Pars 1,380 Posted September 3, 2019 Report Share Posted September 3, 2019 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. Quote Link to post Share on other sites
Applewood 15 Posted April 13 Report Share Posted April 13 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? Quote Link to post Share on other sites
kevin gilmore 1,373 Posted April 13 Report Share Posted April 13 5k is correct value Quote Link to post Share on other sites
Applewood 15 Posted April 14 Report Share Posted April 14 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? Quote Link to post Share on other sites
thuytn 8 Posted April 14 Report Share Posted April 14 I used 50K/5pf for 7x gain which is very suitable for my Utopia. Don’t think I ever need a higher gain. Quote Link to post Share on other sites
Pars 1,380 Posted April 15 Report Share Posted April 15 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? Quote Link to post Share on other sites
Applewood 15 Posted April 15 Report Share Posted April 15 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. Quote Link to post Share on other sites
morphsci 5,168 Posted April 15 Report Share Posted April 15 K710? Quote Link to post Share on other sites
thuytn 8 Posted April 15 Report Share Posted April 15 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. Quote Link to post Share on other sites
Applewood 15 Posted April 15 Report Share Posted April 15 3 hours ago, morphsci said: K710? K701 Quote Link to post Share on other sites
Applewood 15 Posted June 5 Report Share Posted June 5 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. 13 Quote Link to post Share on other sites
Emooze 657 Posted June 16 Report Share Posted June 16 Dang, that is a nice and clean build. Where did you get those heatsinks if you don't mind me asking? Quote Link to post Share on other sites
Applewood 15 Posted June 16 Report Share Posted June 16 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. 1 Quote Link to post Share on other sites
ang728 61 Posted June 16 Report Share Posted June 16 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 Quote Link to post Share on other sites
johnwmclean 550 Posted June 17 Report Share Posted June 17 Real nice build! Quote Link to post Share on other sites
Rossliew 23 Posted June 20 Report Share Posted June 20 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? Quote Link to post Share on other sites
Applewood 15 Posted June 20 Report Share Posted June 20 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. 1 Quote Link to post Share on other sites
dingding123 8 Posted July 7 Report Share Posted July 7 Another Dynahi lives. Sigh... Heatsinks are never enough. 1 Quote Link to post Share on other sites
nopants 127 Posted July 8 Report Share Posted July 8 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? Quote Link to post Share on other sites
Applewood 15 Posted July 8 Report Share Posted July 8 Not from the same store. it's hand made from "Aluminum Square Bar" and just need to cut and drill screw holes. Quote Link to post Share on other sites
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