mods for son of ampzilla & sae 2400L

[madman813]

Hi I am looking for mods for son of ampzilla & sae 2400L
also a service manual for the son of ampzilla & bias settings.
thanks Mike

[Original Burnedfingers]

Mike,

Bypass all electrolytic caps on the driver boards with small silver mica or mylar. Bypass the filter caps in the power supply with small electrolytic caps also(try about 33mfd/100volt) and .1's

You won't succeed in making them sound any better by jacking up the bias setting on these amps. I've measure the thd and Imd of the stock bias settings and increased bias setting.

[MikeBettinger]

Originally posted by burnedfingers
Mike,

Bypass all electrolytic caps on the driver boards with small silver mica or mylar. Bypass the filter caps in the power supply with small electrolytic caps also(try about 33mfd/100volt) and .1's

You won't succeed in making them sound any better by jacking up the bias setting on these amps. I've measure the thd and Imd of the stock bias settings and increased bias setting.

Arrgghh, This is a beautiful amp. If you're going to rebuild it, actually rebuild it. Don't do a Pooge mod bypass job. Replace the caps with Panasonic FM series from Digikey, replace the resistors, replace the 10K and 2.2K electrolytics in the supply. Cleanup the power supply ground to the chassis, but keep EVERYTHING as it was designed. New matched input transistors, remove the sockets, replace the trimpots. Dump the VI limiting... the amp doesn't need them. Don't let anyone get you Improving the design; the only circuit mod I'd suggest is a cascode on the output of the differentials. but it's smooth sounding without it, a better balance in the upper bass and faster (cleaner sounding, but not monumentally so) with it.

Basically do whatever removes the effects of age and then enjoy.

There was never a manual. The schematics should be posted on the SAE_Talk news group on Yahoo. If nobody else jumps in I have a schematic, bias instructions, etc. Posting them with such a small required file size always present challenges. So I leave it to the techno wiz kids.

Regards, Mike.

[madman813]

Thanks for the input on the son of ampzilla but all the schematics I have seen on line
are hard to make out & some resistor & caps are slashed out & replaced with different values. Burnedfingers says Bypass all electrolytic caps but doesn’t say what value. I am assuming .1uf you also say try 33uf in the power supply how can that make a difference if the main B+ is 10,000 uf. Also after all the jumping how much better did it sound any smother? I guess helping would be to know which caps are in the signal path & go to a better sounding non polarized cap. Also MikeBettinger idea of changing out the aged drifting parts is also good but how do I Dump the VI limiting?..& should .is that the protection?
Also it doesn’t say in the manual about bridging this amp or how to, & if you can does that mean that the class A operation goes up from 2 watts into 8 ohms to 4 watts or more of class A listening pleasure? Also if any one has the bias settings email me thanks

[Original Burnedfingers]

MikeBettinger,

Do you have any experience in respect to bypassing the electrolytics in these amplifiers? I don't think so. If you did you would have sampled the increased clarity and detail. This is NOT a pooge as you call it. The bass is tighter, the midrange and high frequency have better detail. It is well worth the $10 in parts and 1.5 hrs of time to do it.

There was never a manual.

Well, maybe not a highly detailed hard bound manual but there is a small (less than 8 pages) that goes into great detail about biasing and rebuilding. I have a copy and if I can find it I will post it.

Bypass caps in the power supply.... 33mfd@100 volt and .1 @ 100 volt X2 are needed to bypass the main filter caps.

Small value silver mica or mylar to bypass caps on the driver board. Value not important.

Added note* I have repaired and modded a number of Ampzilla's, Son of Ampzilla's, Grandson's and SAE2400's over the years. There is a night and day difference between a "Stock" Ampzilla and one with bypasses in it.

I would also suggest digging up Walt Jungs review of the original Ampzilla and read about his re-do of the quad diff input stage and apply.

Arrgghh, This is a beautiful amp.

It was in its day and that day is over. There are better sounding amplifiers out there today.

[MikeBettinger]

Originally posted by madman813
Thanks for the input on the son of ampzilla but all the schematics I have seen on line
are hard to make out & some resistor & caps are slashed out & replaced with different values.Dump the VI limiting?..& should .is that the protection?
Also it doesn’t say in the manual about bridging this amp or how to, & if you can does that mean that the class A operation goes up from 2 watts into 8 ohms to 4 watts or more of class A listening pleasure? Also if any one has the bias settings email me thanks

I'll try to post a clean schematic for you. I have one but whether or not It will still have any resolution after it gets compressed is the problem. The bias is set to 30mv across the .22 ohm 5 watt resistors on the output stage PCB at the bottom, using the trim post located in the middle of the same board. The output offset is adjusted using the trim pot centrally located near the top of the input/drive pcb. The Vi limiters are the protection transistors; just remove them from the pcb/ or not... I don't like the sound.

Originally posted by burnedfingers
MikeBettinger,

Do you have any experience in respect to bypassing the electrolytics in these amplifiers? I don't think so.


Well, maybe not a highly detailed hard bound manual but there is a small (less than 8 pages) that goes into great detail about biasing and rebuilding. I have a copy and if I can find it I will post it.


