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KG Balanced Dynahi build discussion thread

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On 12/19/2017 at 4:15 PM, luvdunhill said:

Just Vf - it’s a voltage reference.

 

Ok, thank you very much! Would wirewound trimpots be ok to use instead of the cermet ones specified? Happen to have some lying around.

Edited by Ariamella

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On 11/16/2017 at 9:40 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

 

It's too bad that Toshiba screwed up on the pinout for the SC3381/SA1349, and an adapter like this would NOT work for the SK389/SJ109 JFETs, even though they are the same package. I know, the JFETs are rarer than hens teeth, but still.

The dual JFET adapter can be done with quite short traces, nice and clean...

 

dual jfet adapter.jpg

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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 :)

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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!

 

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

 

So I took stock of what I had and I have a pair of 2sa1349.  Now, my question is do I have to match the 2sa1349 to the 2sc3381?  Or if I chose to source the K489\J689 as well do I have to match them with each other?  I'd be using them in the newest Dynahi and Dynalo circuits.

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my experience is, maybe, so i would experiment before soldering. 

depending on your brand of LEDs, causing an intentional mismatch in those can also make up some of the difference -- up to about 50mV with ones i've used.

also, it's going to vary depending on transistors used and exactly which amp, but sometimes a perfectly matched amp is not 0mV offset, it's really like -30mV (depending on your gain) due to differences in pnp/npn parts. so this could be why sometimes a slight mismatch actually gives a better result. 

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^ what Justin said. Ideally, yes, you would want the p and n pairs to match. In the real world, that rarely happens or is possible depending on device type. I would think you should be able to dial out most mismatches with the trimpots as well.

 

Has anyone actually measured the THAT340s to see how well they are matched? I know with some of the Toshiba duals that I had, you could get better matches with singles.

 

Sent from my iPhone using Tapatalk

 

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After thinking about it for a few hours I remember doing exactly that when building the original 2 channel dynalo and dynahi.  I only matched singles of P or N when using them and did not match P to N.  I remember socketing the LED's and switching until I got close enough for the servo to swallow up what offset was showing up.  What's the limit of the servo in the current designs of the dynalo and Dynahi?

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How do you like that tester, was thinking of getting that to measure the transistors for the unbalanced/balanced board?

Edited by sbelyo

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I have several tester but this is the most practical and simple for me that I am a beginner :unsure:. I use it for almost all our projects.

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10 hours ago, sbelyo said:

After thinking about it for a few hours I remember doing exactly that when building the original 2 channel dynalo and dynahi.  I only matched singles of P or N when using them and did not match P to N.  I remember socketing the LED's and switching until I got close enough for the servo to swallow up what offset was showing up.  What's the limit of the servo in the current designs of the dynalo and Dynahi?

around +/- 40-50mV in the dynalo

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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

 

Are the gerbers posted for the SC3381/SA1349 devices ?

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Note that the pinout for the 2SA1349/2SC3381 does not line up with the 2SJ109/2SK389 devices, even though they are the same package. So that adapter will work for the bipolars, but not for the JFETs.

  • Like 1

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I wouldn't think so, but you would need to look at the matching on them as far as hFe and possibly Vbe to determine. I would swear that some of the On Semi I've bought recently still had Fairchild markings on it (On Semi bought Fairchild).

Are you talking Fairchild 06 and On Semi 56 or a mixture in the same device type(s)?

  • Like 1

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I jumped on a half price offer for 56 and later checked the title its a Fairchild. The 06 I can only find On Semi. hFe matching shouldn't be a problem since I got one of those AT-Mega testers.

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I'm having some problems with biasing my board. I can't get it to bias higher than 320mV± on both rails. At  first I had a light bulb limiter and thought it might be lowering the bias but after removing it it's still the same.

I'm using 51k for the feedback resistors. Could it be the reason why?

IMG_20180318_203720.jpg

The image is showing around 484+-mV but I cannot get a low offset with it and 270mV is the highest I can get with low output offset.

Edited by penmarker

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Shit. at 270mV bias the offset was less than 5mV suddenly shot up to 8.5V

So after lowering back both trimmers the offset went back down below 50mV. What could this be caused from? My Hfe measurements are
MPSW56 = 201 for one board and 256 for another
MPSW06 = 293 for both boards (bought on tape reels so they're pretty uniform)

I found out when I increase the bias the offset stays low. Then if I turn it off, and then turn it on again the offset shoots up to several volts.

***edit
This post by amb suggests to change the 500Ω resistors with something higher like 620Ω or 680Ωso I'm going to try that in a bit.
https://www.head-fi.org/threads/dynahi-dc-offset-adjustment.165788/#post-1960704

2. Now biasing at 200mV, before putting in OPA445 offset is 1mV. After inserting OPA445 the offset jumps up to several hundred mV on startup, drifts within a few dozen mV, and settles down now at 10-14mV. Now it is dropping again to 7mV, I presume after the parts have started heating up to their operating temperature. Is this normal? With the OPA445 off, the offset does not jump upon startup but drifts around 20mV, goes down to 10-15mV, and starts settling down at 1-3mV

Edited by penmarker

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