Terry Demol said:
I, and plenty of others, can design an amp that gets around 0.001%
or less THD at close to full power right up to 20kHz.
But there's not much point in buying or building an amp that you
don't want to listen to.
Terry,
I think Suzy's point is purely in creating an amp that is as faithful as can be to the source signal - hence the goal of lowest distortion, good bandwidth, high damping factor etc - one that will, if the source signal is bad, essentially produce a sound that you don't want to listen to.
To me, the question really is - is that "other" amplifier you talk about - the one that makes you want to sing, puts a lump into your throat and brings out the goose-bumps whenever you put on your favorite song - producing sonics that were never in the recording in the first place? Or is it the other way around, where the ultra-linear amplifier which measures well is actually the one creating signals that aren't there?
This reminds me of the long on-going debate between the use of tubes vs transistors. Single-ended tube amplifiers, running with 3% distortion, sounding sweeter, warmer, fatter than a solid-state amp. Which would you go with?
Cheers!!
Clem
ps: I certainly hope the debate is not between what sounds "Good" versus what sounds "Right"! Somehow I believe it is not, because a live band embodies both. Could the problems lie higher up in the recording chain, that somehow a higher-distortion amplifier manages to put back what is lost?
"This reminds me of the long on-going debate between the use of tubes vs transistors."
No please not the never ending debate.
the eti5000 was a 1980's design.
compare it to other amps that vintage, price range etc.
friends and I built these amps and they worked very well and a couple were really flogged hard (very large building).
learn't a lot.
stable yes implementation.
audiophile quality? depends what you compare them too. (price range)
the eti6000 was done to improve the high frequency.
Havn't listened to an aksa so cannot comment.
the eti-6000 preamp ok but the ME-25 killed it.
as for an amp adding sonics? I thought they should amplify the signal that they are given.
change the source or speakers for flavor.
Being the best preamp and amp are the ones you don't hear.
Most people will buy systems they can afford, company's make to these price ranges
Others willing to learn or play refer this site (and other sites)
And many thanks to the more educated who give so much help and direction. not all are EE's
I'm sorry to say not all EE's have silk ears but they do have there views and tastes.
As for the ETI-5000
any ideas of improving it?
there maybe some still running.
mine is. been bridged and relegated to subwoofer amp.
allan
No please not the never ending debate.
the eti5000 was a 1980's design.
compare it to other amps that vintage, price range etc.
friends and I built these amps and they worked very well and a couple were really flogged hard (very large building).
learn't a lot.
stable yes implementation.
audiophile quality? depends what you compare them too. (price range)
the eti6000 was done to improve the high frequency.
Havn't listened to an aksa so cannot comment.
the eti-6000 preamp ok but the ME-25 killed it.
as for an amp adding sonics? I thought they should amplify the signal that they are given.
change the source or speakers for flavor.
Being the best preamp and amp are the ones you don't hear.
Most people will buy systems they can afford, company's make to these price ranges
Others willing to learn or play refer this site (and other sites)
And many thanks to the more educated who give so much help and direction. not all are EE's
I'm sorry to say not all EE's have silk ears but they do have there views and tastes.
As for the ETI-5000
any ideas of improving it?
there maybe some still running.
mine is. been bridged and relegated to subwoofer amp.
allan
ETI 5000 and FAITHFUL vs NICE
Hi all,
I built ETI 5000 back in the early 1980s. In the end I discarded most parts, which came with the kit -Jaycar version. With non-inductive resistors around power mosfets, matched upgraded transistors (except for the output mosfets), best caps available in those times and a few design mods the amp worked well (no oscillation or stability problems) and "sounded" not bad in my subjective opinion. AEM 6000/6005s were notably better from the start but also benefited from quality parts.
Now, back to SOUND. At the very end of 1970s I was involved with – let’s call it music/recording industry. In search for the most faithful speakers (for active systems) we involved musicians. In that particular case their main task was to identify the most faithful widerange speaker to be used as midrange. They were comparing various recordings of their voices and performances with their own live performance.
The first interesting thing was that with a couple of speakers, considered the best, some of them voted speaker “A” as the most FAITHFUL and some voted for speaker “B” although they all said that both speakers were close. Obviously, their individual “brain/ear systems” were not identical. In other words human brains appeared to be subjective in this case. That made us curious.
