AMB Laboratories DIY Audio

[gumleguf]

Alright! Straight to the point:

I want to build one of them, but have a hard time deciding. They are going to power my BD DT 770 @ 600 ohms cans.

What are the pro's and con's between the two amps, and how do they differ in sound/signature? Basically, what can I expect from either? It's not clear to me.

Edit: I decided on the M3. Pictures on page 7.

[amb]

I won't get into the "sound signature" aspect because that's highly subjective, but in stock form CK²III could swing more voltage than a 24V-powered M³. This is a plus for ultra-high impedance headphones like yours. On the other hand, M³ could output way more current than CK²III, and is a benefit for low-impedance loads. An M³ with higher supply voltage (and appropriate opamps) will be able to match CK²III in voltage swing and have high output current capability.

The rest of the decision will have to be based on personal preference on what kind of amp you want, and only you could answer that. E.g., Are you adverse to the use of opamps and global negative feedback loop? Does a fully-discrete and complementary circuit interest you more? Do you like MOSFETs? Does a three-channel active ground topology interest you? Do you want an adjustable bass boost feature? Is the possibility of a separate high performance power supply important to you? Is the ability to drive speakers to moderate volumes an attractive option? The list goes on....

[gumleguf]

On the first section I understand that with some customization it would be possible to match the M³'s electrical performance to the CKKIII, but his would require (undocumented) change in some of the parts used. If I somehow managed to do that, I'd end up with the best of two worlds? I also fully understand that you do not wish to get into the sound signature discussion - I was only objectively interested in hearing if some obvious differences existed.

On the second section I don't know what to answer. I'm simply too much of an electronics newb. I do however find the bass boost feature convenient on the M³ since I listen to everything from classical to acoustic to jazz to fusion to hardcore metal. I understand that the M³ needs a regulated 24V DC power supply, and this is fine with me. Not interested in using the amp for anything else but headphone amplification.

As I read it the M³ could be more expensive to build, but I simply can not grasp if one of the two projects is more "difficult/complex/advanced" and thus something a newb should not consider doing? I should mention that even though I'm a newb I have friends who can help me with assembly and electronics.

What I'm trying to achieve is to build a great headphone amp "my self". That simple. I have a burning desire to do that! Hopefully I'll get there eventually...

[amb]

There is nothing "undocumented" in my reply. The M³ website (and σ11 website) contains all you need to know about how to increase the supply voltage and which opamps are recommended. A quick look at the linked datasheets will show you what the maximum supply voltage is for that opamp.

As for difficulty to build, the M³ is slightly more work, but not by much. The CK²III board will slide into a Hammond 1455Q series enclosure and has an onboard power supply regulator, so all you need is to connect a transformer, while M³ needs a larger case, a few more holes to be drilled, a separate power supply board (e.g., σ11), etc. But assembling the M³ PCB itself is about the same difficulty as the CK²III.

[gumleguf]

Sorry if my choice of words could be misinterpreted. I am most grateful for all the helpful replies I have received to my hopeless newb questions so far...

I realize little by little when reading through the project pages again and again that almost everything *is* in fact documented. Guess I'm just overwhelmed by the amount of information. A bit difficult to grasp all details and options.

Here is what I have so far (is it really that simple?).

σ11:

If I want to change the output voltage to 30V, i must change the R10 value to 6.81KΩ, use default D5 zener diode BZX55C12 (12V) and e.g. an Avel Lindberg 30VA 15+ 15V toroidal?

Is 30V enough or should I go for 36V (change the R10 value to 4.99KΩ, use default D5 zener diode BZX55C12 (12V) and e.g. an Avel Lindberg 30VA 16+ 16V toroidal)?

M^3:

I could use default components/values on the entire board except for the opamps, and instead using e.g. the Texas Instruments THS4631D with a maximum supply voltage (VS Supply voltage, VS– to VS+) of 33 V?

By the way, all the links to datasheets for the Analog Devices opamps are dead. And so is the link to the Linear Techonology opamp.

[amb]

σ11:

If I want to change the output voltage to 30V, i must change the R10 value to 6.81KΩ, use default D5 zener diode BZX55C12 (12V) and e.g. an Avel Lindberg 30VA 15+ 15V toroidal?

