ETI-480 100W Amp .. please help


I had built ETI-480 100W amps but I cant make it work the right way is runs on 50+50v 8 ohms load the 100 Ohms resistors "Test resistors" burn every time so I found a way to make it work I jumped the protection transister becuase I have the idea the problem are that. so can somebody please tell me to to get rid of that protection transistor, Q6 I disconected it and put a that varible resister in paralell with the C6 cap and i tried to get the voltage +- 3.5 V and in the RV1 place I put a 470 Ohm resistor and that all worked for a thew hours and them it gets unstable the two amps are om a heat sink with 2 pc supply fans so it keeps cool.

So after a thew hours were coms s sss sss sound out of the speaker output i tested it it's not my speaker, it even blowed up one of my small tested speakers shame hehehe, well anyway can somebody please help me to get that bugger of a protetion out of this amp.


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Your problem is probably HF instability due to your construction - these modules were never designed to have the heatsink/outputs/drivers separated from the main board. Try twisting the wires to each transistor together ie. 3 twisted wires to each tansistor - this may help.

Q6 is not really protection, it is vbe multiplier to set and stabilise quiescent current - with this disconnected the output is in danger of thermal runaway.

Also, if your are using the original 2N3055/MJ2955 transistors, DON'T run them on +-50V - the original +-40V is pushing it.


edit: BTW, shouldn't this thread be in Solid State??
I made one amp without putting that RV1 on parellel with the cap C6, and it worked by taking R14 and R18 out, but the amp do not have all the power it need, becuase the bass dissort so I think that R14,18 that are 47 Ohms must be a larger or smaller Ohms becuase im using 50v maby everthing are mixed up the orginal plans are 40v I dont know if it can make any diffrence but you newer know

Greg Erskine

Paid Member
2002-01-05 11:56 pm
Re: Take a good look into that upgrade.

destroyer X said:
A friend constructed and sent me professional microphone recording and i perceive it sounds excelent.

This one, seems to be some upgrade.

I will construct one, i am finishing Íon Obelisk and will jump into this SC480

Hey Carlos I beat you for once. I've all ready build a SC480 and I even played it once.

Actually I was surprised how good it was as I was not really expecting much from the 2N3055/2N2955 output devices. From time to time you can get a SC480 kit for less than A$40 each so I couldn't resist. IMHO Its not in the same ball park as you know what.
Grege, if you think i am some "reference" to be beated, well, i feel proud of it!

I thank you to have all this respect related my person.... in the reality Grege, i am turning old fast, and i am producing explosions and short circuits here, inverting transistors, forgeting to check supply polarities...doing all the stupid thing that you can imagine, and others that you never imagined.

And i am stopping constructions because of that, now production is less than one amplifier each week, when 10 years ago i could make seven.

Also i am doing everything over "standard" circuit boards, to avoid too much errors, my old system, squared boards, point by point connections, wire jumpers, require precision that i am loosing because of age.

Grege, you know that i respect Hugh, that i love AKSA products because i know the man do not sleep to develop things with enormous care to find qualities not easy to find in common amplifiers... i used Hugh, the 55 drivers and output transistors, also i modified the feedback line with that Silver Mica, also Miller was modified, and emitter resistor is now floating above ground (i am calling ground, the output line, as, alike the ground, both half cicles send eletrons to this central line and goes travelling to earth througth the speaker).

Well, the SC480 turns a SC480-55AK..... and i ensure you...hehe... magnificent brigth, remembering our 55!...but could not beat it..... 55 brigth is even better.

Damned this Australian, now without too much hair, many felt down researching some new system..... keep prepared!...our mouth will be openned, with that surprised expression when he start to offer the incredible new design.... and will be adequate to prepare your pockets too, as this one is using special wood, stainless stell, some Russian electronic tubes, and all stuff top of the line.... but he is developing also transistorized units, do not know what will appear first....he is sleeping over the bench...forgot soldering iron that made a hole over the bench, so tired he was, did not perceive...the cat made him wake up.

