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
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
suzyj said:
Even if these 0.02-03% THD figures are done with a dummy load 8/4 Ohms resistor
(sometimes low inductance resistance)
I would not feel bad about them.
If I build such an amplifier and get those figures
I would be very very happy
... and now we are not talking real life numbers
... as they are on the other side of loudspeaker
...
Suzy,
I built one of these in the early eighties. It was very ordinary, with a shrill, metallic sheen to it. Didn't like it at all. They were, as you say, extremely unstable if not built well, a sure sign of compromised design.
Suppressing H2 is not the way to go. You want to suppress H4 and beyond, and you need to really control the crossover event well to reduce listener fatigue.
High feedback is fine as long as the voltage amp, driver and output devices are fast and lag comp is spot on. Slow devices are more difficult to extract good performance. You need at least 100MHz voltage amps and 30MHz output devices.
The double diff design is not wonderful for bandwidth. SE designs will give much more speed.
The AEM6000 from Tillbrook was a much better sounding amplifier.
Hope this is helpful,
Cheers,
Hugh
I built one of these in the early eighties. It was very ordinary, with a shrill, metallic sheen to it. Didn't like it at all. They were, as you say, extremely unstable if not built well, a sure sign of compromised design.
Suppressing H2 is not the way to go. You want to suppress H4 and beyond, and you need to really control the crossover event well to reduce listener fatigue.
High feedback is fine as long as the voltage amp, driver and output devices are fast and lag comp is spot on. Slow devices are more difficult to extract good performance. You need at least 100MHz voltage amps and 30MHz output devices.
The double diff design is not wonderful for bandwidth. SE designs will give much more speed.
The AEM6000 from Tillbrook was a much better sounding amplifier.
Hope this is helpful,
Cheers,
Hugh
Nad
NAD make Great Amps, we have one, and it has fantastic sound
Try The Silicon Chip, Studio 350 Power Amplifier Module It also has some very good figures. Only Problem is that it has 8 $15AU each transistors(4x MJL21193 and 4x MJL21194). It has a very impressive heatsink on the back of it.
I am Actully in the process of make one at the moment.
NAD make Great Amps, we have one, and it has fantastic sound
Try The Silicon Chip, Studio 350 Power Amplifier Module It also has some very good figures. Only Problem is that it has 8 $15AU each transistors(4x MJL21193 and 4x MJL21194). It has a very impressive heatsink on the back of it.
I am Actully in the process of make one at the moment.
I have heard the ETI5000 amp, built by a friend with the original PCB, Noble output resistors, heat-sink/face plate all supplied by Jaycar from Australia; in other words, the amp was as nearly as good as the one made by Dave Tillbrook himself.
As to the sound, nothing to write home about.
In this very forum, try the SymAssym, one of the Pass amps or Hugh's kits - you will not be disappointed.
If you have the skills and competence, you could make the Stochino amp. It can be rated among the very best. I have made a few of these.
As to the sound, nothing to write home about.
In this very forum, try the SymAssym, one of the Pass amps or Hugh's kits - you will not be disappointed.
If you have the skills and competence, you could make the Stochino amp. It can be rated among the very best. I have made a few of these.
Suzy,
I have scanned copies of the 6000 articles, and status monitor (much thanks to the hard work of Janusz) and also the 6006 dc servo board (thanks to Rherber1).
The scan qualities are good, but as a result the files are not small.
If you would like me to email them to you?
then let me know
poor_lackey@hotmail.com
Also
If you want to avoid the hassel of making the PCB's.
I think they might still be avaible from
www.rcsradio.com.au
Tony
I have scanned copies of the 6000 articles, and status monitor (much thanks to the hard work of Janusz) and also the 6006 dc servo board (thanks to Rherber1).
The scan qualities are good, but as a result the files are not small.
If you would like me to email them to you?
then let me know
poor_lackey@hotmail.com
Also
If you want to avoid the hassel of making the PCB's.
I think they might still be avaible from
www.rcsradio.com.au
Tony
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.Jackson/ETI5000.jpg
It's not the sharpest, but is readable.
ASKA wrote:
> I built one of these in the early eighties. It was very ordinary,
> with a shrill, metallic sheen to it. Didn't like it at all. They were,
> as you say, extremely unstable if not built well, a sure sign of
> compromised design.
> Suppressing H2 is not the way to go. You want to suppress H4
> and beyond, and you need to really control the crossover event
> well to reduce listener fatigue.
