ETI 5000 MOSFET Power amp

[suzyj]

Originally posted by ocaukrell
I havent heard a 5000, BUT I have built, and am still using an AEM6000.
I opted for lower voltage transformers, giving approx 150wrms.

Very cool. Poor_lackey just sent me a scan of the AEM6005 article. Looks really nice - lots of symmetry. I suspect sourcing the matched JFETs for the input (ECG/NTE461) may be problematic - I might try bunging a Vishay U404 in instead. Certainly it's not my intention to slavishly follow Tilbrook's design, but to fiddle at the edges somewhat.

Originally posted by hifryer
I built and still own one of these amps. They sound unbelievably aweful!!! I thought it was OK when I knew no better. Mine took out very expensive tweeters when I first tried it out. It was an x MHz transmitter - turned out it was highly unstable and Tillbrook was no help at the time. Eventually solved with caps across the output devices. Blame was on inductive R's supplied by *aycar!!

I'm not surprised it sounded bad, if it was oscillating. I know from experience that fast circuits can often be difficult to tame.

Originally posted by hifryer
My take is that most such electronics mag designs even since are better but still dont sound great as they are designed by "engineers" who never listen to anything, ridicule tubes and are guided by numbers which bear almost no correlation to actual good sound.

I've gotta confess to being an engineer who ridicules tubes, and is guided by objective data, rather than feel-good garbage and marketing rubbish. I don't want my amp to sound warm, or rich, or anything of the sort. I want it to faithfully reproduce my music, and I know that the way to do that is to minimise distortion and noise.

Regards,

Suzy

[jacco vermeulen]

Originally posted by suzyj
I don't want my amp to sound warm, or rich, or anything of the sort. I want it to faithfully reproduce my music, and I know that the way to do that is to minimise distortion and noise.

Yep,
that sounds like an engineer alright.
Just when i was getting ready to propose class A.

imo, everyone in the 80s spoke about how important layout design was, and all of the designs from then would have benefitted from a better board layout. I've assembled a few designs that are similar to the 5000, it would be interesting how much better you can make something like that.
Then move on.

[macka]

I built the Tilbrook Ultra Fidelity preamp......another complex design okay but not sonically brilliant!

[ralphs99]

Hi Suzy,

You touch on a very important point, something that is often overlooked. That the implementation of a design is just as important as the design itself. Your assement of the 5000 series amp is basically correct. The design is sound as shown on the schematic. The trouble with schematics is what they don't show. The interraction of various currents (particularly ground currents) and all the parasitic elements that make or break a design.

The phyiscal implementation of this design is where there are some problems. With a few modifications the amp sounds very good. I've had one running for many years and it is an excellent performer.
Having said that, I do run it as part of multi-amp active setup, so the performance of any one amplifier in the system is less critical than if it was being used full range. But I'm in no hurry to change the 5000 for something else.

The difference between a good design and a great design is attention to detail, understanding of all the parasitic elements and thorough evaluation. Schematics only tell half the story...

Cheers,
Ralph.

[hifryer]

Dear Suzy,

You asked a question and I tried to help based on my experience in actually building, testing and listening to the amplifier.

I was also actually clever enough to not base my years of listening to it on its initial unstable state.

I haven't heard anyone suggest you should base any decisions on
" feel-good garbage and marketing rubbish" or want your amplifier to sound " warm, or rich, or anything of the sort".

What particular data are you planning to collect to prove your amplifier can "faithfully reproduce music" ????

The ETI5000 probably measures about 100 times below distortion thresholds that people have been able to demonstrate they can hear.

Perhaps you should research the numbers on all available designs and build the one with the best numbers. THD of 0.001% @ 1KHz into a resistor is achievable.

Perhaps you could use spectrum analysis and measure each individual harmonic but then you will need to decide if each of these will receive equal weight or is this more " feel-good garbage and marketing rubbish"????

Being a rigorous engineer can you devise a test that it will "faithfully reproduce music" without using music as the test???

Good luck.

cheers

[Ultima Thule]

Originally posted by suzyj
Hi all,

Ultima Thule wrote:

> Do we have any schematic we can view?

I've done a quick and dirty scan of the schematic, and bunged it on my homepage.

http://www.atnf.csiro.au/people/Suzy...on/ETI5000.jpg

It's not the sharpest, but is readable.

That was really why I was thinking of effectively repackaging the amp (with a much better board layout) and using modern parts.

Just a thought, anyway.

Cheers,

Suzy

Thanks suzy,

it's more than sharp enough for my eyes at least!

