ExtremA, class-A strikes back?

[SSassen]

Alright, I nicked that subject title from someone else, kind of cheesy perhaps, but I like it.

For those of you that can appreciate a properly designed class-A amplifier with a spec sheet and performance figures that the vast majority of commercial amplifiers will never be able to match, take a look at the below url. And yes, to answer the inevitable question that's bound to pop up, there's PCBs available.

But before you get all excited, be warned, this is NOT a project for the novice builder.

ExtremA, a reference class-A DIY amplifier
http://www.hardwareanalysis.com/content/article/1842/

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

[peranders]

A nice piece of work from you and Bruno.

[lineup]

Originally posted by SSassen

ExtremA, a reference class-A DIY amplifier
http://www.hardwareanalysis.com/content/article/1842/
Best regards,
Sander Sassen

It does not look too bad.
No even to our Lineup Audio Lab
Class A amplifiers.

you have done a very good job, by most standards
not at least the magnificent web presentation

Regards
lineup

[Leolabs]

Do the small signal BJTs have to be matched????

[lineup]

Originally posted by Leolabs
Do the small signal BJTs have to be matched????

Refering to this schematic:
http://media.hardwareanalysis.com/ar...arge/11997.gif

There are a lot!!!! of small signal transistors.
What pair of transistor do you mean, Leolabs?

[LineSource]

Hi Sander,

From your experience with this design, would you advise a similar "bridged" output topology for a very low < 0.5 ohm speaker load? The extra power dissipation from the lower efficiency compared to a traditional grounded-output topology is the concern. I'm currently using a symmetric JFET-Bipolar folded cascode with a bridged 16 Sanken Bipolars output topology and really big heatsinks to put 32 Class-A watts into 0.15 ohms. The output stages run from +/- 5V power supply, so each diode drop is power expensive.


FROM ARTICLE: "Neither input nor output is ground referenced. This takes the influence of ground currents and loops out of the equation. The only thing that is referenced to ground is the common mode voltage of both outputs, this is done to insure that both outputs have the same dynamic range and the output remains symmetrical. Since the load is attached between the two outputs, it is not interested in the common mode voltage."

[GK]

"Neither input nor output is ground referenced. This takes the influence of ground currents and loops out of the equation.”


Not entirely. Unless driven from a differential-output preamp, one of the inputs will need to be tied to ground, thus referencing the other input to ground.

Cheers,
Glen

[EUVL]

At 75 Euros for 2 PCBs, it is about the most Hi-End project by quite a big margin.


Patrick

[SSassen]

At 75 Euros for 2 PCBs, it is about the most Hi-End project by quite a big margin.

Oh my, you must've fluked math class at school, let me calculate the price that's associated with this project for you:

The article notes the total price of a mono amplifier to be about $700 (USD) or 500-euro, this includes the PCBs. The PCBs themselves are double sided, silver immersion over 35u copper, with metallization, solder mask and silk screen.

A popular PCB manufacturing outlet that also does small runs for hobbyists is http://www.thepcbshop.com, they're generally considered as having very affordable pricing. Suppose you want two sets of PCBs made, as you're building two amplifiers. According to their pricing, you'll be paying:

- 2x double sided PCB, 105mm x 135mm (amplifier), 15 day delivery, their cheapest option: 69.93-euro

- 2x double sided PCB, 135mm x 155mm (powersupply), 15-day delivery, their cheapest option: 81.56-euro.

Total of 151.49-euro

Hence our offer certainly isn't more expensive. Granted, we could get a discount if we ordered more PCBs, 25, 50, or 100-pcs does bring the price down. But since we ordered just a couple to be able to supply interested DIY-ers with a set of PCBs we're just earning a few euro's per set of PCBs, as that price includes shipping worldwide.

If we sell a lot of PCBs, we might be able to break even with the development cost of the prototypes. However, the time invested in the creation of this design presented for free to the DIY-community we'll never get reimbursed, or at least not at our normal hourly rate. So we'll just write that off as being time spent on our hobby I guess.

Thanks for appreciating the fact that we're offering this design free of charge, some people tend to think that everything should come for free. So my question to you would be, what have you contributed to this community lately?

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

[SSassen]

LineSource,

From your experience with this design, would you advise a similar "bridged" output topology for a very low < 0.5 ohm speaker load?

Well, you'd need to calculate the requirements for bias current and power stage supply voltage as per the example in the article, see what that gets you and what the net efficiency would be. Low impedances are always a bit of challenge, Douglas Self has a number of pages dedicated to the topic in his book, and rightfully so.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com