Added note* I have repaired and modded a number of Ampzilla's, Son of Ampzilla's, Grandson's and SAE2400's over the years. There is a night and day difference between a "Stock" Ampzilla and one with bypasses in it.


It was in its day and that day is over. There are better sounding amplifiers out there today.

Hi burnedfingers,

I do have a lot of experience with all the GAS products. I was one of the few Authorized service stations for the gear while they were still around and did a brisk business supporting the stuff once everyone from the company ran and hid when it closed. I have a fairly complete set of all the availible documentation and promotional literature; even a set of original GAS advertizing posters.

Sorry to sound rude but the standard mod responses that get posted don't normally try to maintain the core values of a design that allow one to hear what the original design sounded like (once the effects of age are removed).

This amp would fair quite well if compared to any sanely priced amp produced today.

My point with the electrolytics is that today's parts , specifically the Panasonic FM series available from DigiKey, have excellent performance without the bypassing. I hear a full range improvement in clarity and low-level resolution, and it makes a cleaner rebuild. I heartily suggest trying them, you might be pleasantly surprised.

From your post it's apparent that you must have noticed the Ampzillas and the other family members to be special stuff, which they are. I felt that way years ago when I heard my first Ampzilla and Theadra system. Compared to what was their competition at the time, the GAS gear was light years ahead if not only sound but it was designed and built by very passionate people. Far different in many ways than today's audio business.

Preserve the past as there are enough examples of today's technology that can fill the land fills as they really won’t be worth saving.

Regards, Mike.

[madman813]

hay I am with you what ever makes the amp sound at it's best.
I would like to try the bypass caps in stages to here the difference & later try the re-do of the quad diff input stage.
if you post the schematic & literature & it doesn't come out good
on line could you email me direct with a bigger file.
thanks Mike

[Original Burnedfingers]

MikeB,

I used to be on the bench about 20yrs ago. We were authorized warranty service centers for a dozen or so brands of audio gear. We repaired what came thru the door and this included the basket cases and units damaged by technician.

I may have come across too strong myself and I apologize for that.

I honestly believe that proper bypassing allows the design to be heard properly and probably the way the designer wanted it to be heard but was not allowed to do so because of corporate
bean counters. I don't believe it colors the sound one bit but allows the fullness to be enjoyed.

While I haven't enjoyed the status of being a SAE or GAS authorized repair center you can be sure I have repaired 100's of these old gems to fitting and proper operation. Yes, I owned one of the first Ampzilla's a kit version as well as about everything amplifier and preamplifier wise in the line up. I have experimented with everything from resistor and capacitor brands to matching all the resistors with 1% selected. I have taken the time and figured out what actually does work and what is a total waste of time. I have taken THD figures far lower than factory specifications. So, I would say I am experienced also.

Yes, I do have a passion for some of the older better designs but cannot join the cult following of Mr. J. B. and consider the SAE forum nothing but a circus devoted to him.

We could also bring up the Tigersarious by Southwest Technical Products Corporation. I still own 2) Tigersarious 250 watt mono block amplifiers. When auditioned next to the Ampzilla will fair just as well. The main diference being the Tigersarious had a much better output stage. I've never blown up the Tigersarious amplifiers and I cannot say that about the SAE or Ampzilla's. If JB
had designed the ampzilla's and SAE's with a heavier output stage he would have had a killer product that would have resulted in people like us eating a little more Burger King and far less steak.

[madman813]

hi I am just glad there are people like you that can help educate
& inform! now when you say The Vi limiters are the protection transistors; just remove them from the pcb/ & are they Q103 & Q104 ? & amp will still work & ? when does the protection come into play when the speaker terminals short at high power or does it limit when playing loud cause I have JBL 4343 & I cant get over 10 watts & its loud! any way if they don't come into paly for my amount of power protection is good right. also no one answered my ? on bridging this amp & thats strange that they didn't make a service manual for this amp with parts list & all unless that is on the schematic I haven't got yet.
thanks Mike

[Original Burnedfingers]

Mike,

I am not a believer in removing the protection transistors. As you have noticed MikeB and I have different opinions on things. We are both experienced in amplifiers in gereral and specifically the Ampzilla's and Sae's.I will not try to guide you with respect to the protection aspect. Therefore I suggest that questions about the protection be directed to MikeB.

Bridging ...

I do not recommend bridging this amplifier either. Actually I do not recommend bridging ANY amplifier that doesn't have the capabilities to do so from the factory. Yes, I have done this in my younger years and yes I have blown the hell out of a few amplifiers and drivers. The JBL speaker is a costly speaker and deserving of only the best in terms of power and protection.

Bridging is very simple.... you build an inverter and input signal into the inverter to one channel and the straight signal into the other channel. Another way is to go inside the amplifier and and input signal to the inverting input of the second channel and non inverting signal into the first channel in the normal mannor. You will then take your output from both hots.

It will take two Ampzilla's, one for each channel. If you are bent on doing this with the "Son" I suggest that you rebuild from the bottom up. The best transistors, higher voltage and current in the driver and output stage too. Replace the bias IC and this is a MUST in any Ampzilla or Son rebuild. I assume MikeB may be able to direct you with respect to finding some. I believe there were 2 different ones that could have been used in the "son". I have the numbers written down but its too early to try to find them this morning.

Any old amplifier should be rebuild before using.