Pars 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 comment Share on other sites More sharing options...
Applewood Posted April 13, 2020 Report Share Posted April 13, 2020 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 comment Share on other sites More sharing options...
kevin gilmore Posted April 13, 2020 Report Share Posted April 13, 2020 5k is correct value Quote Link to comment Share on other sites More sharing options...
Applewood Posted April 14, 2020 Report Share Posted April 14, 2020 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 comment Share on other sites More sharing options...
thuytn Posted April 14, 2020 Report Share Posted April 14, 2020 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 comment Share on other sites More sharing options...
Pars Posted April 15, 2020 Report Share Posted April 15, 2020 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 comment Share on other sites More sharing options...
Applewood Posted April 15, 2020 Report Share Posted April 15, 2020 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 comment Share on other sites More sharing options...
morphsci Posted April 15, 2020 Report Share Posted April 15, 2020 K710? Quote Link to comment Share on other sites More sharing options...
thuytn Posted April 15, 2020 Report Share Posted April 15, 2020 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 comment Share on other sites More sharing options...
Applewood Posted April 15, 2020 Report Share Posted April 15, 2020 3 hours ago, morphsci said: K710? K701 Quote Link to comment Share on other sites More sharing options...
Applewood Posted June 5, 2020 Report Share Posted June 5, 2020 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 comment Share on other sites More sharing options...
Emooze Posted June 16, 2020 Report Share Posted June 16, 2020 Dang, that is a nice and clean build. Where did you get those heatsinks if you don't mind me asking? Quote Link to comment Share on other sites More sharing options...
Applewood Posted June 16, 2020 Report Share Posted June 16, 2020 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. 2 Quote Link to comment Share on other sites More sharing options...
ang728 Posted June 16, 2020 Report Share Posted June 16, 2020 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 comment Share on other sites More sharing options...
johnwmclean Posted June 17, 2020 Report Share Posted June 17, 2020 Real nice build! Quote Link to comment Share on other sites More sharing options...
Rossliew Posted June 20, 2020 Report Share Posted June 20, 2020 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 comment Share on other sites More sharing options...
Applewood Posted June 20, 2020 Report Share Posted June 20, 2020 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 comment Share on other sites More sharing options...
dingding123 Posted July 7, 2020 Report Share Posted July 7, 2020 Another Dynahi lives. Sigh... Heatsinks are never enough. 1 Quote Link to comment Share on other sites More sharing options...
nopants Posted July 8, 2020 Report Share Posted July 8, 2020 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 comment Share on other sites More sharing options...
Applewood Posted July 8, 2020 Report Share Posted July 8, 2020 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 comment Share on other sites More sharing options...
mdr30 Posted January 4, 2021 Report Share Posted January 4, 2021 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? Quote Link to comment Share on other sites More sharing options...
Pars Posted January 4, 2021 Report Share Posted January 4, 2021 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. Quote Link to comment Share on other sites More sharing options...
mdr30 Posted January 5, 2021 Report Share Posted January 5, 2021 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. Quote Link to comment Share on other sites More sharing options...
Pars Posted March 21, 2021 Report Share Posted March 21, 2021 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. Quote Link to comment Share on other sites More sharing options...
mwl168 Posted March 21, 2021 Report Share Posted March 21, 2021 (edited) 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 Quote Link to comment Share on other sites More sharing options...
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