Aye - I can see what you're getting at. Sounds like yours might have had some nasty higher order components. Certainly I would think keeping good phase margin over three stages isn't a trivial task (especially with the sort of dubious parts one buys from the local Jaycars), and the output MOSFETs are plenty fast, so I'd imagine they'd not be at all forgiving of poor layout or excessive inductance.
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
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.Jackson/ETI5000.jpg
It's not the sharpest, but is readable.
ASKA wrote:
> I built one of these in the early eighties. It was very ordinary,
> with a shrill, metallic sheen to it. Didn't like it at all. They were,
> as you say, extremely unstable if not built well, a sure sign of
> compromised design.
> Suppressing H2 is not the way to go. You want to suppress H4
> and beyond, and you need to really control the crossover event
> well to reduce listener fatigue.
Aye - I can see what you're getting at. Sounds like yours might have had some nasty higher order components. Certainly I would think keeping good phase margin over three stages isn't a trivial task (especially with the sort of dubious parts one buys from the local Jaycars), and the output MOSFETs are plenty fast, so I'd imagine they'd not be at all forgiving of poor layout or excessive inductance.
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
I havent heard a 5000, BUT I have built, and am still using an AEM6000.
I opted for lower voltage transformers, giving approx 150wrms.
In a system comprising of ;
Musical fidelity x-ray cd,
Nakamichi st-7,
Nakamichi ca-7,
Home built JBL's (15" 16 ohm, horn mid with lens, slot loaded tweeter)
Comparason between the AEM 6000 and a QUAD 522 Pro, (modified - Bypass input transformers).
AEM has more detail, much better control of the speakers through out the spectrum, slightly deeper bass.
Cannot find anything negative about it at all.
** NOTE **
tilbrook later brought out a 6005 version.
These modules were designed to replace the modules in the 5000 case, an upgrade as it were.
Although they had slighly worse (on paper) performance than the original 6000, it was still (apparently) a massive step foward for those with the 5000.
Personly, for a cheap bang for buck amp, I'd be looking for a quad 405 and doing a few minor mods.
should be able to find one in aus for $200-$400.
The 6000 as a kit was around the $800 mark, when I built mine it cost me about $1,300, due to building it bit by bit and using better parts.
Oh, I still have all the original articles too. including the 'statis monitors' (speaker protectors) and the add on dc servo boards.
I opted for lower voltage transformers, giving approx 150wrms.
In a system comprising of ;
Musical fidelity x-ray cd,
Nakamichi st-7,
Nakamichi ca-7,
Home built JBL's (15" 16 ohm, horn mid with lens, slot loaded tweeter)
Comparason between the AEM 6000 and a QUAD 522 Pro, (modified - Bypass input transformers).
AEM has more detail, much better control of the speakers through out the spectrum, slightly deeper bass.
Cannot find anything negative about it at all.
** NOTE **
tilbrook later brought out a 6005 version.
These modules were designed to replace the modules in the 5000 case, an upgrade as it were.
Although they had slighly worse (on paper) performance than the original 6000, it was still (apparently) a massive step foward for those with the 5000.
Personly, for a cheap bang for buck amp, I'd be looking for a quad 405 and doing a few minor mods.
should be able to find one in aus for $200-$400.
The 6000 as a kit was around the $800 mark, when I built mine it cost me about $1,300, due to building it bit by bit and using better parts.
Oh, I still have all the original articles too. including the 'statis monitors' (speaker protectors) and the add on dc servo boards.
ETI 500 power amp
I built and still own one of these amps.
They sound unbelievably aweful!!! I thought it was OK when I knew no better.
My conclusion is that Tillbrook had no idea. Just another guy copying application notes and relying solely on traditional THD measurements!!
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!!
Steer well clear of and dont waste money on S/H.
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.
Rely on guys like Hugh Dean (AKSA) , Nelson Pass, Bruce Rozenblitz and Jim Hagerman. They care, are smart enough to know what they don't know and have built and refined over many years.
cheers,
I built and still own one of these amps.
They sound unbelievably aweful!!! I thought it was OK when I knew no better.
My conclusion is that Tillbrook had no idea. Just another guy copying application notes and relying solely on traditional THD measurements!!
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!!
Steer well clear of and dont waste money on S/H.
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.
Rely on guys like Hugh Dean (AKSA) , Nelson Pass, Bruce Rozenblitz and Jim Hagerman. They care, are smart enough to know what they don't know and have built and refined over many years.
cheers,
mediocre or not a lot of these eti 5000 amps were built.
