I want my ETI-480 amp stronger

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I just want to ask you people if anyone know how to make the ETI-480 100W to 200W without replacing the power transistors because I want to get more out of my MJ2955 and 2N3055 because it can do 15A and 60/100v and that’s not fare the amp are only using +- 5 amp in total per module and a I use a 500VA 35-35 transformer and 12 one cap are 2200uf I use 6 on the negative side and 6 in the other side in total the amp can like play almost full volume for 10 seconds if I switch the power of

Because I had read it somewhere here

“"Dave Tillbrook and I were involved in the ETI480. Dave originally worked on the ETI413, its predecessor, and the original 50 Watt amp. My involvement was in the bug fixing of the original design and the upgrades firstly to 100 Watts using the paralleled 2N3055/MJ2955's, and then the high powered versions including the bridging options etc. all of which ETI published. The mistakes made in the ETI480 were fixed in my DIGI-125, a really nice sounding simple amp with an output of up to 200Wrms from a single pair of output transistors."


It’s on http://www.alphalink.com.au/~cambie somewhere here’s the website in the Attach file
 

Attachments

  • paul cambie's valve and solid state audio amplifier and vintage tube radio restoration stuff.zip
    19.9 KB · Views: 152
Stepping from 100W to 200W is only plus 3dB, just hearable.

The circut, and the output transistor's wouldn't push out 200W-RMS. (If yes, then you will need a cleric who prays for the life of the amplifer.)
And of cuorse you will need higher psu rails.

If 200W-8ohm would be enogh for you, then bridge a pair of ETI-480. But in this case you the bridge-amp cannot use it for 4ohm speakers!

If you need a simple 200W/4ohm schema, then let's see attachment.
 

Attachments

  • amp_sch_2.gif
    amp_sch_2.gif
    10 KB · Views: 637
jacquesl said:
I just want to ask you people if anyone know how to make the ETI-480 100W to 200W without replacing the power transistors because I want to get more out of my MJ2955 and 2N3055 because it can do 15A and 60/100v and that’s not fare the amp are only using +- 5 amp in total per module and a I use a 500VA 35-35 transformer and 12 one cap are 2200uf I use 6 on the negative side and 6 in the other side in total the amp can like play almost full volume for 10 seconds if I switch the power of

You should read http://sound.westhost.com/soa.htm and http://sound.westhost.com/patd.htm to find out why your 15A 2955/3055 transistors arent enough for 200W output.
 

PRR

Member
Joined 2003
Paid Member
> I want to get more out of my MJ2955 and 2N3055 because it can do 15A and 60/100v and that’s not fare

3055 can do 60V (at zero amps) and "can" do 15A (at low voltage and very heavy drive), but can only do about 40V and 1 Amp at the same time. With a perfect resistor load, 100 watts is possible. With real speakers and their reactances, with original (mesa) 2N3055, even 75 watts/pair is marginally reliable. 50W/pair is a better bet, and at that we may be lucky: Doug Self computes 12W as the limit for absolute worst-case reliability.

So 100 watts out of four 3055/2955 devices is plenty. Don't ask for trouble.

There are newer better devices, and they are not that expensive. But keeping the same power transformer, it won't play louder. Going up 40% in voltage/current and doubling your pile of silicon will double your output watts (if nothing blows); but as edl says, that's not a "WOW!" change.
 
Dear Jacques

Your power supply 500va at 35 0 35 will deliver
50volts + and - at 7.14 amps per rail, Im assuming you
have two 35v taps. The transformer itself appears
adequate for driving a ETI 480. Test it by seeing if
the voltage rail voltage dips below 50 volts on large
music peaks.

Although transformers are important - they are only as
good as what follows, I would check that your bridge
rectifiers can handle the current and heatsink them.
Also check you have wired the power supply correctly
with sufficent wire dimension. You should be using a
35amp bridge rectifier block per channel. Failing this
you could improve the bridge rectifier efficiency by
using inductors and commutating diodes ( a bit complex for
dual rail supplies- take care with diode polarity)
which helps the transformer and power supply efficiency immensely.