I haven't got the time for now to study it closer but at a quick glance I'm with you, repacking it with some mothern transistors was my thought too, I don't really believe in the use of lowish hfe BF469/470 to such an extent as it's used in that schematic.

Never the less an interesting input/VAS topology, at least for the eyes and as a mind exercise!

Wellcome to the board BTW!

Cheers Michael

[Terry Demol]

Originally posted by suzyj
Hi guys,

I recently inherited a gorgeous pair of Infinity RS-5b speakers (mid-80's vintage), and have dutifully replaced the surrounds on the woofers, and brought them up to scratch. My current amplifier (part of a ghastly Sharp 3 in 1 bookshelf system) is patently not up to driving them, so I've been looking for something a little better.

Looking at the specs of the current commercial Rotel, NAD, etc amplifiers in the 50-100W range, I see they all have really disappointing distortion figures, around 0.02-0.03% THD.

Then I remembered a series of articles in ETI (crappy Australian electronics magazine) on the ETI 5000 amp. It was published way back in 1981, and I remember as a teen being pretty blown away by the vanishingly low distortion figures (<0.005% or so THD).

I dutifully dug up the original magazines from the work library (I'm an RF/microwave engineer by trade, and have ready access to most things), and had a looksie. Unfortunately, it appears there's no easy source for the 2SK134/2SJ49 drivers, but I figure I can simply substitute EC10N16 and 10P16s. The BF469/470s also come up as obsolete, but I'm thinking the BF722/723 pair would be a reasonable substitution.

What are people's thoughts on this amp? I seem to recall Tilbrook did a follow-up amp (for AEM?), but we don't have AEM in the library, so that's the most up-to-date design I can easily lay my hands on...

I'm particularly impressed with the differential gain stages, all the way out to the power FETs. That's clearly the ducks guts for suppressing 2nd harmonic distortion. However, it does appear to use a hell of a lot of overall feedback, and methinks the proliferation of small caps kicking around the schematic indicate that it had some stability concerns.

Still, I'm betting that many of the foibles could be ironed out with a decent board layout, with more modern (SMD) passives, for example, and a proper 2 layer PTH board.

Cheers,

Suzy

Hi Suzy,

Good to see you here.

Those RS5 speakers you have can sound very good, in fact I have
a pair sittting in the next room and they were a reference for quite
a few years, albeit somewhat modded.

One thing about the RS5's is they can sound a bit lean and can lack
some timber if matched with the wrong source or amp. The emit
tweeters can also be very revealing and sound harsh with
some SS amps. On the plus side, when they are mated with the
right components they can sound awesome.

I have to agree with some of the views here that the numbers
will tell very little about the sound. I can vouch for this with a lot of
experience and not just in home reply but building front ends for
professional recording engineers doing live stereo to digital
recordings. Front ends (mic pre's) that used discrete zero feedback
circuitry sounded much more real than other designs with ultra
low distortion opamps... the engineers preferred the more lifelike
sound of the (slightly) worse measuring topology!

This has been discussed ad- nauseum here and a search will pull up
many of posts covering different views on this....plenty of heated
discussion too!

Back to the RS5's, I believe the AKSA kit amps from Hugh Dean
will be a very good match for them. In fact Hugh sent me up some
modules recently and I have been listening to them for a couple
of weeks. They are shockingly good for the price.

More importantly, they shouldl beautifully match the characteristics
of the RS5's.

If you would like to have a listen to the AKSA modules PM me, as
I am also in Sydney.

Cheers,

Terry

[nigeljking]

Jaycar are still carrying old stock of these transistors (I picked up some early in the week).

But if you want better designs from magazines, check out Elektor Electronics. They have published many designs over the years. They published a high end design last year (but only 35W) which has a lot of attention paid to the various amplification stages. You can purchase pre made PCBs which are beautfully made. I am still running some amps from 82 that used the 135/50 MOSFET pair.

I have not been much of a fan of the Aus designs with EA being particularly dubious (prone to large scale IP theft).

Nigel

[awpagan]

Originally posted by nigeljking


I have not been much of a fan of the Aus designs with EA being particularly dubious (prone to large scale IP theft).

Nigel

i would like to know more??

allan

[AKSA]

I don't know about IP theft, but certainly the Australian magazine amps have all been designed with low measured distortion the principle concern.

This has resulted in very good specs but mediocre sound quality as auditioning did not appear to be part of the process.

I do not criticise them. They have only months to develop their circuits, their time and budget is very limited, and a large proportion of the effort is given over to the journalistic aspects. Given these considerations, it's commendable they do the job they do. There have been some seminal designs; the AEM6000 was a good sounding amp, for example.

Cheers,

Hugh