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Old 5th July 2008, 09:34 PM   #11
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Default Re: Project 11.1 from Slone "High-Power Amplifier" Book

Quote:
Originally posted by Karl71
Does anyone have experience with the "11.1" project from the Randy Slone book, "High-Power Audio Amplifier Construction Manual"? It is the first and simplest amplifier in Ch. 11. What is the wattage? Can it handle a minimum load of 2.5 Ohms presented by an e-stat? Slone says early on that all of the amps in the book will drive a 2 Ohm load, but only temprarily. The nominal load is 6 Ohms.

BTW, I love the book. I like his approach and design philosophy. I am anxious to get building.

Regards,

Karl Lewis
Hi Karl,

This amp is very similar to the Maplin 100W MOSFET amplifier (55 volt rails) and I think you'll find it's a classic design that pops up quite regularly.

http://www.cpemma.co.uk/map_100w.html

I like this book as well but some of the criticisms are quite valid. Keep a close eye on the schematics as there are a few minor and some not some minor errors (or inconsistencies) as mentioned in a previous post by Nuuk.

For example, if you compare the schematic of 11.1 and the PCB (figure C.1) you'll find the location of the fuses is different. In schematics 11.8 and 11.9 the value of R2 seems wrong.

regards
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Old 5th July 2008, 09:52 PM   #12
taj is offline taj
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Quote:
Originally posted by bear

post the schematic, is what I said??


Bear,

It's a published book, currently available for $. We must respect the intellectual property (and the copyright that "protects" it), and not post his schematics.

I know that's tough to comprehend for those not personally involved in producing intellectual property and depending on its income.

..Todd
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Old 5th July 2008, 10:04 PM   #13
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Quote:
Originally posted by taj



Bear,

It's a published book, currently available for $. We must respect the intellectual property (and the copyright that "protects" it), and not post his schematics.

I know that's tough to comprehend for those not personally involved in producing intellectual property and depending on its income.

..Todd
Hi Todd,

I think it has been discussed before, but it is my understanding that the copyright is only the printed material, not the actual schematic. So you can't photocopy it or scan it but redrawing the schematic is OK.

In this case, it can't really be considered an exclusive Slone design as it is almost the Maplin design and that probably came from someone else anyway.

regards
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Old 5th July 2008, 10:08 PM   #14
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Quote:
Originally posted by Greg Erskine


Hi Todd,

I think it has been discussed before, but it is my understanding that the copyright is only the printed material, not the actual schematic. So you can't photocopy it or scan it but redrawing the schematic is OK.

In this case, it can't really be considered an exclusive Slone design as it is almost the Maplin design and that probably came from someone else anyway.

regards

I bought the Maplin 100W amp and was disappointed with it.
The power output was poor from it.
In the end I went for the Maplin 225WRMS amp and that was good. I coupled it to four Fane 50WRMS speakers an it was very loud.
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Old 5th July 2008, 10:56 PM   #15
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As I understand it, under the "fair use" doctrine/clause one can excerpt sections of copyrighted material and put them up on the internet.

Certainly one could do so for say "half" of the schematic.
Then post the other half...

Or perhaps, if ur worried, remove the parts values, and just publish the topology...

Redrawing is certainly an option...

Dunno what the law is elsewhere, but that is my understanding for the USA and probably all of North America...

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Old 5th July 2008, 11:01 PM   #16
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Quote:
Originally posted by bear


Dunno what the law is elsewhere, but that is my understanding for the USA and probably all of North America...
And there came the most interesting issue, which laws to follow? Does it depend on where the server is located? Or is it the poster who takes risks if violating local laws in his/her country? Can readers violate the law in any country by just looking at the schematic, or at least by saving it as a file?
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Old 5th July 2008, 11:14 PM   #17
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Ok,

I looked at the schematics...

A few comments.

Clearly one is not going to be able to increase the number of output devices with this schematic. So, that leaves it out for driving a 2 ohm load of any sort, with the possible exception of a very low power speaker - not an ESL.

And, it is a fairly horrid example of a very basic amplifier design - one that in essence counts on the global feedback to make acceptable the performance, since without the global feedback the thing would be all over the map in terms of results - meaning the lack of matching of devices would be hyper evident.

It would be nice to enforce or create true balance and differential operation of the long tail pairs as a starter point. The lack of a decent Vbe multiplier at minimum for bias setting is pretty outrageous this being 2008...

OTOH! If you've never built an amp, and this is your first pass, any amp that you build and make work is wonderful!!

But, it still won't work right on the ESL.

That IC from National might work out for you... it eliminates all the guesswork, and the matching issues for the front end (if any), and leaves you building a driver stage and output stage + a perf board with a few parts for the driver IC... not too shabby for a first project!

See what they say in the 1490 app note about driving 4-6 Mosfets per rail... that's ur goal... that and a big **** heatsink to go with it. you can build the whole amp onto the heatsink I think, except for the power supply.

