KG Balanced Dynahi build discussion thread

[Pars]

I would center the trimpots on that board and start comparing voltages in the front end circuitry between the two boards. You do have the inputs shorted?

Post detailed pics of the boards as well; maybe one of us will spot something.

[Applewood]

Need professional help for Dynahi balanced off-board version v1.43 (That340 / OPA445 version)

On the PCB R49 (between R2/R3 to OPA445 pin 6) is printing 5K ohms but on circuit diagram is showing 100R only.

Could you please help, which value (5K or 100R) is correct one?

[kevin gilmore]

5k is correct value

[Applewood]

Thank you very much ! !

One more question. For feedback capacitor value, somewhat confused when I searched for previous discussions on this thread.

I am planning to reduce the gain to half of the original design (use 10K/100K ohms) because have a fair driving headphone. 

Could you please recommend what value the capacitor should use?

[thuytn]

I used 50K/5pf for 7x gain which is very suitable for my Utopia. Don’t think I ever need a higher gain. 

[Pars]

One could ask why you are building a hi-powered amp for an easy to drive phone? Maybe an SS Dynalo would have been a better choice?

[Applewood]

SS dynalo be considered but not easy to get the circuit board on the web.

Although it is an easy-to-drive headphone (K701 & Dharma D1000), it still does not have a good sense of hearing when using several high-power DAP and also headphone amps.

This is the second time I built dynahi balanced, and the first one was sold few weeks ago. I really miss its dynamics and timbre….  so I decided to build again with the first successful experience, of course the second one would be more thoughtful components selected.

[morphsci]

K710?

[thuytn]

1 hour ago, Pars said:

One could ask why you are building a hi-powered amp for an easy to drive phone? Maybe an SS Dynalo would have been a better choice?

Agreed. I actually much prefer the Dynalo than the Dynahi with “medium” headphones like the Utopia and HD800S. Way more relaxing.

[Applewood]

3 hours ago, morphsci said:

K710?

K701

[Applewood]

Finally completed the dynahi. I really enjoyed this DIY processing. Based on previous experience, this time I spent more time on selecting parts and adjustment, also increased heat sink size, quiescent current increased to 75mA. The gain keeps the original design value (200K/10K) and there is no background noise even using high efficiency earphones. Thank you everyone for your experience and information on this thread.

[Emooze]

Dang, that is a nice and clean build. Where did you get those heatsinks if you don't mind me asking?

[Applewood]

7 hours ago, Emooze said:

Dang, that is a nice and clean build. Where did you get those heatsinks if you don't mind me asking?

https://www.shun-teh.com.tw/en/category/Aluminum-Extrusion-Heat-Sink-Above-width-200mm/A03.html

This company can cut heat sink size and drill screw thread holes according your drawing, even if you only need two piece. It is good choice if you want to design your own case.

[ang728]

 

7 hours ago, Applewood said:

https://www.shun-teh.com.tw/en/category/Aluminum-Extrusion-Heat-Sink-Above-width-200mm/A03.html

This company can cut heat sink size and drill screw thread holes according your drawing, even if you only need two piece. It is good choice if you want to design your own case.

nice build ~

BTW , a friend of mine bought your first build,pretty happy about it

 

[johnwmclean]

Real nice build!

[Rossliew]

On 6/5/2020 at 10:03 AM, Applewood said:

Finally completed the dynahi. I really enjoyed this DIY processing. Based on previous experience, this time I spent more time on selecting parts and adjustment, also increased heat sink size, quiescent current increased to 75mA. The gain keeps the original design value (200K/10K) and there is no background noise even using high efficiency earphones. Thank you everyone for your experience and information on this thread.

Is the second pic showing a transparent cover on the amp? 

[Applewood]

1 hour ago, Rossliew said:

Is the second pic showing a transparent cover on the amp? 

Yes, 3mm thick transparent acrylic be used and also heat dissipation hole is opened above the driving transistors stage. (those transistors are equipped TO92 heat sink)

The temperature of internal and both side heat sink are normal and stable after long time operation, heat insulation gasket with 6 screws between top cover and side heat sink.

Heat sinks must have enough volume to be as same designed otherwise the quiescent current must be compromised.

[dingding123]

Another Dynahi lives.

Sigh... Heatsinks are never enough.

[nopants]

On 6/4/2020 at 7:03 PM, Applewood said:

Finally completed the dynahi. I really enjoyed this DIY processing. Based on previous experience, this time I spent more time on selecting parts and adjustment, also increased heat sink size, quiescent current increased to 75mA. The gain keeps the original design value (200K/10K) and there is no background noise even using high efficiency earphones. Thank you everyone for your experience and information on this thread.

Nice build, did you get the angle-brackets done by the same shop?

[Applewood]

Not from the same store. it's hand made from "Aluminum Square Bar" and just need to cut and drill screw holes.

[mdr30]

Am about to test my Dynahi boards but have a little probelm.

The holes were to small for the 0,1 uF servo caps so I made them slightly larger wit a drill. Later I realised I may have ruined and inner layer contact (one leg of the caps have no connection on the back of the board). Is there a way to check this, could a jumper fix it?

 

 

 

 

[Pars]

Those caps should run from V+ or V- to ground. The boards have a ground plane (top side of board). Check for continuity to ground on those; if not, jumper them to ground. Sometimes if you use PCB drills and only enlarge slightly, they will still be good.

[mdr30]

23 hours ago, Pars said:

Those caps should run from V+ or V- to ground. The boards have a ground plane (top side of board). Check for continuity to ground on those; if not, jumper them to ground. Sometimes if you use PCB drills and only enlarge slightly, they will still be good.

Thanks, two jumpers did the trick.

I think I'll lower the gain with 50K/5pF feedback, which I think are the parts at the arrow (don't have a schematic).

The PSU is hopefully ok too, did not populate the transistors that popped at turn-on.

Time to test the beast.

 

 

 

[Pars]

Question: when you do a dual mono amp, with a pair of GRLVs, do you connect the grounds of the two PSUs together? Asking because I ran into a problem on an amp. Offset on one channel jumped up quite high (tripped a Gilmore protect circuit). The pot ground on one channel had opened up from the pot to one channel board, and that was the only common ground point in the amp. I was thinking tieing the grounds together at the power supplies might not be a bad idea.

[mwl168]

I tie the ground of the PSU together when I do a dual mono amp - one wire that goes from the output ground of one PSU to that of the the other one and then, from there, a single wire to the chassis. I do the same thing when tying the LV and HV PSU ground together. So far this has worked well for me.  But I typically do not install a volume pot on my headphone amps. 

Edited March 21, 2021 by mwl168