KG Balanced Dynahi build discussion thread

[JoaMat]

Added a NPN, a trimmer and some resistor. With those it should be possible to set current through output transistors. Well, that’s the idea. If it works I probably let you know…

[MLA]

What could possibly go wrong ? 

Seriously; great idea though! Things could potentially get toasty on a 2U heatsink, so being able to choose current would be welcome flexibility.    

[JoaMat]

Just want to add that the bias control is not my invention. You find similar on Uberamp and AMB’s beta22.

My view on Copyright is - my right, as DIY:er, to “copy and paste” as I wish.

 

Edited March 23 by JoaMat

[Bespav]

On 3/21/2022 at 1:42 PM, JoaMat said:

So here is my first attempt

Hi, JoaMat!

Very nice PCB routing concept.

Something similar:

Let's go ahead, it's time to provide DIYers with the next features:

1. A simple swapping JFET/BJT input stage on the mezzonine with standartized fitting place/connector.
2. Really smaller dimensions with easier through-pcb-screwing.
3. Integrated onboard fitting connector for corresponding voltage regulator.
4. Check transistors availability and, of course, create different versions of the output stage, one for TO-126, other for TO-220 devices and maybe one for TO-3P/TO-247/TO-264.
5. Since you have provided bias control it's time to make output stage 2-stage emitter follower, vertical mosfet source follower or lateral mosfet source follower for those who want to experiment.
6. Input JFET transistors have cascodes, so aren't we ready to provide cascodes for VAS devices?
7. VAS devices on the main heatsink and also an option of the TO-126/220 cases.
8. Really higher dedicated IPS/VAS supply rails, up to +-150 volts.
9. An option to use modern low-ESR solid polymer capacitors for the power stage.
10. Dedicated input stage before volume regulator for common mode error rejection.
11. Second order integration filter for output nulling.

 

So, the concept.

Mezzonine construction. One PCB for JFET/BJT input stage and corresponding cascode devices, second PCB for one OPS shoulder and third PCB for the voltage regulator. All for as-LEGO-construction as possible.

Edited March 24 by Bespav

[JoaMat]

Interesting ideas, wish list, for future Dynahi, Bespav.

Here is a new amp board. Initial tests have been successful. The bias control seems to work.

Heat sink is Modushop 80mm x 200mm. 

[mdr30]

Joamat's build reminded me of some problems with balance and setoff on my own Dynahi. I adjusted the amp a couple a months ago, a bit tricky with DC fluctuating, but got numbers down to 3-15 mV with servo in, depending on volume pot position. However, with headphones connected, DC between hot and cold is 50-80 mV. Anyone got theories why this is?

[JoaMat]

Here is picture of the amplifier in work. Mono version. AMB sigma 22 PSU.

It has four trimmers. Lower middle controls the offset. Middle upper controls the balance. The two outer controls respectively channels bias. Input stage current source/sink approximately 1.7 mA. Output bias 35 mA.

Setup procedure I used:
•    Let heats sink get warmed up to working temperature
•    Trim offset to zero
•    Trim balance to zero
•    Set desired bias of both channels to desired bias

Redo previous procedures if needed.

I find the setup easily done. 

[JoaMat]

...and now a stereo version.

Bias 75mA, 125 degrees F at heat sinks and AMB sigma PSU is working hard.

Might need better chassis.

Edited April 19 by JoaMat

[JoaMat]

Milled a front panel, with inscription, today. With black painted aluminum net as top cover you can see the light from eight red LEDs.

Edited April 21 by JoaMat

[bbest]

Hello!

I could get now DynaMight 4pcs boards version 2004. Does anybody know is there any difference for balance amplifier between: DynaMight and Susy Dynahi v 1.43?

Edited May 27 by bbest