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KG Balanced Dynahi build discussion thread


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43 minutes ago, mwl168 said:

According to the DIYAUDIOSTORE site, that price comes with 2 matched pairs.

I didn't see anything about anything matched. And note that the price that penmarker quoted is for A grade (Idss of 2.5-6.mA). B grade (6-12mA) is probably what most of us would be interested in. The price for those in the K170 is $32.76. The B grade J74s are $65 something (and out of stock).

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According to the DIYAUDIOSTORE site, that price comes with 2 matched pairs.


Yes I bought it and price is for TWO matched pairs.

But.... on DIYAudio you can find reliable sellers that have Toshiba stock (GR and BL grades) at a better price.
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Just checked the link gepardcv posted and it clearly says "...LINEAR SYSTEMS MATCHED LSJ74/LSK170 JFET PAIRS (GRADE B)..."?

Yes, I know the matched pairs item is 2 matched pairs (2xJ74 & 2xK170). I thought you meant that the 8xJ74 or K170 had 2 matched pairs in it.


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@penmarker: Your transformer is really close to your amp boards. Mind the shielding and the wiring, or you'll have EM interference. I did the same thing, and I'm still working through some noise problems. (Though with recent posts on this thread, I'm now wondering if the THATs are partially to blame.)

Edited by gepardcv
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11 hours ago, gepardcv said:

@penmarker: Your transformer is really close to your amp boards. Mind the shielding and the wiring, or you'll have EM interference. I did the same thing, and I'm still working through some noise problems. (Though with recent posts on this thread, I'm now wondering if the THATs are partially to blame.)

Thank you very much. Yeah I've been looking back through the thread and I saw some images of single chassis builds including yours. Initially I've been looking at transformer cans but they're all far too tall to fit in my case. I'd have to get a smaller transformer with a smaller VA, current choice is 160VA.

Rumina does have transformers directly below the amp boards but they're shielded well with sheet band around it. link
That would be very helpful.

My other option is to build a 2 chassis amp, but I think it'll  be too bulky. I mean, it's a headphone amp the size of a power amp.

 

**edit

Heheh. Looking at Nuforce HA-200 gave me some ideas...
If only the case I ordered isn't 70mm tall... more like 40-50mm would be nice for a stack of balanced.

5630345.jpg

Edited by penmarker
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The best solution I've found is to wrap the transformer in a strip of grain oriented steel.  I was able to get mine from Avel Lindberg where I bought the transformer.  Beyond that it seems hard to source by itself.

This place has it https://www.don-audio.com/radiation-shielding-magnetic-shielding-tafo-hum-trafo-shielding-electro-magnetic-sheets-grain-oriented-electric-sheets-electro-magnetic-foil-shielding-foil-shielding-sheets

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14 hours ago, sbelyo said:

The best solution I've found is to wrap the transformer in a strip of grain oriented steel.  I was able to get mine from Avel Lindberg where I bought the transformer.  Beyond that it seems hard to source by itself.

This place has it https://www.don-audio.com/radiation-shielding-magnetic-shielding-tafo-hum-trafo-shielding-electro-magnetic-sheets-grain-oriented-electric-sheets-electro-magnetic-foil-shielding-foil-shielding-sheets

How does it compare with the metal transformer can?
s-l400.jpg

I'm planning to complete the build first and assess the level of interference. If required I'll add in the shielding.

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I'm planning to complete the build first and assess the level of interference. If required I'll add in the shielding.

Good idea... no need chasing problems you don't actually have, though good to think about things such as this in advance.


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9 hours ago, penmarker said:

How does it compare with the metal transformer can?
s-l400.jpg

I'm planning to complete the build first and assess the level of interference. If required I'll add in the shielding.

to shield the trafo enough in your build you need some metal that can shield magnetic fields quit good (mu-metal or grain oriented metal).

i used also this transformator can (when the trafo is not so near sensitive transistors) but i would rate the magnetic shielding the badest. would rate:

mu-metal   100%
grain orientad metal 80-90%
normal metal (this can)  30-40%

due mu-metal is horrible expensive the best way is to go for the grain oriented metal option.

i used this transformator can and grain oriented metal bands in one of my ksa5 builds (bad placed trafo in my first ksa5 (the red one)), looks nice and shield effect in combination is as good as mu-metal. so you can first test the noise with this can and later ad some grain oriented metal bands if needed.

the noiseest part of the trafo is the side where the cables go in and out, place this part away from the transistors (in your build to the front side). also very effectiv is to turn the trafo up 90 degree (stand up), the magnetic field expands more like a frisbee (then a sphere) around the trafo.

the first time putting a grain oriented metal band over the trafo and the hum goes away is magic :-).

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  • 2 weeks later...
On 10/24/2017 at 4:34 PM, kevin gilmore said:

that definitely does suck, I had one noisy one out of a batch of 10.

birgir is making a little mini board, and Justin bought a pile of dual transistors, might be a better solution

the layout of the amp is such that you can replace the that340 with jfets if you can get them

IMG_4251.thumb.jpg.8b93803974c00cd4621babcd527f2dc6.jpg

time to update the pcbs!

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That is one shitload of parts Justin! Where do you find this stuff (I know, trade secret).
As for Mouser PN for a pin strip, one that is cheap is Wurth 711-61304011121 for a 40 pin strip, $1.22.
They do make these in 7 pin strips, no cutting required.


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On 25.10.2017 at 10:20 AM, penmarker said:

 

Also, just a thought. How bad is it to have long flying leads to the front panel for the feedback resistors so I can make a gain switch? Or is it just better to not do it.

Perhaps not a good idea, say the extra stray inductance could have an effect on the compensation.

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On 11/16/2017 at 10:36 AM, justin said:

IMG_4251.thumb.jpg.8b93803974c00cd4621babcd527f2dc6.jpg

time to update the pcbs!

Like, could I get a few pairs from ya?  Those are what went into the original Dynahi back from headwize right?

 

On 11/16/2017 at 10:40 AM, kevin gilmore said:

adapter boards.jpg

and then things like these for the pins

https://www.ebay.com/itm/2-x-2-54mm-Male-40-Pin-Round-Header-Strip-Gold-Plated/161735709722?hash=item25a833141a:g:ehIAAOSw3xJVf2RC

i'm sure there is a mouser part number, but can't find it

 

I'd be willing to do the group buy for these plus anything else needed if there isn't already one

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cool...  I'd be using them for the latest dynahi and dynalo boards.  That'd work right?

I'd be willing to buy a lockyz curve tracer for the matching as long as someone made sure I was using it right and then double checked my findings.  Or I could loan it out for the job

Edited by sbelyo
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they were the original cascade transistors in the dynahi.

can be used as a bipolar input on ssdynalo and ssdynahi. and anything else that has the that340 footprint.

also current mirrors for doing servo and a few other things I may come up with.

all the fet input options are brutally expensive these days

this is another place that has the pins

http://www.king-cart.com/phoenixent/product=HEADERS-MACHINED-PIN+BREAKAWAY+.1SP/exact_match=exact

Edited by kevin gilmore
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1 hour ago, Pars said:


Does it do hfe? If not, it would be kinda worthless for matching transistors. Not clear from the write up what exactly it does do.


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They should be able too. All these transistor testers are based on some open source project

 https://hackaday.com/2015/04/24/review-transistor-tester/

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Yeah the tester does measure HFE, it's based on the ATMEGA328 just not sure how accurate is it.

Back then I got some suggestions from diyaudio to use a DY294 for the higher power 2SA2922 (building NAP200 clone) because it allows adjustment on the testing current. But since the 56/06 transistors are only small TO92 I guess the one I linked could work?

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