Anyway, a few further tests, involving non-musicians as well, produced even more interesting results. A number of people who claimed to hear a difference between say two amps or preamps and described their sound characteristics (as long as they knew which one was playing) could not tell them apart in ABC or AB tests on the same music material. That happened with two or three amps and was especially prominent with preamps. Musicians had no problem to tell speakers apart but in a few cases some could not tell preamps apart in blind tests.
To conclude, it looks that our brains are inventive sometimes. When they are told that “things” are different they try to find differences including illusory but when forced to tell apart phenomena in blind tests they sometimes fail. Interesting, isn’t it?
Cheers,
PS My preference goes to the most FAITHFUL reproduction rather than nice SOUNDING.
Hi all,
I built ETI 5000 back in the early 1980s. In the end I discarded most parts, which came with the kit -Jaycar version. With non-inductive resistors around power mosfets, matched upgraded transistors (except for the output mosfets), best caps available in those times and a few design mods the amp worked well (no oscillation or stability problems) and "sounded" not bad in my subjective opinion. AEM 6000/6005s were notably better from the start but also benefited from quality parts.
Now, back to SOUND. At the very end of 1970s I was involved with – let’s call it music/recording industry. In search for the most faithful speakers (for active systems) we involved musicians. In that particular case their main task was to identify the most faithful widerange speaker to be used as midrange. They were comparing various recordings of their voices and performances with their own live performance.
The first interesting thing was that with a couple of speakers, considered the best, some of them voted speaker “A” as the most FAITHFUL and some voted for speaker “B” although they all said that both speakers were close. Obviously, their individual “brain/ear systems” were not identical. In other words human brains appeared to be subjective in this case. That made us curious.
Anyway, a few further tests, involving non-musicians as well, produced even more interesting results. A number of people who claimed to hear a difference between say two amps or preamps and described their sound characteristics (as long as they knew which one was playing) could not tell them apart in ABC or AB tests on the same music material. That happened with two or three amps and was especially prominent with preamps. Musicians had no problem to tell speakers apart but in a few cases some could not tell preamps apart in blind tests.
To conclude, it looks that our brains are inventive sometimes. When they are told that “things” are different they try to find differences including illusory but when forced to tell apart phenomena in blind tests they sometimes fail. Interesting, isn’t it?
Cheers,
PS My preference goes to the most FAITHFUL reproduction rather than nice SOUNDING.
Oh if only it were so simple. I disagree with Hugh, engineering jargon is not an issue - most just keep repeating the same old mantra without any scientific method which is "if I haven't measured it, it doesnt exist". Or "this measure has improved so without regrad to all the things I dont / can't measure, it must sound better".
They ONLY meausure what is easy to measure and are very similar and in this regard are very similar to the man in the night looking for a lost coin under a street light and later admitting it is not near where he lost it but the light is good!!
Let's make one thing clear.
I, for one, am NOT advocating, "nice", "warm", "enhanced"or in other way coloured performance from an amplifier.
The amplifier for me is the one which most faithfully comes close to my experience of live music and gives me the best emotional response to this music as a result. This to me is "accurate". I dont want to add, remove or ameliorate anything!!
Unfortunately, via many, many years of listening to and enjoying reproduced music I have found there is MUCH more to this than a few crude so called objective measurements. And I for one, have no interest in labels, reviews, brand names, price or "engineering" statistics. I do not read "Hi-Fi" magazines.
I am fully aware of "scientific method" and particularly its major limitations. One being the staus quo and politics of the current scientific establishment in any age. It really lacks scope when it must encompass subjective human experience. There is no room here and no point in debating the total inadequacies of A:B testing and its ilk. Its objectives are honourable but most implementations total failures. A far better test is to live with some piece of equipment for a long period of time then have someone ask you to pay for it or they will take it away!
We talk of amplifiers here but loudspeakers, rooms and sources lag far behind. Most loudspeakers are so bad that here THD measurements ( almost never published) might be very useful but we are talking close to whole percentage points!!!!!!
cheers,
They ONLY meausure what is easy to measure and are very similar and in this regard are very similar to the man in the night looking for a lost coin under a street light and later admitting it is not near where he lost it but the light is good!!
Let's make one thing clear.
I, for one, am NOT advocating, "nice", "warm", "enhanced"or in other way coloured performance from an amplifier.
The amplifier for me is the one which most faithfully comes close to my experience of live music and gives me the best emotional response to this music as a result. This to me is "accurate". I dont want to add, remove or ameliorate anything!!