Another very nice amplifier, is the Symassym made by Michael Bittner, our forum MikeB friend, but he did not made it to publish, not made to sale, made only to create a better sound to his own use...i assemble it, and also an old veteran of audio constructions, Mr. John Mateus...we feel good with his amplifier.
He do not said that we can publish, he is shy, and do not like to paint himself red and put some watermellow over his head, with spot ligths, to appear....the opposite.... the want to be free of those things, he has his own company to dedicate his time, and audio is just a hobbie for him....The Symassym i understand it as "The Judge!", because so precise that bad recordings will appear awfull!, only good recordings are good to hear, so, it is more one precision instrument than one home amplifier, as you will be damned with common standard recordings, were all defects will be shown to you.

Regards Grege....Australians are very good in audio, isn't?

Mod Evil, i am constructing my own transformers, i dismout them to remove secondary and i use the cheap AC voltage stabilizers made to PC computer.....those 220 to 110 auto-transformers have enormous quantities of wire.... 1 milimeter diameter wire.... so i dismount to have its is not easy to buy small quantities of this kind of wire here.

I remove some already know voltage secondary...... i count turns...lets imagine, for instance, as an example only, that a 35 Volts transformer have 70 turns plus 70 turns (35 plus 35 volts)...and let's imagine that i need 40 plus 40 i enter a simple calculation you already our language is called the "rule of three numbers"...regra de três.

If 35 Volts needed 70 turns, how many turns will be needed to produce 40 Volts?

40......................... X

Now multiply making an "X" letter shape...this will produce:

35X = 40 X 70

X = 40 X 70

X = 80

So, i make the coil again....using two wires in parallell, the length is easy, as have dismounted the 35 V coil and i already have it as a reference of length..... those two wires, removed from AC Stabilizer, i fixed them into some door metal part (maçaneta) and i run those wires inside my will need something alike 8 meters of room to do that.....and i keep them stretched, but i do not use power....because you can broke the insulation material that is surrounding the copper wire.... the electrical insulation varnish...carefull with those wires...cannot stretch...cannot use power to make them longer!.

Well, you already perceived that now the work is easy to make, take your tranformer coil, the one you want to reconstruct with more voltage, twist the wires that are fixed into the door metal holding part (a maçaneta), they will be soldered together after, as cannot resist to a 60 watts soldering iron heat, that will destruct the varnish insulation and the solder will melt put them soldered and electrically together producing low resistance soldering and very good mechanical resistance..... produce your coils with calm and two wires will be the end.... exactly 40 plus 40 volts...without errors....production result perfect when you run two wires together...voltage resulted will be matched.

Off course, i do those things only if the transformer i decided to make modifications use large diameter wire, because i will need room to put more coils .... so, i need to replace the transformer wires for another a little bit thinner....or, having space, having room enougth.... i can go on with the same wire diameter...depends on the sittuation you face.

This is made only when secondary is mounted over the primary, or even when secondary is constructed side be side with the primary...if not i do not touch primary coils, because there you need complicated calculations, and hand work do not result good, as wire is thin and easy to broke and to destroy the not touch the primary.... 70 percent changes to fail and loose your transformer....use only secondary...of course you can put some turns to have other auxiliary voltage over the coil....25 turns will produce 12 volts, and this can be helpfull to pre-amplifiers, to lamps, to motors or other can put other coils over the first one.....if used to audio purposes, those added coils must be referenced by the same earth.... the twisted wires have to be the start contact to every new voltage you produce to be used to audio appliances that will work together the main amplifier constructed.

Transformer is dismouted removing shield if the unit have it.... must remove screws and put a soft cloth over your left absorb inmpacts.... the rigth hand with a hammer will heat the magnetic plates.... they will broken the varnish that connect one each other.... remove the first two blades (this is not easy!)...and them all the blades will be loosen to removal.... have attention, as you will re-assembled it again.... there are some logical way to put blades that form letter "E" shape and letter "I" shape...if you re-assembled wrong, will construct a buzzer!.... every bass produced by the amplifier, will make some noise vibrating the transformer plates.... so...they must be well assembled...tigth in place, must receive not use too much strength when screw is mounted...have to use some varnish to avoid vibrations..or some ink if you prefere...hehe...can paint it Red..or even yellow.... hehe...will be nice (sometimes).

