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Old 27th September 2014, 03:13 PM   #1
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Default Burmeister 933 Mk2 Clone

I'm just playing with amplifiers as my F5 build was sadly very disappointing.

I've bought a few of these Chinese Burmeister 933 Mk2 Clone kits and have a few questions.

Ebay item 271524655114

Some of the components supplied were different from the values on the PCB. OK I accept that he has supplied some E48 values in place of E24 parts, I have no problem that 216R is close enough to 220R.

However he has supplied 0R27 emitter resistors, the board shows 0R47. Is this an issue or should I obtain the 0R47 parts ?

I ordered the output transistors from the item photo, 2SC3264 and 2SA1295. The PCB shows 2SA1216 and 2SC29??. Will this be an issue ?

The advert states 120W into 4 Ohms. What can I expect into 8 Ohms. I am using the rails as suggested in the advert. I'll be using a 40-0-40VAC 800VA transformer.

Last edited by KatieandDad; 27th September 2014 at 03:19 PM.
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Old 27th September 2014, 08:41 PM   #2
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Nice kit.

Your 2sa/c Sankens will be a perfect match for the older (other ones).

.47R to .27R will slightly change the settling time - thermally , your
current/bias calculations will be different if the documentation is
calculating for the .47's.

With those sankens , 120w/4R - 70w/8R is a "honest" spec.
An 800VA trafo is total overkill. (no harm )
I use 600-800VA units for 2 X 300W "monster amps" .

good luck ,

OS
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Old 28th September 2014, 04:53 AM   #3
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The 800VA transformers were a good price, half the price of the 300VA.
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Old 28th September 2014, 02:24 PM   #4
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Default Having difficulty uploading

I did try to upload the schematics for the Clone yesterday but Internet Explorer was having none of it. I did uninstall Google Chrome because that wasn't working either. I've just re-installed Google Chrome and can now upload the schematics for anyone who wants to comment.

Vendor states that 22K and 27K are interchangeable with no consequences.

He also states that 0R27 is fine in place of 0R47. I've got the correct components so I'm going to stick with the schematics, the only difference is the more modern output transistors.
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Old 28th September 2014, 02:33 PM   #5
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The PCBs are of a good weight and are well made.

Any comments about the layout or design ?

Building these is fairly intuitive, just as well as there are absolutely no instructions.

There are two test points marked TEST. You have to reverse engineer the board to discover that they are across the upper emitter resistor.

The bias current is 200mA but with the wrong resistors supplied.

Some of the transistors are second hand but for the price I've got no qualms with that, at least they are probably genuine.
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Old 29th September 2014, 01:21 AM   #6
fab is offline fab  Canada
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I have difficulty to find a real frequency compensation based on the layout...

Fab
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Old 2nd October 2014, 01:02 PM   #7
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Studying the schematic against the component count there are a few questions.

I'm presuming that LD5 and LD6 are the two CCS semis fitted.

LZ1, LZ2, LD7 - 10 are the zeners fitted.

How has the vendor got rid of the diodes between LQ6 and LQ7, there are no other diodes on the board.
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Old 2nd October 2014, 02:19 PM   #8
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Never has one thread had so few comments.
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Old 3rd October 2014, 08:02 AM   #9
scalpel is offline scalpel  United Kingdom
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Hi,pm your email address.I have a bom and schematic for a clone from another supplier that seems to have all the diodes that you are looking for
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Old 3rd October 2014, 08:46 AM   #10
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by KatieandDad View Post
Vendor states that 22K and 27K are interchangeable with no consequences.


If that would be true, why put effort in designing an amplifier...
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