Unfortunately, via many, many years of listening to and enjoying reproduced music I have found there is MUCH more to this than a few crude so called objective measurements. And I for one, have no interest in labels, reviews, brand names, price or "engineering" statistics. I do not read "Hi-Fi" magazines.
I am fully aware of "scientific method" and particularly its major limitations. One being the staus quo and politics of the current scientific establishment in any age. It really lacks scope when it must encompass subjective human experience. There is no room here and no point in debating the total inadequacies of A:B testing and its ilk. Its objectives are honourable but most implementations total failures. A far better test is to live with some piece of equipment for a long period of time then have someone ask you to pay for it or they will take it away!
We talk of amplifiers here but loudspeakers, rooms and sources lag far behind. Most loudspeakers are so bad that here THD measurements ( almost never published) might be very useful but we are talking close to whole percentage points!!!!!!
cheers,
suzyj said:Maybe what's needed is a dictionary, so that engineers can understand audiophile-speak, and audiophiles can understand engineering jargon.
Here's some (slightly tongue in cheek) definitions I've just chucked together over lunch:
Warm: Excessive second order distortion.
Tinny: Excessive third order distortion.
Fatiguing: Excessive fourth (and above?) order distortion, or intermods.
Transparent: Low THD and IMD.
Good imaging: High slew rate - low IMD.
Noisy: Well here's one we can all agree on
Muddy: Poor high frequency response, poor slew rate, excessive IMD.
Any other thoughts?
Cheers,
Suzy
Hi Suzy,
Good to see a bit of humour about the place. Don't worry,
plenty of audiophiles can have a laugh at themselves.
In fact, I have a friend who has an incredible sounding system,
very smart, well educated guy. His unit name for the smallest
perceivable sonic incremental change is called a 'w@nk'.
All this talk of soft/hard/warm/lean etc is just jargon... we
don't think too much about it... and you'd be forgiven for
thinking that some of us are a bunch non-tech neanderthals.
So.......
What have you decided to do? There's lots of talk here
but no real decisions.
Are you going to go with a solid recommendation or are you
going to shoot for the lowest numbers and see what transpires?
Either way, you are going to have fun and learn something.
If you are adament that low numbers are a must, I think
Greg Ball's SKA is probably a good choice. It has had some great
reports here and AFAIK it does measure very well.
Maybe Greg can post some FFT spectrum plots here if he would be
so kind.
How it will sound with the RS5's I'm not sure. They are pretty
fussy speakers WRT what you drive them with.
If your amp sounds a bit cold they will not like it at all.....
oooops I slipped.... did you have a descriptor up there
for cold
Cheers,
Terry
Harman Intl did some consumer research recently and following a study they evolved a set of criteria for evaluation of what listeners from test sample saw as favourable and unfavourable preferences.
These traits were then subject to ruthless scientific appraisal and analysis in terms of marketing (product appearance), acoustics and loudspeaker characteristics.
The upshot of this very expensive research was an insight into consumer demographics, their preferences and from an engineering perspective what was required produce product characterstics that met and agreed with these preferences.
Unfortunately, only large corporations can afford such research and I think this is why it is largely a hit and miss affair for what is in many ways boutique "hi end" amplifier industry.
While some firms may do consumer surveys and apply scientific analysis, many no doubt apply their designers years of collective experience and weight this against competitor offerings and specifications so as their own product offering has that certain characteristic (sound) that a consumer will associate with the brand and marketing hype.
We then see the lead designer sell-in the illusion of what he and firms wants the customer to believe as the correct set of characteristics before the customer hears the product.
The customer clearly hears these characteristics on audition and this gives credibility to the designers re-sales pitch and with some positive renforcement the sale is closed.
None of this of course means the customer is buying the best or right amplifier with so many amplifiers being painted as offering utopia by their designers. Before long the designers reach such a status that they take on a hierarchy mantle in the buyer decision making process and we see customer being led purely by what they are told.
I am sure this post will un nerve many designers if they read it and so it should. Its called misleading and deceptive conduct.
When I attended a New York Stereophile Show in 2004 I overheard several hi profile industry figures bragging about who's illusion of nirvana was winning the most deals among well healed New Yorkers.
It therefore might be interesting and wise to compare a range of amplifers (without the designers input) by a sample group (blind tested) and analyse their responses.
Happy listening
Macka
These traits were then subject to ruthless scientific appraisal and analysis in terms of marketing (product appearance), acoustics and loudspeaker characteristics.
