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?
Thanks.
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?
Thanks.
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.😀
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.😀
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.
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.
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.
Sincerely,
Cambe 😱
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.
Sincerely,
Cambe 😱
Hi,
You can find the schematic for the lovely Son of Ampzilla and the Thoebe at my website www.audio-circuit.dk under Schematics 😉
You can find the schematic for the lovely Son of Ampzilla and the Thoebe at my website www.audio-circuit.dk under Schematics 😉
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.
Sincerely,
Cambe:
Thank you ACD,
On the SAE forum Jim B. talks about how difficult it is for the average tech to work on these products.
Sincerely,
Cambe:
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.
Cambe
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.
Cambe
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.
Jocko
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.
Jocko
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.
Cambe😎
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.
Cambe😎
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.
Still repairing Son's ???
Burnedfingers, do you still work on Son's? New to DIY - found this post through search.... I have one that is getting sicker by the day and needs some help.
Burnedfingers, do you still work on Son's? New to DIY - found this post through search.... I have one that is getting sicker by the day and needs some help.
Being 40 some years old could the electrolitic caps be starting
to fail (dry out) ? The increasing hum kind of points to this.
Any way it's a good place to start.
to fail (dry out) ? The increasing hum kind of points to this.
Any way it's a good place to start.
Hi hyposplash,
Love those 500's like the one in your avatar. Those are next to impossible for the average tech to repair properly.
Joe still services amps, I'll send him the link to this thread.
My opinion of the average service technician is pretty low, so I agree with the following statement ...
Joe is able to properly repair your amp.
-Chris
Love those 500's like the one in your avatar. Those are next to impossible for the average tech to repair properly.
Joe still services amps, I'll send him the link to this thread.
My opinion of the average service technician is pretty low, so I agree with the following statement ...
Sadly, he is correct from what I have seen.
Joe is able to properly repair your amp.
-Chris
Chris,
You are way too kind. I manage to get by but I'm not qualified to walk in your shadow or Mr. DJK's just to name a few.
You are way too kind. I manage to get by but I'm not qualified to walk in your shadow or Mr. DJK's just to name a few.
Hey Joe,
If you take care with a repair, you are qualified to walk beside anyone. Don't sell yourself short. It's the lazy hacker that shouldn't show his / her face around me.
I know you have repaired some tough ones, so there you go!
-Chris 😉
Edit: Keith, you must enable the "show email" in your profile. This only shows the button, not your address. Joe can't email you until you fix that. I can try to do it for you if you want.
If you take care with a repair, you are qualified to walk beside anyone. Don't sell yourself short. It's the lazy hacker that shouldn't show his / her face around me.
I know you have repaired some tough ones, so there you go!
-Chris 😉
Edit: Keith, you must enable the "show email" in your profile. This only shows the button, not your address. Joe can't email you until you fix that. I can try to do it for you if you want.
- Status
- Not open for further replies.