_-_-bear
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Old 5th July 2008, 11:22 PM   #18
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Bear, don't bash Slone to hard. This amp is the first of twelve in his book and is intended as a simple beginners project. He points out in the book that it has problems, lika rising distorsion at high frequenicies. It isn't intended to be good, but simple. I think all the other 11 amps have both some form of current or SOA limiter and Vbe multiplier (even the others with lateral MOSFETs, which may not strictly need it). Elsewhere in the book he also shows an elaborate speaker protection circuit, which is the only one I have seen that even tries to detect amp oscillation!
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Old 5th July 2008, 11:55 PM   #19
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"It would be nice to enforce or create true balance and differential operation of the long tail pairs as a starter point. The lack of a decent Vbe multiplier at minimum for bias setting is pretty outrageous this being 2008..."

Laterals don't need a vbe multiplier. At 100mA Id the temperature coefficient of the current is zero. The bias will vary with + rail voltage though as LTP tail current sets the bias current through the VAS and bias pot too. A vbe multiplier or current source for the diff pair would make the bias more stable with rail voltage.

Not having gate resistors on the FETs looks a bit scary though, it might oscillate if the lauout is not perfect.

For protection: Add 10V zeners in series with diodes to limit gate voltage and you will have a very hard time destroying those FETs.

I tried to destroy a lateral fet by mounting it on a very undersized heatsink, connecting 50V drain to source and apply 10V current limited to the gate. The transistor did not blow up - when it got overheated some kind of internal thyristor structure shorts gate-source turning the transistor off until gate current is removed.

One pair driving 2 ohms won't give much power though before current limiting, but if this just is the impedance at the highest frequencies you will probably be fine unless you like high power 20kHz sinewaves :P

"Clearly one is not going to be able to increase the number of output devices with this schematic. So, that leaves it out for driving a 2 ohm load of any sort, with the possible exception of a very low power speaker - not an ESL."

Why not? The laterals have very low capacitances. The +-14mA available from the VAS is enough to slew the output at about 100V/uS. (Cgs is mostly bootstrapped away and Cgd is very low) The VAS transistors might actually be what limits the slew rate in this example.
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Old 6th July 2008, 01:43 AM   #20
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Quote:
Originally posted by megajocke
"It would be nice to enforce or create true balance and differential operation of the long tail pairs as a starter point. The lack of a decent Vbe multiplier at minimum for bias setting is pretty outrageous this being 2008..."

Laterals don't need a vbe multiplier. At 100mA Id the temperature coefficient of the current is zero. The bias will vary with + rail voltage though as LTP tail current sets the bias current through the VAS and bias pot too. A vbe multiplier or current source for the diff pair would make the bias more stable with rail voltage.


Exactly.
Stability is something to strive for?

Quote:
Not having gate resistors on the FETs looks a bit scary though, it might oscillate if the lauout is not perfect.

For protection: Add 10V zeners in series with diodes to limit gate voltage and you will have a very hard time destroying those FETs.

I tried to destroy a lateral fet by mounting it on a very undersized heatsink, connecting 50V drain to source and apply 10V current limited to the gate. The transistor did not blow up - when it got overheated some kind of internal thyristor structure shorts gate-source turning the transistor off until gate current is removed.
Not sure ur english isn't causing a mis-translation here.
Within reason these Mosfets have a negative tempco.
No thyristor I am aware of inside it... ?
Maybe you meant thermistor??
If so, then you mean negative temperature coefficient.

Quote:
One pair driving 2 ohms won't give much power though before current limiting, but if this just is the impedance at the highest frequencies you will probably be fine unless you like high power 20kHz sinewaves :P
Except for one important detail - clipping of high frequencies on an ESL sounds rather awful. Doesn't matter much if it is voltage or current clipping, imho... you'll hear hard clipping, and hear the increase of distortion with level without much difficulty.

Quote:
"Clearly one is not going to be able to increase the number of output devices with this schematic. So, that leaves it out for driving a 2 ohm load of any sort, with the possible exception of a very low power speaker - not an ESL."

Why not? The laterals have very low capacitances. The +-14mA available from the VAS is enough to slew the output at about 100V/uS. (Cgs is mostly bootstrapped away and Cgd is very low) The VAS transistors might actually be what limits the slew rate in this example.
Ummm?
Not no capacitance though.
You scared me, and I pulled my Hitachi book just to check.
The devices called for on the K side are the 2SK1058, spec'd at 600-900pf per gate. (usually around 800pf on a good day)

I guess it depends on how slow you want your amp to go maybe?
I doubt that the amp as shown will slew anywhere near 100v/us.
More like 10v/us.
Dunno.
The usual is a coupla watts or more to shove a row of those around... but ymmv. I don't have the spec's handy on the VAS xistors... my guess was that they were smallish...

Anyhow they show a 3 amp fuse on the rails to the outputs... so it ain't makin much power...

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