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KG Balanced Dynahi build discussion thread

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18 hours ago, joehpj said:

Made some multi-coated front panel recently. This is a small project  @ang728  and I ran together. This is our first attempt to try multi-coated for the front panels. I don't know if this kind of finishing will start to peel off in longterm. We'll see. We are thinking making more interesting colors, too. Maybe "Hulk" green or something like that...

The blue one has tapered feet while the red one has real spiked feet. 

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Sweet! Chassis are? ebay? Very nice looking!

EDIT: I spot ang728's GRLV boards as well :)

Edited by Pars

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I am thinking about building this amp. Is V1.43 that uses MJE15030/15031 the latest board?

Anyone has boards for sale? 

I have 2SJ109/2SK389 on hand so I may be able to build older versions that use JFET input too.

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Not sure on board versions, and will have to wait until I am home to check. Not sure that I would build an older version either, even with the parts.
I presume the newer versions are also supersymmetry? The real old original versions weren’t really set up as balanced as they used (1) 2Sj109 and 2SK389 per channel (so 4 pair total for balanced), which essentially wasted 2 pair.
I think I have a pair of boards at home that I won’t be using. I’ll check tonight.


Sent from my iPhone using Tapatalk

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I think the latest "on board" version is the one I have. 1.4. I don´t have other PCB set available (I only bought a set ). 

Make sure you have enough MPSW06 and 56. They are no longer available.

Edited by jose

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The off-board heatsink version I built is marked 1.5, and the file in Kevin's archive is ssdynahibalsmtm.zip. It was the most recent revision in mid-2016, but I'm not aware of any changes since then. I don't have any extra boards left, though.

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I just checked, couldn't find them, and then remembered that I sold them to another user (anorphirith) about a year ago. They were v1.5 boards. Sorry!

I do still have a pair of the originals (2004), but that would be single-ended and not SuSy. You might check with Steve (sbeylo) and see if he has any left over?

Edited by Pars

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Thanks guys! I’ll need to do some more research.

There are plenty of v1.43 boards available on eBay but I really don’t want to buy them because I consider those pirated products.

I do have enough MPSW06 and MPSW56 on hand.

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I´m afraid that eBay is the only place where you can buy some (bad thing :unsure:) although maybe Steve or Soren have one.

At the time, I was looking for a set to have a spare but I did ´t find any.

Michael, If I had to do a new Dynahi, I would choose the "off board" versión. B)

 

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Gonna start Dynahi next, on board heatsinks and double mono in two boxes, and wonder if anyone konows where I can source two SJ109 jfets to go with the SK389s I got.

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6 hours ago, jose said:

 

Michael, If I had to do a new Dynahi, I would choose the "off board" versión. B)

 

Thanks Jose. And, yes, I will be building an "off board" version and most likely with a dual-mono GRLV power supply. 

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5 hours ago, mdr30 said:

Gonna start Dynahi next, on board heatsinks and double mono in two boxes, and wonder if anyone konows where I can source two SJ109 jfets to go with the SK389s I got.

SJ109 (and sk389) are extinct for ages...Your best shot is to find linear systems parts, lsj689. But it is pricey

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For the off board version can I safely use the following substitute parts?

MPSA06/56 for MPSW06/56

MJF15030/15031 for MJE15030/15031

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1) You should be able to, but I don't have a sim to measure power dissipation in these. Since they are only used as drivers (and not as the outputs as in the SS Dynalo) I think you should be OK. I thought you said you had these?

2) Yes. The MJF is an isolated package, so you can bolt straight to the heatsink. It is rated at 36W vs. 50W for the MJE (with metal tab). I think they are the same die, just package difference.

 

  • Like 1

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Thanks Chris!

I do have MPSW parts on hand but would like to save them in case I need them for other applications.

The differences in spec are that MPSA parts are rated for .650W dissipation (vs 1W for MPSW parts) and .25V collector-emitter saturation voltage ( vs .4V for MPSW parts).

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On 12/29/2017 at 9:09 PM, luvdunhill said:

Chris, interestingly, the drain and source of the Toshibas JFETs are interchangeable. I have exploited this to clean up some layouts. Just a fun fact, not useful here :)

I received a batch of 2SJ74 and 2SK170 from BDent today. I proceeded to test them using one of those ATMG328 testers I got. 

Interestingly, the tester shows the 2SJ74 pinout to be 1=S, 2=G, 3=D, the S and D pinout are reversed from the datasheet. 

What gives?

C0D202E5-9A54-4E7F-A68C-01F2DF167FE4.jpeg

Edited by mwl168

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It is very difficult to find any explicit data on asymmetrical JFETs, other than that they are rare and used mainly in high RF work or similar specialised applications. I think is is almost certain that the ones we typically use in audio are symmetrical.

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Very interesting. I had not noticed until now. 

I have reviewed some J74 of my inventory (including a Linear Systems LSJ74) with several transistor testers and S and D appear reversed as well.

Edit: If they are all symmetrical, could you connect them to the opposite?

 

Edited by jose
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Yes you can. As I mention above, when laying out boards this can be exploited to ensure better signal routing.

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Thanks all. That’s very good to know. 

Also happy to know the 2SJ74’s appear to be authentic and the tester is not defective. It’s almost funny - the cost of 3 of those SJ74 exceeds what I paid for the tester.

4 hours ago, jose said:

Very interesting. I had not noticed until now. 

I have reviewed some J74 of my inventory (including a Linear Systems LSJ74) with several transistor testers and S and D appear reversed as well.

Edit: If they are all symmetrical, could you connect them to the opposite?

 

Jose, do your testers show similar SJ74 results as what I posted (value wise)? 

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They are something different from yours.

2SJ74GR bought in AMB:


79759191833e270652bcbc62be8423f9.jpg

 

LSJ74 grade B bought in DIYAudio Store:
 

ce9e3d672603b0b8cdad9b3efd5a03f4.jpg

 

2SJ74GR bought from a member of DIYAudio:

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I have measured some units of each group and they all very similarly.

Edited by jose

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