematic for the Son of Ampzilla,Theobe and Goliath would be very helpful. Worst case being,having to pack them up and send them to Jim B.
  Reply With Quote
Old 28th September 2004, 03:11 PM   #5
diyAudio Member
Jan Dupont's Avatar
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
You can find the schematic for the lovely Son of Ampzilla and the Thoebe at my website under Schematics
Free Schematic and Service Manual downloads, Spare time company (just for fun):
  Reply With Quote
Old 28th September 2004, 03:49 PM   #6
diyAudio Member
Join Date: Aug 2001
Location: USA,NorthCarolina
Default Gas Components

Thank you ACD,
On the SAE forum Jim B. talks about how difficult it is for the average tech to work on these products.
  Reply With Quote
Old 28th September 2004, 03:54 PM   #7
diyAudio Member
Join Date: Aug 2001
Location: USA,NorthCarolina
Default Son of Ampzilla Repair

I tried to get one of my son of ampzilla's fixed only to be told it could not be fixed. I made the mistake of letting them keep that
one for parts.
  Reply With Quote
Old 28th September 2004, 04:36 PM   #8
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default Couldn't be fixed............?

It was designed in the 70s. We didn't have great parts back then. May not be able to get the exact part, but I can not see any reason why it can't be fixed. Might need a minor tweak if parts are substituted.

The Grandson may have been to best of the 3 amps in the line.

  Reply With Quote
Old 28th September 2004, 05:13 PM   #9
diyAudio Member
Join Date: Aug 2001
Location: USA,NorthCarolina
Hello Jocko,
You may be right. Esp. since yours is working properly. James B.
said many technician's don't have the skill's to perform the necessary repairs.
  Reply With Quote
Old 28th September 2004, 09:21 PM   #10
diyAudio Member
Join Date: Nov 2002
Send me an email. I'm sure I can help. I have fixed over 100 Ampzilla's and Sons over the years. They aren't difficult like James says.
  Reply With Quote


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
Gas Ampzilla mharry Solid State 22 6th August 2010 07:08 AM
Help with Ampzilla II native Solid State 11 6th March 2009 04:56 AM
Ampzilla 1 flashmajik Solid State 8 7th February 2009 03:34 PM
FS GAS ampzilla's need repair one gasworks Kip Swap Meet 1 22nd October 2007 06:51 PM

New To Site? Need Help?

All times are GMT. The time now is 06:01 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2