Is 30V enough or should I go for 36V (change the R10 value to 4.99KΩ, use default D5 zener diode BZX55C12 (12V) and e.g. an Avel Lindberg 30VA 16+ 16V toroidal)?

Yes, that's it. With a 36V power supply, M³ would almost match the CK²III in voltage swing capability.

M^3:

I could use default components/values on the entire board except for the opamps, and instead using e.g. the Texas Instruments THS4631D with a maximum supply voltage (VS Supply voltage, VS– to VS+) of 33 V?

Yes, and many of the other opamps in the list can handle 36V or more (but the limit is 40V due to the TLE2426).

By the way, all the links to datasheets for the Analog Devices opamps are dead. And so is the link to the Linear Techonology opamp.

Sigh. The companies change their websites without redirect links, it's hard to keep up. But google also works...

[gumleguf]

Oh, I see. I really thought it would require a comprehensive hack, but no...

Regarding going for 36V I can't really find a 30 VA 16+16V toroidal (http://www.avellindberg.com/transformer ... _specs.htm). Looks like next step up is a 18+18V. Should I have 16+16V custom made instead?

Regarding opamps I "simply" need to find one that can handle 36V or more (so for example the THS4631D will *not* work when going for 36V, correct)?

Ok about the dead links. Just thought you'd might like to know. In case you want to update the links for the Analog Devices opamps here are the new links:

Analog Devices AD8610AR -> http://www.analog.com/en/amplifiers-and ... oduct.html
Analog Devices AD8065AR -> http://www.analog.com/en/amplifiers-and ... oduct.html
Analog Devices AD744JN -> http://www.analog.com/en/amplifiers-and ... oduct.html
Analog Devices AD825AR -> http://www.analog.com/en/amplifiers-and ... oduct.html
Analog Devices AD843JN -> http://www.analog.com/en/other-products ... oduct.html
Analog Devices AD845JN -> http://www.analog.com/en/other-products ... oduct.html

[amb]

Regarding going for 36V I can't really find a 30 VA 16+16V toroidal (http://www.avellindberg.com/transformer ... _specs.htm). Looks like next step up is a 18+18V. Should I have 16+16V custom made instead?

Those are just guidelines, chances are 15+15 would also work well, or you could also use 18+18 (the σ11 MOSFETs will run a little hotter).

Regarding opamps I "simply" need to find one that can handle 36V or more (so for example the THS4631D will *not* work when going for 36V, correct)?

Correct, except that M³'s D1 and Q5+/Q5- willl drop a few volts, so what the opamps will "see" is less than what the PSUs output. You have about 3V of margin.

Ok about the dead links. Just thought you'd might like to know. In case you want to update the links for the Analog Devices opamps here are the new links

Already done... Try refreshing the parts list frame.

[gumleguf]

Just so I understand:

Is the 15+15 something I should go ahead and use, or would it be "better" if I wen ahead and had someone make me a 16+16 or perhaps bought a 18+18 instead? Also, there is no need to upgrade the heatsinks?

I have some difficulties understanding the opamp datasheets. Maybe you could educate me a little and tell me which parameters/specifications to look for? For the AD8065 for example I see a supply voltage range of 5 V to 24 V but no maximum indication. Help plz.

[amb]

Is the 15+15 something I should go ahead and use, or would it be "better" if I wen ahead and had someone make me a 16+16 or perhaps bought a 18+18 instead?

15+15 = 30V, and the rectified voltage is 30V * 1.4142 = 42.4V, less about 2V for rectifier drop you still have ~40V, which is 4V over the 36V you need. This calculation assumes a full load on the transformer, but if you use a 30VA transformer it will not be running at full load, so the voltage will be a little higher yet. Given this, and read the notes about transformer selection at the σ11 website, you'll see that a 15+15V 30VA transformer should be enough voltage, if only barely.

Also, there is no need to upgrade the heatsinks?
No, just make sure the case is ventilated.

I have some difficulties understanding the opamp datasheets. Maybe you could educate me a little and tell me which parameters/specifications to look for? For the AD8065 for example I see a supply voltage range of 5 V to 24 V but no maximum indication. Help plz.

Look for the "Absolute Maximum Ratings" section. For AD8065 it's 26.4V.