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KG Balanced Dynahi build discussion thread


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Now that the PCBs are finding their ways to us -Balanced Dynahi Builders-, I think that it's time for starting a build discussion thread for this beloved amplifier.

The purpose of this thread is to create a place for builders to discuss all topics related to the build of this amp (parts, constructions, troubleshooting...), to share experiences and to consolidate the information and discussions about this project.

Schematics of the Balanced Dynahi and the associated Power Supply by KG.

Background information about the original KG Dynahi can be found here.

Based on the preliminary BOM posted by Lil Knight earlier, an updated version for the Dynahi and the associated power supply, including Mouser parts numbers for the not yet specified parts in the preliminary BOM can be found in the attachment.

For the resistors, Vishay-Dale alternative parts numbers are added for people who like to use Vishay-Dale resistors.

Happy building. cool.png


Edited by Vortex
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Thanks vortex, for starting this thread.

Guys, newb here but Im eager to learn so Id appreciate any help. Right now I'm acquiring the parts for the Dynahi but I'm having some issues. When you look at the BOM and this layout(http://gilmore.chem....u/dynahibal.jpg) you can see there are two capacitors (470 uF/50v) Yet on the amplifier board itself there are six places for capacitors 470 uF / 35 v. Can anyone tell me which ones I need, preferably with a part number?

And my second question, would it be a good thing to spent a bit more for higher quality parts or should you strictly follow the BOM with its part numbers?

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You are correct that the final Dynahi PCB is a bit different than the layout under that link.

The PCB indeed has place for 6 capacitors: 3 on the positive rail and 3 on the negative rail.

These are local filter capacitors, the amp will work fine with 1 or 3 capacitors on each rail.

Since the amp is feeding by ±30V DC rail voltages, the used caps need to be rated at a higher voltage than 30V.

Capacitors rated at 35V (minimum) or higher (50V, 63V) can be used, as long as they fit the board.

Some examples of 470µF capacitors are:

Panasonic FM (Digi-Key P12400-ND)

Nichicon HE (Mouser 647-UHE1J471MHD)

About spending on higher quality parts, there is no general answer for that.

For the active parts (transistors/JFets), you have to follow the specified parts (or alternative parts in some cases).

For the passive parts (resistors, capacitors, volume pot…), one can go for boutique parts, but as long as they fit the board of course. (things you have to find out yourself)

Edited by Vortex
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One little note about the parts list for the power supply board.

As most of you already know, the PS board consists of a ±30VDC section and a lower voltages (3.3V, 5V and 12V) section.

The ±30VDC PS is used by the Dynahi. The lower voltages are only necessary if you are going to use relay-based stepped attenuator (for example: KG stepped attenuator or AMB δ1 stepped attenuator…). Otherwise you can skip the lower voltages section.

More precisely, the following parts can be left out of the PS:

Bridge Rectifier for 18V AC section

LM7805 - 5V regulator

LM7812 - 12V regulator

Murata 3.3V DC converter

1x 4700uf/63V capacitor

3x 1000uf/25V capacitors

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  • 3 weeks later...

Has anyone started stuffing (or touching smile.png ) the Dyna PCBs yet?

I was busy today and this is what my boards now look like.

The small things on the back are stacked KG stepped attenuators (for balanced use) and a LCDuino-1 processor.

Still lots of (case)work to do...


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Looks nice Vortex. Did you need to make any changes to the lcduino to work with KG's attenuators?

I have not tried it out yet (will do soon), but I think that LCDuino will have no problem with KG attenuators.

For the processor, it’s just an 8 bits relay-based stepped attenuator (like any others from the same family).

Only point that needs attention is the 12V PS for the relays on KG attenuator boards.

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Has anyone started stuffing (or touching smile.png ) the Dyna PCBs yet?

I was busy today and this is what my boards now look like.

The small things on the back are stacked KG stepped attenuators (for balanced use) and a LCDuino-1 processor.

Still lots of (case)work to do...


Well work even faster, as I always look forward to seeing your final products! :)

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Thanks for the note on the Dynahi power supply board, Kevin. cool.png

I just wanted going to ask you about that resistor labeled 40KDT (40K for dual tracking).

There is also another resistor on the power supply PCB labeled 10KLO (on the negative rail section), which I couldn’t find in the schematic. (I’m using the schematic you have posted ).

Also, The value of R15 on the schematic is 10K.

To my opinion, R15 = R5 = 20K ? (correct me if I'm wrong or overlooked something)

Edited by Vortex
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On the power supply board, do not populate Q9,Q10,Q24,Q14,Q15,Q26

While it works great on the bench with dummy loads, when you try to power it up

with a real amplifier, the current limit comes up so fast that those transistors pop.

Likely need 1k ohm series base resistors on these, or the next size up in transistors,

something in a to92-mod case.


andy/steve have a working balanced dynahi now, a few teething issues...

Hopefully he will post the pictures he sent to me.

second edit:

only board from the group buy not tested now is the balanced dynafet board.

(obviously the most complicated of the dynamics)

Edited by kevin gilmore
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After some trial and error, we got the Dynahi to make music. And it sounds fantastic – prefer it to my balanced Dynalo with my grados (although it was built for Andy’s LCD-2). The following is what I learned in the process.

There are a few discrepancies in the PS silkscreen as compared to the schematic:

-R9 and R20 are 5K in the schematic and 10K in the silkscreen.

-R15 is 10K in the schematic and 20K in the silkscreen.

In both cases I followed the silkscreen. When powering up the amp boards the PS was blowing transistors. So I removed Q24, Q9, Q10, Q15, Q14, and Q26 (as per Dr. Gilmore’s suggestion), and populated 10KLO (left 40KDT unpopulated).

With this configuration I was able to power up both amp boards.

Initially I had a little trouble biasing and removing the offset in the amps. After some experimentation I got the offset down to 0. There was about 470 ohms across R1/R4 resulting in about 80 mv across the 20 ohm resistors. It ran really hot (about 60C on the heatsinks after about 15 minutes). To try to lower the heat I replaced R1 and R4 with a 680 ohm resistor and preset RV1 and RV2 to give 500 ohms across R1 and R4. This gave about 75 mv across the 20 ohm resistors. Still ran really hot. The problem is that my heatsinks have horizontal fins (as you can see from the photos). They don’t dissipate enough heat. Until these are replaced I’ll need to use a fan. Now to start building a case!

Many thanks to all involved with this project - looking forward to listening with Andy’s LCD-2s!


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