The upshot of this very expensive research was an insight into consumer demographics, their preferences and from an engineering perspective what was required produce product characterstics that met and agreed with these preferences.
Unfortunately, only large corporations can afford such research and I think this is why it is largely a hit and miss affair for what is in many ways boutique "hi end" amplifier industry.
While some firms may do consumer surveys and apply scientific analysis, many no doubt apply their designers years of collective experience and weight this against competitor offerings and specifications so as their own product offering has that certain characteristic (sound) that a consumer will associate with the brand and marketing hype.
We then see the lead designer sell-in the illusion of what he and firms wants the customer to believe as the correct set of characteristics before the customer hears the product.
The customer clearly hears these characteristics on audition and this gives credibility to the designers re-sales pitch and with some positive renforcement the sale is closed.
None of this of course means the customer is buying the best or right amplifier with so many amplifiers being painted as offering utopia by their designers. Before long the designers reach such a status that they take on a hierarchy mantle in the buyer decision making process and we see customer being led purely by what they are told.
I am sure this post will un nerve many designers if they read it and so it should. Its called misleading and deceptive conduct.
When I attended a New York Stereophile Show in 2004 I overheard several hi profile industry figures bragging about who's illusion of nirvana was winning the most deals among well healed New Yorkers.
It therefore might be interesting and wise to compare a range of amplifers (without the designers input) by a sample group (blind tested) and analyse their responses.
Happy listening
Macka
Wooo Hooo!
Yes, aren't marketing and consumer tests marvelllous!
This is how we first got CD's as "perfect sound forever"
and then "proved" we cant hear the compression on Mini Discs
culminating in the wonders of MP3!!! Descent into hell?
These same people previously promoted the wonders of 1KHz THD into a resistor specs!! So the "cognisenti" could spec read and know which amp was best!
I'm the first to admit the problems with subjectivism are legion - not the least of which is hearing what you want to hear from thoughts dropped in your head!
British Hi-Fi mag readers being among the most gullible. Ivor at Linn was a master at this - almost mass hypnotism. The guy at Naim tried to follow and we got evil amps full of so called "PRAT" BS.
I was once trying to promote an amplifier to a highly successful high-end Hi-Fi salesman and he told me it didn't matter to him what it sounded like, just make sure it looks very different and it is not yet another plain black box and he would sell it OK.
Now Plasma TV screens...........
The guy who buys the Audi A4 will buy a NAD system.
The biggest sellers are the 2nd most expensive and second cheapest wines on the menu!
so, how many watts are your speakers???
Hell, maybe measuring distortion isn't such a sin?
Cheers
( no one ever got fired for buying IBM ;-)
Yes, aren't marketing and consumer tests marvelllous!
This is how we first got CD's as "perfect sound forever"
and then "proved" we cant hear the compression on Mini Discs
culminating in the wonders of MP3!!! Descent into hell?
These same people previously promoted the wonders of 1KHz THD into a resistor specs!! So the "cognisenti" could spec read and know which amp was best!
I'm the first to admit the problems with subjectivism are legion - not the least of which is hearing what you want to hear from thoughts dropped in your head!
British Hi-Fi mag readers being among the most gullible. Ivor at Linn was a master at this - almost mass hypnotism. The guy at Naim tried to follow and we got evil amps full of so called "PRAT" BS.
I was once trying to promote an amplifier to a highly successful high-end Hi-Fi salesman and he told me it didn't matter to him what it sounded like, just make sure it looks very different and it is not yet another plain black box and he would sell it OK.
Now Plasma TV screens...........
The guy who buys the Audi A4 will buy a NAD system.
The biggest sellers are the 2nd most expensive and second cheapest wines on the menu!
so, how many watts are your speakers???
Hell, maybe measuring distortion isn't such a sin?
Cheers
( no one ever got fired for buying IBM ;-)
Terry Demol said:
I've decided to go with a later amp by Tilbrook, called the AEM6000, but modified to use SMD transistors in the front end (U404 JFET cascoded with an MMBTA06).
Oh, and also using flatpack (EC10N16/10P16) power FETs.
I've laid it out using Beyschlag metal film MELF resistors (we use them at work for RF use, and they're nice), and a mix of polyester and mica caps, depending on value (except for the power supply caps, which are 3 x 4700uF 105 degree electrolytics for each rail, and live on the PCB with the other parts).
The whole thing is on a 6.2 x 3.5 inch double sided PCB, with the FETs and driver transistors (MJE340/350) underneath.
