PCB pattern for 100W Amp

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Sometime back in the 70s Electronics for You International, an Australian magazine carried a project on a 50/100W amp. It has 1/2 pairs of 2N3055 and 2955 transistors with BD139-40 in the driver stage. I have tried to post the schematic but have some problems in doing so.

Does anybody have a downloadable pcb pattern for this amp?
Hi Shashidhar,
There was a very popular article in 70's about 100w amp from Australia known as ETI-480. Then the same designer recently redesigned it with the name digi-125. It is available on the net. If u need the pcb pattern of the above mentined circuit then let me know.
Mahendra Palesha
Hi Vivek,
20 yrs ago I built 2 ETI-480 modules onto one heatsink and fitted them into a Nikko amplifier with blown output stage - it was in the back shed and my boss gave it to me.
I used Jap flatpack output transistors, high quality capacitors with bypassing lower values, and power fed direct to the output stage (bypassing the fuses).
With 2 5-1/4" placed ontop of this amp, it ran perfectly reliably at full power at a million parties.
The sound quality was really good, everybody danced all night, and the neighbours never complained.
You should read all Paul Cambies stuff.
As an easy to build and reliable amp, and sonically decent, this one is quite okay.
If you run modern better than 3055 outputs and 50v rails and fan cooling, this amp will go quite loud.
Dick Smith and other suppliers still stock this as a kit.

Regards, Eric.
PCB Pattern for 100W Amp

Vivek, Palesha and Mr. Feedback,

Thanks all.

I shall check the sites you have mentioned.

I have designed a PCB myself on Protel for this 50/100 Amp. But I do not know how to attach the Schematic and PCB to this email page (not as a separate file). Can anyone enlighten me. I know the process -- I am a fairly computer literate chap, but I have problems with this particular site.

Good amp for the money, at the time.

Early 1978 I made a pair of the 50 watt versions of this amp and at the time a friend had a system with a Dynavector strain gauge cartridge, Crown (Amcron) IC150 preamp, DC300A power amp, and Crown/RTR electrostatics with 2x10" woofers per side. We compared the power amps and the ETI-480's (stands for Electronics Today International magazine) didn't quite have the rock solid bottom end, and the upper mids had the very, very slightest film or veil on the sound. I only had 2x4700uF ps caps and the speakers were 4 ohm but the amp was meant for 8 ohm.

The verdict? 80 percent as good, but only about 1/12 the price at the time.

Looks like this is one more amp worth investigating. But how does this amp compare (sonically) to the Zens, Project 3As, JLHs, Leach amps and so on.
Eric, yes, the site does have a lot of stuff I could learn.
Shashidhar, I too had a similar problem uploading a jpg file sometime ago.
Old Benchmark

Circlotron said:
Crown (Amcron) IC150 preamp, DC300A power amp, and Crown/RTR electrostatics with 2x10" woofers per side.
Hi Graham, as a 12yo youngster a friend of my parents had the above system.
I can still hear the jazz music with big fat plummy double bass playing in my memory.
Indeed hearing that system is one of the influences that got me interested in audio.

Regards, Eric.

PS - the panoramic control on the IC150 preamp is a very usefull circuit, and sadly missing on modern gear.
Dear Vivek & sridhar,
It is very easy to upload .jpg file. Just check the size of the image. Use the software Thumbs up or irfanview to check the size & to resize. After this u can very well post the schematic. If u need more clarification then let me know.
Mahendra Palesha
Good Starting Kit

Hi Vivek, for the money ($AUS 35 or so) this amp module with some improvements is perfectly fine for most purposes and is completely stable, well mannered, and pretty much idiot proof, and replacement parts are cheap and readily available and the pcb is easily modied as required.
If you are into playing your music loud and have decent size speakers, this one works great.

