ETI-480 100W Amp .. please help

[jacquesl]

Jacquesl

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.

[MOER]

Dear Jaques

Can you post the schematic so we can see how to help?


Vlat hom flaffie!

[Centauri]

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.

Cheers
Graeme


edit: BTW, shouldn't this thread be in Solid State??

[jacquesl]

here are the url of the website

ETI-480 100W

http://www.alphalink.com.au/~cambie/

[jacquesl]

this are my front of my amp nice marantz I modified becuase it had blown and somebody give it to me. so I just going to use that casing but I like it

[jacquesl]

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

[jacquesl]

ok the one channel works now the other one I must still work on I'm waiting for the Power Transistors the only probleme I have.

I hear I a soft buzz on the speakers can somebody please tell me how to get that away

[jacquesl]

ok, I found al my error that humm or buzz it was a lose ground wire on the input signal.

[destroyer X]

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

Regards,

Carlos

[Greg Erskine]

Originally posted by destroyer X
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.