I'll also drive it from about 5V RMS maximum (from a PGA2310 volume control on the preamp board), which means I can use more local feedback, and linearise things up a little better.
They're my thoughts, anyway. The topology is set (having done the layout), the component values may change
So I guess my goal is as good an objective performance as I can muster, with a nod to the subjective people in the use of mica/poly capacitors, and using mainly local feedback rather than global to keep things linear.
They're my thoughts, anyway
Comments are more than welcome, but I reserve the right to filter any comments through my prejudices.Terry Demol said:
If you are adament that low numbers are a must, I think
Greg Ball's SKA is probably a good choice. It has had some great
reports here and AFAIK it does measure very well.
Maybe Greg can post some FFT spectrum plots here if he would be
so kind.
How it will sound with the RS5's I'm not sure. They are pretty
fussy speakers WRT what you drive them with.
If your amp sounds a bit cold they will not like it at all.....
oooops I slipped.... did you have a descriptor up there
for cold
<grin> But of course it'll sound cold, as cold is the opposite of warm, and warm means excessive second order harmonic distortion. Given that my goal is the lowest distortion figures I can muster, it must therefore be cold.
Cheers,
Suzy
Hi suzyj
You are using the Exicon devices.
What was the cost of them?
I can supply the Semelab devices both Single and Dual die types
well under Exicon prices.
Its not well known but Semelab supply all their die to Exicon.
So when you get Exicon devices you are actually buying Semelab.
We are actually buying Semelab die and having it packaged into our own devices.
Here is a diagram of the first package we will be producing it will have 4 x N-channel devices in one pack, later we will be producing 8 die into a similar pack.
These will be used in my Commercial production amplifiers.
If you are interested email me and I can give you a quote.
You are using the Exicon devices.
What was the cost of them?
I can supply the Semelab devices both Single and Dual die types
well under Exicon prices.
Its not well known but Semelab supply all their die to Exicon.
So when you get Exicon devices you are actually buying Semelab.
We are actually buying Semelab die and having it packaged into our own devices.
Here is a diagram of the first package we will be producing it will have 4 x N-channel devices in one pack, later we will be producing 8 die into a similar pack.
These will be used in my Commercial production amplifiers.
If you are interested email me and I can give you a quote.
THD versus good sounding!
For those interested in why THD measurements have been proven not to work as a key indicator of amplifier quality.
I suggest you read:
Audio, Acoustics and Perception by Earle Geddes.
Chapter 4 Measurement
Measuring non linear effects p72 - 75
This is online at: gedlee.com/audio.htm
cheers
For those interested in why THD measurements have been proven not to work as a key indicator of amplifier quality.
I suggest you read:
Audio, Acoustics and Perception by Earle Geddes.
Chapter 4 Measurement
Measuring non linear effects p72 - 75
This is online at: gedlee.com/audio.htm
cheers
Hi Terry
Yes it will and not only that because the devices are very close
together they will track thermally much better.
The die are mounted onto a ceramic substrate which help a hugh amount in getting the heat out of the package and what I have not mentioned is there is a thermistor in the pack as well for thermal monitoring and or management.
Yes it will and not only that because the devices are very close
together they will track thermally much better.
The die are mounted onto a ceramic substrate which help a hugh amount in getting the heat out of the package and what I have not mentioned is there is a thermistor in the pack as well for thermal monitoring and or management.
The Saint said:
Very interesting.
What sort of junction to case thermal impedance does this acheive?
It must be getting prettty low.
Also, if you don't mind me asking, what is the total resulting
transconductance at say 0.5A?
Are these only N channel devices, is there a P available?
Cheers,
Terry
Hai Anthony,
The devices you are packaging together with Semelab die look good. You have mentioned about the ceramic substrate that helps with thermal issues. But aren't you packaging too many devices which may result in a hot spot in the ceramic substrate itself or the heat sink for that matter; in other words, the spread of the devices within one package makes for a denser package that might negate the benefits of the ceramic substrate.
If we take the one with 4 x N-channel devices in one pack and run them in typical Class-A mode/conditions, will they be able to withstand the rigour and then what about device lifespan?
Nevertheless, a great effort on your part. And it is good to see you here active again.
Cheers,
The devices you are packaging together with Semelab die look good. You have mentioned about the ceramic substrate that helps with thermal issues. But aren't you packaging too many devices which may result in a hot spot in the ceramic substrate itself or the heat sink for that matter; in other words, the spread of the devices within one package makes for a denser package that might negate the benefits of the ceramic substrate.