Standard ETI 480' used MJ2955 and 2N3055 devices
a good substitute would be MJ15004 and MJ15003.

You might want to also try Supra cable or other good leads
for the speaker connection and try and keep leads short leading to the speaker which would help. Hope this helps.

Cheers / Chris
 
Good point big panda but the ETI-480 is the only module can build, and I understand it good if I have troubles with it, my cooling are very good I’m busy building a wind tunnel in the amp self in a mini tower pc box, and every transistor have a heat sink example “Q5 and Q4” so everything what is getting hot have a heat sink and that and that’s 33 Ohms resisters “R15 and R17” that I replaced with 5W resisters on and if have 4 pc fans blowing over BIG pieces of aluminum it’s to 32cm X 12cm and like I said al the stuff is in there what’s giving of heat even the 35A bridge and then the amp get hot the fans automatic go on and blow on the heat out in the back side of the tunnel and it have 3 sensors on the bridge and on the 2 modules where the T shape connects on the big heat sink
 
Dear Jacques
Sounds like someting like a short is really enjoying your amp rather than its intended purpose of reproducing sound, ie
you are talking about a lot of heat dissipation. Check your
speakers ( the load for the amp ) and cables too for their
resistance. The speaker should be somewhere between
4 and 8 ohms.

With the amplifier turned off carefully check your heatsink for shorts between the TO3 devices with a good multimeter
as the heatsink supplied with ETI 480 was notorious for
requiring further drilling. Also use silicon washers as they are much better than washers and paste.

Cheers / Chris
 
No, it doesn’t get hot, what I meant is if it gets hot then I have enough support to get the heat away.

Because my other amp I’ve build all sound the same, I first fought it were to small transformer but now I used a big transformer and it still sound the same not even more bass now that’s sucks!


So can someone tell me how to like over clock an amp?

Is it like example to increase the base current on the output transistors and the drivers?

Because I can do that I’ve got enough cooling I hoop
 
Dear jacques

The base current around transistors in the ETI 480
are designed to bias the transistor
for operation in essentially Class B operation.
the designer has carefully traded distortion for
performance so that the amplifier module
can reliably function time after time with the
amount of distortion for that model into a
speaker load of 4-8 ohms.

Reducing the resistance with more bias here will just
make the transistor conduct more heavily and produce more
heat. If you go further still you approach destruction
of the transistor and other components in sympathy
which is spectacular but then gets expensive to rebuild.

Carefully study the schematic you will find that the
designer of the ET480 has certainly done their
homework in producing a reliable amplifier, but in
terms of modern equivalents outdated, but nevertheless
still a valid design albiet with some shortcomings.

One final thing the TO3 transistors in this amp
attached to a bracket which then bolted to a
heatsink if I recall- so you will need a heatsink.

Cheers / Chris
 
You would have to add more (better) transistors, and increase the rail voltage. Increasing the rail voltage may then mean you are over ratings for some of the transistors, and resistor values for some parts of the circuit would need to be changed. It is not a simple modification.
 
OK so I understand that rail voltage are the voltage what is going into your amp after it’s passes the bridge and the caps I have a 35-35 center tap and the voltage going that is going in my amp is -50V DC and +50 DC and if I put it loud it goes down to +- 47 for both


Jaycee I understand “resistor values for some parts of the circuit would need to be changed” but why must I get (better) transistors will it not be the same if I just add more, what’s the deference
 
Transistors have a max voltagerating, lousy 60v for the 2n3055...
You were quite lucky with your +/-50v, this gives nearly 100v drop
across the outputtransistors, 40v above the rating.
By putting in more transistors in paralell you can only increase
currentcapability, not voltagehandling. And putting transistors in
series is not that easy.
And by increasing supplyvoltage you also risk to overheat other
devices, and depending on the design biasing might get completely
wrong and blow up the whole amp.
Increasing the power would require a redesign.

Mike
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.