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MDAC First Listen (part 00100001)

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Bruce,

No problem, when I next order salvaged MDAC's or MB's for the VFET amps from IAG I'll ask for a couple of spare handsets and post one to you :)
 
moosemeat said:
Oh, bother. I'm in Singapore. Thank you John.
Click to expand...
Bruce,

I live in Singapore, too, and I find that the heat and humidity affect many plastic/rubber coatings - they start to feel sticky can't be simply wiped clean.

This is what I did with my handset (though only follow at your own risk, please):

1. Opening requires a thin blade, much like what is needed for an iPod. You will likely break an internal clip or two.
2. Once the affected top surface is free of the buttons, I used a cloth and some Zif (JIF?) cleaning compound to lightly clean the surface. Rinse and repeat until the stickiness is gone. I managed to do this without rubbing away the labels for the buttons.
3. Dry thoroughly.
4. Spray several light coats of clear lacquer (I used Nippon spray paint), drying after each coat, until you end up with a smooth finish.
5. Reassemble, using glue if necessary.

I have to say, they clear finish looks and feels great, but only lasts a year or two before needing to be done again.

Good luck!

Patrick
 
Hi Patrick,

Thanks very much for the tips. I'll definitely give it a go as my remote is really horrible following my attempted clean with a smidge of dish washing liquid on a cloth!

Yes, it's amazing how damaging the heat/humidity combo is.

Cheers,
Bruce
 
John,

I bought a secondhand amplifier, for the time until the release of the MAMPs. Its a hybrid design with tubes in the input stage: http://www.audio-exklusiv.de/en/products/poweramplifier-p11/

It sounds wonderful, with a lot of air and transparency.

But there is one disadvantage: it has no balanced inputs, only RCA. Will the XLR connection of the mdac2 be superior to the RCA or is there also a benefit of the new output stage for the RCA?
Would you recommend a XLR-RCA converter?

Sorry for my bad english...

Best regards,
Uwe
 
For the next week, I'm working on the lab before the weather sets in - I need to install the wiring for the lab, Power, Network, security system, Lab reference clock etc.. Once I've completed installing the wiring and other systems, then I can leave the work to the builders - and get back to the MDAC2.

I'll be more active here by the end of the week.

Today, the VFET MB donor units arrived :) - and they take up some serious storage space!

Also, the recently ordered salvaged MDACs - and my new curve tracer arrived so that I can fully characterise the VFETs.

I quickly dissembled an MB to refresh my memory - and its its going to workout better then I expected - I can have a serious PSU on one side of the chassis - with the Power stage on the other (with local PSU decoupling).... I can also salvage a few more components then I expected.

The VFET AMP is going to be stunning! :)

I'll post pictures later on in the week, once I have a few moments to spare.
 
JohnW said:
For the next week, I'm working on the lab before the weather sets in - I need to install the wiring for the lab, Power, Network, security system, Lab reference clock etc.. Once I've completed installing the wiring and other systems, then I can leave the work to the builders - and get back to the MDAC2.

I'll be more active here by the end of the week.

Today, the VFET MB donor units arrived :) - and they take up some serious storage space!

Also, the recently ordered salvaged MDACs - and my new curve tracer arrived so that I can fully characterise the VFETs.

I quickly dissembled an MB to refresh my memory - and its its going to workout better then I expected - I can have a serious PSU on one side of the chassis - with the Power stage on the other (with local PSU decoupling).... I can also salvage a few more components then I expected.

The VFET AMP is going to be stunning! :)

I'll post pictures later on in the week, once I have a few moments to spare.
Click to expand...
John,
Will you reuse the transformers?
I read here that it was where Audiolab had scaled down the performance of the MB8200 compared to the Tag Mclaren 250MR. 380VA vs 650VA.
 
Rune said:
John,
Will you reuse the transformers?
I read here that it was where Audiolab had scaled down the performance of the MB8200 compared to the Tag Mclaren 250MR. 380VA vs 650VA.
Click to expand...

Surely the size of the transformer is related to the circuit design.