If we take the one with 4 x N-channel devices in one pack and run them in typical Class-A mode/conditions, will they be able to withstand the rigour and then what about device lifespan?
Nevertheless, a great effort on your part. And it is good to see you here active again.
Cheers,
Hi Terry and Samuel
I don't know exactly the thermal resistance between the die
and substrate at this time as the package is still in development
and the guys in spain are handling that kind of thing.
But I am told it will be very good indeed.
The pack is designed for class B-AB amplfiers at this stage.
Class A designs have not been considered.
The transconductance will be around 2 S
I don't know exactly the thermal resistance between the die
and substrate at this time as the package is still in development
and the guys in spain are handling that kind of thing.
But I am told it will be very good indeed.
The pack is designed for class B-AB amplfiers at this stage.
Class A designs have not been considered.
The transconductance will be around 2 S
suzyj said:
I checked the schematic for 6000. Looks like lots of open loop gain
(4 stages) despite some degeneration. It should fit your criterion for
low THD numbers. I couldn't find any specs on it, do you have any
handy with decent OP power at higher frequencies (all closed loop
designs do pretty well at 8ohms /low power/1kHz).
I have come to question the use of low gm fets on the IP dif pair
as it is my experience that higher gm fets or bjt's with degeneration
are more linear.
It may be worth trying some better quality drivers such as
those recommended by Pavel (PMA), 2SC3955 and 2SA1540.
However, some of the advantages of these devices
(very low, linear cap) will be lost due to the fact that they are
driving the extremely non linear cap of the OP MOSFETs.
This is one aspect I -really- liked about Greg Balls SKA design,
it drove the OP MOS with high Ft/HFE emitter follower BJT's,
very smart IMO.
I'll also drive it from about 5V RMS maximum (from a PGA2310 volume control on the preamp board), which means I can use more local feedback, and linearise things up a little better.
They're my thoughts, anyway. The topology is set (having done the layout), the component values may change
So I guess my goal is as good an objective performance as I can muster, with a nod to the subjective people in the use of mica/poly capacitors, and using mainly local feedback rather than global to keep things linear.
I don't see a way out of using a fair amount of global feedback
in this (and most other similar) design if you want good numbers
because of the inherent non linearity of the last voltage
stage driving the MOSFETS estremely non linear IP. You can
degenerate the front end as much as you like but the real action is
getting the back end drive linear. Especially at higher frequencies,
4 ohms and larger power. This is where you will start getting much
more g-s modulation of the OP MOSFET.
They're my thoughts, anyway
Prejudices.... I never would have known you had any
Don't be fooled by all the hype WRT warm = H2. There are -many-
things that add warmth and I don't mind admitting I don't fully
understand the mechanisms behind all of them.
Let us know how you progress and good luck.
Cheers,
Terry
Terry Demol said:
My understanding is that Tillbrook used the JFETs on the input to raise the input impedance and reduce input offsets caused by the gate current on a normal BJT input stage. As you say, there's plenty of stages, and hence gobs of gain available. I'm thinking along the lines of reducing the gain a tad by driving the front end harder. The PGA2310 appears to work better (lower THD) at higher output levels anyway.
Terry Demol said:
I'll probably give these (or perhaps even a Toshiba 2SK389/whatever) pair a go. In any case, they all share a common pinout (I think!).
Terry Demol said:
I haven't looked at this amp - maybe I should check it out... I'd have thought that the output swing was already crappy enough with MOSFETs. Adding a BJT emitter follower before the MOSFETs only degrades this by a further 1.4V...
Terry Demol said:
My speakers are nominally "4 to 8" Ohms. I've read that they can be bastards to drive, and that makes sense, as the current requirements would be rather higher than normal.
I guess I could always linearise the output FETs by further increasing their source degeneration resistors... Is this a common practice? Strikes me as an expensive (power-wise) solution.
Terry Demol said:
Will do.
For now, I have a schematic and PCB layout. I've bunged them on the net:
Protel schematic:
http://www.atnf.csiro.au/~sjackson/aem6005.sch
PDF of schematic:
http://www.atnf.csiro.au/~sjackson/aem6005.pdf
Protel PCB:
http://www.atnf.csiro.au/~sjackson/aem6005.pcb
Gif of PCB:
http://www.atnf.csiro.au/~sjackson/aem6005.gif
Many thanks for the advice.
Cheers,
Suzy
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