Do not cover coil with tape.... that thing need to loose heat to air.... cover with card..... (papelão, cartão ou cartolina) but keep it loosen, not tigth (frouxo para permitir a saída do ar quente).... keep it loosen to allow air ventilation.

Coils cannot touch metal.... coils cannot be stretched...coils cannot be covered with wounds of adhesive tape...have to breath to have heath!

Put your mail adress here, so i will try to unblock the Spam that is terrible, nothing form Brazil is entering...when in portuguese language all is blocked...because of schematic dirty sites i visited...they are asking for money and i said not.... so, they are keeping me in their "black list" am receiving hundred of communcations...all thread copies are beeing send to my adress...damned those guys...i do not like that, but i am start to think to call my hacker friend to enter that site and confuse that dirty thing from now to eternity... they are dirty as a hell!...i asked them many times to unsubscribe me...i will have to make protect myself against those guys.... stupid thing, attack to defend myself...war to peace...i hate that...but i am realising that i have not other way..... hummmmmm, maybe change my adress...but i have thousands of friends to tell them new adress!

Good luck!


Mod Evil, the SC480 board was published, and Mr. John Mateus made his own board.

You can go directly to him...he is a very nice guy, and talk Portuguese, as he born in Portugal and is living 35 years in the United States.

So, can go with your language.... do not forget to send your picture, as we do not like (our culture) to talk with invisible guys!...ahahahahah!

If can send MP3 16K sample small audio will be better, as we like (our culture) to hear the man's watch directly in the eyes to feel the guy!

He made his own SC480 board, and he loved this amplifier....he can send you the published board or the one he made, and can send you both too.

Remenber that this guys talk Portuguese from Portugal, the language is more precise than the mess we made with that language.... ideas must be complete.

So, when asking him, i would like you to send me circuit board...he will ask you with one.....and you will ask him from SC480, he will ask you again...wich one?....there are two!...they are not idiots!.... simply, their language is more precise, our half communications, waiting that the Portuguese guys conclude do not work...they do not conclude nothing, as they think this is not fair to be made.... they think people must talk with precision, without lefting room to misunderstandings...when we use language exactly with double intentions...ahahahaha!

Do you know what i think!...we are terrible!!!

[email protected]

Go slowly with him, he is an old Baron, the man has many employees and is someone respectable member of old Royalties tradition....people used to ask permition to talk with him.

Showing here, to you, the Ìon Obelisk board i made, not to produce mistakes and explosions..... what a shame, when i think about Jan Dupont and Jens Rasmussenboards.... this is a trash compared to their work!...the are the world best in boards design and construction, simply the world best, they are unbeatable, Jans and Jens, both are incredible competent in this area.

Íon Obelisk is some amplifier already posted in our forum, i think the scientist Padamiechi have something related to it..Eastern Europe wonderfull guys....alike Pavel, Epupa and some others.




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Greg Erskine

Paid Member
2002-01-05 11:56 pm
Hey carlos,

I like the new picture. It looks like the picture in my mind when I read one of your posts. Your personality from your words is represented well with this picture.

There does seem to be a lot of Australian audio enthusists considering there aren't that many Australians in the world. And there is definitely a few that are very clever.

I have read that they reckon the original ETI-480 is (or was) the most popular AMP kit in the world.

I can understand that popularity, it do not show audio defects that you find

In better amplifiers, it is precise, but not too much, so, those bad recordings are well reproduced using it.

But if you connect a very special chance to hear bad recordings, deffects appear clear, with too much evidence.

480 acts alike some filter, produces good sound and accept anything in its output...this will satisfied the biggest majority of people...but those hi ended hears will not like it.

Thank you, i normally use pictures my eldest daugther makes to me...this way, the smile is always open, because i love her deeply...the best expression i can do.


I already made 480..... now pumping here...but my unit...

Is not sounding very well...very poor sound this unit is producing, and i am sure may be some error or defect in my own unit...this unit!

Because John Mateus made it and sounded very nice.

I will check carefully tomorrow, with dayligth.....may be some mistake, or underbiased transistor.

Also it is oscilating too much easy!...... i have to control that too.

This amplifier was tested, thousands units constructed, so, the problem may be my unit, do not take it into account as some evaluation, as the unit is "Under Construction"