Having said that they were one of those amps that suffered from the so called MOSFET mist, the central imaging,,, well there was none... was very poor, the AEM 6000 was much better and very stable, but again suffered from MOSFET mist.
One needs to remember back then MOSFETs had just been released and no body knew how to drive them Properly. 20 odd years down the track we have the benefit of hind sight and the Experience and knowledge of those that have gone before us.
I have a lot of respect for David Tillbrook as he was one of the founding designers of some good amplifiers for their time.
and he for me was an inspiration to getting into amplifier design.
Dispite their problems, The question must be asked where were you in Jan, Feb 1981. I didn't see any ones name here in ETI or EA or AEM and I have read everyone of them...
Flame Suit On....
Having said that they were one of those amps that suffered from the so called MOSFET mist, the central imaging,,, well there was none... was very poor, the AEM 6000 was much better and very stable, but again suffered from MOSFET mist.
One needs to remember back then MOSFETs had just been released and no body knew how to drive them Properly. 20 odd years down the track we have the benefit of hind sight and the Experience and knowledge of those that have gone before us.
I have a lot of respect for David Tillbrook as he was one of the founding designers of some good amplifiers for their time.
and he for me was an inspiration to getting into amplifier design.
Dispite their problems, The question must be asked where were you in Jan, Feb 1981. I didn't see any ones name here in ETI or EA or AEM and I have read everyone of them...
Flame Suit On....
The Saint said:mediocre or not a lot of these eti 5000 amps were built.
Having said that they were one of those amps that suffered from the so called MOSFET mist, the central imaging,,, ................. I didn't see any ones name here in ETI or EA or AEM and I have read everyone of them...
Flame Suit On....
Good post, put into perspective as you have done many Aussies have respect for DT, indeed he can be credited for DIY Audio being very strong here. As a younger person I remember waiting for his next contribution and indeed the next ETI / EA / AEM publication.
Your point about breaking new ground with these new "MOSFETS" is also well defined and I guess everything has a beginning. My only real point is that I made only simple changes to the recommended layout and the performance improved significantly. So it may have been a compromise made to suit a kit-set approach or some other market criteria.
But as you say, DT will always be known for his contributions and the innovations he provided.
Cheers
I would point out the SKA at least to my earrs is one of the better simple mostfet amps and no doubt there are others.
There is no hint of that mostfet mist at all in this instance nor that hard metalic or glare sound of the BJTs.
I think the more modern output devices have a lot to do with it and also the designers ability to hardness and optimise their performance characteristics.
Macka
There is no hint of that mostfet mist at all in this instance nor that hard metalic or glare sound of the BJTs.
I think the more modern output devices have a lot to do with it and also the designers ability to hardness and optimise their performance characteristics.
Macka
Yes, I should be thankful that DT made something available to build. I got a real kick out of it until someone let me hear the real Hi-Fi of the time but of course this was very expensive and well beyond my abilities to copy at that time.
There wasn't a lot of original design in the ETI5000 - he really just packaged the published Hitachi application notes and his bit where he decided that the two transformers were better in parallel than used as a supply per channel was most likely a poor call.
I also built his overly complex pre-amp and this was detailed but harsh. cascaded 5534 op-amps. Again knowing what we know today it is easy to do better re power supplies, bypassing and cap quality etc.
My point is that the Silicon Chip type designers refuse to acknowledge a lot of this and consider it lunatic tweak fashion stuff as things measure well without it!!
I agree we have much better devices to play with today and at least part of our advance is down to this.
As a result, a very simple traditional design can sound very fine if impecably implemented.
DIY has come a long way and most enthusiasts now expect close to the state of the art!! Audio Express and forums like this are generally a long way ahead of Elektor or S.C.
cheers
There wasn't a lot of original design in the ETI5000 - he really just packaged the published Hitachi application notes and his bit where he decided that the two transformers were better in parallel than used as a supply per channel was most likely a poor call.
I also built his overly complex pre-amp and this was detailed but harsh. cascaded 5534 op-amps. Again knowing what we know today it is easy to do better re power supplies, bypassing and cap quality etc.
My point is that the Silicon Chip type designers refuse to acknowledge a lot of this and consider it lunatic tweak fashion stuff as things measure well without it!!
I agree we have much better devices to play with today and at least part of our advance is down to this.
As a result, a very simple traditional design can sound very fine if impecably implemented.
DIY has come a long way and most enthusiasts now expect close to the state of the art!! Audio Express and forums like this are generally a long way ahead of Elektor or S.C.
cheers
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