The biggest transformer in the world does not make for the best amplifier, if coupled to a crap circuit design.
 
misterdog said:
Surely the size of the transformer is related to the circuit design.

The biggest transformer in the world does not make for the best amplifier, if coupled to a crap circuit design.
Click to expand...

I am aware of the obvious, but it does have an influence on the current the amp can provide.
 
moosemeat said:
Hi John,

Can you please advise how to open the MDAC remote? I've opened the battery cover, removed the single screw beneath it then pried the two plastic sections apart a little but I'm worried if I keep forcing it, I'm going to break something... there's got to be a trick to it.

My purpose is to wash the cover as it feels dirty. Merely wiping it just makes it worse!

Thanks in advance.

Cheers,
Bruce
Click to expand...

Hi Bruce,

try cleaning with a microfibre cloth soaked in destilled water.

Cheers,
Achim
 
MatiasN said:
I would like to find the answer to this question as well.
Click to expand...

Imagine designing mains electric connections where the live pin engages first, and there is no earth. :eek::eek:

That is the equivalant of the RCA design.

Back in 1940 someone thought it a good design, and we have been misled ever since.
 
Rune said:
I am aware of the obvious, but it does have an influence on the current the amp can provide.
Click to expand...

Its rather more complex - sure the transformer size does have an influence, but for "real life music signals" and complex speaker load the Bulk capacitors play a more important part in power delivery. When you read amplifiers Specs of 45A peak or 60A short term Peak output current - this peak current is supplied by the Bulk capacitors, the transformer fuses are typicality 6.3A, these fuse will blow if around 6A's is drawn for any significant time.

For the reference VFET AMP design I plan to have two transformers - the Original 8200MB's transformer will supply the Current dumping output stage - while a second transformer will supply the "Reference" VFET ClassA stage & Tube Input stage. The VFET ClassA Reference Amplifier will also have the benefit of a fully Shunt regulated supply.

To provide the high peak currents, I plan to use multi-paralleled 4 pole Capacitors - which by separating the input and output current paths with individual connection points within the capacitor maximises there performance - these capacitors are OEM manufactured by SuperCap in Taiwan under licence from Denis Morcroft at DNM.

The 4 Pole "Separated" Input & Output current path capacitors:-

https://dl.dropboxusercontent.com/u/86116171/4 Terminal Capacitors.JPG

Here, dear little Paris is indicating the "empty side" of the 8200MS which will contain the second transformer + multi paralleled 4 Pole capacitor reservoir bank in the new VFET design:-

https://dl.dropboxusercontent.com/u/86116171/MB2.JPG

(If you take a close look at the capacitors, you can see them covered in dust from the Lab building works outside!!! :( :( :( - the dust is EVERYWHERE! )

Heres a top view of a 8200MB donor unit showing the internal layout:-

https://dl.dropboxusercontent.com/u/86116171/MB1.JPG

Here is a close-up of the transformer - showing its not possible to fit a larger transformer within the 8200MB chassis, with just 9.6mm clearance to the front panel, and about 5mm clearance to the heatsink...

https://dl.dropboxusercontent.com/u/86116171/MB3.JPG

Also, today the extra order of 30 pairs of VFETS arrived, I now have a total of 45 Pairs :)

https://dl.dropboxusercontent.com/u/86116171/45 Paus of VFETs.JPG
 
Regarding the miniXLR connector discussion - it seems that what I thought of as Switchcraft are actually some noname connectors (which look exactly the same on the outside), so disregard my comments on Switchcraft being low quality.

John, did you buy your sample as "real" Switchcraft (http://rover.ebay.com/rover/1/711-5...0001&campid=5338728743&icep_item=371110860109) or without the name (http://rover.ebay.com/rover/1/711-5...0001&campid=5338728743&icep_item=291042186346)? .. The latter is much cheaper (price). Does your Switchcraft have the Neutrik-like "cable leads" (the ones that fill with solder) or just contacts with holes (like cheap jack plugs)?

Thanks,
Jiri
 
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