It is pretty low distortion really, and those distortions are inoffensive, and it goes into and out of overload without getting nasty, so you can run it into overdrive without cooking tweeters.
If you can find a junked 100W+100W amp chassis (late 70's, 80's) you might be able to fit these in, and you would end up with something much better than the original.

First step mod is to ditch the 2N3055/2955 and replace them with one of these pairs - " in his test the MJ 15024/15025 comes in third, with MJ21193/21194 second and the often used japanese 2SA1302/2SC3281 as the very best of the ones tested. ".

I have always liked the local feedback arrangement in the output stage and although there are other variations this is the only example of this connection that I have seen.
If you have all of Paul Cambies ETI-480 stuff you should have a good starting point.
With this amp you can do plenty of tweaking and modding and learn a lot.

Regards, Eric.
ETI 480 or DIGI 125? Which is better? This is a question comes in mind. According to author DIGI 125 is a refined model of ETI 480. Already there was a discussion about digi 125 modifications. Now atlast come to conclusion about which to assemble? This question comes in mind many times.
Mahendra Palesha
PCB Pattern for 100W Amp


I am entirely with you in your opinion regarding the ETI480 amp. Those projects were so assuring and confidence giving! On the other hand, just look at some of the recent projects that have appeared in the Elektor! With the kind of high precision resistors and caps that they require, I am sure only people in NASA can hope to build them. No doubt, one might be able to improve distortion figures by a fraction of a fraction. But at the end of the day, is it worth all that?

By the way would it be possible to replace the 2N and MJ transistors in the output stage by IRF540 and 9540 by, again, making suitable replacement in the predriver stage (say by some video transistors in the BF series in the place of the BD transistors)?

Thanks, again, for your comments.
Why overdo Amp Circuits?

I agree with you,
most complicated junk they put into design,
does provide as much trouble into circuit,
as they contribute with benefits.

Look at these small, easy built circuits
with Standard co ponents.

and all that is needed is there!


Groman doesn't like to overdo things
thinks it is a waste of time and money
Hi all,
Yes, the older circuits are so simple. You feel you can tackle it with ease.

Do we get Elektor in India because I have not seen any around. Electronics For You is becoming more of a business magazine and I stopped buying it. Tell me if there are any other electronics magazines around.
Which layout would you use for the ETI 480 50 W and 100 W versions?

palesha said:
ETI 480 or DIGI 125? Which is better?
I have never built a DIGI 125, only the ETI-480, but I reckon the '125 was originally a '480 and they kept on snipping parts out till it stopped, then they put the last one back in again! ;) The original article gave me the impression that the '125 was meant to be a dead simple amp that worked better than expected, whereas the '480 was more thoroughly done, with all the i's dotted and the t's crossed, so to speak. If you want a basis to start modding from, then I think the 480 would be best. The '125 only has limited options in this regard, e.g. no bootstrapped driver stage, (the '480 has no need - the o/p stage has voltage gain), no differential input long tailed pair (from memory), and hardly enough room on the pcb for sticking on extra stuff. The '125 doesn't have thermal bias stabilisation either, although the designer decided it wasn't warranted in this case. Buying and then modding a '125 would be like going out and buying a cheap axe, then giving it a carbon fibre handle and a titanium head. I think the '125's best feature is it's simplicity.
In ETI 480 output devices must be changed. When i used 2n 3055 etc. they were very hot. When i changed it to 2sc3858 and matching pair it was not that hot & only 1 pair to be used instead of 2 pairs of original 2n3055etc. Further the power resistors in the output stages must be more than 3 watts in indian conditions.
Next week i am going to assemble digi 125 for fun.
In the elektor book " designing audio circuits" there is one general purpose amp with just 5 devices. It is universal amp from 20~100w by changing output devices & 2 resistors for different power levels. The output devices are darlington type. If anybody has assembled the one then just let us know.
How many of us have assembled DIGI 125?
Any body assebled 100W amp from Electronics 2000 site.
Hoping of good replies from other members.
Mahendra Palesha
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