Eti 480 trouble

[efren sabio]

Hi,

Amazing! I still have ETI 480. I bought it here in Hongkong, more
than 20 yrs ago , at the Dick Smith shop. It was sold as 'guitar
amp' but only a pair of 3055/2955. I looked at the link and, yes
the pcb is exactly like mine. The link also traced the original
designer.

efren

 

[Hayden]

No just wait the problem was Q8 and Q7 wasn’t insulated from the heat sink the kit didn’t supply the mica washers
Now to my original problem it is running at half power I turn up the gain and it distorts the bios voltage is set to 3.7volts the outputs get warm. Can I modify the amp to use high level input?

 

[Greg Erskine]

Hi Hayden,

Incase you want to start all over, I notice that the ETI480 is on special for $28 at Dick Smith.

 

[Hayden]

Maybe it was designed for high level input? I’m running line out from a cd player.

I just recently bought all the transistors and most of the resistors for it and found out that the ones that I was replacing all worked so I have a lot of spares
could I put 2 eti 480‘s together and run one sub at 200 watts?

Thanks grege I’ll think about that special

 

[Hayden]

Thanks grege I got another 480 and when they swiped it came up with $23 so it was a bargain.
I have built it and it works but I’m not convinced that it’s running at full power because I connected it to a 12” woofer rated at 80 watts max and I put a tone of 40 Hz input to the amp but the speaker moves about 1 cm I have varied the intensity of the input but it distorts if I go too high, so why isn’t it running at 100 watts?

Thanks for your time guys

 

[Centauri]

It will only run at 100W max if the speaker impedance is 4 ohms. An 8 ohm speaker will only allow the amp to run to around 60W maximum. The amount of cone movement is not much of an indicator of power - cone movement will depend on speaker sensitivity, frequency, box type (if it is in a box at all) etc. Measure the AC voltage on the speaker with a multimeter with your 40Hz tone - if you measure around 28V ac, the your amp is fine. How does volume compare to the other module?

Cheers

 

[Wyatt Turk]

I was just passing this subject and noticed that somebody actually has trouble with an eti-480. I built a stereo out of the 100w version some 24 years ago and still work and the only problem I ever had was that I blew up a horn tweater.

One of the probelms is that you must use a preamp that delivers 1v output to the amp anything else and it distorts when wound up. I used a preamp out of a Kriesler stereo that I got when I worked for them many years ago I don't know if they are still available as Phillips bought the company out and closed it down 22 years ago.

Contact a friend of mine that use to be a field tech for Kriesler that owns his own repair shop.

Richard at Kings Television Repairs Padstow, Nsw, Australia.

 

[Hayden]

I powered it up with a 1khz tone and tested it with a oscilloscope and found that it’s clipping.
And also I have a tone that goes from 25hz to 20khz played it through the amp and hook it up to a speaker that is 15watts max 8 ohms (I think) and nothing much came out of it.
Are there any known problems with the design of this amp?
Yes I did have it on a 4 ohm woofer not in a box and I tried it in a box as well but still nothing.

maybe a faulty output?

Thanks

 

[Centauri]

Design of this amp is very simple and normally very reliable - have used / built heaps over the years.

More info - was the clipping symetrical (same top and bottom)? , what voltage level?

Difficult to fault find when remote - a list of DC voltages at each leg of each transistor would help pin it down.

Cheers

 

[Wyatt Turk]

I guess the reason I have never had a problem with mine is that I tested every part before I put it together all those years ago.

I used digital meters and if it was not in the 5% tollerance range I changed the part for another.

I think that's why all of never have heard a problem with these amps is that they are bullet proof. Try testing every part individually I know it sound strange but believe me when you get it powered up and working you will never need to touch it ever again, as I have said mine is 24 years old and I have never lifted the cover off the amp yet... and it's seen a lot of work as I use to use it for parties and disco's in the 80"s.


Good Luck

Wyatt

 

[Hayden]

Yes I did test it all the components before assembly, one resistor was out a bit but it was just in its 5% range.
How hot do Q4 and Q5 get after 5 minutes of running 40hz at about half level? they get hot but you can still touch them for as long as you want.

I’ll get the voltages for you.

Thanks

 

[efren sabio]

I think if the 480 is still easily available- & cheap- it should be
the best choice for a beginning builder. The 1st step is just
to change all the transistors to the modern fast devices like
the A872A, D699/B649, and MJ15003/4.

 

[Hayden]

Well these are the first 2 amps I’ve ever built. I have built hundreds of other projects and my own designs as well. Yes I’ll think about changing the transistors, what benefit do you gain?

 

[Wyatt Turk]

The transistors get bloody hot my heat sink takes up the back of my amp... You would not see it on todays through away pieces of crap..

Bye the way what power supply are you using?....

Wyatt

 

[Hayden]

The power supply is out of another dead amp; it does supply it with a good voltage and can handle more than enough current. Do you know what voltages the transistors run at with no input or speaker connected?

Thanks again

 

[Wyatt Turk]

I'm file attaching an atticle which should explain you problems it has all the tech stuff your after...

Wyatt

 

[Hayden]

I work out what was wrong with my amp. I have just done a volts test on the rails and 37volts but when it clips the voltage drops by 10, so I took out the dropper resistors out of the power supply and no more clipping and the voltage stays at 37, it works at its full 100watts I think I still got to tune it with an oscilloscope so thanks guys for your help.

Now for a pre-amp with gain control, are the dicksmiths or jaycar kits good enough for that?

 

[Centauri]

"dropper resistors out of the power supply" ???????????

 

[Wyatt Turk]

Do dah,


Blame the amp..... Good to hear that we have helped in some way as I said before I made my stereo some 20 odd years ago and I used a preamp from a Kriesler amp. I can not find a kit that can deliver the 1v rms output suitable for this amp maybe you can put another post up and have someone design one for you.

I could get you the diagram of the preamp I used, but it may take some time it's hard going through stuff that I have not touched in at least the last 8 years...


Wyatt

 

[Hayden]

Resistors to drop the voltage a little "my own designed power supply"

Thanks Wyatt